[PATCH] D102367: [Intrinsics] is_constant intrinsic on undef evaluates to false

[Nick Desaulniers via Phabricator via llvm-commits]

nickdesaulniers added inline comments.


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Comment at: llvm/lib/Analysis/ConstantFolding.cpp:1843-1848
+    if (isa<UndefValue>(Operands[0]))
+      return ConstantInt::getFalse(Ty->getContext());
     // We know we have a "Constant" argument. But we want to only
     // return true for manifest constants, not those that depend on
     // constants with unknowable values, e.g. GlobalValue or BlockAddress.
     if (isManifestConstant(Operands[0]))
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nickdesaulniers wrote:
> probably should just update `isManifestConstant`
Ah, no, then InstCombine would fail to fold `i1 @llvm.is.constant.i32(i32 undef)` into `i1 0`.


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  https://reviews.llvm.org/D102367/new/

https://reviews.llvm.org/D102367