[PATCH, i386]: Fix PR 59021, new vzeroupper instructions generated with -mavx

[Eric Botcazou]

> Attached patch fixes PR 59021, where new vzeroupper instructions are
> generated for -mavx after Vlad's useless insn removal patch.
> 
> The problem was, that we depent on (useless) moves to AVX256 function
> argument registers in front of the function call to switch the mode to
> DIRTY mode. This is not true anymore, so call_insn has to switch to
> DIRTY mode by itself.

Thanks for fixing this!

> The patch will be backported to 4.7 and 4.8 branch in a couple of days.

The 4.7 branch uses a different mechanism so I'm not sure that's needed.

-- 
Eric Botcazou