[all-commits] [llvm/llvm-project] 0bc1ec: [GlobalISel] Reduce KnownBits usage in matcher com...

[Pierre van Houtryve via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 0bc1ec5cda8d68a681534bda9fd121b7f58fb495
      https://github.com/llvm/llvm-project/commit/0bc1ec5cda8d68a681534bda9fd121b7f58fb495
  Author: Pierre van Houtryve <pierre.vanhoutryve at amd.com>
  Date:   2024-05-16 (Thu, 16 May 2024)

  Changed paths:
    M llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp

  Log Message:
  -----------
  [GlobalISel] Reduce KnownBits usage in matcher combines (#92381)

Two icmp/and combines forced computation of KnownBits on all operands
everytime. We can avoid computing KnownBits on the LHS by exploiting a
couple of properties:
- Constants are always on the RHS for those instructions. If we have no
KnownBits on the RHS, we can bail out early and avoid computing LHS
knownbits.
- For icmp uge/ult 0, we don't need to know the KBs of the LHS to infer
the result

This allows to save some KnownBits calls, which are very expensive,
without affecting codegen.



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