[SCEV] Do not cache S -> V if S is not equivalent of V
SCEV tracks the correspondence of created SCEV to original instruction.
However during creation of SCEV it is possible that nuw/nsw/exact flags are
lost.
As a result during expansion of the SCEV the instruction with nuw/nsw/exact
will be used where it was expected and we produce poison incorreclty.
Reviewers: sanjoy, mkazantsev, sebpop, jbhateja
Reviewed By: sanjoy
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D41578
llvm-svn: 322058
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 10b5c74..7a9fddf 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -3774,6 +3774,24 @@
}
}
+/// Check whether value has nuw/nsw/exact set but SCEV does not.
+/// TODO: In reality it is better to check the poison recursevely
+/// but this is better than nothing.
+static bool SCEVLostPoisonFlags(const SCEV *S, const Value *V) {
+ if (auto *I = dyn_cast<Instruction>(V)) {
+ if (isa<OverflowingBinaryOperator>(I)) {
+ if (auto *NS = dyn_cast<SCEVNAryExpr>(S)) {
+ if (I->hasNoSignedWrap() && !NS->hasNoSignedWrap())
+ return true;
+ if (I->hasNoUnsignedWrap() && !NS->hasNoUnsignedWrap())
+ return true;
+ }
+ } else if (isa<PossiblyExactOperator>(I) && I->isExact())
+ return true;
+ }
+ return false;
+}
+
/// Return an existing SCEV if it exists, otherwise analyze the expression and
/// create a new one.
const SCEV *ScalarEvolution::getSCEV(Value *V) {
@@ -3787,7 +3805,7 @@
// ValueExprMap before insert S->{V, 0} into ExprValueMap.
std::pair<ValueExprMapType::iterator, bool> Pair =
ValueExprMap.insert({SCEVCallbackVH(V, this), S});
- if (Pair.second) {
+ if (Pair.second && !SCEVLostPoisonFlags(S, V)) {
ExprValueMap[S].insert({V, nullptr});
// If S == Stripped + Offset, add Stripped -> {V, Offset} into