On Tue, Aug 22, 2023 at 09:02:29PM +0800, Hongtao Liu wrote:
> > Agreed. And I still think -mevex512 vs. -mno-evex512 is the best option
> > name to represent whether the effective ISA set allows 512-bit vectors or
> > not. I think -mavx10.1 -mno-avx512cd should be fine. And, -mavx10.1-256
> > option IMHO should be in the same spirit to all the others a positive
> > enablement,
> > not both positive (enable avx512{f,cd,bw,dq,...} and negative (disallow
> > 512-bit vectors). So, if one uses -mavx512f -mavx10.1-256, because the
> > former would allow 512-bit vectors, the latter shouldn't disable those again
> > because it isn't a -mno-* option. Sure, instructions which are specific to
> But there's implicit negative (disallow 512-bit vector), I think
That is wrong.
> -mav512f -mavx10.1-256 or -mavx10.1-256 -mavx512f shouldn't enable
> 512-bit vector.
Because then the -mavx10.1-256 option behaves completely differently from
all the other isa options.
We have the -march= options which are processed separately, but the normal
ISA options either only enable something (when -mwhatever), or only disable
something
(when -mno-whatever). -mavx512f -mavx10.1-256 should be a union of those
ISAs, like say -mavx2 -mbmi is, not an intersection or something even
harder to understand.
> Further, we should disallow a mix of exex512 and non-evex512 (e.g.
> -mavx10.1-512 -mavx10.2-256),they should be a unified separate switch
> that either disallows both or allows both. Instead of some isa
> allowing it and some isa disallowing it.
No, it will be really terrible user experience if the new options behave
completely differently from everything else. Because then we'll need to
document it in detail how it behaves and users will have hard time to figure
it out, and specify what it does not just on the command line, but also when
mixing with target attribute or pragmas. -mavx10.1-512 -mavx10.2-256 should
be a union of those two ISAs. Either internally there is an ISA flag whether
the instructions in the avx10.2 ISA but not avx10.1 ISA can operate on
512-bit vectors or not, in that case -mavx10.1-512 -mavx10.2-256 should
enable the AVX10.1 set including 512-bit vectors + just the < 512-bit
instructions from the 10.1 to 10.2 delta, or if there is no such separation
internally, it will just enable full AVX10.2-512. User has asked for it.
Jakub
