Re: [PATCH v2 2/3] target/arm: Fix SVE2 WHILEWR/WHILERW zero diff boundary case

On Mon, 17 Aug 2026 at 17:37, Peter Maydell <[email protected]> wrote:
>
> On Tue, 11 Aug 2026 at 20:16, Richard Henderson
> <[email protected]> wrote:
> >
> > The trans_WHILE_ptr function incorrectly handles the case where the
> > address difference divided by ESIZE results in zero. This happens when
> > the address difference is less than ESIZE but greater than zero.
> >
> > Fix by dropping direct comparisons of op0 vs op1, and instead
> > testing the scaled diff vs 0.  Merge with the bounding to the
> > maximum vector length via wrapping arithmetic.
> >
> > Reported-by: YanjunYang <[email protected]>
> > Signed-off-by: Richard Henderson <[email protected]>
> > ---
> >  target/arm/tcg/translate-sve.c | 38 +++++++++++++++++++++-------------
> >  1 file changed, 24 insertions(+), 14 deletions(-)
>
>
> > -    /* Since we're bounded, pass as a 32-bit type.  */
> > +    /*
> > +     * If diff == 0, the condition is always true.  Also, bound to max.
> > +     * Simplify
> > +     *    diff = diff ? diff : max;
> > +     *    diff = umin(diff, max);
> > +     * via
> > +     *    diff -= 1;
> > +     *    diff = umin(diff, max - 1);
> > +     *    diff += 1;
> > +     * via 0 - 1 == UINT64_MAX.
> > +     */
> > +    tcg_gen_addi_i64(diff, diff, -1);
> > +    tcg_gen_umin_i64(diff, diff, tcg_constant_i64((vsz >> a->esz) - 1));
> > +
> > +    /*
> > +     * Since we're bounded, pass as a 32-bit type.
> > +     * Sink the diff += 1 from above into the 32-bit type.
>
> Is it worth doing that? Hosts are all 64-bits now, and surely there's
> not going to be a perf or codesize difference between "add 1"
> on a 32-bit type vs a 64-bit type ?

Other than that
Reviewed-by: Peter Maydell <[email protected]>

thanks
-- PMM