[PATCH] D145468: [X86] Optimize (and (srl X 30) 2)

[Kazu Hirata via Phabricator via llvm-commits]

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This patch transforms (and (srl X 30) 2) into (add Y Y), where
Y = (srl X 31).  In x86 assembly:

  c1 e8 1e                   shr    $0x1e,%eax
  83 e0 fe                   and    $0xfffffffe,%eax

is transformed into:

  c1 e8 1f                   shr    $0x1f,%eax
  01 c0                      add    %eax,%eax

When the source and destination operand are different, we can emit
lea:

  c1 ef 1f                   shr    $0x1f,%edi
  8d 04 3f                   lea    (%rdi,%rdi,1),%eax

eliminating the need for a mov instruction.

This patch fixes:

https://github.com/llvm/llvm-project/issues/61073


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D145468

Files:
  llvm/lib/Target/X86/X86ISelLowering.cpp
  llvm/test/CodeGen/X86/and-shift.ll

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