Avoid doing conservative phi checks in aliasSameBasePointerGEPs() if no phis have been visited yet.
Reviewers: Daniel Berlin
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D34478
llvm-svn: 307581
diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index b52a1d7..758a907 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -922,11 +922,11 @@
/// Provide ad-hoc rules to disambiguate accesses through two GEP operators,
/// both having the exact same pointer operand.
-static AliasResult aliasSameBasePointerGEPs(const GEPOperator *GEP1,
- uint64_t V1Size,
- const GEPOperator *GEP2,
- uint64_t V2Size,
- const DataLayout &DL) {
+AliasResult BasicAAResult::aliasSameBasePointerGEPs(const GEPOperator *GEP1,
+ uint64_t V1Size,
+ const GEPOperator *GEP2,
+ uint64_t V2Size,
+ const DataLayout &DL) {
assert(GEP1->getPointerOperand()->stripPointerCastsAndBarriers() ==
GEP2->getPointerOperand()->stripPointerCastsAndBarriers() &&
@@ -1006,7 +1006,7 @@
// Because they cannot partially overlap and because fields in an array
// cannot overlap, if we can prove the final indices are different between
// GEP1 and GEP2, we can conclude GEP1 and GEP2 don't alias.
-
+
// If the last indices are constants, we've already checked they don't
// equal each other so we can exit early.
if (C1 && C2)
@@ -1014,11 +1014,15 @@
{
Value *GEP1LastIdx = GEP1->getOperand(GEP1->getNumOperands() - 1);
Value *GEP2LastIdx = GEP2->getOperand(GEP2->getNumOperands() - 1);
- if (isa<PHINode>(GEP1LastIdx) || isa<PHINode>(GEP2LastIdx)) {
+ if ((isa<PHINode>(GEP1LastIdx) || isa<PHINode>(GEP2LastIdx)) &&
+ !VisitedPhiBBs.empty()) {
// If one of the indices is a PHI node, be safe and only use
// computeKnownBits so we don't make any assumptions about the
// relationships between the two indices. This is important if we're
// asking about values from different loop iterations. See PR32314.
+ // But, with empty visitedPhiBBs we can guarantee that the values are
+ // from the same iteration. Therefore, we can avoid doing this
+ // conservative check.
// TODO: We may be able to change the check so we only do this when
// we definitely looked through a PHINode.
if (GEP1LastIdx != GEP2LastIdx &&