Author: resistor
Date: Tue Jan 29 00:18:36 2008
New Revision: 46494
URL: http://llvm.org/viewvc/llvm-project?rev=46494&view=rev
Log:
Add support for eliminating memcpy's at the end of functions. Also fix some
errors I noticed in
the handling of eliminating stores to byval arguments.
Modified:
llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
URL:
http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp?rev=46494&r1=46493&r2=46494&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp Tue Jan 29
00:18:36 2008
@@ -20,6 +20,7 @@
#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"
@@ -53,7 +54,7 @@
bool handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead);
bool RemoveUndeadPointers(Value* pointer,
BasicBlock::iterator& BBI,
- SmallPtrSet<AllocaInst*, 64>& deadPointers,
+ SmallPtrSet<Value*, 64>& deadPointers,
SetVector<Instruction*>& possiblyDead);
void DeleteDeadInstructionChains(Instruction *I,
SetVector<Instruction*> &DeadInsts);
@@ -249,13 +250,17 @@
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(); ){
@@ -270,10 +275,7 @@
// Alloca'd pointers or byval arguments (which are functionally like
// alloca's) are valid candidates for removal.
- if ( (isa<AllocaInst>(pointerOperand) &&
- deadPointers.count(cast<AllocaInst>(pointerOperand))) ||
- (isa<Argument>(pointerOperand) &&
- cast<Argument>(pointerOperand)->hasByValAttr())) {
+ if (deadPointers.count(pointerOperand)) {
// Remove it!
MD.removeInstruction(S);
@@ -291,6 +293,32 @@
}
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;
@@ -314,8 +342,8 @@
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
@@ -328,9 +356,15 @@
// Get size information for the alloca
unsigned pointerSize = ~0U;
- if (ConstantInt* C = dyn_cast<ConstantInt>((*I)->getArraySize()))
- pointerSize = C->getZExtValue() * \
- TD.getABITypeSize((*I)->getAllocatedType());
+ 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(CS, *I, pointerSize);
@@ -344,10 +378,9 @@
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)
- if (AllocaInst *AI = dyn_cast<AllocaInst>(*I))
- deadPointers.erase(AI);
+ deadPointers.erase(*I);
continue;
}
@@ -369,7 +402,7 @@
/// undead when scanning for dead stores to alloca's.
bool DSE::RemoveUndeadPointers(Value* killPointer,
BasicBlock::iterator& BBI,
- SmallPtrSet<AllocaInst*, 64>& deadPointers,
+ SmallPtrSet<Value*, 64>& deadPointers,
SetVector<Instruction*>& possiblyDead) {
TargetData &TD = getAnalysis<TargetData>();
AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
@@ -377,9 +410,8 @@
// If the kill pointer can be easily reduced to an alloca,
// don't bother doing extraneous AA queries
- if (AllocaInst* A = dyn_cast<AllocaInst>(killPointer)) {
- if (deadPointers.count(A))
- deadPointers.erase(A);
+ if (deadPointers.count(killPointer)) {
+ deadPointers.erase(killPointer);
return false;
} else if (isa<GlobalValue>(killPointer)) {
// A global can't be in the dead pointer set
@@ -388,15 +420,21 @@
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 = ~0U;
- if (ConstantInt* C = dyn_cast<ConstantInt>((*I)->getArraySize()))
- pointerSize = C->getZExtValue() * \
- TD.getABITypeSize((*I)->getAllocatedType());
+ 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,
@@ -427,10 +465,9 @@
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)
- if (AllocaInst *AI = dyn_cast<AllocaInst>(*I))
- deadPointers.erase(AI);
+ deadPointers.erase(*I);
return MadeChange;
}
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