[llvm] [IR] Add zext nneg flag (PR #67982)

[Craig Topper via llvm-commits]

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@@ -37,6 +37,10 @@ bool Operator::hasPoisonGeneratingFlags() const {
     // Note: inrange exists on constexpr only
     return GEP->isInBounds() || GEP->getInRangeIndex() != std::nullopt;
   }
+  case Instruction::ZExt:
+    if (auto *NNI = dyn_cast<PossiblyNonNegInst>(this))
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topperc wrote:

Why do we need a dyn_cast instead of a cast?

https://github.com/llvm/llvm-project/pull/67982