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have loop-idiom nuke instructions that feed stores that get removed.

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llvm-svn: 122574
This commit is contained in:
Chris Lattner 2010-12-27 00:03:23 +00:00
parent d4daf9f002
commit a4249272b5
1 changed files with 45 additions and 6 deletions
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51
lib/Transforms/Scalar/LoopIdiomRecognize.cpp
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@ -20,6 +20,7 @@
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/IRBuilder.h"
#include "llvm/Support/raw_ostream.h"
@ -77,6 +78,40 @@ INITIALIZE_PASS_END(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
Pass *llvm::createLoopIdiomPass() { return new LoopIdiomRecognize(); }
/// 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.
///
static void DeleteDeadInstruction(Instruction *I, ScalarEvolution &SE) {
SmallVector<Instruction*, 32> NowDeadInsts;
NowDeadInsts.push_back(I);
// Before we touch this instruction, remove it from SE!
do {
Instruction *DeadInst = NowDeadInsts.pop_back_val();
// This instruction is dead, zap it, in stages. Start by removing it from
// SCEV.
SE.forgetValue(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();
} while (!NowDeadInsts.empty());
}
bool LoopIdiomRecognize::runOnLoop(Loop *L, LPPassManager &LPM) {
CurLoop = L;
@ -106,8 +141,13 @@ bool LoopIdiomRecognize::runOnLoop(Loop *L, LPPassManager &LPM) {
StoreInst *SI = dyn_cast<StoreInst>(I++);
if (SI == 0 || SI->isVolatile()) continue;
MadeChange |= processLoopStore(SI, BECount);
WeakVH InstPtr;
if (processLoopStore(SI, BECount)) {
// If processing the store invalidated our iterator, start over from the
// head of the loop.
if (InstPtr == 0)
I = BB->begin();
}
}
return MadeChange;
@ -205,10 +245,9 @@ processLoopStoreOfSplatValue(StoreInst *SI, unsigned StoreSize,
DEBUG(dbgs() << " Formed memset: " << *NewCall << "\n"
<< " from store to: " << *Ev << " at: " << *SI << "\n");
// Okay, the memset has been formed. Zap the original store.
// FIXME: We want to recursively delete dead instructions, but we have to
// update SCEV.
SI->eraseFromParent();
// Okay, the memset has been formed. Zap the original store and anything that
// feeds into it.
DeleteDeadInstruction(SI, *SE);
return true;
}