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Add support for eliminating memcpy's at the end of functions. Also fix some errors I noticed in

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the handling of eliminating stores to byval arguments.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@46494 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson
2008-01-29 06:18:36 +00:00
parent b7cbab8b28
commit a34d8a0d83
1 changed files with 63 additions and 26 deletions
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89
lib/Transforms/Scalar/DeadStoreElimination.cpp
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@@ -20,6 +20,7 @@
#include "llvm/Constants.h" #include "llvm/Constants.h"
#include "llvm/Function.h" #include "llvm/Function.h"
#include "llvm/Instructions.h" #include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Pass.h" #include "llvm/Pass.h"
#include "llvm/ADT/SetVector.h" #include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/SmallPtrSet.h"
@@ -53,7 +54,7 @@ namespace {
bool handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead); bool handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead);
bool RemoveUndeadPointers(Value* pointer, bool RemoveUndeadPointers(Value* pointer,
BasicBlock::iterator& BBI, BasicBlock::iterator& BBI,
SmallPtrSet<AllocaInst*, 64>& deadPointers, SmallPtrSet<Value*, 64>& deadPointers,
SetVector<Instruction*>& possiblyDead); SetVector<Instruction*>& possiblyDead);
void DeleteDeadInstructionChains(Instruction *I, void DeleteDeadInstructionChains(Instruction *I,
SetVector<Instruction*> &DeadInsts); SetVector<Instruction*> &DeadInsts);
@@ -249,13 +250,17 @@ bool DSE::handleEndBlock(BasicBlock& BB,
bool MadeChange = false; bool MadeChange = false;
// Pointers alloca'd in this function are dead in the end block // 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(); BasicBlock *Entry = BB.getParent()->begin();
for (BasicBlock::iterator I = Entry->begin(), E = Entry->end(); I != E; ++I) for (BasicBlock::iterator I = Entry->begin(), E = Entry->end(); I != E; ++I)
if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
deadPointers.insert(AI); 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 // Scan the basic block backwards
for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){ for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
@@ -270,10 +275,7 @@ bool DSE::handleEndBlock(BasicBlock& BB,
// Alloca'd pointers or byval arguments (which are functionally like // Alloca'd pointers or byval arguments (which are functionally like
// alloca's) are valid candidates for removal. // alloca's) are valid candidates for removal.
if ( (isa<AllocaInst>(pointerOperand) && if (deadPointers.count(pointerOperand)) {
deadPointers.count(cast<AllocaInst>(pointerOperand))) ||
(isa<Argument>(pointerOperand) &&
cast<Argument>(pointerOperand)->hasByValAttr())) {
// Remove it! // Remove it!
MD.removeInstruction(S); MD.removeInstruction(S);
@@ -291,6 +293,32 @@ bool DSE::handleEndBlock(BasicBlock& BB,
} }
continue; 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->getSource()))
possiblyDead.insert(D);
if (Instruction* D = dyn_cast<Instruction>(M->getLength()))
possiblyDead.insert(D);
if (Instruction* D = dyn_cast<Instruction>(M->getRawDest()))
possiblyDead.insert(D);
BBI++;
M->eraseFromParent();
NumFastOther++;
MadeChange = true;
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;
@@ -314,8 +342,8 @@ bool DSE::handleEndBlock(BasicBlock& BB,
unsigned other = 0; unsigned other = 0;
// Remove any pointers made undead by the call from the dead set // Remove any pointers made undead by the call from the dead set
std::vector<Instruction*> dead; std::vector<Value*> dead;
for (SmallPtrSet<AllocaInst*, 64>::iterator I = deadPointers.begin(), for (SmallPtrSet<Value*, 64>::iterator I = deadPointers.begin(),
E = deadPointers.end(); I != E; ++I) { E = deadPointers.end(); I != E; ++I) {
// HACK: if we detect that our AA is imprecise, it's not // HACK: if we detect that our AA is imprecise, it's not
// worth it to scan the rest of the deadPointers set. Just // worth it to scan the rest of the deadPointers set. Just
@@ -328,9 +356,15 @@ bool DSE::handleEndBlock(BasicBlock& BB,
// Get size information for the alloca // Get size information for the alloca
unsigned pointerSize = ~0U; unsigned pointerSize = ~0U;
if (ConstantInt* C = dyn_cast<ConstantInt>((*I)->getArraySize())) if (AllocaInst* A = dyn_cast<AllocaInst>(*I)) {
pointerSize = C->getZExtValue() * \ if (ConstantInt* C = dyn_cast<ConstantInt>(A->getArraySize()))
TD.getABITypeSize((*I)->getAllocatedType()); 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 // See if the call site touches it
AliasAnalysis::ModRefResult A = AA.getModRefInfo(CS, *I, pointerSize); AliasAnalysis::ModRefResult A = AA.getModRefInfo(CS, *I, pointerSize);
@@ -344,10 +378,9 @@ bool DSE::handleEndBlock(BasicBlock& BB,
dead.push_back(*I); 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) I != E; ++I)
if (AllocaInst *AI = dyn_cast<AllocaInst>(*I)) deadPointers.erase(*I);
deadPointers.erase(AI);
continue; continue;
} }
@@ -369,7 +402,7 @@ bool DSE::handleEndBlock(BasicBlock& BB,
/// undead when scanning for dead stores to alloca's. /// undead when scanning for dead stores to alloca's.
bool DSE::RemoveUndeadPointers(Value* killPointer, bool DSE::RemoveUndeadPointers(Value* killPointer,
BasicBlock::iterator& BBI, BasicBlock::iterator& BBI,
SmallPtrSet<AllocaInst*, 64>& deadPointers, SmallPtrSet<Value*, 64>& deadPointers,
SetVector<Instruction*>& possiblyDead) { SetVector<Instruction*>& possiblyDead) {
TargetData &TD = getAnalysis<TargetData>(); TargetData &TD = getAnalysis<TargetData>();
AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
@@ -377,9 +410,8 @@ bool DSE::RemoveUndeadPointers(Value* killPointer,
// If the kill pointer can be easily reduced to an alloca, // If the kill pointer can be easily reduced to an alloca,
// don't bother doing extraneous AA queries // don't bother doing extraneous AA queries
if (AllocaInst* A = dyn_cast<AllocaInst>(killPointer)) { if (deadPointers.count(killPointer)) {
if (deadPointers.count(A)) deadPointers.erase(killPointer);
deadPointers.erase(A);
return false; return false;
} else if (isa<GlobalValue>(killPointer)) { } else if (isa<GlobalValue>(killPointer)) {
// A global can't be in the dead pointer set // A global can't be in the dead pointer set
@@ -388,15 +420,21 @@ bool DSE::RemoveUndeadPointers(Value* killPointer,
bool MadeChange = 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) { E = deadPointers.end(); I != E; ++I) {
// Get size information for the alloca // Get size information for the alloca
unsigned pointerSize = ~0U; unsigned pointerSize = ~0U;
if (ConstantInt* C = dyn_cast<ConstantInt>((*I)->getArraySize())) if (AllocaInst* A = dyn_cast<AllocaInst>(*I)) {
pointerSize = C->getZExtValue() * \ if (ConstantInt* C = dyn_cast<ConstantInt>(A->getArraySize()))
TD.getABITypeSize((*I)->getAllocatedType()); 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 // See if this pointer could alias it
AliasAnalysis::AliasResult A = AA.alias(*I, pointerSize, AliasAnalysis::AliasResult A = AA.alias(*I, pointerSize,
@@ -427,10 +465,9 @@ bool DSE::RemoveUndeadPointers(Value* killPointer,
undead.push_back(*I); 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) I != E; ++I)
if (AllocaInst *AI = dyn_cast<AllocaInst>(*I)) deadPointers.erase(*I);
deadPointers.erase(AI);
return MadeChange; return MadeChange;
} }