BasicAA: Only query twice if the result of the more general query was MayAlias
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
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178045 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index 4139336..ae6da1a 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -851,9 +851,13 @@
// 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,
@@ -881,10 +885,6 @@
GEP1VariableIndices.clear();
}
}
-
- // 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.