[llvm] [GlobalIsel] Combine zext of trunc (episode II) (PR #108305)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

We have a redundant `and` combine, but it queries known bits on both sides. For modularity, we could keep in this combine only `and` s and leave it to the redundant `and` check, but the first combine in this PR only calls known bits on one register, which ought to be cheaper.

https://github.com/llvm/llvm-project/blob/dbc90b55e832695c96d8dc1427e9df3bfeb73e5a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp#L3211

https://github.com/llvm/llvm-project/pull/108305