[AMDGPU] Recognize x & ((1 << y) - 1) pattern.
Summary:
As a followup for D48007.
Since we already handle `x << (bitwidth - y) >> (bitwidth - y)` pattern,
which does not have ub for both the edge cases (`y == 0`, `y == bitwidth`),
i think also handling a pattern that is ub for `y == bitwidth` should be fine.
Reviewers: nhaehnle, bogner, tstellar, arsenm
Reviewed By: arsenm
Subscribers: arsenm, kzhuravl, wdng, yaxunl, dstuttard, tpr, t-tye, llvm-commits
Tags: #amdgpu
Differential Revision: https://reviews.llvm.org/D48010
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@334816
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