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Add some more comments to GVN.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@41129 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson 2007-08-16 22:02:55 +00:00
parent 0fee3ff93e
commit 62bc33c954
1 changed files with 14 additions and 0 deletions
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14
lib/Transforms/Scalar/GVN.cpp
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@ -756,6 +756,7 @@ Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,
PN->addIncoming(val, *PI);
}
// Attempt to collapse PHI nodes that are trivially redundant
Value* v = PN->hasConstantValue();
if (v) {
if (Instruction* inst = dyn_cast<Instruction>(v)) {
@ -804,19 +805,24 @@ Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,
}
}
// Cache our phi construction results
phiMap[orig->getPointerOperand()].insert(PN);
return PN;
}
/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
/// non-local by performing PHI construction.
bool GVN::processNonLocalLoad(LoadInst* L,
SmallVector<Instruction*, 4>& toErase) {
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
// Find the non-local dependencies of the load
DenseMap<BasicBlock*, Value*> deps;
MD.getNonLocalDependency(L, deps);
DenseMap<BasicBlock*, Value*> repl;
// Filter out useless results (non-locals, etc)
for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end();
I != E; ++I)
if (I->second == MemoryDependenceAnalysis::None) {
@ -837,6 +843,7 @@ bool GVN::processNonLocalLoad(LoadInst* L,
return false;
}
// Use cached PHI construction information from previous runs
SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()];
for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
I != E; ++I) {
@ -852,6 +859,7 @@ bool GVN::processNonLocalLoad(LoadInst* L,
}
}
// Perform PHI construction
SmallPtrSet<BasicBlock*, 4> visited;
Value* v = GetValueForBlock(L->getParent(), L, repl, true);
@ -863,6 +871,8 @@ bool GVN::processNonLocalLoad(LoadInst* L,
return true;
}
/// processLoad - Attempt to eliminate a load, first by eliminating it
/// locally, and then attempting non-local elimination if that fails.
bool GVN::processLoad(LoadInst* L,
DenseMap<Value*, LoadInst*>& lastLoad,
SmallVector<Instruction*, 4>& toErase) {
@ -891,6 +901,8 @@ bool GVN::processLoad(LoadInst* L,
bool deletedLoad = false;
// Walk up the dependency chain until we either find
// a dependency we can use, or we can't walk any further
while (dep != MemoryDependenceAnalysis::None &&
dep != MemoryDependenceAnalysis::NonLocal &&
(isa<LoadInst>(dep) || isa<StoreInst>(dep))) {
@ -946,6 +958,7 @@ bool GVN::processInstruction(Instruction* I,
unsigned num = VN.lookup_or_add(I);
// Collapse PHI nodes
if (PHINode* p = dyn_cast<PHINode>(I)) {
Value* constVal = p->hasConstantValue();
@ -966,6 +979,7 @@ bool GVN::processInstruction(Instruction* I,
toErase.push_back(p);
}
}
// Perform value-number based elimination
} else if (currAvail.test(num)) {
Value* repl = find_leader(currAvail, num);