[PATCH] D141204: [GlobalISel] Extending G_SBFX/G_UBFX combine to consider G_SEXT_INREG as well

[David Ferenc Szabo via Phabricator via llvm-commits]

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Currently simple C code like

  typedef struct { int a:1; int b:4; int c:3; } s_t;
  int f(s_t s) { return s.b; }

will produce the following assembly with O3 <https://reviews.llvm.org/owners/package/3/>

  lsl     w8, w0, #3
  sxtb    w8, w8
  sbfx    w0, w8, #4, #8
  ret

while GCC produce this

  sbfx    x0, x0, 1, 4
  ret

Extended the implementation of matchBitfieldExtractFromShr to consider cases where the shifts fed to a G_SEXT_INREG.
Extended the implementation of matchRedundantSExtInReg to ignore G_SEXT_INREG instruction if the source is a G_SBFX.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D141204

Files:
  llvm/include/llvm/CodeGen/GlobalISel/MIPatternMatch.h
  llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
  llvm/test/CodeGen/AArch64/GlobalISel/combine-sext-inreg-sbfx.mir
  llvm/test/CodeGen/AArch64/GlobalISel/form-bitfield-extract-from-shr.mir

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