[PATCH] D110857: X86InstrInfo: Refactor and cleanup optimizeCompareInstr; NFC

[Matthias Braun via Phabricator via llvm-commits]

MatzeB created this revision.
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This changes the first part of `optimizeCompareInstr` being split into a loop with a forward scan for cases that re-use zero flags from a producer in case of compare with zero and a backward scan for finding an instruction equivalent to a compare.

The code now uses a single backward scan searching for the next instructions that reads or writes EFLAGS.

Also:

- Add comments giving examples for the 3 cases handled.
- Check `MI` which contains the result of the zero-compare cases, instead of re-checking `IsCmpZero`.
- Tweak coding style in some loops.

This does not change any behavior but prepares for a series of changes that extend the functionality of `optimizeCompareInstr`.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D110857

Files:
  llvm/lib/Target/X86/X86InstrInfo.cpp
  llvm/test/CodeGen/X86/optimize-compare.mir

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