[llvm] r248250 - [X86][SSE] Match zero/any extension shuffles that don't start from the first element

[Jeroen Ketema via llvm-commits]

Hi Simon,

This change breaks a number of shuffles for me. For example,

shufflevector <16 x i16> %0, <16 x i16> undef, <16 x i32> <i32 10, i32 
3, i32 13, i32 3, i32 8, i32 14, i32 13, i32 14, i32 5, i32 7, i32 12, 
i32 2, i32 13, i32 6, i32 3, i32 6>

Now shuffles to

10, 3, 13, 3, 8, 14, 13, 14, 5, 7, 10, 2, 11, 6, 3, 6

so the 10th and 12th element are wrong.

Best,

  Jeroen

On 22/09/15 09:16, llvm-commits at lists.llvm.org (Simon Pilgrim via 
llvm-commits) wrote:
> Author: rksimon
> Date: Tue Sep 22 03:16:08 2015
> New Revision: 248250
>
> URL: http://llvm.org/viewvc/llvm-project?rev=248250&view=rev
> Log:
> [X86][SSE] Match zero/any extension shuffles that don't start from the first element
>
> This patch generalizes the lowering of shuffles as zero extensions to allow extensions that don't start from the first element. It now recognises extensions starting anywhere in the lower 128-bits or at the start of any higher 128-bit lane.
>
> The motivation was to reduce the number of high cost pshufb calls, but it also improves the SSE2 case as well.
>
> Differential Revision: http://reviews.llvm.org/D12561
>
> Modified:
>      llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
>      llvm/trunk/test/CodeGen/X86/machine-cp.ll
>      llvm/trunk/test/CodeGen/X86/vec_cast2.ll
>      llvm/trunk/test/CodeGen/X86/vec_int_to_fp.ll
>      llvm/trunk/test/CodeGen/X86/vector-sext.ll
>      llvm/trunk/test/CodeGen/X86/vector-shuffle-256-v16.ll
>      llvm/trunk/test/CodeGen/X86/vector-shuffle-256-v32.ll
>      llvm/trunk/test/CodeGen/X86/vector-shuffle-sse4a.ll
>      llvm/trunk/test/CodeGen/X86/vector-zext.ll
>