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[CFLAA] Be more conservative with values we haven't seen.

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There were issues with simply reporting AttrUnknown on
previously-unknown values in CFLAnders. So, we now act *entirely*
conservatively for values we haven't seen before. As in the prior patch
(r277362), writing a lit test for this isn't exactly trivial. If someone
wants a test badly, I'm willing to try to write one.

Patch by Jia Chen.

Differential Revision: https://reviews.llvm.org/D23077

llvm-svn: 277533
This commit is contained in:
George Burgess IV 2016-08-02 22:17:25 +00:00
parent fa1f2ddd00
commit 0e6700a0ef
1 changed files with 16 additions and 11 deletions
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27
lib/Analysis/CFLAndersAliasAnalysis.cpp
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@ -305,7 +305,7 @@ class CFLAndersAAResult::FunctionInfo {
/// Summary of externally visible effects.
AliasSummary Summary;
AliasAttrs getAttrs(const Value *) const;
Optional<AliasAttrs> getAttrs(const Value *) const;
public:
FunctionInfo(const Function &, const SmallVectorImpl<Value *> &,
@ -479,17 +479,14 @@ CFLAndersAAResult::FunctionInfo::FunctionInfo(
populateExternalRelations(Summary.RetParamRelations, Fn, RetVals, ReachSet);
}
AliasAttrs CFLAndersAAResult::FunctionInfo::getAttrs(const Value *V) const {
Optional<AliasAttrs>
CFLAndersAAResult::FunctionInfo::getAttrs(const Value *V) const {
assert(V != nullptr);
// Return AttrUnknown if V is not found in AttrMap. Sometimes V can be created
// after the analysis gets executed, and we want to be conservative in
// those cases.
AliasAttrs Attr = getAttrUnknown();
auto Itr = AttrMap.find(V);
if (Itr != AttrMap.end())
Attr = Itr->second;
return Attr;
return Itr->second;
return None;
}
bool CFLAndersAAResult::FunctionInfo::mayAlias(const Value *LHS,
@ -498,9 +495,17 @@ bool CFLAndersAAResult::FunctionInfo::mayAlias(const Value *LHS,
uint64_t RHSSize) const {
assert(LHS && RHS);
// Check AliasAttrs first since it's cheaper
auto AttrsA = getAttrs(LHS);
auto AttrsB = getAttrs(RHS);
// Check if we've seen LHS and RHS before. Sometimes LHS or RHS can be created
// after the analysis gets executed, and we want to be conservative in those
// cases.
auto MaybeAttrsA = getAttrs(LHS);
auto MaybeAttrsB = getAttrs(RHS);
if (!MaybeAttrsA || !MaybeAttrsB)
return true;
// Check AliasAttrs before AliasMap lookup since it's cheaper
auto AttrsA = *MaybeAttrsA;
auto AttrsB = *MaybeAttrsB;
if (hasUnknownOrCallerAttr(AttrsA))
return AttrsB.any();
if (hasUnknownOrCallerAttr(AttrsB))