//
// 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.
//
//===----------------------------------------------------------------------===//
//
#include "llvm/Constants.h"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
+#include "llvm/IntrinsicInst.h"
#include "llvm/Pass.h"
-#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#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((intptr_t)&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,
- Instruction* dependency,
- SetVector<Instruction*>& possiblyDead);
- bool handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead);
- bool RemoveUndeadPointers(Value* pointer,
- BasicBlock::iterator& BBI,
- SmallPtrSet<AllocaInst*, 64>& deadPointers,
- SetVector<Instruction*>& possiblyDead);
- void DeleteDeadInstructionChains(Instruction *I,
- SetVector<Instruction*> &DeadInsts);
+ 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);
+ void DeleteDeadInstruction(Instruction *I,
+ SmallPtrSet<Value*, 64> *deadPointers = 0);
- /// 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;
- }
- }
// getAnalysisUsage - We require post dominance frontiers (aka Control
// Dependence Graph)
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
- AU.addRequired<TargetData>();
+ AU.addRequired<DominatorTree>();
AU.addRequired<AliasAnalysis>();
AU.addRequired<MemoryDependenceAnalysis>();
- AU.addPreserved<AliasAnalysis>();
+ AU.addPreserved<DominatorTree>();
AU.addPreserved<MemoryDependenceAnalysis>();
}
+
+ unsigned getPointerSize(Value *V) const;
};
- char DSE::ID = 0;
- RegisterPass<DSE> X("dse", "Dead Store Elimination");
}
+char DSE::ID = 0;
+INITIALIZE_PASS(DSE, "dse", "Dead Store Elimination", false, false);
+
FunctionPass *llvm::createDeadStoreEliminationPass() { return new DSE(); }
-bool DSE::runOnBasicBlock(BasicBlock &BB) {
- MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
+/// 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();
- // Record the last-seen store to this pointer
- DenseMap<Value*, StoreInst*> lastStore;
- // Record instructions possibly made dead by deleting a store
- SetVector<Instruction*> possiblyDead;
+ // 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>();
+ TD = getAnalysisIfAvailable<TargetData>();
+
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++;
+
+ // If we find a store or a free, get its memory dependence.
+ if (!doesClobberMemory(Inst) && !isFreeCall(Inst))
continue;
-
- Value* pointer = 0;
- if (StoreInst* S = dyn_cast<StoreInst>(BBI))
- pointer = S->getPointerOperand();
- else
- pointer = cast<FreeInst>(BBI)->getPointerOperand();
-
- 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);
- 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;
+
+ 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);
+ continue;
+ }
+
+ // 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 (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))
+ 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) {
+ // DeleteDeadInstruction can delete the current instruction. Save BBI
+ // in case we need it.
+ WeakVH NextInst(BBI);
+
+ DeleteDeadInstruction(SI);
- break;
+ if (NextInst == 0) // Next instruction deleted.
+ BBI = BB.begin();
+ else if (BBI != BB.begin()) // Revisit this instruction if possible.
+ --BBI;
+ ++NumFastStores;
+ MadeChange = true;
+ continue;
+ }
}
}
- // 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;
- } else {
- // Update our most-recent-store map.
- last = cast<StoreInst>(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;
+ }
}
}
- // If this block ends in a return, unwind, unreachable, and eventually
- // tailcall, then all allocas are dead at its end.
+ // 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, possiblyDead);
-
- // Do a trivial DCE
- while (!possiblyDead.empty()) {
- Instruction *I = possiblyDead.back();
- possiblyDead.pop_back();
- DeleteDeadInstructionChains(I, possiblyDead);
- }
+ 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(FreeInst* F, Instruction* dep,
- SetVector<Instruction*>& possiblyDead) {
- TargetData &TD = getAnalysis<TargetData>();
+/// dependency is a store to a field of that structure.
+bool DSE::handleFreeWithNonTrivialDependency(const CallInst *F,
+ MemDepResult Dep) {
AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
- MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
- if (dep == MemoryDependenceAnalysis::None ||
- dep == MemoryDependenceAnalysis::NonLocal)
+ Instruction *Dependency = Dep.getInst();
+ if (!Dependency || !doesClobberMemory(Dependency) || !isElidable(Dependency))
return false;
- StoreInst* dependency = dyn_cast<StoreInst>(dep);
- if (!dependency)
+ Value *DepPointer = getPointerOperand(Dependency)->getUnderlyingObject();
+
+ // Check for aliasing.
+ if (AA.alias(F->getArgOperand(0), 1, DepPointer, 1) !=
+ AliasAnalysis::MustAlias)
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;
- }
-
- return false;
+ // DCE instructions only used to calculate that store
+ DeleteDeadInstruction(Dependency);
+ ++NumFastStores;
+ return true;
}
/// handleEndBlock - Remove dead stores to stack-allocated locations in the
/// ...
/// store i32 1, i32* %A
/// ret void
-bool DSE::handleEndBlock(BasicBlock& BB,
- SetVector<Instruction*>& possiblyDead) {
- TargetData &TD = getAnalysis<TargetData>();
+bool DSE::handleEndBlock(BasicBlock &BB) {
AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
- MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
bool MadeChange = false;
// Pointers alloca'd in this function are dead in the end block
- SmallPtrSet<AllocaInst*, 64> deadPointers;
+ SmallPtrSet<Value*, 64> deadPointers;
- // Find all of the alloca'd pointers in the entry block
+ // 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 (Function::arg_iterator AI = BB.getParent()->arg_begin(),
+ AE = BB.getParent()->arg_end(); AI != AE; ++AI)
+ if (AI->hasByValAttr())
+ deadPointers.insert(AI);
+
// Scan the basic block backwards
for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
--BBI;
- if (deadPointers.empty())
- break;
-
- // If we find a store whose pointer is dead...
- if (StoreInst* S = dyn_cast<StoreInst>(BBI)) {
- Value* pointerOperand = S->getPointerOperand();
- // 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++;
- MadeChange = true;
+ // 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;
+ }
}
- continue;
+ // 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;
+ Value *killPointer = 0;
+ uint64_t killPointerSize = ~0UL;
// If we encounter a use of the pointer, it is no longer considered dead
- if (LoadInst* L = dyn_cast<LoadInst>(BBI)) {
+ 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)) {
+ } else if (VAArgInst *V = dyn_cast<VAArgInst>(BBI)) {
killPointer = V->getOperand(0);
- } else if (AllocaInst* A = dyn_cast<AllocaInst>(BBI)) {
+ } 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;
+ MadeChange = true;
+ }
+
continue;
} else if (CallSite::get(BBI).getInstruction() != 0) {
// If this call does not access memory, it can't
// be undeadifying any of our pointers.
CallSite CS = CallSite::get(BBI);
- if (CS.getCalledFunction() &&
- AA.doesNotAccessMemory(CS.getCalledFunction()))
+ 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<Instruction*> dead;
- for (SmallPtrSet<AllocaInst*, 64>::iterator I = deadPointers.begin(),
+ std::vector<Value*> dead;
+ for (SmallPtrSet<Value*, 64>::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());
+ // 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, pointerSize);
+ 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<Instruction*>::iterator I = dead.begin(), E = dead.end();
+ 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);
+ ++NumFastOther;
+ MadeChange = true;
+ continue;
}
if (!killPointer)
continue;
-
+
+ killPointer = killPointer->getUnderlyingObject();
+
// Deal with undead pointers
- MadeChange |= RemoveUndeadPointers(killPointer, BBI,
- deadPointers, possiblyDead);
+ MadeChange |= RemoveUndeadPointers(killPointer, killPointerSize, BBI,
+ deadPointers);
}
return MadeChange;
}
-/// RemoveUndeadPointers - takes an instruction and a setvector of
-/// dead instructions. If I is dead, it is erased, and its operands are
-/// checked for deadness. If they are dead, they are added to the dead
-/// setvector.
-bool DSE::RemoveUndeadPointers(Value* killPointer,
- BasicBlock::iterator& BBI,
- SmallPtrSet<AllocaInst*, 64>& deadPointers,
- SetVector<Instruction*>& possiblyDead) {
- TargetData &TD = getAnalysis<TargetData>();
+/// 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>();
- MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
-
+
+ // 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;
- std::vector<Instruction*> undead;
-
- for (SmallPtrSet<AllocaInst*, 64>::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());
-
+ 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, pointerSize,
- killPointer, ~0UL);
+ 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!
- 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++;
+ ++BBI;
+ DeleteDeadInstruction(S, &deadPointers);
+ ++NumFastStores;
MadeChange = true;
continue;
// Otherwise, it is undead
- } else if (A != AliasAnalysis::NoAlias)
- undead.push_back(*I);
+ } else if (A != AliasAnalysis::NoAlias)
+ undead.push_back(*I);
}
- for (std::vector<Instruction*>::iterator I = undead.begin(), E = undead.end();
+ for (SmallVector<Value*, 16>::iterator I = undead.begin(), E = undead.end();
I != E; ++I)
- deadPointers.erase(*I);
+ deadPointers.erase(*I);
return MadeChange;
}
-/// DeleteDeadInstructionChains - takes an instruction and a setvector of
-/// dead instructions. If I is dead, it is erased, and its operands are
-/// checked for deadness. If they are dead, they are added to the dead
-/// setvector.
-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.
+/// 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;
+
+ // Before we touch this instruction, remove it from memdep!
+ MemoryDependenceAnalysis &MDA = getAnalysis<MemoryDependenceAnalysis>();
+ do {
+ Instruction *DeadInst = NowDeadInsts.pop_back_val();
- I->setOperand(i, 0); // Drop from the operand list.
- }
+ ++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);
+ }
+
+ DeadInst->eraseFromParent();
+
+ if (ValueSet) ValueSet->erase(DeadInst);
+ } while (!NowDeadInsts.empty());
+}
- I->eraseFromParent();
- ++NumFastOther;
+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