[PATCH] D56155: [docs] cttz and ctlz return poison, not undef, when argument is 0

[Nuno Lopes via Phabricator via llvm-commits]

nlopes added a comment.

As a justification why it doesn't matter whether it's undef or poison, clang emits__builtin_ffs as:
ffs(x) -> x ? cttz(x) + 1 : 0

https://clang.llvm.org/doxygen/CGBuiltin_8cpp_source.html#l01814

So I support this change to poison, since it makes things easier than undef.


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  rL LLVM

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https://reviews.llvm.org/D56155