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Use information already present in the ValueTable to fast-fail when we know there won't be a value number match. This speeds up GVN on a case where there are very few redundancies by ~25%. 

llvm-svn: 53108
This commit is contained in:
Owen Anderson 2008-07-03 17:44:33 +00:00
parent 4cab581bc0
commit 3ea90a7d55
1 changed files with 11 additions and 2 deletions
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13
llvm/lib/Transforms/Scalar/GVN.cpp
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@ -166,6 +166,7 @@ namespace {
void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
void setDomTree(DominatorTree* D) { DT = D; }
uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
};
}
@ -1058,11 +1059,12 @@ bool GVN::processInstruction(Instruction *I,
return changed;
}
uint32_t nextNum = VN.getNextUnusedValueNumber();
unsigned num = VN.lookup_or_add(I);
// Allocations are always uniquely numbered, so we can save time and memory
// by fast failing them.
if (isa<AllocationInst>(I)) {
if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
return false;
}
@ -1082,6 +1084,13 @@ bool GVN::processInstruction(Instruction *I,
} else {
localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
}
// If the number we were assigned was a brand new VN, then we don't
// need to do a lookup to see if the number already exists
// somewhere in the domtree: it can't!
} else if (num == nextNum) {
localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
// Perform value-number based elimination
} else if (Value* repl = lookupNumber(I->getParent(), num)) {
// Remove it!
@ -1092,7 +1101,7 @@ bool GVN::processInstruction(Instruction *I,
I->replaceAllUsesWith(repl);
toErase.push_back(I);
return true;
} else if (!I->isTerminator()) {
} else {
localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
}