Re: [PATCH 07/28] tcg/ppc: Split out tcg_out_bswap16

[Richard Henderson]

On 6/21/21 7:29 AM, Peter Maydell wrote:
> > +static void tcg_out_bswap16(TCGContext *s, TCGReg dst, TCGReg src)
> > +{
> > +    TCGReg tmp = dst == src ? TCG_REG_R0 : dst;
> > +
> > +                                                   /* src = abcd */
> > +    tcg_out_rlw(s, RLWINM, tmp, src, 24, 24, 31);  /* tmp = 000c */
> > +    tcg_out_rlw(s, RLWIMI, tmp, src, 8, 16, 23);   /* tmp = 00dc */
> > +    tcg_out_mov(s, TCG_TYPE_REG, dst, tmp);
> > +}
>
> TCG_REG_R0 is implicitly available as a temp because it's not
> listed in tcg_target_reg_alloc_order[], right?

Slightly better than that:

    tcg_regset_set_reg(s->reserved_regs, TCG_REG_R0); /* tcg temp */


> (There's a comment
> in the definition of that array that says V0 and V1 are reserved
> as temporaries, but not a comment about R0.)

Yeah, tcg/ppc/ is due for a bit of cleanup.

> Would be nice to keep these comments about what operations we think
> the insns are doing, given that RLWINM and RLWIMI are pretty confusing.

Hmm, I guess.  I found them intrusive.


r~