//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "dse"
#include "llvm/Transforms/Scalar.h"
-#include "llvm/Constants.h"
-#include "llvm/Function.h"
-#include "llvm/Instructions.h"
-#include "llvm/IntrinsicInst.h"
-#include "llvm/Pass.h"
-#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
-#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/CaptureTracking.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
-#include "llvm/Target/TargetData.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/Target/TargetLibraryInfo.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
+#define DEBUG_TYPE "dse"
+
STATISTIC(NumFastStores, "Number of stores deleted");
STATISTIC(NumFastOther , "Number of other instrs removed");
namespace {
struct DSE : public FunctionPass {
- TargetData *TD;
+ AliasAnalysis *AA;
+ MemoryDependenceAnalysis *MD;
+ DominatorTree *DT;
+ const TargetLibraryInfo *TLI;
static char ID; // Pass identification, replacement for typeid
- DSE() : FunctionPass(ID) {
+ DSE() : FunctionPass(ID), AA(nullptr), MD(nullptr), DT(nullptr) {
initializeDSEPass(*PassRegistry::getPassRegistry());
}
- virtual bool runOnFunction(Function &F) {
+ bool runOnFunction(Function &F) override {
+ if (skipOptnoneFunction(F))
+ return false;
+
+ AA = &getAnalysis<AliasAnalysis>();
+ MD = &getAnalysis<MemoryDependenceAnalysis>();
+ DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+ TLI = AA->getTargetLibraryInfo();
+
bool Changed = false;
-
- DominatorTree &DT = getAnalysis<DominatorTree>();
-
for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
// Only check non-dead blocks. Dead blocks may have strange pointer
// cycles that will confuse alias analysis.
- if (DT.isReachableFromEntry(I))
+ if (DT->isReachableFromEntry(I))
Changed |= runOnBasicBlock(*I);
+
+ AA = nullptr; MD = nullptr; DT = nullptr;
return Changed;
}
-
+
bool runOnBasicBlock(BasicBlock &BB);
- bool handleFreeWithNonTrivialDependency(const CallInst *F,
- MemDepResult Dep);
+ bool HandleFree(CallInst *F);
bool handleEndBlock(BasicBlock &BB);
- bool RemoveUndeadPointers(Value *Ptr, uint64_t killPointerSize,
- BasicBlock::iterator &BBI,
- SmallPtrSet<Value*, 64> &deadPointers);
- void DeleteDeadInstruction(Instruction *I,
- SmallPtrSet<Value*, 64> *deadPointers = 0);
-
-
- // getAnalysisUsage - We require post dominance frontiers (aka Control
- // Dependence Graph)
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ void RemoveAccessedObjects(const AliasAnalysis::Location &LoadedLoc,
+ SmallSetVector<Value*, 16> &DeadStackObjects);
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
- AU.addRequired<DominatorTree>();
+ AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<AliasAnalysis>();
AU.addRequired<MemoryDependenceAnalysis>();
- AU.addPreserved<DominatorTree>();
+ AU.addPreserved<AliasAnalysis>();
+ AU.addPreserved<DominatorTreeWrapperPass>();
AU.addPreserved<MemoryDependenceAnalysis>();
}
-
- uint64_t getPointerSize(Value *V) const;
};
}
char DSE::ID = 0;
INITIALIZE_PASS_BEGIN(DSE, "dse", "Dead Store Elimination", false, false)
-INITIALIZE_PASS_DEPENDENCY(DominatorTree)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_PASS_END(DSE, "dse", "Dead Store Elimination", false, false)
FunctionPass *llvm::createDeadStoreEliminationPass() { return new DSE(); }
-/// doesClobberMemory - Does this instruction clobber (write without reading)
-/// some memory?
-static bool doesClobberMemory(Instruction *I) {
+//===----------------------------------------------------------------------===//
+// 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)) {
return true;
}
}
+ if (CallSite CS = I) {
+ if (Function *F = CS.getCalledFunction()) {
+ if (TLI && TLI->has(LibFunc::strcpy) &&
+ F->getName() == TLI->getName(LibFunc::strcpy)) {
+ return true;
+ }
+ if (TLI && TLI->has(LibFunc::strncpy) &&
+ F->getName() == TLI->getName(LibFunc::strncpy)) {
+ return true;
+ }
+ if (TLI && TLI->has(LibFunc::strcat) &&
+ F->getName() == TLI->getName(LibFunc::strcat)) {
+ return true;
+ }
+ if (TLI && TLI->has(LibFunc::strncat) &&
+ F->getName() == TLI->getName(LibFunc::strncat)) {
+ return true;
+ }
+ }
+ }
return false;
}
-/// isElidable - If the value of this instruction and the memory it writes to is
-/// unused, may we delete this instrtction?
-static bool isElidable(Instruction *I) {
- assert(doesClobberMemory(I));
- if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
- return II->getIntrinsicID() != Intrinsic::lifetime_end;
- if (StoreInst *SI = dyn_cast<StoreInst>(I))
- return !SI->isVolatile();
- return true;
-}
+/// 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 AliasAnalysis::Location
+getLocForWrite(Instruction *Inst, AliasAnalysis &AA) {
+ const DataLayout *DL = AA.getDataLayout();
+ if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
+ return AA.getLocation(SI);
+
+ if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(Inst)) {
+ // memcpy/memmove/memset.
+ AliasAnalysis::Location Loc = AA.getLocationForDest(MI);
+ // If we don't have target data around, an unknown size in Location means
+ // that we should use the size of the pointee type. This isn't valid for
+ // memset/memcpy, which writes more than an i8.
+ if (Loc.Size == AliasAnalysis::UnknownSize && DL == nullptr)
+ return AliasAnalysis::Location();
+ return Loc;
+ }
-/// getPointerOperand - Return the pointer that is being clobbered.
-static Value *getPointerOperand(Instruction *I) {
- assert(doesClobberMemory(I));
- if (StoreInst *SI = dyn_cast<StoreInst>(I))
- return SI->getPointerOperand();
- if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I))
- return MI->getArgOperand(0);
+ IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst);
+ if (!II) return AliasAnalysis::Location();
- IntrinsicInst *II = cast<IntrinsicInst>(I);
switch (II->getIntrinsicID()) {
- default: assert(false && "Unexpected intrinsic!");
+ default: return AliasAnalysis::Location(); // Unhandled intrinsic.
case Intrinsic::init_trampoline:
- return II->getArgOperand(0);
- case Intrinsic::lifetime_end:
- return II->getArgOperand(1);
+ // If we don't have target data around, an unknown size in Location means
+ // that we should use the size of the pointee type. This isn't valid for
+ // init.trampoline, which writes more than an i8.
+ if (!DL) return AliasAnalysis::Location();
+
+ // FIXME: We don't know the size of the trampoline, so we can't really
+ // handle it here.
+ return AliasAnalysis::Location(II->getArgOperand(0));
+ case Intrinsic::lifetime_end: {
+ uint64_t Len = cast<ConstantInt>(II->getArgOperand(0))->getZExtValue();
+ return AliasAnalysis::Location(II->getArgOperand(1), Len);
}
+ }
+}
+
+/// getLocForRead - Return the location read by the specified "hasMemoryWrite"
+/// instruction if any.
+static AliasAnalysis::Location
+getLocForRead(Instruction *Inst, AliasAnalysis &AA) {
+ assert(hasMemoryWrite(Inst, AA.getTargetLibraryInfo()) &&
+ "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 AA.getLocationForSource(MTI);
+ return AliasAnalysis::Location();
}
-/// getStoreSize - Return the length in bytes of the write by the clobbering
-/// instruction. If variable or unknown, returns AliasAnalysis::UnknownSize.
-static uint64_t getStoreSize(Instruction *I, const TargetData *TD) {
- assert(doesClobberMemory(I));
- if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
- if (!TD) return AliasAnalysis::UnknownSize;
- return TD->getTypeStoreSize(SI->getOperand(0)->getType());
+
+/// 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();
+ }
}
- Value *Len;
- if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
- Len = MI->getLength();
- } else {
- IntrinsicInst *II = cast<IntrinsicInst>(I);
+ if (CallSite CS = 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: assert(false && "Unexpected intrinsic!");
+ default: llvm_unreachable("Unexpected intrinsic!");
case Intrinsic::init_trampoline:
- return AliasAnalysis::UnknownSize;
- case Intrinsic::lifetime_end:
- Len = II->getArgOperand(0);
- break;
+ return II->getArgOperand(0);
}
}
- if (ConstantInt *LenCI = dyn_cast<ConstantInt>(Len))
- if (!LenCI->isAllOnesValue())
- return LenCI->getZExtValue();
+
+ 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, AliasAnalysis &AA) {
+ uint64_t Size;
+ if (getObjectSize(V, Size, AA.getDataLayout(), AA.getTargetLibraryInfo()))
+ return Size;
return AliasAnalysis::UnknownSize;
}
-/// isStoreAtLeastAsWideAs - Return true if the size of the store in I1 is
-/// greater than or equal to the store in I2. This returns false if we don't
-/// know.
+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 AliasAnalysis::Location &Later,
+ const AliasAnalysis::Location &Earlier,
+ AliasAnalysis &AA,
+ int64_t &EarlierOff,
+ int64_t &LaterOff) {
+ const DataLayout *DL = AA.getDataLayout();
+ 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 == AliasAnalysis::UnknownSize ||
+ Earlier.Size == AliasAnalysis::UnknownSize) {
+ // If we have no DataLayout information around, then the size of the store
+ // is inferrable from the pointee type. If they are the same type, then
+ // we know that the store is safe.
+ if (DL == nullptr && Later.Ptr->getType() == Earlier.Ptr->getType())
+ return OverwriteComplete;
+
+ 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 == AliasAnalysis::UnknownSize ||
+ Earlier.Size == AliasAnalysis::UnknownSize || DL == nullptr)
+ 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, AA);
+ if (ObjectSize != AliasAnalysis::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:
///
-static bool isStoreAtLeastAsWideAs(Instruction *I1, Instruction *I2,
- const TargetData *TD) {
- const Type *I1Ty = getPointerOperand(I1)->getType();
- const Type *I2Ty = getPointerOperand(I2)->getType();
-
- // Exactly the same type, must have exactly the same size.
- if (I1Ty == I2Ty) return true;
-
- uint64_t I1Size = getStoreSize(I1, TD);
- uint64_t I2Size = getStoreSize(I2, TD);
-
- return I1Size != AliasAnalysis::UnknownSize &&
- I2Size != AliasAnalysis::UnknownSize &&
- I1Size >= I2Size;
+/// 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 AliasAnalysis::Location &InstStoreLoc,
+ Instruction *DepWrite, AliasAnalysis &AA) {
+ // Self reads can only happen for instructions that read memory. Get the
+ // location read.
+ AliasAnalysis::Location InstReadLoc = getLocForRead(Inst, AA);
+ 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.
+ AliasAnalysis::Location DepReadLoc = getLocForRead(DepWrite, AA);
+
+ 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;
}
-bool DSE::runOnBasicBlock(BasicBlock &BB) {
- MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
- TD = getAnalysisIfAvailable<TargetData>();
+//===----------------------------------------------------------------------===//
+// DSE Pass
+//===----------------------------------------------------------------------===//
+
+bool DSE::runOnBasicBlock(BasicBlock &BB) {
bool MadeChange = false;
-
+
// Do a top-down walk on the BB.
for (BasicBlock::iterator BBI = BB.begin(), BBE = BB.end(); BBI != BBE; ) {
Instruction *Inst = BBI++;
-
- // If we find a store or a free, get its memory dependence.
- if (!doesClobberMemory(Inst) && !isFreeCall(Inst))
- continue;
-
- MemDepResult InstDep = MD.getDependency(Inst);
-
- // Ignore non-local stores.
- // FIXME: cross-block DSE would be fun. :)
- if (InstDep.isNonLocal()) continue;
-
- // Handle frees whose dependencies are non-trivial.
- if (const CallInst *F = isFreeCall(Inst)) {
- MadeChange |= handleFreeWithNonTrivialDependency(F, InstDep);
+
+ // Handle 'free' calls specially.
+ if (CallInst *F = isFreeCall(Inst, TLI)) {
+ MadeChange |= HandleFree(F);
continue;
}
-
- // If not a definite must-alias dependency, ignore it.
- if (!InstDep.isDef())
+
+ // If we find something that writes memory, get its memory dependence.
+ if (!hasMemoryWrite(Inst, TLI))
continue;
-
- // If this is a store-store dependence, then the previous store is dead so
- // long as this store is at least as big as it.
- if (doesClobberMemory(InstDep.getInst())) {
- Instruction *DepStore = InstDep.getInst();
- if (isStoreAtLeastAsWideAs(Inst, DepStore, TD) &&
- isElidable(DepStore)) {
- // Delete the store and now-dead instructions that feed it.
- DeleteDeadInstruction(DepStore);
- ++NumFastStores;
- MadeChange = true;
- // DeleteDeadInstruction can delete the current instruction in loop
- // cases, reset BBI.
- BBI = Inst;
- if (BBI != BB.begin())
- --BBI;
- continue;
- }
- }
-
- if (!isElidable(Inst))
+ 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;
-
+
// 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>(InstDep.getInst())) {
if (SI->getPointerOperand() == DepLoad->getPointerOperand() &&
- SI->getOperand(0) == DepLoad) {
+ SI->getOperand(0) == DepLoad && isRemovable(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);
-
- if (NextInst == 0) // Next instruction deleted.
+
+ DeleteDeadInstruction(SI, *MD, TLI);
+
+ if (!NextInst) // Next instruction deleted.
BBI = BB.begin();
else if (BBI != BB.begin()) // Revisit this instruction if possible.
--BBI;
}
}
}
-
- // If this is a lifetime end marker, we can throw away the store.
- if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(InstDep.getInst())) {
- if (II->getIntrinsicID() == Intrinsic::lifetime_end) {
- // Delete the store and now-dead instructions that feed it.
- // DeleteDeadInstruction can delete the current instruction. Save BBI
- // in case we need it.
- WeakVH NextInst(BBI);
-
- DeleteDeadInstruction(Inst);
-
- if (NextInst == 0) // Next instruction deleted.
- BBI = BB.begin();
- else if (BBI != BB.begin()) // Revisit this instruction if possible.
- --BBI;
- ++NumFastStores;
- MadeChange = true;
- continue;
+
+ // Figure out what location is being stored to.
+ AliasAnalysis::Location 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();
+ AliasAnalysis::Location 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, *AA)) {
+ int64_t InstWriteOffset, DepWriteOffset;
+ OverwriteResult OR = isOverwrite(Loc, DepLoc, *AA,
+ 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) & AliasAnalysis::Ref)
+ break;
+
+ InstDep = MD->getPointerDependencyFrom(Loc, false, DepWrite, &BB);
}
}
-
+
// 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;
}
-/// handleFreeWithNonTrivialDependency - Handle frees of entire structures whose
-/// dependency is a store to a field of that structure.
-bool DSE::handleFreeWithNonTrivialDependency(const CallInst *F,
- MemDepResult Dep) {
- AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
-
- Instruction *Dependency = Dep.getInst();
- if (!Dependency || !doesClobberMemory(Dependency) || !isElidable(Dependency))
- return false;
-
- Value *DepPointer = getPointerOperand(Dependency)->getUnderlyingObject();
+/// 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;
- // Check for aliasing.
- if (AA.alias(F->getArgOperand(0), 1, DepPointer, 1) !=
- AliasAnalysis::MustAlias)
- return false;
-
- // DCE instructions only used to calculate that store
- DeleteDeadInstruction(Dependency);
- ++NumFastStores;
- return true;
+ if (DT->isReachableFromEntry(Pred))
+ Blocks.push_back(Pred);
+ }
+}
+
+/// 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;
+
+ AliasAnalysis::Location Loc = AliasAnalysis::Location(F->getOperand(0));
+ SmallVector<BasicBlock *, 16> Blocks;
+ Blocks.push_back(F->getParent());
+
+ 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));
+
+ // 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 MadeChange;
}
/// handleEndBlock - Remove dead stores to stack-allocated locations in the
/// store i32 1, i32* %A
/// ret void
bool DSE::handleEndBlock(BasicBlock &BB) {
- AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
-
bool MadeChange = false;
-
- // Pointers alloca'd in this function are dead in the end block
- SmallPtrSet<Value*, 64> deadPointers;
-
+
+ // 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);
-
- // Treat byval arguments the same, stores to them are dead at the end of the
- // function.
+ 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->hasByValAttr())
- deadPointers.insert(AI);
-
+ if (AI->hasByValOrInAllocaAttr())
+ DeadStackObjects.insert(AI);
+
// Scan the basic block backwards
for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
--BBI;
-
- // If we find a store whose pointer is dead.
- if (doesClobberMemory(BBI)) {
- if (isElidable(BBI)) {
- // See through pointer-to-pointer bitcasts
- Value *pointerOperand = getPointerOperand(BBI)->getUnderlyingObject();
-
- // Alloca'd pointers or byval arguments (which are functionally like
- // alloca's) are valid candidates for removal.
- if (deadPointers.count(pointerOperand)) {
- // DCE instructions only used to calculate that store.
- Instruction *Dead = BBI;
- ++BBI;
- DeleteDeadInstruction(Dead, &deadPointers);
- ++NumFastStores;
- MadeChange = true;
- continue;
+
+ // 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
+ SmallVector<Value *, 4> Pointers;
+ GetUnderlyingObjects(getStoredPointerOperand(BBI), Pointers);
+
+ // 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;
}
- }
-
- // Because a memcpy or memmove is also a load, we can't skip it if we
- // didn't remove it.
- if (!isa<MemTransferInst>(BBI))
- continue;
- }
-
- Value *killPointer = 0;
- uint64_t killPointerSize = AliasAnalysis::UnknownSize;
-
- // If we encounter a use of the pointer, it is no longer considered dead
- if (LoadInst *L = dyn_cast<LoadInst>(BBI)) {
- // However, if this load is unused and not volatile, we can go ahead and
- // remove it, and not have to worry about it making our pointer undead!
- if (L->use_empty() && !L->isVolatile()) {
- ++BBI;
- DeleteDeadInstruction(L, &deadPointers);
- ++NumFastOther;
- MadeChange = true;
- continue;
- }
-
- killPointer = L->getPointerOperand();
- } else if (VAArgInst *V = dyn_cast<VAArgInst>(BBI)) {
- killPointer = V->getOperand(0);
- } else if (isa<MemTransferInst>(BBI) &&
- isa<ConstantInt>(cast<MemTransferInst>(BBI)->getLength())) {
- killPointer = cast<MemTransferInst>(BBI)->getSource();
- killPointerSize = cast<ConstantInt>(
- cast<MemTransferInst>(BBI)->getLength())->getZExtValue();
- } else if (AllocaInst *A = dyn_cast<AllocaInst>(BBI)) {
- deadPointers.erase(A);
-
- // Dead alloca's can be DCE'd when we reach them
- if (A->use_empty()) {
- ++BBI;
- DeleteDeadInstruction(A, &deadPointers);
- ++NumFastOther;
+
+ 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;
- } else if (CallSite CS = cast<Value>(BBI)) {
- // If this call does not access memory, it can't
- // be undeadifying any of our pointers.
- if (AA.doesNotAccessMemory(CS))
continue;
-
- unsigned modRef = 0;
- unsigned other = 0;
-
- // Remove any pointers made undead by the call from the dead set
- std::vector<Value*> dead;
- for (SmallPtrSet<Value*, 64>::iterator I = deadPointers.begin(),
- E = deadPointers.end(); I != E; ++I) {
- // HACK: if we detect that our AA is imprecise, it's not
- // worth it to scan the rest of the deadPointers set. Just
- // assume that the AA will return ModRef for everything, and
- // go ahead and bail.
- if (modRef >= 16 && other == 0) {
- deadPointers.clear();
- return MadeChange;
- }
-
- // See if the call site touches it
- AliasAnalysis::ModRefResult A = AA.getModRefInfo(CS, *I,
- getPointerSize(*I));
-
- if (A == AliasAnalysis::ModRef)
- ++modRef;
- else
- ++other;
-
- if (A == AliasAnalysis::ModRef || A == AliasAnalysis::Ref)
- dead.push_back(*I);
}
+ }
- for (std::vector<Value*>::iterator I = dead.begin(), E = dead.end();
- I != E; ++I)
- deadPointers.erase(*I);
-
- continue;
- } else if (isInstructionTriviallyDead(BBI)) {
- // For any non-memory-affecting non-terminators, DCE them as we reach them
- Instruction *Inst = BBI;
- ++BBI;
- DeleteDeadInstruction(Inst, &deadPointers);
+ // 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;
+ }
- killPointer = killPointer->getUnderlyingObject();
+ if (CallSite CS = cast<Value>(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);
- // Deal with undead pointers
- MadeChange |= RemoveUndeadPointers(killPointer, killPointerSize, BBI,
- deadPointers);
- }
-
- return MadeChange;
-}
+ // If this call does not access memory, it can't be loading any of our
+ // pointers.
+ if (AA->doesNotAccessMemory(CS))
+ continue;
-/// RemoveUndeadPointers - check for uses of a pointer that make it
-/// undead when scanning for dead stores to alloca's.
-bool DSE::RemoveUndeadPointers(Value *killPointer, uint64_t killPointerSize,
- BasicBlock::iterator &BBI,
- SmallPtrSet<Value*, 64> &deadPointers) {
- AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
-
- // If the kill pointer can be easily reduced to an alloca,
- // don't bother doing extraneous AA queries.
- if (deadPointers.count(killPointer)) {
- deadPointers.erase(killPointer);
- return false;
- }
-
- // A global can't be in the dead pointer set.
- if (isa<GlobalValue>(killPointer))
- return false;
-
- bool MadeChange = false;
-
- SmallVector<Value*, 16> undead;
-
- for (SmallPtrSet<Value*, 64>::iterator I = deadPointers.begin(),
- E = deadPointers.end(); I != E; ++I) {
- // See if this pointer could alias it
- AliasAnalysis::AliasResult A = AA.alias(*I, getPointerSize(*I),
- 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!
- ++BBI;
- DeleteDeadInstruction(S, &deadPointers);
- ++NumFastStores;
- MadeChange = true;
+ // 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.
+ AliasAnalysis::ModRefResult A =
+ AA->getModRefInfo(CS, I, getPointerSize(I, *AA));
- continue;
+ return A == AliasAnalysis::ModRef || A == AliasAnalysis::Ref;
+ });
- // Otherwise, it is undead
- } else if (A != AliasAnalysis::NoAlias)
- undead.push_back(*I);
- }
+ // 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;
- for (SmallVector<Value*, 16>::iterator I = undead.begin(), E = undead.end();
- I != E; ++I)
- deadPointers.erase(*I);
-
- return MadeChange;
-}
+ continue;
+ }
-/// 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.
-///
-void DSE::DeleteDeadInstruction(Instruction *I,
- SmallPtrSet<Value*, 64> *ValueSet) {
- SmallVector<Instruction*, 32> NowDeadInsts;
-
- NowDeadInsts.push_back(I);
- --NumFastOther;
+ AliasAnalysis::Location LoadedLoc;
- // Before we touch this instruction, remove it from memdep!
- MemoryDependenceAnalysis &MDA = getAnalysis<MemoryDependenceAnalysis>();
- 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.
- MDA.removeInstruction(DeadInst);
-
- for (unsigned op = 0, e = DeadInst->getNumOperands(); op != e; ++op) {
- Value *Op = DeadInst->getOperand(op);
- DeadInst->setOperand(op, 0);
-
- // 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))
- NowDeadInsts.push_back(OpI);
+ // 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 = AA->getLocation(L);
+ } else if (VAArgInst *V = dyn_cast<VAArgInst>(BBI)) {
+ LoadedLoc = AA->getLocation(V);
+ } else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(BBI)) {
+ LoadedLoc = AA->getLocationForSource(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;
}
-
- DeadInst->eraseFromParent();
-
- if (ValueSet) ValueSet->erase(DeadInst);
- } while (!NowDeadInsts.empty());
+
+ // Remove any allocas from the DeadPointer set that are loaded, as this
+ // makes any stores above the access live.
+ RemoveAccessedObjects(LoadedLoc, DeadStackObjects);
+
+ // 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;
+ }
+
+ return MadeChange;
}
-uint64_t DSE::getPointerSize(Value *V) const {
- if (TD) {
- if (AllocaInst *A = dyn_cast<AllocaInst>(V)) {
- // Get size information for the alloca
- if (ConstantInt *C = dyn_cast<ConstantInt>(A->getArraySize()))
- return C->getZExtValue() * TD->getTypeAllocSize(A->getAllocatedType());
- } else {
- assert(isa<Argument>(V) && "Expected AllocaInst or Argument!");
- const PointerType *PT = cast<PointerType>(V->getType());
- return TD->getTypeAllocSize(PT->getElementType());
- }
+/// 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 AliasAnalysis::Location &LoadedLoc,
+ SmallSetVector<Value*, 16> &DeadStackObjects) {
+ const Value *UnderlyingPointer = GetUnderlyingObject(LoadedLoc.Ptr);
+
+ // 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;
}
- return AliasAnalysis::UnknownSize;
+
+ // Remove objects that could alias LoadedLoc.
+ DeadStackObjects.remove_if([&](Value *I) {
+ // See if the loaded location could alias the stack location.
+ AliasAnalysis::Location StackLoc(I, getPointerSize(I, *AA));
+ return !AA->isNoAlias(StackLoc, LoadedLoc);
+ });
}