[PATCH] D110867: X86InstrInfo: Support immediates that are +1/-1 different in optimizeCompareInstr

[Matthias Braun via Phabricator via llvm-commits]

MatzeB created this revision.
MatzeB added reviewers: RKSimon, craig.topper, nikic, manmanren.
Herald added subscribers: wenlei, pengfei, hiraditya, mcrosier.
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This extends `optimizeCompareInstr` to re-use previous comparison results if the previous comparison was with an immediate that was 1 bigger or smaller when this is possible by switching between `>=/>`, `</<=`, ...

Motivation: This case is not rare in practice as SelectionDAG canonicalization tends to add/subtract 1 often when optimizing for fallthrough blocks. Example for `x > C` the fallthrough optimization switches true/false blocks with `!(x > C)` --> `x <= C` and canonicalization turns this into `x < C + 1`.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D110867

Files:
  llvm/lib/Target/X86/X86InstrInfo.cpp
  llvm/lib/Target/X86/X86InstrInfo.h
  llvm/test/CodeGen/X86/jump_sign.ll
  llvm/test/CodeGen/X86/optimize-compare.mir
  llvm/test/CodeGen/X86/peep-test-5.ll
  llvm/test/CodeGen/X86/use-cr-result-of-dom-icmp-st.ll

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