vec_gather and vec_scatter would be useful to have for float32/64 and int32/64

[openpower-gitea-migrator]

Originally Gitea issue #87 by @ChipKerchner on 2022-03-08

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v = vec_gather(ptr0, ptr1, ptr2, ptr2)
vec_scatter(v, ptr0, ptr1, ptr2, ptr2)

[openpower-gitea-migrator]

@ChipKerchner commented on 2022-03-08

Should ptr1, ptr2, ptr3 be optional?

[openpower-gitea-migrator]

@ChipKerchner commented on 2022-03-08

Another option is to have a single base pointer and a stride.

[openpower-gitea-migrator]

@munroesj52 commented on 2022-03-09

I have versions of these implemented in PVECLIB (master but not release 1.0.4).
For example: https://munroesj52.github.io/vec__f32__ppc_8h.html#a80b2d79f8d3afb30b92638ad78c80ca9

Also: https://munroesj52.github.io/vec__int32__ppc_8h.html#aedabb123d258fd438bda778262d5b33f
https://munroesj52.github.io/vec__f64__ppc_8h.html#aeb96abe1cd1f78c4eee978add6268c80
https://munroesj52.github.io/vec__int64__ppc_8h.html#af18331cf83e5ec6965978589f812ead9

As you can see it covers both scalar offset and vector index forms. The scalar form is the best performing as the vector forms require a transfer/shift left to GPR scalars for the actual load/store.

You can pull from https://github.com/open-power-sdk/pveclib and try this yourself.

[openpower-gitea-migrator]

@ChipKerchner commented on 2022-03-11

Any plans for P10 support since there are new ISA 3.1 commands that might be helpful. Also does your version support both BE and LE?

[openpower-gitea-migrator]

@munroesj52 commented on 2022-03-12

Have already updated/added ~70 operations for P10. Mostly exploiting P10 instructions for existing pveclib double/quadword integer operations.

Still need to get a handle on integer divide for P7/8/9.
Currently working on Float128 round-to-odd operations for P7/8. The compiler has not always been helpful with a number of exposed bugz.

If you are looking for P10's VSX Matrix-Multiply Assist (MMA), the compile (GCC 11) already provides builtin support:
https://gcc.gnu.org/onlinedocs/gcc-11.2.0/gcc/PowerPC-Matrix-Multiply-Assist-Built-in-Functions.html#PowerPC-Matrix-Multiply-Assist-Built-in-Functions

If you are looking for transparent pveclib support for MMA, that is a bigger kettle of fish. For P7/8/9 this would require emulation of the MMA Accumulators and software MMA kernels for the various matrix operations and types.

This is a big job for one person's part-time hobby.

And it is not clear how many users there are for this low level API. I assume there are a small number of library developers, with the majority just using the library APIs? But library developers seem to be the target audience for pveclib.

Anyway for now I need to complete Float128 and vector integer divide.