//
// The LLVM Compiler Infrastructure
//
-// This file was developed by Owen Anderson and is distributed under
-// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "dse"
#include "llvm/Transforms/Scalar.h"
-#include "llvm/Constants.h"
-#include "llvm/Function.h"
-#include "llvm/Instructions.h"
-#include "llvm/Pass.h"
+#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
-#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/CaptureTracking.h"
+#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
-#include "llvm/Target/TargetData.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/Local.h"
-#include "llvm/Support/Compiler.h"
using namespace llvm;
+#define DEBUG_TYPE "dse"
+
+STATISTIC(NumRedundantStores, "Number of redundant stores deleted");
STATISTIC(NumFastStores, "Number of stores deleted");
STATISTIC(NumFastOther , "Number of other instrs removed");
namespace {
- struct VISIBILITY_HIDDEN DSE : public FunctionPass {
+ struct DSE : public FunctionPass {
+ AliasAnalysis *AA;
+ MemoryDependenceAnalysis *MD;
+ DominatorTree *DT;
+ const TargetLibraryInfo *TLI;
+
static char ID; // Pass identification, replacement for typeid
- DSE() : FunctionPass((intptr_t)&ID) {}
+ DSE() : FunctionPass(ID), AA(nullptr), MD(nullptr), DT(nullptr) {
+ initializeDSEPass(*PassRegistry::getPassRegistry());
+ }
+
+ bool runOnFunction(Function &F) override {
+ if (skipOptnoneFunction(F))
+ return false;
+
+ AA = &getAnalysis<AliasAnalysis>();
+ MD = &getAnalysis<MemoryDependenceAnalysis>();
+ DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+ TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
- virtual bool runOnFunction(Function &F) {
bool Changed = false;
for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
- Changed |= runOnBasicBlock(*I);
+ // Only check non-dead blocks. Dead blocks may have strange pointer
+ // cycles that will confuse alias analysis.
+ if (DT->isReachableFromEntry(I))
+ Changed |= runOnBasicBlock(*I);
+
+ AA = nullptr; MD = nullptr; DT = nullptr;
return Changed;
}
bool runOnBasicBlock(BasicBlock &BB);
- bool handleFreeWithNonTrivialDependency(FreeInst* F,
- Instruction* dependency,
- SetVector<Instruction*>& possiblyDead);
- bool handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead);
- bool RemoveUndeadPointers(Value* pointer, unsigned pointerSize,
- BasicBlock::iterator& BBI,
- SmallPtrSet<AllocaInst*, 4>& deadPointers,
- SetVector<Instruction*>& possiblyDead);
- void DeleteDeadInstructionChains(Instruction *I,
- SetVector<Instruction*> &DeadInsts);
-
- // Find the base pointer that a pointer came from
- // Because this is used to find pointers that originate
- // from allocas, it is safe to ignore GEP indices, since
- // either the store will be in the alloca, and thus dead,
- // or beyond the end of the alloca, and thus undefined.
- void TranslatePointerBitCasts(Value*& v) {
- assert(isa<PointerType>(v->getType()) &&
- "Translating a non-pointer type?");
- while (true) {
- if (BitCastInst* C = dyn_cast<BitCastInst>(v))
- v = C->getOperand(0);
- else if (GetElementPtrInst* G = dyn_cast<GetElementPtrInst>(v))
- v = G->getOperand(0);
- else
- break;
- }
- }
+ bool MemoryIsNotModifiedBetween(LoadInst *LI, StoreInst *SI);
+ bool HandleFree(CallInst *F);
+ bool handleEndBlock(BasicBlock &BB);
+ void RemoveAccessedObjects(const MemoryLocation &LoadedLoc,
+ SmallSetVector<Value *, 16> &DeadStackObjects,
+ const DataLayout &DL);
- // getAnalysisUsage - We require post dominance frontiers (aka Control
- // Dependence Graph)
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
- AU.addRequired<TargetData>();
+ AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<AliasAnalysis>();
AU.addRequired<MemoryDependenceAnalysis>();
+ AU.addRequired<TargetLibraryInfoWrapperPass>();
AU.addPreserved<AliasAnalysis>();
+ AU.addPreserved<DominatorTreeWrapperPass>();
AU.addPreserved<MemoryDependenceAnalysis>();
}
};
- char DSE::ID = 0;
- RegisterPass<DSE> X("dse", "Dead Store Elimination");
}
+char DSE::ID = 0;
+INITIALIZE_PASS_BEGIN(DSE, "dse", "Dead Store Elimination", false, false)
+INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
+INITIALIZE_PASS_END(DSE, "dse", "Dead Store Elimination", false, false)
+
FunctionPass *llvm::createDeadStoreEliminationPass() { return new DSE(); }
+//===----------------------------------------------------------------------===//
+// Helper functions
+//===----------------------------------------------------------------------===//
+
+/// DeleteDeadInstruction - Delete this instruction. Before we do, go through
+/// and zero out all the operands of this instruction. If any of them become
+/// dead, delete them and the computation tree that feeds them.
+///
+/// If ValueSet is non-null, remove any deleted instructions from it as well.
+///
+static void DeleteDeadInstruction(Instruction *I,
+ MemoryDependenceAnalysis &MD,
+ const TargetLibraryInfo &TLI,
+ SmallSetVector<Value*, 16> *ValueSet = nullptr) {
+ SmallVector<Instruction*, 32> NowDeadInsts;
+
+ NowDeadInsts.push_back(I);
+ --NumFastOther;
+
+ // Before we touch this instruction, remove it from memdep!
+ do {
+ Instruction *DeadInst = NowDeadInsts.pop_back_val();
+ ++NumFastOther;
+
+ // This instruction is dead, zap it, in stages. Start by removing it from
+ // MemDep, which needs to know the operands and needs it to be in the
+ // function.
+ MD.removeInstruction(DeadInst);
+
+ for (unsigned op = 0, e = DeadInst->getNumOperands(); op != e; ++op) {
+ Value *Op = DeadInst->getOperand(op);
+ DeadInst->setOperand(op, nullptr);
+
+ // If this operand just became dead, add it to the NowDeadInsts list.
+ if (!Op->use_empty()) continue;
+
+ if (Instruction *OpI = dyn_cast<Instruction>(Op))
+ if (isInstructionTriviallyDead(OpI, &TLI))
+ NowDeadInsts.push_back(OpI);
+ }
+
+ DeadInst->eraseFromParent();
+
+ if (ValueSet) ValueSet->remove(DeadInst);
+ } while (!NowDeadInsts.empty());
+}
+
+
+/// hasMemoryWrite - Does this instruction write some memory? This only returns
+/// true for things that we can analyze with other helpers below.
+static bool hasMemoryWrite(Instruction *I, const TargetLibraryInfo &TLI) {
+ if (isa<StoreInst>(I))
+ return true;
+ if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
+ switch (II->getIntrinsicID()) {
+ default:
+ return false;
+ case Intrinsic::memset:
+ case Intrinsic::memmove:
+ case Intrinsic::memcpy:
+ case Intrinsic::init_trampoline:
+ case Intrinsic::lifetime_end:
+ return true;
+ }
+ }
+ if (auto CS = CallSite(I)) {
+ if (Function *F = CS.getCalledFunction()) {
+ if (TLI.has(LibFunc::strcpy) &&
+ F->getName() == TLI.getName(LibFunc::strcpy)) {
+ return true;
+ }
+ if (TLI.has(LibFunc::strncpy) &&
+ F->getName() == TLI.getName(LibFunc::strncpy)) {
+ return true;
+ }
+ if (TLI.has(LibFunc::strcat) &&
+ F->getName() == TLI.getName(LibFunc::strcat)) {
+ return true;
+ }
+ if (TLI.has(LibFunc::strncat) &&
+ F->getName() == TLI.getName(LibFunc::strncat)) {
+ return true;
+ }
+ }
+ }
+ return false;
+}
+
+/// getLocForWrite - Return a Location stored to by the specified instruction.
+/// If isRemovable returns true, this function and getLocForRead completely
+/// describe the memory operations for this instruction.
+static MemoryLocation getLocForWrite(Instruction *Inst, AliasAnalysis &AA) {
+ if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
+ return MemoryLocation::get(SI);
+
+ if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(Inst)) {
+ // memcpy/memmove/memset.
+ MemoryLocation Loc = MemoryLocation::getForDest(MI);
+ return Loc;
+ }
+
+ IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst);
+ if (!II)
+ return MemoryLocation();
+
+ switch (II->getIntrinsicID()) {
+ default:
+ return MemoryLocation(); // Unhandled intrinsic.
+ case Intrinsic::init_trampoline:
+ // FIXME: We don't know the size of the trampoline, so we can't really
+ // handle it here.
+ return MemoryLocation(II->getArgOperand(0));
+ case Intrinsic::lifetime_end: {
+ uint64_t Len = cast<ConstantInt>(II->getArgOperand(0))->getZExtValue();
+ return MemoryLocation(II->getArgOperand(1), Len);
+ }
+ }
+}
+
+/// getLocForRead - Return the location read by the specified "hasMemoryWrite"
+/// instruction if any.
+static MemoryLocation getLocForRead(Instruction *Inst,
+ const TargetLibraryInfo &TLI) {
+ assert(hasMemoryWrite(Inst, TLI) && "Unknown instruction case");
+
+ // The only instructions that both read and write are the mem transfer
+ // instructions (memcpy/memmove).
+ if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(Inst))
+ return MemoryLocation::getForSource(MTI);
+ return MemoryLocation();
+}
+
+
+/// isRemovable - If the value of this instruction and the memory it writes to
+/// is unused, may we delete this instruction?
+static bool isRemovable(Instruction *I) {
+ // Don't remove volatile/atomic stores.
+ if (StoreInst *SI = dyn_cast<StoreInst>(I))
+ return SI->isUnordered();
+
+ if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
+ switch (II->getIntrinsicID()) {
+ default: llvm_unreachable("doesn't pass 'hasMemoryWrite' predicate");
+ case Intrinsic::lifetime_end:
+ // Never remove dead lifetime_end's, e.g. because it is followed by a
+ // free.
+ return false;
+ case Intrinsic::init_trampoline:
+ // Always safe to remove init_trampoline.
+ return true;
+
+ case Intrinsic::memset:
+ case Intrinsic::memmove:
+ case Intrinsic::memcpy:
+ // Don't remove volatile memory intrinsics.
+ return !cast<MemIntrinsic>(II)->isVolatile();
+ }
+ }
+
+ if (auto CS = CallSite(I))
+ return CS.getInstruction()->use_empty();
+
+ return false;
+}
+
+
+/// isShortenable - Returns true if this instruction can be safely shortened in
+/// length.
+static bool isShortenable(Instruction *I) {
+ // Don't shorten stores for now
+ if (isa<StoreInst>(I))
+ return false;
+
+ if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
+ switch (II->getIntrinsicID()) {
+ default: return false;
+ case Intrinsic::memset:
+ case Intrinsic::memcpy:
+ // Do shorten memory intrinsics.
+ return true;
+ }
+ }
+
+ // Don't shorten libcalls calls for now.
+
+ return false;
+}
+
+/// getStoredPointerOperand - Return the pointer that is being written to.
+static Value *getStoredPointerOperand(Instruction *I) {
+ if (StoreInst *SI = dyn_cast<StoreInst>(I))
+ return SI->getPointerOperand();
+ if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I))
+ return MI->getDest();
+
+ if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
+ switch (II->getIntrinsicID()) {
+ default: llvm_unreachable("Unexpected intrinsic!");
+ case Intrinsic::init_trampoline:
+ return II->getArgOperand(0);
+ }
+ }
+
+ CallSite CS(I);
+ // All the supported functions so far happen to have dest as their first
+ // argument.
+ return CS.getArgument(0);
+}
+
+static uint64_t getPointerSize(const Value *V, const DataLayout &DL,
+ const TargetLibraryInfo &TLI) {
+ uint64_t Size;
+ if (getObjectSize(V, Size, DL, &TLI))
+ return Size;
+ return MemoryLocation::UnknownSize;
+}
+
+namespace {
+ enum OverwriteResult
+ {
+ OverwriteComplete,
+ OverwriteEnd,
+ OverwriteUnknown
+ };
+}
+
+/// isOverwrite - Return 'OverwriteComplete' if a store to the 'Later' location
+/// completely overwrites a store to the 'Earlier' location.
+/// 'OverwriteEnd' if the end of the 'Earlier' location is completely
+/// overwritten by 'Later', or 'OverwriteUnknown' if nothing can be determined
+static OverwriteResult isOverwrite(const MemoryLocation &Later,
+ const MemoryLocation &Earlier,
+ const DataLayout &DL,
+ const TargetLibraryInfo &TLI,
+ int64_t &EarlierOff, int64_t &LaterOff) {
+ const Value *P1 = Earlier.Ptr->stripPointerCasts();
+ const Value *P2 = Later.Ptr->stripPointerCasts();
+
+ // If the start pointers are the same, we just have to compare sizes to see if
+ // the later store was larger than the earlier store.
+ if (P1 == P2) {
+ // If we don't know the sizes of either access, then we can't do a
+ // comparison.
+ if (Later.Size == MemoryLocation::UnknownSize ||
+ Earlier.Size == MemoryLocation::UnknownSize)
+ return OverwriteUnknown;
+
+ // Make sure that the Later size is >= the Earlier size.
+ if (Later.Size >= Earlier.Size)
+ return OverwriteComplete;
+ }
+
+ // Otherwise, we have to have size information, and the later store has to be
+ // larger than the earlier one.
+ if (Later.Size == MemoryLocation::UnknownSize ||
+ Earlier.Size == MemoryLocation::UnknownSize)
+ return OverwriteUnknown;
+
+ // Check to see if the later store is to the entire object (either a global,
+ // an alloca, or a byval/inalloca argument). If so, then it clearly
+ // overwrites any other store to the same object.
+ const Value *UO1 = GetUnderlyingObject(P1, DL),
+ *UO2 = GetUnderlyingObject(P2, DL);
+
+ // If we can't resolve the same pointers to the same object, then we can't
+ // analyze them at all.
+ if (UO1 != UO2)
+ return OverwriteUnknown;
+
+ // If the "Later" store is to a recognizable object, get its size.
+ uint64_t ObjectSize = getPointerSize(UO2, DL, TLI);
+ if (ObjectSize != MemoryLocation::UnknownSize)
+ if (ObjectSize == Later.Size && ObjectSize >= Earlier.Size)
+ return OverwriteComplete;
+
+ // Okay, we have stores to two completely different pointers. Try to
+ // decompose the pointer into a "base + constant_offset" form. If the base
+ // pointers are equal, then we can reason about the two stores.
+ EarlierOff = 0;
+ LaterOff = 0;
+ const Value *BP1 = GetPointerBaseWithConstantOffset(P1, EarlierOff, DL);
+ const Value *BP2 = GetPointerBaseWithConstantOffset(P2, LaterOff, DL);
+
+ // If the base pointers still differ, we have two completely different stores.
+ if (BP1 != BP2)
+ return OverwriteUnknown;
+
+ // The later store completely overlaps the earlier store if:
+ //
+ // 1. Both start at the same offset and the later one's size is greater than
+ // or equal to the earlier one's, or
+ //
+ // |--earlier--|
+ // |-- later --|
+ //
+ // 2. The earlier store has an offset greater than the later offset, but which
+ // still lies completely within the later store.
+ //
+ // |--earlier--|
+ // |----- later ------|
+ //
+ // We have to be careful here as *Off is signed while *.Size is unsigned.
+ if (EarlierOff >= LaterOff &&
+ Later.Size >= Earlier.Size &&
+ uint64_t(EarlierOff - LaterOff) + Earlier.Size <= Later.Size)
+ return OverwriteComplete;
+
+ // The other interesting case is if the later store overwrites the end of
+ // the earlier store
+ //
+ // |--earlier--|
+ // |-- later --|
+ //
+ // In this case we may want to trim the size of earlier to avoid generating
+ // writes to addresses which will definitely be overwritten later
+ if (LaterOff > EarlierOff &&
+ LaterOff < int64_t(EarlierOff + Earlier.Size) &&
+ int64_t(LaterOff + Later.Size) >= int64_t(EarlierOff + Earlier.Size))
+ return OverwriteEnd;
+
+ // Otherwise, they don't completely overlap.
+ return OverwriteUnknown;
+}
+
+/// isPossibleSelfRead - If 'Inst' might be a self read (i.e. a noop copy of a
+/// memory region into an identical pointer) then it doesn't actually make its
+/// input dead in the traditional sense. Consider this case:
+///
+/// memcpy(A <- B)
+/// memcpy(A <- A)
+///
+/// In this case, the second store to A does not make the first store to A dead.
+/// The usual situation isn't an explicit A<-A store like this (which can be
+/// trivially removed) but a case where two pointers may alias.
+///
+/// This function detects when it is unsafe to remove a dependent instruction
+/// because the DSE inducing instruction may be a self-read.
+static bool isPossibleSelfRead(Instruction *Inst,
+ const MemoryLocation &InstStoreLoc,
+ Instruction *DepWrite,
+ const TargetLibraryInfo &TLI,
+ AliasAnalysis &AA) {
+ // Self reads can only happen for instructions that read memory. Get the
+ // location read.
+ MemoryLocation InstReadLoc = getLocForRead(Inst, TLI);
+ if (!InstReadLoc.Ptr) return false; // Not a reading instruction.
+
+ // If the read and written loc obviously don't alias, it isn't a read.
+ if (AA.isNoAlias(InstReadLoc, InstStoreLoc)) return false;
+
+ // Okay, 'Inst' may copy over itself. However, we can still remove a the
+ // DepWrite instruction if we can prove that it reads from the same location
+ // as Inst. This handles useful cases like:
+ // memcpy(A <- B)
+ // memcpy(A <- B)
+ // Here we don't know if A/B may alias, but we do know that B/B are must
+ // aliases, so removing the first memcpy is safe (assuming it writes <= #
+ // bytes as the second one.
+ MemoryLocation DepReadLoc = getLocForRead(DepWrite, TLI);
+
+ if (DepReadLoc.Ptr && AA.isMustAlias(InstReadLoc.Ptr, DepReadLoc.Ptr))
+ return false;
+
+ // If DepWrite doesn't read memory or if we can't prove it is a must alias,
+ // then it can't be considered dead.
+ return true;
+}
+
+
+//===----------------------------------------------------------------------===//
+// DSE Pass
+//===----------------------------------------------------------------------===//
+
bool DSE::runOnBasicBlock(BasicBlock &BB) {
- MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
-
- // Record the last-seen store to this pointer
- DenseMap<Value*, StoreInst*> lastStore;
- // Record instructions possibly made dead by deleting a store
- SetVector<Instruction*> possiblyDead;
-
bool MadeChange = false;
-
- // Do a top-down walk on the BB
- for (BasicBlock::iterator BBI = BB.begin(), BBE = BB.end();
- BBI != BBE; ++BBI) {
- // If we find a store or a free...
- if (!isa<StoreInst>(BBI) && !isa<FreeInst>(BBI))
+
+ // Do a top-down walk on the BB.
+ for (BasicBlock::iterator BBI = BB.begin(), BBE = BB.end(); BBI != BBE; ) {
+ Instruction *Inst = BBI++;
+
+ // Handle 'free' calls specially.
+ if (CallInst *F = isFreeCall(Inst, TLI)) {
+ MadeChange |= HandleFree(F);
+ continue;
+ }
+
+ // If we find something that writes memory, get its memory dependence.
+ if (!hasMemoryWrite(Inst, *TLI))
continue;
-
- Value* pointer = 0;
- if (StoreInst* S = dyn_cast<StoreInst>(BBI))
- pointer = S->getPointerOperand();
- else if (FreeInst* F = dyn_cast<FreeInst>(BBI))
- pointer = F->getPointerOperand();
-
- assert(pointer && "Not a free or a store?");
-
- StoreInst*& last = lastStore[pointer];
- bool deletedStore = false;
-
- // ... to a pointer that has been stored to before...
- if (last) {
- Instruction* dep = MD.getDependency(BBI);
-
- // ... and no other memory dependencies are between them....
- while (dep != MemoryDependenceAnalysis::None &&
- dep != MemoryDependenceAnalysis::NonLocal &&
- isa<StoreInst>(dep)) {
- if (dep != last) {
- dep = MD.getDependency(BBI, dep);
+
+ // If we're storing the same value back to a pointer that we just
+ // loaded from, then the store can be removed.
+ if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
+ if (LoadInst *DepLoad = dyn_cast<LoadInst>(SI->getValueOperand())) {
+ if (SI->getPointerOperand() == DepLoad->getPointerOperand() &&
+ isRemovable(SI) &&
+ MemoryIsNotModifiedBetween(DepLoad, SI)) {
+
+ DEBUG(dbgs() << "DSE: Remove Store Of Load from same pointer:\n "
+ << "LOAD: " << *DepLoad << "\n STORE: " << *SI << '\n');
+
+ // DeleteDeadInstruction can delete the current instruction. Save BBI
+ // in case we need it.
+ WeakVH NextInst(BBI);
+
+ DeleteDeadInstruction(SI, *MD, *TLI);
+
+ if (!NextInst) // Next instruction deleted.
+ BBI = BB.begin();
+ else if (BBI != BB.begin()) // Revisit this instruction if possible.
+ --BBI;
+ ++NumRedundantStores;
+ MadeChange = true;
continue;
}
-
- // Remove it!
- MD.removeInstruction(last);
-
- // DCE instructions only used to calculate that store
- if (Instruction* D = dyn_cast<Instruction>(last->getOperand(0)))
- possiblyDead.insert(D);
- if (Instruction* D = dyn_cast<Instruction>(last->getOperand(1)))
- possiblyDead.insert(D);
-
- last->eraseFromParent();
- NumFastStores++;
- deletedStore = true;
- MadeChange = true;
-
+ }
+ }
+
+ MemDepResult InstDep = MD->getDependency(Inst);
+
+ // Ignore any store where we can't find a local dependence.
+ // FIXME: cross-block DSE would be fun. :)
+ if (!InstDep.isDef() && !InstDep.isClobber())
+ continue;
+
+ // Figure out what location is being stored to.
+ MemoryLocation Loc = getLocForWrite(Inst, *AA);
+
+ // If we didn't get a useful location, fail.
+ if (!Loc.Ptr)
+ continue;
+
+ while (InstDep.isDef() || InstDep.isClobber()) {
+ // Get the memory clobbered by the instruction we depend on. MemDep will
+ // skip any instructions that 'Loc' clearly doesn't interact with. If we
+ // end up depending on a may- or must-aliased load, then we can't optimize
+ // away the store and we bail out. However, if we depend on on something
+ // that overwrites the memory location we *can* potentially optimize it.
+ //
+ // Find out what memory location the dependent instruction stores.
+ Instruction *DepWrite = InstDep.getInst();
+ MemoryLocation DepLoc = getLocForWrite(DepWrite, *AA);
+ // If we didn't get a useful location, or if it isn't a size, bail out.
+ if (!DepLoc.Ptr)
break;
+
+ // If we find a write that is a) removable (i.e., non-volatile), b) is
+ // completely obliterated by the store to 'Loc', and c) which we know that
+ // 'Inst' doesn't load from, then we can remove it.
+ if (isRemovable(DepWrite) &&
+ !isPossibleSelfRead(Inst, Loc, DepWrite, *TLI, *AA)) {
+ int64_t InstWriteOffset, DepWriteOffset;
+ const DataLayout &DL = BB.getModule()->getDataLayout();
+ OverwriteResult OR =
+ isOverwrite(Loc, DepLoc, DL, *TLI, DepWriteOffset, InstWriteOffset);
+ if (OR == OverwriteComplete) {
+ DEBUG(dbgs() << "DSE: Remove Dead Store:\n DEAD: "
+ << *DepWrite << "\n KILLER: " << *Inst << '\n');
+
+ // Delete the store and now-dead instructions that feed it.
+ DeleteDeadInstruction(DepWrite, *MD, *TLI);
+ ++NumFastStores;
+ MadeChange = true;
+
+ // DeleteDeadInstruction can delete the current instruction in loop
+ // cases, reset BBI.
+ BBI = Inst;
+ if (BBI != BB.begin())
+ --BBI;
+ break;
+ } else if (OR == OverwriteEnd && isShortenable(DepWrite)) {
+ // TODO: base this on the target vector size so that if the earlier
+ // store was too small to get vector writes anyway then its likely
+ // a good idea to shorten it
+ // Power of 2 vector writes are probably always a bad idea to optimize
+ // as any store/memset/memcpy is likely using vector instructions so
+ // shortening it to not vector size is likely to be slower
+ MemIntrinsic* DepIntrinsic = cast<MemIntrinsic>(DepWrite);
+ unsigned DepWriteAlign = DepIntrinsic->getAlignment();
+ if (llvm::isPowerOf2_64(InstWriteOffset) ||
+ ((DepWriteAlign != 0) && InstWriteOffset % DepWriteAlign == 0)) {
+
+ DEBUG(dbgs() << "DSE: Remove Dead Store:\n OW END: "
+ << *DepWrite << "\n KILLER (offset "
+ << InstWriteOffset << ", "
+ << DepLoc.Size << ")"
+ << *Inst << '\n');
+
+ Value* DepWriteLength = DepIntrinsic->getLength();
+ Value* TrimmedLength = ConstantInt::get(DepWriteLength->getType(),
+ InstWriteOffset -
+ DepWriteOffset);
+ DepIntrinsic->setLength(TrimmedLength);
+ MadeChange = true;
+ }
+ }
}
+
+ // If this is a may-aliased store that is clobbering the store value, we
+ // can keep searching past it for another must-aliased pointer that stores
+ // to the same location. For example, in:
+ // store -> P
+ // store -> Q
+ // store -> P
+ // we can remove the first store to P even though we don't know if P and Q
+ // alias.
+ if (DepWrite == &BB.front()) break;
+
+ // Can't look past this instruction if it might read 'Loc'.
+ if (AA->getModRefInfo(DepWrite, Loc) & MRI_Ref)
+ break;
+
+ InstDep = MD->getPointerDependencyFrom(Loc, false, DepWrite, &BB);
}
-
- // Handle frees whose dependencies are non-trivial.
- if (FreeInst* F = dyn_cast<FreeInst>(BBI)) {
- if (!deletedStore)
- MadeChange |= handleFreeWithNonTrivialDependency(F,
- MD.getDependency(F),
- possiblyDead);
- // No known stores after the free
- last = 0;
+ }
+
+ // If this block ends in a return, unwind, or unreachable, all allocas are
+ // dead at its end, which means stores to them are also dead.
+ if (BB.getTerminator()->getNumSuccessors() == 0)
+ MadeChange |= handleEndBlock(BB);
+
+ return MadeChange;
+}
+
+/// Returns true if the memory which is accessed by the store instruction is not
+/// modified between the load and the store instruction.
+/// Precondition: The store instruction must be dominated by the load
+/// instruction.
+bool DSE::MemoryIsNotModifiedBetween(LoadInst *LI, StoreInst *SI) {
+ SmallVector<BasicBlock *, 16> WorkList;
+ SmallPtrSet<BasicBlock *, 8> Visited;
+ BasicBlock::iterator LoadBBI(LI);
+ ++LoadBBI;
+ BasicBlock::iterator StoreBBI(SI);
+ BasicBlock *LoadBB = LI->getParent();
+ BasicBlock *StoreBB = SI->getParent();
+ MemoryLocation StoreLoc = MemoryLocation::get(SI);
+
+ // Start checking the store-block.
+ WorkList.push_back(StoreBB);
+ bool isFirstBlock = true;
+
+ // Check all blocks going backward until we reach the load-block.
+ while (!WorkList.empty()) {
+ BasicBlock *B = WorkList.pop_back_val();
+
+ // Ignore instructions before LI if this is the LoadBB.
+ BasicBlock::iterator BI = (B == LoadBB ? LoadBBI : B->begin());
+
+ BasicBlock::iterator EI;
+ if (isFirstBlock) {
+ // Ignore instructions after SI if this is the first visit of StoreBB.
+ assert(B == StoreBB && "first block is not the store block");
+ EI = StoreBBI;
+ isFirstBlock = false;
} else {
- // Update our most-recent-store map.
- last = cast<StoreInst>(BBI);
+ // It's not StoreBB or (in case of a loop) the second visit of StoreBB.
+ // In this case we also have to look at instructions after SI.
+ EI = B->end();
+ }
+ for (; BI != EI; ++BI) {
+ Instruction *I = BI;
+ if (I->mayWriteToMemory() && I != SI) {
+ auto Res = AA->getModRefInfo(I, StoreLoc);
+ if (Res != MRI_NoModRef)
+ return false;
+ }
+ }
+ if (B != LoadBB) {
+ assert(B != &LoadBB->getParent()->getEntryBlock() &&
+ "Should not hit the entry block because SI must be dominated by LI");
+ for (auto PredI = pred_begin(B), PE = pred_end(B); PredI != PE; ++PredI) {
+ if (!Visited.insert(*PredI).second)
+ continue;
+ WorkList.push_back(*PredI);
+ }
}
}
-
- // If this block ends in a return, unwind, unreachable, and eventually
- // tailcall, then all allocas are dead at its end.
- if (BB.getTerminator()->getNumSuccessors() == 0)
- MadeChange |= handleEndBlock(BB, possiblyDead);
-
- // Do a trivial DCE
- while (!possiblyDead.empty()) {
- Instruction *I = possiblyDead.back();
- possiblyDead.pop_back();
- DeleteDeadInstructionChains(I, possiblyDead);
+ return true;
+}
+
+/// Find all blocks that will unconditionally lead to the block BB and append
+/// them to F.
+static void FindUnconditionalPreds(SmallVectorImpl<BasicBlock *> &Blocks,
+ BasicBlock *BB, DominatorTree *DT) {
+ for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
+ BasicBlock *Pred = *I;
+ if (Pred == BB) continue;
+ TerminatorInst *PredTI = Pred->getTerminator();
+ if (PredTI->getNumSuccessors() != 1)
+ continue;
+
+ if (DT->isReachableFromEntry(Pred))
+ Blocks.push_back(Pred);
}
-
- return MadeChange;
}
-/// handleFreeWithNonTrivialDependency - Handle frees of entire structures whose
-/// dependency is a store to a field of that structure
-bool DSE::handleFreeWithNonTrivialDependency(FreeInst* F, Instruction* dep,
- SetVector<Instruction*>& possiblyDead) {
- TargetData &TD = getAnalysis<TargetData>();
- AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
- MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
-
- if (dep == MemoryDependenceAnalysis::None ||
- dep == MemoryDependenceAnalysis::NonLocal)
- return false;
-
- StoreInst* dependency = dyn_cast<StoreInst>(dep);
- if (!dependency)
- return false;
-
- Value* depPointer = dependency->getPointerOperand();
- const Type* depType = dependency->getOperand(0)->getType();
- unsigned depPointerSize = TD.getTypeSize(depType);
-
- // Check for aliasing
- AliasAnalysis::AliasResult A = AA.alias(F->getPointerOperand(), ~0UL,
- depPointer, depPointerSize);
-
- if (A == AliasAnalysis::MustAlias) {
- // Remove it!
- MD.removeInstruction(dependency);
-
- // DCE instructions only used to calculate that store
- if (Instruction* D = dyn_cast<Instruction>(dependency->getOperand(0)))
- possiblyDead.insert(D);
- if (Instruction* D = dyn_cast<Instruction>(dependency->getOperand(1)))
- possiblyDead.insert(D);
-
- dependency->eraseFromParent();
- NumFastStores++;
- return true;
+/// HandleFree - Handle frees of entire structures whose dependency is a store
+/// to a field of that structure.
+bool DSE::HandleFree(CallInst *F) {
+ bool MadeChange = false;
+
+ MemoryLocation Loc = MemoryLocation(F->getOperand(0));
+ SmallVector<BasicBlock *, 16> Blocks;
+ Blocks.push_back(F->getParent());
+ const DataLayout &DL = F->getModule()->getDataLayout();
+
+ while (!Blocks.empty()) {
+ BasicBlock *BB = Blocks.pop_back_val();
+ Instruction *InstPt = BB->getTerminator();
+ if (BB == F->getParent()) InstPt = F;
+
+ MemDepResult Dep = MD->getPointerDependencyFrom(Loc, false, InstPt, BB);
+ while (Dep.isDef() || Dep.isClobber()) {
+ Instruction *Dependency = Dep.getInst();
+ if (!hasMemoryWrite(Dependency, *TLI) || !isRemovable(Dependency))
+ break;
+
+ Value *DepPointer =
+ GetUnderlyingObject(getStoredPointerOperand(Dependency), DL);
+
+ // Check for aliasing.
+ if (!AA->isMustAlias(F->getArgOperand(0), DepPointer))
+ break;
+
+ Instruction *Next = std::next(BasicBlock::iterator(Dependency));
+
+ // DCE instructions only used to calculate that store
+ DeleteDeadInstruction(Dependency, *MD, *TLI);
+ ++NumFastStores;
+ MadeChange = true;
+
+ // Inst's old Dependency is now deleted. Compute the next dependency,
+ // which may also be dead, as in
+ // s[0] = 0;
+ // s[1] = 0; // This has just been deleted.
+ // free(s);
+ Dep = MD->getPointerDependencyFrom(Loc, false, Next, BB);
+ }
+
+ if (Dep.isNonLocal())
+ FindUnconditionalPreds(Blocks, BB, DT);
}
-
- return false;
+
+ return MadeChange;
}
/// handleEndBlock - Remove dead stores to stack-allocated locations in the
-/// function end block
-bool DSE::handleEndBlock(BasicBlock& BB,
- SetVector<Instruction*>& possiblyDead) {
- TargetData &TD = getAnalysis<TargetData>();
- AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
- MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
-
+/// function end block. Ex:
+/// %A = alloca i32
+/// ...
+/// store i32 1, i32* %A
+/// ret void
+bool DSE::handleEndBlock(BasicBlock &BB) {
bool MadeChange = false;
-
- // Pointers alloca'd in this function are dead in the end block
- SmallPtrSet<AllocaInst*, 4> deadPointers;
-
- // Find all of the alloca'd pointers in the entry block
+
+ // Keep track of all of the stack objects that are dead at the end of the
+ // function.
+ SmallSetVector<Value*, 16> DeadStackObjects;
+
+ // Find all of the alloca'd pointers in the entry block.
BasicBlock *Entry = BB.getParent()->begin();
- for (BasicBlock::iterator I = Entry->begin(), E = Entry->end(); I != E; ++I)
- if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
- deadPointers.insert(AI);
-
+ for (BasicBlock::iterator I = Entry->begin(), E = Entry->end(); I != E; ++I) {
+ if (isa<AllocaInst>(I))
+ DeadStackObjects.insert(I);
+
+ // Okay, so these are dead heap objects, but if the pointer never escapes
+ // then it's leaked by this function anyways.
+ else if (isAllocLikeFn(I, TLI) && !PointerMayBeCaptured(I, true, true))
+ DeadStackObjects.insert(I);
+ }
+
+ // Treat byval or inalloca arguments the same, stores to them are dead at the
+ // end of the function.
+ for (Function::arg_iterator AI = BB.getParent()->arg_begin(),
+ AE = BB.getParent()->arg_end(); AI != AE; ++AI)
+ if (AI->hasByValOrInAllocaAttr())
+ DeadStackObjects.insert(AI);
+
+ const DataLayout &DL = BB.getModule()->getDataLayout();
+
// Scan the basic block backwards
for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
--BBI;
-
- if (deadPointers.empty())
- break;
-
- Value* killPointer = 0;
- unsigned killPointerSize = 0;
-
- // If we find a store whose pointer is dead...
- if (StoreInst* S = dyn_cast<StoreInst>(BBI)) {
- Value* pointerOperand = S->getPointerOperand();
+
+ // If we find a store, check to see if it points into a dead stack value.
+ if (hasMemoryWrite(BBI, *TLI) && isRemovable(BBI)) {
// See through pointer-to-pointer bitcasts
- TranslatePointerBitCasts(pointerOperand);
-
- if (deadPointers.count(pointerOperand)){
- // Remove it!
- MD.removeInstruction(S);
-
- // DCE instructions only used to calculate that store
- if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
- possiblyDead.insert(D);
- if (Instruction* D = dyn_cast<Instruction>(S->getOperand(1)))
- possiblyDead.insert(D);
-
- BBI++;
- S->eraseFromParent();
- NumFastStores++;
+ SmallVector<Value *, 4> Pointers;
+ GetUnderlyingObjects(getStoredPointerOperand(BBI), Pointers, DL);
+
+ // Stores to stack values are valid candidates for removal.
+ bool AllDead = true;
+ for (SmallVectorImpl<Value *>::iterator I = Pointers.begin(),
+ E = Pointers.end(); I != E; ++I)
+ if (!DeadStackObjects.count(*I)) {
+ AllDead = false;
+ break;
+ }
+
+ if (AllDead) {
+ Instruction *Dead = BBI++;
+
+ DEBUG(dbgs() << "DSE: Dead Store at End of Block:\n DEAD: "
+ << *Dead << "\n Objects: ";
+ for (SmallVectorImpl<Value *>::iterator I = Pointers.begin(),
+ E = Pointers.end(); I != E; ++I) {
+ dbgs() << **I;
+ if (std::next(I) != E)
+ dbgs() << ", ";
+ }
+ dbgs() << '\n');
+
+ // DCE instructions only used to calculate that store.
+ DeleteDeadInstruction(Dead, *MD, *TLI, &DeadStackObjects);
+ ++NumFastStores;
MadeChange = true;
+ continue;
}
-
- // If we encounter a use of the pointer, it is no longer considered dead
- } else if (LoadInst* L = dyn_cast<LoadInst>(BBI)) {
- killPointer = L->getPointerOperand();
- killPointerSize = TD.getTypeSize(L->getType());
- } else if (VAArgInst* V = dyn_cast<VAArgInst>(BBI)) {
- killPointer = V->getOperand(0);
- killPointerSize = TD.getTypeSize(V->getType());
- } else if (FreeInst* F = dyn_cast<FreeInst>(BBI)) {
- killPointer = F->getPointerOperand();
- killPointerSize = ~0UL;
- } else if (AllocaInst* A = dyn_cast<AllocaInst>(BBI)) {
- deadPointers.erase(A);
- continue;
- } else if (CallSite::get(BBI).getInstruction() != 0) {
- // Remove any pointers made undead by the call from the dead set
- std::vector<Instruction*> dead;
- for (SmallPtrSet<AllocaInst*, 4>::iterator I = deadPointers.begin(),
- E = deadPointers.end(); I != E; ++I) {
- // Get size information for the alloca
- unsigned pointerSize = ~0UL;
- if (ConstantInt* C = dyn_cast<ConstantInt>((*I)->getArraySize()))
- pointerSize = C->getZExtValue() * \
- TD.getTypeSize((*I)->getAllocatedType());
-
- // See if the call site touches it
- AliasAnalysis::ModRefResult A = AA.getModRefInfo(CallSite::get(BBI),
- *I, pointerSize);
- if (A == AliasAnalysis::ModRef || A == AliasAnalysis::Ref)
- dead.push_back(*I);
- }
+ }
- for (std::vector<Instruction*>::iterator I = dead.begin(), E = dead.end();
- I != E; ++I)
- deadPointers.erase(*I);
-
+ // Remove any dead non-memory-mutating instructions.
+ if (isInstructionTriviallyDead(BBI, TLI)) {
+ Instruction *Inst = BBI++;
+ DeleteDeadInstruction(Inst, *MD, *TLI, &DeadStackObjects);
+ ++NumFastOther;
+ MadeChange = true;
continue;
}
-
- if (!killPointer)
+
+ if (isa<AllocaInst>(BBI)) {
+ // Remove allocas from the list of dead stack objects; there can't be
+ // any references before the definition.
+ DeadStackObjects.remove(BBI);
continue;
-
- // Deal with undead pointers
- MadeChange |= RemoveUndeadPointers(killPointer, killPointerSize, BBI,
- deadPointers, possiblyDead);
- }
-
- return MadeChange;
-}
+ }
-bool DSE::RemoveUndeadPointers(Value* killPointer, unsigned killPointerSize,
- BasicBlock::iterator& BBI,
- SmallPtrSet<AllocaInst*, 4>& deadPointers,
- SetVector<Instruction*>& possiblyDead) {
- TargetData &TD = getAnalysis<TargetData>();
- AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
- MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
-
- bool MadeChange = false;
-
- std::vector<Instruction*> undead;
-
- for (SmallPtrSet<AllocaInst*, 4>::iterator I = deadPointers.begin(),
- E = deadPointers.end(); I != E; ++I) {
- // Get size information for the alloca
- unsigned pointerSize = ~0UL;
- if (ConstantInt* C = dyn_cast<ConstantInt>((*I)->getArraySize()))
- pointerSize = C->getZExtValue() * \
- TD.getTypeSize((*I)->getAllocatedType());
-
- // See if this pointer could alias it
- AliasAnalysis::AliasResult A = AA.alias(*I, pointerSize,
- killPointer, killPointerSize);
-
- // If it must-alias and a store, we can delete it
- if (isa<StoreInst>(BBI) && A == AliasAnalysis::MustAlias) {
- StoreInst* S = cast<StoreInst>(BBI);
-
- // Remove it!
- MD.removeInstruction(S);
+ if (auto CS = CallSite(BBI)) {
+ // Remove allocation function calls from the list of dead stack objects;
+ // there can't be any references before the definition.
+ if (isAllocLikeFn(BBI, TLI))
+ DeadStackObjects.remove(BBI);
- // DCE instructions only used to calculate that store
- if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
- possiblyDead.insert(D);
- if (Instruction* D = dyn_cast<Instruction>(S->getOperand(1)))
- possiblyDead.insert(D);
-
- BBI++;
- S->eraseFromParent();
- NumFastStores++;
- MadeChange = true;
+ // If this call does not access memory, it can't be loading any of our
+ // pointers.
+ if (AA->doesNotAccessMemory(CS))
+ continue;
+
+ // If the call might load from any of our allocas, then any store above
+ // the call is live.
+ DeadStackObjects.remove_if([&](Value *I) {
+ // See if the call site touches the value.
+ ModRefInfo A = AA->getModRefInfo(CS, I, getPointerSize(I, DL, *TLI));
+
+ return A == MRI_ModRef || A == MRI_Ref;
+ });
+
+ // If all of the allocas were clobbered by the call then we're not going
+ // to find anything else to process.
+ if (DeadStackObjects.empty())
+ break;
+
+ continue;
+ }
+ MemoryLocation LoadedLoc;
+
+ // If we encounter a use of the pointer, it is no longer considered dead
+ if (LoadInst *L = dyn_cast<LoadInst>(BBI)) {
+ if (!L->isUnordered()) // Be conservative with atomic/volatile load
+ break;
+ LoadedLoc = MemoryLocation::get(L);
+ } else if (VAArgInst *V = dyn_cast<VAArgInst>(BBI)) {
+ LoadedLoc = MemoryLocation::get(V);
+ } else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(BBI)) {
+ LoadedLoc = MemoryLocation::getForSource(MTI);
+ } else if (!BBI->mayReadFromMemory()) {
+ // Instruction doesn't read memory. Note that stores that weren't removed
+ // above will hit this case.
continue;
+ } else {
+ // Unknown inst; assume it clobbers everything.
+ break;
+ }
+
+ // Remove any allocas from the DeadPointer set that are loaded, as this
+ // makes any stores above the access live.
+ RemoveAccessedObjects(LoadedLoc, DeadStackObjects, DL);
- // Otherwise, it is undead
- } else if (A != AliasAnalysis::NoAlias)
- undead.push_back(*I);
+ // If all of the allocas were clobbered by the access then we're not going
+ // to find anything else to process.
+ if (DeadStackObjects.empty())
+ break;
}
- for (std::vector<Instruction*>::iterator I = undead.begin(), E = undead.end();
- I != E; ++I)
- deadPointers.erase(*I);
-
return MadeChange;
}
-void DSE::DeleteDeadInstructionChains(Instruction *I,
- SetVector<Instruction*> &DeadInsts) {
- // Instruction must be dead.
- if (!I->use_empty() || !isInstructionTriviallyDead(I)) return;
-
- // Let the memory dependence know
- getAnalysis<MemoryDependenceAnalysis>().removeInstruction(I);
-
- // See if this made any operands dead. We do it this way in case the
- // instruction uses the same operand twice. We don't want to delete a
- // value then reference it.
- for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
- if (I->getOperand(i)->hasOneUse())
- if (Instruction* Op = dyn_cast<Instruction>(I->getOperand(i)))
- DeadInsts.insert(Op); // Attempt to nuke it later.
-
- I->setOperand(i, 0); // Drop from the operand list.
+/// RemoveAccessedObjects - Check to see if the specified location may alias any
+/// of the stack objects in the DeadStackObjects set. If so, they become live
+/// because the location is being loaded.
+void DSE::RemoveAccessedObjects(const MemoryLocation &LoadedLoc,
+ SmallSetVector<Value *, 16> &DeadStackObjects,
+ const DataLayout &DL) {
+ const Value *UnderlyingPointer = GetUnderlyingObject(LoadedLoc.Ptr, DL);
+
+ // A constant can't be in the dead pointer set.
+ if (isa<Constant>(UnderlyingPointer))
+ return;
+
+ // If the kill pointer can be easily reduced to an alloca, don't bother doing
+ // extraneous AA queries.
+ if (isa<AllocaInst>(UnderlyingPointer) || isa<Argument>(UnderlyingPointer)) {
+ DeadStackObjects.remove(const_cast<Value*>(UnderlyingPointer));
+ return;
}
- I->eraseFromParent();
- ++NumFastOther;
+ // Remove objects that could alias LoadedLoc.
+ DeadStackObjects.remove_if([&](Value *I) {
+ // See if the loaded location could alias the stack location.
+ MemoryLocation StackLoc(I, getPointerSize(I, DL, *TLI));
+ return !AA->isNoAlias(StackLoc, LoadedLoc);
+ });
}
projects / oota-llvm.git / blobdiff