[PATCH] D125041: [GlobalISel] Combine G_SHL, G_ASHR, G_SHL of undef shifts to undef.

[Jay Foad via Phabricator via llvm-commits]

foad added a comment.

> Actually G_SHL with undef LHS needs to be optimized to zero, not undef.

At the IR level, InstSimplify does this for all shifts (in the absence of exact/nsw/nuw flags). See SimplifyRightShift and SimplifyShlInst.


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https://reviews.llvm.org/D125041