[PATCH] D76844: [InstCombine] try to reduce shuffle with bitcasted operand

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
spatel added reviewers: lebedev.ri, nlopes, regehr, RKSimon.
Herald added subscribers: hiraditya, mcrosier.

shuf (bitcast X), undef, Mask --> bitcast X'

The 'inverse shuffles' test (shuf_bitcast_operand) is a pattern that would emerge in the motivating examples from PR35454:
https://bugs.llvm.org/show_bug.cgi?id=35454
(if we proceed with D76727 <https://reviews.llvm.org/D76727>)

We can deal with this class of patterns in generic instcombine because we are not creating any new shuffles, just a bitcast.

This provides an opportunity to exercise Alive2's vector support:
http://volta.cs.utah.edu:8080/z/mwDUZf


https://reviews.llvm.org/D76844

Files:
  llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
  llvm/test/Transforms/InstCombine/shufflevec-bitcast.ll

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