1 files changed, 7 insertions, 0 deletions
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 1c839fed171..851306bfe20 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -3045,9 +3045,16 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
     std::swap(LHS, RHS);
     Pred = CmpInst::getSwappedPredicate(Pred);
   }
+  assert(!isa<UndefValue>(LHS) && "Unexpected icmp undef,%X");
 
   Type *ITy = GetCompareTy(LHS); // The return type.
 
+  // For EQ and NE, we can always pick a value for the undef to make the
+  // predicate pass or fail, so we can return undef.
+  // Matches behavior in llvm::ConstantFoldCompareInstruction.
+  if (isa<UndefValue>(RHS) && ICmpInst::isEquality(Pred))
+    return UndefValue::get(ITy);
+
   // icmp X, X -> true/false
   // icmp X, undef -> true/false because undef could be X.
   if (LHS == RHS || isa<UndefValue>(RHS))