Mercurial > hg > Members > tobaru > cbc > CbC_llvm
view lib/Transforms/Scalar/GVN.cpp @ 83:60c9769439b8
LLVM 3.7
author | Tatsuki IHA <e125716@ie.u-ryukyu.ac.jp> |
---|---|
date | Wed, 18 Feb 2015 14:55:36 +0900 |
parents | 54457678186b |
children | afa8332a0e37 |
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line source
//===- GVN.cpp - Eliminate redundant values and loads ---------------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This pass performs global value numbering to eliminate fully redundant // instructions. It also performs simple dead load elimination. // // Note that this pass does the value numbering itself; it does not use the // ValueNumbering analysis passes. // //===----------------------------------------------------------------------===// #include "llvm/Transforms/Scalar.h" #include "llvm/ADT/DenseMap.h" #include "llvm/ADT/DepthFirstIterator.h" #include "llvm/ADT/Hashing.h" #include "llvm/ADT/MapVector.h" #include "llvm/ADT/PostOrderIterator.h" #include "llvm/ADT/SetVector.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/Statistic.h" #include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/AssumptionCache.h" #include "llvm/Analysis/CFG.h" #include "llvm/Analysis/ConstantFolding.h" #include "llvm/Analysis/InstructionSimplify.h" #include "llvm/Analysis/Loads.h" #include "llvm/Analysis/MemoryBuiltins.h" #include "llvm/Analysis/MemoryDependenceAnalysis.h" #include "llvm/Analysis/PHITransAddr.h" #include "llvm/Analysis/ValueTracking.h" #include "llvm/IR/DataLayout.h" #include "llvm/IR/Dominators.h" #include "llvm/IR/GlobalVariable.h" #include "llvm/IR/IRBuilder.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/LLVMContext.h" #include "llvm/IR/Metadata.h" #include "llvm/IR/PatternMatch.h" #include "llvm/Support/Allocator.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" #include "llvm/Analysis/TargetLibraryInfo.h" #include "llvm/Transforms/Utils/BasicBlockUtils.h" #include "llvm/Transforms/Utils/Local.h" #include "llvm/Transforms/Utils/SSAUpdater.h" #include <vector> using namespace llvm; using namespace PatternMatch; #define DEBUG_TYPE "gvn" STATISTIC(NumGVNInstr, "Number of instructions deleted"); STATISTIC(NumGVNLoad, "Number of loads deleted"); STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); STATISTIC(NumGVNBlocks, "Number of blocks merged"); STATISTIC(NumGVNSimpl, "Number of instructions simplified"); STATISTIC(NumGVNEqProp, "Number of equalities propagated"); STATISTIC(NumPRELoad, "Number of loads PRE'd"); static cl::opt<bool> EnablePRE("enable-pre", cl::init(true), cl::Hidden); static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true)); // Maximum allowed recursion depth. static cl::opt<uint32_t> MaxRecurseDepth("max-recurse-depth", cl::Hidden, cl::init(1000), cl::ZeroOrMore, cl::desc("Max recurse depth (default = 1000)")); //===----------------------------------------------------------------------===// // ValueTable Class //===----------------------------------------------------------------------===// /// This class holds the mapping between values and value numbers. It is used /// as an efficient mechanism to determine the expression-wise equivalence of /// two values. namespace { struct Expression { uint32_t opcode; Type *type; SmallVector<uint32_t, 4> varargs; Expression(uint32_t o = ~2U) : opcode(o) { } bool operator==(const Expression &other) const { if (opcode != other.opcode) return false; if (opcode == ~0U || opcode == ~1U) return true; if (type != other.type) return false; if (varargs != other.varargs) return false; return true; } friend hash_code hash_value(const Expression &Value) { return hash_combine(Value.opcode, Value.type, hash_combine_range(Value.varargs.begin(), Value.varargs.end())); } }; class ValueTable { DenseMap<Value*, uint32_t> valueNumbering; DenseMap<Expression, uint32_t> expressionNumbering; AliasAnalysis *AA; MemoryDependenceAnalysis *MD; DominatorTree *DT; uint32_t nextValueNumber; Expression create_expression(Instruction* I); Expression create_cmp_expression(unsigned Opcode, CmpInst::Predicate Predicate, Value *LHS, Value *RHS); Expression create_extractvalue_expression(ExtractValueInst* EI); uint32_t lookup_or_add_call(CallInst* C); public: ValueTable() : nextValueNumber(1) { } uint32_t lookup_or_add(Value *V); uint32_t lookup(Value *V) const; uint32_t lookup_or_add_cmp(unsigned Opcode, CmpInst::Predicate Pred, Value *LHS, Value *RHS); void add(Value *V, uint32_t num); void clear(); void erase(Value *v); void setAliasAnalysis(AliasAnalysis* A) { AA = A; } AliasAnalysis *getAliasAnalysis() const { return AA; } void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } void setDomTree(DominatorTree* D) { DT = D; } uint32_t getNextUnusedValueNumber() { return nextValueNumber; } void verifyRemoved(const Value *) const; }; } namespace llvm { template <> struct DenseMapInfo<Expression> { static inline Expression getEmptyKey() { return ~0U; } static inline Expression getTombstoneKey() { return ~1U; } static unsigned getHashValue(const Expression e) { using llvm::hash_value; return static_cast<unsigned>(hash_value(e)); } static bool isEqual(const Expression &LHS, const Expression &RHS) { return LHS == RHS; } }; } //===----------------------------------------------------------------------===// // ValueTable Internal Functions //===----------------------------------------------------------------------===// Expression ValueTable::create_expression(Instruction *I) { Expression e; e.type = I->getType(); e.opcode = I->getOpcode(); for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end(); OI != OE; ++OI) e.varargs.push_back(lookup_or_add(*OI)); if (I->isCommutative()) { // Ensure that commutative instructions that only differ by a permutation // of their operands get the same value number by sorting the operand value // numbers. Since all commutative instructions have two operands it is more // efficient to sort by hand rather than using, say, std::sort. assert(I->getNumOperands() == 2 && "Unsupported commutative instruction!"); if (e.varargs[0] > e.varargs[1]) std::swap(e.varargs[0], e.varargs[1]); } if (CmpInst *C = dyn_cast<CmpInst>(I)) { // Sort the operand value numbers so x<y and y>x get the same value number. CmpInst::Predicate Predicate = C->getPredicate(); if (e.varargs[0] > e.varargs[1]) { std::swap(e.varargs[0], e.varargs[1]); Predicate = CmpInst::getSwappedPredicate(Predicate); } e.opcode = (C->getOpcode() << 8) | Predicate; } else if (InsertValueInst *E = dyn_cast<InsertValueInst>(I)) { for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end(); II != IE; ++II) e.varargs.push_back(*II); } return e; } Expression ValueTable::create_cmp_expression(unsigned Opcode, CmpInst::Predicate Predicate, Value *LHS, Value *RHS) { assert((Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) && "Not a comparison!"); Expression e; e.type = CmpInst::makeCmpResultType(LHS->getType()); e.varargs.push_back(lookup_or_add(LHS)); e.varargs.push_back(lookup_or_add(RHS)); // Sort the operand value numbers so x<y and y>x get the same value number. if (e.varargs[0] > e.varargs[1]) { std::swap(e.varargs[0], e.varargs[1]); Predicate = CmpInst::getSwappedPredicate(Predicate); } e.opcode = (Opcode << 8) | Predicate; return e; } Expression ValueTable::create_extractvalue_expression(ExtractValueInst *EI) { assert(EI && "Not an ExtractValueInst?"); Expression e; e.type = EI->getType(); e.opcode = 0; IntrinsicInst *I = dyn_cast<IntrinsicInst>(EI->getAggregateOperand()); if (I != nullptr && EI->getNumIndices() == 1 && *EI->idx_begin() == 0 ) { // EI might be an extract from one of our recognised intrinsics. If it // is we'll synthesize a semantically equivalent expression instead on // an extract value expression. switch (I->getIntrinsicID()) { case Intrinsic::sadd_with_overflow: case Intrinsic::uadd_with_overflow: e.opcode = Instruction::Add; break; case Intrinsic::ssub_with_overflow: case Intrinsic::usub_with_overflow: e.opcode = Instruction::Sub; break; case Intrinsic::smul_with_overflow: case Intrinsic::umul_with_overflow: e.opcode = Instruction::Mul; break; default: break; } if (e.opcode != 0) { // Intrinsic recognized. Grab its args to finish building the expression. assert(I->getNumArgOperands() == 2 && "Expect two args for recognised intrinsics."); e.varargs.push_back(lookup_or_add(I->getArgOperand(0))); e.varargs.push_back(lookup_or_add(I->getArgOperand(1))); return e; } } // Not a recognised intrinsic. Fall back to producing an extract value // expression. e.opcode = EI->getOpcode(); for (Instruction::op_iterator OI = EI->op_begin(), OE = EI->op_end(); OI != OE; ++OI) e.varargs.push_back(lookup_or_add(*OI)); for (ExtractValueInst::idx_iterator II = EI->idx_begin(), IE = EI->idx_end(); II != IE; ++II) e.varargs.push_back(*II); return e; } //===----------------------------------------------------------------------===// // ValueTable External Functions //===----------------------------------------------------------------------===// /// add - Insert a value into the table with a specified value number. void ValueTable::add(Value *V, uint32_t num) { valueNumbering.insert(std::make_pair(V, num)); } uint32_t ValueTable::lookup_or_add_call(CallInst *C) { if (AA->doesNotAccessMemory(C)) { Expression exp = create_expression(C); uint32_t &e = expressionNumbering[exp]; if (!e) e = nextValueNumber++; valueNumbering[C] = e; return e; } else if (AA->onlyReadsMemory(C)) { Expression exp = create_expression(C); uint32_t &e = expressionNumbering[exp]; if (!e) { e = nextValueNumber++; valueNumbering[C] = e; return e; } if (!MD) { e = nextValueNumber++; valueNumbering[C] = e; return e; } MemDepResult local_dep = MD->getDependency(C); if (!local_dep.isDef() && !local_dep.isNonLocal()) { valueNumbering[C] = nextValueNumber; return nextValueNumber++; } if (local_dep.isDef()) { CallInst* local_cdep = cast<CallInst>(local_dep.getInst()); if (local_cdep->getNumArgOperands() != C->getNumArgOperands()) { valueNumbering[C] = nextValueNumber; return nextValueNumber++; } for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { uint32_t c_vn = lookup_or_add(C->getArgOperand(i)); uint32_t cd_vn = lookup_or_add(local_cdep->getArgOperand(i)); if (c_vn != cd_vn) { valueNumbering[C] = nextValueNumber; return nextValueNumber++; } } uint32_t v = lookup_or_add(local_cdep); valueNumbering[C] = v; return v; } // Non-local case. const MemoryDependenceAnalysis::NonLocalDepInfo &deps = MD->getNonLocalCallDependency(CallSite(C)); // FIXME: Move the checking logic to MemDep! CallInst* cdep = nullptr; // Check to see if we have a single dominating call instruction that is // identical to C. for (unsigned i = 0, e = deps.size(); i != e; ++i) { const NonLocalDepEntry *I = &deps[i]; if (I->getResult().isNonLocal()) continue; // We don't handle non-definitions. If we already have a call, reject // instruction dependencies. if (!I->getResult().isDef() || cdep != nullptr) { cdep = nullptr; break; } CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst()); // FIXME: All duplicated with non-local case. if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){ cdep = NonLocalDepCall; continue; } cdep = nullptr; break; } if (!cdep) { valueNumbering[C] = nextValueNumber; return nextValueNumber++; } if (cdep->getNumArgOperands() != C->getNumArgOperands()) { valueNumbering[C] = nextValueNumber; return nextValueNumber++; } for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { uint32_t c_vn = lookup_or_add(C->getArgOperand(i)); uint32_t cd_vn = lookup_or_add(cdep->getArgOperand(i)); if (c_vn != cd_vn) { valueNumbering[C] = nextValueNumber; return nextValueNumber++; } } uint32_t v = lookup_or_add(cdep); valueNumbering[C] = v; return v; } else { valueNumbering[C] = nextValueNumber; return nextValueNumber++; } } /// lookup_or_add - Returns the value number for the specified value, assigning /// it a new number if it did not have one before. uint32_t ValueTable::lookup_or_add(Value *V) { DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); if (VI != valueNumbering.end()) return VI->second; if (!isa<Instruction>(V)) { valueNumbering[V] = nextValueNumber; return nextValueNumber++; } Instruction* I = cast<Instruction>(V); Expression exp; switch (I->getOpcode()) { case Instruction::Call: return lookup_or_add_call(cast<CallInst>(I)); case Instruction::Add: case Instruction::FAdd: case Instruction::Sub: case Instruction::FSub: case Instruction::Mul: case Instruction::FMul: case Instruction::UDiv: case Instruction::SDiv: case Instruction::FDiv: case Instruction::URem: case Instruction::SRem: case Instruction::FRem: case Instruction::Shl: case Instruction::LShr: case Instruction::AShr: case Instruction::And: case Instruction::Or: case Instruction::Xor: case Instruction::ICmp: case Instruction::FCmp: case Instruction::Trunc: case Instruction::ZExt: case Instruction::SExt: case Instruction::FPToUI: case Instruction::FPToSI: case Instruction::UIToFP: case Instruction::SIToFP: case Instruction::FPTrunc: case Instruction::FPExt: case Instruction::PtrToInt: case Instruction::IntToPtr: case Instruction::BitCast: case Instruction::Select: case Instruction::ExtractElement: case Instruction::InsertElement: case Instruction::ShuffleVector: case Instruction::InsertValue: case Instruction::GetElementPtr: exp = create_expression(I); break; case Instruction::ExtractValue: exp = create_extractvalue_expression(cast<ExtractValueInst>(I)); break; default: valueNumbering[V] = nextValueNumber; return nextValueNumber++; } uint32_t& e = expressionNumbering[exp]; if (!e) e = nextValueNumber++; valueNumbering[V] = e; return e; } /// lookup - Returns the value number of the specified value. Fails if /// the value has not yet been numbered. uint32_t ValueTable::lookup(Value *V) const { DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V); assert(VI != valueNumbering.end() && "Value not numbered?"); return VI->second; } /// lookup_or_add_cmp - Returns the value number of the given comparison, /// assigning it a new number if it did not have one before. Useful when /// we deduced the result of a comparison, but don't immediately have an /// instruction realizing that comparison to hand. uint32_t ValueTable::lookup_or_add_cmp(unsigned Opcode, CmpInst::Predicate Predicate, Value *LHS, Value *RHS) { Expression exp = create_cmp_expression(Opcode, Predicate, LHS, RHS); uint32_t& e = expressionNumbering[exp]; if (!e) e = nextValueNumber++; return e; } /// clear - Remove all entries from the ValueTable. void ValueTable::clear() { valueNumbering.clear(); expressionNumbering.clear(); nextValueNumber = 1; } /// erase - Remove a value from the value numbering. void ValueTable::erase(Value *V) { valueNumbering.erase(V); } /// verifyRemoved - Verify that the value is removed from all internal data /// structures. void ValueTable::verifyRemoved(const Value *V) const { for (DenseMap<Value*, uint32_t>::const_iterator I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) { assert(I->first != V && "Inst still occurs in value numbering map!"); } } //===----------------------------------------------------------------------===// // GVN Pass //===----------------------------------------------------------------------===// namespace { class GVN; struct AvailableValueInBlock { /// BB - The basic block in question. BasicBlock *BB; enum ValType { SimpleVal, // A simple offsetted value that is accessed. LoadVal, // A value produced by a load. MemIntrin, // A memory intrinsic which is loaded from. UndefVal // A UndefValue representing a value from dead block (which // is not yet physically removed from the CFG). }; /// V - The value that is live out of the block. PointerIntPair<Value *, 2, ValType> Val; /// Offset - The byte offset in Val that is interesting for the load query. unsigned Offset; static AvailableValueInBlock get(BasicBlock *BB, Value *V, unsigned Offset = 0) { AvailableValueInBlock Res; Res.BB = BB; Res.Val.setPointer(V); Res.Val.setInt(SimpleVal); Res.Offset = Offset; return Res; } static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI, unsigned Offset = 0) { AvailableValueInBlock Res; Res.BB = BB; Res.Val.setPointer(MI); Res.Val.setInt(MemIntrin); Res.Offset = Offset; return Res; } static AvailableValueInBlock getLoad(BasicBlock *BB, LoadInst *LI, unsigned Offset = 0) { AvailableValueInBlock Res; Res.BB = BB; Res.Val.setPointer(LI); Res.Val.setInt(LoadVal); Res.Offset = Offset; return Res; } static AvailableValueInBlock getUndef(BasicBlock *BB) { AvailableValueInBlock Res; Res.BB = BB; Res.Val.setPointer(nullptr); Res.Val.setInt(UndefVal); Res.Offset = 0; return Res; } bool isSimpleValue() const { return Val.getInt() == SimpleVal; } bool isCoercedLoadValue() const { return Val.getInt() == LoadVal; } bool isMemIntrinValue() const { return Val.getInt() == MemIntrin; } bool isUndefValue() const { return Val.getInt() == UndefVal; } Value *getSimpleValue() const { assert(isSimpleValue() && "Wrong accessor"); return Val.getPointer(); } LoadInst *getCoercedLoadValue() const { assert(isCoercedLoadValue() && "Wrong accessor"); return cast<LoadInst>(Val.getPointer()); } MemIntrinsic *getMemIntrinValue() const { assert(isMemIntrinValue() && "Wrong accessor"); return cast<MemIntrinsic>(Val.getPointer()); } /// MaterializeAdjustedValue - Emit code into this block to adjust the value /// defined here to the specified type. This handles various coercion cases. Value *MaterializeAdjustedValue(Type *LoadTy, GVN &gvn) const; }; class GVN : public FunctionPass { bool NoLoads; MemoryDependenceAnalysis *MD; DominatorTree *DT; const DataLayout *DL; const TargetLibraryInfo *TLI; AssumptionCache *AC; SetVector<BasicBlock *> DeadBlocks; ValueTable VN; /// LeaderTable - A mapping from value numbers to lists of Value*'s that /// have that value number. Use findLeader to query it. struct LeaderTableEntry { Value *Val; const BasicBlock *BB; LeaderTableEntry *Next; }; DenseMap<uint32_t, LeaderTableEntry> LeaderTable; BumpPtrAllocator TableAllocator; SmallVector<Instruction*, 8> InstrsToErase; typedef SmallVector<NonLocalDepResult, 64> LoadDepVect; typedef SmallVector<AvailableValueInBlock, 64> AvailValInBlkVect; typedef SmallVector<BasicBlock*, 64> UnavailBlkVect; public: static char ID; // Pass identification, replacement for typeid explicit GVN(bool noloads = false) : FunctionPass(ID), NoLoads(noloads), MD(nullptr) { initializeGVNPass(*PassRegistry::getPassRegistry()); } bool runOnFunction(Function &F) override; /// markInstructionForDeletion - This removes the specified instruction from /// our various maps and marks it for deletion. void markInstructionForDeletion(Instruction *I) { VN.erase(I); InstrsToErase.push_back(I); } const DataLayout *getDataLayout() const { return DL; } DominatorTree &getDominatorTree() const { return *DT; } AliasAnalysis *getAliasAnalysis() const { return VN.getAliasAnalysis(); } MemoryDependenceAnalysis &getMemDep() const { return *MD; } private: /// addToLeaderTable - Push a new Value to the LeaderTable onto the list for /// its value number. void addToLeaderTable(uint32_t N, Value *V, const BasicBlock *BB) { LeaderTableEntry &Curr = LeaderTable[N]; if (!Curr.Val) { Curr.Val = V; Curr.BB = BB; return; } LeaderTableEntry *Node = TableAllocator.Allocate<LeaderTableEntry>(); Node->Val = V; Node->BB = BB; Node->Next = Curr.Next; Curr.Next = Node; } /// removeFromLeaderTable - Scan the list of values corresponding to a given /// value number, and remove the given instruction if encountered. void removeFromLeaderTable(uint32_t N, Instruction *I, BasicBlock *BB) { LeaderTableEntry* Prev = nullptr; LeaderTableEntry* Curr = &LeaderTable[N]; while (Curr->Val != I || Curr->BB != BB) { Prev = Curr; Curr = Curr->Next; } if (Prev) { Prev->Next = Curr->Next; } else { if (!Curr->Next) { Curr->Val = nullptr; Curr->BB = nullptr; } else { LeaderTableEntry* Next = Curr->Next; Curr->Val = Next->Val; Curr->BB = Next->BB; Curr->Next = Next->Next; } } } // List of critical edges to be split between iterations. SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; // This transformation requires dominator postdominator info void getAnalysisUsage(AnalysisUsage &AU) const override { AU.addRequired<AssumptionCacheTracker>(); AU.addRequired<DominatorTreeWrapperPass>(); AU.addRequired<TargetLibraryInfoWrapperPass>(); if (!NoLoads) AU.addRequired<MemoryDependenceAnalysis>(); AU.addRequired<AliasAnalysis>(); AU.addPreserved<DominatorTreeWrapperPass>(); AU.addPreserved<AliasAnalysis>(); } // Helper fuctions of redundant load elimination bool processLoad(LoadInst *L); bool processNonLocalLoad(LoadInst *L); void AnalyzeLoadAvailability(LoadInst *LI, LoadDepVect &Deps, AvailValInBlkVect &ValuesPerBlock, UnavailBlkVect &UnavailableBlocks); bool PerformLoadPRE(LoadInst *LI, AvailValInBlkVect &ValuesPerBlock, UnavailBlkVect &UnavailableBlocks); // Other helper routines bool processInstruction(Instruction *I); bool processBlock(BasicBlock *BB); void dump(DenseMap<uint32_t, Value*> &d); bool iterateOnFunction(Function &F); bool performPRE(Function &F); bool performScalarPRE(Instruction *I); bool performScalarPREInsertion(Instruction *Instr, BasicBlock *Pred, unsigned int ValNo); Value *findLeader(const BasicBlock *BB, uint32_t num); void cleanupGlobalSets(); void verifyRemoved(const Instruction *I) const; bool splitCriticalEdges(); BasicBlock *splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ); unsigned replaceAllDominatedUsesWith(Value *From, Value *To, const BasicBlockEdge &Root); bool propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root); bool processFoldableCondBr(BranchInst *BI); void addDeadBlock(BasicBlock *BB); void assignValNumForDeadCode(); }; char GVN::ID = 0; } // createGVNPass - The public interface to this file... FunctionPass *llvm::createGVNPass(bool NoLoads) { return new GVN(NoLoads); } INITIALIZE_PASS_BEGIN(GVN, "gvn", "Global Value Numbering", false, false) INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis) INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) INITIALIZE_AG_DEPENDENCY(AliasAnalysis) INITIALIZE_PASS_END(GVN, "gvn", "Global Value Numbering", false, false) #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) void GVN::dump(DenseMap<uint32_t, Value*>& d) { errs() << "{\n"; for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), E = d.end(); I != E; ++I) { errs() << I->first << "\n"; I->second->dump(); } errs() << "}\n"; } #endif /// IsValueFullyAvailableInBlock - Return true if we can prove that the value /// we're analyzing is fully available in the specified block. As we go, keep /// track of which blocks we know are fully alive in FullyAvailableBlocks. This /// map is actually a tri-state map with the following values: /// 0) we know the block *is not* fully available. /// 1) we know the block *is* fully available. /// 2) we do not know whether the block is fully available or not, but we are /// currently speculating that it will be. /// 3) we are speculating for this block and have used that to speculate for /// other blocks. static bool IsValueFullyAvailableInBlock(BasicBlock *BB, DenseMap<BasicBlock*, char> &FullyAvailableBlocks, uint32_t RecurseDepth) { if (RecurseDepth > MaxRecurseDepth) return false; // Optimistically assume that the block is fully available and check to see // if we already know about this block in one lookup. std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = FullyAvailableBlocks.insert(std::make_pair(BB, 2)); // If the entry already existed for this block, return the precomputed value. if (!IV.second) { // If this is a speculative "available" value, mark it as being used for // speculation of other blocks. if (IV.first->second == 2) IV.first->second = 3; return IV.first->second != 0; } // Otherwise, see if it is fully available in all predecessors. pred_iterator PI = pred_begin(BB), PE = pred_end(BB); // If this block has no predecessors, it isn't live-in here. if (PI == PE) goto SpeculationFailure; for (; PI != PE; ++PI) // If the value isn't fully available in one of our predecessors, then it // isn't fully available in this block either. Undo our previous // optimistic assumption and bail out. if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks,RecurseDepth+1)) goto SpeculationFailure; return true; // SpeculationFailure - If we get here, we found out that this is not, after // all, a fully-available block. We have a problem if we speculated on this and // used the speculation to mark other blocks as available. SpeculationFailure: char &BBVal = FullyAvailableBlocks[BB]; // If we didn't speculate on this, just return with it set to false. if (BBVal == 2) { BBVal = 0; return false; } // If we did speculate on this value, we could have blocks set to 1 that are // incorrect. Walk the (transitive) successors of this block and mark them as // 0 if set to one. SmallVector<BasicBlock*, 32> BBWorklist; BBWorklist.push_back(BB); do { BasicBlock *Entry = BBWorklist.pop_back_val(); // Note that this sets blocks to 0 (unavailable) if they happen to not // already be in FullyAvailableBlocks. This is safe. char &EntryVal = FullyAvailableBlocks[Entry]; if (EntryVal == 0) continue; // Already unavailable. // Mark as unavailable. EntryVal = 0; BBWorklist.append(succ_begin(Entry), succ_end(Entry)); } while (!BBWorklist.empty()); return false; } /// CanCoerceMustAliasedValueToLoad - Return true if /// CoerceAvailableValueToLoadType will succeed. static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal, Type *LoadTy, const DataLayout &DL) { // If the loaded or stored value is an first class array or struct, don't try // to transform them. We need to be able to bitcast to integer. if (LoadTy->isStructTy() || LoadTy->isArrayTy() || StoredVal->getType()->isStructTy() || StoredVal->getType()->isArrayTy()) return false; // The store has to be at least as big as the load. if (DL.getTypeSizeInBits(StoredVal->getType()) < DL.getTypeSizeInBits(LoadTy)) return false; return true; } /// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and /// then a load from a must-aliased pointer of a different type, try to coerce /// the stored value. LoadedTy is the type of the load we want to replace and /// InsertPt is the place to insert new instructions. /// /// If we can't do it, return null. static Value *CoerceAvailableValueToLoadType(Value *StoredVal, Type *LoadedTy, Instruction *InsertPt, const DataLayout &DL) { if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, DL)) return nullptr; // If this is already the right type, just return it. Type *StoredValTy = StoredVal->getType(); uint64_t StoreSize = DL.getTypeSizeInBits(StoredValTy); uint64_t LoadSize = DL.getTypeSizeInBits(LoadedTy); // If the store and reload are the same size, we can always reuse it. if (StoreSize == LoadSize) { // Pointer to Pointer -> use bitcast. if (StoredValTy->getScalarType()->isPointerTy() && LoadedTy->getScalarType()->isPointerTy()) return new BitCastInst(StoredVal, LoadedTy, "", InsertPt); // Convert source pointers to integers, which can be bitcast. if (StoredValTy->getScalarType()->isPointerTy()) { StoredValTy = DL.getIntPtrType(StoredValTy); StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); } Type *TypeToCastTo = LoadedTy; if (TypeToCastTo->getScalarType()->isPointerTy()) TypeToCastTo = DL.getIntPtrType(TypeToCastTo); if (StoredValTy != TypeToCastTo) StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt); // Cast to pointer if the load needs a pointer type. if (LoadedTy->getScalarType()->isPointerTy()) StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt); return StoredVal; } // If the loaded value is smaller than the available value, then we can // extract out a piece from it. If the available value is too small, then we // can't do anything. assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail"); // Convert source pointers to integers, which can be manipulated. if (StoredValTy->getScalarType()->isPointerTy()) { StoredValTy = DL.getIntPtrType(StoredValTy); StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); } // Convert vectors and fp to integer, which can be manipulated. if (!StoredValTy->isIntegerTy()) { StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize); StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt); } // If this is a big-endian system, we need to shift the value down to the low // bits so that a truncate will work. if (DL.isBigEndian()) { Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize); StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt); } // Truncate the integer to the right size now. Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize); StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt); if (LoadedTy == NewIntTy) return StoredVal; // If the result is a pointer, inttoptr. if (LoadedTy->getScalarType()->isPointerTy()) return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt); // Otherwise, bitcast. return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt); } /// AnalyzeLoadFromClobberingWrite - This function is called when we have a /// memdep query of a load that ends up being a clobbering memory write (store, /// memset, memcpy, memmove). This means that the write *may* provide bits used /// by the load but we can't be sure because the pointers don't mustalias. /// /// Check this case to see if there is anything more we can do before we give /// up. This returns -1 if we have to give up, or a byte number in the stored /// value of the piece that feeds the load. static int AnalyzeLoadFromClobberingWrite(Type *LoadTy, Value *LoadPtr, Value *WritePtr, uint64_t WriteSizeInBits, const DataLayout &DL) { // If the loaded or stored value is a first class array or struct, don't try // to transform them. We need to be able to bitcast to integer. if (LoadTy->isStructTy() || LoadTy->isArrayTy()) return -1; int64_t StoreOffset = 0, LoadOffset = 0; Value *StoreBase = GetPointerBaseWithConstantOffset(WritePtr,StoreOffset,&DL); Value *LoadBase = GetPointerBaseWithConstantOffset(LoadPtr, LoadOffset, &DL); if (StoreBase != LoadBase) return -1; // If the load and store are to the exact same address, they should have been // a must alias. AA must have gotten confused. // FIXME: Study to see if/when this happens. One case is forwarding a memset // to a load from the base of the memset. #if 0 if (LoadOffset == StoreOffset) { dbgs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n" << "Base = " << *StoreBase << "\n" << "Store Ptr = " << *WritePtr << "\n" << "Store Offs = " << StoreOffset << "\n" << "Load Ptr = " << *LoadPtr << "\n"; abort(); } #endif // If the load and store don't overlap at all, the store doesn't provide // anything to the load. In this case, they really don't alias at all, AA // must have gotten confused. uint64_t LoadSize = DL.getTypeSizeInBits(LoadTy); if ((WriteSizeInBits & 7) | (LoadSize & 7)) return -1; uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes. LoadSize >>= 3; bool isAAFailure = false; if (StoreOffset < LoadOffset) isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset; else isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset; if (isAAFailure) { #if 0 dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n" << "Base = " << *StoreBase << "\n" << "Store Ptr = " << *WritePtr << "\n" << "Store Offs = " << StoreOffset << "\n" << "Load Ptr = " << *LoadPtr << "\n"; abort(); #endif return -1; } // If the Load isn't completely contained within the stored bits, we don't // have all the bits to feed it. We could do something crazy in the future // (issue a smaller load then merge the bits in) but this seems unlikely to be // valuable. if (StoreOffset > LoadOffset || StoreOffset+StoreSize < LoadOffset+LoadSize) return -1; // Okay, we can do this transformation. Return the number of bytes into the // store that the load is. return LoadOffset-StoreOffset; } /// AnalyzeLoadFromClobberingStore - This function is called when we have a /// memdep query of a load that ends up being a clobbering store. static int AnalyzeLoadFromClobberingStore(Type *LoadTy, Value *LoadPtr, StoreInst *DepSI, const DataLayout &DL) { // Cannot handle reading from store of first-class aggregate yet. if (DepSI->getValueOperand()->getType()->isStructTy() || DepSI->getValueOperand()->getType()->isArrayTy()) return -1; Value *StorePtr = DepSI->getPointerOperand(); uint64_t StoreSize =DL.getTypeSizeInBits(DepSI->getValueOperand()->getType()); return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, StorePtr, StoreSize, DL); } /// AnalyzeLoadFromClobberingLoad - This function is called when we have a /// memdep query of a load that ends up being clobbered by another load. See if /// the other load can feed into the second load. static int AnalyzeLoadFromClobberingLoad(Type *LoadTy, Value *LoadPtr, LoadInst *DepLI, const DataLayout &DL){ // Cannot handle reading from store of first-class aggregate yet. if (DepLI->getType()->isStructTy() || DepLI->getType()->isArrayTy()) return -1; Value *DepPtr = DepLI->getPointerOperand(); uint64_t DepSize = DL.getTypeSizeInBits(DepLI->getType()); int R = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, DepPtr, DepSize, DL); if (R != -1) return R; // If we have a load/load clobber an DepLI can be widened to cover this load, // then we should widen it! int64_t LoadOffs = 0; const Value *LoadBase = GetPointerBaseWithConstantOffset(LoadPtr, LoadOffs, &DL); unsigned LoadSize = DL.getTypeStoreSize(LoadTy); unsigned Size = MemoryDependenceAnalysis:: getLoadLoadClobberFullWidthSize(LoadBase, LoadOffs, LoadSize, DepLI, DL); if (Size == 0) return -1; return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, DepPtr, Size*8, DL); } static int AnalyzeLoadFromClobberingMemInst(Type *LoadTy, Value *LoadPtr, MemIntrinsic *MI, const DataLayout &DL) { // If the mem operation is a non-constant size, we can't handle it. ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength()); if (!SizeCst) return -1; uint64_t MemSizeInBits = SizeCst->getZExtValue()*8; // If this is memset, we just need to see if the offset is valid in the size // of the memset.. if (MI->getIntrinsicID() == Intrinsic::memset) return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(), MemSizeInBits, DL); // If we have a memcpy/memmove, the only case we can handle is if this is a // copy from constant memory. In that case, we can read directly from the // constant memory. MemTransferInst *MTI = cast<MemTransferInst>(MI); Constant *Src = dyn_cast<Constant>(MTI->getSource()); if (!Src) return -1; GlobalVariable *GV = dyn_cast<GlobalVariable>(GetUnderlyingObject(Src, &DL)); if (!GV || !GV->isConstant()) return -1; // See if the access is within the bounds of the transfer. int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(), MemSizeInBits, DL); if (Offset == -1) return Offset; unsigned AS = Src->getType()->getPointerAddressSpace(); // Otherwise, see if we can constant fold a load from the constant with the // offset applied as appropriate. Src = ConstantExpr::getBitCast(Src, Type::getInt8PtrTy(Src->getContext(), AS)); Constant *OffsetCst = ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); Src = ConstantExpr::getGetElementPtr(Src, OffsetCst); Src = ConstantExpr::getBitCast(Src, PointerType::get(LoadTy, AS)); if (ConstantFoldLoadFromConstPtr(Src, &DL)) return Offset; return -1; } /// GetStoreValueForLoad - This function is called when we have a /// memdep query of a load that ends up being a clobbering store. This means /// that the store provides bits used by the load but we the pointers don't /// mustalias. Check this case to see if there is anything more we can do /// before we give up. static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset, Type *LoadTy, Instruction *InsertPt, const DataLayout &DL){ LLVMContext &Ctx = SrcVal->getType()->getContext(); uint64_t StoreSize = (DL.getTypeSizeInBits(SrcVal->getType()) + 7) / 8; uint64_t LoadSize = (DL.getTypeSizeInBits(LoadTy) + 7) / 8; IRBuilder<> Builder(InsertPt->getParent(), InsertPt); // Compute which bits of the stored value are being used by the load. Convert // to an integer type to start with. if (SrcVal->getType()->getScalarType()->isPointerTy()) SrcVal = Builder.CreatePtrToInt(SrcVal, DL.getIntPtrType(SrcVal->getType())); if (!SrcVal->getType()->isIntegerTy()) SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8)); // Shift the bits to the least significant depending on endianness. unsigned ShiftAmt; if (DL.isLittleEndian()) ShiftAmt = Offset*8; else ShiftAmt = (StoreSize-LoadSize-Offset)*8; if (ShiftAmt) SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt); if (LoadSize != StoreSize) SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8)); return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, DL); } /// GetLoadValueForLoad - This function is called when we have a /// memdep query of a load that ends up being a clobbering load. This means /// that the load *may* provide bits used by the load but we can't be sure /// because the pointers don't mustalias. Check this case to see if there is /// anything more we can do before we give up. static Value *GetLoadValueForLoad(LoadInst *SrcVal, unsigned Offset, Type *LoadTy, Instruction *InsertPt, GVN &gvn) { const DataLayout &DL = *gvn.getDataLayout(); // If Offset+LoadTy exceeds the size of SrcVal, then we must be wanting to // widen SrcVal out to a larger load. unsigned SrcValSize = DL.getTypeStoreSize(SrcVal->getType()); unsigned LoadSize = DL.getTypeStoreSize(LoadTy); if (Offset+LoadSize > SrcValSize) { assert(SrcVal->isSimple() && "Cannot widen volatile/atomic load!"); assert(SrcVal->getType()->isIntegerTy() && "Can't widen non-integer load"); // If we have a load/load clobber an DepLI can be widened to cover this // load, then we should widen it to the next power of 2 size big enough! unsigned NewLoadSize = Offset+LoadSize; if (!isPowerOf2_32(NewLoadSize)) NewLoadSize = NextPowerOf2(NewLoadSize); Value *PtrVal = SrcVal->getPointerOperand(); // Insert the new load after the old load. This ensures that subsequent // memdep queries will find the new load. We can't easily remove the old // load completely because it is already in the value numbering table. IRBuilder<> Builder(SrcVal->getParent(), ++BasicBlock::iterator(SrcVal)); Type *DestPTy = IntegerType::get(LoadTy->getContext(), NewLoadSize*8); DestPTy = PointerType::get(DestPTy, PtrVal->getType()->getPointerAddressSpace()); Builder.SetCurrentDebugLocation(SrcVal->getDebugLoc()); PtrVal = Builder.CreateBitCast(PtrVal, DestPTy); LoadInst *NewLoad = Builder.CreateLoad(PtrVal); NewLoad->takeName(SrcVal); NewLoad->setAlignment(SrcVal->getAlignment()); DEBUG(dbgs() << "GVN WIDENED LOAD: " << *SrcVal << "\n"); DEBUG(dbgs() << "TO: " << *NewLoad << "\n"); // Replace uses of the original load with the wider load. On a big endian // system, we need to shift down to get the relevant bits. Value *RV = NewLoad; if (DL.isBigEndian()) RV = Builder.CreateLShr(RV, NewLoadSize*8-SrcVal->getType()->getPrimitiveSizeInBits()); RV = Builder.CreateTrunc(RV, SrcVal->getType()); SrcVal->replaceAllUsesWith(RV); // We would like to use gvn.markInstructionForDeletion here, but we can't // because the load is already memoized into the leader map table that GVN // tracks. It is potentially possible to remove the load from the table, // but then there all of the operations based on it would need to be // rehashed. Just leave the dead load around. gvn.getMemDep().removeInstruction(SrcVal); SrcVal = NewLoad; } return GetStoreValueForLoad(SrcVal, Offset, LoadTy, InsertPt, DL); } /// GetMemInstValueForLoad - This function is called when we have a /// memdep query of a load that ends up being a clobbering mem intrinsic. static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset, Type *LoadTy, Instruction *InsertPt, const DataLayout &DL){ LLVMContext &Ctx = LoadTy->getContext(); uint64_t LoadSize = DL.getTypeSizeInBits(LoadTy)/8; IRBuilder<> Builder(InsertPt->getParent(), InsertPt); // We know that this method is only called when the mem transfer fully // provides the bits for the load. if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) { // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and // independently of what the offset is. Value *Val = MSI->getValue(); if (LoadSize != 1) Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8)); Value *OneElt = Val; // Splat the value out to the right number of bits. for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) { // If we can double the number of bytes set, do it. if (NumBytesSet*2 <= LoadSize) { Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8); Val = Builder.CreateOr(Val, ShVal); NumBytesSet <<= 1; continue; } // Otherwise insert one byte at a time. Value *ShVal = Builder.CreateShl(Val, 1*8); Val = Builder.CreateOr(OneElt, ShVal); ++NumBytesSet; } return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, DL); } // Otherwise, this is a memcpy/memmove from a constant global. MemTransferInst *MTI = cast<MemTransferInst>(SrcInst); Constant *Src = cast<Constant>(MTI->getSource()); unsigned AS = Src->getType()->getPointerAddressSpace(); // Otherwise, see if we can constant fold a load from the constant with the // offset applied as appropriate. Src = ConstantExpr::getBitCast(Src, Type::getInt8PtrTy(Src->getContext(), AS)); Constant *OffsetCst = ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); Src = ConstantExpr::getGetElementPtr(Src, OffsetCst); Src = ConstantExpr::getBitCast(Src, PointerType::get(LoadTy, AS)); return ConstantFoldLoadFromConstPtr(Src, &DL); } /// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock, /// construct SSA form, allowing us to eliminate LI. This returns the value /// that should be used at LI's definition site. static Value *ConstructSSAForLoadSet(LoadInst *LI, SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock, GVN &gvn) { // Check for the fully redundant, dominating load case. In this case, we can // just use the dominating value directly. if (ValuesPerBlock.size() == 1 && gvn.getDominatorTree().properlyDominates(ValuesPerBlock[0].BB, LI->getParent())) { assert(!ValuesPerBlock[0].isUndefValue() && "Dead BB dominate this block"); return ValuesPerBlock[0].MaterializeAdjustedValue(LI->getType(), gvn); } // Otherwise, we have to construct SSA form. SmallVector<PHINode*, 8> NewPHIs; SSAUpdater SSAUpdate(&NewPHIs); SSAUpdate.Initialize(LI->getType(), LI->getName()); Type *LoadTy = LI->getType(); for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { const AvailableValueInBlock &AV = ValuesPerBlock[i]; BasicBlock *BB = AV.BB; if (SSAUpdate.HasValueForBlock(BB)) continue; SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LoadTy, gvn)); } // Perform PHI construction. Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent()); // If new PHI nodes were created, notify alias analysis. if (V->getType()->getScalarType()->isPointerTy()) { AliasAnalysis *AA = gvn.getAliasAnalysis(); for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) AA->copyValue(LI, NewPHIs[i]); // Now that we've copied information to the new PHIs, scan through // them again and inform alias analysis that we've added potentially // escaping uses to any values that are operands to these PHIs. for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) { PHINode *P = NewPHIs[i]; for (unsigned ii = 0, ee = P->getNumIncomingValues(); ii != ee; ++ii) { unsigned jj = PHINode::getOperandNumForIncomingValue(ii); AA->addEscapingUse(P->getOperandUse(jj)); } } } return V; } Value *AvailableValueInBlock::MaterializeAdjustedValue(Type *LoadTy, GVN &gvn) const { Value *Res; if (isSimpleValue()) { Res = getSimpleValue(); if (Res->getType() != LoadTy) { const DataLayout *DL = gvn.getDataLayout(); assert(DL && "Need target data to handle type mismatch case"); Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(), *DL); DEBUG(dbgs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " " << *getSimpleValue() << '\n' << *Res << '\n' << "\n\n\n"); } } else if (isCoercedLoadValue()) { LoadInst *Load = getCoercedLoadValue(); if (Load->getType() == LoadTy && Offset == 0) { Res = Load; } else { Res = GetLoadValueForLoad(Load, Offset, LoadTy, BB->getTerminator(), gvn); DEBUG(dbgs() << "GVN COERCED NONLOCAL LOAD:\nOffset: " << Offset << " " << *getCoercedLoadValue() << '\n' << *Res << '\n' << "\n\n\n"); } } else if (isMemIntrinValue()) { const DataLayout *DL = gvn.getDataLayout(); assert(DL && "Need target data to handle type mismatch case"); Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset, LoadTy, BB->getTerminator(), *DL); DEBUG(dbgs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset << " " << *getMemIntrinValue() << '\n' << *Res << '\n' << "\n\n\n"); } else { assert(isUndefValue() && "Should be UndefVal"); DEBUG(dbgs() << "GVN COERCED NONLOCAL Undef:\n";); return UndefValue::get(LoadTy); } return Res; } static bool isLifetimeStart(const Instruction *Inst) { if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst)) return II->getIntrinsicID() == Intrinsic::lifetime_start; return false; } void GVN::AnalyzeLoadAvailability(LoadInst *LI, LoadDepVect &Deps, AvailValInBlkVect &ValuesPerBlock, UnavailBlkVect &UnavailableBlocks) { // Filter out useless results (non-locals, etc). Keep track of the blocks // where we have a value available in repl, also keep track of whether we see // dependencies that produce an unknown value for the load (such as a call // that could potentially clobber the load). unsigned NumDeps = Deps.size(); for (unsigned i = 0, e = NumDeps; i != e; ++i) { BasicBlock *DepBB = Deps[i].getBB(); MemDepResult DepInfo = Deps[i].getResult(); if (DeadBlocks.count(DepBB)) { // Dead dependent mem-op disguise as a load evaluating the same value // as the load in question. ValuesPerBlock.push_back(AvailableValueInBlock::getUndef(DepBB)); continue; } if (!DepInfo.isDef() && !DepInfo.isClobber()) { UnavailableBlocks.push_back(DepBB); continue; } if (DepInfo.isClobber()) { // The address being loaded in this non-local block may not be the same as // the pointer operand of the load if PHI translation occurs. Make sure // to consider the right address. Value *Address = Deps[i].getAddress(); // If the dependence is to a store that writes to a superset of the bits // read by the load, we can extract the bits we need for the load from the // stored value. if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) { if (DL && Address) { int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address, DepSI, *DL); if (Offset != -1) { ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, DepSI->getValueOperand(), Offset)); continue; } } } // Check to see if we have something like this: // load i32* P // load i8* (P+1) // if we have this, replace the later with an extraction from the former. if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInfo.getInst())) { // If this is a clobber and L is the first instruction in its block, then // we have the first instruction in the entry block. if (DepLI != LI && Address && DL) { int Offset = AnalyzeLoadFromClobberingLoad(LI->getType(), Address, DepLI, *DL); if (Offset != -1) { ValuesPerBlock.push_back(AvailableValueInBlock::getLoad(DepBB,DepLI, Offset)); continue; } } } // If the clobbering value is a memset/memcpy/memmove, see if we can // forward a value on from it. if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) { if (DL && Address) { int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address, DepMI, *DL); if (Offset != -1) { ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI, Offset)); continue; } } } UnavailableBlocks.push_back(DepBB); continue; } // DepInfo.isDef() here Instruction *DepInst = DepInfo.getInst(); // Loading the allocation -> undef. if (isa<AllocaInst>(DepInst) || isMallocLikeFn(DepInst, TLI) || // Loading immediately after lifetime begin -> undef. isLifetimeStart(DepInst)) { ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, UndefValue::get(LI->getType()))); continue; } // Loading from calloc (which zero initializes memory) -> zero if (isCallocLikeFn(DepInst, TLI)) { ValuesPerBlock.push_back(AvailableValueInBlock::get( DepBB, Constant::getNullValue(LI->getType()))); continue; } if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) { // Reject loads and stores that are to the same address but are of // different types if we have to. if (S->getValueOperand()->getType() != LI->getType()) { // If the stored value is larger or equal to the loaded value, we can // reuse it. if (!DL || !CanCoerceMustAliasedValueToLoad(S->getValueOperand(), LI->getType(), *DL)) { UnavailableBlocks.push_back(DepBB); continue; } } ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, S->getValueOperand())); continue; } if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) { // If the types mismatch and we can't handle it, reject reuse of the load. if (LD->getType() != LI->getType()) { // If the stored value is larger or equal to the loaded value, we can // reuse it. if (!DL || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*DL)) { UnavailableBlocks.push_back(DepBB); continue; } } ValuesPerBlock.push_back(AvailableValueInBlock::getLoad(DepBB, LD)); continue; } UnavailableBlocks.push_back(DepBB); } } bool GVN::PerformLoadPRE(LoadInst *LI, AvailValInBlkVect &ValuesPerBlock, UnavailBlkVect &UnavailableBlocks) { // Okay, we have *some* definitions of the value. This means that the value // is available in some of our (transitive) predecessors. Lets think about // doing PRE of this load. This will involve inserting a new load into the // predecessor when it's not available. We could do this in general, but // prefer to not increase code size. As such, we only do this when we know // that we only have to insert *one* load (which means we're basically moving // the load, not inserting a new one). SmallPtrSet<BasicBlock *, 4> Blockers; for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) Blockers.insert(UnavailableBlocks[i]); // Let's find the first basic block with more than one predecessor. Walk // backwards through predecessors if needed. BasicBlock *LoadBB = LI->getParent(); BasicBlock *TmpBB = LoadBB; while (TmpBB->getSinglePredecessor()) { TmpBB = TmpBB->getSinglePredecessor(); if (TmpBB == LoadBB) // Infinite (unreachable) loop. return false; if (Blockers.count(TmpBB)) return false; // If any of these blocks has more than one successor (i.e. if the edge we // just traversed was critical), then there are other paths through this // block along which the load may not be anticipated. Hoisting the load // above this block would be adding the load to execution paths along // which it was not previously executed. if (TmpBB->getTerminator()->getNumSuccessors() != 1) return false; } assert(TmpBB); LoadBB = TmpBB; // Check to see how many predecessors have the loaded value fully // available. MapVector<BasicBlock *, Value *> PredLoads; DenseMap<BasicBlock*, char> FullyAvailableBlocks; for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) FullyAvailableBlocks[ValuesPerBlock[i].BB] = true; for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) FullyAvailableBlocks[UnavailableBlocks[i]] = false; SmallVector<BasicBlock *, 4> CriticalEdgePred; for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); PI != E; ++PI) { BasicBlock *Pred = *PI; if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks, 0)) { continue; } if (Pred->getTerminator()->getNumSuccessors() != 1) { if (isa<IndirectBrInst>(Pred->getTerminator())) { DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '" << Pred->getName() << "': " << *LI << '\n'); return false; } if (LoadBB->isLandingPad()) { DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF LANDING PAD CRITICAL EDGE '" << Pred->getName() << "': " << *LI << '\n'); return false; } CriticalEdgePred.push_back(Pred); } else { // Only add the predecessors that will not be split for now. PredLoads[Pred] = nullptr; } } // Decide whether PRE is profitable for this load. unsigned NumUnavailablePreds = PredLoads.size() + CriticalEdgePred.size(); assert(NumUnavailablePreds != 0 && "Fully available value should already be eliminated!"); // If this load is unavailable in multiple predecessors, reject it. // FIXME: If we could restructure the CFG, we could make a common pred with // all the preds that don't have an available LI and insert a new load into // that one block. if (NumUnavailablePreds != 1) return false; // Split critical edges, and update the unavailable predecessors accordingly. for (BasicBlock *OrigPred : CriticalEdgePred) { BasicBlock *NewPred = splitCriticalEdges(OrigPred, LoadBB); assert(!PredLoads.count(OrigPred) && "Split edges shouldn't be in map!"); PredLoads[NewPred] = nullptr; DEBUG(dbgs() << "Split critical edge " << OrigPred->getName() << "->" << LoadBB->getName() << '\n'); } // Check if the load can safely be moved to all the unavailable predecessors. bool CanDoPRE = true; SmallVector<Instruction*, 8> NewInsts; for (auto &PredLoad : PredLoads) { BasicBlock *UnavailablePred = PredLoad.first; // Do PHI translation to get its value in the predecessor if necessary. The // returned pointer (if non-null) is guaranteed to dominate UnavailablePred. // If all preds have a single successor, then we know it is safe to insert // the load on the pred (?!?), so we can insert code to materialize the // pointer if it is not available. PHITransAddr Address(LI->getPointerOperand(), DL, AC); Value *LoadPtr = nullptr; LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred, *DT, NewInsts); // If we couldn't find or insert a computation of this phi translated value, // we fail PRE. if (!LoadPtr) { DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: " << *LI->getPointerOperand() << "\n"); CanDoPRE = false; break; } PredLoad.second = LoadPtr; } if (!CanDoPRE) { while (!NewInsts.empty()) { Instruction *I = NewInsts.pop_back_val(); if (MD) MD->removeInstruction(I); I->eraseFromParent(); } // HINT: Don't revert the edge-splitting as following transformation may // also need to split these critical edges. return !CriticalEdgePred.empty(); } // Okay, we can eliminate this load by inserting a reload in the predecessor // and using PHI construction to get the value in the other predecessors, do // it. DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n'); DEBUG(if (!NewInsts.empty()) dbgs() << "INSERTED " << NewInsts.size() << " INSTS: " << *NewInsts.back() << '\n'); // Assign value numbers to the new instructions. for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) { // FIXME: We really _ought_ to insert these value numbers into their // parent's availability map. However, in doing so, we risk getting into // ordering issues. If a block hasn't been processed yet, we would be // marking a value as AVAIL-IN, which isn't what we intend. VN.lookup_or_add(NewInsts[i]); } for (const auto &PredLoad : PredLoads) { BasicBlock *UnavailablePred = PredLoad.first; Value *LoadPtr = PredLoad.second; Instruction *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, LI->getAlignment(), UnavailablePred->getTerminator()); // Transfer the old load's AA tags to the new load. AAMDNodes Tags; LI->getAAMetadata(Tags); if (Tags) NewLoad->setAAMetadata(Tags); // Transfer DebugLoc. NewLoad->setDebugLoc(LI->getDebugLoc()); // Add the newly created load. ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred, NewLoad)); MD->invalidateCachedPointerInfo(LoadPtr); DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n'); } // Perform PHI construction. Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this); LI->replaceAllUsesWith(V); if (isa<PHINode>(V)) V->takeName(LI); if (V->getType()->getScalarType()->isPointerTy()) MD->invalidateCachedPointerInfo(V); markInstructionForDeletion(LI); ++NumPRELoad; return true; } /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are /// non-local by performing PHI construction. bool GVN::processNonLocalLoad(LoadInst *LI) { // Step 1: Find the non-local dependencies of the load. LoadDepVect Deps; MD->getNonLocalPointerDependency(LI, Deps); // If we had to process more than one hundred blocks to find the // dependencies, this load isn't worth worrying about. Optimizing // it will be too expensive. unsigned NumDeps = Deps.size(); if (NumDeps > 100) return false; // If we had a phi translation failure, we'll have a single entry which is a // clobber in the current block. Reject this early. if (NumDeps == 1 && !Deps[0].getResult().isDef() && !Deps[0].getResult().isClobber()) { DEBUG( dbgs() << "GVN: non-local load "; LI->printAsOperand(dbgs()); dbgs() << " has unknown dependencies\n"; ); return false; } // If this load follows a GEP, see if we can PRE the indices before analyzing. if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(LI->getOperand(0))) { for (GetElementPtrInst::op_iterator OI = GEP->idx_begin(), OE = GEP->idx_end(); OI != OE; ++OI) if (Instruction *I = dyn_cast<Instruction>(OI->get())) performScalarPRE(I); } // Step 2: Analyze the availability of the load AvailValInBlkVect ValuesPerBlock; UnavailBlkVect UnavailableBlocks; AnalyzeLoadAvailability(LI, Deps, ValuesPerBlock, UnavailableBlocks); // If we have no predecessors that produce a known value for this load, exit // early. if (ValuesPerBlock.empty()) return false; // Step 3: Eliminate fully redundancy. // // If all of the instructions we depend on produce a known value for this // load, then it is fully redundant and we can use PHI insertion to compute // its value. Insert PHIs and remove the fully redundant value now. if (UnavailableBlocks.empty()) { DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n'); // Perform PHI construction. Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this); LI->replaceAllUsesWith(V); if (isa<PHINode>(V)) V->takeName(LI); if (V->getType()->getScalarType()->isPointerTy()) MD->invalidateCachedPointerInfo(V); markInstructionForDeletion(LI); ++NumGVNLoad; return true; } // Step 4: Eliminate partial redundancy. if (!EnablePRE || !EnableLoadPRE) return false; return PerformLoadPRE(LI, ValuesPerBlock, UnavailableBlocks); } static void patchReplacementInstruction(Instruction *I, Value *Repl) { // Patch the replacement so that it is not more restrictive than the value // being replaced. BinaryOperator *Op = dyn_cast<BinaryOperator>(I); BinaryOperator *ReplOp = dyn_cast<BinaryOperator>(Repl); if (Op && ReplOp && isa<OverflowingBinaryOperator>(Op) && isa<OverflowingBinaryOperator>(ReplOp)) { if (ReplOp->hasNoSignedWrap() && !Op->hasNoSignedWrap()) ReplOp->setHasNoSignedWrap(false); if (ReplOp->hasNoUnsignedWrap() && !Op->hasNoUnsignedWrap()) ReplOp->setHasNoUnsignedWrap(false); } if (Instruction *ReplInst = dyn_cast<Instruction>(Repl)) { // FIXME: If both the original and replacement value are part of the // same control-flow region (meaning that the execution of one // guarentees the executation of the other), then we can combine the // noalias scopes here and do better than the general conservative // answer used in combineMetadata(). // In general, GVN unifies expressions over different control-flow // regions, and so we need a conservative combination of the noalias // scopes. unsigned KnownIDs[] = { LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope, LLVMContext::MD_noalias, LLVMContext::MD_range, LLVMContext::MD_fpmath, LLVMContext::MD_invariant_load, }; combineMetadata(ReplInst, I, KnownIDs); } } static void patchAndReplaceAllUsesWith(Instruction *I, Value *Repl) { patchReplacementInstruction(I, Repl); I->replaceAllUsesWith(Repl); } /// processLoad - Attempt to eliminate a load, first by eliminating it /// locally, and then attempting non-local elimination if that fails. bool GVN::processLoad(LoadInst *L) { if (!MD) return false; if (!L->isSimple()) return false; if (L->use_empty()) { markInstructionForDeletion(L); return true; } // ... to a pointer that has been loaded from before... MemDepResult Dep = MD->getDependency(L); // If we have a clobber and target data is around, see if this is a clobber // that we can fix up through code synthesis. if (Dep.isClobber() && DL) { // Check to see if we have something like this: // store i32 123, i32* %P // %A = bitcast i32* %P to i8* // %B = gep i8* %A, i32 1 // %C = load i8* %B // // We could do that by recognizing if the clobber instructions are obviously // a common base + constant offset, and if the previous store (or memset) // completely covers this load. This sort of thing can happen in bitfield // access code. Value *AvailVal = nullptr; if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst())) { int Offset = AnalyzeLoadFromClobberingStore(L->getType(), L->getPointerOperand(), DepSI, *DL); if (Offset != -1) AvailVal = GetStoreValueForLoad(DepSI->getValueOperand(), Offset, L->getType(), L, *DL); } // Check to see if we have something like this: // load i32* P // load i8* (P+1) // if we have this, replace the later with an extraction from the former. if (LoadInst *DepLI = dyn_cast<LoadInst>(Dep.getInst())) { // If this is a clobber and L is the first instruction in its block, then // we have the first instruction in the entry block. if (DepLI == L) return false; int Offset = AnalyzeLoadFromClobberingLoad(L->getType(), L->getPointerOperand(), DepLI, *DL); if (Offset != -1) AvailVal = GetLoadValueForLoad(DepLI, Offset, L->getType(), L, *this); } // If the clobbering value is a memset/memcpy/memmove, see if we can forward // a value on from it. if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) { int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(), L->getPointerOperand(), DepMI, *DL); if (Offset != -1) AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L, *DL); } if (AvailVal) { DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n' << *AvailVal << '\n' << *L << "\n\n\n"); // Replace the load! L->replaceAllUsesWith(AvailVal); if (AvailVal->getType()->getScalarType()->isPointerTy()) MD->invalidateCachedPointerInfo(AvailVal); markInstructionForDeletion(L); ++NumGVNLoad; return true; } } // If the value isn't available, don't do anything! if (Dep.isClobber()) { DEBUG( // fast print dep, using operator<< on instruction is too slow. dbgs() << "GVN: load "; L->printAsOperand(dbgs()); Instruction *I = Dep.getInst(); dbgs() << " is clobbered by " << *I << '\n'; ); return false; } // If it is defined in another block, try harder. if (Dep.isNonLocal()) return processNonLocalLoad(L); if (!Dep.isDef()) { DEBUG( // fast print dep, using operator<< on instruction is too slow. dbgs() << "GVN: load "; L->printAsOperand(dbgs()); dbgs() << " has unknown dependence\n"; ); return false; } Instruction *DepInst = Dep.getInst(); if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { Value *StoredVal = DepSI->getValueOperand(); // The store and load are to a must-aliased pointer, but they may not // actually have the same type. See if we know how to reuse the stored // value (depending on its type). if (StoredVal->getType() != L->getType()) { if (DL) { StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(), L, *DL); if (!StoredVal) return false; DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal << '\n' << *L << "\n\n\n"); } else return false; } // Remove it! L->replaceAllUsesWith(StoredVal); if (StoredVal->getType()->getScalarType()->isPointerTy()) MD->invalidateCachedPointerInfo(StoredVal); markInstructionForDeletion(L); ++NumGVNLoad; return true; } if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { Value *AvailableVal = DepLI; // The loads are of a must-aliased pointer, but they may not actually have // the same type. See if we know how to reuse the previously loaded value // (depending on its type). if (DepLI->getType() != L->getType()) { if (DL) { AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L, *DL); if (!AvailableVal) return false; DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal << "\n" << *L << "\n\n\n"); } else return false; } // Remove it! patchAndReplaceAllUsesWith(L, AvailableVal); if (DepLI->getType()->getScalarType()->isPointerTy()) MD->invalidateCachedPointerInfo(DepLI); markInstructionForDeletion(L); ++NumGVNLoad; return true; } // If this load really doesn't depend on anything, then we must be loading an // undef value. This can happen when loading for a fresh allocation with no // intervening stores, for example. if (isa<AllocaInst>(DepInst) || isMallocLikeFn(DepInst, TLI)) { L->replaceAllUsesWith(UndefValue::get(L->getType())); markInstructionForDeletion(L); ++NumGVNLoad; return true; } // If this load occurs either right after a lifetime begin, // then the loaded value is undefined. if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(DepInst)) { if (II->getIntrinsicID() == Intrinsic::lifetime_start) { L->replaceAllUsesWith(UndefValue::get(L->getType())); markInstructionForDeletion(L); ++NumGVNLoad; return true; } } // If this load follows a calloc (which zero initializes memory), // then the loaded value is zero if (isCallocLikeFn(DepInst, TLI)) { L->replaceAllUsesWith(Constant::getNullValue(L->getType())); markInstructionForDeletion(L); ++NumGVNLoad; return true; } return false; } // findLeader - In order to find a leader for a given value number at a // specific basic block, we first obtain the list of all Values for that number, // and then scan the list to find one whose block dominates the block in // question. This is fast because dominator tree queries consist of only // a few comparisons of DFS numbers. Value *GVN::findLeader(const BasicBlock *BB, uint32_t num) { LeaderTableEntry Vals = LeaderTable[num]; if (!Vals.Val) return nullptr; Value *Val = nullptr; if (DT->dominates(Vals.BB, BB)) { Val = Vals.Val; if (isa<Constant>(Val)) return Val; } LeaderTableEntry* Next = Vals.Next; while (Next) { if (DT->dominates(Next->BB, BB)) { if (isa<Constant>(Next->Val)) return Next->Val; if (!Val) Val = Next->Val; } Next = Next->Next; } return Val; } /// replaceAllDominatedUsesWith - Replace all uses of 'From' with 'To' if the /// use is dominated by the given basic block. Returns the number of uses that /// were replaced. unsigned GVN::replaceAllDominatedUsesWith(Value *From, Value *To, const BasicBlockEdge &Root) { unsigned Count = 0; for (Value::use_iterator UI = From->use_begin(), UE = From->use_end(); UI != UE; ) { Use &U = *UI++; if (DT->dominates(Root, U)) { U.set(To); ++Count; } } return Count; } /// isOnlyReachableViaThisEdge - There is an edge from 'Src' to 'Dst'. Return /// true if every path from the entry block to 'Dst' passes via this edge. In /// particular 'Dst' must not be reachable via another edge from 'Src'. static bool isOnlyReachableViaThisEdge(const BasicBlockEdge &E, DominatorTree *DT) { // While in theory it is interesting to consider the case in which Dst has // more than one predecessor, because Dst might be part of a loop which is // only reachable from Src, in practice it is pointless since at the time // GVN runs all such loops have preheaders, which means that Dst will have // been changed to have only one predecessor, namely Src. const BasicBlock *Pred = E.getEnd()->getSinglePredecessor(); const BasicBlock *Src = E.getStart(); assert((!Pred || Pred == Src) && "No edge between these basic blocks!"); (void)Src; return Pred != nullptr; } /// propagateEquality - The given values are known to be equal in every block /// dominated by 'Root'. Exploit this, for example by replacing 'LHS' with /// 'RHS' everywhere in the scope. Returns whether a change was made. bool GVN::propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root) { SmallVector<std::pair<Value*, Value*>, 4> Worklist; Worklist.push_back(std::make_pair(LHS, RHS)); bool Changed = false; // For speed, compute a conservative fast approximation to // DT->dominates(Root, Root.getEnd()); bool RootDominatesEnd = isOnlyReachableViaThisEdge(Root, DT); while (!Worklist.empty()) { std::pair<Value*, Value*> Item = Worklist.pop_back_val(); LHS = Item.first; RHS = Item.second; if (LHS == RHS) continue; assert(LHS->getType() == RHS->getType() && "Equality but unequal types!"); // Don't try to propagate equalities between constants. if (isa<Constant>(LHS) && isa<Constant>(RHS)) continue; // Prefer a constant on the right-hand side, or an Argument if no constants. if (isa<Constant>(LHS) || (isa<Argument>(LHS) && !isa<Constant>(RHS))) std::swap(LHS, RHS); assert((isa<Argument>(LHS) || isa<Instruction>(LHS)) && "Unexpected value!"); // If there is no obvious reason to prefer the left-hand side over the // right-hand side, ensure the longest lived term is on the right-hand side, // so the shortest lived term will be replaced by the longest lived. // This tends to expose more simplifications. uint32_t LVN = VN.lookup_or_add(LHS); if ((isa<Argument>(LHS) && isa<Argument>(RHS)) || (isa<Instruction>(LHS) && isa<Instruction>(RHS))) { // Move the 'oldest' value to the right-hand side, using the value number // as a proxy for age. uint32_t RVN = VN.lookup_or_add(RHS); if (LVN < RVN) { std::swap(LHS, RHS); LVN = RVN; } } // If value numbering later sees that an instruction in the scope is equal // to 'LHS' then ensure it will be turned into 'RHS'. In order to preserve // the invariant that instructions only occur in the leader table for their // own value number (this is used by removeFromLeaderTable), do not do this // if RHS is an instruction (if an instruction in the scope is morphed into // LHS then it will be turned into RHS by the next GVN iteration anyway, so // using the leader table is about compiling faster, not optimizing better). // The leader table only tracks basic blocks, not edges. Only add to if we // have the simple case where the edge dominates the end. if (RootDominatesEnd && !isa<Instruction>(RHS)) addToLeaderTable(LVN, RHS, Root.getEnd()); // Replace all occurrences of 'LHS' with 'RHS' everywhere in the scope. As // LHS always has at least one use that is not dominated by Root, this will // never do anything if LHS has only one use. if (!LHS->hasOneUse()) { unsigned NumReplacements = replaceAllDominatedUsesWith(LHS, RHS, Root); Changed |= NumReplacements > 0; NumGVNEqProp += NumReplacements; } // Now try to deduce additional equalities from this one. For example, if // the known equality was "(A != B)" == "false" then it follows that A and B // are equal in the scope. Only boolean equalities with an explicit true or // false RHS are currently supported. if (!RHS->getType()->isIntegerTy(1)) // Not a boolean equality - bail out. continue; ConstantInt *CI = dyn_cast<ConstantInt>(RHS); if (!CI) // RHS neither 'true' nor 'false' - bail out. continue; // Whether RHS equals 'true'. Otherwise it equals 'false'. bool isKnownTrue = CI->isAllOnesValue(); bool isKnownFalse = !isKnownTrue; // If "A && B" is known true then both A and B are known true. If "A || B" // is known false then both A and B are known false. Value *A, *B; if ((isKnownTrue && match(LHS, m_And(m_Value(A), m_Value(B)))) || (isKnownFalse && match(LHS, m_Or(m_Value(A), m_Value(B))))) { Worklist.push_back(std::make_pair(A, RHS)); Worklist.push_back(std::make_pair(B, RHS)); continue; } // If we are propagating an equality like "(A == B)" == "true" then also // propagate the equality A == B. When propagating a comparison such as // "(A >= B)" == "true", replace all instances of "A < B" with "false". if (CmpInst *Cmp = dyn_cast<CmpInst>(LHS)) { Value *Op0 = Cmp->getOperand(0), *Op1 = Cmp->getOperand(1); // If "A == B" is known true, or "A != B" is known false, then replace // A with B everywhere in the scope. if ((isKnownTrue && Cmp->getPredicate() == CmpInst::ICMP_EQ) || (isKnownFalse && Cmp->getPredicate() == CmpInst::ICMP_NE)) Worklist.push_back(std::make_pair(Op0, Op1)); // Handle the floating point versions of equality comparisons too. if ((isKnownTrue && Cmp->getPredicate() == CmpInst::FCMP_OEQ) || (isKnownFalse && Cmp->getPredicate() == CmpInst::FCMP_UNE)) { // Floating point -0.0 and 0.0 compare equal, so we can't // propagate a constant based on that comparison. // FIXME: We should do this optimization if 'no signed zeros' is // applicable via an instruction-level fast-math-flag or some other // indicator that relaxed FP semantics are being used. if (!isa<ConstantFP>(Op1) || !cast<ConstantFP>(Op1)->isZero()) Worklist.push_back(std::make_pair(Op0, Op1)); } // If "A >= B" is known true, replace "A < B" with false everywhere. CmpInst::Predicate NotPred = Cmp->getInversePredicate(); Constant *NotVal = ConstantInt::get(Cmp->getType(), isKnownFalse); // Since we don't have the instruction "A < B" immediately to hand, work // out the value number that it would have and use that to find an // appropriate instruction (if any). uint32_t NextNum = VN.getNextUnusedValueNumber(); uint32_t Num = VN.lookup_or_add_cmp(Cmp->getOpcode(), NotPred, Op0, Op1); // If the number we were assigned was brand new then there is no point in // looking for an instruction realizing it: there cannot be one! if (Num < NextNum) { Value *NotCmp = findLeader(Root.getEnd(), Num); if (NotCmp && isa<Instruction>(NotCmp)) { unsigned NumReplacements = replaceAllDominatedUsesWith(NotCmp, NotVal, Root); Changed |= NumReplacements > 0; NumGVNEqProp += NumReplacements; } } // Ensure that any instruction in scope that gets the "A < B" value number // is replaced with false. // The leader table only tracks basic blocks, not edges. Only add to if we // have the simple case where the edge dominates the end. if (RootDominatesEnd) addToLeaderTable(Num, NotVal, Root.getEnd()); continue; } } return Changed; } /// processInstruction - When calculating availability, handle an instruction /// by inserting it into the appropriate sets bool GVN::processInstruction(Instruction *I) { // Ignore dbg info intrinsics. if (isa<DbgInfoIntrinsic>(I)) return false; // If the instruction can be easily simplified then do so now in preference // to value numbering it. Value numbering often exposes redundancies, for // example if it determines that %y is equal to %x then the instruction // "%z = and i32 %x, %y" becomes "%z = and i32 %x, %x" which we now simplify. if (Value *V = SimplifyInstruction(I, DL, TLI, DT, AC)) { I->replaceAllUsesWith(V); if (MD && V->getType()->getScalarType()->isPointerTy()) MD->invalidateCachedPointerInfo(V); markInstructionForDeletion(I); ++NumGVNSimpl; return true; } if (LoadInst *LI = dyn_cast<LoadInst>(I)) { if (processLoad(LI)) return true; unsigned Num = VN.lookup_or_add(LI); addToLeaderTable(Num, LI, LI->getParent()); return false; } // For conditional branches, we can perform simple conditional propagation on // the condition value itself. if (BranchInst *BI = dyn_cast<BranchInst>(I)) { if (!BI->isConditional()) return false; if (isa<Constant>(BI->getCondition())) return processFoldableCondBr(BI); Value *BranchCond = BI->getCondition(); BasicBlock *TrueSucc = BI->getSuccessor(0); BasicBlock *FalseSucc = BI->getSuccessor(1); // Avoid multiple edges early. if (TrueSucc == FalseSucc) return false; BasicBlock *Parent = BI->getParent(); bool Changed = false; Value *TrueVal = ConstantInt::getTrue(TrueSucc->getContext()); BasicBlockEdge TrueE(Parent, TrueSucc); Changed |= propagateEquality(BranchCond, TrueVal, TrueE); Value *FalseVal = ConstantInt::getFalse(FalseSucc->getContext()); BasicBlockEdge FalseE(Parent, FalseSucc); Changed |= propagateEquality(BranchCond, FalseVal, FalseE); return Changed; } // For switches, propagate the case values into the case destinations. if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) { Value *SwitchCond = SI->getCondition(); BasicBlock *Parent = SI->getParent(); bool Changed = false; // Remember how many outgoing edges there are to every successor. SmallDenseMap<BasicBlock *, unsigned, 16> SwitchEdges; for (unsigned i = 0, n = SI->getNumSuccessors(); i != n; ++i) ++SwitchEdges[SI->getSuccessor(i)]; for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i) { BasicBlock *Dst = i.getCaseSuccessor(); // If there is only a single edge, propagate the case value into it. if (SwitchEdges.lookup(Dst) == 1) { BasicBlockEdge E(Parent, Dst); Changed |= propagateEquality(SwitchCond, i.getCaseValue(), E); } } return Changed; } // Instructions with void type don't return a value, so there's // no point in trying to find redundancies in them. if (I->getType()->isVoidTy()) return false; uint32_t NextNum = VN.getNextUnusedValueNumber(); unsigned Num = VN.lookup_or_add(I); // Allocations are always uniquely numbered, so we can save time and memory // by fast failing them. if (isa<AllocaInst>(I) || isa<TerminatorInst>(I) || isa<PHINode>(I)) { addToLeaderTable(Num, I, I->getParent()); return false; } // If the number we were assigned was a brand new VN, then we don't // need to do a lookup to see if the number already exists // somewhere in the domtree: it can't! if (Num >= NextNum) { addToLeaderTable(Num, I, I->getParent()); return false; } // Perform fast-path value-number based elimination of values inherited from // dominators. Value *repl = findLeader(I->getParent(), Num); if (!repl) { // Failure, just remember this instance for future use. addToLeaderTable(Num, I, I->getParent()); return false; } // Remove it! patchAndReplaceAllUsesWith(I, repl); if (MD && repl->getType()->getScalarType()->isPointerTy()) MD->invalidateCachedPointerInfo(repl); markInstructionForDeletion(I); return true; } /// runOnFunction - This is the main transformation entry point for a function. bool GVN::runOnFunction(Function& F) { if (skipOptnoneFunction(F)) return false; if (!NoLoads) MD = &getAnalysis<MemoryDependenceAnalysis>(); DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>(); DL = DLP ? &DLP->getDataLayout() : nullptr; AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(); VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); VN.setMemDep(MD); VN.setDomTree(DT); bool Changed = false; bool ShouldContinue = true; // Merge unconditional branches, allowing PRE to catch more // optimization opportunities. for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { BasicBlock *BB = FI++; bool removedBlock = MergeBlockIntoPredecessor( BB, DT, /* LoopInfo */ nullptr, VN.getAliasAnalysis(), MD); if (removedBlock) ++NumGVNBlocks; Changed |= removedBlock; } unsigned Iteration = 0; while (ShouldContinue) { DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n"); ShouldContinue = iterateOnFunction(F); Changed |= ShouldContinue; ++Iteration; } if (EnablePRE) { // Fabricate val-num for dead-code in order to suppress assertion in // performPRE(). assignValNumForDeadCode(); bool PREChanged = true; while (PREChanged) { PREChanged = performPRE(F); Changed |= PREChanged; } } // FIXME: Should perform GVN again after PRE does something. PRE can move // computations into blocks where they become fully redundant. Note that // we can't do this until PRE's critical edge splitting updates memdep. // Actually, when this happens, we should just fully integrate PRE into GVN. cleanupGlobalSets(); // Do not cleanup DeadBlocks in cleanupGlobalSets() as it's called for each // iteration. DeadBlocks.clear(); return Changed; } bool GVN::processBlock(BasicBlock *BB) { // FIXME: Kill off InstrsToErase by doing erasing eagerly in a helper function // (and incrementing BI before processing an instruction). assert(InstrsToErase.empty() && "We expect InstrsToErase to be empty across iterations"); if (DeadBlocks.count(BB)) return false; bool ChangedFunction = false; for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) { ChangedFunction |= processInstruction(BI); if (InstrsToErase.empty()) { ++BI; continue; } // If we need some instructions deleted, do it now. NumGVNInstr += InstrsToErase.size(); // Avoid iterator invalidation. bool AtStart = BI == BB->begin(); if (!AtStart) --BI; for (SmallVectorImpl<Instruction *>::iterator I = InstrsToErase.begin(), E = InstrsToErase.end(); I != E; ++I) { DEBUG(dbgs() << "GVN removed: " << **I << '\n'); if (MD) MD->removeInstruction(*I); DEBUG(verifyRemoved(*I)); (*I)->eraseFromParent(); } InstrsToErase.clear(); if (AtStart) BI = BB->begin(); else ++BI; } return ChangedFunction; } // Instantiate an expression in a predecessor that lacked it. bool GVN::performScalarPREInsertion(Instruction *Instr, BasicBlock *Pred, unsigned int ValNo) { // Because we are going top-down through the block, all value numbers // will be available in the predecessor by the time we need them. Any // that weren't originally present will have been instantiated earlier // in this loop. bool success = true; for (unsigned i = 0, e = Instr->getNumOperands(); i != e; ++i) { Value *Op = Instr->getOperand(i); if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) continue; if (Value *V = findLeader(Pred, VN.lookup(Op))) { Instr->setOperand(i, V); } else { success = false; break; } } // Fail out if we encounter an operand that is not available in // the PRE predecessor. This is typically because of loads which // are not value numbered precisely. if (!success) return false; Instr->insertBefore(Pred->getTerminator()); Instr->setName(Instr->getName() + ".pre"); Instr->setDebugLoc(Instr->getDebugLoc()); VN.add(Instr, ValNo); // Update the availability map to include the new instruction. addToLeaderTable(ValNo, Instr, Pred); return true; } bool GVN::performScalarPRE(Instruction *CurInst) { SmallVector<std::pair<Value*, BasicBlock*>, 8> predMap; if (isa<AllocaInst>(CurInst) || isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) || CurInst->getType()->isVoidTy() || CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || isa<DbgInfoIntrinsic>(CurInst)) return false; // Don't do PRE on compares. The PHI would prevent CodeGenPrepare from // sinking the compare again, and it would force the code generator to // move the i1 from processor flags or predicate registers into a general // purpose register. if (isa<CmpInst>(CurInst)) return false; // We don't currently value number ANY inline asm calls. if (CallInst *CallI = dyn_cast<CallInst>(CurInst)) if (CallI->isInlineAsm()) return false; uint32_t ValNo = VN.lookup(CurInst); // Look for the predecessors for PRE opportunities. We're // only trying to solve the basic diamond case, where // a value is computed in the successor and one predecessor, // but not the other. We also explicitly disallow cases // where the successor is its own predecessor, because they're // more complicated to get right. unsigned NumWith = 0; unsigned NumWithout = 0; BasicBlock *PREPred = nullptr; BasicBlock *CurrentBlock = CurInst->getParent(); predMap.clear(); for (pred_iterator PI = pred_begin(CurrentBlock), PE = pred_end(CurrentBlock); PI != PE; ++PI) { BasicBlock *P = *PI; // We're not interested in PRE where the block is its // own predecessor, or in blocks with predecessors // that are not reachable. if (P == CurrentBlock) { NumWithout = 2; break; } else if (!DT->isReachableFromEntry(P)) { NumWithout = 2; break; } Value *predV = findLeader(P, ValNo); if (!predV) { predMap.push_back(std::make_pair(static_cast<Value *>(nullptr), P)); PREPred = P; ++NumWithout; } else if (predV == CurInst) { /* CurInst dominates this predecessor. */ NumWithout = 2; break; } else { predMap.push_back(std::make_pair(predV, P)); ++NumWith; } } // Don't do PRE when it might increase code size, i.e. when // we would need to insert instructions in more than one pred. if (NumWithout > 1 || NumWith == 0) return false; // We may have a case where all predecessors have the instruction, // and we just need to insert a phi node. Otherwise, perform // insertion. Instruction *PREInstr = nullptr; if (NumWithout != 0) { // Don't do PRE across indirect branch. if (isa<IndirectBrInst>(PREPred->getTerminator())) return false; // We can't do PRE safely on a critical edge, so instead we schedule // the edge to be split and perform the PRE the next time we iterate // on the function. unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock); if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) { toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum)); return false; } // We need to insert somewhere, so let's give it a shot PREInstr = CurInst->clone(); if (!performScalarPREInsertion(PREInstr, PREPred, ValNo)) { // If we failed insertion, make sure we remove the instruction. DEBUG(verifyRemoved(PREInstr)); delete PREInstr; return false; } } // Either we should have filled in the PRE instruction, or we should // not have needed insertions. assert (PREInstr != nullptr || NumWithout == 0); ++NumGVNPRE; // Create a PHI to make the value available in this block. PHINode *Phi = PHINode::Create(CurInst->getType(), predMap.size(), CurInst->getName() + ".pre-phi", CurrentBlock->begin()); for (unsigned i = 0, e = predMap.size(); i != e; ++i) { if (Value *V = predMap[i].first) Phi->addIncoming(V, predMap[i].second); else Phi->addIncoming(PREInstr, PREPred); } VN.add(Phi, ValNo); addToLeaderTable(ValNo, Phi, CurrentBlock); Phi->setDebugLoc(CurInst->getDebugLoc()); CurInst->replaceAllUsesWith(Phi); if (Phi->getType()->getScalarType()->isPointerTy()) { // Because we have added a PHI-use of the pointer value, it has now // "escaped" from alias analysis' perspective. We need to inform // AA of this. for (unsigned ii = 0, ee = Phi->getNumIncomingValues(); ii != ee; ++ii) { unsigned jj = PHINode::getOperandNumForIncomingValue(ii); VN.getAliasAnalysis()->addEscapingUse(Phi->getOperandUse(jj)); } if (MD) MD->invalidateCachedPointerInfo(Phi); } VN.erase(CurInst); removeFromLeaderTable(ValNo, CurInst, CurrentBlock); DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n'); if (MD) MD->removeInstruction(CurInst); DEBUG(verifyRemoved(CurInst)); CurInst->eraseFromParent(); ++NumGVNInstr; return true; } /// performPRE - Perform a purely local form of PRE that looks for diamond /// control flow patterns and attempts to perform simple PRE at the join point. bool GVN::performPRE(Function &F) { bool Changed = false; for (BasicBlock *CurrentBlock : depth_first(&F.getEntryBlock())) { // Nothing to PRE in the entry block. if (CurrentBlock == &F.getEntryBlock()) continue; // Don't perform PRE on a landing pad. if (CurrentBlock->isLandingPad()) continue; for (BasicBlock::iterator BI = CurrentBlock->begin(), BE = CurrentBlock->end(); BI != BE;) { Instruction *CurInst = BI++; Changed = performScalarPRE(CurInst); } } if (splitCriticalEdges()) Changed = true; return Changed; } /// Split the critical edge connecting the given two blocks, and return /// the block inserted to the critical edge. BasicBlock *GVN::splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ) { BasicBlock *BB = SplitCriticalEdge( Pred, Succ, CriticalEdgeSplittingOptions(getAliasAnalysis(), DT)); if (MD) MD->invalidateCachedPredecessors(); return BB; } /// splitCriticalEdges - Split critical edges found during the previous /// iteration that may enable further optimization. bool GVN::splitCriticalEdges() { if (toSplit.empty()) return false; do { std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val(); SplitCriticalEdge(Edge.first, Edge.second, CriticalEdgeSplittingOptions(getAliasAnalysis(), DT)); } while (!toSplit.empty()); if (MD) MD->invalidateCachedPredecessors(); return true; } /// iterateOnFunction - Executes one iteration of GVN bool GVN::iterateOnFunction(Function &F) { cleanupGlobalSets(); // Top-down walk of the dominator tree bool Changed = false; // Save the blocks this function have before transformation begins. GVN may // split critical edge, and hence may invalidate the RPO/DT iterator. // std::vector<BasicBlock *> BBVect; BBVect.reserve(256); // Needed for value numbering with phi construction to work. ReversePostOrderTraversal<Function *> RPOT(&F); for (ReversePostOrderTraversal<Function *>::rpo_iterator RI = RPOT.begin(), RE = RPOT.end(); RI != RE; ++RI) BBVect.push_back(*RI); for (std::vector<BasicBlock *>::iterator I = BBVect.begin(), E = BBVect.end(); I != E; I++) Changed |= processBlock(*I); return Changed; } void GVN::cleanupGlobalSets() { VN.clear(); LeaderTable.clear(); TableAllocator.Reset(); } /// verifyRemoved - Verify that the specified instruction does not occur in our /// internal data structures. void GVN::verifyRemoved(const Instruction *Inst) const { VN.verifyRemoved(Inst); // Walk through the value number scope to make sure the instruction isn't // ferreted away in it. for (DenseMap<uint32_t, LeaderTableEntry>::const_iterator I = LeaderTable.begin(), E = LeaderTable.end(); I != E; ++I) { const LeaderTableEntry *Node = &I->second; assert(Node->Val != Inst && "Inst still in value numbering scope!"); while (Node->Next) { Node = Node->Next; assert(Node->Val != Inst && "Inst still in value numbering scope!"); } } } // BB is declared dead, which implied other blocks become dead as well. This // function is to add all these blocks to "DeadBlocks". For the dead blocks' // live successors, update their phi nodes by replacing the operands // corresponding to dead blocks with UndefVal. // void GVN::addDeadBlock(BasicBlock *BB) { SmallVector<BasicBlock *, 4> NewDead; SmallSetVector<BasicBlock *, 4> DF; NewDead.push_back(BB); while (!NewDead.empty()) { BasicBlock *D = NewDead.pop_back_val(); if (DeadBlocks.count(D)) continue; // All blocks dominated by D are dead. SmallVector<BasicBlock *, 8> Dom; DT->getDescendants(D, Dom); DeadBlocks.insert(Dom.begin(), Dom.end()); // Figure out the dominance-frontier(D). for (SmallVectorImpl<BasicBlock *>::iterator I = Dom.begin(), E = Dom.end(); I != E; I++) { BasicBlock *B = *I; for (succ_iterator SI = succ_begin(B), SE = succ_end(B); SI != SE; SI++) { BasicBlock *S = *SI; if (DeadBlocks.count(S)) continue; bool AllPredDead = true; for (pred_iterator PI = pred_begin(S), PE = pred_end(S); PI != PE; PI++) if (!DeadBlocks.count(*PI)) { AllPredDead = false; break; } if (!AllPredDead) { // S could be proved dead later on. That is why we don't update phi // operands at this moment. DF.insert(S); } else { // While S is not dominated by D, it is dead by now. This could take // place if S already have a dead predecessor before D is declared // dead. NewDead.push_back(S); } } } } // For the dead blocks' live successors, update their phi nodes by replacing // the operands corresponding to dead blocks with UndefVal. for(SmallSetVector<BasicBlock *, 4>::iterator I = DF.begin(), E = DF.end(); I != E; I++) { BasicBlock *B = *I; if (DeadBlocks.count(B)) continue; SmallVector<BasicBlock *, 4> Preds(pred_begin(B), pred_end(B)); for (SmallVectorImpl<BasicBlock *>::iterator PI = Preds.begin(), PE = Preds.end(); PI != PE; PI++) { BasicBlock *P = *PI; if (!DeadBlocks.count(P)) continue; if (isCriticalEdge(P->getTerminator(), GetSuccessorNumber(P, B))) { if (BasicBlock *S = splitCriticalEdges(P, B)) DeadBlocks.insert(P = S); } for (BasicBlock::iterator II = B->begin(); isa<PHINode>(II); ++II) { PHINode &Phi = cast<PHINode>(*II); Phi.setIncomingValue(Phi.getBasicBlockIndex(P), UndefValue::get(Phi.getType())); } } } } // If the given branch is recognized as a foldable branch (i.e. conditional // branch with constant condition), it will perform following analyses and // transformation. // 1) If the dead out-coming edge is a critical-edge, split it. Let // R be the target of the dead out-coming edge. // 1) Identify the set of dead blocks implied by the branch's dead outcoming // edge. The result of this step will be {X| X is dominated by R} // 2) Identify those blocks which haves at least one dead prodecessor. The // result of this step will be dominance-frontier(R). // 3) Update the PHIs in DF(R) by replacing the operands corresponding to // dead blocks with "UndefVal" in an hope these PHIs will optimized away. // // Return true iff *NEW* dead code are found. bool GVN::processFoldableCondBr(BranchInst *BI) { if (!BI || BI->isUnconditional()) return false; ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition()); if (!Cond) return false; BasicBlock *DeadRoot = Cond->getZExtValue() ? BI->getSuccessor(1) : BI->getSuccessor(0); if (DeadBlocks.count(DeadRoot)) return false; if (!DeadRoot->getSinglePredecessor()) DeadRoot = splitCriticalEdges(BI->getParent(), DeadRoot); addDeadBlock(DeadRoot); return true; } // performPRE() will trigger assert if it comes across an instruction without // associated val-num. As it normally has far more live instructions than dead // instructions, it makes more sense just to "fabricate" a val-number for the // dead code than checking if instruction involved is dead or not. void GVN::assignValNumForDeadCode() { for (SetVector<BasicBlock *>::iterator I = DeadBlocks.begin(), E = DeadBlocks.end(); I != E; I++) { BasicBlock *BB = *I; for (BasicBlock::iterator II = BB->begin(), EE = BB->end(); II != EE; II++) { Instruction *Inst = &*II; unsigned ValNum = VN.lookup_or_add(Inst); addToLeaderTable(ValNum, Inst, BB); } } }