[LLVMdev] Selecting Vector Shuffle of Different Types

[Eli Friedman]

On Wed, Dec 2, 2009 at 3:46 PM, David Greene <dag at cray.com> wrote:
> The AVX saga continues.
>
> I am attempting to write a pattern for VEXTRACTF128 but am having some
> problems.  My attempt looks something like this:
>
> defm EXTRACTF128 : avx_fp_extract_vector_osta_node_mri_256<0x19, MRMDestReg,
>                      MRMDestMem, "extractf128", undef, X86f32, X86i32i8,
>                   // rr
>                   [(set VR128:$dst,
>                         (v4f32 (vector_shuffle
>                                     (v8f32 undef), (v8f32 VR256:$src1),
>                                     VEXTRACTF128_shuffle_mask:$src2)))]>;
>
> (This is simplified for the sake of exposition but this gets the idea across).
>
> TableGen reports a type contradition:
>
> VEXTRACTF128_256mri:    (st:isVoid (vector_shuffle:v4f32 (undef:v8f32),
> VR256:v8f32:$src1, (build_vector)<<P:Predicate_VEXTRACTF128_shuffle_mask>>:
> $src2), addr:iPTR:
> $dst)<<P:Predicate_unindexedstore>><<P:Predicate_store>><<P:Predicate_alignedstore>>
> tblgen: In VEXTRACTF128_256mri: Type inference contradiction found in node
> vector_shuffle!
>
> Well, it's right!  So how do I express this kind of thing?  Since LLVM 2.5
> shufflevector supports creating a vector of a difference size than the
> inputs.  Which is exactly what we need for VEXTRACTF128 and VINSERTF128.

Perhaps EXTRACT_SUBVECTOR would be more appropriate here?

-Eli