[PATCH] D104790: [x86] fix mm*_undefined* intrinsics to use arbitrary frozen bit pattern

[Juneyoung Lee via Phabricator via cfe-commits]

aqjune added a comment.

In D104790#2842523 <https://reviews.llvm.org/D104790#2842523>, @nikic wrote:

> Is this actually better in any meaningful way? InstCombine will turn `freeze poison` into `zeroinitializer`, and until then this is just a completely opaque value.

I think to correctly emit IR for intrinsics like mm256_castsi128_si256 (D103874 <https://reviews.llvm.org/D103874> has more context) efficient handling of this kind of pattern is necessary:

  %v = freeze <n x ty> poison
  %w = shufflevector %a, %v, mask

The zeroinitializer folding is done by InstCombine's visitFreeze, which should be fixed maybe.
I'll play with some patterns and create patches for this.


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https://reviews.llvm.org/D104790