[PATCH] D36498: [InstCombine] Teach foldSelectICmpAnd to recognize a (icmp slt trunc X, 0) and (icmp sgt trunc X, -1) as equivalent to an and with the sign bit of the truncated type

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.

This is similar to what was already done in foldSelectICmpAndOr.  Ultimately I'd like to see if we can call foldSelectICmpAnd from foldSelectIntoOp if we detect a power of 2 constant. This would allow us to remove foldSelectICmpAndOr entirely.

As I'm writing this I wonder if we're also missing (icmp slt X, 0) and (icmp sgt X, -1) without any truncates.

The vector tests added should already work without this change since we don't turn compares with ands into truncate for vectors.


https://reviews.llvm.org/D36498

Files:
  lib/Transforms/InstCombine/InstCombineSelect.cpp
  test/Transforms/InstCombine/select-with-bitwise-ops.ll

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