[llvm-dev] SDAG: Type legalization woes (context insensitivity)

[Craig Topper via llvm-dev]

Is v64i1 not a legal type for Hexagon? What assertion are you hitting?

~Craig


On Mon, Mar 22, 2021 at 11:30 AM Krzysztof Parzyszek via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Summary: some types need more contextual information to properly legalize
> than what TLI queries give.
>
> Example: consider v32i1:
> 1.  v32i1 = compare v32i32, v32i32    ; all good
> 2.  v32i1 = compare v32i16, v32i16    ; problem: v32i16 not legal, but
> v32i1 is
>
>   The type v32i1 is legal because there it can be represented in a
> register and can be a result of a legal comparison of legally-typed
> vectors.  But it can also be a result of comparing illegally-typed vectors,
> which causes a problem.
>   The type legalization first looks at the value type, sees v32i1, takes
> note that it's legal.  Then, for the second case, it will attempt to
> legalize the operand types, but that action would also cause the result
> type to change (e.g. widen everything: v32i16->v64i16, v32i1->v64i1),
> hitting an assertion.
>
> I'm seeing this issue on Hexagon, but it seems to be fairly generic in its
> nature.  Has anyone else experienced this?
>
> I want to fix this somehow.  My current idea is to simply allow a known
> legal type to be replaced with another legal type, but there may be
> different approaches, like using SDValue in the TLI.whatAbouThisType family.
>
> Does anybody have concerns, thoughts?
>
> --
> Krzysztof Parzyszek  kparzysz at quicinc.com   AI tools development
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20210322/4b5f14fc/attachment.html>