1 files changed, 12 insertions, 2 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 8c8fc69..6b67b48 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -544,8 +544,18 @@ Instruction *InstCombinerImpl::foldSelectIntoOp(SelectInst &SI, Value *TrueVal,
 
     Value *NewSel = Builder.CreateSelect(SI.getCondition(), Swapped ? C : OOp,
                                          Swapped ? OOp : C, "", &SI);
-    if (isa<FPMathOperator>(&SI))
-      cast<Instruction>(NewSel)->setFastMathFlags(FMF);
+    if (isa<FPMathOperator>(&SI)) {
+      FastMathFlags NewSelFMF = FMF;
+      // We cannot propagate ninf from the original select, because OOp may be
+      // inf and the flag only guarantees that FalseVal (op OOp) is never
+      // infinity.
+      // Examples: -inf + +inf = NaN, -inf - -inf = NaN, 0 * inf = NaN
+      // Specifically, if the original select has both ninf and nnan, we can
+      // safely propagate the flag.
+      NewSelFMF.setNoInfs(TVI->hasNoInfs() ||
+                          (NewSelFMF.noInfs() && NewSelFMF.noNaNs()));
+      cast<Instruction>(NewSel)->setFastMathFlags(NewSelFMF);
+    }
     NewSel->takeName(TVI);
     BinaryOperator *BO =
         BinaryOperator::Create(TVI->getOpcode(), FalseVal, NewSel);