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Re: [Qemu-devel] [PATCH v5 11/19] target/i386: optimize cross-page direc

From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH v5 11/19] target/i386: optimize cross-page direct jumps in softmmu
Date: Sat, 29 Apr 2017 11:14:09 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.0

On 04/28/2017 06:56 PM, Alex Bennée wrote:

Richard Henderson <address@hidden> writes:

From: "Emilio G. Cota" <address@hidden>

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 <address@hidden>
Signed-off-by: Emilio G. Cota <address@hidden>
Message-Id: <address@hidden>
Signed-off-by: Richard Henderson <address@hidden>
  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)
          tcg_gen_exit_tb((uintptr_t)s->tb + tb_num);
      } else {
-        /* jump to another page: currently not optimized */
+        /* jump to another page */
-        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.

It's mostly hysterical raisins, and that no one has rewritten it yet.

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

Yeah.  :-/


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