Re: [PATCH v2 07/81] target/arm: Do not test TCG_TARGET_HAS_bitsel_vec

[Philippe Mathieu-Daudé]

On 8/1/25 23:30, Richard Henderson wrote:
> On 1/8/25 14:14, Philippe Mathieu-Daudé wrote:
> > > > >   static void gen_bsl1n_vec(unsigned vece, TCGv_vec d, TCGv_vec n,
> > > > >                             TCGv_vec m, TCGv_vec k)
> > > > >   {
> > > > > -    if (TCG_TARGET_HAS_bitsel_vec) {
> > > > > -        tcg_gen_not_vec(vece, n, n);
> > > > > -        tcg_gen_bitsel_vec(vece, d, k, n, m);
> > > > > -    } else {
> > > >
> > > > Why aren't we doing the NOT n operation here?
> > > >
> > > > > -        tcg_gen_andc_vec(vece, n, k, n);

[*]

> > > > > -        tcg_gen_andc_vec(vece, m, m, k);
> > > > > -        tcg_gen_or_vec(vece, d, n, m);
> > > > > -    }
> > > > > +    tcg_gen_not_vec(vece, n, n);
> > > > > +    tcg_gen_bitsel_vec(vece, d, k, n, m);
> > >
> > > Pardon?  It's right there, unindented.
> >
> > Sorry I'm not clear. Previous to your change, in the
> > TCG_TARGET_HAS_bitsel_vec side we use the NOT opcode,
> > but not in the other side where we expand, why?
>
> Are you asking about the code being removed?
>
> Recall that bitsel = (n & k) | (m & ~k).
>
> Passing n = ~n' we get (~n & k) | (m & ~k),
>                       = (k & ~n) | (m & ~k).
>
> which is the two andc + or operations above.

Sorry, I misread the first ANDC [*] as AND...

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>