Mercurial > hg > Members > tobaru > cbc > CbC_llvm
view lib/Transforms/Scalar/SROA.cpp @ 83:60c9769439b8
LLVM 3.7
author | Tatsuki IHA <e125716@ie.u-ryukyu.ac.jp> |
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date | Wed, 18 Feb 2015 14:55:36 +0900 |
parents | 54457678186b |
children | 5e5d649e25d2 afa8332a0e37 |
line wrap: on
line source
//===- SROA.cpp - Scalar Replacement Of Aggregates ------------------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// /// \file /// This transformation implements the well known scalar replacement of /// aggregates transformation. It tries to identify promotable elements of an /// aggregate alloca, and promote them to registers. It will also try to /// convert uses of an element (or set of elements) of an alloca into a vector /// or bitfield-style integer scalar if appropriate. /// /// It works to do this with minimal slicing of the alloca so that regions /// which are merely transferred in and out of external memory remain unchanged /// and are not decomposed to scalar code. /// /// Because this also performs alloca promotion, it can be thought of as also /// serving the purpose of SSA formation. The algorithm iterates on the /// function until all opportunities for promotion have been realized. /// //===----------------------------------------------------------------------===// #include "llvm/Transforms/Scalar.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SetVector.h" #include "llvm/ADT/SmallVector.h" #include "llvm/ADT/Statistic.h" #include "llvm/Analysis/AssumptionCache.h" #include "llvm/Analysis/Loads.h" #include "llvm/Analysis/PtrUseVisitor.h" #include "llvm/Analysis/ValueTracking.h" #include "llvm/IR/Constants.h" #include "llvm/IR/DIBuilder.h" #include "llvm/IR/DataLayout.h" #include "llvm/IR/DebugInfo.h" #include "llvm/IR/DerivedTypes.h" #include "llvm/IR/Dominators.h" #include "llvm/IR/Function.h" #include "llvm/IR/IRBuilder.h" #include "llvm/IR/InstVisitor.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/LLVMContext.h" #include "llvm/IR/Operator.h" #include "llvm/Pass.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Compiler.h" #include "llvm/Support/Debug.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/MathExtras.h" #include "llvm/Support/TimeValue.h" #include "llvm/Support/raw_ostream.h" #include "llvm/Transforms/Utils/Local.h" #include "llvm/Transforms/Utils/PromoteMemToReg.h" #include "llvm/Transforms/Utils/SSAUpdater.h" #if __cplusplus >= 201103L && !defined(NDEBUG) // We only use this for a debug check in C++11 #include <random> #endif using namespace llvm; #define DEBUG_TYPE "sroa" STATISTIC(NumAllocasAnalyzed, "Number of allocas analyzed for replacement"); STATISTIC(NumAllocaPartitions, "Number of alloca partitions formed"); STATISTIC(MaxPartitionsPerAlloca, "Maximum number of partitions per alloca"); STATISTIC(NumAllocaPartitionUses, "Number of alloca partition uses rewritten"); STATISTIC(MaxUsesPerAllocaPartition, "Maximum number of uses of a partition"); STATISTIC(NumNewAllocas, "Number of new, smaller allocas introduced"); STATISTIC(NumPromoted, "Number of allocas promoted to SSA values"); STATISTIC(NumLoadsSpeculated, "Number of loads speculated to allow promotion"); STATISTIC(NumDeleted, "Number of instructions deleted"); STATISTIC(NumVectorized, "Number of vectorized aggregates"); /// Hidden option to force the pass to not use DomTree and mem2reg, instead /// forming SSA values through the SSAUpdater infrastructure. static cl::opt<bool> ForceSSAUpdater("force-ssa-updater", cl::init(false), cl::Hidden); /// Hidden option to enable randomly shuffling the slices to help uncover /// instability in their order. static cl::opt<bool> SROARandomShuffleSlices("sroa-random-shuffle-slices", cl::init(false), cl::Hidden); /// Hidden option to experiment with completely strict handling of inbounds /// GEPs. static cl::opt<bool> SROAStrictInbounds("sroa-strict-inbounds", cl::init(false), cl::Hidden); namespace { /// \brief A custom IRBuilder inserter which prefixes all names if they are /// preserved. template <bool preserveNames = true> class IRBuilderPrefixedInserter : public IRBuilderDefaultInserter<preserveNames> { std::string Prefix; public: void SetNamePrefix(const Twine &P) { Prefix = P.str(); } protected: void InsertHelper(Instruction *I, const Twine &Name, BasicBlock *BB, BasicBlock::iterator InsertPt) const { IRBuilderDefaultInserter<preserveNames>::InsertHelper( I, Name.isTriviallyEmpty() ? Name : Prefix + Name, BB, InsertPt); } }; // Specialization for not preserving the name is trivial. template <> class IRBuilderPrefixedInserter<false> : public IRBuilderDefaultInserter<false> { public: void SetNamePrefix(const Twine &P) {} }; /// \brief Provide a typedef for IRBuilder that drops names in release builds. #ifndef NDEBUG typedef llvm::IRBuilder<true, ConstantFolder, IRBuilderPrefixedInserter<true>> IRBuilderTy; #else typedef llvm::IRBuilder<false, ConstantFolder, IRBuilderPrefixedInserter<false>> IRBuilderTy; #endif } namespace { /// \brief A used slice of an alloca. /// /// This structure represents a slice of an alloca used by some instruction. It /// stores both the begin and end offsets of this use, a pointer to the use /// itself, and a flag indicating whether we can classify the use as splittable /// or not when forming partitions of the alloca. class Slice { /// \brief The beginning offset of the range. uint64_t BeginOffset; /// \brief The ending offset, not included in the range. uint64_t EndOffset; /// \brief Storage for both the use of this slice and whether it can be /// split. PointerIntPair<Use *, 1, bool> UseAndIsSplittable; public: Slice() : BeginOffset(), EndOffset() {} Slice(uint64_t BeginOffset, uint64_t EndOffset, Use *U, bool IsSplittable) : BeginOffset(BeginOffset), EndOffset(EndOffset), UseAndIsSplittable(U, IsSplittable) {} uint64_t beginOffset() const { return BeginOffset; } uint64_t endOffset() const { return EndOffset; } bool isSplittable() const { return UseAndIsSplittable.getInt(); } void makeUnsplittable() { UseAndIsSplittable.setInt(false); } Use *getUse() const { return UseAndIsSplittable.getPointer(); } bool isDead() const { return getUse() == nullptr; } void kill() { UseAndIsSplittable.setPointer(nullptr); } /// \brief Support for ordering ranges. /// /// This provides an ordering over ranges such that start offsets are /// always increasing, and within equal start offsets, the end offsets are /// decreasing. Thus the spanning range comes first in a cluster with the /// same start position. bool operator<(const Slice &RHS) const { if (beginOffset() < RHS.beginOffset()) return true; if (beginOffset() > RHS.beginOffset()) return false; if (isSplittable() != RHS.isSplittable()) return !isSplittable(); if (endOffset() > RHS.endOffset()) return true; return false; } /// \brief Support comparison with a single offset to allow binary searches. friend LLVM_ATTRIBUTE_UNUSED bool operator<(const Slice &LHS, uint64_t RHSOffset) { return LHS.beginOffset() < RHSOffset; } friend LLVM_ATTRIBUTE_UNUSED bool operator<(uint64_t LHSOffset, const Slice &RHS) { return LHSOffset < RHS.beginOffset(); } bool operator==(const Slice &RHS) const { return isSplittable() == RHS.isSplittable() && beginOffset() == RHS.beginOffset() && endOffset() == RHS.endOffset(); } bool operator!=(const Slice &RHS) const { return !operator==(RHS); } }; } // end anonymous namespace namespace llvm { template <typename T> struct isPodLike; template <> struct isPodLike<Slice> { static const bool value = true; }; } namespace { /// \brief Representation of the alloca slices. /// /// This class represents the slices of an alloca which are formed by its /// various uses. If a pointer escapes, we can't fully build a representation /// for the slices used and we reflect that in this structure. The uses are /// stored, sorted by increasing beginning offset and with unsplittable slices /// starting at a particular offset before splittable slices. class AllocaSlices { public: /// \brief Construct the slices of a particular alloca. AllocaSlices(const DataLayout &DL, AllocaInst &AI); /// \brief Test whether a pointer to the allocation escapes our analysis. /// /// If this is true, the slices are never fully built and should be /// ignored. bool isEscaped() const { return PointerEscapingInstr; } /// \brief Support for iterating over the slices. /// @{ typedef SmallVectorImpl<Slice>::iterator iterator; typedef iterator_range<iterator> range; iterator begin() { return Slices.begin(); } iterator end() { return Slices.end(); } typedef SmallVectorImpl<Slice>::const_iterator const_iterator; typedef iterator_range<const_iterator> const_range; const_iterator begin() const { return Slices.begin(); } const_iterator end() const { return Slices.end(); } /// @} /// \brief Erase a range of slices. void erase(iterator Start, iterator Stop) { Slices.erase(Start, Stop); } /// \brief Insert new slices for this alloca. /// /// This moves the slices into the alloca's slices collection, and re-sorts /// everything so that the usual ordering properties of the alloca's slices /// hold. void insert(ArrayRef<Slice> NewSlices) { int OldSize = Slices.size(); std::move(NewSlices.begin(), NewSlices.end(), std::back_inserter(Slices)); auto SliceI = Slices.begin() + OldSize; std::sort(SliceI, Slices.end()); std::inplace_merge(Slices.begin(), SliceI, Slices.end()); } // Forward declare an iterator to befriend it. class partition_iterator; /// \brief A partition of the slices. /// /// An ephemeral representation for a range of slices which can be viewed as /// a partition of the alloca. This range represents a span of the alloca's /// memory which cannot be split, and provides access to all of the slices /// overlapping some part of the partition. /// /// Objects of this type are produced by traversing the alloca's slices, but /// are only ephemeral and not persistent. class Partition { private: friend class AllocaSlices; friend class AllocaSlices::partition_iterator; /// \brief The begining and ending offsets of the alloca for this partition. uint64_t BeginOffset, EndOffset; /// \brief The start end end iterators of this partition. iterator SI, SJ; /// \brief A collection of split slice tails overlapping the partition. SmallVector<Slice *, 4> SplitTails; /// \brief Raw constructor builds an empty partition starting and ending at /// the given iterator. Partition(iterator SI) : SI(SI), SJ(SI) {} public: /// \brief The start offset of this partition. /// /// All of the contained slices start at or after this offset. uint64_t beginOffset() const { return BeginOffset; } /// \brief The end offset of this partition. /// /// All of the contained slices end at or before this offset. uint64_t endOffset() const { return EndOffset; } /// \brief The size of the partition. /// /// Note that this can never be zero. uint64_t size() const { assert(BeginOffset < EndOffset && "Partitions must span some bytes!"); return EndOffset - BeginOffset; } /// \brief Test whether this partition contains no slices, and merely spans /// a region occupied by split slices. bool empty() const { return SI == SJ; } /// \name Iterate slices that start within the partition. /// These may be splittable or unsplittable. They have a begin offset >= the /// partition begin offset. /// @{ // FIXME: We should probably define a "concat_iterator" helper and use that // to stitch together pointee_iterators over the split tails and the // contiguous iterators of the partition. That would give a much nicer // interface here. We could then additionally expose filtered iterators for // split, unsplit, and unsplittable splices based on the usage patterns. iterator begin() const { return SI; } iterator end() const { return SJ; } /// @} /// \brief Get the sequence of split slice tails. /// /// These tails are of slices which start before this partition but are /// split and overlap into the partition. We accumulate these while forming /// partitions. ArrayRef<Slice *> splitSliceTails() const { return SplitTails; } }; /// \brief An iterator over partitions of the alloca's slices. /// /// This iterator implements the core algorithm for partitioning the alloca's /// slices. It is a forward iterator as we don't support backtracking for /// efficiency reasons, and re-use a single storage area to maintain the /// current set of split slices. /// /// It is templated on the slice iterator type to use so that it can operate /// with either const or non-const slice iterators. class partition_iterator : public iterator_facade_base<partition_iterator, std::forward_iterator_tag, Partition> { friend class AllocaSlices; /// \brief Most of the state for walking the partitions is held in a class /// with a nice interface for examining them. Partition P; /// \brief We need to keep the end of the slices to know when to stop. AllocaSlices::iterator SE; /// \brief We also need to keep track of the maximum split end offset seen. /// FIXME: Do we really? uint64_t MaxSplitSliceEndOffset; /// \brief Sets the partition to be empty at given iterator, and sets the /// end iterator. partition_iterator(AllocaSlices::iterator SI, AllocaSlices::iterator SE) : P(SI), SE(SE), MaxSplitSliceEndOffset(0) { // If not already at the end, advance our state to form the initial // partition. if (SI != SE) advance(); } /// \brief Advance the iterator to the next partition. /// /// Requires that the iterator not be at the end of the slices. void advance() { assert((P.SI != SE || !P.SplitTails.empty()) && "Cannot advance past the end of the slices!"); // Clear out any split uses which have ended. if (!P.SplitTails.empty()) { if (P.EndOffset >= MaxSplitSliceEndOffset) { // If we've finished all splits, this is easy. P.SplitTails.clear(); MaxSplitSliceEndOffset = 0; } else { // Remove the uses which have ended in the prior partition. This // cannot change the max split slice end because we just checked that // the prior partition ended prior to that max. P.SplitTails.erase( std::remove_if( P.SplitTails.begin(), P.SplitTails.end(), [&](Slice *S) { return S->endOffset() <= P.EndOffset; }), P.SplitTails.end()); assert(std::any_of(P.SplitTails.begin(), P.SplitTails.end(), [&](Slice *S) { return S->endOffset() == MaxSplitSliceEndOffset; }) && "Could not find the current max split slice offset!"); assert(std::all_of(P.SplitTails.begin(), P.SplitTails.end(), [&](Slice *S) { return S->endOffset() <= MaxSplitSliceEndOffset; }) && "Max split slice end offset is not actually the max!"); } } // If P.SI is already at the end, then we've cleared the split tail and // now have an end iterator. if (P.SI == SE) { assert(P.SplitTails.empty() && "Failed to clear the split slices!"); return; } // If we had a non-empty partition previously, set up the state for // subsequent partitions. if (P.SI != P.SJ) { // Accumulate all the splittable slices which started in the old // partition into the split list. for (Slice &S : P) if (S.isSplittable() && S.endOffset() > P.EndOffset) { P.SplitTails.push_back(&S); MaxSplitSliceEndOffset = std::max(S.endOffset(), MaxSplitSliceEndOffset); } // Start from the end of the previous partition. P.SI = P.SJ; // If P.SI is now at the end, we at most have a tail of split slices. if (P.SI == SE) { P.BeginOffset = P.EndOffset; P.EndOffset = MaxSplitSliceEndOffset; return; } // If the we have split slices and the next slice is after a gap and is // not splittable immediately form an empty partition for the split // slices up until the next slice begins. if (!P.SplitTails.empty() && P.SI->beginOffset() != P.EndOffset && !P.SI->isSplittable()) { P.BeginOffset = P.EndOffset; P.EndOffset = P.SI->beginOffset(); return; } } // OK, we need to consume new slices. Set the end offset based on the // current slice, and step SJ past it. The beginning offset of the // parttion is the beginning offset of the next slice unless we have // pre-existing split slices that are continuing, in which case we begin // at the prior end offset. P.BeginOffset = P.SplitTails.empty() ? P.SI->beginOffset() : P.EndOffset; P.EndOffset = P.SI->endOffset(); ++P.SJ; // There are two strategies to form a partition based on whether the // partition starts with an unsplittable slice or a splittable slice. if (!P.SI->isSplittable()) { // When we're forming an unsplittable region, it must always start at // the first slice and will extend through its end. assert(P.BeginOffset == P.SI->beginOffset()); // Form a partition including all of the overlapping slices with this // unsplittable slice. while (P.SJ != SE && P.SJ->beginOffset() < P.EndOffset) { if (!P.SJ->isSplittable()) P.EndOffset = std::max(P.EndOffset, P.SJ->endOffset()); ++P.SJ; } // We have a partition across a set of overlapping unsplittable // partitions. return; } // If we're starting with a splittable slice, then we need to form // a synthetic partition spanning it and any other overlapping splittable // splices. assert(P.SI->isSplittable() && "Forming a splittable partition!"); // Collect all of the overlapping splittable slices. while (P.SJ != SE && P.SJ->beginOffset() < P.EndOffset && P.SJ->isSplittable()) { P.EndOffset = std::max(P.EndOffset, P.SJ->endOffset()); ++P.SJ; } // Back upiP.EndOffset if we ended the span early when encountering an // unsplittable slice. This synthesizes the early end offset of // a partition spanning only splittable slices. if (P.SJ != SE && P.SJ->beginOffset() < P.EndOffset) { assert(!P.SJ->isSplittable()); P.EndOffset = P.SJ->beginOffset(); } } public: bool operator==(const partition_iterator &RHS) const { assert(SE == RHS.SE && "End iterators don't match between compared partition iterators!"); // The observed positions of partitions is marked by the P.SI iterator and // the emptyness of the split slices. The latter is only relevant when // P.SI == SE, as the end iterator will additionally have an empty split // slices list, but the prior may have the same P.SI and a tail of split // slices. if (P.SI == RHS.P.SI && P.SplitTails.empty() == RHS.P.SplitTails.empty()) { assert(P.SJ == RHS.P.SJ && "Same set of slices formed two different sized partitions!"); assert(P.SplitTails.size() == RHS.P.SplitTails.size() && "Same slice position with differently sized non-empty split " "slice tails!"); return true; } return false; } partition_iterator &operator++() { advance(); return *this; } Partition &operator*() { return P; } }; /// \brief A forward range over the partitions of the alloca's slices. /// /// This accesses an iterator range over the partitions of the alloca's /// slices. It computes these partitions on the fly based on the overlapping /// offsets of the slices and the ability to split them. It will visit "empty" /// partitions to cover regions of the alloca only accessed via split /// slices. iterator_range<partition_iterator> partitions() { return make_range(partition_iterator(begin(), end()), partition_iterator(end(), end())); } /// \brief Access the dead users for this alloca. ArrayRef<Instruction *> getDeadUsers() const { return DeadUsers; } /// \brief Access the dead operands referring to this alloca. /// /// These are operands which have cannot actually be used to refer to the /// alloca as they are outside its range and the user doesn't correct for /// that. These mostly consist of PHI node inputs and the like which we just /// need to replace with undef. ArrayRef<Use *> getDeadOperands() const { return DeadOperands; } #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) void print(raw_ostream &OS, const_iterator I, StringRef Indent = " ") const; void printSlice(raw_ostream &OS, const_iterator I, StringRef Indent = " ") const; void printUse(raw_ostream &OS, const_iterator I, StringRef Indent = " ") const; void print(raw_ostream &OS) const; void dump(const_iterator I) const; void dump() const; #endif private: template <typename DerivedT, typename RetT = void> class BuilderBase; class SliceBuilder; friend class AllocaSlices::SliceBuilder; #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) /// \brief Handle to alloca instruction to simplify method interfaces. AllocaInst &AI; #endif /// \brief The instruction responsible for this alloca not having a known set /// of slices. /// /// When an instruction (potentially) escapes the pointer to the alloca, we /// store a pointer to that here and abort trying to form slices of the /// alloca. This will be null if the alloca slices are analyzed successfully. Instruction *PointerEscapingInstr; /// \brief The slices of the alloca. /// /// We store a vector of the slices formed by uses of the alloca here. This /// vector is sorted by increasing begin offset, and then the unsplittable /// slices before the splittable ones. See the Slice inner class for more /// details. SmallVector<Slice, 8> Slices; /// \brief Instructions which will become dead if we rewrite the alloca. /// /// Note that these are not separated by slice. This is because we expect an /// alloca to be completely rewritten or not rewritten at all. If rewritten, /// all these instructions can simply be removed and replaced with undef as /// they come from outside of the allocated space. SmallVector<Instruction *, 8> DeadUsers; /// \brief Operands which will become dead if we rewrite the alloca. /// /// These are operands that in their particular use can be replaced with /// undef when we rewrite the alloca. These show up in out-of-bounds inputs /// to PHI nodes and the like. They aren't entirely dead (there might be /// a GEP back into the bounds using it elsewhere) and nor is the PHI, but we /// want to swap this particular input for undef to simplify the use lists of /// the alloca. SmallVector<Use *, 8> DeadOperands; }; } static Value *foldSelectInst(SelectInst &SI) { // If the condition being selected on is a constant or the same value is // being selected between, fold the select. Yes this does (rarely) happen // early on. if (ConstantInt *CI = dyn_cast<ConstantInt>(SI.getCondition())) return SI.getOperand(1 + CI->isZero()); if (SI.getOperand(1) == SI.getOperand(2)) return SI.getOperand(1); return nullptr; } /// \brief A helper that folds a PHI node or a select. static Value *foldPHINodeOrSelectInst(Instruction &I) { if (PHINode *PN = dyn_cast<PHINode>(&I)) { // If PN merges together the same value, return that value. return PN->hasConstantValue(); } return foldSelectInst(cast<SelectInst>(I)); } /// \brief Builder for the alloca slices. /// /// This class builds a set of alloca slices by recursively visiting the uses /// of an alloca and making a slice for each load and store at each offset. class AllocaSlices::SliceBuilder : public PtrUseVisitor<SliceBuilder> { friend class PtrUseVisitor<SliceBuilder>; friend class InstVisitor<SliceBuilder>; typedef PtrUseVisitor<SliceBuilder> Base; const uint64_t AllocSize; AllocaSlices &AS; SmallDenseMap<Instruction *, unsigned> MemTransferSliceMap; SmallDenseMap<Instruction *, uint64_t> PHIOrSelectSizes; /// \brief Set to de-duplicate dead instructions found in the use walk. SmallPtrSet<Instruction *, 4> VisitedDeadInsts; public: SliceBuilder(const DataLayout &DL, AllocaInst &AI, AllocaSlices &AS) : PtrUseVisitor<SliceBuilder>(DL), AllocSize(DL.getTypeAllocSize(AI.getAllocatedType())), AS(AS) {} private: void markAsDead(Instruction &I) { if (VisitedDeadInsts.insert(&I).second) AS.DeadUsers.push_back(&I); } void insertUse(Instruction &I, const APInt &Offset, uint64_t Size, bool IsSplittable = false) { // Completely skip uses which have a zero size or start either before or // past the end of the allocation. if (Size == 0 || Offset.uge(AllocSize)) { DEBUG(dbgs() << "WARNING: Ignoring " << Size << " byte use @" << Offset << " which has zero size or starts outside of the " << AllocSize << " byte alloca:\n" << " alloca: " << AS.AI << "\n" << " use: " << I << "\n"); return markAsDead(I); } uint64_t BeginOffset = Offset.getZExtValue(); uint64_t EndOffset = BeginOffset + Size; // Clamp the end offset to the end of the allocation. Note that this is // formulated to handle even the case where "BeginOffset + Size" overflows. // This may appear superficially to be something we could ignore entirely, // but that is not so! There may be widened loads or PHI-node uses where // some instructions are dead but not others. We can't completely ignore // them, and so have to record at least the information here. assert(AllocSize >= BeginOffset); // Established above. if (Size > AllocSize - BeginOffset) { DEBUG(dbgs() << "WARNING: Clamping a " << Size << " byte use @" << Offset << " to remain within the " << AllocSize << " byte alloca:\n" << " alloca: " << AS.AI << "\n" << " use: " << I << "\n"); EndOffset = AllocSize; } AS.Slices.push_back(Slice(BeginOffset, EndOffset, U, IsSplittable)); } void visitBitCastInst(BitCastInst &BC) { if (BC.use_empty()) return markAsDead(BC); return Base::visitBitCastInst(BC); } void visitGetElementPtrInst(GetElementPtrInst &GEPI) { if (GEPI.use_empty()) return markAsDead(GEPI); if (SROAStrictInbounds && GEPI.isInBounds()) { // FIXME: This is a manually un-factored variant of the basic code inside // of GEPs with checking of the inbounds invariant specified in the // langref in a very strict sense. If we ever want to enable // SROAStrictInbounds, this code should be factored cleanly into // PtrUseVisitor, but it is easier to experiment with SROAStrictInbounds // by writing out the code here where we have tho underlying allocation // size readily available. APInt GEPOffset = Offset; for (gep_type_iterator GTI = gep_type_begin(GEPI), GTE = gep_type_end(GEPI); GTI != GTE; ++GTI) { ConstantInt *OpC = dyn_cast<ConstantInt>(GTI.getOperand()); if (!OpC) break; // Handle a struct index, which adds its field offset to the pointer. if (StructType *STy = dyn_cast<StructType>(*GTI)) { unsigned ElementIdx = OpC->getZExtValue(); const StructLayout *SL = DL.getStructLayout(STy); GEPOffset += APInt(Offset.getBitWidth(), SL->getElementOffset(ElementIdx)); } else { // For array or vector indices, scale the index by the size of the // type. APInt Index = OpC->getValue().sextOrTrunc(Offset.getBitWidth()); GEPOffset += Index * APInt(Offset.getBitWidth(), DL.getTypeAllocSize(GTI.getIndexedType())); } // If this index has computed an intermediate pointer which is not // inbounds, then the result of the GEP is a poison value and we can // delete it and all uses. if (GEPOffset.ugt(AllocSize)) return markAsDead(GEPI); } } return Base::visitGetElementPtrInst(GEPI); } void handleLoadOrStore(Type *Ty, Instruction &I, const APInt &Offset, uint64_t Size, bool IsVolatile) { // We allow splitting of non-volatile loads and stores where the type is an // integer type. These may be used to implement 'memcpy' or other "transfer // of bits" patterns. bool IsSplittable = Ty->isIntegerTy() && !IsVolatile; insertUse(I, Offset, Size, IsSplittable); } void visitLoadInst(LoadInst &LI) { assert((!LI.isSimple() || LI.getType()->isSingleValueType()) && "All simple FCA loads should have been pre-split"); if (!IsOffsetKnown) return PI.setAborted(&LI); uint64_t Size = DL.getTypeStoreSize(LI.getType()); return handleLoadOrStore(LI.getType(), LI, Offset, Size, LI.isVolatile()); } void visitStoreInst(StoreInst &SI) { Value *ValOp = SI.getValueOperand(); if (ValOp == *U) return PI.setEscapedAndAborted(&SI); if (!IsOffsetKnown) return PI.setAborted(&SI); uint64_t Size = DL.getTypeStoreSize(ValOp->getType()); // If this memory access can be shown to *statically* extend outside the // bounds of of the allocation, it's behavior is undefined, so simply // ignore it. Note that this is more strict than the generic clamping // behavior of insertUse. We also try to handle cases which might run the // risk of overflow. // FIXME: We should instead consider the pointer to have escaped if this // function is being instrumented for addressing bugs or race conditions. if (Size > AllocSize || Offset.ugt(AllocSize - Size)) { DEBUG(dbgs() << "WARNING: Ignoring " << Size << " byte store @" << Offset << " which extends past the end of the " << AllocSize << " byte alloca:\n" << " alloca: " << AS.AI << "\n" << " use: " << SI << "\n"); return markAsDead(SI); } assert((!SI.isSimple() || ValOp->getType()->isSingleValueType()) && "All simple FCA stores should have been pre-split"); handleLoadOrStore(ValOp->getType(), SI, Offset, Size, SI.isVolatile()); } void visitMemSetInst(MemSetInst &II) { assert(II.getRawDest() == *U && "Pointer use is not the destination?"); ConstantInt *Length = dyn_cast<ConstantInt>(II.getLength()); if ((Length && Length->getValue() == 0) || (IsOffsetKnown && Offset.uge(AllocSize))) // Zero-length mem transfer intrinsics can be ignored entirely. return markAsDead(II); if (!IsOffsetKnown) return PI.setAborted(&II); insertUse(II, Offset, Length ? Length->getLimitedValue() : AllocSize - Offset.getLimitedValue(), (bool)Length); } void visitMemTransferInst(MemTransferInst &II) { ConstantInt *Length = dyn_cast<ConstantInt>(II.getLength()); if (Length && Length->getValue() == 0) // Zero-length mem transfer intrinsics can be ignored entirely. return markAsDead(II); // Because we can visit these intrinsics twice, also check to see if the // first time marked this instruction as dead. If so, skip it. if (VisitedDeadInsts.count(&II)) return; if (!IsOffsetKnown) return PI.setAborted(&II); // This side of the transfer is completely out-of-bounds, and so we can // nuke the entire transfer. However, we also need to nuke the other side // if already added to our partitions. // FIXME: Yet another place we really should bypass this when // instrumenting for ASan. if (Offset.uge(AllocSize)) { SmallDenseMap<Instruction *, unsigned>::iterator MTPI = MemTransferSliceMap.find(&II); if (MTPI != MemTransferSliceMap.end()) AS.Slices[MTPI->second].kill(); return markAsDead(II); } uint64_t RawOffset = Offset.getLimitedValue(); uint64_t Size = Length ? Length->getLimitedValue() : AllocSize - RawOffset; // Check for the special case where the same exact value is used for both // source and dest. if (*U == II.getRawDest() && *U == II.getRawSource()) { // For non-volatile transfers this is a no-op. if (!II.isVolatile()) return markAsDead(II); return insertUse(II, Offset, Size, /*IsSplittable=*/false); } // If we have seen both source and destination for a mem transfer, then // they both point to the same alloca. bool Inserted; SmallDenseMap<Instruction *, unsigned>::iterator MTPI; std::tie(MTPI, Inserted) = MemTransferSliceMap.insert(std::make_pair(&II, AS.Slices.size())); unsigned PrevIdx = MTPI->second; if (!Inserted) { Slice &PrevP = AS.Slices[PrevIdx]; // Check if the begin offsets match and this is a non-volatile transfer. // In that case, we can completely elide the transfer. if (!II.isVolatile() && PrevP.beginOffset() == RawOffset) { PrevP.kill(); return markAsDead(II); } // Otherwise we have an offset transfer within the same alloca. We can't // split those. PrevP.makeUnsplittable(); } // Insert the use now that we've fixed up the splittable nature. insertUse(II, Offset, Size, /*IsSplittable=*/Inserted && Length); // Check that we ended up with a valid index in the map. assert(AS.Slices[PrevIdx].getUse()->getUser() == &II && "Map index doesn't point back to a slice with this user."); } // Disable SRoA for any intrinsics except for lifetime invariants. // FIXME: What about debug intrinsics? This matches old behavior, but // doesn't make sense. void visitIntrinsicInst(IntrinsicInst &II) { if (!IsOffsetKnown) return PI.setAborted(&II); if (II.getIntrinsicID() == Intrinsic::lifetime_start || II.getIntrinsicID() == Intrinsic::lifetime_end) { ConstantInt *Length = cast<ConstantInt>(II.getArgOperand(0)); uint64_t Size = std::min(AllocSize - Offset.getLimitedValue(), Length->getLimitedValue()); insertUse(II, Offset, Size, true); return; } Base::visitIntrinsicInst(II); } Instruction *hasUnsafePHIOrSelectUse(Instruction *Root, uint64_t &Size) { // We consider any PHI or select that results in a direct load or store of // the same offset to be a viable use for slicing purposes. These uses // are considered unsplittable and the size is the maximum loaded or stored // size. SmallPtrSet<Instruction *, 4> Visited; SmallVector<std::pair<Instruction *, Instruction *>, 4> Uses; Visited.insert(Root); Uses.push_back(std::make_pair(cast<Instruction>(*U), Root)); // If there are no loads or stores, the access is dead. We mark that as // a size zero access. Size = 0; do { Instruction *I, *UsedI; std::tie(UsedI, I) = Uses.pop_back_val(); if (LoadInst *LI = dyn_cast<LoadInst>(I)) { Size = std::max(Size, DL.getTypeStoreSize(LI->getType())); continue; } if (StoreInst *SI = dyn_cast<StoreInst>(I)) { Value *Op = SI->getOperand(0); if (Op == UsedI) return SI; Size = std::max(Size, DL.getTypeStoreSize(Op->getType())); continue; } if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) { if (!GEP->hasAllZeroIndices()) return GEP; } else if (!isa<BitCastInst>(I) && !isa<PHINode>(I) && !isa<SelectInst>(I)) { return I; } for (User *U : I->users()) if (Visited.insert(cast<Instruction>(U)).second) Uses.push_back(std::make_pair(I, cast<Instruction>(U))); } while (!Uses.empty()); return nullptr; } void visitPHINodeOrSelectInst(Instruction &I) { assert(isa<PHINode>(I) || isa<SelectInst>(I)); if (I.use_empty()) return markAsDead(I); // TODO: We could use SimplifyInstruction here to fold PHINodes and // SelectInsts. However, doing so requires to change the current // dead-operand-tracking mechanism. For instance, suppose neither loading // from %U nor %other traps. Then "load (select undef, %U, %other)" does not // trap either. However, if we simply replace %U with undef using the // current dead-operand-tracking mechanism, "load (select undef, undef, // %other)" may trap because the select may return the first operand // "undef". if (Value *Result = foldPHINodeOrSelectInst(I)) { if (Result == *U) // If the result of the constant fold will be the pointer, recurse // through the PHI/select as if we had RAUW'ed it. enqueueUsers(I); else // Otherwise the operand to the PHI/select is dead, and we can replace // it with undef. AS.DeadOperands.push_back(U); return; } if (!IsOffsetKnown) return PI.setAborted(&I); // See if we already have computed info on this node. uint64_t &Size = PHIOrSelectSizes[&I]; if (!Size) { // This is a new PHI/Select, check for an unsafe use of it. if (Instruction *UnsafeI = hasUnsafePHIOrSelectUse(&I, Size)) return PI.setAborted(UnsafeI); } // For PHI and select operands outside the alloca, we can't nuke the entire // phi or select -- the other side might still be relevant, so we special // case them here and use a separate structure to track the operands // themselves which should be replaced with undef. // FIXME: This should instead be escaped in the event we're instrumenting // for address sanitization. if (Offset.uge(AllocSize)) { AS.DeadOperands.push_back(U); return; } insertUse(I, Offset, Size); } void visitPHINode(PHINode &PN) { visitPHINodeOrSelectInst(PN); } void visitSelectInst(SelectInst &SI) { visitPHINodeOrSelectInst(SI); } /// \brief Disable SROA entirely if there are unhandled users of the alloca. void visitInstruction(Instruction &I) { PI.setAborted(&I); } }; AllocaSlices::AllocaSlices(const DataLayout &DL, AllocaInst &AI) : #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) AI(AI), #endif PointerEscapingInstr(nullptr) { SliceBuilder PB(DL, AI, *this); SliceBuilder::PtrInfo PtrI = PB.visitPtr(AI); if (PtrI.isEscaped() || PtrI.isAborted()) { // FIXME: We should sink the escape vs. abort info into the caller nicely, // possibly by just storing the PtrInfo in the AllocaSlices. PointerEscapingInstr = PtrI.getEscapingInst() ? PtrI.getEscapingInst() : PtrI.getAbortingInst(); assert(PointerEscapingInstr && "Did not track a bad instruction"); return; } Slices.erase(std::remove_if(Slices.begin(), Slices.end(), [](const Slice &S) { return S.isDead(); }), Slices.end()); #if __cplusplus >= 201103L && !defined(NDEBUG) if (SROARandomShuffleSlices) { std::mt19937 MT(static_cast<unsigned>(sys::TimeValue::now().msec())); std::shuffle(Slices.begin(), Slices.end(), MT); } #endif // Sort the uses. This arranges for the offsets to be in ascending order, // and the sizes to be in descending order. std::sort(Slices.begin(), Slices.end()); } #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) void AllocaSlices::print(raw_ostream &OS, const_iterator I, StringRef Indent) const { printSlice(OS, I, Indent); OS << "\n"; printUse(OS, I, Indent); } void AllocaSlices::printSlice(raw_ostream &OS, const_iterator I, StringRef Indent) const { OS << Indent << "[" << I->beginOffset() << "," << I->endOffset() << ")" << " slice #" << (I - begin()) << (I->isSplittable() ? " (splittable)" : ""); } void AllocaSlices::printUse(raw_ostream &OS, const_iterator I, StringRef Indent) const { OS << Indent << " used by: " << *I->getUse()->getUser() << "\n"; } void AllocaSlices::print(raw_ostream &OS) const { if (PointerEscapingInstr) { OS << "Can't analyze slices for alloca: " << AI << "\n" << " A pointer to this alloca escaped by:\n" << " " << *PointerEscapingInstr << "\n"; return; } OS << "Slices of alloca: " << AI << "\n"; for (const_iterator I = begin(), E = end(); I != E; ++I) print(OS, I); } LLVM_DUMP_METHOD void AllocaSlices::dump(const_iterator I) const { print(dbgs(), I); } LLVM_DUMP_METHOD void AllocaSlices::dump() const { print(dbgs()); } #endif // !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) namespace { /// \brief Implementation of LoadAndStorePromoter for promoting allocas. /// /// This subclass of LoadAndStorePromoter adds overrides to handle promoting /// the loads and stores of an alloca instruction, as well as updating its /// debug information. This is used when a domtree is unavailable and thus /// mem2reg in its full form can't be used to handle promotion of allocas to /// scalar values. class AllocaPromoter : public LoadAndStorePromoter { AllocaInst &AI; DIBuilder &DIB; SmallVector<DbgDeclareInst *, 4> DDIs; SmallVector<DbgValueInst *, 4> DVIs; public: AllocaPromoter(const SmallVectorImpl<Instruction *> &Insts, SSAUpdater &S, AllocaInst &AI, DIBuilder &DIB) : LoadAndStorePromoter(Insts, S), AI(AI), DIB(DIB) {} void run(const SmallVectorImpl<Instruction *> &Insts) { // Retain the debug information attached to the alloca for use when // rewriting loads and stores. if (auto *L = LocalAsMetadata::getIfExists(&AI)) { if (auto *DebugNode = MetadataAsValue::getIfExists(AI.getContext(), L)) { for (User *U : DebugNode->users()) if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U)) DDIs.push_back(DDI); else if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(U)) DVIs.push_back(DVI); } } LoadAndStorePromoter::run(Insts); // While we have the debug information, clear it off of the alloca. The // caller takes care of deleting the alloca. while (!DDIs.empty()) DDIs.pop_back_val()->eraseFromParent(); while (!DVIs.empty()) DVIs.pop_back_val()->eraseFromParent(); } bool isInstInList(Instruction *I, const SmallVectorImpl<Instruction *> &Insts) const override { Value *Ptr; if (LoadInst *LI = dyn_cast<LoadInst>(I)) Ptr = LI->getOperand(0); else Ptr = cast<StoreInst>(I)->getPointerOperand(); // Only used to detect cycles, which will be rare and quickly found as // we're walking up a chain of defs rather than down through uses. SmallPtrSet<Value *, 4> Visited; do { if (Ptr == &AI) return true; if (BitCastInst *BCI = dyn_cast<BitCastInst>(Ptr)) Ptr = BCI->getOperand(0); else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Ptr)) Ptr = GEPI->getPointerOperand(); else return false; } while (Visited.insert(Ptr).second); return false; } void updateDebugInfo(Instruction *Inst) const override { for (DbgDeclareInst *DDI : DDIs) if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) ConvertDebugDeclareToDebugValue(DDI, SI, DIB); else if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) ConvertDebugDeclareToDebugValue(DDI, LI, DIB); for (DbgValueInst *DVI : DVIs) { Value *Arg = nullptr; if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { // If an argument is zero extended then use argument directly. The ZExt // may be zapped by an optimization pass in future. if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0))) Arg = dyn_cast<Argument>(ZExt->getOperand(0)); else if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0))) Arg = dyn_cast<Argument>(SExt->getOperand(0)); if (!Arg) Arg = SI->getValueOperand(); } else if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) { Arg = LI->getPointerOperand(); } else { continue; } Instruction *DbgVal = DIB.insertDbgValueIntrinsic(Arg, 0, DIVariable(DVI->getVariable()), DIExpression(DVI->getExpression()), Inst); DbgVal->setDebugLoc(DVI->getDebugLoc()); } } }; } // end anon namespace namespace { /// \brief An optimization pass providing Scalar Replacement of Aggregates. /// /// This pass takes allocations which can be completely analyzed (that is, they /// don't escape) and tries to turn them into scalar SSA values. There are /// a few steps to this process. /// /// 1) It takes allocations of aggregates and analyzes the ways in which they /// are used to try to split them into smaller allocations, ideally of /// a single scalar data type. It will split up memcpy and memset accesses /// as necessary and try to isolate individual scalar accesses. /// 2) It will transform accesses into forms which are suitable for SSA value /// promotion. This can be replacing a memset with a scalar store of an /// integer value, or it can involve speculating operations on a PHI or /// select to be a PHI or select of the results. /// 3) Finally, this will try to detect a pattern of accesses which map cleanly /// onto insert and extract operations on a vector value, and convert them to /// this form. By doing so, it will enable promotion of vector aggregates to /// SSA vector values. class SROA : public FunctionPass { const bool RequiresDomTree; LLVMContext *C; const DataLayout *DL; DominatorTree *DT; AssumptionCache *AC; /// \brief Worklist of alloca instructions to simplify. /// /// Each alloca in the function is added to this. Each new alloca formed gets /// added to it as well to recursively simplify unless that alloca can be /// directly promoted. Finally, each time we rewrite a use of an alloca other /// the one being actively rewritten, we add it back onto the list if not /// already present to ensure it is re-visited. SetVector<AllocaInst *, SmallVector<AllocaInst *, 16>> Worklist; /// \brief A collection of instructions to delete. /// We try to batch deletions to simplify code and make things a bit more /// efficient. SetVector<Instruction *, SmallVector<Instruction *, 8>> DeadInsts; /// \brief Post-promotion worklist. /// /// Sometimes we discover an alloca which has a high probability of becoming /// viable for SROA after a round of promotion takes place. In those cases, /// the alloca is enqueued here for re-processing. /// /// Note that we have to be very careful to clear allocas out of this list in /// the event they are deleted. SetVector<AllocaInst *, SmallVector<AllocaInst *, 16>> PostPromotionWorklist; /// \brief A collection of alloca instructions we can directly promote. std::vector<AllocaInst *> PromotableAllocas; /// \brief A worklist of PHIs to speculate prior to promoting allocas. /// /// All of these PHIs have been checked for the safety of speculation and by /// being speculated will allow promoting allocas currently in the promotable /// queue. SetVector<PHINode *, SmallVector<PHINode *, 2>> SpeculatablePHIs; /// \brief A worklist of select instructions to speculate prior to promoting /// allocas. /// /// All of these select instructions have been checked for the safety of /// speculation and by being speculated will allow promoting allocas /// currently in the promotable queue. SetVector<SelectInst *, SmallVector<SelectInst *, 2>> SpeculatableSelects; public: SROA(bool RequiresDomTree = true) : FunctionPass(ID), RequiresDomTree(RequiresDomTree), C(nullptr), DL(nullptr), DT(nullptr) { initializeSROAPass(*PassRegistry::getPassRegistry()); } bool runOnFunction(Function &F) override; void getAnalysisUsage(AnalysisUsage &AU) const override; const char *getPassName() const override { return "SROA"; } static char ID; private: friend class PHIOrSelectSpeculator; friend class AllocaSliceRewriter; bool presplitLoadsAndStores(AllocaInst &AI, AllocaSlices &AS); AllocaInst *rewritePartition(AllocaInst &AI, AllocaSlices &AS, AllocaSlices::Partition &P); bool splitAlloca(AllocaInst &AI, AllocaSlices &AS); bool runOnAlloca(AllocaInst &AI); void clobberUse(Use &U); void deleteDeadInstructions(SmallPtrSetImpl<AllocaInst *> &DeletedAllocas); bool promoteAllocas(Function &F); }; } char SROA::ID = 0; FunctionPass *llvm::createSROAPass(bool RequiresDomTree) { return new SROA(RequiresDomTree); } INITIALIZE_PASS_BEGIN(SROA, "sroa", "Scalar Replacement Of Aggregates", false, false) INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) INITIALIZE_PASS_END(SROA, "sroa", "Scalar Replacement Of Aggregates", false, false) /// Walk the range of a partitioning looking for a common type to cover this /// sequence of slices. static Type *findCommonType(AllocaSlices::const_iterator B, AllocaSlices::const_iterator E, uint64_t EndOffset) { Type *Ty = nullptr; bool TyIsCommon = true; IntegerType *ITy = nullptr; // Note that we need to look at *every* alloca slice's Use to ensure we // always get consistent results regardless of the order of slices. for (AllocaSlices::const_iterator I = B; I != E; ++I) { Use *U = I->getUse(); if (isa<IntrinsicInst>(*U->getUser())) continue; if (I->beginOffset() != B->beginOffset() || I->endOffset() != EndOffset) continue; Type *UserTy = nullptr; if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser())) { UserTy = LI->getType(); } else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser())) { UserTy = SI->getValueOperand()->getType(); } if (IntegerType *UserITy = dyn_cast_or_null<IntegerType>(UserTy)) { // If the type is larger than the partition, skip it. We only encounter // this for split integer operations where we want to use the type of the // entity causing the split. Also skip if the type is not a byte width // multiple. if (UserITy->getBitWidth() % 8 != 0 || UserITy->getBitWidth() / 8 > (EndOffset - B->beginOffset())) continue; // Track the largest bitwidth integer type used in this way in case there // is no common type. if (!ITy || ITy->getBitWidth() < UserITy->getBitWidth()) ITy = UserITy; } // To avoid depending on the order of slices, Ty and TyIsCommon must not // depend on types skipped above. if (!UserTy || (Ty && Ty != UserTy)) TyIsCommon = false; // Give up on anything but an iN type. else Ty = UserTy; } return TyIsCommon ? Ty : ITy; } /// PHI instructions that use an alloca and are subsequently loaded can be /// rewritten to load both input pointers in the pred blocks and then PHI the /// results, allowing the load of the alloca to be promoted. /// From this: /// %P2 = phi [i32* %Alloca, i32* %Other] /// %V = load i32* %P2 /// to: /// %V1 = load i32* %Alloca -> will be mem2reg'd /// ... /// %V2 = load i32* %Other /// ... /// %V = phi [i32 %V1, i32 %V2] /// /// We can do this to a select if its only uses are loads and if the operands /// to the select can be loaded unconditionally. /// /// FIXME: This should be hoisted into a generic utility, likely in /// Transforms/Util/Local.h static bool isSafePHIToSpeculate(PHINode &PN, const DataLayout *DL = nullptr) { // For now, we can only do this promotion if the load is in the same block // as the PHI, and if there are no stores between the phi and load. // TODO: Allow recursive phi users. // TODO: Allow stores. BasicBlock *BB = PN.getParent(); unsigned MaxAlign = 0; bool HaveLoad = false; for (User *U : PN.users()) { LoadInst *LI = dyn_cast<LoadInst>(U); if (!LI || !LI->isSimple()) return false; // For now we only allow loads in the same block as the PHI. This is // a common case that happens when instcombine merges two loads through // a PHI. if (LI->getParent() != BB) return false; // Ensure that there are no instructions between the PHI and the load that // could store. for (BasicBlock::iterator BBI = &PN; &*BBI != LI; ++BBI) if (BBI->mayWriteToMemory()) return false; MaxAlign = std::max(MaxAlign, LI->getAlignment()); HaveLoad = true; } if (!HaveLoad) return false; // We can only transform this if it is safe to push the loads into the // predecessor blocks. The only thing to watch out for is that we can't put // a possibly trapping load in the predecessor if it is a critical edge. for (unsigned Idx = 0, Num = PN.getNumIncomingValues(); Idx != Num; ++Idx) { TerminatorInst *TI = PN.getIncomingBlock(Idx)->getTerminator(); Value *InVal = PN.getIncomingValue(Idx); // If the value is produced by the terminator of the predecessor (an // invoke) or it has side-effects, there is no valid place to put a load // in the predecessor. if (TI == InVal || TI->mayHaveSideEffects()) return false; // If the predecessor has a single successor, then the edge isn't // critical. if (TI->getNumSuccessors() == 1) continue; // If this pointer is always safe to load, or if we can prove that there // is already a load in the block, then we can move the load to the pred // block. if (InVal->isDereferenceablePointer(DL) || isSafeToLoadUnconditionally(InVal, TI, MaxAlign, DL)) continue; return false; } return true; } static void speculatePHINodeLoads(PHINode &PN) { DEBUG(dbgs() << " original: " << PN << "\n"); Type *LoadTy = cast<PointerType>(PN.getType())->getElementType(); IRBuilderTy PHIBuilder(&PN); PHINode *NewPN = PHIBuilder.CreatePHI(LoadTy, PN.getNumIncomingValues(), PN.getName() + ".sroa.speculated"); // Get the AA tags and alignment to use from one of the loads. It doesn't // matter which one we get and if any differ. LoadInst *SomeLoad = cast<LoadInst>(PN.user_back()); AAMDNodes AATags; SomeLoad->getAAMetadata(AATags); unsigned Align = SomeLoad->getAlignment(); // Rewrite all loads of the PN to use the new PHI. while (!PN.use_empty()) { LoadInst *LI = cast<LoadInst>(PN.user_back()); LI->replaceAllUsesWith(NewPN); LI->eraseFromParent(); } // Inject loads into all of the pred blocks. for (unsigned Idx = 0, Num = PN.getNumIncomingValues(); Idx != Num; ++Idx) { BasicBlock *Pred = PN.getIncomingBlock(Idx); TerminatorInst *TI = Pred->getTerminator(); Value *InVal = PN.getIncomingValue(Idx); IRBuilderTy PredBuilder(TI); LoadInst *Load = PredBuilder.CreateLoad( InVal, (PN.getName() + ".sroa.speculate.load." + Pred->getName())); ++NumLoadsSpeculated; Load->setAlignment(Align); if (AATags) Load->setAAMetadata(AATags); NewPN->addIncoming(Load, Pred); } DEBUG(dbgs() << " speculated to: " << *NewPN << "\n"); PN.eraseFromParent(); } /// Select instructions that use an alloca and are subsequently loaded can be /// rewritten to load both input pointers and then select between the result, /// allowing the load of the alloca to be promoted. /// From this: /// %P2 = select i1 %cond, i32* %Alloca, i32* %Other /// %V = load i32* %P2 /// to: /// %V1 = load i32* %Alloca -> will be mem2reg'd /// %V2 = load i32* %Other /// %V = select i1 %cond, i32 %V1, i32 %V2 /// /// We can do this to a select if its only uses are loads and if the operand /// to the select can be loaded unconditionally. static bool isSafeSelectToSpeculate(SelectInst &SI, const DataLayout *DL = nullptr) { Value *TValue = SI.getTrueValue(); Value *FValue = SI.getFalseValue(); bool TDerefable = TValue->isDereferenceablePointer(DL); bool FDerefable = FValue->isDereferenceablePointer(DL); for (User *U : SI.users()) { LoadInst *LI = dyn_cast<LoadInst>(U); if (!LI || !LI->isSimple()) return false; // Both operands to the select need to be dereferencable, either // absolutely (e.g. allocas) or at this point because we can see other // accesses to it. if (!TDerefable && !isSafeToLoadUnconditionally(TValue, LI, LI->getAlignment(), DL)) return false; if (!FDerefable && !isSafeToLoadUnconditionally(FValue, LI, LI->getAlignment(), DL)) return false; } return true; } static void speculateSelectInstLoads(SelectInst &SI) { DEBUG(dbgs() << " original: " << SI << "\n"); IRBuilderTy IRB(&SI); Value *TV = SI.getTrueValue(); Value *FV = SI.getFalseValue(); // Replace the loads of the select with a select of two loads. while (!SI.use_empty()) { LoadInst *LI = cast<LoadInst>(SI.user_back()); assert(LI->isSimple() && "We only speculate simple loads"); IRB.SetInsertPoint(LI); LoadInst *TL = IRB.CreateLoad(TV, LI->getName() + ".sroa.speculate.load.true"); LoadInst *FL = IRB.CreateLoad(FV, LI->getName() + ".sroa.speculate.load.false"); NumLoadsSpeculated += 2; // Transfer alignment and AA info if present. TL->setAlignment(LI->getAlignment()); FL->setAlignment(LI->getAlignment()); AAMDNodes Tags; LI->getAAMetadata(Tags); if (Tags) { TL->setAAMetadata(Tags); FL->setAAMetadata(Tags); } Value *V = IRB.CreateSelect(SI.getCondition(), TL, FL, LI->getName() + ".sroa.speculated"); DEBUG(dbgs() << " speculated to: " << *V << "\n"); LI->replaceAllUsesWith(V); LI->eraseFromParent(); } SI.eraseFromParent(); } /// \brief Build a GEP out of a base pointer and indices. /// /// This will return the BasePtr if that is valid, or build a new GEP /// instruction using the IRBuilder if GEP-ing is needed. static Value *buildGEP(IRBuilderTy &IRB, Value *BasePtr, SmallVectorImpl<Value *> &Indices, Twine NamePrefix) { if (Indices.empty()) return BasePtr; // A single zero index is a no-op, so check for this and avoid building a GEP // in that case. if (Indices.size() == 1 && cast<ConstantInt>(Indices.back())->isZero()) return BasePtr; return IRB.CreateInBoundsGEP(BasePtr, Indices, NamePrefix + "sroa_idx"); } /// \brief Get a natural GEP off of the BasePtr walking through Ty toward /// TargetTy without changing the offset of the pointer. /// /// This routine assumes we've already established a properly offset GEP with /// Indices, and arrived at the Ty type. The goal is to continue to GEP with /// zero-indices down through type layers until we find one the same as /// TargetTy. If we can't find one with the same type, we at least try to use /// one with the same size. If none of that works, we just produce the GEP as /// indicated by Indices to have the correct offset. static Value *getNaturalGEPWithType(IRBuilderTy &IRB, const DataLayout &DL, Value *BasePtr, Type *Ty, Type *TargetTy, SmallVectorImpl<Value *> &Indices, Twine NamePrefix) { if (Ty == TargetTy) return buildGEP(IRB, BasePtr, Indices, NamePrefix); // Pointer size to use for the indices. unsigned PtrSize = DL.getPointerTypeSizeInBits(BasePtr->getType()); // See if we can descend into a struct and locate a field with the correct // type. unsigned NumLayers = 0; Type *ElementTy = Ty; do { if (ElementTy->isPointerTy()) break; if (ArrayType *ArrayTy = dyn_cast<ArrayType>(ElementTy)) { ElementTy = ArrayTy->getElementType(); Indices.push_back(IRB.getIntN(PtrSize, 0)); } else if (VectorType *VectorTy = dyn_cast<VectorType>(ElementTy)) { ElementTy = VectorTy->getElementType(); Indices.push_back(IRB.getInt32(0)); } else if (StructType *STy = dyn_cast<StructType>(ElementTy)) { if (STy->element_begin() == STy->element_end()) break; // Nothing left to descend into. ElementTy = *STy->element_begin(); Indices.push_back(IRB.getInt32(0)); } else { break; } ++NumLayers; } while (ElementTy != TargetTy); if (ElementTy != TargetTy) Indices.erase(Indices.end() - NumLayers, Indices.end()); return buildGEP(IRB, BasePtr, Indices, NamePrefix); } /// \brief Recursively compute indices for a natural GEP. /// /// This is the recursive step for getNaturalGEPWithOffset that walks down the /// element types adding appropriate indices for the GEP. static Value *getNaturalGEPRecursively(IRBuilderTy &IRB, const DataLayout &DL, Value *Ptr, Type *Ty, APInt &Offset, Type *TargetTy, SmallVectorImpl<Value *> &Indices, Twine NamePrefix) { if (Offset == 0) return getNaturalGEPWithType(IRB, DL, Ptr, Ty, TargetTy, Indices, NamePrefix); // We can't recurse through pointer types. if (Ty->isPointerTy()) return nullptr; // We try to analyze GEPs over vectors here, but note that these GEPs are // extremely poorly defined currently. The long-term goal is to remove GEPing // over a vector from the IR completely. if (VectorType *VecTy = dyn_cast<VectorType>(Ty)) { unsigned ElementSizeInBits = DL.getTypeSizeInBits(VecTy->getScalarType()); if (ElementSizeInBits % 8 != 0) { // GEPs over non-multiple of 8 size vector elements are invalid. return nullptr; } APInt ElementSize(Offset.getBitWidth(), ElementSizeInBits / 8); APInt NumSkippedElements = Offset.sdiv(ElementSize); if (NumSkippedElements.ugt(VecTy->getNumElements())) return nullptr; Offset -= NumSkippedElements * ElementSize; Indices.push_back(IRB.getInt(NumSkippedElements)); return getNaturalGEPRecursively(IRB, DL, Ptr, VecTy->getElementType(), Offset, TargetTy, Indices, NamePrefix); } if (ArrayType *ArrTy = dyn_cast<ArrayType>(Ty)) { Type *ElementTy = ArrTy->getElementType(); APInt ElementSize(Offset.getBitWidth(), DL.getTypeAllocSize(ElementTy)); APInt NumSkippedElements = Offset.sdiv(ElementSize); if (NumSkippedElements.ugt(ArrTy->getNumElements())) return nullptr; Offset -= NumSkippedElements * ElementSize; Indices.push_back(IRB.getInt(NumSkippedElements)); return getNaturalGEPRecursively(IRB, DL, Ptr, ElementTy, Offset, TargetTy, Indices, NamePrefix); } StructType *STy = dyn_cast<StructType>(Ty); if (!STy) return nullptr; const StructLayout *SL = DL.getStructLayout(STy); uint64_t StructOffset = Offset.getZExtValue(); if (StructOffset >= SL->getSizeInBytes()) return nullptr; unsigned Index = SL->getElementContainingOffset(StructOffset); Offset -= APInt(Offset.getBitWidth(), SL->getElementOffset(Index)); Type *ElementTy = STy->getElementType(Index); if (Offset.uge(DL.getTypeAllocSize(ElementTy))) return nullptr; // The offset points into alignment padding. Indices.push_back(IRB.getInt32(Index)); return getNaturalGEPRecursively(IRB, DL, Ptr, ElementTy, Offset, TargetTy, Indices, NamePrefix); } /// \brief Get a natural GEP from a base pointer to a particular offset and /// resulting in a particular type. /// /// The goal is to produce a "natural" looking GEP that works with the existing /// composite types to arrive at the appropriate offset and element type for /// a pointer. TargetTy is the element type the returned GEP should point-to if /// possible. We recurse by decreasing Offset, adding the appropriate index to /// Indices, and setting Ty to the result subtype. /// /// If no natural GEP can be constructed, this function returns null. static Value *getNaturalGEPWithOffset(IRBuilderTy &IRB, const DataLayout &DL, Value *Ptr, APInt Offset, Type *TargetTy, SmallVectorImpl<Value *> &Indices, Twine NamePrefix) { PointerType *Ty = cast<PointerType>(Ptr->getType()); // Don't consider any GEPs through an i8* as natural unless the TargetTy is // an i8. if (Ty == IRB.getInt8PtrTy(Ty->getAddressSpace()) && TargetTy->isIntegerTy(8)) return nullptr; Type *ElementTy = Ty->getElementType(); if (!ElementTy->isSized()) return nullptr; // We can't GEP through an unsized element. APInt ElementSize(Offset.getBitWidth(), DL.getTypeAllocSize(ElementTy)); if (ElementSize == 0) return nullptr; // Zero-length arrays can't help us build a natural GEP. APInt NumSkippedElements = Offset.sdiv(ElementSize); Offset -= NumSkippedElements * ElementSize; Indices.push_back(IRB.getInt(NumSkippedElements)); return getNaturalGEPRecursively(IRB, DL, Ptr, ElementTy, Offset, TargetTy, Indices, NamePrefix); } /// \brief Compute an adjusted pointer from Ptr by Offset bytes where the /// resulting pointer has PointerTy. /// /// This tries very hard to compute a "natural" GEP which arrives at the offset /// and produces the pointer type desired. Where it cannot, it will try to use /// the natural GEP to arrive at the offset and bitcast to the type. Where that /// fails, it will try to use an existing i8* and GEP to the byte offset and /// bitcast to the type. /// /// The strategy for finding the more natural GEPs is to peel off layers of the /// pointer, walking back through bit casts and GEPs, searching for a base /// pointer from which we can compute a natural GEP with the desired /// properties. The algorithm tries to fold as many constant indices into /// a single GEP as possible, thus making each GEP more independent of the /// surrounding code. static Value *getAdjustedPtr(IRBuilderTy &IRB, const DataLayout &DL, Value *Ptr, APInt Offset, Type *PointerTy, Twine NamePrefix) { // Even though we don't look through PHI nodes, we could be called on an // instruction in an unreachable block, which may be on a cycle. SmallPtrSet<Value *, 4> Visited; Visited.insert(Ptr); SmallVector<Value *, 4> Indices; // We may end up computing an offset pointer that has the wrong type. If we // never are able to compute one directly that has the correct type, we'll // fall back to it, so keep it and the base it was computed from around here. Value *OffsetPtr = nullptr; Value *OffsetBasePtr; // Remember any i8 pointer we come across to re-use if we need to do a raw // byte offset. Value *Int8Ptr = nullptr; APInt Int8PtrOffset(Offset.getBitWidth(), 0); Type *TargetTy = PointerTy->getPointerElementType(); do { // First fold any existing GEPs into the offset. while (GEPOperator *GEP = dyn_cast<GEPOperator>(Ptr)) { APInt GEPOffset(Offset.getBitWidth(), 0); if (!GEP->accumulateConstantOffset(DL, GEPOffset)) break; Offset += GEPOffset; Ptr = GEP->getPointerOperand(); if (!Visited.insert(Ptr).second) break; } // See if we can perform a natural GEP here. Indices.clear(); if (Value *P = getNaturalGEPWithOffset(IRB, DL, Ptr, Offset, TargetTy, Indices, NamePrefix)) { // If we have a new natural pointer at the offset, clear out any old // offset pointer we computed. Unless it is the base pointer or // a non-instruction, we built a GEP we don't need. Zap it. if (OffsetPtr && OffsetPtr != OffsetBasePtr) if (Instruction *I = dyn_cast<Instruction>(OffsetPtr)) { assert(I->use_empty() && "Built a GEP with uses some how!"); I->eraseFromParent(); } OffsetPtr = P; OffsetBasePtr = Ptr; // If we also found a pointer of the right type, we're done. if (P->getType() == PointerTy) return P; } // Stash this pointer if we've found an i8*. if (Ptr->getType()->isIntegerTy(8)) { Int8Ptr = Ptr; Int8PtrOffset = Offset; } // Peel off a layer of the pointer and update the offset appropriately. if (Operator::getOpcode(Ptr) == Instruction::BitCast) { Ptr = cast<Operator>(Ptr)->getOperand(0); } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(Ptr)) { if (GA->mayBeOverridden()) break; Ptr = GA->getAliasee(); } else { break; } assert(Ptr->getType()->isPointerTy() && "Unexpected operand type!"); } while (Visited.insert(Ptr).second); if (!OffsetPtr) { if (!Int8Ptr) { Int8Ptr = IRB.CreateBitCast( Ptr, IRB.getInt8PtrTy(PointerTy->getPointerAddressSpace()), NamePrefix + "sroa_raw_cast"); Int8PtrOffset = Offset; } OffsetPtr = Int8PtrOffset == 0 ? Int8Ptr : IRB.CreateInBoundsGEP(Int8Ptr, IRB.getInt(Int8PtrOffset), NamePrefix + "sroa_raw_idx"); } Ptr = OffsetPtr; // On the off chance we were targeting i8*, guard the bitcast here. if (Ptr->getType() != PointerTy) Ptr = IRB.CreateBitCast(Ptr, PointerTy, NamePrefix + "sroa_cast"); return Ptr; } /// \brief Compute the adjusted alignment for a load or store from an offset. static unsigned getAdjustedAlignment(Instruction *I, uint64_t Offset, const DataLayout &DL) { unsigned Alignment; Type *Ty; if (auto *LI = dyn_cast<LoadInst>(I)) { Alignment = LI->getAlignment(); Ty = LI->getType(); } else if (auto *SI = dyn_cast<StoreInst>(I)) { Alignment = SI->getAlignment(); Ty = SI->getValueOperand()->getType(); } else { llvm_unreachable("Only loads and stores are allowed!"); } if (!Alignment) Alignment = DL.getABITypeAlignment(Ty); return MinAlign(Alignment, Offset); } /// \brief Test whether we can convert a value from the old to the new type. /// /// This predicate should be used to guard calls to convertValue in order to /// ensure that we only try to convert viable values. The strategy is that we /// will peel off single element struct and array wrappings to get to an /// underlying value, and convert that value. static bool canConvertValue(const DataLayout &DL, Type *OldTy, Type *NewTy) { if (OldTy == NewTy) return true; if (IntegerType *OldITy = dyn_cast<IntegerType>(OldTy)) if (IntegerType *NewITy = dyn_cast<IntegerType>(NewTy)) if (NewITy->getBitWidth() >= OldITy->getBitWidth()) return true; if (DL.getTypeSizeInBits(NewTy) != DL.getTypeSizeInBits(OldTy)) return false; if (!NewTy->isSingleValueType() || !OldTy->isSingleValueType()) return false; // We can convert pointers to integers and vice-versa. Same for vectors // of pointers and integers. OldTy = OldTy->getScalarType(); NewTy = NewTy->getScalarType(); if (NewTy->isPointerTy() || OldTy->isPointerTy()) { if (NewTy->isPointerTy() && OldTy->isPointerTy()) return true; if (NewTy->isIntegerTy() || OldTy->isIntegerTy()) return true; return false; } return true; } /// \brief Generic routine to convert an SSA value to a value of a different /// type. /// /// This will try various different casting techniques, such as bitcasts, /// inttoptr, and ptrtoint casts. Use the \c canConvertValue predicate to test /// two types for viability with this routine. static Value *convertValue(const DataLayout &DL, IRBuilderTy &IRB, Value *V, Type *NewTy) { Type *OldTy = V->getType(); assert(canConvertValue(DL, OldTy, NewTy) && "Value not convertable to type"); if (OldTy == NewTy) return V; if (IntegerType *OldITy = dyn_cast<IntegerType>(OldTy)) if (IntegerType *NewITy = dyn_cast<IntegerType>(NewTy)) if (NewITy->getBitWidth() > OldITy->getBitWidth()) return IRB.CreateZExt(V, NewITy); // See if we need inttoptr for this type pair. A cast involving both scalars // and vectors requires and additional bitcast. if (OldTy->getScalarType()->isIntegerTy() && NewTy->getScalarType()->isPointerTy()) { // Expand <2 x i32> to i8* --> <2 x i32> to i64 to i8* if (OldTy->isVectorTy() && !NewTy->isVectorTy()) return IRB.CreateIntToPtr(IRB.CreateBitCast(V, DL.getIntPtrType(NewTy)), NewTy); // Expand i128 to <2 x i8*> --> i128 to <2 x i64> to <2 x i8*> if (!OldTy->isVectorTy() && NewTy->isVectorTy()) return IRB.CreateIntToPtr(IRB.CreateBitCast(V, DL.getIntPtrType(NewTy)), NewTy); return IRB.CreateIntToPtr(V, NewTy); } // See if we need ptrtoint for this type pair. A cast involving both scalars // and vectors requires and additional bitcast. if (OldTy->getScalarType()->isPointerTy() && NewTy->getScalarType()->isIntegerTy()) { // Expand <2 x i8*> to i128 --> <2 x i8*> to <2 x i64> to i128 if (OldTy->isVectorTy() && !NewTy->isVectorTy()) return IRB.CreateBitCast(IRB.CreatePtrToInt(V, DL.getIntPtrType(OldTy)), NewTy); // Expand i8* to <2 x i32> --> i8* to i64 to <2 x i32> if (!OldTy->isVectorTy() && NewTy->isVectorTy()) return IRB.CreateBitCast(IRB.CreatePtrToInt(V, DL.getIntPtrType(OldTy)), NewTy); return IRB.CreatePtrToInt(V, NewTy); } return IRB.CreateBitCast(V, NewTy); } /// \brief Test whether the given slice use can be promoted to a vector. /// /// This function is called to test each entry in a partioning which is slated /// for a single slice. static bool isVectorPromotionViableForSlice(AllocaSlices::Partition &P, const Slice &S, VectorType *Ty, uint64_t ElementSize, const DataLayout &DL) { // First validate the slice offsets. uint64_t BeginOffset = std::max(S.beginOffset(), P.beginOffset()) - P.beginOffset(); uint64_t BeginIndex = BeginOffset / ElementSize; if (BeginIndex * ElementSize != BeginOffset || BeginIndex >= Ty->getNumElements()) return false; uint64_t EndOffset = std::min(S.endOffset(), P.endOffset()) - P.beginOffset(); uint64_t EndIndex = EndOffset / ElementSize; if (EndIndex * ElementSize != EndOffset || EndIndex > Ty->getNumElements()) return false; assert(EndIndex > BeginIndex && "Empty vector!"); uint64_t NumElements = EndIndex - BeginIndex; Type *SliceTy = (NumElements == 1) ? Ty->getElementType() : VectorType::get(Ty->getElementType(), NumElements); Type *SplitIntTy = Type::getIntNTy(Ty->getContext(), NumElements * ElementSize * 8); Use *U = S.getUse(); if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U->getUser())) { if (MI->isVolatile()) return false; if (!S.isSplittable()) return false; // Skip any unsplittable intrinsics. } else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(U->getUser())) { if (II->getIntrinsicID() != Intrinsic::lifetime_start && II->getIntrinsicID() != Intrinsic::lifetime_end) return false; } else if (U->get()->getType()->getPointerElementType()->isStructTy()) { // Disable vector promotion when there are loads or stores of an FCA. return false; } else if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser())) { if (LI->isVolatile()) return false; Type *LTy = LI->getType(); if (P.beginOffset() > S.beginOffset() || P.endOffset() < S.endOffset()) { assert(LTy->isIntegerTy()); LTy = SplitIntTy; } if (!canConvertValue(DL, SliceTy, LTy)) return false; } else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser())) { if (SI->isVolatile()) return false; Type *STy = SI->getValueOperand()->getType(); if (P.beginOffset() > S.beginOffset() || P.endOffset() < S.endOffset()) { assert(STy->isIntegerTy()); STy = SplitIntTy; } if (!canConvertValue(DL, STy, SliceTy)) return false; } else { return false; } return true; } /// \brief Test whether the given alloca partitioning and range of slices can be /// promoted to a vector. /// /// This is a quick test to check whether we can rewrite a particular alloca /// partition (and its newly formed alloca) into a vector alloca with only /// whole-vector loads and stores such that it could be promoted to a vector /// SSA value. We only can ensure this for a limited set of operations, and we /// don't want to do the rewrites unless we are confident that the result will /// be promotable, so we have an early test here. static VectorType *isVectorPromotionViable(AllocaSlices::Partition &P, const DataLayout &DL) { // Collect the candidate types for vector-based promotion. Also track whether // we have different element types. SmallVector<VectorType *, 4> CandidateTys; Type *CommonEltTy = nullptr; bool HaveCommonEltTy = true; auto CheckCandidateType = [&](Type *Ty) { if (auto *VTy = dyn_cast<VectorType>(Ty)) { CandidateTys.push_back(VTy); if (!CommonEltTy) CommonEltTy = VTy->getElementType(); else if (CommonEltTy != VTy->getElementType()) HaveCommonEltTy = false; } }; // Consider any loads or stores that are the exact size of the slice. for (const Slice &S : P) if (S.beginOffset() == P.beginOffset() && S.endOffset() == P.endOffset()) { if (auto *LI = dyn_cast<LoadInst>(S.getUse()->getUser())) CheckCandidateType(LI->getType()); else if (auto *SI = dyn_cast<StoreInst>(S.getUse()->getUser())) CheckCandidateType(SI->getValueOperand()->getType()); } // If we didn't find a vector type, nothing to do here. if (CandidateTys.empty()) return nullptr; // Remove non-integer vector types if we had multiple common element types. // FIXME: It'd be nice to replace them with integer vector types, but we can't // do that until all the backends are known to produce good code for all // integer vector types. if (!HaveCommonEltTy) { CandidateTys.erase(std::remove_if(CandidateTys.begin(), CandidateTys.end(), [](VectorType *VTy) { return !VTy->getElementType()->isIntegerTy(); }), CandidateTys.end()); // If there were no integer vector types, give up. if (CandidateTys.empty()) return nullptr; // Rank the remaining candidate vector types. This is easy because we know // they're all integer vectors. We sort by ascending number of elements. auto RankVectorTypes = [&DL](VectorType *RHSTy, VectorType *LHSTy) { assert(DL.getTypeSizeInBits(RHSTy) == DL.getTypeSizeInBits(LHSTy) && "Cannot have vector types of different sizes!"); assert(RHSTy->getElementType()->isIntegerTy() && "All non-integer types eliminated!"); assert(LHSTy->getElementType()->isIntegerTy() && "All non-integer types eliminated!"); return RHSTy->getNumElements() < LHSTy->getNumElements(); }; std::sort(CandidateTys.begin(), CandidateTys.end(), RankVectorTypes); CandidateTys.erase( std::unique(CandidateTys.begin(), CandidateTys.end(), RankVectorTypes), CandidateTys.end()); } else { // The only way to have the same element type in every vector type is to // have the same vector type. Check that and remove all but one. #ifndef NDEBUG for (VectorType *VTy : CandidateTys) { assert(VTy->getElementType() == CommonEltTy && "Unaccounted for element type!"); assert(VTy == CandidateTys[0] && "Different vector types with the same element type!"); } #endif CandidateTys.resize(1); } // Try each vector type, and return the one which works. auto CheckVectorTypeForPromotion = [&](VectorType *VTy) { uint64_t ElementSize = DL.getTypeSizeInBits(VTy->getElementType()); // While the definition of LLVM vectors is bitpacked, we don't support sizes // that aren't byte sized. if (ElementSize % 8) return false; assert((DL.getTypeSizeInBits(VTy) % 8) == 0 && "vector size not a multiple of element size?"); ElementSize /= 8; for (const Slice &S : P) if (!isVectorPromotionViableForSlice(P, S, VTy, ElementSize, DL)) return false; for (const Slice *S : P.splitSliceTails()) if (!isVectorPromotionViableForSlice(P, *S, VTy, ElementSize, DL)) return false; return true; }; for (VectorType *VTy : CandidateTys) if (CheckVectorTypeForPromotion(VTy)) return VTy; return nullptr; } /// \brief Test whether a slice of an alloca is valid for integer widening. /// /// This implements the necessary checking for the \c isIntegerWideningViable /// test below on a single slice of the alloca. static bool isIntegerWideningViableForSlice(const Slice &S, uint64_t AllocBeginOffset, Type *AllocaTy, const DataLayout &DL, bool &WholeAllocaOp) { uint64_t Size = DL.getTypeStoreSize(AllocaTy); uint64_t RelBegin = S.beginOffset() - AllocBeginOffset; uint64_t RelEnd = S.endOffset() - AllocBeginOffset; // We can't reasonably handle cases where the load or store extends past // the end of the aloca's type and into its padding. if (RelEnd > Size) return false; Use *U = S.getUse(); if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser())) { if (LI->isVolatile()) return false; // Note that we don't count vector loads or stores as whole-alloca // operations which enable integer widening because we would prefer to use // vector widening instead. if (!isa<VectorType>(LI->getType()) && RelBegin == 0 && RelEnd == Size) WholeAllocaOp = true; if (IntegerType *ITy = dyn_cast<IntegerType>(LI->getType())) { if (ITy->getBitWidth() < DL.getTypeStoreSizeInBits(ITy)) return false; } else if (RelBegin != 0 || RelEnd != Size || !canConvertValue(DL, AllocaTy, LI->getType())) { // Non-integer loads need to be convertible from the alloca type so that // they are promotable. return false; } } else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser())) { Type *ValueTy = SI->getValueOperand()->getType(); if (SI->isVolatile()) return false; // Note that we don't count vector loads or stores as whole-alloca // operations which enable integer widening because we would prefer to use // vector widening instead. if (!isa<VectorType>(ValueTy) && RelBegin == 0 && RelEnd == Size) WholeAllocaOp = true; if (IntegerType *ITy = dyn_cast<IntegerType>(ValueTy)) { if (ITy->getBitWidth() < DL.getTypeStoreSizeInBits(ITy)) return false; } else if (RelBegin != 0 || RelEnd != Size || !canConvertValue(DL, ValueTy, AllocaTy)) { // Non-integer stores need to be convertible to the alloca type so that // they are promotable. return false; } } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U->getUser())) { if (MI->isVolatile() || !isa<Constant>(MI->getLength())) return false; if (!S.isSplittable()) return false; // Skip any unsplittable intrinsics. } else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(U->getUser())) { if (II->getIntrinsicID() != Intrinsic::lifetime_start && II->getIntrinsicID() != Intrinsic::lifetime_end) return false; } else { return false; } return true; } /// \brief Test whether the given alloca partition's integer operations can be /// widened to promotable ones. /// /// This is a quick test to check whether we can rewrite the integer loads and /// stores to a particular alloca into wider loads and stores and be able to /// promote the resulting alloca. static bool isIntegerWideningViable(AllocaSlices::Partition &P, Type *AllocaTy, const DataLayout &DL) { uint64_t SizeInBits = DL.getTypeSizeInBits(AllocaTy); // Don't create integer types larger than the maximum bitwidth. if (SizeInBits > IntegerType::MAX_INT_BITS) return false; // Don't try to handle allocas with bit-padding. if (SizeInBits != DL.getTypeStoreSizeInBits(AllocaTy)) return false; // We need to ensure that an integer type with the appropriate bitwidth can // be converted to the alloca type, whatever that is. We don't want to force // the alloca itself to have an integer type if there is a more suitable one. Type *IntTy = Type::getIntNTy(AllocaTy->getContext(), SizeInBits); if (!canConvertValue(DL, AllocaTy, IntTy) || !canConvertValue(DL, IntTy, AllocaTy)) return false; // While examining uses, we ensure that the alloca has a covering load or // store. We don't want to widen the integer operations only to fail to // promote due to some other unsplittable entry (which we may make splittable // later). However, if there are only splittable uses, go ahead and assume // that we cover the alloca. // FIXME: We shouldn't consider split slices that happen to start in the // partition here... bool WholeAllocaOp = P.begin() != P.end() ? false : DL.isLegalInteger(SizeInBits); for (const Slice &S : P) if (!isIntegerWideningViableForSlice(S, P.beginOffset(), AllocaTy, DL, WholeAllocaOp)) return false; for (const Slice *S : P.splitSliceTails()) if (!isIntegerWideningViableForSlice(*S, P.beginOffset(), AllocaTy, DL, WholeAllocaOp)) return false; return WholeAllocaOp; } static Value *extractInteger(const DataLayout &DL, IRBuilderTy &IRB, Value *V, IntegerType *Ty, uint64_t Offset, const Twine &Name) { DEBUG(dbgs() << " start: " << *V << "\n"); IntegerType *IntTy = cast<IntegerType>(V->getType()); assert(DL.getTypeStoreSize(Ty) + Offset <= DL.getTypeStoreSize(IntTy) && "Element extends past full value"); uint64_t ShAmt = 8 * Offset; if (DL.isBigEndian()) ShAmt = 8 * (DL.getTypeStoreSize(IntTy) - DL.getTypeStoreSize(Ty) - Offset); if (ShAmt) { V = IRB.CreateLShr(V, ShAmt, Name + ".shift"); DEBUG(dbgs() << " shifted: " << *V << "\n"); } assert(Ty->getBitWidth() <= IntTy->getBitWidth() && "Cannot extract to a larger integer!"); if (Ty != IntTy) { V = IRB.CreateTrunc(V, Ty, Name + ".trunc"); DEBUG(dbgs() << " trunced: " << *V << "\n"); } return V; } static Value *insertInteger(const DataLayout &DL, IRBuilderTy &IRB, Value *Old, Value *V, uint64_t Offset, const Twine &Name) { IntegerType *IntTy = cast<IntegerType>(Old->getType()); IntegerType *Ty = cast<IntegerType>(V->getType()); assert(Ty->getBitWidth() <= IntTy->getBitWidth() && "Cannot insert a larger integer!"); DEBUG(dbgs() << " start: " << *V << "\n"); if (Ty != IntTy) { V = IRB.CreateZExt(V, IntTy, Name + ".ext"); DEBUG(dbgs() << " extended: " << *V << "\n"); } assert(DL.getTypeStoreSize(Ty) + Offset <= DL.getTypeStoreSize(IntTy) && "Element store outside of alloca store"); uint64_t ShAmt = 8 * Offset; if (DL.isBigEndian()) ShAmt = 8 * (DL.getTypeStoreSize(IntTy) - DL.getTypeStoreSize(Ty) - Offset); if (ShAmt) { V = IRB.CreateShl(V, ShAmt, Name + ".shift"); DEBUG(dbgs() << " shifted: " << *V << "\n"); } if (ShAmt || Ty->getBitWidth() < IntTy->getBitWidth()) { APInt Mask = ~Ty->getMask().zext(IntTy->getBitWidth()).shl(ShAmt); Old = IRB.CreateAnd(Old, Mask, Name + ".mask"); DEBUG(dbgs() << " masked: " << *Old << "\n"); V = IRB.CreateOr(Old, V, Name + ".insert"); DEBUG(dbgs() << " inserted: " << *V << "\n"); } return V; } static Value *extractVector(IRBuilderTy &IRB, Value *V, unsigned BeginIndex, unsigned EndIndex, const Twine &Name) { VectorType *VecTy = cast<VectorType>(V->getType()); unsigned NumElements = EndIndex - BeginIndex; assert(NumElements <= VecTy->getNumElements() && "Too many elements!"); if (NumElements == VecTy->getNumElements()) return V; if (NumElements == 1) { V = IRB.CreateExtractElement(V, IRB.getInt32(BeginIndex), Name + ".extract"); DEBUG(dbgs() << " extract: " << *V << "\n"); return V; } SmallVector<Constant *, 8> Mask; Mask.reserve(NumElements); for (unsigned i = BeginIndex; i != EndIndex; ++i) Mask.push_back(IRB.getInt32(i)); V = IRB.CreateShuffleVector(V, UndefValue::get(V->getType()), ConstantVector::get(Mask), Name + ".extract"); DEBUG(dbgs() << " shuffle: " << *V << "\n"); return V; } static Value *insertVector(IRBuilderTy &IRB, Value *Old, Value *V, unsigned BeginIndex, const Twine &Name) { VectorType *VecTy = cast<VectorType>(Old->getType()); assert(VecTy && "Can only insert a vector into a vector"); VectorType *Ty = dyn_cast<VectorType>(V->getType()); if (!Ty) { // Single element to insert. V = IRB.CreateInsertElement(Old, V, IRB.getInt32(BeginIndex), Name + ".insert"); DEBUG(dbgs() << " insert: " << *V << "\n"); return V; } assert(Ty->getNumElements() <= VecTy->getNumElements() && "Too many elements!"); if (Ty->getNumElements() == VecTy->getNumElements()) { assert(V->getType() == VecTy && "Vector type mismatch"); return V; } unsigned EndIndex = BeginIndex + Ty->getNumElements(); // When inserting a smaller vector into the larger to store, we first // use a shuffle vector to widen it with undef elements, and then // a second shuffle vector to select between the loaded vector and the // incoming vector. SmallVector<Constant *, 8> Mask; Mask.reserve(VecTy->getNumElements()); for (unsigned i = 0; i != VecTy->getNumElements(); ++i) if (i >= BeginIndex && i < EndIndex) Mask.push_back(IRB.getInt32(i - BeginIndex)); else Mask.push_back(UndefValue::get(IRB.getInt32Ty())); V = IRB.CreateShuffleVector(V, UndefValue::get(V->getType()), ConstantVector::get(Mask), Name + ".expand"); DEBUG(dbgs() << " shuffle: " << *V << "\n"); Mask.clear(); for (unsigned i = 0; i != VecTy->getNumElements(); ++i) Mask.push_back(IRB.getInt1(i >= BeginIndex && i < EndIndex)); V = IRB.CreateSelect(ConstantVector::get(Mask), V, Old, Name + "blend"); DEBUG(dbgs() << " blend: " << *V << "\n"); return V; } namespace { /// \brief Visitor to rewrite instructions using p particular slice of an alloca /// to use a new alloca. /// /// Also implements the rewriting to vector-based accesses when the partition /// passes the isVectorPromotionViable predicate. Most of the rewriting logic /// lives here. class AllocaSliceRewriter : public InstVisitor<AllocaSliceRewriter, bool> { // Befriend the base class so it can delegate to private visit methods. friend class llvm::InstVisitor<AllocaSliceRewriter, bool>; typedef llvm::InstVisitor<AllocaSliceRewriter, bool> Base; const DataLayout &DL; AllocaSlices &AS; SROA &Pass; AllocaInst &OldAI, &NewAI; const uint64_t NewAllocaBeginOffset, NewAllocaEndOffset; Type *NewAllocaTy; // This is a convenience and flag variable that will be null unless the new // alloca's integer operations should be widened to this integer type due to // passing isIntegerWideningViable above. If it is non-null, the desired // integer type will be stored here for easy access during rewriting. IntegerType *IntTy; // If we are rewriting an alloca partition which can be written as pure // vector operations, we stash extra information here. When VecTy is // non-null, we have some strict guarantees about the rewritten alloca: // - The new alloca is exactly the size of the vector type here. // - The accesses all either map to the entire vector or to a single // element. // - The set of accessing instructions is only one of those handled above // in isVectorPromotionViable. Generally these are the same access kinds // which are promotable via mem2reg. VectorType *VecTy; Type *ElementTy; uint64_t ElementSize; // The original offset of the slice currently being rewritten relative to // the original alloca. uint64_t BeginOffset, EndOffset; // The new offsets of the slice currently being rewritten relative to the // original alloca. uint64_t NewBeginOffset, NewEndOffset; uint64_t SliceSize; bool IsSplittable; bool IsSplit; Use *OldUse; Instruction *OldPtr; // Track post-rewrite users which are PHI nodes and Selects. SmallPtrSetImpl<PHINode *> &PHIUsers; SmallPtrSetImpl<SelectInst *> &SelectUsers; // Utility IR builder, whose name prefix is setup for each visited use, and // the insertion point is set to point to the user. IRBuilderTy IRB; public: AllocaSliceRewriter(const DataLayout &DL, AllocaSlices &AS, SROA &Pass, AllocaInst &OldAI, AllocaInst &NewAI, uint64_t NewAllocaBeginOffset, uint64_t NewAllocaEndOffset, bool IsIntegerPromotable, VectorType *PromotableVecTy, SmallPtrSetImpl<PHINode *> &PHIUsers, SmallPtrSetImpl<SelectInst *> &SelectUsers) : DL(DL), AS(AS), Pass(Pass), OldAI(OldAI), NewAI(NewAI), NewAllocaBeginOffset(NewAllocaBeginOffset), NewAllocaEndOffset(NewAllocaEndOffset), NewAllocaTy(NewAI.getAllocatedType()), IntTy(IsIntegerPromotable ? Type::getIntNTy( NewAI.getContext(), DL.getTypeSizeInBits(NewAI.getAllocatedType())) : nullptr), VecTy(PromotableVecTy), ElementTy(VecTy ? VecTy->getElementType() : nullptr), ElementSize(VecTy ? DL.getTypeSizeInBits(ElementTy) / 8 : 0), BeginOffset(), EndOffset(), IsSplittable(), IsSplit(), OldUse(), OldPtr(), PHIUsers(PHIUsers), SelectUsers(SelectUsers), IRB(NewAI.getContext(), ConstantFolder()) { if (VecTy) { assert((DL.getTypeSizeInBits(ElementTy) % 8) == 0 && "Only multiple-of-8 sized vector elements are viable"); ++NumVectorized; } assert((!IntTy && !VecTy) || (IntTy && !VecTy) || (!IntTy && VecTy)); } bool visit(AllocaSlices::const_iterator I) { bool CanSROA = true; BeginOffset = I->beginOffset(); EndOffset = I->endOffset(); IsSplittable = I->isSplittable(); IsSplit = BeginOffset < NewAllocaBeginOffset || EndOffset > NewAllocaEndOffset; DEBUG(dbgs() << " rewriting " << (IsSplit ? "split " : "")); DEBUG(AS.printSlice(dbgs(), I, "")); DEBUG(dbgs() << "\n"); // Compute the intersecting offset range. assert(BeginOffset < NewAllocaEndOffset); assert(EndOffset > NewAllocaBeginOffset); NewBeginOffset = std::max(BeginOffset, NewAllocaBeginOffset); NewEndOffset = std::min(EndOffset, NewAllocaEndOffset); SliceSize = NewEndOffset - NewBeginOffset; OldUse = I->getUse(); OldPtr = cast<Instruction>(OldUse->get()); Instruction *OldUserI = cast<Instruction>(OldUse->getUser()); IRB.SetInsertPoint(OldUserI); IRB.SetCurrentDebugLocation(OldUserI->getDebugLoc()); IRB.SetNamePrefix(Twine(NewAI.getName()) + "." + Twine(BeginOffset) + "."); CanSROA &= visit(cast<Instruction>(OldUse->getUser())); if (VecTy || IntTy) assert(CanSROA); return CanSROA; } private: // Make sure the other visit overloads are visible. using Base::visit; // Every instruction which can end up as a user must have a rewrite rule. bool visitInstruction(Instruction &I) { DEBUG(dbgs() << " !!!! Cannot rewrite: " << I << "\n"); llvm_unreachable("No rewrite rule for this instruction!"); } Value *getNewAllocaSlicePtr(IRBuilderTy &IRB, Type *PointerTy) { // Note that the offset computation can use BeginOffset or NewBeginOffset // interchangeably for unsplit slices. assert(IsSplit || BeginOffset == NewBeginOffset); uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset; #ifndef NDEBUG StringRef OldName = OldPtr->getName(); // Skip through the last '.sroa.' component of the name. size_t LastSROAPrefix = OldName.rfind(".sroa."); if (LastSROAPrefix != StringRef::npos) { OldName = OldName.substr(LastSROAPrefix + strlen(".sroa.")); // Look for an SROA slice index. size_t IndexEnd = OldName.find_first_not_of("0123456789"); if (IndexEnd != StringRef::npos && OldName[IndexEnd] == '.') { // Strip the index and look for the offset. OldName = OldName.substr(IndexEnd + 1); size_t OffsetEnd = OldName.find_first_not_of("0123456789"); if (OffsetEnd != StringRef::npos && OldName[OffsetEnd] == '.') // Strip the offset. OldName = OldName.substr(OffsetEnd + 1); } } // Strip any SROA suffixes as well. OldName = OldName.substr(0, OldName.find(".sroa_")); #endif return getAdjustedPtr(IRB, DL, &NewAI, APInt(DL.getPointerSizeInBits(), Offset), PointerTy, #ifndef NDEBUG Twine(OldName) + "." #else Twine() #endif ); } /// \brief Compute suitable alignment to access this slice of the *new* /// alloca. /// /// You can optionally pass a type to this routine and if that type's ABI /// alignment is itself suitable, this will return zero. unsigned getSliceAlign(Type *Ty = nullptr) { unsigned NewAIAlign = NewAI.getAlignment(); if (!NewAIAlign) NewAIAlign = DL.getABITypeAlignment(NewAI.getAllocatedType()); unsigned Align = MinAlign(NewAIAlign, NewBeginOffset - NewAllocaBeginOffset); return (Ty && Align == DL.getABITypeAlignment(Ty)) ? 0 : Align; } unsigned getIndex(uint64_t Offset) { assert(VecTy && "Can only call getIndex when rewriting a vector"); uint64_t RelOffset = Offset - NewAllocaBeginOffset; assert(RelOffset / ElementSize < UINT32_MAX && "Index out of bounds"); uint32_t Index = RelOffset / ElementSize; assert(Index * ElementSize == RelOffset); return Index; } void deleteIfTriviallyDead(Value *V) { Instruction *I = cast<Instruction>(V); if (isInstructionTriviallyDead(I)) Pass.DeadInsts.insert(I); } Value *rewriteVectorizedLoadInst() { unsigned BeginIndex = getIndex(NewBeginOffset); unsigned EndIndex = getIndex(NewEndOffset); assert(EndIndex > BeginIndex && "Empty vector!"); Value *V = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "load"); return extractVector(IRB, V, BeginIndex, EndIndex, "vec"); } Value *rewriteIntegerLoad(LoadInst &LI) { assert(IntTy && "We cannot insert an integer to the alloca"); assert(!LI.isVolatile()); Value *V = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "load"); V = convertValue(DL, IRB, V, IntTy); assert(NewBeginOffset >= NewAllocaBeginOffset && "Out of bounds offset"); uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset; if (Offset > 0 || NewEndOffset < NewAllocaEndOffset) V = extractInteger(DL, IRB, V, cast<IntegerType>(LI.getType()), Offset, "extract"); return V; } bool visitLoadInst(LoadInst &LI) { DEBUG(dbgs() << " original: " << LI << "\n"); Value *OldOp = LI.getOperand(0); assert(OldOp == OldPtr); Type *TargetTy = IsSplit ? Type::getIntNTy(LI.getContext(), SliceSize * 8) : LI.getType(); bool IsPtrAdjusted = false; Value *V; if (VecTy) { V = rewriteVectorizedLoadInst(); } else if (IntTy && LI.getType()->isIntegerTy()) { V = rewriteIntegerLoad(LI); } else if (NewBeginOffset == NewAllocaBeginOffset && canConvertValue(DL, NewAllocaTy, LI.getType())) { V = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), LI.isVolatile(), LI.getName()); } else { Type *LTy = TargetTy->getPointerTo(); V = IRB.CreateAlignedLoad(getNewAllocaSlicePtr(IRB, LTy), getSliceAlign(TargetTy), LI.isVolatile(), LI.getName()); IsPtrAdjusted = true; } V = convertValue(DL, IRB, V, TargetTy); if (IsSplit) { assert(!LI.isVolatile()); assert(LI.getType()->isIntegerTy() && "Only integer type loads and stores are split"); assert(SliceSize < DL.getTypeStoreSize(LI.getType()) && "Split load isn't smaller than original load"); assert(LI.getType()->getIntegerBitWidth() == DL.getTypeStoreSizeInBits(LI.getType()) && "Non-byte-multiple bit width"); // Move the insertion point just past the load so that we can refer to it. IRB.SetInsertPoint(std::next(BasicBlock::iterator(&LI))); // Create a placeholder value with the same type as LI to use as the // basis for the new value. This allows us to replace the uses of LI with // the computed value, and then replace the placeholder with LI, leaving // LI only used for this computation. Value *Placeholder = new LoadInst(UndefValue::get(LI.getType()->getPointerTo())); V = insertInteger(DL, IRB, Placeholder, V, NewBeginOffset - BeginOffset, "insert"); LI.replaceAllUsesWith(V); Placeholder->replaceAllUsesWith(&LI); delete Placeholder; } else { LI.replaceAllUsesWith(V); } Pass.DeadInsts.insert(&LI); deleteIfTriviallyDead(OldOp); DEBUG(dbgs() << " to: " << *V << "\n"); return !LI.isVolatile() && !IsPtrAdjusted; } bool rewriteVectorizedStoreInst(Value *V, StoreInst &SI, Value *OldOp) { if (V->getType() != VecTy) { unsigned BeginIndex = getIndex(NewBeginOffset); unsigned EndIndex = getIndex(NewEndOffset); assert(EndIndex > BeginIndex && "Empty vector!"); unsigned NumElements = EndIndex - BeginIndex; assert(NumElements <= VecTy->getNumElements() && "Too many elements!"); Type *SliceTy = (NumElements == 1) ? ElementTy : VectorType::get(ElementTy, NumElements); if (V->getType() != SliceTy) V = convertValue(DL, IRB, V, SliceTy); // Mix in the existing elements. Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "load"); V = insertVector(IRB, Old, V, BeginIndex, "vec"); } StoreInst *Store = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlignment()); Pass.DeadInsts.insert(&SI); (void)Store; DEBUG(dbgs() << " to: " << *Store << "\n"); return true; } bool rewriteIntegerStore(Value *V, StoreInst &SI) { assert(IntTy && "We cannot extract an integer from the alloca"); assert(!SI.isVolatile()); if (DL.getTypeSizeInBits(V->getType()) != IntTy->getBitWidth()) { Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "oldload"); Old = convertValue(DL, IRB, Old, IntTy); assert(BeginOffset >= NewAllocaBeginOffset && "Out of bounds offset"); uint64_t Offset = BeginOffset - NewAllocaBeginOffset; V = insertInteger(DL, IRB, Old, SI.getValueOperand(), Offset, "insert"); } V = convertValue(DL, IRB, V, NewAllocaTy); StoreInst *Store = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlignment()); Pass.DeadInsts.insert(&SI); (void)Store; DEBUG(dbgs() << " to: " << *Store << "\n"); return true; } bool visitStoreInst(StoreInst &SI) { DEBUG(dbgs() << " original: " << SI << "\n"); Value *OldOp = SI.getOperand(1); assert(OldOp == OldPtr); Value *V = SI.getValueOperand(); // Strip all inbounds GEPs and pointer casts to try to dig out any root // alloca that should be re-examined after promoting this alloca. if (V->getType()->isPointerTy()) if (AllocaInst *AI = dyn_cast<AllocaInst>(V->stripInBoundsOffsets())) Pass.PostPromotionWorklist.insert(AI); if (SliceSize < DL.getTypeStoreSize(V->getType())) { assert(!SI.isVolatile()); assert(V->getType()->isIntegerTy() && "Only integer type loads and stores are split"); assert(V->getType()->getIntegerBitWidth() == DL.getTypeStoreSizeInBits(V->getType()) && "Non-byte-multiple bit width"); IntegerType *NarrowTy = Type::getIntNTy(SI.getContext(), SliceSize * 8); V = extractInteger(DL, IRB, V, NarrowTy, NewBeginOffset - BeginOffset, "extract"); } if (VecTy) return rewriteVectorizedStoreInst(V, SI, OldOp); if (IntTy && V->getType()->isIntegerTy()) return rewriteIntegerStore(V, SI); StoreInst *NewSI; if (NewBeginOffset == NewAllocaBeginOffset && NewEndOffset == NewAllocaEndOffset && canConvertValue(DL, V->getType(), NewAllocaTy)) { V = convertValue(DL, IRB, V, NewAllocaTy); NewSI = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlignment(), SI.isVolatile()); } else { Value *NewPtr = getNewAllocaSlicePtr(IRB, V->getType()->getPointerTo()); NewSI = IRB.CreateAlignedStore(V, NewPtr, getSliceAlign(V->getType()), SI.isVolatile()); } (void)NewSI; Pass.DeadInsts.insert(&SI); deleteIfTriviallyDead(OldOp); DEBUG(dbgs() << " to: " << *NewSI << "\n"); return NewSI->getPointerOperand() == &NewAI && !SI.isVolatile(); } /// \brief Compute an integer value from splatting an i8 across the given /// number of bytes. /// /// Note that this routine assumes an i8 is a byte. If that isn't true, don't /// call this routine. /// FIXME: Heed the advice above. /// /// \param V The i8 value to splat. /// \param Size The number of bytes in the output (assuming i8 is one byte) Value *getIntegerSplat(Value *V, unsigned Size) { assert(Size > 0 && "Expected a positive number of bytes."); IntegerType *VTy = cast<IntegerType>(V->getType()); assert(VTy->getBitWidth() == 8 && "Expected an i8 value for the byte"); if (Size == 1) return V; Type *SplatIntTy = Type::getIntNTy(VTy->getContext(), Size * 8); V = IRB.CreateMul( IRB.CreateZExt(V, SplatIntTy, "zext"), ConstantExpr::getUDiv( Constant::getAllOnesValue(SplatIntTy), ConstantExpr::getZExt(Constant::getAllOnesValue(V->getType()), SplatIntTy)), "isplat"); return V; } /// \brief Compute a vector splat for a given element value. Value *getVectorSplat(Value *V, unsigned NumElements) { V = IRB.CreateVectorSplat(NumElements, V, "vsplat"); DEBUG(dbgs() << " splat: " << *V << "\n"); return V; } bool visitMemSetInst(MemSetInst &II) { DEBUG(dbgs() << " original: " << II << "\n"); assert(II.getRawDest() == OldPtr); // If the memset has a variable size, it cannot be split, just adjust the // pointer to the new alloca. if (!isa<Constant>(II.getLength())) { assert(!IsSplit); assert(NewBeginOffset == BeginOffset); II.setDest(getNewAllocaSlicePtr(IRB, OldPtr->getType())); Type *CstTy = II.getAlignmentCst()->getType(); II.setAlignment(ConstantInt::get(CstTy, getSliceAlign())); deleteIfTriviallyDead(OldPtr); return false; } // Record this instruction for deletion. Pass.DeadInsts.insert(&II); Type *AllocaTy = NewAI.getAllocatedType(); Type *ScalarTy = AllocaTy->getScalarType(); // If this doesn't map cleanly onto the alloca type, and that type isn't // a single value type, just emit a memset. if (!VecTy && !IntTy && (BeginOffset > NewAllocaBeginOffset || EndOffset < NewAllocaEndOffset || SliceSize != DL.getTypeStoreSize(AllocaTy) || !AllocaTy->isSingleValueType() || !DL.isLegalInteger(DL.getTypeSizeInBits(ScalarTy)) || DL.getTypeSizeInBits(ScalarTy) % 8 != 0)) { Type *SizeTy = II.getLength()->getType(); Constant *Size = ConstantInt::get(SizeTy, NewEndOffset - NewBeginOffset); CallInst *New = IRB.CreateMemSet( getNewAllocaSlicePtr(IRB, OldPtr->getType()), II.getValue(), Size, getSliceAlign(), II.isVolatile()); (void)New; DEBUG(dbgs() << " to: " << *New << "\n"); return false; } // If we can represent this as a simple value, we have to build the actual // value to store, which requires expanding the byte present in memset to // a sensible representation for the alloca type. This is essentially // splatting the byte to a sufficiently wide integer, splatting it across // any desired vector width, and bitcasting to the final type. Value *V; if (VecTy) { // If this is a memset of a vectorized alloca, insert it. assert(ElementTy == ScalarTy); unsigned BeginIndex = getIndex(NewBeginOffset); unsigned EndIndex = getIndex(NewEndOffset); assert(EndIndex > BeginIndex && "Empty vector!"); unsigned NumElements = EndIndex - BeginIndex; assert(NumElements <= VecTy->getNumElements() && "Too many elements!"); Value *Splat = getIntegerSplat(II.getValue(), DL.getTypeSizeInBits(ElementTy) / 8); Splat = convertValue(DL, IRB, Splat, ElementTy); if (NumElements > 1) Splat = getVectorSplat(Splat, NumElements); Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "oldload"); V = insertVector(IRB, Old, Splat, BeginIndex, "vec"); } else if (IntTy) { // If this is a memset on an alloca where we can widen stores, insert the // set integer. assert(!II.isVolatile()); uint64_t Size = NewEndOffset - NewBeginOffset; V = getIntegerSplat(II.getValue(), Size); if (IntTy && (BeginOffset != NewAllocaBeginOffset || EndOffset != NewAllocaBeginOffset)) { Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "oldload"); Old = convertValue(DL, IRB, Old, IntTy); uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset; V = insertInteger(DL, IRB, Old, V, Offset, "insert"); } else { assert(V->getType() == IntTy && "Wrong type for an alloca wide integer!"); } V = convertValue(DL, IRB, V, AllocaTy); } else { // Established these invariants above. assert(NewBeginOffset == NewAllocaBeginOffset); assert(NewEndOffset == NewAllocaEndOffset); V = getIntegerSplat(II.getValue(), DL.getTypeSizeInBits(ScalarTy) / 8); if (VectorType *AllocaVecTy = dyn_cast<VectorType>(AllocaTy)) V = getVectorSplat(V, AllocaVecTy->getNumElements()); V = convertValue(DL, IRB, V, AllocaTy); } Value *New = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlignment(), II.isVolatile()); (void)New; DEBUG(dbgs() << " to: " << *New << "\n"); return !II.isVolatile(); } bool visitMemTransferInst(MemTransferInst &II) { // Rewriting of memory transfer instructions can be a bit tricky. We break // them into two categories: split intrinsics and unsplit intrinsics. DEBUG(dbgs() << " original: " << II << "\n"); bool IsDest = &II.getRawDestUse() == OldUse; assert((IsDest && II.getRawDest() == OldPtr) || (!IsDest && II.getRawSource() == OldPtr)); unsigned SliceAlign = getSliceAlign(); // For unsplit intrinsics, we simply modify the source and destination // pointers in place. This isn't just an optimization, it is a matter of // correctness. With unsplit intrinsics we may be dealing with transfers // within a single alloca before SROA ran, or with transfers that have // a variable length. We may also be dealing with memmove instead of // memcpy, and so simply updating the pointers is the necessary for us to // update both source and dest of a single call. if (!IsSplittable) { Value *AdjustedPtr = getNewAllocaSlicePtr(IRB, OldPtr->getType()); if (IsDest) II.setDest(AdjustedPtr); else II.setSource(AdjustedPtr); if (II.getAlignment() > SliceAlign) { Type *CstTy = II.getAlignmentCst()->getType(); II.setAlignment( ConstantInt::get(CstTy, MinAlign(II.getAlignment(), SliceAlign))); } DEBUG(dbgs() << " to: " << II << "\n"); deleteIfTriviallyDead(OldPtr); return false; } // For split transfer intrinsics we have an incredibly useful assurance: // the source and destination do not reside within the same alloca, and at // least one of them does not escape. This means that we can replace // memmove with memcpy, and we don't need to worry about all manner of // downsides to splitting and transforming the operations. // If this doesn't map cleanly onto the alloca type, and that type isn't // a single value type, just emit a memcpy. bool EmitMemCpy = !VecTy && !IntTy && (BeginOffset > NewAllocaBeginOffset || EndOffset < NewAllocaEndOffset || SliceSize != DL.getTypeStoreSize(NewAI.getAllocatedType()) || !NewAI.getAllocatedType()->isSingleValueType()); // If we're just going to emit a memcpy, the alloca hasn't changed, and the // size hasn't been shrunk based on analysis of the viable range, this is // a no-op. if (EmitMemCpy && &OldAI == &NewAI) { // Ensure the start lines up. assert(NewBeginOffset == BeginOffset); // Rewrite the size as needed. if (NewEndOffset != EndOffset) II.setLength(ConstantInt::get(II.getLength()->getType(), NewEndOffset - NewBeginOffset)); return false; } // Record this instruction for deletion. Pass.DeadInsts.insert(&II); // Strip all inbounds GEPs and pointer casts to try to dig out any root // alloca that should be re-examined after rewriting this instruction. Value *OtherPtr = IsDest ? II.getRawSource() : II.getRawDest(); if (AllocaInst *AI = dyn_cast<AllocaInst>(OtherPtr->stripInBoundsOffsets())) { assert(AI != &OldAI && AI != &NewAI && "Splittable transfers cannot reach the same alloca on both ends."); Pass.Worklist.insert(AI); } Type *OtherPtrTy = OtherPtr->getType(); unsigned OtherAS = OtherPtrTy->getPointerAddressSpace(); // Compute the relative offset for the other pointer within the transfer. unsigned IntPtrWidth = DL.getPointerSizeInBits(OtherAS); APInt OtherOffset(IntPtrWidth, NewBeginOffset - BeginOffset); unsigned OtherAlign = MinAlign(II.getAlignment() ? II.getAlignment() : 1, OtherOffset.zextOrTrunc(64).getZExtValue()); if (EmitMemCpy) { // Compute the other pointer, folding as much as possible to produce // a single, simple GEP in most cases. OtherPtr = getAdjustedPtr(IRB, DL, OtherPtr, OtherOffset, OtherPtrTy, OtherPtr->getName() + "."); Value *OurPtr = getNewAllocaSlicePtr(IRB, OldPtr->getType()); Type *SizeTy = II.getLength()->getType(); Constant *Size = ConstantInt::get(SizeTy, NewEndOffset - NewBeginOffset); CallInst *New = IRB.CreateMemCpy( IsDest ? OurPtr : OtherPtr, IsDest ? OtherPtr : OurPtr, Size, MinAlign(SliceAlign, OtherAlign), II.isVolatile()); (void)New; DEBUG(dbgs() << " to: " << *New << "\n"); return false; } bool IsWholeAlloca = NewBeginOffset == NewAllocaBeginOffset && NewEndOffset == NewAllocaEndOffset; uint64_t Size = NewEndOffset - NewBeginOffset; unsigned BeginIndex = VecTy ? getIndex(NewBeginOffset) : 0; unsigned EndIndex = VecTy ? getIndex(NewEndOffset) : 0; unsigned NumElements = EndIndex - BeginIndex; IntegerType *SubIntTy = IntTy ? Type::getIntNTy(IntTy->getContext(), Size * 8) : nullptr; // Reset the other pointer type to match the register type we're going to // use, but using the address space of the original other pointer. if (VecTy && !IsWholeAlloca) { if (NumElements == 1) OtherPtrTy = VecTy->getElementType(); else OtherPtrTy = VectorType::get(VecTy->getElementType(), NumElements); OtherPtrTy = OtherPtrTy->getPointerTo(OtherAS); } else if (IntTy && !IsWholeAlloca) { OtherPtrTy = SubIntTy->getPointerTo(OtherAS); } else { OtherPtrTy = NewAllocaTy->getPointerTo(OtherAS); } Value *SrcPtr = getAdjustedPtr(IRB, DL, OtherPtr, OtherOffset, OtherPtrTy, OtherPtr->getName() + "."); unsigned SrcAlign = OtherAlign; Value *DstPtr = &NewAI; unsigned DstAlign = SliceAlign; if (!IsDest) { std::swap(SrcPtr, DstPtr); std::swap(SrcAlign, DstAlign); } Value *Src; if (VecTy && !IsWholeAlloca && !IsDest) { Src = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "load"); Src = extractVector(IRB, Src, BeginIndex, EndIndex, "vec"); } else if (IntTy && !IsWholeAlloca && !IsDest) { Src = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "load"); Src = convertValue(DL, IRB, Src, IntTy); uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset; Src = extractInteger(DL, IRB, Src, SubIntTy, Offset, "extract"); } else { Src = IRB.CreateAlignedLoad(SrcPtr, SrcAlign, II.isVolatile(), "copyload"); } if (VecTy && !IsWholeAlloca && IsDest) { Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "oldload"); Src = insertVector(IRB, Old, Src, BeginIndex, "vec"); } else if (IntTy && !IsWholeAlloca && IsDest) { Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "oldload"); Old = convertValue(DL, IRB, Old, IntTy); uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset; Src = insertInteger(DL, IRB, Old, Src, Offset, "insert"); Src = convertValue(DL, IRB, Src, NewAllocaTy); } StoreInst *Store = cast<StoreInst>( IRB.CreateAlignedStore(Src, DstPtr, DstAlign, II.isVolatile())); (void)Store; DEBUG(dbgs() << " to: " << *Store << "\n"); return !II.isVolatile(); } bool visitIntrinsicInst(IntrinsicInst &II) { assert(II.getIntrinsicID() == Intrinsic::lifetime_start || II.getIntrinsicID() == Intrinsic::lifetime_end); DEBUG(dbgs() << " original: " << II << "\n"); assert(II.getArgOperand(1) == OldPtr); // Record this instruction for deletion. Pass.DeadInsts.insert(&II); ConstantInt *Size = ConstantInt::get(cast<IntegerType>(II.getArgOperand(0)->getType()), NewEndOffset - NewBeginOffset); Value *Ptr = getNewAllocaSlicePtr(IRB, OldPtr->getType()); Value *New; if (II.getIntrinsicID() == Intrinsic::lifetime_start) New = IRB.CreateLifetimeStart(Ptr, Size); else New = IRB.CreateLifetimeEnd(Ptr, Size); (void)New; DEBUG(dbgs() << " to: " << *New << "\n"); return true; } bool visitPHINode(PHINode &PN) { DEBUG(dbgs() << " original: " << PN << "\n"); assert(BeginOffset >= NewAllocaBeginOffset && "PHIs are unsplittable"); assert(EndOffset <= NewAllocaEndOffset && "PHIs are unsplittable"); // We would like to compute a new pointer in only one place, but have it be // as local as possible to the PHI. To do that, we re-use the location of // the old pointer, which necessarily must be in the right position to // dominate the PHI. IRBuilderTy PtrBuilder(IRB); if (isa<PHINode>(OldPtr)) PtrBuilder.SetInsertPoint(OldPtr->getParent()->getFirstInsertionPt()); else PtrBuilder.SetInsertPoint(OldPtr); PtrBuilder.SetCurrentDebugLocation(OldPtr->getDebugLoc()); Value *NewPtr = getNewAllocaSlicePtr(PtrBuilder, OldPtr->getType()); // Replace the operands which were using the old pointer. std::replace(PN.op_begin(), PN.op_end(), cast<Value>(OldPtr), NewPtr); DEBUG(dbgs() << " to: " << PN << "\n"); deleteIfTriviallyDead(OldPtr); // PHIs can't be promoted on their own, but often can be speculated. We // check the speculation outside of the rewriter so that we see the // fully-rewritten alloca. PHIUsers.insert(&PN); return true; } bool visitSelectInst(SelectInst &SI) { DEBUG(dbgs() << " original: " << SI << "\n"); assert((SI.getTrueValue() == OldPtr || SI.getFalseValue() == OldPtr) && "Pointer isn't an operand!"); assert(BeginOffset >= NewAllocaBeginOffset && "Selects are unsplittable"); assert(EndOffset <= NewAllocaEndOffset && "Selects are unsplittable"); Value *NewPtr = getNewAllocaSlicePtr(IRB, OldPtr->getType()); // Replace the operands which were using the old pointer. if (SI.getOperand(1) == OldPtr) SI.setOperand(1, NewPtr); if (SI.getOperand(2) == OldPtr) SI.setOperand(2, NewPtr); DEBUG(dbgs() << " to: " << SI << "\n"); deleteIfTriviallyDead(OldPtr); // Selects can't be promoted on their own, but often can be speculated. We // check the speculation outside of the rewriter so that we see the // fully-rewritten alloca. SelectUsers.insert(&SI); return true; } }; } namespace { /// \brief Visitor to rewrite aggregate loads and stores as scalar. /// /// This pass aggressively rewrites all aggregate loads and stores on /// a particular pointer (or any pointer derived from it which we can identify) /// with scalar loads and stores. class AggLoadStoreRewriter : public InstVisitor<AggLoadStoreRewriter, bool> { // Befriend the base class so it can delegate to private visit methods. friend class llvm::InstVisitor<AggLoadStoreRewriter, bool>; const DataLayout &DL; /// Queue of pointer uses to analyze and potentially rewrite. SmallVector<Use *, 8> Queue; /// Set to prevent us from cycling with phi nodes and loops. SmallPtrSet<User *, 8> Visited; /// The current pointer use being rewritten. This is used to dig up the used /// value (as opposed to the user). Use *U; public: AggLoadStoreRewriter(const DataLayout &DL) : DL(DL) {} /// Rewrite loads and stores through a pointer and all pointers derived from /// it. bool rewrite(Instruction &I) { DEBUG(dbgs() << " Rewriting FCA loads and stores...\n"); enqueueUsers(I); bool Changed = false; while (!Queue.empty()) { U = Queue.pop_back_val(); Changed |= visit(cast<Instruction>(U->getUser())); } return Changed; } private: /// Enqueue all the users of the given instruction for further processing. /// This uses a set to de-duplicate users. void enqueueUsers(Instruction &I) { for (Use &U : I.uses()) if (Visited.insert(U.getUser()).second) Queue.push_back(&U); } // Conservative default is to not rewrite anything. bool visitInstruction(Instruction &I) { return false; } /// \brief Generic recursive split emission class. template <typename Derived> class OpSplitter { protected: /// The builder used to form new instructions. IRBuilderTy IRB; /// The indices which to be used with insert- or extractvalue to select the /// appropriate value within the aggregate. SmallVector<unsigned, 4> Indices; /// The indices to a GEP instruction which will move Ptr to the correct slot /// within the aggregate. SmallVector<Value *, 4> GEPIndices; /// The base pointer of the original op, used as a base for GEPing the /// split operations. Value *Ptr; /// Initialize the splitter with an insertion point, Ptr and start with a /// single zero GEP index. OpSplitter(Instruction *InsertionPoint, Value *Ptr) : IRB(InsertionPoint), GEPIndices(1, IRB.getInt32(0)), Ptr(Ptr) {} public: /// \brief Generic recursive split emission routine. /// /// This method recursively splits an aggregate op (load or store) into /// scalar or vector ops. It splits recursively until it hits a single value /// and emits that single value operation via the template argument. /// /// The logic of this routine relies on GEPs and insertvalue and /// extractvalue all operating with the same fundamental index list, merely /// formatted differently (GEPs need actual values). /// /// \param Ty The type being split recursively into smaller ops. /// \param Agg The aggregate value being built up or stored, depending on /// whether this is splitting a load or a store respectively. void emitSplitOps(Type *Ty, Value *&Agg, const Twine &Name) { if (Ty->isSingleValueType()) return static_cast<Derived *>(this)->emitFunc(Ty, Agg, Name); if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) { unsigned OldSize = Indices.size(); (void)OldSize; for (unsigned Idx = 0, Size = ATy->getNumElements(); Idx != Size; ++Idx) { assert(Indices.size() == OldSize && "Did not return to the old size"); Indices.push_back(Idx); GEPIndices.push_back(IRB.getInt32(Idx)); emitSplitOps(ATy->getElementType(), Agg, Name + "." + Twine(Idx)); GEPIndices.pop_back(); Indices.pop_back(); } return; } if (StructType *STy = dyn_cast<StructType>(Ty)) { unsigned OldSize = Indices.size(); (void)OldSize; for (unsigned Idx = 0, Size = STy->getNumElements(); Idx != Size; ++Idx) { assert(Indices.size() == OldSize && "Did not return to the old size"); Indices.push_back(Idx); GEPIndices.push_back(IRB.getInt32(Idx)); emitSplitOps(STy->getElementType(Idx), Agg, Name + "." + Twine(Idx)); GEPIndices.pop_back(); Indices.pop_back(); } return; } llvm_unreachable("Only arrays and structs are aggregate loadable types"); } }; struct LoadOpSplitter : public OpSplitter<LoadOpSplitter> { LoadOpSplitter(Instruction *InsertionPoint, Value *Ptr) : OpSplitter<LoadOpSplitter>(InsertionPoint, Ptr) {} /// Emit a leaf load of a single value. This is called at the leaves of the /// recursive emission to actually load values. void emitFunc(Type *Ty, Value *&Agg, const Twine &Name) { assert(Ty->isSingleValueType()); // Load the single value and insert it using the indices. Value *GEP = IRB.CreateInBoundsGEP(Ptr, GEPIndices, Name + ".gep"); Value *Load = IRB.CreateLoad(GEP, Name + ".load"); Agg = IRB.CreateInsertValue(Agg, Load, Indices, Name + ".insert"); DEBUG(dbgs() << " to: " << *Load << "\n"); } }; bool visitLoadInst(LoadInst &LI) { assert(LI.getPointerOperand() == *U); if (!LI.isSimple() || LI.getType()->isSingleValueType()) return false; // We have an aggregate being loaded, split it apart. DEBUG(dbgs() << " original: " << LI << "\n"); LoadOpSplitter Splitter(&LI, *U); Value *V = UndefValue::get(LI.getType()); Splitter.emitSplitOps(LI.getType(), V, LI.getName() + ".fca"); LI.replaceAllUsesWith(V); LI.eraseFromParent(); return true; } struct StoreOpSplitter : public OpSplitter<StoreOpSplitter> { StoreOpSplitter(Instruction *InsertionPoint, Value *Ptr) : OpSplitter<StoreOpSplitter>(InsertionPoint, Ptr) {} /// Emit a leaf store of a single value. This is called at the leaves of the /// recursive emission to actually produce stores. void emitFunc(Type *Ty, Value *&Agg, const Twine &Name) { assert(Ty->isSingleValueType()); // Extract the single value and store it using the indices. Value *Store = IRB.CreateStore( IRB.CreateExtractValue(Agg, Indices, Name + ".extract"), IRB.CreateInBoundsGEP(Ptr, GEPIndices, Name + ".gep")); (void)Store; DEBUG(dbgs() << " to: " << *Store << "\n"); } }; bool visitStoreInst(StoreInst &SI) { if (!SI.isSimple() || SI.getPointerOperand() != *U) return false; Value *V = SI.getValueOperand(); if (V->getType()->isSingleValueType()) return false; // We have an aggregate being stored, split it apart. DEBUG(dbgs() << " original: " << SI << "\n"); StoreOpSplitter Splitter(&SI, *U); Splitter.emitSplitOps(V->getType(), V, V->getName() + ".fca"); SI.eraseFromParent(); return true; } bool visitBitCastInst(BitCastInst &BC) { enqueueUsers(BC); return false; } bool visitGetElementPtrInst(GetElementPtrInst &GEPI) { enqueueUsers(GEPI); return false; } bool visitPHINode(PHINode &PN) { enqueueUsers(PN); return false; } bool visitSelectInst(SelectInst &SI) { enqueueUsers(SI); return false; } }; } /// \brief Strip aggregate type wrapping. /// /// This removes no-op aggregate types wrapping an underlying type. It will /// strip as many layers of types as it can without changing either the type /// size or the allocated size. static Type *stripAggregateTypeWrapping(const DataLayout &DL, Type *Ty) { if (Ty->isSingleValueType()) return Ty; uint64_t AllocSize = DL.getTypeAllocSize(Ty); uint64_t TypeSize = DL.getTypeSizeInBits(Ty); Type *InnerTy; if (ArrayType *ArrTy = dyn_cast<ArrayType>(Ty)) { InnerTy = ArrTy->getElementType(); } else if (StructType *STy = dyn_cast<StructType>(Ty)) { const StructLayout *SL = DL.getStructLayout(STy); unsigned Index = SL->getElementContainingOffset(0); InnerTy = STy->getElementType(Index); } else { return Ty; } if (AllocSize > DL.getTypeAllocSize(InnerTy) || TypeSize > DL.getTypeSizeInBits(InnerTy)) return Ty; return stripAggregateTypeWrapping(DL, InnerTy); } /// \brief Try to find a partition of the aggregate type passed in for a given /// offset and size. /// /// This recurses through the aggregate type and tries to compute a subtype /// based on the offset and size. When the offset and size span a sub-section /// of an array, it will even compute a new array type for that sub-section, /// and the same for structs. /// /// Note that this routine is very strict and tries to find a partition of the /// type which produces the *exact* right offset and size. It is not forgiving /// when the size or offset cause either end of type-based partition to be off. /// Also, this is a best-effort routine. It is reasonable to give up and not /// return a type if necessary. static Type *getTypePartition(const DataLayout &DL, Type *Ty, uint64_t Offset, uint64_t Size) { if (Offset == 0 && DL.getTypeAllocSize(Ty) == Size) return stripAggregateTypeWrapping(DL, Ty); if (Offset > DL.getTypeAllocSize(Ty) || (DL.getTypeAllocSize(Ty) - Offset) < Size) return nullptr; if (SequentialType *SeqTy = dyn_cast<SequentialType>(Ty)) { // We can't partition pointers... if (SeqTy->isPointerTy()) return nullptr; Type *ElementTy = SeqTy->getElementType(); uint64_t ElementSize = DL.getTypeAllocSize(ElementTy); uint64_t NumSkippedElements = Offset / ElementSize; if (ArrayType *ArrTy = dyn_cast<ArrayType>(SeqTy)) { if (NumSkippedElements >= ArrTy->getNumElements()) return nullptr; } else if (VectorType *VecTy = dyn_cast<VectorType>(SeqTy)) { if (NumSkippedElements >= VecTy->getNumElements()) return nullptr; } Offset -= NumSkippedElements * ElementSize; // First check if we need to recurse. if (Offset > 0 || Size < ElementSize) { // Bail if the partition ends in a different array element. if ((Offset + Size) > ElementSize) return nullptr; // Recurse through the element type trying to peel off offset bytes. return getTypePartition(DL, ElementTy, Offset, Size); } assert(Offset == 0); if (Size == ElementSize) return stripAggregateTypeWrapping(DL, ElementTy); assert(Size > ElementSize); uint64_t NumElements = Size / ElementSize; if (NumElements * ElementSize != Size) return nullptr; return ArrayType::get(ElementTy, NumElements); } StructType *STy = dyn_cast<StructType>(Ty); if (!STy) return nullptr; const StructLayout *SL = DL.getStructLayout(STy); if (Offset >= SL->getSizeInBytes()) return nullptr; uint64_t EndOffset = Offset + Size; if (EndOffset > SL->getSizeInBytes()) return nullptr; unsigned Index = SL->getElementContainingOffset(Offset); Offset -= SL->getElementOffset(Index); Type *ElementTy = STy->getElementType(Index); uint64_t ElementSize = DL.getTypeAllocSize(ElementTy); if (Offset >= ElementSize) return nullptr; // The offset points into alignment padding. // See if any partition must be contained by the element. if (Offset > 0 || Size < ElementSize) { if ((Offset + Size) > ElementSize) return nullptr; return getTypePartition(DL, ElementTy, Offset, Size); } assert(Offset == 0); if (Size == ElementSize) return stripAggregateTypeWrapping(DL, ElementTy); StructType::element_iterator EI = STy->element_begin() + Index, EE = STy->element_end(); if (EndOffset < SL->getSizeInBytes()) { unsigned EndIndex = SL->getElementContainingOffset(EndOffset); if (Index == EndIndex) return nullptr; // Within a single element and its padding. // Don't try to form "natural" types if the elements don't line up with the // expected size. // FIXME: We could potentially recurse down through the last element in the // sub-struct to find a natural end point. if (SL->getElementOffset(EndIndex) != EndOffset) return nullptr; assert(Index < EndIndex); EE = STy->element_begin() + EndIndex; } // Try to build up a sub-structure. StructType *SubTy = StructType::get(STy->getContext(), makeArrayRef(EI, EE), STy->isPacked()); const StructLayout *SubSL = DL.getStructLayout(SubTy); if (Size != SubSL->getSizeInBytes()) return nullptr; // The sub-struct doesn't have quite the size needed. return SubTy; } /// \brief Pre-split loads and stores to simplify rewriting. /// /// We want to break up the splittable load+store pairs as much as /// possible. This is important to do as a preprocessing step, as once we /// start rewriting the accesses to partitions of the alloca we lose the /// necessary information to correctly split apart paired loads and stores /// which both point into this alloca. The case to consider is something like /// the following: /// /// %a = alloca [12 x i8] /// %gep1 = getelementptr [12 x i8]* %a, i32 0, i32 0 /// %gep2 = getelementptr [12 x i8]* %a, i32 0, i32 4 /// %gep3 = getelementptr [12 x i8]* %a, i32 0, i32 8 /// %iptr1 = bitcast i8* %gep1 to i64* /// %iptr2 = bitcast i8* %gep2 to i64* /// %fptr1 = bitcast i8* %gep1 to float* /// %fptr2 = bitcast i8* %gep2 to float* /// %fptr3 = bitcast i8* %gep3 to float* /// store float 0.0, float* %fptr1 /// store float 1.0, float* %fptr2 /// %v = load i64* %iptr1 /// store i64 %v, i64* %iptr2 /// %f1 = load float* %fptr2 /// %f2 = load float* %fptr3 /// /// Here we want to form 3 partitions of the alloca, each 4 bytes large, and /// promote everything so we recover the 2 SSA values that should have been /// there all along. /// /// \returns true if any changes are made. bool SROA::presplitLoadsAndStores(AllocaInst &AI, AllocaSlices &AS) { DEBUG(dbgs() << "Pre-splitting loads and stores\n"); // Track the loads and stores which are candidates for pre-splitting here, in // the order they first appear during the partition scan. These give stable // iteration order and a basis for tracking which loads and stores we // actually split. SmallVector<LoadInst *, 4> Loads; SmallVector<StoreInst *, 4> Stores; // We need to accumulate the splits required of each load or store where we // can find them via a direct lookup. This is important to cross-check loads // and stores against each other. We also track the slice so that we can kill // all the slices that end up split. struct SplitOffsets { Slice *S; std::vector<uint64_t> Splits; }; SmallDenseMap<Instruction *, SplitOffsets, 8> SplitOffsetsMap; // Track loads out of this alloca which cannot, for any reason, be pre-split. // This is important as we also cannot pre-split stores of those loads! // FIXME: This is all pretty gross. It means that we can be more aggressive // in pre-splitting when the load feeding the store happens to come from // a separate alloca. Put another way, the effectiveness of SROA would be // decreased by a frontend which just concatenated all of its local allocas // into one big flat alloca. But defeating such patterns is exactly the job // SROA is tasked with! Sadly, to not have this discrepancy we would have // change store pre-splitting to actually force pre-splitting of the load // that feeds it *and all stores*. That makes pre-splitting much harder, but // maybe it would make it more principled? SmallPtrSet<LoadInst *, 8> UnsplittableLoads; DEBUG(dbgs() << " Searching for candidate loads and stores\n"); for (auto &P : AS.partitions()) { for (Slice &S : P) { Instruction *I = cast<Instruction>(S.getUse()->getUser()); if (!S.isSplittable() ||S.endOffset() <= P.endOffset()) { // If this was a load we have to track that it can't participate in any // pre-splitting! if (auto *LI = dyn_cast<LoadInst>(I)) UnsplittableLoads.insert(LI); continue; } assert(P.endOffset() > S.beginOffset() && "Empty or backwards partition!"); // Determine if this is a pre-splittable slice. if (auto *LI = dyn_cast<LoadInst>(I)) { assert(!LI->isVolatile() && "Cannot split volatile loads!"); // The load must be used exclusively to store into other pointers for // us to be able to arbitrarily pre-split it. The stores must also be // simple to avoid changing semantics. auto IsLoadSimplyStored = [](LoadInst *LI) { for (User *LU : LI->users()) { auto *SI = dyn_cast<StoreInst>(LU); if (!SI || !SI->isSimple()) return false; } return true; }; if (!IsLoadSimplyStored(LI)) { UnsplittableLoads.insert(LI); continue; } Loads.push_back(LI); } else if (auto *SI = dyn_cast<StoreInst>(S.getUse()->getUser())) { if (!SI || S.getUse() != &SI->getOperandUse(SI->getPointerOperandIndex())) continue; auto *StoredLoad = dyn_cast<LoadInst>(SI->getValueOperand()); if (!StoredLoad || !StoredLoad->isSimple()) continue; assert(!SI->isVolatile() && "Cannot split volatile stores!"); Stores.push_back(SI); } else { // Other uses cannot be pre-split. continue; } // Record the initial split. DEBUG(dbgs() << " Candidate: " << *I << "\n"); auto &Offsets = SplitOffsetsMap[I]; assert(Offsets.Splits.empty() && "Should not have splits the first time we see an instruction!"); Offsets.S = &S; Offsets.Splits.push_back(P.endOffset() - S.beginOffset()); } // Now scan the already split slices, and add a split for any of them which // we're going to pre-split. for (Slice *S : P.splitSliceTails()) { auto SplitOffsetsMapI = SplitOffsetsMap.find(cast<Instruction>(S->getUse()->getUser())); if (SplitOffsetsMapI == SplitOffsetsMap.end()) continue; auto &Offsets = SplitOffsetsMapI->second; assert(Offsets.S == S && "Found a mismatched slice!"); assert(!Offsets.Splits.empty() && "Cannot have an empty set of splits on the second partition!"); assert(Offsets.Splits.back() == P.beginOffset() - Offsets.S->beginOffset() && "Previous split does not end where this one begins!"); // Record each split. The last partition's end isn't needed as the size // of the slice dictates that. if (S->endOffset() > P.endOffset()) Offsets.Splits.push_back(P.endOffset() - Offsets.S->beginOffset()); } } // We may have split loads where some of their stores are split stores. For // such loads and stores, we can only pre-split them if their splits exactly // match relative to their starting offset. We have to verify this prior to // any rewriting. Stores.erase( std::remove_if(Stores.begin(), Stores.end(), [&UnsplittableLoads, &SplitOffsetsMap](StoreInst *SI) { // Lookup the load we are storing in our map of split // offsets. auto *LI = cast<LoadInst>(SI->getValueOperand()); // If it was completely unsplittable, then we're done, // and this store can't be pre-split. if (UnsplittableLoads.count(LI)) return true; auto LoadOffsetsI = SplitOffsetsMap.find(LI); if (LoadOffsetsI == SplitOffsetsMap.end()) return false; // Unrelated loads are definitely safe. auto &LoadOffsets = LoadOffsetsI->second; // Now lookup the store's offsets. auto &StoreOffsets = SplitOffsetsMap[SI]; // If the relative offsets of each split in the load and // store match exactly, then we can split them and we // don't need to remove them here. if (LoadOffsets.Splits == StoreOffsets.Splits) return false; DEBUG(dbgs() << " Mismatched splits for load and store:\n" << " " << *LI << "\n" << " " << *SI << "\n"); // We've found a store and load that we need to split // with mismatched relative splits. Just give up on them // and remove both instructions from our list of // candidates. UnsplittableLoads.insert(LI); return true; }), Stores.end()); // Now we have to go *back* through all te stores, because a later store may // have caused an earlier store's load to become unsplittable and if it is // unsplittable for the later store, then we can't rely on it being split in // the earlier store either. Stores.erase(std::remove_if(Stores.begin(), Stores.end(), [&UnsplittableLoads](StoreInst *SI) { auto *LI = cast<LoadInst>(SI->getValueOperand()); return UnsplittableLoads.count(LI); }), Stores.end()); // Once we've established all the loads that can't be split for some reason, // filter any that made it into our list out. Loads.erase(std::remove_if(Loads.begin(), Loads.end(), [&UnsplittableLoads](LoadInst *LI) { return UnsplittableLoads.count(LI); }), Loads.end()); // If no loads or stores are left, there is no pre-splitting to be done for // this alloca. if (Loads.empty() && Stores.empty()) return false; // From here on, we can't fail and will be building new accesses, so rig up // an IR builder. IRBuilderTy IRB(&AI); // Collect the new slices which we will merge into the alloca slices. SmallVector<Slice, 4> NewSlices; // Track any allocas we end up splitting loads and stores for so we iterate // on them. SmallPtrSet<AllocaInst *, 4> ResplitPromotableAllocas; // At this point, we have collected all of the loads and stores we can // pre-split, and the specific splits needed for them. We actually do the // splitting in a specific order in order to handle when one of the loads in // the value operand to one of the stores. // // First, we rewrite all of the split loads, and just accumulate each split // load in a parallel structure. We also build the slices for them and append // them to the alloca slices. SmallDenseMap<LoadInst *, std::vector<LoadInst *>, 1> SplitLoadsMap; std::vector<LoadInst *> SplitLoads; for (LoadInst *LI : Loads) { SplitLoads.clear(); IntegerType *Ty = cast<IntegerType>(LI->getType()); uint64_t LoadSize = Ty->getBitWidth() / 8; assert(LoadSize > 0 && "Cannot have a zero-sized integer load!"); auto &Offsets = SplitOffsetsMap[LI]; assert(LoadSize == Offsets.S->endOffset() - Offsets.S->beginOffset() && "Slice size should always match load size exactly!"); uint64_t BaseOffset = Offsets.S->beginOffset(); assert(BaseOffset + LoadSize > BaseOffset && "Cannot represent alloca access size using 64-bit integers!"); Instruction *BasePtr = cast<Instruction>(LI->getPointerOperand()); IRB.SetInsertPoint(BasicBlock::iterator(LI)); DEBUG(dbgs() << " Splitting load: " << *LI << "\n"); uint64_t PartOffset = 0, PartSize = Offsets.Splits.front(); int Idx = 0, Size = Offsets.Splits.size(); for (;;) { auto *PartTy = Type::getIntNTy(Ty->getContext(), PartSize * 8); auto *PartPtrTy = PartTy->getPointerTo(LI->getPointerAddressSpace()); LoadInst *PLoad = IRB.CreateAlignedLoad( getAdjustedPtr(IRB, *DL, BasePtr, APInt(DL->getPointerSizeInBits(), PartOffset), PartPtrTy, BasePtr->getName() + "."), getAdjustedAlignment(LI, PartOffset, *DL), /*IsVolatile*/ false, LI->getName()); // Append this load onto the list of split loads so we can find it later // to rewrite the stores. SplitLoads.push_back(PLoad); // Now build a new slice for the alloca. NewSlices.push_back( Slice(BaseOffset + PartOffset, BaseOffset + PartOffset + PartSize, &PLoad->getOperandUse(PLoad->getPointerOperandIndex()), /*IsSplittable*/ false)); DEBUG(dbgs() << " new slice [" << NewSlices.back().beginOffset() << ", " << NewSlices.back().endOffset() << "): " << *PLoad << "\n"); // See if we've handled all the splits. if (Idx >= Size) break; // Setup the next partition. PartOffset = Offsets.Splits[Idx]; ++Idx; PartSize = (Idx < Size ? Offsets.Splits[Idx] : LoadSize) - PartOffset; } // Now that we have the split loads, do the slow walk over all uses of the // load and rewrite them as split stores, or save the split loads to use // below if the store is going to be split there anyways. bool DeferredStores = false; for (User *LU : LI->users()) { StoreInst *SI = cast<StoreInst>(LU); if (!Stores.empty() && SplitOffsetsMap.count(SI)) { DeferredStores = true; DEBUG(dbgs() << " Deferred splitting of store: " << *SI << "\n"); continue; } Value *StoreBasePtr = SI->getPointerOperand(); IRB.SetInsertPoint(BasicBlock::iterator(SI)); DEBUG(dbgs() << " Splitting store of load: " << *SI << "\n"); for (int Idx = 0, Size = SplitLoads.size(); Idx < Size; ++Idx) { LoadInst *PLoad = SplitLoads[Idx]; uint64_t PartOffset = Idx == 0 ? 0 : Offsets.Splits[Idx - 1]; auto *PartPtrTy = PLoad->getType()->getPointerTo(SI->getPointerAddressSpace()); StoreInst *PStore = IRB.CreateAlignedStore( PLoad, getAdjustedPtr(IRB, *DL, StoreBasePtr, APInt(DL->getPointerSizeInBits(), PartOffset), PartPtrTy, StoreBasePtr->getName() + "."), getAdjustedAlignment(SI, PartOffset, *DL), /*IsVolatile*/ false); (void)PStore; DEBUG(dbgs() << " +" << PartOffset << ":" << *PStore << "\n"); } // We want to immediately iterate on any allocas impacted by splitting // this store, and we have to track any promotable alloca (indicated by // a direct store) as needing to be resplit because it is no longer // promotable. if (AllocaInst *OtherAI = dyn_cast<AllocaInst>(StoreBasePtr)) { ResplitPromotableAllocas.insert(OtherAI); Worklist.insert(OtherAI); } else if (AllocaInst *OtherAI = dyn_cast<AllocaInst>( StoreBasePtr->stripInBoundsOffsets())) { Worklist.insert(OtherAI); } // Mark the original store as dead. DeadInsts.insert(SI); } // Save the split loads if there are deferred stores among the users. if (DeferredStores) SplitLoadsMap.insert(std::make_pair(LI, std::move(SplitLoads))); // Mark the original load as dead and kill the original slice. DeadInsts.insert(LI); Offsets.S->kill(); } // Second, we rewrite all of the split stores. At this point, we know that // all loads from this alloca have been split already. For stores of such // loads, we can simply look up the pre-existing split loads. For stores of // other loads, we split those loads first and then write split stores of // them. for (StoreInst *SI : Stores) { auto *LI = cast<LoadInst>(SI->getValueOperand()); IntegerType *Ty = cast<IntegerType>(LI->getType()); uint64_t StoreSize = Ty->getBitWidth() / 8; assert(StoreSize > 0 && "Cannot have a zero-sized integer store!"); auto &Offsets = SplitOffsetsMap[SI]; assert(StoreSize == Offsets.S->endOffset() - Offsets.S->beginOffset() && "Slice size should always match load size exactly!"); uint64_t BaseOffset = Offsets.S->beginOffset(); assert(BaseOffset + StoreSize > BaseOffset && "Cannot represent alloca access size using 64-bit integers!"); Value *LoadBasePtr = LI->getPointerOperand(); Instruction *StoreBasePtr = cast<Instruction>(SI->getPointerOperand()); DEBUG(dbgs() << " Splitting store: " << *SI << "\n"); // Check whether we have an already split load. auto SplitLoadsMapI = SplitLoadsMap.find(LI); std::vector<LoadInst *> *SplitLoads = nullptr; if (SplitLoadsMapI != SplitLoadsMap.end()) { SplitLoads = &SplitLoadsMapI->second; assert(SplitLoads->size() == Offsets.Splits.size() + 1 && "Too few split loads for the number of splits in the store!"); } else { DEBUG(dbgs() << " of load: " << *LI << "\n"); } uint64_t PartOffset = 0, PartSize = Offsets.Splits.front(); int Idx = 0, Size = Offsets.Splits.size(); for (;;) { auto *PartTy = Type::getIntNTy(Ty->getContext(), PartSize * 8); auto *PartPtrTy = PartTy->getPointerTo(SI->getPointerAddressSpace()); // Either lookup a split load or create one. LoadInst *PLoad; if (SplitLoads) { PLoad = (*SplitLoads)[Idx]; } else { IRB.SetInsertPoint(BasicBlock::iterator(LI)); PLoad = IRB.CreateAlignedLoad( getAdjustedPtr(IRB, *DL, LoadBasePtr, APInt(DL->getPointerSizeInBits(), PartOffset), PartPtrTy, LoadBasePtr->getName() + "."), getAdjustedAlignment(LI, PartOffset, *DL), /*IsVolatile*/ false, LI->getName()); } // And store this partition. IRB.SetInsertPoint(BasicBlock::iterator(SI)); StoreInst *PStore = IRB.CreateAlignedStore( PLoad, getAdjustedPtr(IRB, *DL, StoreBasePtr, APInt(DL->getPointerSizeInBits(), PartOffset), PartPtrTy, StoreBasePtr->getName() + "."), getAdjustedAlignment(SI, PartOffset, *DL), /*IsVolatile*/ false); // Now build a new slice for the alloca. NewSlices.push_back( Slice(BaseOffset + PartOffset, BaseOffset + PartOffset + PartSize, &PStore->getOperandUse(PStore->getPointerOperandIndex()), /*IsSplittable*/ false)); DEBUG(dbgs() << " new slice [" << NewSlices.back().beginOffset() << ", " << NewSlices.back().endOffset() << "): " << *PStore << "\n"); if (!SplitLoads) { DEBUG(dbgs() << " of split load: " << *PLoad << "\n"); } // See if we've finished all the splits. if (Idx >= Size) break; // Setup the next partition. PartOffset = Offsets.Splits[Idx]; ++Idx; PartSize = (Idx < Size ? Offsets.Splits[Idx] : StoreSize) - PartOffset; } // We want to immediately iterate on any allocas impacted by splitting // this load, which is only relevant if it isn't a load of this alloca and // thus we didn't already split the loads above. We also have to keep track // of any promotable allocas we split loads on as they can no longer be // promoted. if (!SplitLoads) { if (AllocaInst *OtherAI = dyn_cast<AllocaInst>(LoadBasePtr)) { assert(OtherAI != &AI && "We can't re-split our own alloca!"); ResplitPromotableAllocas.insert(OtherAI); Worklist.insert(OtherAI); } else if (AllocaInst *OtherAI = dyn_cast<AllocaInst>( LoadBasePtr->stripInBoundsOffsets())) { assert(OtherAI != &AI && "We can't re-split our own alloca!"); Worklist.insert(OtherAI); } } // Mark the original store as dead now that we've split it up and kill its // slice. Note that we leave the original load in place unless this store // was its ownly use. It may in turn be split up if it is an alloca load // for some other alloca, but it may be a normal load. This may introduce // redundant loads, but where those can be merged the rest of the optimizer // should handle the merging, and this uncovers SSA splits which is more // important. In practice, the original loads will almost always be fully // split and removed eventually, and the splits will be merged by any // trivial CSE, including instcombine. if (LI->hasOneUse()) { assert(*LI->user_begin() == SI && "Single use isn't this store!"); DeadInsts.insert(LI); } DeadInsts.insert(SI); Offsets.S->kill(); } // Remove the killed slices that have ben pre-split. AS.erase(std::remove_if(AS.begin(), AS.end(), [](const Slice &S) { return S.isDead(); }), AS.end()); // Insert our new slices. This will sort and merge them into the sorted // sequence. AS.insert(NewSlices); DEBUG(dbgs() << " Pre-split slices:\n"); #ifndef NDEBUG for (auto I = AS.begin(), E = AS.end(); I != E; ++I) DEBUG(AS.print(dbgs(), I, " ")); #endif // Finally, don't try to promote any allocas that new require re-splitting. // They have already been added to the worklist above. PromotableAllocas.erase( std::remove_if( PromotableAllocas.begin(), PromotableAllocas.end(), [&](AllocaInst *AI) { return ResplitPromotableAllocas.count(AI); }), PromotableAllocas.end()); return true; } /// \brief Rewrite an alloca partition's users. /// /// This routine drives both of the rewriting goals of the SROA pass. It tries /// to rewrite uses of an alloca partition to be conducive for SSA value /// promotion. If the partition needs a new, more refined alloca, this will /// build that new alloca, preserving as much type information as possible, and /// rewrite the uses of the old alloca to point at the new one and have the /// appropriate new offsets. It also evaluates how successful the rewrite was /// at enabling promotion and if it was successful queues the alloca to be /// promoted. AllocaInst *SROA::rewritePartition(AllocaInst &AI, AllocaSlices &AS, AllocaSlices::Partition &P) { // Try to compute a friendly type for this partition of the alloca. This // won't always succeed, in which case we fall back to a legal integer type // or an i8 array of an appropriate size. Type *SliceTy = nullptr; if (Type *CommonUseTy = findCommonType(P.begin(), P.end(), P.endOffset())) if (DL->getTypeAllocSize(CommonUseTy) >= P.size()) SliceTy = CommonUseTy; if (!SliceTy) if (Type *TypePartitionTy = getTypePartition(*DL, AI.getAllocatedType(), P.beginOffset(), P.size())) SliceTy = TypePartitionTy; if ((!SliceTy || (SliceTy->isArrayTy() && SliceTy->getArrayElementType()->isIntegerTy())) && DL->isLegalInteger(P.size() * 8)) SliceTy = Type::getIntNTy(*C, P.size() * 8); if (!SliceTy) SliceTy = ArrayType::get(Type::getInt8Ty(*C), P.size()); assert(DL->getTypeAllocSize(SliceTy) >= P.size()); bool IsIntegerPromotable = isIntegerWideningViable(P, SliceTy, *DL); VectorType *VecTy = IsIntegerPromotable ? nullptr : isVectorPromotionViable(P, *DL); if (VecTy) SliceTy = VecTy; // Check for the case where we're going to rewrite to a new alloca of the // exact same type as the original, and with the same access offsets. In that // case, re-use the existing alloca, but still run through the rewriter to // perform phi and select speculation. AllocaInst *NewAI; if (SliceTy == AI.getAllocatedType()) { assert(P.beginOffset() == 0 && "Non-zero begin offset but same alloca type"); NewAI = &AI; // FIXME: We should be able to bail at this point with "nothing changed". // FIXME: We might want to defer PHI speculation until after here. // FIXME: return nullptr; } else { unsigned Alignment = AI.getAlignment(); if (!Alignment) { // The minimum alignment which users can rely on when the explicit // alignment is omitted or zero is that required by the ABI for this // type. Alignment = DL->getABITypeAlignment(AI.getAllocatedType()); } Alignment = MinAlign(Alignment, P.beginOffset()); // If we will get at least this much alignment from the type alone, leave // the alloca's alignment unconstrained. if (Alignment <= DL->getABITypeAlignment(SliceTy)) Alignment = 0; NewAI = new AllocaInst( SliceTy, nullptr, Alignment, AI.getName() + ".sroa." + Twine(P.begin() - AS.begin()), &AI); ++NumNewAllocas; } DEBUG(dbgs() << "Rewriting alloca partition " << "[" << P.beginOffset() << "," << P.endOffset() << ") to: " << *NewAI << "\n"); // Track the high watermark on the worklist as it is only relevant for // promoted allocas. We will reset it to this point if the alloca is not in // fact scheduled for promotion. unsigned PPWOldSize = PostPromotionWorklist.size(); unsigned NumUses = 0; SmallPtrSet<PHINode *, 8> PHIUsers; SmallPtrSet<SelectInst *, 8> SelectUsers; AllocaSliceRewriter Rewriter(*DL, AS, *this, AI, *NewAI, P.beginOffset(), P.endOffset(), IsIntegerPromotable, VecTy, PHIUsers, SelectUsers); bool Promotable = true; for (Slice *S : P.splitSliceTails()) { Promotable &= Rewriter.visit(S); ++NumUses; } for (Slice &S : P) { Promotable &= Rewriter.visit(&S); ++NumUses; } NumAllocaPartitionUses += NumUses; MaxUsesPerAllocaPartition = std::max<unsigned>(NumUses, MaxUsesPerAllocaPartition); // Now that we've processed all the slices in the new partition, check if any // PHIs or Selects would block promotion. for (SmallPtrSetImpl<PHINode *>::iterator I = PHIUsers.begin(), E = PHIUsers.end(); I != E; ++I) if (!isSafePHIToSpeculate(**I, DL)) { Promotable = false; PHIUsers.clear(); SelectUsers.clear(); break; } for (SmallPtrSetImpl<SelectInst *>::iterator I = SelectUsers.begin(), E = SelectUsers.end(); I != E; ++I) if (!isSafeSelectToSpeculate(**I, DL)) { Promotable = false; PHIUsers.clear(); SelectUsers.clear(); break; } if (Promotable) { if (PHIUsers.empty() && SelectUsers.empty()) { // Promote the alloca. PromotableAllocas.push_back(NewAI); } else { // If we have either PHIs or Selects to speculate, add them to those // worklists and re-queue the new alloca so that we promote in on the // next iteration. for (PHINode *PHIUser : PHIUsers) SpeculatablePHIs.insert(PHIUser); for (SelectInst *SelectUser : SelectUsers) SpeculatableSelects.insert(SelectUser); Worklist.insert(NewAI); } } else { // If we can't promote the alloca, iterate on it to check for new // refinements exposed by splitting the current alloca. Don't iterate on an // alloca which didn't actually change and didn't get promoted. if (NewAI != &AI) Worklist.insert(NewAI); // Drop any post-promotion work items if promotion didn't happen. while (PostPromotionWorklist.size() > PPWOldSize) PostPromotionWorklist.pop_back(); } return NewAI; } /// \brief Walks the slices of an alloca and form partitions based on them, /// rewriting each of their uses. bool SROA::splitAlloca(AllocaInst &AI, AllocaSlices &AS) { if (AS.begin() == AS.end()) return false; unsigned NumPartitions = 0; bool Changed = false; // First try to pre-split loads and stores. Changed |= presplitLoadsAndStores(AI, AS); // Now that we have identified any pre-splitting opportunities, mark any // splittable (non-whole-alloca) loads and stores as unsplittable. If we fail // to split these during pre-splitting, we want to force them to be // rewritten into a partition. bool IsSorted = true; for (Slice &S : AS) { if (!S.isSplittable()) continue; // FIXME: We currently leave whole-alloca splittable loads and stores. This // used to be the only splittable loads and stores and we need to be // confident that the above handling of splittable loads and stores is // completely sufficient before we forcibly disable the remaining handling. if (S.beginOffset() == 0 && S.endOffset() >= DL->getTypeAllocSize(AI.getAllocatedType())) continue; if (isa<LoadInst>(S.getUse()->getUser()) || isa<StoreInst>(S.getUse()->getUser())) { S.makeUnsplittable(); IsSorted = false; } } if (!IsSorted) std::sort(AS.begin(), AS.end()); /// \brief Describes the allocas introduced by rewritePartition /// in order to migrate the debug info. struct Piece { AllocaInst *Alloca; uint64_t Offset; uint64_t Size; Piece(AllocaInst *AI, uint64_t O, uint64_t S) : Alloca(AI), Offset(O), Size(S) {} }; SmallVector<Piece, 4> Pieces; // Rewrite each partition. for (auto &P : AS.partitions()) { if (AllocaInst *NewAI = rewritePartition(AI, AS, P)) { Changed = true; if (NewAI != &AI) { uint64_t SizeOfByte = 8; uint64_t AllocaSize = DL->getTypeSizeInBits(NewAI->getAllocatedType()); // Don't include any padding. uint64_t Size = std::min(AllocaSize, P.size() * SizeOfByte); Pieces.push_back(Piece(NewAI, P.beginOffset() * SizeOfByte, Size)); } } ++NumPartitions; } NumAllocaPartitions += NumPartitions; MaxPartitionsPerAlloca = std::max<unsigned>(NumPartitions, MaxPartitionsPerAlloca); // Migrate debug information from the old alloca to the new alloca(s) // and the individial partitions. if (DbgDeclareInst *DbgDecl = FindAllocaDbgDeclare(&AI)) { DIVariable Var(DbgDecl->getVariable()); DIExpression Expr(DbgDecl->getExpression()); DIBuilder DIB(*AI.getParent()->getParent()->getParent(), /*AllowUnresolved*/ false); bool IsSplit = Pieces.size() > 1; for (auto Piece : Pieces) { // Create a piece expression describing the new partition or reuse AI's // expression if there is only one partition. DIExpression PieceExpr = Expr; if (IsSplit || Expr.isBitPiece()) { // If this alloca is already a scalar replacement of a larger aggregate, // Piece.Offset describes the offset inside the scalar. uint64_t Offset = Expr.isBitPiece() ? Expr.getBitPieceOffset() : 0; uint64_t Start = Offset + Piece.Offset; uint64_t Size = Piece.Size; if (Expr.isBitPiece()) { uint64_t AbsEnd = Expr.getBitPieceOffset() + Expr.getBitPieceSize(); if (Start >= AbsEnd) // No need to describe a SROAed padding. continue; Size = std::min(Size, AbsEnd - Start); } PieceExpr = DIB.createBitPieceExpression(Start, Size); } // Remove any existing dbg.declare intrinsic describing the same alloca. if (DbgDeclareInst *OldDDI = FindAllocaDbgDeclare(Piece.Alloca)) OldDDI->eraseFromParent(); auto *NewDDI = DIB.insertDeclare(Piece.Alloca, Var, PieceExpr, &AI); NewDDI->setDebugLoc(DbgDecl->getDebugLoc()); } } return Changed; } /// \brief Clobber a use with undef, deleting the used value if it becomes dead. void SROA::clobberUse(Use &U) { Value *OldV = U; // Replace the use with an undef value. U = UndefValue::get(OldV->getType()); // Check for this making an instruction dead. We have to garbage collect // all the dead instructions to ensure the uses of any alloca end up being // minimal. if (Instruction *OldI = dyn_cast<Instruction>(OldV)) if (isInstructionTriviallyDead(OldI)) { DeadInsts.insert(OldI); } } /// \brief Analyze an alloca for SROA. /// /// This analyzes the alloca to ensure we can reason about it, builds /// the slices of the alloca, and then hands it off to be split and /// rewritten as needed. bool SROA::runOnAlloca(AllocaInst &AI) { DEBUG(dbgs() << "SROA alloca: " << AI << "\n"); ++NumAllocasAnalyzed; // Special case dead allocas, as they're trivial. if (AI.use_empty()) { AI.eraseFromParent(); return true; } // Skip alloca forms that this analysis can't handle. if (AI.isArrayAllocation() || !AI.getAllocatedType()->isSized() || DL->getTypeAllocSize(AI.getAllocatedType()) == 0) return false; bool Changed = false; // First, split any FCA loads and stores touching this alloca to promote // better splitting and promotion opportunities. AggLoadStoreRewriter AggRewriter(*DL); Changed |= AggRewriter.rewrite(AI); // Build the slices using a recursive instruction-visiting builder. AllocaSlices AS(*DL, AI); DEBUG(AS.print(dbgs())); if (AS.isEscaped()) return Changed; // Delete all the dead users of this alloca before splitting and rewriting it. for (Instruction *DeadUser : AS.getDeadUsers()) { // Free up everything used by this instruction. for (Use &DeadOp : DeadUser->operands()) clobberUse(DeadOp); // Now replace the uses of this instruction. DeadUser->replaceAllUsesWith(UndefValue::get(DeadUser->getType())); // And mark it for deletion. DeadInsts.insert(DeadUser); Changed = true; } for (Use *DeadOp : AS.getDeadOperands()) { clobberUse(*DeadOp); Changed = true; } // No slices to split. Leave the dead alloca for a later pass to clean up. if (AS.begin() == AS.end()) return Changed; Changed |= splitAlloca(AI, AS); DEBUG(dbgs() << " Speculating PHIs\n"); while (!SpeculatablePHIs.empty()) speculatePHINodeLoads(*SpeculatablePHIs.pop_back_val()); DEBUG(dbgs() << " Speculating Selects\n"); while (!SpeculatableSelects.empty()) speculateSelectInstLoads(*SpeculatableSelects.pop_back_val()); return Changed; } /// \brief Delete the dead instructions accumulated in this run. /// /// Recursively deletes the dead instructions we've accumulated. This is done /// at the very end to maximize locality of the recursive delete and to /// minimize the problems of invalidated instruction pointers as such pointers /// are used heavily in the intermediate stages of the algorithm. /// /// We also record the alloca instructions deleted here so that they aren't /// subsequently handed to mem2reg to promote. void SROA::deleteDeadInstructions( SmallPtrSetImpl<AllocaInst *> &DeletedAllocas) { while (!DeadInsts.empty()) { Instruction *I = DeadInsts.pop_back_val(); DEBUG(dbgs() << "Deleting dead instruction: " << *I << "\n"); I->replaceAllUsesWith(UndefValue::get(I->getType())); for (Use &Operand : I->operands()) if (Instruction *U = dyn_cast<Instruction>(Operand)) { // Zero out the operand and see if it becomes trivially dead. Operand = nullptr; if (isInstructionTriviallyDead(U)) DeadInsts.insert(U); } if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) { DeletedAllocas.insert(AI); if (DbgDeclareInst *DbgDecl = FindAllocaDbgDeclare(AI)) DbgDecl->eraseFromParent(); } ++NumDeleted; I->eraseFromParent(); } } static void enqueueUsersInWorklist(Instruction &I, SmallVectorImpl<Instruction *> &Worklist, SmallPtrSetImpl<Instruction *> &Visited) { for (User *U : I.users()) if (Visited.insert(cast<Instruction>(U)).second) Worklist.push_back(cast<Instruction>(U)); } /// \brief Promote the allocas, using the best available technique. /// /// This attempts to promote whatever allocas have been identified as viable in /// the PromotableAllocas list. If that list is empty, there is nothing to do. /// If there is a domtree available, we attempt to promote using the full power /// of mem2reg. Otherwise, we build and use the AllocaPromoter above which is /// based on the SSAUpdater utilities. This function returns whether any /// promotion occurred. bool SROA::promoteAllocas(Function &F) { if (PromotableAllocas.empty()) return false; NumPromoted += PromotableAllocas.size(); if (DT && !ForceSSAUpdater) { DEBUG(dbgs() << "Promoting allocas with mem2reg...\n"); PromoteMemToReg(PromotableAllocas, *DT, nullptr, AC); PromotableAllocas.clear(); return true; } DEBUG(dbgs() << "Promoting allocas with SSAUpdater...\n"); SSAUpdater SSA; DIBuilder DIB(*F.getParent(), /*AllowUnresolved*/ false); SmallVector<Instruction *, 64> Insts; // We need a worklist to walk the uses of each alloca. SmallVector<Instruction *, 8> Worklist; SmallPtrSet<Instruction *, 8> Visited; SmallVector<Instruction *, 32> DeadInsts; for (unsigned Idx = 0, Size = PromotableAllocas.size(); Idx != Size; ++Idx) { AllocaInst *AI = PromotableAllocas[Idx]; Insts.clear(); Worklist.clear(); Visited.clear(); enqueueUsersInWorklist(*AI, Worklist, Visited); while (!Worklist.empty()) { Instruction *I = Worklist.pop_back_val(); // FIXME: Currently the SSAUpdater infrastructure doesn't reason about // lifetime intrinsics and so we strip them (and the bitcasts+GEPs // leading to them) here. Eventually it should use them to optimize the // scalar values produced. if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { assert(II->getIntrinsicID() == Intrinsic::lifetime_start || II->getIntrinsicID() == Intrinsic::lifetime_end); II->eraseFromParent(); continue; } // Push the loads and stores we find onto the list. SROA will already // have validated that all loads and stores are viable candidates for // promotion. if (LoadInst *LI = dyn_cast<LoadInst>(I)) { assert(LI->getType() == AI->getAllocatedType()); Insts.push_back(LI); continue; } if (StoreInst *SI = dyn_cast<StoreInst>(I)) { assert(SI->getValueOperand()->getType() == AI->getAllocatedType()); Insts.push_back(SI); continue; } // For everything else, we know that only no-op bitcasts and GEPs will // make it this far, just recurse through them and recall them for later // removal. DeadInsts.push_back(I); enqueueUsersInWorklist(*I, Worklist, Visited); } AllocaPromoter(Insts, SSA, *AI, DIB).run(Insts); while (!DeadInsts.empty()) DeadInsts.pop_back_val()->eraseFromParent(); AI->eraseFromParent(); } PromotableAllocas.clear(); return true; } bool SROA::runOnFunction(Function &F) { if (skipOptnoneFunction(F)) return false; DEBUG(dbgs() << "SROA function: " << F.getName() << "\n"); C = &F.getContext(); DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>(); if (!DLP) { DEBUG(dbgs() << " Skipping SROA -- no target data!\n"); return false; } DL = &DLP->getDataLayout(); DominatorTreeWrapperPass *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>(); DT = DTWP ? &DTWP->getDomTree() : nullptr; AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); BasicBlock &EntryBB = F.getEntryBlock(); for (BasicBlock::iterator I = EntryBB.begin(), E = std::prev(EntryBB.end()); I != E; ++I) { if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) Worklist.insert(AI); } bool Changed = false; // A set of deleted alloca instruction pointers which should be removed from // the list of promotable allocas. SmallPtrSet<AllocaInst *, 4> DeletedAllocas; do { while (!Worklist.empty()) { Changed |= runOnAlloca(*Worklist.pop_back_val()); deleteDeadInstructions(DeletedAllocas); // Remove the deleted allocas from various lists so that we don't try to // continue processing them. if (!DeletedAllocas.empty()) { auto IsInSet = [&](AllocaInst *AI) { return DeletedAllocas.count(AI); }; Worklist.remove_if(IsInSet); PostPromotionWorklist.remove_if(IsInSet); PromotableAllocas.erase(std::remove_if(PromotableAllocas.begin(), PromotableAllocas.end(), IsInSet), PromotableAllocas.end()); DeletedAllocas.clear(); } } Changed |= promoteAllocas(F); Worklist = PostPromotionWorklist; PostPromotionWorklist.clear(); } while (!Worklist.empty()); return Changed; } void SROA::getAnalysisUsage(AnalysisUsage &AU) const { AU.addRequired<AssumptionCacheTracker>(); if (RequiresDomTree) AU.addRequired<DominatorTreeWrapperPass>(); AU.setPreservesCFG(); }