//
// 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"
Instruction* dependency,
SetVector<Instruction*>& possiblyDead);
bool handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead);
- bool RemoveUndeadPointers(Value* pointer,
+ bool RemoveUndeadPointers(Value* pointer, uint64_t killPointerSize,
BasicBlock::iterator& BBI,
- SmallPtrSet<AllocaInst*, 64>& deadPointers,
+ SmallPtrSet<Value*, 64>& deadPointers,
SetVector<Instruction*>& possiblyDead);
void DeleteDeadInstructionChains(Instruction *I,
SetVector<Instruction*> &DeadInsts);
/// 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) {
+ void TranslatePointerBitCasts(Value*& v, bool zeroGepsOnly = false) {
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);
+ if (!zeroGepsOnly || G->hasAllZeroIndices()) {
+ v = G->getOperand(0);
+ } else {
+ break;
+ }
else
break;
}
bool DSE::runOnBasicBlock(BasicBlock &BB) {
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
-
+ TargetData &TD = getAnalysis<TargetData>();
+
// Record the last-seen store to this pointer
DenseMap<Value*, StoreInst*> lastStore;
// Record instructions possibly made dead by deleting a store
continue;
Value* pointer = 0;
- if (StoreInst* S = dyn_cast<StoreInst>(BBI))
- pointer = S->getPointerOperand();
- else
+ if (StoreInst* S = dyn_cast<StoreInst>(BBI)) {
+ if (!S->isVolatile())
+ pointer = S->getPointerOperand();
+ else
+ continue;
+ } else
pointer = cast<FreeInst>(BBI)->getPointerOperand();
+ TranslatePointerBitCasts(pointer, true);
StoreInst*& last = lastStore[pointer];
bool deletedStore = false;
while (dep != MemoryDependenceAnalysis::None &&
dep != MemoryDependenceAnalysis::NonLocal &&
isa<StoreInst>(dep)) {
- if (dep != last) {
+ if (dep != last ||
+ TD.getTypeStoreSize(last->getOperand(0)->getType()) >
+ TD.getTypeStoreSize(BBI->getOperand(0)->getType())) {
dep = MD.getDependency(BBI, dep);
continue;
}
possiblyDead.insert(D);
if (Instruction* D = dyn_cast<Instruction>(last->getOperand(1)))
possiblyDead.insert(D);
-
+
last->eraseFromParent();
NumFastStores++;
deletedStore = true;
StoreInst* dependency = dyn_cast<StoreInst>(dep);
if (!dependency)
return false;
+ else if (dependency->isVolatile())
+ return false;
Value* depPointer = dependency->getPointerOperand();
const Type* depType = dependency->getOperand(0)->getType();
- unsigned depPointerSize = TD.getTypeSize(depType);
-
+ unsigned depPointerSize = TD.getTypeStoreSize(depType);
+
// Check for aliasing
- AliasAnalysis::AliasResult A = AA.alias(F->getPointerOperand(), ~0UL,
+ AliasAnalysis::AliasResult A = AA.alias(F->getPointerOperand(), ~0U,
depPointer, depPointerSize);
-
+
if (A == AliasAnalysis::MustAlias) {
// Remove it!
MD.removeInstruction(dependency);
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
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 (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 (!S->isVolatile()) {
+ Value* pointerOperand = S->getPointerOperand();
+ // See through pointer-to-pointer bitcasts
+ TranslatePointerBitCasts(pointerOperand);
- if (deadPointers.count(pointerOperand)){
- // Remove it!
- MD.removeInstruction(S);
+ // Alloca'd pointers or byval arguments (which are functionally like
+ // alloca's) are valid candidates for removal.
+ 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)))
+ // 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;
+ }
+ }
+
+ continue;
+
+ // We can also remove memcpy's to local variables at the end of a function
+ } else if (MemCpyInst* M = dyn_cast<MemCpyInst>(BBI)) {
+ Value* dest = M->getDest();
+ TranslatePointerBitCasts(dest);
+
+ if (deadPointers.count(dest)) {
+ MD.removeInstruction(M);
+
+ // DCE instructions only used to calculate that memcpy
+ if (Instruction* D = dyn_cast<Instruction>(M->getRawSource()))
+ possiblyDead.insert(D);
+ if (Instruction* D = dyn_cast<Instruction>(M->getLength()))
possiblyDead.insert(D);
- if (Instruction* D = dyn_cast<Instruction>(S->getOperand(1)))
+ if (Instruction* D = dyn_cast<Instruction>(M->getRawDest()))
possiblyDead.insert(D);
BBI++;
- S->eraseFromParent();
- NumFastStores++;
+ M->eraseFromParent();
+ NumFastOther++;
MadeChange = true;
+
+ continue;
}
- continue;
+ // Because a memcpy is also a load, we can't skip it if we didn't remove it
}
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)) {
+ // However, if this load is unused, we can go ahead and remove it, and
+ // not have to worry about it making our pointer undead!
+ if (L->use_empty()) {
+ MD.removeInstruction(L);
+
+ // DCE instructions only used to calculate that load
+ if (Instruction* D = dyn_cast<Instruction>(L->getPointerOperand()))
+ possiblyDead.insert(D);
+
+ BBI++;
+ L->eraseFromParent();
+ NumFastOther++;
+ MadeChange = true;
+ possiblyDead.remove(L);
+
+ continue;
+ }
+
killPointer = L->getPointerOperand();
} 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();
+ killPointerSize = cast<ConstantInt>(
+ cast<MemCpyInst>(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()) {
+ MD.removeInstruction(A);
+
+ // DCE instructions only used to calculate that load
+ if (Instruction* D = dyn_cast<Instruction>(A->getArraySize()))
+ possiblyDead.insert(D);
+
+ BBI++;
+ A->eraseFromParent();
+ NumFastOther++;
+ MadeChange = true;
+ possiblyDead.remove(A);
+ }
+
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 (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) {
+ // 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;
+ }
+
// Get size information for the alloca
- unsigned pointerSize = ~0UL;
- if (ConstantInt* C = dyn_cast<ConstantInt>((*I)->getArraySize()))
- pointerSize = C->getZExtValue() * \
- TD.getTypeSize((*I)->getAllocatedType());
-
+ unsigned pointerSize = ~0U;
+ if (AllocaInst* A = dyn_cast<AllocaInst>(*I)) {
+ if (ConstantInt* C = dyn_cast<ConstantInt>(A->getArraySize()))
+ pointerSize = C->getZExtValue() * \
+ TD.getABITypeSize(A->getAllocatedType());
+ } else {
+ const PointerType* PT = cast<PointerType>(
+ cast<Argument>(*I)->getType());
+ pointerSize = TD.getABITypeSize(PT->getElementType());
+ }
+
// See if the call site touches it
- AliasAnalysis::ModRefResult A = AA.getModRefInfo(CallSite::get(BBI),
- *I, pointerSize);
+ AliasAnalysis::ModRefResult A = AA.getModRefInfo(CS, *I, pointerSize);
+
+ 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 {
+ // For any non-memory-affecting non-terminators, DCE them as we reach them
+ Instruction *CI = BBI;
+ if (!CI->isTerminator() && CI->use_empty() && !isa<FreeInst>(CI)) {
+
+ // DCE instructions only used to calculate that load
+ for (Instruction::op_iterator OI = CI->op_begin(), OE = CI->op_end();
+ OI != OE; ++OI)
+ if (Instruction* D = dyn_cast<Instruction>(OI))
+ possiblyDead.insert(D);
+
+ BBI++;
+ CI->eraseFromParent();
+ NumFastOther++;
+ MadeChange = true;
+ possiblyDead.remove(CI);
+
+ continue;
+ }
}
if (!killPointer)
continue;
+ TranslatePointerBitCasts(killPointer);
+
// Deal with undead pointers
- MadeChange |= RemoveUndeadPointers(killPointer, BBI,
+ MadeChange |= RemoveUndeadPointers(killPointer, killPointerSize, BBI,
deadPointers, possiblyDead);
}
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,
+/// 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<AllocaInst*, 64>& deadPointers,
+ SmallPtrSet<Value*, 64>& deadPointers,
SetVector<Instruction*>& possiblyDead) {
TargetData &TD = getAnalysis<TargetData>();
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;
+ } else if (isa<GlobalValue>(killPointer)) {
+ // A global can't be in the dead pointer set
+ return false;
+ }
+
bool MadeChange = false;
- std::vector<Instruction*> undead;
+ std::vector<Value*> undead;
- for (SmallPtrSet<AllocaInst*, 64>::iterator I = deadPointers.begin(),
+ 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());
-
+ unsigned pointerSize = ~0U;
+ if (AllocaInst* A = dyn_cast<AllocaInst>(*I)) {
+ if (ConstantInt* C = dyn_cast<ConstantInt>(A->getArraySize()))
+ pointerSize = C->getZExtValue() * \
+ TD.getABITypeSize(A->getAllocatedType());
+ } else {
+ const PointerType* PT = cast<PointerType>(
+ cast<Argument>(*I)->getType());
+ pointerSize = TD.getABITypeSize(PT->getElementType());
+ }
+
// See if this pointer could alias it
AliasAnalysis::AliasResult A = AA.alias(*I, pointerSize,
- killPointer, ~0UL);
+ killPointer, killPointerSize);
// If it must-alias and a store, we can delete it
if (isa<StoreInst>(BBI) && A == AliasAnalysis::MustAlias) {
undead.push_back(*I);
}
- for (std::vector<Instruction*>::iterator I = undead.begin(), E = undead.end();
+ for (std::vector<Value*>::iterator I = undead.begin(), E = undead.end();
I != E; ++I)
- deadPointers.erase(*I);
+ deadPointers.erase(*I);
return MadeChange;
}
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