[llvm] [AMDGPU] Recognise bitmask operations as srcmods on select (PR #152119)

[Chris Jackson via llvm-commits]

chrisjbris wrote:

> LGTM but can you add some negative tests for the case where this was trigger for canonicalizing instructions? I assume those required looking through a bitcast?

I've added a test for this using v_cvt, which was the specific instruction that was failing on the buildbot. I had a shorter version of this test to hand to check the fix. There was no bitcast involved.

https://github.com/llvm/llvm-project/pull/152119