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rewrite RecursivelyDeleteTriviallyDeadInstructions to use a more efficient

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formulation that doesn't require set lookups or scanning a set.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60203 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2008-11-28 01:20:46 +00:00
parent 2872177834
commit 7605730ba8
1 changed files with 26 additions and 16 deletions
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42
lib/Transforms/Utils/Local.cpp
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@ -22,7 +22,6 @@
#include "llvm/Target/TargetData.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
using namespace llvm;
//===----------------------------------------------------------------------===//
@ -182,26 +181,37 @@ bool llvm::isInstructionTriviallyDead(Instruction *I) {
void llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
SmallVectorImpl<Instruction*> *DeadInst) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I || !I->use_empty()) return;
if (!I || !I->use_empty() || !isInstructionTriviallyDead(I))
return;
SmallPtrSet<Instruction*, 16> Insts;
Insts.insert(I);
SmallVector<Instruction*, 16> DeadInsts;
DeadInsts.push_back(I);
while (!Insts.empty()) {
I = *Insts.begin();
Insts.erase(I);
while (!DeadInsts.empty()) {
I = DeadInsts.back();
DeadInsts.pop_back();
// Okay, if the instruction is dead, delete it.
if (!isInstructionTriviallyDead(I))
continue;
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
if (Instruction *U = dyn_cast<Instruction>(I->getOperand(i)))
Insts.insert(U);
I->eraseFromParent();
// If the client wanted to know, tell it about deleted instructions.
if (DeadInst)
DeadInst->push_back(I);
// Null out all of the instruction's operands to see if any operand becomes
// dead as we go.
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
Value *OpV = I->getOperand(i);
I->setOperand(i, 0);
if (!OpV->use_empty()) continue;
// If the operand is an instruction that became dead as we nulled out the
// operand, and if it is 'trivially' dead, delete it in a future loop
// iteration.
if (Instruction *OpI = dyn_cast<Instruction>(OpV))
if (isInstructionTriviallyDead(OpI))
DeadInsts.push_back(OpI);
}
I->eraseFromParent();
}
}