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Implement PartialAlias checking in BasicAA.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121520 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
2010-12-10 20:47:03 +00:00
parent 6ce219ec64
commit 3bd5e52676
2 changed files with 38 additions and 2 deletions
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lib/Analysis/BasicAliasAnalysis.cpp
+11
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@@ -857,6 +857,17 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty())
return MustAlias;
// If there is a difference betwen the pointers, but the difference is
// less than the size of the associated memory object, then we know
// that the objects are partially overlapping.
if (GEP1BaseOffset != 0 && GEP1VariableIndices.empty()) {
if (GEP1BaseOffset >= 0 ?
(V2Size != UnknownSize && (uint64_t)GEP1BaseOffset < V2Size) :
(V1Size != UnknownSize && -(uint64_t)GEP1BaseOffset < V1Size &&
GEP1BaseOffset != INT64_MIN))
return PartialAlias;
}
// If we have a known constant offset, see if this offset is larger than the
// access size being queried. If so, and if no variable indices can remove
// pieces of this constant, then we know we have a no-alias. For example,