[IndVars] Fix a bug introduced in r317012
Turns out we can have comparisons which are indirect users of the induction variable that we can make invariant. In this case, there is no loop invariant value contributing and we'd fail an assert.
The test case was found by a java fuzzer and reduced. It's a real cornercase. You have to have a static loop which we've already proven only executes once, but haven't broken the backedge on, and an inner phi whose result can be constant folded by SCEV using exit count reasoning but not proven by isKnownPredicate. To my knowledge, only the fuzzer has hit this case.
llvm-svn: 319583
diff --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
index fce7f8b..96b5139 100644
--- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -200,13 +200,23 @@
// TODO: Support multiple entry loops? (We currently bail out of these in
// the IndVarSimplify pass)
if (auto *BB = L->getLoopPredecessor()) {
- Value *Incoming = PN->getIncomingValueForBlock(BB);
- const SCEV *IncomingS = SE->getSCEV(Incoming);
- CheapExpansions[IncomingS] = Incoming;
+ const int Idx = PN->getBasicBlockIndex(BB);
+ if (Idx >= 0) {
+ Value *Incoming = PN->getIncomingValue(Idx);
+ const SCEV *IncomingS = SE->getSCEV(Incoming);
+ CheapExpansions[IncomingS] = Incoming;
+ }
}
Value *NewLHS = CheapExpansions[InvariantLHS];
Value *NewRHS = CheapExpansions[InvariantRHS];
+ if (!NewLHS)
+ if (auto *ConstLHS = dyn_cast<SCEVConstant>(InvariantLHS))
+ NewLHS = ConstLHS->getValue();
+ if (!NewRHS)
+ if (auto *ConstRHS = dyn_cast<SCEVConstant>(InvariantRHS))
+ NewRHS = ConstRHS->getValue();
+
if (!NewLHS || !NewRHS)
// We could not find an existing value to replace either LHS or RHS.
// Generating new instructions has subtler tradeoffs, so avoid doing that