[PATCH] D31319: [PPC] Eliminate redundant sign- and zero-extensions in PPC MI Peephole pass

[Hiroshi Inoue via Phabricator via llvm-commits]

inouehrs created this revision.
Herald added a subscriber: mehdi_amini.

This patch enables redundant sign- and zero-extension elimination in PowerPC MI Peephole pass.
If the input value of a sign- or zero-extension is known to be already sign- or zero-extended, the operation is redundant and can be eliminated.
One common case is sign-extensions for a method parameter or for a method return value; they must be sign- or zero-extended as defined in PPC ELF ABI. For example of the following simple code, two extsw instructions are generated before the invocation of int_func and before the return. With this patch, both extsw are eliminated.

  void int_func(int);
  void ii_test(int a) {
      if (a & 1) return int_func(a);
  }

Such redundant sign- or zero-extensions are common in many programs; e.g. I observed about 45,000 occurrences of the elimination while compiling the LLVM+CLANG for PPC.


https://reviews.llvm.org/D31319

Files:
  lib/Target/PowerPC/PPCISelLowering.cpp
  lib/Target/PowerPC/PPCInstrInfo.cpp
  lib/Target/PowerPC/PPCInstrInfo.h
  lib/Target/PowerPC/PPCMIPeephole.cpp
  lib/Target/PowerPC/PPCMachineFunctionInfo.cpp
  lib/Target/PowerPC/PPCMachineFunctionInfo.h
  test/CodeGen/PowerPC/eliminate_ext.ll

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