[llvm] [clang] [Instcombine] use zext's nneg flag for icmp folding (PR #70845)

[Nikita Popov via cfe-commits]

================
@@ -5587,11 +5587,17 @@ Instruction *InstCombinerImpl::foldICmpWithZextOrSext(ICmpInst &ICmp) {
         return new ICmpInst(ICmp.getPredicate(), Builder.CreateOr(X, Y),
                             Constant::getNullValue(X->getType()));
 
+      // Treat "zext nneg" as "sext"
+      bool IsNonNeg0 = isa<PossiblyNonNegInst>(ICmp.getOperand(0));
+      bool IsNonNeg1 = isa<PossiblyNonNegInst>(ICmp.getOperand(1));
----------------
nikic wrote:

This only checks whether the instruction *can* have an nneg flag, not whether it has it. You need to check `isNonNeg()` for that.

https://github.com/llvm/llvm-project/pull/70845