[PATCH] D140314: [X86] Replace (31/63 -/^ X) with (NOT X) and ignore (32/64 ^ X) when computing shift count

[Noah Goldstein via Phabricator via llvm-commits]

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Shift count is masked by hardware so these peepholes just extend
common patterns for NOT to the lower bits of shift count.

As well (32/64 ^ X) is masked off by the shift so can be safely
ignored.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D140314

Files:
  llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
  llvm/test/CodeGen/X86/legalize-shift-64.ll
  llvm/test/CodeGen/X86/not-shift.ll

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