Re: [Qemu-devel] [PATCH v5 12/19] target/i386: optimize indirect branches

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

Richard Henderson <rth@twiddle.net> writes:

> From: "Emilio G. Cota" <cota@braap.org>
>
> Speed up indirect branches by jumping to the target if it is valid.
>
> Softmmu measurements (see later commit for user-mode numbers):
>
> Note: baseline (i.e. speedup == 1x) is QEMU v2.9.0.
>
> -                  SPECint06 (test set), x86_64-softmmu (Ubuntu 16.04 guest). Host: Intel i7-4790K @ 4.00GHz
>
>  2.4x +-+--------------------------------------------------------------------------------------------------------------+-+
>       |                                                                                                                  |
>       |   cross                                                                                                          |
>  2.2x +cross+jr..........................................................................+++...........................+-+
>       |                                                                                   |                              |
>       |                                                                               +++ |                              |
>    2x +-+..............................................................................|..|............................+-+
>       |                                                                                |  |                              |
>       |                                                                                |  |                              |
>  1.8x +-+..............................................................................|####...........................+-+
>       |                                                                                |# |#                             |
>       |                                                                              **** |#                             |
>  1.6x +-+............................................................................*.|*.|#...........................+-+
>       |                                                                              * |* |#                             |
>       |                                                                              * |* |#                             |
>  1.4x +-+.......................................................................+++..*.|*.|#...........................+-+
>       |                                                      ++++++             #### * |*++#             +++             |
>       |                        +++                            |  |              #++# *++*  #          +++ |              |
>  1.2x +-+......................###.....####....+++............|..|...........****..#.*..*..#....####...|.###.....####..+-+
>       |        +++          **** #  ****  #    ####          ***###          *++*  # *  *  #    #++#  ****|#  +++#++#    |
>       |    ****###     +++  *++* #  *++*  #  ++#  #    ####  *|* |#     +++  *  *  # *  *  #  ***  #  *| *|#  ****  #    |
>    1x +-++-*++*++#++***###++*++*+#++*+-*++#+****++#++***++#+-*+*++#-+****##++*++*-+#+*++*-+#++*+*++#++*-+*+#++*++*++#-++-+
>       |    *  *  #  * *  #  *  * #  *  *  # *  *  #  * *  #  *|* |#  *++* #  *  *  # *  *  #  * *  #  *  * #  *  *  #    |
>       |    *  *  #  * *  #  *  * #  *  *  # *  *  #  * *  #  *+*++#  *  * #  *  *  # *  *  #  * *  #  *  * #  *  *  #    |
>  0.8x +-+--****###--***###--****##--****###-****###--***###--***###--****##--****###-****###--***###--****##--****###--+-+
>          astar   bzip2      gcc   gobmk h264ref   hmmlibquantum      mcf omnetpperlbench   sjengxalancbmk   hmean
>   png: http://imgur.com/DU36YFU
>
> NB. 'cross' represents the previous commit.
>
> Reviewed-by: Richard Henderson <rth@twiddle.net>
> Signed-off-by: Emilio G. Cota <cota@braap.org>
> Message-Id: <1493263764-18657-11-git-send-email-cota@braap.org>
> Signed-off-by: Richard Henderson <rth@twiddle.net>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

> ---
>  target/i386/translate.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/target/i386/translate.c b/target/i386/translate.c
> index ea113fe..674ec96 100644
> --- a/target/i386/translate.c
> +++ b/target/i386/translate.c
> @@ -4996,7 +4996,7 @@ static target_ulong disas_insn(CPUX86State *env, DisasContext *s,
>              gen_push_v(s, cpu_T1);
>              gen_op_jmp_v(cpu_T0);
>              gen_bnd_jmp(s);
> -            gen_eob(s);
> +            gen_jr(s, cpu_T0);
>              break;
>          case 3: /* lcall Ev */
>              gen_op_ld_v(s, ot, cpu_T1, cpu_A0);
> @@ -5014,7 +5014,8 @@ static target_ulong disas_insn(CPUX86State *env, DisasContext *s,
>                                        tcg_const_i32(dflag - 1),
>                                        tcg_const_i32(s->pc - s->cs_base));
>              }
> -            gen_eob(s);
> +            tcg_gen_ld_tl(cpu_tmp4, cpu_env, offsetof(CPUX86State, eip));
> +            gen_jr(s, cpu_tmp4);
>              break;
>          case 4: /* jmp Ev */
>              if (dflag == MO_16) {
> @@ -5022,7 +5023,7 @@ static target_ulong disas_insn(CPUX86State *env, DisasContext *s,
>              }
>              gen_op_jmp_v(cpu_T0);
>              gen_bnd_jmp(s);
> -            gen_eob(s);
> +            gen_jr(s, cpu_T0);
>              break;
>          case 5: /* ljmp Ev */
>              gen_op_ld_v(s, ot, cpu_T1, cpu_A0);
> @@ -5037,7 +5038,8 @@ static target_ulong disas_insn(CPUX86State *env, DisasContext *s,
>                  gen_op_movl_seg_T0_vm(R_CS);
>                  gen_op_jmp_v(cpu_T1);
>              }
> -            gen_eob(s);
> +            tcg_gen_ld_tl(cpu_tmp4, cpu_env, offsetof(CPUX86State, eip));
> +            gen_jr(s, cpu_tmp4);
>              break;
>          case 6: /* push Ev */
>              gen_push_v(s, cpu_T0);
> @@ -6417,7 +6419,7 @@ static target_ulong disas_insn(CPUX86State *env, DisasContext *s,
>          /* Note that gen_pop_T0 uses a zero-extending load.  */
>          gen_op_jmp_v(cpu_T0);
>          gen_bnd_jmp(s);
> -        gen_eob(s);
> +        gen_jr(s, cpu_T0);
>          break;
>      case 0xc3: /* ret */
>          ot = gen_pop_T0(s);
> @@ -6425,7 +6427,7 @@ static target_ulong disas_insn(CPUX86State *env, DisasContext *s,
>          /* Note that gen_pop_T0 uses a zero-extending load.  */
>          gen_op_jmp_v(cpu_T0);
>          gen_bnd_jmp(s);
> -        gen_eob(s);
> +        gen_jr(s, cpu_T0);
>          break;
>      case 0xca: /* lret im */
>          val = cpu_ldsw_code(env, s->pc);


--
Alex Bennée