[PATCH] D140087: [X86] Replace (31/63 -/^ X) with (NOT X) and ignore (32/64 ^ X) when computing shift count

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n added a comment.

@pengfei Somewhat unrelated so if this is not the right place the ask, can you let me know where is.

I was looking to add a peephole to change something like:

  ptr[x / 32] |= (1 << (x % 32))

Currently codegen is something like:

  mov    $0x1,%gpr1
  shlx   %cnt,%gpr1,%mask
  shr    $0x5,%cnt
  or  %mask, (%ptr, %cnt, 4)

And it could be as simple as:

  bts %cnt, (%ptr)

(other pattern with `bt{s|r|c}` could also be improved)

I saw `one_bit_patterns` in `X86InstrCompiler` but don't see a way to extend
the peephole s.t `addr` is a function of the inputs and not just one of the inputs.

Any chance you could direct me as where I should look at add this type of
peephole?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D140087/new/

https://reviews.llvm.org/D140087