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Eliminate generality that is not buying us anything. In particular, this

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will cause us to miss cases where the input pointer to a load could be value
numbered to another load.  Something like this:


  %X = load int* %P1
  %Y = load int* %P2

Those are obviously the same if P1/P2 are the same.  The code this patch
removes attempts to handle that.  However, since GCSE iterates, this doesn't
actually buy us anything: GCSE will first replace P1 or P2 with the other
one, then the load can be value numbered as equal.

Removing this code speeds up gcse a lot.  On 176.gcc in debug mode, this
speeds up gcse from 29.08s -> 25.73s, a 13% savings.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@19906 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2005-01-29 06:11:16 +00:00
parent 2652da6af9
commit e233b8c64b
1 changed files with 13 additions and 32 deletions
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45
lib/Analysis/LoadValueNumbering.cpp
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@ -284,17 +284,7 @@ void LoadVN::getEqualNumberNodes(Value *V,
if (LI->isVolatile())
return getAnalysis<ValueNumbering>().getEqualNumberNodes(V, RetVals);
// If we have a load instruction, find all of the load and store instructions
// that use the same source operand. We implement this recursively, because
// there could be a load of a load of a load that are all identical. We are
// guaranteed that this cannot be an infinite recursion because load
// instructions would have to pass through a PHI node in order for there to be
// a cycle. The PHI node would be handled by the else case here, breaking the
// infinite recursion.
//
std::vector<Value*> PointerSources;
getEqualNumberNodes(LI->getOperand(0), PointerSources);
PointerSources.push_back(LI->getOperand(0));
Value *PointerSource = LI->getOperand(0);
BasicBlock *LoadBB = LI->getParent();
Function *F = LoadBB->getParent();
@ -305,27 +295,18 @@ void LoadVN::getEqualNumberNodes(Value *V,
//
std::map<BasicBlock*, std::vector<LoadInst*> > CandidateLoads;
std::map<BasicBlock*, std::vector<StoreInst*> > CandidateStores;
std::set<AllocationInst*> Allocations;
while (!PointerSources.empty()) {
Value *Source = PointerSources.back();
PointerSources.pop_back(); // Get a source pointer...
if (AllocationInst *AI = dyn_cast<AllocationInst>(Source))
Allocations.insert(AI);
for (Value::use_iterator UI = Source->use_begin(), UE = Source->use_end();
UI != UE; ++UI)
if (LoadInst *Cand = dyn_cast<LoadInst>(*UI)) {// Is a load of source?
if (Cand->getParent()->getParent() == F && // In the same function?
Cand != LI && !Cand->isVolatile()) // Not LI itself?
CandidateLoads[Cand->getParent()].push_back(Cand); // Got one...
} else if (StoreInst *Cand = dyn_cast<StoreInst>(*UI)) {
if (Cand->getParent()->getParent() == F && !Cand->isVolatile() &&
Cand->getOperand(1) == Source) // It's a store THROUGH the ptr...
CandidateStores[Cand->getParent()].push_back(Cand);
}
}
for (Value::use_iterator UI = PointerSource->use_begin(),
UE = PointerSource->use_end(); UI != UE; ++UI)
if (LoadInst *Cand = dyn_cast<LoadInst>(*UI)) {// Is a load of source?
if (Cand->getParent()->getParent() == F && // In the same function?
Cand != LI && !Cand->isVolatile()) // Not LI itself?
CandidateLoads[Cand->getParent()].push_back(Cand); // Got one...
} else if (StoreInst *Cand = dyn_cast<StoreInst>(*UI)) {
if (Cand->getParent()->getParent() == F && !Cand->isVolatile() &&
Cand->getOperand(1) == PointerSource) // It's a store THROUGH the ptr.
CandidateStores[Cand->getParent()].push_back(Cand);
}
// Get alias analysis & dominators.
AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
@ -358,7 +339,7 @@ void LoadVN::getEqualNumberNodes(Value *V,
} else if (AllocationInst *AI = dyn_cast<AllocationInst>(I)) {
// If we run into an allocation of the value being loaded, then the
// contents are not initialized.
if (Allocations.count(AI)) {
if ((Value*)AI == PointerSource) {
LoadInvalidatedInBBBefore = true;
RetVals.push_back(UndefValue::get(LI->getType()));
break;