[PATCH] D32293: InstructionSimplify: Simplify a shuffle with a undef mask to undef

[Davide Italiano via Phabricator via llvm-commits]

davide added a comment.

Uhm, I don't follow you. Maybe DAGCombiner has a similar transformation, but instsimplify is powerful enough to handle the case I pointed out.

  [davide at cupiditate bin]$ ./opt -instsimplify tinkywinky.ll -S
  ; ModuleID = 'tinkywinky.ll'
  source_filename = "tinkywinky.ll"
  
  define <4 x i32> @undef_mask(<4 x i32> %x) {
    ret <4 x i32> undef
  }
  [davide at cupiditate bin]$ cat tinkywinky.ll
  define <4 x i32> @undef_mask(<4 x i32> %x) {
    %shuf = shufflevector <4 x i32> %x, <4 x i32> undef, <4 x i32> undef
    ret <4 x i32> %shuf
  }


Repository:
  rL LLVM

https://reviews.llvm.org/D32293