Re: [Qemu-devel] [PATCH v5 11/19] target/i386: optimize cross-page direct jumps in softmmu

["Alex Bennée" <alex.bennee@linaro.org>]

Richard Henderson <rth@twiddle.net> writes:

> From: "Emilio G. Cota" <cota@braap.org>
>
> Instead of unconditionally exiting to the exec loop, use the
> gen_jr helper to jump to the target if it is valid.
>
> Perf impact: see next commit's log.
>
> Reviewed-by: Richard Henderson <rth@twiddle.net>
> Signed-off-by: Emilio G. Cota <cota@braap.org>
> Message-Id: <1493263764-18657-10-git-send-email-cota@braap.org>
> Signed-off-by: Richard Henderson <rth@twiddle.net>
> ---
>  target/i386/translate.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/target/i386/translate.c b/target/i386/translate.c
> index f0e48dc..ea113fe 100644
> --- a/target/i386/translate.c
> +++ b/target/i386/translate.c
> @@ -2154,9 +2154,9 @@ static inline void gen_goto_tb(DisasContext *s, int tb_num, target_ulong eip)
>          gen_jmp_im(eip);
>          tcg_gen_exit_tb((uintptr_t)s->tb + tb_num);
>      } else {
> -        /* jump to another page: currently not optimized */
> +        /* jump to another page */
>          gen_jmp_im(eip);
> -        gen_eob(s);
> +        gen_jr(s, cpu_tmp0);


I had to look up what was going on with cpu_tmp0 there. Is there a
particular reason i386 has these global temps with implied setting
rules? It does seem somewhat hacky.

Given cmp_tmp0 seems to be a heavily used across i386 I guess it keeps
to the style of the translator :-/


>      }
>  }


--
Alex Bennée