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target/arm: optimize indirect branches 

Speed up indirect branches by jumping to the target if it is valid.

Softmmu measurements (see later commit for user-mode results):

Note: baseline (i.e. speedup == 1x) is QEMU v2.9.0.

- Impact on Boot time

| setup  | ARM debian jessie boot+shutdown time | stddev |
|--------+--------------------------------------+--------|
| v2.9.0 |                                 8.84 |   0.07 |
| +cross |                                 8.85 |   0.03 |
| +jr    |                                 8.83 |   0.06 |

-                            NBench, arm-softmmu (debian jessie guest). Host: Intel i7-4790K @ 4.00GHz

  1.3x +-+-------------------------------------------------------------------------------------------------------------+-+
       |                                                                                                                 |
       |   cross                                                          ####                                           |
 1.25x +cross+jr..........................................................#++#.........................................+-+
       |                                                        ####      #  #                                           |
       |                                                     +++#  #      #  #                                           |
       |                                      +++            ****  #      #  #                                           |
  1.2x +-+...................................####............*..*..#......#..#.........................................+-+
       |                                  ****  #            *  *  #      #  #     ####                                  |
       |                                  *  *  #            *  *  #      #  #     #  #                                  |
 1.15x +-+................................*..*..#............*..*..#......#..#.....#..#................................+-+
       |                                  *  *  #            *  *  #      #  #     #  #                                  |
       |                                  *  *  #      ####  *  *  #      #  #     #  #                                  |
       |                                  *  *  #      #  #  *  *  #      #  #     #  #                         ####     |
  1.1x +-+................................*..*..#......#..#..*..*..#......#..#.....#..#.........................#..#...+-+
       |                                  *  *  #      #  #  *  *  #      #  #     #  #                         #  #     |
       |                                  *  *  #      #  #  *  *  #      #  #     #  #                         #  #     |
 1.05x +-+..........................####..*..*..#......#..#..*..*..#......#..#.....#..#......+++............*****..#...+-+
       |                        *****  #  *  *  #      #  #  *  *  #  *****  #     #  #   +++ |    ****###  *   *  #     |
       |                        *+++*  #  *  *  #      #  #  *  *  #  *+++*  #  ****  #  *****###  *  *  #  *   *  #     |
       |     *****###  +++####  *   *  #  *  *  #  *****  #  *  *  #  *   *  #  *  *  #  * | *++#  *  *  #  *   *  #     |
    1x +-++-+*+++*-+#++****++#++*+-+*++#+-*++*++#-+*+++*-+#++*++*++#++*+-+*++#+-*++*++#-+*+++*-+#++*++*++#++*+-+*++#+-++-+
       |     *   *  #  *  *  #  *   *  #  *  *  #  *   *  #  *  *  #  *   *  #  *  *  #  *   *  #  *  *  #  *   *  #     |
       |     *   *  #  *  *  #  *   *  #  *  *  #  *   *  #  *  *  #  *   *  #  *  *  #  *   *  #  *  *  #  *   *  #     |
 0.95x +-+---*****###--****###--*****###--****###--*****###--****###--*****###--****###--*****###--****###--*****###---+-+
       ASSIGNMENT BITFIELD   FOURFP EMULATION   HUFFMAN   LU DECOMPOSITIONEURAL NNUMERIC SOSTRING SORT     hmean
  png: http://imgur.com/eOLmZNR

NB. 'cross' represents the previous commit.

Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <1493263764-18657-8-git-send-email-cota@braap.org>
[rth: Replace gen_jr global variable with DISAS_EXIT state.]
Signed-off-by: Richard Henderson <rth@twiddle.net>
This commit is contained in:
Emilio G. Cota 2017-04-26 23:29:20 -04:00 committed by Richard Henderson
parent 7ad55b4ffd
commit 8a6b28c7b5
2 changed files with 20 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
target/arm/translate.c
View File

@ -1182,7 +1182,7 @@ static void gen_exception_internal_insn(DisasContext *s, int offset, int excp)
gen_set_condexec(s);
gen_set_pc_im(s, s->pc - offset);
gen_exception_internal(excp);
s->is_jmp = DISAS_JUMP;
s->is_jmp = DISAS_EXC;
}
static void gen_exception_insn(DisasContext *s, int offset, int excp,
@ -1191,14 +1191,14 @@ static void gen_exception_insn(DisasContext *s, int offset, int excp,
gen_set_condexec(s);
gen_set_pc_im(s, s->pc - offset);
gen_exception(excp, syn, target_el);
s->is_jmp = DISAS_JUMP;
s->is_jmp = DISAS_EXC;
}
/* Force a TB lookup after an instruction that changes the CPU state. */
static inline void gen_lookup_tb(DisasContext *s)
{
tcg_gen_movi_i32(cpu_R[15], s->pc & ~1);
s->is_jmp = DISAS_JUMP;
s->is_jmp = DISAS_EXIT;
}
static inline void gen_hlt(DisasContext *s, int imm)
@ -4150,19 +4150,23 @@ static inline bool use_goto_tb(DisasContext *s, target_ulong dest)
#endif
}
static inline void gen_goto_tb(DisasContext *s, int n, target_ulong dest)
static void gen_goto_ptr(void)
{
TCGv addr = tcg_temp_new();
tcg_gen_extu_i32_tl(addr, cpu_R[15]);
tcg_gen_lookup_and_goto_ptr(addr);
tcg_temp_free(addr);
}
static void gen_goto_tb(DisasContext *s, int n, target_ulong dest)
{
if (use_goto_tb(s, dest)) {
tcg_gen_goto_tb(n);
gen_set_pc_im(s, dest);
tcg_gen_exit_tb((uintptr_t)s->tb + n);
} else {
TCGv addr = tcg_temp_new();
gen_set_pc_im(s, dest);
tcg_gen_extu_i32_tl(addr, cpu_R[15]);
tcg_gen_lookup_and_goto_ptr(addr);
tcg_temp_free(addr);
gen_goto_ptr();
}
}
@ -12095,11 +12099,14 @@ void gen_intermediate_code(CPUARMState *env, TranslationBlock *tb)
gen_set_pc_im(dc, dc->pc);
/* fall through */
case DISAS_JUMP:
gen_goto_ptr();
break;
default:
/* indicate that the hash table must be used to find the next TB */
tcg_gen_exit_tb(0);
break;
case DISAS_TB_JUMP:
case DISAS_EXC:
/* nothing more to generate */
break;
case DISAS_WFI:

4
target/arm/translate.h
View File

@ -139,6 +139,10 @@ static void disas_set_insn_syndrome(DisasContext *s, uint32_t syn)
* custom end-of-TB code)
*/
#define DISAS_BX_EXCRET 11
/* For instructions which want an immediate exit to the main loop,
* as opposed to attempting to use lookup_and_goto_ptr.
*/
#define DISAS_EXIT 12
#ifdef TARGET_AARCH64
void a64_translate_init(void);