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Improve the accuracy of memdep for determining the dependencies of loads. 

This brings GVN to parity with GCSE+LoadVN.

llvm-svn: 40882
This commit is contained in:
Owen Anderson 2007-08-06 23:26:03 +00:00
parent a010822b45
commit 4898513d96
1 changed files with 13 additions and 2 deletions
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15
llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
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@ -275,8 +275,14 @@ Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
pointerSize = ~0UL;
} else if (CallSite::get(QI).getInstruction() != 0) {
// Call insts need special handling. Check is they can modify our pointer
if (AA.getModRefInfo(CallSite::get(QI), dependee, dependeeSize) !=
AliasAnalysis::NoModRef) {
AliasAnalysis::ModRefResult MR = AA.getModRefInfo(CallSite::get(QI),
dependee, dependeeSize);
if (MR != AliasAnalysis::NoModRef) {
// Loads don't depend on read-only calls
if (isa<LoadInst>(query) && MR == AliasAnalysis::Ref)
continue;
if (!start || block) {
depGraphLocal.insert(std::make_pair(query, std::make_pair(QI, true)));
reverseDep.insert(std::make_pair(QI, query));
@ -294,6 +300,11 @@ Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
dependee, dependeeSize);
if (R != AliasAnalysis::NoAlias) {
// May-alias loads don't depend on each other
if (isa<LoadInst>(query) && isa<LoadInst>(QI) &&
R == AliasAnalysis::MayAlias)
continue;
if (!start || block) {
depGraphLocal.insert(std::make_pair(query, std::make_pair(QI, true)));
reverseDep.insert(std::make_pair(QI, query));