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Make handleEndBlock significantly faster with one trivial improvement,

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and one hack to avoid hitting a bad case when the alias analysis is imprecise.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@40935 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson 2007-08-08 18:38:28 +00:00
parent df359c264e
commit 362bb52108
1 changed files with 30 additions and 4 deletions
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34
lib/Transforms/Scalar/DeadStoreElimination.cpp
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@ -294,10 +294,22 @@ bool DSE::handleEndBlock(BasicBlock& BB,
AA.doesNotAccessMemory(CS.getCalledFunction()))
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(),
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()))
@ -306,6 +318,12 @@ bool DSE::handleEndBlock(BasicBlock& BB,
// See if the call site touches it
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);
}
@ -320,6 +338,8 @@ bool DSE::handleEndBlock(BasicBlock& BB,
if (!killPointer)
continue;
TranslatePointerBitCasts(killPointer);
// Deal with undead pointers
MadeChange |= RemoveUndeadPointers(killPointer, BBI,
deadPointers, possiblyDead);
@ -328,10 +348,8 @@ bool DSE::handleEndBlock(BasicBlock& BB,
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.
/// RemoveUndeadPointers - check for uses of a pointer that make it
/// undead when scanning for dead stores to alloca's.
bool DSE::RemoveUndeadPointers(Value* killPointer,
BasicBlock::iterator& BBI,
SmallPtrSet<AllocaInst*, 64>& deadPointers,
@ -340,6 +358,14 @@ bool DSE::RemoveUndeadPointers(Value* killPointer,
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 (AllocaInst* A = dyn_cast<AllocaInst>(killPointer)) {
if (deadPointers.count(A))
deadPointers.erase(A);
return false;
}
bool MadeChange = false;
std::vector<Instruction*> undead;