Roman Lebedev 3d492d7503 [DAGCombine][X86][Thumb2/LowOverheadLoops] A - (A & C) -> A & (~C) fold (PR44448) ...

While we do manage to fold integer-typed IR in middle-end,
we can't do that for the main motivational case of pointers.

There is @llvm.ptrmask() intrinsic which may or may not be helpful,
but i'm not sure it is fully considered canonical yet,
not everything is fully aware of it likely.

Name: PR44448  ptr - (ptr & C) -> ptr & (~C)
%bias = and i32 %ptr, C
%r = sub i32 %ptr, %bias
  =>
%r = and i32 %ptr, ~C

See
  https://bugs.llvm.org/show_bug.cgi?id=44448
  https://reviews.llvm.org/D71499

2020-01-03 17:55:45 +03:00

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