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Allow GVN to eliminate read-only function calls when it can detect that they are redundant.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@44323 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson
2007-11-26 02:26:36 +00:00
parent fd94dd58ff
commit 00a6d1448d
3 changed files with 24 additions and 6 deletions
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19
lib/Transforms/Scalar/GVN.cpp
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@@ -476,7 +476,8 @@ uint32_t ValueTable::lookup_or_add(Value* V) {
if (CallInst* C = dyn_cast<CallInst>(V)) {
if (C->getCalledFunction() &&
AA->doesNotAccessMemory(C->getCalledFunction())) {
(AA->doesNotAccessMemory(C->getCalledFunction()) ||
AA->onlyReadsMemory(C->getCalledFunction()))) {
Expression e = create_expression(C);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
@@ -1038,6 +1039,22 @@ bool GVN::processInstruction(Instruction* I,
} else if (currAvail.test(num)) {
Value* repl = find_leader(currAvail, num);
if (CallInst* CI = dyn_cast<CallInst>(I)) {
AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
if (CI->getCalledFunction() &&
!AA.doesNotAccessMemory(CI->getCalledFunction())) {
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
if (MD.getDependency(CI) != MD.getDependency(cast<CallInst>(repl))) {
// There must be an intervening may-alias store, so nothing from
// this point on will be able to be replaced with the preceding call
currAvail.erase(repl);
currAvail.insert(I);
return false;
}
}
}
VN.erase(I);
I->replaceAllUsesWith(repl);
toErase.push_back(I);