Re: [PATCH for-9.1 04/19] target/i386: do not use s->tmp0 and s->tmp4 to compute flags

[Richard Henderson <richard.henderson@linaro.org>]

On 4/9/24 06:43, Paolo Bonzini wrote:
> Create a new temporary whenever flags have to use one, instead of using
> s->tmp0 or s->tmp4.  NULL can now be passed as the scratch register
> to gen_prepare_*.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   target/i386/tcg/translate.c | 54 +++++++++++++++++++++----------------
>   1 file changed, 31 insertions(+), 23 deletions(-)
> 
> diff --git a/target/i386/tcg/translate.c b/target/i386/tcg/translate.c
> index 197cccb6c96..debc1b27283 100644
> --- a/target/i386/tcg/translate.c
> +++ b/target/i386/tcg/translate.c
> @@ -947,9 +947,9 @@ static CCPrepare gen_prepare_eflags_c(DisasContext *s, TCGv reg)
>       case CC_OP_SUBB ... CC_OP_SUBQ:
>           /* (DATA_TYPE)CC_SRCT < (DATA_TYPE)CC_SRC */
>           size = s->cc_op - CC_OP_SUBB;
> -        t1 = gen_ext_tl(s->tmp0, cpu_cc_src, size, false);
> -        /* If no temporary was used, be careful not to alias t1 and t0.  */
> -        t0 = t1 == cpu_cc_src ? s->tmp0 : reg;
> +        /* Be careful not to alias t1 and t0.  */
> +        t1 = gen_ext_tl(NULL, cpu_cc_src, size, false);
> +        t0 = (reg == t1 || !reg) ? tcg_temp_new() : reg;
>           tcg_gen_mov_tl(t0, s->cc_srcT);
>           gen_extu(size, t0);

The tcg_temp_new, mov, and extu can be had with gen_ext_tl...

>           goto add_sub;
> @@ -957,8 +957,9 @@ static CCPrepare gen_prepare_eflags_c(DisasContext *s, TCGv reg)
>       case CC_OP_ADDB ... CC_OP_ADDQ:
>           /* (DATA_TYPE)CC_DST < (DATA_TYPE)CC_SRC */
>           size = s->cc_op - CC_OP_ADDB;
> -        t1 = gen_ext_tl(s->tmp0, cpu_cc_src, size, false);
> -        t0 = gen_ext_tl(reg, cpu_cc_dst, size, false);
> +        /* Be careful not to alias t1 and t0.  */
> +        t1 = gen_ext_tl(NULL, cpu_cc_src, size, false);
> +        t0 = gen_ext_tl(reg == t1 ? NULL : reg, cpu_cc_dst, size, false);

... like this.

It would be helpful to update the function comments (nothing is 'compute ... to reg' in 
these functions).  Future cleanup, perhaps rename 'reg' to 'scratch', or remove the 
argument entirely where applicable.

> @@ -1109,11 +1113,13 @@ static CCPrepare gen_prepare_cc(DisasContext *s, int b, TCGv reg)
>           size = s->cc_op - CC_OP_SUBB;
>           switch (jcc_op) {
>           case JCC_BE:
> -            tcg_gen_mov_tl(s->tmp4, s->cc_srcT);
> -            gen_extu(size, s->tmp4);
> -            t0 = gen_ext_tl(s->tmp0, cpu_cc_src, size, false);
> -            cc = (CCPrepare) { .cond = TCG_COND_LEU, .reg = s->tmp4,
> -                               .reg2 = t0, .use_reg2 = true };
> +            /* Be careful not to alias t1 and t0.  */
> +            t1 = gen_ext_tl(NULL, cpu_cc_src, size, false);
> +            t0 = (reg == t1 || !reg) ? tcg_temp_new() : reg;
> +            tcg_gen_mov_tl(t0, s->cc_srcT);
> +            gen_extu(size, t0);

gen_ext_tl

> +            cc = (CCPrepare) { .cond = TCG_COND_LEU, .reg = t0,
> +                               .reg2 = t1, .use_reg2 = true };
>               break;
>   
>           case JCC_L:
> @@ -1122,11 +1128,13 @@ static CCPrepare gen_prepare_cc(DisasContext *s, int b, TCGv reg)
>           case JCC_LE:
>               cond = TCG_COND_LE;
>           fast_jcc_l:
> -            tcg_gen_mov_tl(s->tmp4, s->cc_srcT);
> -            gen_exts(size, s->tmp4);
> -            t0 = gen_ext_tl(s->tmp0, cpu_cc_src, size, true);
> -            cc = (CCPrepare) { .cond = cond, .reg = s->tmp4,
> -                               .reg2 = t0, .use_reg2 = true };
> +            /* Be careful not to alias t1 and t0.  */
> +            t1 = gen_ext_tl(NULL, cpu_cc_src, size, true);
> +            t0 = (reg == t1 || !reg) ? tcg_temp_new() : reg;
> +            tcg_gen_mov_tl(t0, s->cc_srcT);
> +            gen_exts(size, t0);

gen_ext_tl

With that,
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~