Re: [Qemu-devel] [PATCH 3/5] target-arm: convert shl and shr helpers to TCG

[Laurent Desnogues]

On Mon, Sep 17, 2012 at 1:08 AM, Aurelien Jarno <address@hidden> wrote:
> Now that the setcond TCG op is available, it's possible to replace
> shl and shr helpers by TCG code. The code generated by TCG is slightly
> longer than the code generated by GCC for the helper but is still worth
> it as this avoid all the consequences of using an helper: globals saved
> back to memory, no possible optimization, call overhead, etc.
>
> Cc: Peter Maydell <address@hidden>
> Signed-off-by: Aurelien Jarno <address@hidden>
> ---
>  target-arm/helper.h    |    2 --
>  target-arm/op_helper.c |   16 ----------------
>  target-arm/translate.c |   32 ++++++++++++++++++++++++++++----
>  3 files changed, 28 insertions(+), 22 deletions(-)
>
> diff --git a/target-arm/helper.h b/target-arm/helper.h
> index 7151e28..b123d3e 100644
> --- a/target-arm/helper.h
> +++ b/target-arm/helper.h
> @@ -145,8 +145,6 @@ DEF_HELPER_5(neon_tbl, i32, env, i32, i32, i32, i32)
>  DEF_HELPER_3(adc_cc, i32, env, i32, i32)
>  DEF_HELPER_3(sbc_cc, i32, env, i32, i32)
>
> -DEF_HELPER_3(shl, i32, env, i32, i32)
> -DEF_HELPER_3(shr, i32, env, i32, i32)
>  DEF_HELPER_3(sar, i32, env, i32, i32)
>  DEF_HELPER_3(shl_cc, i32, env, i32, i32)
>  DEF_HELPER_3(shr_cc, i32, env, i32, i32)
> diff --git a/target-arm/op_helper.c b/target-arm/op_helper.c
> index 6095f24..5fcd12c 100644
> --- a/target-arm/op_helper.c
> +++ b/target-arm/op_helper.c
> @@ -355,22 +355,6 @@ uint32_t HELPER(sbc_cc)(CPUARMState *env, uint32_t a, 
> uint32_t b)
>
>  /* Similarly for variable shift instructions.  */
>
> -uint32_t HELPER(shl)(CPUARMState *env, uint32_t x, uint32_t i)
> -{
> -    int shift = i & 0xff;
> -    if (shift >= 32)
> -        return 0;
> -    return x << shift;
> -}
> -
> -uint32_t HELPER(shr)(CPUARMState *env, uint32_t x, uint32_t i)
> -{
> -    int shift = i & 0xff;
> -    if (shift >= 32)
> -        return 0;
> -    return (uint32_t)x >> shift;
> -}
> -
>  uint32_t HELPER(sar)(CPUARMState *env, uint32_t x, uint32_t i)
>  {
>      int shift = i & 0xff;
> diff --git a/target-arm/translate.c b/target-arm/translate.c
> index 19bb1e8..9c29065 100644
> --- a/target-arm/translate.c
> +++ b/target-arm/translate.c
> @@ -440,6 +440,26 @@ static void gen_sub_CC(TCGv dest, TCGv t0, TCGv t1)
>      tcg_gen_mov_i32(dest, cpu_NF);
>  }
>
> +#define GEN_SHIFT(name)                                \
> +static void gen_##name(TCGv dest, TCGv t0, TCGv t1)    \
> +{                                                      \
> +    TCGv tmp1, tmp2;                                   \
> +    tmp1 = tcg_temp_new_i32();                         \
> +    tcg_gen_andi_i32(tmp1, t1, 0xff);                  \
> +    tmp2 = tcg_temp_new_i32();                         \
> +    tcg_gen_setcondi_i32(TCG_COND_GE, tmp2, tmp1, 32); \
> +    tcg_gen_andi_i32(tmp1, tmp1, 0x1f);                \

I don't think the 'and 0x1f' is needed given that later you'll and
with 0 if the shift amount is >= 32.

> +    tcg_gen_##name##_i32(dest, t0, tmp1);              \
> +    tcg_temp_free_i32(tmp1);                           \
> +    tcg_gen_subi_i32(tmp2, tmp2, 1);                   \
> +    tcg_gen_and_i32(dest, dest, tmp2);                 \
> +    tcg_temp_free_i32(tmp2);                           \
> +}


Laurent

> +GEN_SHIFT(shl)
> +GEN_SHIFT(shr)
> +#undef GEN_SHIFT
> +
> +
>  /* FIXME:  Implement this natively.  */
>  #define tcg_gen_abs_i32(t0, t1) gen_helper_abs(t0, t1)
>
> @@ -516,8 +536,12 @@ static inline void gen_arm_shift_reg(TCGv var, int 
> shiftop,
>          }
>      } else {
>          switch (shiftop) {
> -        case 0: gen_helper_shl(var, cpu_env, var, shift); break;
> -        case 1: gen_helper_shr(var, cpu_env, var, shift); break;
> +        case 0:
> +            gen_shl(var, var, shift);
> +            break;
> +        case 1:
> +            gen_shr(var, var, shift);
> +            break;
>          case 2: gen_helper_sar(var, cpu_env, var, shift); break;
>          case 3: tcg_gen_andi_i32(shift, shift, 0x1f);
>                  tcg_gen_rotr_i32(var, var, shift); break;
> @@ -9161,7 +9185,7 @@ static void disas_thumb_insn(CPUARMState *env, 
> DisasContext *s)
>              break;
>          case 0x2: /* lsl */
>              if (s->condexec_mask) {
> -                gen_helper_shl(tmp2, cpu_env, tmp2, tmp);
> +                gen_shl(tmp2, tmp2, tmp);
>              } else {
>                  gen_helper_shl_cc(tmp2, cpu_env, tmp2, tmp);
>                  gen_logic_CC(tmp2);
> @@ -9169,7 +9193,7 @@ static void disas_thumb_insn(CPUARMState *env, 
> DisasContext *s)
>              break;
>          case 0x3: /* lsr */
>              if (s->condexec_mask) {
> -                gen_helper_shr(tmp2, cpu_env, tmp2, tmp);
> +                gen_shr(tmp2, tmp2, tmp);
>              } else {
>                  gen_helper_shr_cc(tmp2, cpu_env, tmp2, tmp);
>                  gen_logic_CC(tmp2);
> --
> 1.7.10.4
>
>