[PATCH] D71363: [MIPS GlobalISel] Select bitreverse

[Petar Avramovic via Phabricator via llvm-commits]

Petar.Avramovic added a comment.

Buildbot failures depend on compiler used to build clang.
Problem was in order which new MachineInstructions get inserted into MachineFunction.
Generated assembler does the same thing, but regression tests require consistent behavior regardless of compiler used.
In:

  return B.buildOr(Dst, B.buildLShr(Ty, B.buildAnd(Ty, Src, MaskLoNTo0), C_N),
                   B.buildAnd(Ty, B.buildShl(Ty, Src, C_N), MaskLoNTo0));

it is important which method was executed first since they insert MachineInstructions into MachineFunction. Order of execution:
gcc

  B.buildAnd(Ty, B.buildShl(Ty, Src, C_N), MaskLoNTo0)
  B.buildLShr(Ty, B.buildAnd(Ty, Src, MaskLoNTo0), C_N)

clang

  B.buildLShr(Ty, B.buildAnd(Ty, Src, MaskLoNTo0), C_N)
  B.buildAnd(Ty, B.buildShl(Ty, Src, C_N), MaskLoNTo0)

recommit notes: 
Introduce temporary variables in order to make sure instructions get inserted into MachineFunction in same order regardless of compiler used to build llvm.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D71363/new/

https://reviews.llvm.org/D71363