[PATCH] D31426: [DAGCombine] Combine shuffle of splat with multiple uses

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

This seems unnecessarily complicated. Why can't we just match any shuffle of a splat before we get here and simplify it?

Also, would you be interested in fixing this in IR? :)

$ ./opt -instsimplify shufsplat.ll -S

  define <4 x i32> @foo(<4 x i32> %x) {
    %splat = shufflevector <4 x i32> %x, <4 x i32> undef, <4 x i32> zeroinitializer
    %shuf = shufflevector <4 x i32> %splat, <4 x i32> undef, <4 x i32> <i32 0, i32 3, i32 2, i32 1>
    ret <4 x i32> %shuf
  }

This example is handled by instcombine...but in a very inefficient way.


Repository:
  rL LLVM

https://reviews.llvm.org/D31426