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BasicAA: Only query twice if the result of the more general query was MayAlias

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This is a compile time optimization. Before the patch we would do two traversals
on each call to aliasGEP - one with a set size parameter one with UnknownSize.
We can do better by first checking the result of the alias query with
UnknownSize.
Only if this one returns MayAlias do we query a second time using size and type.

This recovers an about 7% compile time regression on spec/ammp.

radar://12349960

llvm-svn: 178045
This commit is contained in:
Arnold Schwaighofer 2013-03-26 18:07:53 +00:00
parent 969ef73c31
commit e44b3e3570
1 changed files with 5 additions and 5 deletions
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10
lib/Analysis/BasicAliasAnalysis.cpp
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@ -851,9 +851,13 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
// pointers, figure out if the indexes to the GEP tell us anything about the
// derived pointer.
if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
// Do the base pointers alias?
AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, 0,
UnderlyingV2, UnknownSize, 0);
// Check for geps of non-aliasing underlying pointers where the offsets are
// identical.
if (V1Size == V2Size) {
if ((BaseAlias == MayAlias) && V1Size == V2Size) {
// Do the base pointers alias assuming type and size.
AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size,
V1TBAAInfo, UnderlyingV2,
@ -882,10 +886,6 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
}
}
// Do the base pointers alias?
AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, 0,
UnderlyingV2, UnknownSize, 0);
// If we get a No or May, then return it immediately, no amount of analysis
// will improve this situation.
if (BaseAlias != MustAlias) return BaseAlias;