Re: [PATCH 6/6] target/mips: Convert Loongson [D]MULT[U].G opcodes to decodetree

[Philippe Mathieu-Daudé]

On 31/8/23 21:12, Philippe Mathieu-Daudé wrote:
> On 21/1/21 21:06, Richard Henderson wrote:
> > On 1/12/21 11:55 AM, Philippe Mathieu-Daudé wrote:
> > > Convert the following opcodes to decodetree:
> > >
> > > - MULT.G - multiply 32-bit signed integers
> > > - MULTU.G - multiply 32-bit unsigned integers
> > > - DMULT.G - multiply 64-bit signed integers
> > > - DMULTU.G - multiply 64-bit unsigned integers
> > >
> > > Now that all opcodes from the extension have been converted, we
> > > can remove completely gen_loongson_integer() and its 2 calls in
> > > decode_opc_special2_legacy() and decode_opc_special3_legacy().
> > >
> > > Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> > > ---
> > >   target/mips/godson2.decode    |  5 ++
> > >   target/mips/loong-ext.decode  |  5 ++
> > >   target/mips/loong_translate.c | 58 ++++++++++++++++++++++
> > >   target/mips/translate.c       | 92 +----------------------------------
> > >   4 files changed, 70 insertions(+), 90 deletions(-)


> > > +static bool gen_lext_MULT_G(DisasContext *s, int rd, int rs, int rt,
> > > +                            bool is_double, bool is_unsigned)
> > > +{
> > > +    TCGv t0, t1;
> > > +
> > > +    if (is_double) {
> > > +        if (TARGET_LONG_BITS != 64) {
> > > +            return false;
> > > +        }
> > > +        check_mips_64(s);
> > > +    }
> > > +
> > > +    if (rd == 0) {
> > > +        /* Treat as NOP. */
> > > +        return true;
> > > +    }
> > > +
> > > +    t0 = tcg_temp_new();
> > > +    t1 = tcg_temp_new();
> > > +
> > > +    gen_load_gpr(t0, rs);
> > > +    gen_load_gpr(t1, rt);
> > > +
> > > +    if (is_unsigned && !is_double) {
> > > +        tcg_gen_ext32u_tl(t0, t0);
> > > +        tcg_gen_ext32u_tl(t1, t1);
> > > +    }
> >
> > While this is a faithful conversion of the existing code, these 
> > extensions make
> > no difference to the result.  They are redundant with
> >
> > > +    tcg_gen_mul_tl(cpu_gpr[rd], t0, t1);
> > > +    if (!is_double) {
> > > +        tcg_gen_ext32s_tl(cpu_gpr[rd], cpu_gpr[rd]);
> >
> > this one, which discards any bit that might have been set by the input 
> > bits
> > that are cleared.
>
> I see.
>
> > There is no actual difference between MULT.G and MULTU.G, or DMULT.G and
> > DMULTU.G, because they don't record the most significant bits of the 
> > infinite
> > result in any way.
>
> Right.
>
> > > +static bool trans_MULT_G(DisasContext *s, arg_muldiv *a)
> > > +{
> > > +    return gen_lext_MULT_G(s, a->rt, a->rs, a->rd, false, false);
> > > +}
> > > +
> > > +static bool trans_MULTU_G(DisasContext *s, arg_muldiv *a)
> > > +{
> > > +    return gen_lext_MULT_G(s, a->rt, a->rs, a->rd, false, true);
> > > +}
> > > +
> > > +static bool trans_DMULT_G(DisasContext *s, arg_muldiv *a)
> > > +{
> > > +    return gen_lext_MULT_G(s, a->rt, a->rs, a->rd, true, false);
> > > +}
> > > +
> > > +static bool trans_DMULTU_G(DisasContext *s, arg_muldiv *a)
> > > +{
> > > +    return gen_lext_MULT_G(s, a->rt, a->rs, a->rd, true, true);
> > > +}
> >
> > So... if you want to clean this up afterward, or before is up to you.

"before" ended being way simpler :>