Re: [PATCH v5 16/36] tcg: Add tcg_gen_{non}atomic_cmpxchg_i128

[Philippe Mathieu-Daudé]

On 27/1/23 07:39, Richard Henderson wrote:
> On 1/26/23 14:45, Philippe Mathieu-Daudé wrote:
> > > +        /* Compare i128 */
> > > +        tcg_gen_xor_i64(t0, TCGV128_LOW(oldv), TCGV128_LOW(cmpv));
> > > +        tcg_gen_xor_i64(t1, TCGV128_HIGH(oldv), TCGV128_HIGH(cmpv));
> > > +        tcg_gen_or_i64(t0, t0, t1);
> >
> > Can we skip the OR ...
> >
> > > +        /* tmpv = equal ? newv : oldv */
> > > +        tcg_gen_movcond_i64(TCG_COND_EQ, TCGV128_LOW(tmpv), t0, z,
> > > +                            TCGV128_LOW(newv), TCGV128_LOW(oldv));
> > > +        tcg_gen_movcond_i64(TCG_COND_EQ, TCGV128_HIGH(tmpv), t0, z,
> >
> > ... and test t1 here to partially update LO/HI? (we could remove t1 and
> > just use t0 as twice 'xor + movcond' but the code is less readable).
>
> No.
>
> We want equality on the entire 128-bit comparison to control the 
> conditional moves.

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