Reapply r121520, PartialAlias implementation for BasicAA, now that
memdep is updated to handle it.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121725 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index 3ab18fd..17a502e 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -857,6 +857,17 @@
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,