[PATCH] D85463: [GlobalISel] Add combine for (x & mask) -> x when (x & mask) == x

[Jessica Paquette via Phabricator via llvm-commits]

paquette created this revision.
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If we have a mask, and a value x, where (x & mask) == x, we can drop the AND and just use x.

This is about a 0.4% geomean code size improvement on CTMark at -O3 for AArch64.

In AArch64, this is most useful post-legalization. Patterns like this often show up when legalizing s1s, which must be extended to larger types.

e.g.

  %cmp:_(s32) = G_ICMP ...
  %and:_(s32) = G_AND %cmp, 1

Since G_ICMP only produces a single bit, there's no reason to mask it with the G_AND.


https://reviews.llvm.org/D85463

Files:
  llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
  llvm/include/llvm/Target/GlobalISel/Combine.td
  llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
  llvm/lib/Target/AArch64/AArch64Combine.td
  llvm/test/CodeGen/AArch64/GlobalISel/postlegalizer-combiner-and-trivial-mask.mir

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