[llvm-dev] Question on pattern matching extractelt

[Craig Topper via llvm-dev]

I think it’s disallowed by the SDTypeProfile in TargetSelectionDAG.td. You
can use vector_extract instead of extractelt which is what some other
targets like WebAssembly are doing for this issue. It's type profile is
more relaxed on this.


On Thu, Nov 28, 2019 at 8:51 AM Sebastien Le Duc via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi,
> I have an issue with pattern matching.
>
> I have the following SelectionDAG:
>
> t13: i32 = extract_vector_elt t2, Constant:i64<1>
>
> That I am trying to match with the following pattern:
>
> def : Pat<(extractelt (v4i16 SingleReg:$v), 1), (SRADd1 SingleReg :$v, (i64 16))>;
>
>
> But for some reason the pattern does not match.
> It seems to be  due to the fact extract_vector_elt's result type is i32
> (because i16 is not a legal type on our processor), but according to the
> comment in ISDOpcodes.h, it is allowed for EXTRACT_VECTOR_ELT to have a
> result type larger than the element type of the vector, so I would expect
> to be able to match such pattern.
>
> I tried specifying the result type in the pattern:
>
> def : Pat<(i32 (extractelt (v4i16 SingleReg:$v), 1)), (SRADd1 SingleReg :$v, (i64 16))>;
>
>
> But in that case I get a tblgen error:
>
> possible type contradiction in the pattern below (use -print-records with
> llvm-tblgen to see all expanded records).
> anonymous_1188: (extractelt:{ *:[] } SingleReg:{ *:[] }:$v, 0:{ *:[i64] })
>
> Is there anyway to match such pattern?
>
> Thanks in advacne!
> regards,
> Sebastien
>
>
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