Re: [PATCH for-6.2 17/34] target/arm: Implement MVE VMLAS

[Peter Maydell]

On Fri, 16 Jul 2021 at 23:12, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> On 7/13/21 6:37 AM, Peter Maydell wrote:
> > Implement the MVE VMLAS insn, which multiplies a vector by a vector
> > and adds a scalar.
> >
> > Signed-off-by: Peter Maydell<peter.maydell@linaro.org>
> > ---
> >   target/arm/helper-mve.h    |  8 ++++++++
> >   target/arm/mve.decode      |  3 +++
> >   target/arm/mve_helper.c    | 31 +++++++++++++++++++++++++++++++
> >   target/arm/translate-mve.c |  2 ++
> >   4 files changed, 44 insertions(+)
> ...
>
> > +/* Vector by vector plus scalar */
> > +#define DO_VMLAS(D, N, M) ((N) * (D) + (M))
> > +
> > +DO_2OP_ACC_SCALAR_S(vmlass, DO_VMLAS)
> > +DO_2OP_ACC_SCALAR_U(vmlasu, DO_VMLAS)
>
> This is confusing.  The ARM says
>
> # Operations that do not perform
> # widening are always unsigned (encoded with U=1),

I have noticed that that text often appears for insns where it doesn't
really apply. I mostly ignore the text in favour of looking at
the pseudocode for working out what is supposed to be done.

-- PMM