[PATCH] D124894: Prefer 32bit and 64bit switch conditions for x86

[Matthias Braun via Phabricator via llvm-commits]

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This adds a `TargetLoweringBase::shouldExtendSwitch` callback to give targets a chance to control the preferred types in `CodeGenPrepare::optimizeSwitchInst`.

Implement it for X86 and choose i32 and i64 types where possible as they can be used immediately in address calculations. Previously we would use types like i8 or i16, while they are legal types on X86 they require additional zero extension operations before we can use them in address calculations.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D124894

Files:
  llvm/include/llvm/CodeGen/TargetLowering.h
  llvm/lib/CodeGen/CodeGenPrepare.cpp
  llvm/lib/CodeGen/TargetLoweringBase.cpp
  llvm/lib/Target/X86/X86ISelLowering.cpp
  llvm/lib/Target/X86/X86ISelLowering.h
  llvm/test/CodeGen/X86/2008-12-01-loop-iv-used-outside-loop.ll
  llvm/test/CodeGen/X86/SwitchLowering.ll
  llvm/test/CodeGen/X86/conditional-tailcall.ll
  llvm/test/CodeGen/X86/switch-phi-const.ll
  llvm/test/CodeGen/X86/switch.ll
  llvm/test/CodeGen/X86/tail-dup-multiple-latch-loop.ll
  llvm/test/CodeGen/X86/tail-opts.ll
  llvm/test/Transforms/CodeGenPrepare/X86/widen_switch.ll

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