Re: [PATCH v2 43/45] target/arm/vec_helper: Add gvec fp indexed multiply-and-add operations

[Peter Maydell]

On Sat, 29 Aug 2020 at 00:24, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> On 8/28/20 11:33 AM, Peter Maydell wrote:
> > +#define float16_nop(N, M, S) (M)
> > +#define float32_nop(N, M, S) (M)
> > +#define float64_nop(N, M, S) (M)
> >
> > +DO_FMUL_IDX(gvec_fmul_idx_h, nop, float16, H2)
> > +DO_FMUL_IDX(gvec_fmul_idx_s, nop, float32, H4)
> > +DO_FMUL_IDX(gvec_fmul_idx_d, nop, float64, )
> > +
> > +/*
> > + * Non-fused multiply-accumulate operations, for Neon. NB that unlike
> > + * the fused ops below they assume accumulate both from and into Vd.
> > + */
> > +DO_FMUL_IDX(gvec_fmla_nf_idx_h, add, float16, H2)
> > +DO_FMUL_IDX(gvec_fmla_nf_idx_s, add, float32, H4)
> > +DO_FMUL_IDX(gvec_fmls_nf_idx_h, sub, float16, H2)
> > +DO_FMUL_IDX(gvec_fmls_nf_idx_s, sub, float32, H4)
> > +
> > +#undef float16_nop
> > +#undef float32_nop
> > +#undef float64_nop
>
> This floatN_nop stuff is pretty ugly.
>
> Better to pass in either floatN_mul, or the floatN_muladd_nf helpers that you
> added earlier.  Although I guess you're missing float64_muladd_nf so far.

I thought about doing that, but the float*_muladd_nf functions
don't have the same signature as float*_mul -- they take
(dest, op1, op2, stat) and float*_mul only takes (op1, op2, stat) --
so it doesn't work. You'd have to construct a wrapper for
the mul function that took and ignored the dest argument,
or split out mul entirely into its own macro rather than
using DO_FMUL_IDX for mul and muladd. The nop macros seemed
the simplest.

thanks
-- PMM