Re: Will GCC eventually support SSE2 or SSE4.1?

[Jonathan Wakely <jwakely.gcc@gmail.com>]

On Fri, 26 May 2023 at 15:34, Stefan Kanthak <stefan.kanthak@nexgo.de> wrote:
>
> "Jonathan Wakely" <jwakely.gcc@gmail.com> wrote:
>
> > On Fri, 26 May 2023 at 14:55, Stefan Kanthak <stefan.kanthak@nexgo.de> wrote:
>
> [...]
>
> >> NOT obvious is but that -m<feature> -march=<lowerISA> does not clear any
> >> <feature> not supported in <lowerISA>, i.e the last one does NOT win here.
> >
> > The last -march option selects the base set of instructions. The -mISA
> > options modify that base.
>
> You but missed the point, AGAIN: the modifications per -mISA and -mno-ISA
> persist, i.e. they are NOT reset by the last -march= option.

Nobody said they are reset, and the docs don't say that, so assume they are not.

The last -march option selects a base and the -mISA options modify the
base. Note *the* base. The one that was selected. By the last -march
option. The base.

> Is this SOOOO hard to grok?

I understand your question. It's based on failing to read or
understand what has been said.

There is a base ISA. Then there are additions or subtractions relative
to that base. That's it. That actually tells you everything you need
to know, if you just apply some thought.

Choosing a base does not remove the effects of the additions or
subtractions, because they are additions and subtractions relative to
whichever base arch is in effect.

Where the -misa options appear on the command line relative to -march
doesn't matter, which is why it doesn't need to be stated explicitly.
The order only matters for -march relative to other -march options,
and -misa options relative to other -misa options.


> Is this soooo hard to document?

I prefer arguing with trolls, it's even easier.