Re: [PATCH 28/37] target/i386: reimplement 0x0f 0x38, add AVX

[Richard Henderson]

On 9/14/22 18:04, Paolo Bonzini wrote:
> > > +void glue(helper_vpgatherdd, SUFFIX)(CPUX86State *env,
> > > +        Reg *d, Reg *v, Reg *s, target_ulong a0, unsigned scale)
> > > +{
> > > +    int i;
> > > +    for (i = 0; i < (2 << SHIFT); i++) {
> > > +        if (v->L(i) >> 31) {
> > > +            target_ulong addr = a0
> > > +                + ((target_ulong)(int32_t)s->L(i) << scale);
> > > +            d->L(i) = cpu_ldl_data_ra(env, addr, GETPC());
> > > +        }
> > > +        v->L(i) = 0;
> > > +    }
> > > +}
> >
> > Better to not modify registers until all potential #GP are raised.
>
> This is actually intentional: elements of v are zeroes whenever an
> element is read successfully, so that values are not reread when the
> instruction restarts. The manual says "If a fault is triggered by an
> element and delivered, all elements closer to the LSB of the
> destination zmm will be completed".

Ooo, I had never noticed that.


r~