[llvm-dev] [RFC] Optional parameter tuples

[Nicolai Hähnle via llvm-dev]

Hi Simon,

On Wed, Feb 12, 2020 at 10:28 AM Simon Moll via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> For constrained fp and VP, we only require a very restricted form of this. That is:
>
> - Tuples are only allowed on intrinsic function calls.
>
> - There is a builtin list of allowed tuple types (eg tablegen file).
>
> - Tuple types are opt in: Intrinsics define a list of permissible tuple types.
>
> - Tuple parameters have default values when a tuple is absent at a call site. Eg, for `fpenv` the default fp environment `fpenv(fpround.tonearest, fpexcept.ignore)` is implied in the first example above.

This seems a pretty interesting idea. It's something we could consider
long-term for the AMDGPU image.sample intrinsics. Image sample
intrinsics have fairly complex "address" parameters, consisting of a
"body" (s,t,r coordinates, depending on the image dimensionality) and
optional extra parameters such as "lod bias", "z compare reference
variable", "texel offsets". Those optional extra parameters could be
an application of optional parameter tuples.

Have you given any thought to how this would be presented in
MachineIR, especially through the GlobalISel path?

Cheers,
Nicolai



>
>
> Btw, different to operand bundles, optional parameter tuples are much more restricted and do not imply side effects of any kind. We might want to re-use the OpBundle logic for this though.
>
> There are probably more use cases for this and i'd like to hear about them.
>
> Looking forward to your feedback
>
> - Simon
>
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