[PATCH] D148637: [LangRef] Update shufflevector's semantics to return poison if the mask is undef

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


================
Comment at: llvm/docs/LangRef.rst:10026
+using ``undef`` for ``val`` is not recommended because it prohibits
+optimizations to '``shufflevector``' with ``poison`` masks.
+
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nikic wrote:
> I don't think this sentence really adds anything. It just introduces a new ill-defined term "don't-care vector".
(The recommendation to use poison instead of undef is a general one, that applies not only to insertelement.)


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https://reviews.llvm.org/D148637