Mercurial > hg > Members > tobaru > cbc > CbC_llvm
view lib/Transforms/Scalar/MemCpyOptimizer.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 | afa8332a0e37 |
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//===- MemCpyOptimizer.cpp - Optimize use of memcpy and friends -----------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This pass performs various transformations related to eliminating memcpy // calls, or transforming sets of stores into memset's. // //===----------------------------------------------------------------------===// #include "llvm/Transforms/Scalar.h" #include "llvm/ADT/SmallVector.h" #include "llvm/ADT/Statistic.h" #include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/AssumptionCache.h" #include "llvm/Analysis/MemoryDependenceAnalysis.h" #include "llvm/Analysis/ValueTracking.h" #include "llvm/IR/DataLayout.h" #include "llvm/IR/Dominators.h" #include "llvm/IR/GetElementPtrTypeIterator.h" #include "llvm/IR/GlobalVariable.h" #include "llvm/IR/IRBuilder.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/Support/Debug.h" #include "llvm/Support/raw_ostream.h" #include "llvm/Analysis/TargetLibraryInfo.h" #include "llvm/Transforms/Utils/Local.h" #include <list> using namespace llvm; #define DEBUG_TYPE "memcpyopt" STATISTIC(NumMemCpyInstr, "Number of memcpy instructions deleted"); STATISTIC(NumMemSetInfer, "Number of memsets inferred"); STATISTIC(NumMoveToCpy, "Number of memmoves converted to memcpy"); STATISTIC(NumCpyToSet, "Number of memcpys converted to memset"); static int64_t GetOffsetFromIndex(const GEPOperator *GEP, unsigned Idx, bool &VariableIdxFound, const DataLayout &TD){ // Skip over the first indices. gep_type_iterator GTI = gep_type_begin(GEP); for (unsigned i = 1; i != Idx; ++i, ++GTI) /*skip along*/; // Compute the offset implied by the rest of the indices. int64_t Offset = 0; for (unsigned i = Idx, e = GEP->getNumOperands(); i != e; ++i, ++GTI) { ConstantInt *OpC = dyn_cast<ConstantInt>(GEP->getOperand(i)); if (!OpC) return VariableIdxFound = true; if (OpC->isZero()) continue; // No offset. // Handle struct indices, which add their field offset to the pointer. if (StructType *STy = dyn_cast<StructType>(*GTI)) { Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue()); continue; } // Otherwise, we have a sequential type like an array or vector. Multiply // the index by the ElementSize. uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()); Offset += Size*OpC->getSExtValue(); } return Offset; } /// IsPointerOffset - Return true if Ptr1 is provably equal to Ptr2 plus a /// constant offset, and return that constant offset. For example, Ptr1 might /// be &A[42], and Ptr2 might be &A[40]. In this case offset would be -8. static bool IsPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset, const DataLayout &TD) { Ptr1 = Ptr1->stripPointerCasts(); Ptr2 = Ptr2->stripPointerCasts(); // Handle the trivial case first. if (Ptr1 == Ptr2) { Offset = 0; return true; } GEPOperator *GEP1 = dyn_cast<GEPOperator>(Ptr1); GEPOperator *GEP2 = dyn_cast<GEPOperator>(Ptr2); bool VariableIdxFound = false; // If one pointer is a GEP and the other isn't, then see if the GEP is a // constant offset from the base, as in "P" and "gep P, 1". if (GEP1 && !GEP2 && GEP1->getOperand(0)->stripPointerCasts() == Ptr2) { Offset = -GetOffsetFromIndex(GEP1, 1, VariableIdxFound, TD); return !VariableIdxFound; } if (GEP2 && !GEP1 && GEP2->getOperand(0)->stripPointerCasts() == Ptr1) { Offset = GetOffsetFromIndex(GEP2, 1, VariableIdxFound, TD); return !VariableIdxFound; } // Right now we handle the case when Ptr1/Ptr2 are both GEPs with an identical // base. After that base, they may have some number of common (and // potentially variable) indices. After that they handle some constant // offset, which determines their offset from each other. At this point, we // handle no other case. if (!GEP1 || !GEP2 || GEP1->getOperand(0) != GEP2->getOperand(0)) return false; // Skip any common indices and track the GEP types. unsigned Idx = 1; for (; Idx != GEP1->getNumOperands() && Idx != GEP2->getNumOperands(); ++Idx) if (GEP1->getOperand(Idx) != GEP2->getOperand(Idx)) break; int64_t Offset1 = GetOffsetFromIndex(GEP1, Idx, VariableIdxFound, TD); int64_t Offset2 = GetOffsetFromIndex(GEP2, Idx, VariableIdxFound, TD); if (VariableIdxFound) return false; Offset = Offset2-Offset1; return true; } /// MemsetRange - Represents a range of memset'd bytes with the ByteVal value. /// This allows us to analyze stores like: /// store 0 -> P+1 /// store 0 -> P+0 /// store 0 -> P+3 /// store 0 -> P+2 /// which sometimes happens with stores to arrays of structs etc. When we see /// the first store, we make a range [1, 2). The second store extends the range /// to [0, 2). The third makes a new range [2, 3). The fourth store joins the /// two ranges into [0, 3) which is memset'able. namespace { struct MemsetRange { // Start/End - A semi range that describes the span that this range covers. // The range is closed at the start and open at the end: [Start, End). int64_t Start, End; /// StartPtr - The getelementptr instruction that points to the start of the /// range. Value *StartPtr; /// Alignment - The known alignment of the first store. unsigned Alignment; /// TheStores - The actual stores that make up this range. SmallVector<Instruction*, 16> TheStores; bool isProfitableToUseMemset(const DataLayout &TD) const; }; } // end anon namespace bool MemsetRange::isProfitableToUseMemset(const DataLayout &TD) const { // If we found more than 4 stores to merge or 16 bytes, use memset. if (TheStores.size() >= 4 || End-Start >= 16) return true; // If there is nothing to merge, don't do anything. if (TheStores.size() < 2) return false; // If any of the stores are a memset, then it is always good to extend the // memset. for (unsigned i = 0, e = TheStores.size(); i != e; ++i) if (!isa<StoreInst>(TheStores[i])) return true; // Assume that the code generator is capable of merging pairs of stores // together if it wants to. if (TheStores.size() == 2) return false; // If we have fewer than 8 stores, it can still be worthwhile to do this. // For example, merging 4 i8 stores into an i32 store is useful almost always. // However, merging 2 32-bit stores isn't useful on a 32-bit architecture (the // memset will be split into 2 32-bit stores anyway) and doing so can // pessimize the llvm optimizer. // // Since we don't have perfect knowledge here, make some assumptions: assume // the maximum GPR width is the same size as the largest legal integer // size. If so, check to see whether we will end up actually reducing the // number of stores used. unsigned Bytes = unsigned(End-Start); unsigned MaxIntSize = TD.getLargestLegalIntTypeSize(); if (MaxIntSize == 0) MaxIntSize = 1; unsigned NumPointerStores = Bytes / MaxIntSize; // Assume the remaining bytes if any are done a byte at a time. unsigned NumByteStores = Bytes - NumPointerStores * MaxIntSize; // If we will reduce the # stores (according to this heuristic), do the // transformation. This encourages merging 4 x i8 -> i32 and 2 x i16 -> i32 // etc. return TheStores.size() > NumPointerStores+NumByteStores; } namespace { class MemsetRanges { /// Ranges - A sorted list of the memset ranges. We use std::list here /// because each element is relatively large and expensive to copy. std::list<MemsetRange> Ranges; typedef std::list<MemsetRange>::iterator range_iterator; const DataLayout &DL; public: MemsetRanges(const DataLayout &DL) : DL(DL) {} typedef std::list<MemsetRange>::const_iterator const_iterator; const_iterator begin() const { return Ranges.begin(); } const_iterator end() const { return Ranges.end(); } bool empty() const { return Ranges.empty(); } void addInst(int64_t OffsetFromFirst, Instruction *Inst) { if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) addStore(OffsetFromFirst, SI); else addMemSet(OffsetFromFirst, cast<MemSetInst>(Inst)); } void addStore(int64_t OffsetFromFirst, StoreInst *SI) { int64_t StoreSize = DL.getTypeStoreSize(SI->getOperand(0)->getType()); addRange(OffsetFromFirst, StoreSize, SI->getPointerOperand(), SI->getAlignment(), SI); } void addMemSet(int64_t OffsetFromFirst, MemSetInst *MSI) { int64_t Size = cast<ConstantInt>(MSI->getLength())->getZExtValue(); addRange(OffsetFromFirst, Size, MSI->getDest(), MSI->getAlignment(), MSI); } void addRange(int64_t Start, int64_t Size, Value *Ptr, unsigned Alignment, Instruction *Inst); }; } // end anon namespace /// addRange - Add a new store to the MemsetRanges data structure. This adds a /// new range for the specified store at the specified offset, merging into /// existing ranges as appropriate. /// /// Do a linear search of the ranges to see if this can be joined and/or to /// find the insertion point in the list. We keep the ranges sorted for /// simplicity here. This is a linear search of a linked list, which is ugly, /// however the number of ranges is limited, so this won't get crazy slow. void MemsetRanges::addRange(int64_t Start, int64_t Size, Value *Ptr, unsigned Alignment, Instruction *Inst) { int64_t End = Start+Size; range_iterator I = Ranges.begin(), E = Ranges.end(); while (I != E && Start > I->End) ++I; // We now know that I == E, in which case we didn't find anything to merge // with, or that Start <= I->End. If End < I->Start or I == E, then we need // to insert a new range. Handle this now. if (I == E || End < I->Start) { MemsetRange &R = *Ranges.insert(I, MemsetRange()); R.Start = Start; R.End = End; R.StartPtr = Ptr; R.Alignment = Alignment; R.TheStores.push_back(Inst); return; } // This store overlaps with I, add it. I->TheStores.push_back(Inst); // At this point, we may have an interval that completely contains our store. // If so, just add it to the interval and return. if (I->Start <= Start && I->End >= End) return; // Now we know that Start <= I->End and End >= I->Start so the range overlaps // but is not entirely contained within the range. // See if the range extends the start of the range. In this case, it couldn't // possibly cause it to join the prior range, because otherwise we would have // stopped on *it*. if (Start < I->Start) { I->Start = Start; I->StartPtr = Ptr; I->Alignment = Alignment; } // Now we know that Start <= I->End and Start >= I->Start (so the startpoint // is in or right at the end of I), and that End >= I->Start. Extend I out to // End. if (End > I->End) { I->End = End; range_iterator NextI = I; while (++NextI != E && End >= NextI->Start) { // Merge the range in. I->TheStores.append(NextI->TheStores.begin(), NextI->TheStores.end()); if (NextI->End > I->End) I->End = NextI->End; Ranges.erase(NextI); NextI = I; } } } //===----------------------------------------------------------------------===// // MemCpyOpt Pass //===----------------------------------------------------------------------===// namespace { class MemCpyOpt : public FunctionPass { MemoryDependenceAnalysis *MD; TargetLibraryInfo *TLI; const DataLayout *DL; public: static char ID; // Pass identification, replacement for typeid MemCpyOpt() : FunctionPass(ID) { initializeMemCpyOptPass(*PassRegistry::getPassRegistry()); MD = nullptr; TLI = nullptr; DL = nullptr; } bool runOnFunction(Function &F) override; private: // This transformation requires dominator postdominator info void getAnalysisUsage(AnalysisUsage &AU) const override { AU.setPreservesCFG(); AU.addRequired<AssumptionCacheTracker>(); AU.addRequired<DominatorTreeWrapperPass>(); AU.addRequired<MemoryDependenceAnalysis>(); AU.addRequired<AliasAnalysis>(); AU.addRequired<TargetLibraryInfoWrapperPass>(); AU.addPreserved<AliasAnalysis>(); AU.addPreserved<MemoryDependenceAnalysis>(); } // Helper fuctions bool processStore(StoreInst *SI, BasicBlock::iterator &BBI); bool processMemSet(MemSetInst *SI, BasicBlock::iterator &BBI); bool processMemCpy(MemCpyInst *M); bool processMemMove(MemMoveInst *M); bool performCallSlotOptzn(Instruction *cpy, Value *cpyDst, Value *cpySrc, uint64_t cpyLen, unsigned cpyAlign, CallInst *C); bool processMemCpyMemCpyDependence(MemCpyInst *M, MemCpyInst *MDep, uint64_t MSize); bool processByValArgument(CallSite CS, unsigned ArgNo); Instruction *tryMergingIntoMemset(Instruction *I, Value *StartPtr, Value *ByteVal); bool iterateOnFunction(Function &F); }; char MemCpyOpt::ID = 0; } // createMemCpyOptPass - The public interface to this file... FunctionPass *llvm::createMemCpyOptPass() { return new MemCpyOpt(); } INITIALIZE_PASS_BEGIN(MemCpyOpt, "memcpyopt", "MemCpy Optimization", false, false) INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis) INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) INITIALIZE_AG_DEPENDENCY(AliasAnalysis) INITIALIZE_PASS_END(MemCpyOpt, "memcpyopt", "MemCpy Optimization", false, false) /// tryMergingIntoMemset - When scanning forward over instructions, we look for /// some other patterns to fold away. In particular, this looks for stores to /// neighboring locations of memory. If it sees enough consecutive ones, it /// attempts to merge them together into a memcpy/memset. Instruction *MemCpyOpt::tryMergingIntoMemset(Instruction *StartInst, Value *StartPtr, Value *ByteVal) { if (!DL) return nullptr; // Okay, so we now have a single store that can be splatable. Scan to find // all subsequent stores of the same value to offset from the same pointer. // Join these together into ranges, so we can decide whether contiguous blocks // are stored. MemsetRanges Ranges(*DL); BasicBlock::iterator BI = StartInst; for (++BI; !isa<TerminatorInst>(BI); ++BI) { if (!isa<StoreInst>(BI) && !isa<MemSetInst>(BI)) { // If the instruction is readnone, ignore it, otherwise bail out. We // don't even allow readonly here because we don't want something like: // A[1] = 2; strlen(A); A[2] = 2; -> memcpy(A, ...); strlen(A). if (BI->mayWriteToMemory() || BI->mayReadFromMemory()) break; continue; } if (StoreInst *NextStore = dyn_cast<StoreInst>(BI)) { // If this is a store, see if we can merge it in. if (!NextStore->isSimple()) break; // Check to see if this stored value is of the same byte-splattable value. if (ByteVal != isBytewiseValue(NextStore->getOperand(0))) break; // Check to see if this store is to a constant offset from the start ptr. int64_t Offset; if (!IsPointerOffset(StartPtr, NextStore->getPointerOperand(), Offset, *DL)) break; Ranges.addStore(Offset, NextStore); } else { MemSetInst *MSI = cast<MemSetInst>(BI); if (MSI->isVolatile() || ByteVal != MSI->getValue() || !isa<ConstantInt>(MSI->getLength())) break; // Check to see if this store is to a constant offset from the start ptr. int64_t Offset; if (!IsPointerOffset(StartPtr, MSI->getDest(), Offset, *DL)) break; Ranges.addMemSet(Offset, MSI); } } // If we have no ranges, then we just had a single store with nothing that // could be merged in. This is a very common case of course. if (Ranges.empty()) return nullptr; // If we had at least one store that could be merged in, add the starting // store as well. We try to avoid this unless there is at least something // interesting as a small compile-time optimization. Ranges.addInst(0, StartInst); // If we create any memsets, we put it right before the first instruction that // isn't part of the memset block. This ensure that the memset is dominated // by any addressing instruction needed by the start of the block. IRBuilder<> Builder(BI); // Now that we have full information about ranges, loop over the ranges and // emit memset's for anything big enough to be worthwhile. Instruction *AMemSet = nullptr; for (MemsetRanges::const_iterator I = Ranges.begin(), E = Ranges.end(); I != E; ++I) { const MemsetRange &Range = *I; if (Range.TheStores.size() == 1) continue; // If it is profitable to lower this range to memset, do so now. if (!Range.isProfitableToUseMemset(*DL)) continue; // Otherwise, we do want to transform this! Create a new memset. // Get the starting pointer of the block. StartPtr = Range.StartPtr; // Determine alignment unsigned Alignment = Range.Alignment; if (Alignment == 0) { Type *EltType = cast<PointerType>(StartPtr->getType())->getElementType(); Alignment = DL->getABITypeAlignment(EltType); } AMemSet = Builder.CreateMemSet(StartPtr, ByteVal, Range.End-Range.Start, Alignment); DEBUG(dbgs() << "Replace stores:\n"; for (unsigned i = 0, e = Range.TheStores.size(); i != e; ++i) dbgs() << *Range.TheStores[i] << '\n'; dbgs() << "With: " << *AMemSet << '\n'); if (!Range.TheStores.empty()) AMemSet->setDebugLoc(Range.TheStores[0]->getDebugLoc()); // Zap all the stores. for (SmallVectorImpl<Instruction *>::const_iterator SI = Range.TheStores.begin(), SE = Range.TheStores.end(); SI != SE; ++SI) { MD->removeInstruction(*SI); (*SI)->eraseFromParent(); } ++NumMemSetInfer; } return AMemSet; } bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) { if (!SI->isSimple()) return false; if (!DL) return false; // Detect cases where we're performing call slot forwarding, but // happen to be using a load-store pair to implement it, rather than // a memcpy. if (LoadInst *LI = dyn_cast<LoadInst>(SI->getOperand(0))) { if (LI->isSimple() && LI->hasOneUse() && LI->getParent() == SI->getParent()) { MemDepResult ldep = MD->getDependency(LI); CallInst *C = nullptr; if (ldep.isClobber() && !isa<MemCpyInst>(ldep.getInst())) C = dyn_cast<CallInst>(ldep.getInst()); if (C) { // Check that nothing touches the dest of the "copy" between // the call and the store. AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); AliasAnalysis::Location StoreLoc = AA.getLocation(SI); for (BasicBlock::iterator I = --BasicBlock::iterator(SI), E = C; I != E; --I) { if (AA.getModRefInfo(&*I, StoreLoc) != AliasAnalysis::NoModRef) { C = nullptr; break; } } } if (C) { unsigned storeAlign = SI->getAlignment(); if (!storeAlign) storeAlign = DL->getABITypeAlignment(SI->getOperand(0)->getType()); unsigned loadAlign = LI->getAlignment(); if (!loadAlign) loadAlign = DL->getABITypeAlignment(LI->getType()); bool changed = performCallSlotOptzn(LI, SI->getPointerOperand()->stripPointerCasts(), LI->getPointerOperand()->stripPointerCasts(), DL->getTypeStoreSize(SI->getOperand(0)->getType()), std::min(storeAlign, loadAlign), C); if (changed) { MD->removeInstruction(SI); SI->eraseFromParent(); MD->removeInstruction(LI); LI->eraseFromParent(); ++NumMemCpyInstr; return true; } } } } // There are two cases that are interesting for this code to handle: memcpy // and memset. Right now we only handle memset. // Ensure that the value being stored is something that can be memset'able a // byte at a time like "0" or "-1" or any width, as well as things like // 0xA0A0A0A0 and 0.0. if (Value *ByteVal = isBytewiseValue(SI->getOperand(0))) if (Instruction *I = tryMergingIntoMemset(SI, SI->getPointerOperand(), ByteVal)) { BBI = I; // Don't invalidate iterator. return true; } return false; } bool MemCpyOpt::processMemSet(MemSetInst *MSI, BasicBlock::iterator &BBI) { // See if there is another memset or store neighboring this memset which // allows us to widen out the memset to do a single larger store. if (isa<ConstantInt>(MSI->getLength()) && !MSI->isVolatile()) if (Instruction *I = tryMergingIntoMemset(MSI, MSI->getDest(), MSI->getValue())) { BBI = I; // Don't invalidate iterator. return true; } return false; } /// performCallSlotOptzn - takes a memcpy and a call that it depends on, /// and checks for the possibility of a call slot optimization by having /// the call write its result directly into the destination of the memcpy. bool MemCpyOpt::performCallSlotOptzn(Instruction *cpy, Value *cpyDest, Value *cpySrc, uint64_t cpyLen, unsigned cpyAlign, CallInst *C) { // The general transformation to keep in mind is // // call @func(..., src, ...) // memcpy(dest, src, ...) // // -> // // memcpy(dest, src, ...) // call @func(..., dest, ...) // // Since moving the memcpy is technically awkward, we additionally check that // src only holds uninitialized values at the moment of the call, meaning that // the memcpy can be discarded rather than moved. // Deliberately get the source and destination with bitcasts stripped away, // because we'll need to do type comparisons based on the underlying type. CallSite CS(C); // Require that src be an alloca. This simplifies the reasoning considerably. AllocaInst *srcAlloca = dyn_cast<AllocaInst>(cpySrc); if (!srcAlloca) return false; // Check that all of src is copied to dest. if (!DL) return false; ConstantInt *srcArraySize = dyn_cast<ConstantInt>(srcAlloca->getArraySize()); if (!srcArraySize) return false; uint64_t srcSize = DL->getTypeAllocSize(srcAlloca->getAllocatedType()) * srcArraySize->getZExtValue(); if (cpyLen < srcSize) return false; // Check that accessing the first srcSize bytes of dest will not cause a // trap. Otherwise the transform is invalid since it might cause a trap // to occur earlier than it otherwise would. if (AllocaInst *A = dyn_cast<AllocaInst>(cpyDest)) { // The destination is an alloca. Check it is larger than srcSize. ConstantInt *destArraySize = dyn_cast<ConstantInt>(A->getArraySize()); if (!destArraySize) return false; uint64_t destSize = DL->getTypeAllocSize(A->getAllocatedType()) * destArraySize->getZExtValue(); if (destSize < srcSize) return false; } else if (Argument *A = dyn_cast<Argument>(cpyDest)) { if (A->getDereferenceableBytes() < srcSize) { // If the destination is an sret parameter then only accesses that are // outside of the returned struct type can trap. if (!A->hasStructRetAttr()) return false; Type *StructTy = cast<PointerType>(A->getType())->getElementType(); if (!StructTy->isSized()) { // The call may never return and hence the copy-instruction may never // be executed, and therefore it's not safe to say "the destination // has at least <cpyLen> bytes, as implied by the copy-instruction", return false; } uint64_t destSize = DL->getTypeAllocSize(StructTy); if (destSize < srcSize) return false; } } else { return false; } // Check that dest points to memory that is at least as aligned as src. unsigned srcAlign = srcAlloca->getAlignment(); if (!srcAlign) srcAlign = DL->getABITypeAlignment(srcAlloca->getAllocatedType()); bool isDestSufficientlyAligned = srcAlign <= cpyAlign; // If dest is not aligned enough and we can't increase its alignment then // bail out. if (!isDestSufficientlyAligned && !isa<AllocaInst>(cpyDest)) return false; // Check that src is not accessed except via the call and the memcpy. This // guarantees that it holds only undefined values when passed in (so the final // memcpy can be dropped), that it is not read or written between the call and // the memcpy, and that writing beyond the end of it is undefined. SmallVector<User*, 8> srcUseList(srcAlloca->user_begin(), srcAlloca->user_end()); while (!srcUseList.empty()) { User *U = srcUseList.pop_back_val(); if (isa<BitCastInst>(U) || isa<AddrSpaceCastInst>(U)) { for (User *UU : U->users()) srcUseList.push_back(UU); continue; } if (GetElementPtrInst *G = dyn_cast<GetElementPtrInst>(U)) { if (!G->hasAllZeroIndices()) return false; for (User *UU : U->users()) srcUseList.push_back(UU); continue; } if (const IntrinsicInst *IT = dyn_cast<IntrinsicInst>(U)) if (IT->getIntrinsicID() == Intrinsic::lifetime_start || IT->getIntrinsicID() == Intrinsic::lifetime_end) continue; if (U != C && U != cpy) return false; } // Check that src isn't captured by the called function since the // transformation can cause aliasing issues in that case. for (unsigned i = 0, e = CS.arg_size(); i != e; ++i) if (CS.getArgument(i) == cpySrc && !CS.doesNotCapture(i)) return false; // Since we're changing the parameter to the callsite, we need to make sure // that what would be the new parameter dominates the callsite. DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree(); if (Instruction *cpyDestInst = dyn_cast<Instruction>(cpyDest)) if (!DT.dominates(cpyDestInst, C)) return false; // In addition to knowing that the call does not access src in some // unexpected manner, for example via a global, which we deduce from // the use analysis, we also need to know that it does not sneakily // access dest. We rely on AA to figure this out for us. AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); AliasAnalysis::ModRefResult MR = AA.getModRefInfo(C, cpyDest, srcSize); // If necessary, perform additional analysis. if (MR != AliasAnalysis::NoModRef) MR = AA.callCapturesBefore(C, cpyDest, srcSize, &DT); if (MR != AliasAnalysis::NoModRef) return false; // All the checks have passed, so do the transformation. bool changedArgument = false; for (unsigned i = 0; i < CS.arg_size(); ++i) if (CS.getArgument(i)->stripPointerCasts() == cpySrc) { Value *Dest = cpySrc->getType() == cpyDest->getType() ? cpyDest : CastInst::CreatePointerCast(cpyDest, cpySrc->getType(), cpyDest->getName(), C); changedArgument = true; if (CS.getArgument(i)->getType() == Dest->getType()) CS.setArgument(i, Dest); else CS.setArgument(i, CastInst::CreatePointerCast(Dest, CS.getArgument(i)->getType(), Dest->getName(), C)); } if (!changedArgument) return false; // If the destination wasn't sufficiently aligned then increase its alignment. if (!isDestSufficientlyAligned) { assert(isa<AllocaInst>(cpyDest) && "Can only increase alloca alignment!"); cast<AllocaInst>(cpyDest)->setAlignment(srcAlign); } // Drop any cached information about the call, because we may have changed // its dependence information by changing its parameter. MD->removeInstruction(C); // Update AA metadata // FIXME: MD_tbaa_struct and MD_mem_parallel_loop_access should also be // handled here, but combineMetadata doesn't support them yet unsigned KnownIDs[] = { LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope, LLVMContext::MD_noalias, }; combineMetadata(C, cpy, KnownIDs); // Remove the memcpy. MD->removeInstruction(cpy); ++NumMemCpyInstr; return true; } /// processMemCpyMemCpyDependence - We've found that the (upward scanning) /// memory dependence of memcpy 'M' is the memcpy 'MDep'. Try to simplify M to /// copy from MDep's input if we can. MSize is the size of M's copy. /// bool MemCpyOpt::processMemCpyMemCpyDependence(MemCpyInst *M, MemCpyInst *MDep, uint64_t MSize) { // We can only transforms memcpy's where the dest of one is the source of the // other. if (M->getSource() != MDep->getDest() || MDep->isVolatile()) return false; // If dep instruction is reading from our current input, then it is a noop // transfer and substituting the input won't change this instruction. Just // ignore the input and let someone else zap MDep. This handles cases like: // memcpy(a <- a) // memcpy(b <- a) if (M->getSource() == MDep->getSource()) return false; // Second, the length of the memcpy's must be the same, or the preceding one // must be larger than the following one. ConstantInt *MDepLen = dyn_cast<ConstantInt>(MDep->getLength()); ConstantInt *MLen = dyn_cast<ConstantInt>(M->getLength()); if (!MDepLen || !MLen || MDepLen->getZExtValue() < MLen->getZExtValue()) return false; AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); // Verify that the copied-from memory doesn't change in between the two // transfers. For example, in: // memcpy(a <- b) // *b = 42; // memcpy(c <- a) // It would be invalid to transform the second memcpy into memcpy(c <- b). // // TODO: If the code between M and MDep is transparent to the destination "c", // then we could still perform the xform by moving M up to the first memcpy. // // NOTE: This is conservative, it will stop on any read from the source loc, // not just the defining memcpy. MemDepResult SourceDep = MD->getPointerDependencyFrom(AA.getLocationForSource(MDep), false, M, M->getParent()); if (!SourceDep.isClobber() || SourceDep.getInst() != MDep) return false; // If the dest of the second might alias the source of the first, then the // source and dest might overlap. We still want to eliminate the intermediate // value, but we have to generate a memmove instead of memcpy. bool UseMemMove = false; if (!AA.isNoAlias(AA.getLocationForDest(M), AA.getLocationForSource(MDep))) UseMemMove = true; // If all checks passed, then we can transform M. // Make sure to use the lesser of the alignment of the source and the dest // since we're changing where we're reading from, but don't want to increase // the alignment past what can be read from or written to. // TODO: Is this worth it if we're creating a less aligned memcpy? For // example we could be moving from movaps -> movq on x86. unsigned Align = std::min(MDep->getAlignment(), M->getAlignment()); IRBuilder<> Builder(M); if (UseMemMove) Builder.CreateMemMove(M->getRawDest(), MDep->getRawSource(), M->getLength(), Align, M->isVolatile()); else Builder.CreateMemCpy(M->getRawDest(), MDep->getRawSource(), M->getLength(), Align, M->isVolatile()); // Remove the instruction we're replacing. MD->removeInstruction(M); M->eraseFromParent(); ++NumMemCpyInstr; return true; } /// processMemCpy - perform simplification of memcpy's. If we have memcpy A /// which copies X to Y, and memcpy B which copies Y to Z, then we can rewrite /// B to be a memcpy from X to Z (or potentially a memmove, depending on /// circumstances). This allows later passes to remove the first memcpy /// altogether. bool MemCpyOpt::processMemCpy(MemCpyInst *M) { // We can only optimize non-volatile memcpy's. if (M->isVolatile()) return false; // If the source and destination of the memcpy are the same, then zap it. if (M->getSource() == M->getDest()) { MD->removeInstruction(M); M->eraseFromParent(); return false; } // If copying from a constant, try to turn the memcpy into a memset. if (GlobalVariable *GV = dyn_cast<GlobalVariable>(M->getSource())) if (GV->isConstant() && GV->hasDefinitiveInitializer()) if (Value *ByteVal = isBytewiseValue(GV->getInitializer())) { IRBuilder<> Builder(M); Builder.CreateMemSet(M->getRawDest(), ByteVal, M->getLength(), M->getAlignment(), false); MD->removeInstruction(M); M->eraseFromParent(); ++NumCpyToSet; return true; } // The optimizations after this point require the memcpy size. ConstantInt *CopySize = dyn_cast<ConstantInt>(M->getLength()); if (!CopySize) return false; // The are three possible optimizations we can do for memcpy: // a) memcpy-memcpy xform which exposes redundance for DSE. // b) call-memcpy xform for return slot optimization. // c) memcpy from freshly alloca'd space or space that has just started its // lifetime copies undefined data, and we can therefore eliminate the // memcpy in favor of the data that was already at the destination. MemDepResult DepInfo = MD->getDependency(M); if (DepInfo.isClobber()) { if (CallInst *C = dyn_cast<CallInst>(DepInfo.getInst())) { if (performCallSlotOptzn(M, M->getDest(), M->getSource(), CopySize->getZExtValue(), M->getAlignment(), C)) { MD->removeInstruction(M); M->eraseFromParent(); return true; } } } AliasAnalysis::Location SrcLoc = AliasAnalysis::getLocationForSource(M); MemDepResult SrcDepInfo = MD->getPointerDependencyFrom(SrcLoc, true, M, M->getParent()); if (SrcDepInfo.isClobber()) { if (MemCpyInst *MDep = dyn_cast<MemCpyInst>(SrcDepInfo.getInst())) return processMemCpyMemCpyDependence(M, MDep, CopySize->getZExtValue()); } else if (SrcDepInfo.isDef()) { Instruction *I = SrcDepInfo.getInst(); bool hasUndefContents = false; if (isa<AllocaInst>(I)) { hasUndefContents = true; } else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { if (II->getIntrinsicID() == Intrinsic::lifetime_start) if (ConstantInt *LTSize = dyn_cast<ConstantInt>(II->getArgOperand(0))) if (LTSize->getZExtValue() >= CopySize->getZExtValue()) hasUndefContents = true; } if (hasUndefContents) { MD->removeInstruction(M); M->eraseFromParent(); ++NumMemCpyInstr; return true; } } return false; } /// processMemMove - Transforms memmove calls to memcpy calls when the src/dst /// are guaranteed not to alias. bool MemCpyOpt::processMemMove(MemMoveInst *M) { AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); if (!TLI->has(LibFunc::memmove)) return false; // See if the pointers alias. if (!AA.isNoAlias(AA.getLocationForDest(M), AA.getLocationForSource(M))) return false; DEBUG(dbgs() << "MemCpyOpt: Optimizing memmove -> memcpy: " << *M << "\n"); // If not, then we know we can transform this. Module *Mod = M->getParent()->getParent()->getParent(); Type *ArgTys[3] = { M->getRawDest()->getType(), M->getRawSource()->getType(), M->getLength()->getType() }; M->setCalledFunction(Intrinsic::getDeclaration(Mod, Intrinsic::memcpy, ArgTys)); // MemDep may have over conservative information about this instruction, just // conservatively flush it from the cache. MD->removeInstruction(M); ++NumMoveToCpy; return true; } /// processByValArgument - This is called on every byval argument in call sites. bool MemCpyOpt::processByValArgument(CallSite CS, unsigned ArgNo) { if (!DL) return false; // Find out what feeds this byval argument. Value *ByValArg = CS.getArgument(ArgNo); Type *ByValTy = cast<PointerType>(ByValArg->getType())->getElementType(); uint64_t ByValSize = DL->getTypeAllocSize(ByValTy); MemDepResult DepInfo = MD->getPointerDependencyFrom(AliasAnalysis::Location(ByValArg, ByValSize), true, CS.getInstruction(), CS.getInstruction()->getParent()); if (!DepInfo.isClobber()) return false; // If the byval argument isn't fed by a memcpy, ignore it. If it is fed by // a memcpy, see if we can byval from the source of the memcpy instead of the // result. MemCpyInst *MDep = dyn_cast<MemCpyInst>(DepInfo.getInst()); if (!MDep || MDep->isVolatile() || ByValArg->stripPointerCasts() != MDep->getDest()) return false; // The length of the memcpy must be larger or equal to the size of the byval. ConstantInt *C1 = dyn_cast<ConstantInt>(MDep->getLength()); if (!C1 || C1->getValue().getZExtValue() < ByValSize) return false; // Get the alignment of the byval. If the call doesn't specify the alignment, // then it is some target specific value that we can't know. unsigned ByValAlign = CS.getParamAlignment(ArgNo+1); if (ByValAlign == 0) return false; // If it is greater than the memcpy, then we check to see if we can force the // source of the memcpy to the alignment we need. If we fail, we bail out. AssumptionCache &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache( *CS->getParent()->getParent()); DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree(); if (MDep->getAlignment() < ByValAlign && getOrEnforceKnownAlignment(MDep->getSource(), ByValAlign, DL, &AC, CS.getInstruction(), &DT) < ByValAlign) return false; // Verify that the copied-from memory doesn't change in between the memcpy and // the byval call. // memcpy(a <- b) // *b = 42; // foo(*a) // It would be invalid to transform the second memcpy into foo(*b). // // NOTE: This is conservative, it will stop on any read from the source loc, // not just the defining memcpy. MemDepResult SourceDep = MD->getPointerDependencyFrom(AliasAnalysis::getLocationForSource(MDep), false, CS.getInstruction(), MDep->getParent()); if (!SourceDep.isClobber() || SourceDep.getInst() != MDep) return false; Value *TmpCast = MDep->getSource(); if (MDep->getSource()->getType() != ByValArg->getType()) TmpCast = new BitCastInst(MDep->getSource(), ByValArg->getType(), "tmpcast", CS.getInstruction()); DEBUG(dbgs() << "MemCpyOpt: Forwarding memcpy to byval:\n" << " " << *MDep << "\n" << " " << *CS.getInstruction() << "\n"); // Otherwise we're good! Update the byval argument. CS.setArgument(ArgNo, TmpCast); ++NumMemCpyInstr; return true; } /// iterateOnFunction - Executes one iteration of MemCpyOpt. bool MemCpyOpt::iterateOnFunction(Function &F) { bool MadeChange = false; // Walk all instruction in the function. for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) { for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) { // Avoid invalidating the iterator. Instruction *I = BI++; bool RepeatInstruction = false; if (StoreInst *SI = dyn_cast<StoreInst>(I)) MadeChange |= processStore(SI, BI); else if (MemSetInst *M = dyn_cast<MemSetInst>(I)) RepeatInstruction = processMemSet(M, BI); else if (MemCpyInst *M = dyn_cast<MemCpyInst>(I)) RepeatInstruction = processMemCpy(M); else if (MemMoveInst *M = dyn_cast<MemMoveInst>(I)) RepeatInstruction = processMemMove(M); else if (CallSite CS = (Value*)I) { for (unsigned i = 0, e = CS.arg_size(); i != e; ++i) if (CS.isByValArgument(i)) MadeChange |= processByValArgument(CS, i); } // Reprocess the instruction if desired. if (RepeatInstruction) { if (BI != BB->begin()) --BI; MadeChange = true; } } } return MadeChange; } // MemCpyOpt::runOnFunction - This is the main transformation entry point for a // function. // bool MemCpyOpt::runOnFunction(Function &F) { if (skipOptnoneFunction(F)) return false; bool MadeChange = false; MD = &getAnalysis<MemoryDependenceAnalysis>(); DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>(); DL = DLP ? &DLP->getDataLayout() : nullptr; TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(); // If we don't have at least memset and memcpy, there is little point of doing // anything here. These are required by a freestanding implementation, so if // even they are disabled, there is no point in trying hard. if (!TLI->has(LibFunc::memset) || !TLI->has(LibFunc::memcpy)) return false; while (1) { if (!iterateOnFunction(F)) break; MadeChange = true; } MD = nullptr; return MadeChange; }