Il mer 10 apr 2024, 08:35 Richard Henderson
ha scritto:
> 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
> > ---
> > 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...
>
There's actually a lot more that can be done now that I looked more closely
at gen_ext_tl. It is fine (modulo bugs elsewhere) to just extend cc_* in
place. In fact this lets the optimizer work better, even allows (rare)
cross tb optimization because it effectively bumps CC_OP_ADD* to
target_long size, and is just as effective in removing tmp0/tmp4.
Paolo
> > 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
>
>
> r~
>
>
