#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/Local.h"
-#include "llvm/Support/Compiler.h"
using namespace llvm;
STATISTIC(NumFastStores, "Number of stores deleted");
STATISTIC(NumFastOther , "Number of other instrs removed");
namespace {
- struct VISIBILITY_HIDDEN DSE : public FunctionPass {
+ struct DSE : public FunctionPass {
+ TargetData *TD;
+
static char ID; // Pass identification, replacement for typeid
- DSE() : FunctionPass(&ID) {}
+ DSE() : FunctionPass(ID) {}
virtual bool runOnFunction(Function &F) {
bool Changed = false;
+
+ DominatorTree &DT = getAnalysis<DominatorTree>();
+
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);
return Changed;
}
bool runOnBasicBlock(BasicBlock &BB);
- bool handleFreeWithNonTrivialDependency(FreeInst *F, MemDepResult Dep);
+ bool handleFreeWithNonTrivialDependency(const CallInst *F,
+ MemDepResult Dep);
bool handleEndBlock(BasicBlock &BB);
- bool RemoveUndeadPointers(Value* Ptr, uint64_t killPointerSize,
- BasicBlock::iterator& BBI,
- SmallPtrSet<Value*, 64>& deadPointers);
+ bool RemoveUndeadPointers(Value *Ptr, uint64_t killPointerSize,
+ BasicBlock::iterator &BBI,
+ SmallPtrSet<Value*, 64> &deadPointers);
void DeleteDeadInstruction(Instruction *I,
SmallPtrSet<Value*, 64> *deadPointers = 0);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<DominatorTree>();
- AU.addRequired<TargetData>();
AU.addRequired<AliasAnalysis>();
AU.addRequired<MemoryDependenceAnalysis>();
AU.addPreserved<DominatorTree>();
- AU.addPreserved<AliasAnalysis>();
AU.addPreserved<MemoryDependenceAnalysis>();
}
+
+ unsigned getPointerSize(Value *V) const;
};
}
char DSE::ID = 0;
-static RegisterPass<DSE> X("dse", "Dead Store Elimination");
+INITIALIZE_PASS(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) {
+ 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;
+ }
+ }
+ 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;
+}
+
+/// 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 = cast<IntrinsicInst>(I);
+ switch (II->getIntrinsicID()) {
+ default: assert(false && "Unexpected intrinsic!");
+ case Intrinsic::init_trampoline:
+ return II->getArgOperand(0);
+ case Intrinsic::lifetime_end:
+ return II->getArgOperand(1);
+ }
+}
+
+/// getStoreSize - Return the length in bytes of the write by the clobbering
+/// instruction. If variable or unknown, returns -1.
+static unsigned getStoreSize(Instruction *I, const TargetData *TD) {
+ assert(doesClobberMemory(I));
+ if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
+ if (!TD) return -1u;
+ return TD->getTypeStoreSize(SI->getOperand(0)->getType());
+ }
+
+ Value *Len;
+ if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
+ Len = MI->getLength();
+ } else {
+ IntrinsicInst *II = cast<IntrinsicInst>(I);
+ switch (II->getIntrinsicID()) {
+ default: assert(false && "Unexpected intrinsic!");
+ case Intrinsic::init_trampoline:
+ return -1u;
+ case Intrinsic::lifetime_end:
+ Len = II->getArgOperand(0);
+ break;
+ }
+ }
+ if (ConstantInt *LenCI = dyn_cast<ConstantInt>(Len))
+ if (!LenCI->isAllOnesValue())
+ return LenCI->getZExtValue();
+ return -1u;
+}
+
+/// 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.
+///
+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;
+
+ int I1Size = getStoreSize(I1, TD);
+ int I2Size = getStoreSize(I2, TD);
+
+ return I1Size != -1 && I2Size != -1 && I1Size >= I2Size;
+}
+
bool DSE::runOnBasicBlock(BasicBlock &BB) {
- MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
- TargetData &TD = getAnalysis<TargetData>();
+ MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
+ TD = getAnalysisIfAvailable<TargetData>();
bool MadeChange = false;
- // Do a top-down walk on the BB
+ // 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 it's memory dependence.
- if (!isa<StoreInst>(Inst) && !isa<FreeInst>(Inst))
+ // If we find a store or a free, get its memory dependence.
+ if (!doesClobberMemory(Inst) && !isFreeCall(Inst))
continue;
- // Don't molest volatile stores or do queries that will return "clobber".
- if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
- if (SI->isVolatile())
- continue;
-
MemDepResult InstDep = MD.getDependency(Inst);
// Ignore non-local stores.
if (InstDep.isNonLocal()) continue;
// Handle frees whose dependencies are non-trivial.
- if (FreeInst *FI = dyn_cast<FreeInst>(Inst)) {
- MadeChange |= handleFreeWithNonTrivialDependency(FI, InstDep);
+ if (const CallInst *F = isFreeCall(Inst)) {
+ MadeChange |= handleFreeWithNonTrivialDependency(F, InstDep);
continue;
}
- StoreInst *SI = cast<StoreInst>(Inst);
-
// If not a definite must-alias dependency, ignore it.
if (!InstDep.isDef())
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 (StoreInst *DepStore = dyn_cast<StoreInst>(InstDep.getInst()))
- if (TD.getTypeStoreSize(DepStore->getOperand(0)->getType()) <=
- TD.getTypeStoreSize(SI->getOperand(0)->getType())) {
+ 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++;
+ ++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))
+ continue;
// If we're storing the same value back to a pointer that we just
// loaded from, then the store can be removed.
- if (LoadInst *DepLoad = dyn_cast<LoadInst>(InstDep.getInst())) {
- if (SI->getPointerOperand() == DepLoad->getPointerOperand() &&
- SI->getOperand(0) == DepLoad) {
- DeleteDeadInstruction(SI);
- if (BBI != BB.begin())
+ if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
+ if (LoadInst *DepLoad = dyn_cast<LoadInst>(InstDep.getInst())) {
+ if (SI->getPointerOperand() == DepLoad->getPointerOperand() &&
+ SI->getOperand(0) == DepLoad) {
+ // DeleteDeadInstruction can delete the current instruction. Save BBI
+ // in case we need it.
+ WeakVH NextInst(BBI);
+
+ DeleteDeadInstruction(SI);
+
+ if (NextInst == 0) // Next instruction deleted.
+ BBI = BB.begin();
+ else if (BBI != BB.begin()) // Revisit this instruction if possible.
+ --BBI;
+ ++NumFastStores;
+ MadeChange = true;
+ continue;
+ }
+ }
+ }
+
+ // 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++;
+ ++NumFastStores;
MadeChange = true;
continue;
}
/// handleFreeWithNonTrivialDependency - Handle frees of entire structures whose
/// dependency is a store to a field of that structure.
-bool DSE::handleFreeWithNonTrivialDependency(FreeInst *F, MemDepResult Dep) {
+bool DSE::handleFreeWithNonTrivialDependency(const CallInst *F,
+ MemDepResult Dep) {
AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
- StoreInst *Dependency = dyn_cast_or_null<StoreInst>(Dep.getInst());
- if (!Dependency || Dependency->isVolatile())
+ Instruction *Dependency = Dep.getInst();
+ if (!Dependency || !doesClobberMemory(Dependency) || !isElidable(Dependency))
return false;
- Value *DepPointer = Dependency->getPointerOperand()->getUnderlyingObject();
+ Value *DepPointer = getPointerOperand(Dependency)->getUnderlyingObject();
// Check for aliasing.
- if (AA.alias(F->getPointerOperand(), 1, DepPointer, 1) !=
+ if (AA.alias(F->getArgOperand(0), 1, DepPointer, 1) !=
AliasAnalysis::MustAlias)
return false;
// DCE instructions only used to calculate that store
DeleteDeadInstruction(Dependency);
- NumFastStores++;
+ ++NumFastStores;
return true;
}
/// store i32 1, i32* %A
/// ret void
bool DSE::handleEndBlock(BasicBlock &BB) {
- TargetData &TD = getAnalysis<TargetData>();
AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
bool MadeChange = false;
--BBI;
// If we find a store whose pointer is dead.
- if (StoreInst* S = dyn_cast<StoreInst>(BBI)) {
- if (!S->isVolatile()) {
+ if (doesClobberMemory(BBI)) {
+ if (isElidable(BBI)) {
// See through pointer-to-pointer bitcasts
- Value* pointerOperand = S->getPointerOperand()->getUnderlyingObject();
+ 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.
- BBI++;
- DeleteDeadInstruction(S, &deadPointers);
- NumFastStores++;
+ Instruction *Dead = BBI;
+ ++BBI;
+ DeleteDeadInstruction(Dead, &deadPointers);
+ ++NumFastStores;
MadeChange = true;
+ continue;
}
}
- continue;
- }
-
- // We can also remove memcpy's to local variables at the end of a function.
- if (MemCpyInst *M = dyn_cast<MemCpyInst>(BBI)) {
- Value *dest = M->getDest()->getUnderlyingObject();
-
- if (deadPointers.count(dest)) {
- BBI++;
- DeleteDeadInstruction(M, &deadPointers);
- NumFastOther++;
- MadeChange = true;
+ // 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;
- }
-
- // Because a memcpy is also a load, we can't skip it if we didn't remove
- // it.
}
- Value* killPointer = 0;
+ Value *killPointer = 0;
uint64_t killPointerSize = ~0UL;
// If we encounter a use of the pointer, it is no longer considered dead
// 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++;
+ ++BBI;
DeleteDeadInstruction(L, &deadPointers);
- NumFastOther++;
+ ++NumFastOther;
MadeChange = true;
continue;
}
killPointer = L->getPointerOperand();
- } else if (VAArgInst* V = dyn_cast<VAArgInst>(BBI)) {
+ } else if (VAArgInst *V = dyn_cast<VAArgInst>(BBI)) {
killPointer = V->getOperand(0);
- } else if (isa<MemCpyInst>(BBI) &&
- isa<ConstantInt>(cast<MemCpyInst>(BBI)->getLength())) {
- killPointer = cast<MemCpyInst>(BBI)->getSource();
+ } else if (isa<MemTransferInst>(BBI) &&
+ isa<ConstantInt>(cast<MemTransferInst>(BBI)->getLength())) {
+ killPointer = cast<MemTransferInst>(BBI)->getSource();
killPointerSize = cast<ConstantInt>(
- cast<MemCpyInst>(BBI)->getLength())->getZExtValue();
- } else if (AllocaInst
* A = dyn_cast<AllocaInst>(BBI)) {
+ 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++;
+ ++BBI;
DeleteDeadInstruction(A, &deadPointers);
- NumFastOther++;
+ ++NumFastOther;
MadeChange = true;
}
continue;
- } else if (CallSite::get(BBI).getInstruction() != 0) {
+ } else if (CallSite CS = cast<Value>(BBI)) {
// If this call does not access memory, it can't
// be undeadifying any of our pointers.
- CallSite CS = CallSite::get(BBI);
if (AA.doesNotAccessMemory(CS))
continue;
deadPointers.clear();
return MadeChange;
}
-
- // Get size information for the alloca
- unsigned pointerSize = ~0U;
- if (AllocaInst* A = dyn_cast<AllocaInst>(*I)) {
- if (ConstantInt* C = dyn_cast<ConstantInt>(A->getArraySize()))
- pointerSize = C->getZExtValue() *
- TD.getTypeAllocSize(A->getAllocatedType());
- } else {
- const PointerType* PT = cast<PointerType>(
- cast<Argument>(*I)->getType());
- pointerSize = TD.getTypeAllocSize(PT->getElementType());
- }
-
+
// See if the call site touches it
- AliasAnalysis::ModRefResult A = AA.getModRefInfo(CS, *I, pointerSize);
+ AliasAnalysis::ModRefResult A = AA.getModRefInfo(CS, *I,
+ getPointerSize(*I));
if (A == AliasAnalysis::ModRef)
- modRef++;
+ ++modRef;
else
- other++;
+ ++other;
if (A == AliasAnalysis::ModRef || A == AliasAnalysis::Ref)
dead.push_back(*I);
} else if (isInstructionTriviallyDead(BBI)) {
// For any non-memory-affecting non-terminators, DCE them as we reach them
Instruction *Inst = BBI;
- BBI++;
+ ++BBI;
DeleteDeadInstruction(Inst, &deadPointers);
- NumFastOther++;
+ ++NumFastOther;
MadeChange = true;
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,
+bool DSE::RemoveUndeadPointers(Value *killPointer, uint64_t killPointerSize,
BasicBlock::iterator &BBI,
- SmallPtrSet<Value*, 64>& deadPointers) {
- TargetData &TD = getAnalysis<TargetData>();
+ 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)) {
bool MadeChange = false;
SmallVector<Value*, 16> undead;
-
+
for (SmallPtrSet<Value*, 64>::iterator I = deadPointers.begin(),
- E = deadPointers.end(); I != E; ++I) {
- // Get size information for the alloca.
- unsigned pointerSize = ~0U;
- if (AllocaInst* A = dyn_cast<AllocaInst>(*I)) {
- if (ConstantInt* C = dyn_cast<ConstantInt>(A->getArraySize()))
- pointerSize = C->getZExtValue() *
- TD.getTypeAllocSize(A->getAllocatedType());
- } else {
- const PointerType* PT = cast<PointerType>(cast<Argument>(*I)->getType());
- pointerSize = TD.getTypeAllocSize(PT->getElementType());
- }
-
+ E = deadPointers.end(); I != E; ++I) {
// See if this pointer could alias it
- AliasAnalysis::AliasResult A = AA.alias(*I, pointerSize,
+ 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);
+ StoreInst *S = cast<StoreInst>(BBI);
// Remove it!
- BBI++;
+ ++BBI;
DeleteDeadInstruction(S, &deadPointers);
- NumFastStores++;
+ ++NumFastStores;
MadeChange = true;
continue;
// Before we touch this instruction, remove it from memdep!
MemoryDependenceAnalysis &MDA = getAnalysis<MemoryDependenceAnalysis>();
- while (!NowDeadInsts.empty()) {
- Instruction *DeadInst = NowDeadInsts.back();
- NowDeadInsts.pop_back();
+ do {
+ Instruction *DeadInst = NowDeadInsts.pop_back_val();
++NumFastOther;
DeadInst->eraseFromParent();
if (ValueSet) ValueSet->erase(DeadInst);
+ } while (!NowDeadInsts.empty());
+}
+
+unsigned 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());
+ }
}
+ return ~0U;
}
projects / oota-llvm.git / blobdiff