Re: [PATCH 01/10] softfloat: Use post test for floatN_mul

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

Richard Henderson <richard.henderson@linaro.org> writes:

> The existing f{32,64}_addsub_post test, which checks for zero
> inputs, is identical to f{32,64}_mul_fast_test.  Which means
> we can eliminate the fast_test/fast_op hooks in favor of
> reusing the same post hook.
>
> This means we have one fewer test along the fast path for multiply.

I was worried that we were missing an opportunity for the early fast
path but fp-bench disagrees.

Before:
  ./fp-bench -o mul                               
  139.01 MFlops

After:
  ./fp-bench -o mul                        
  155.28 MFlops

So:

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

>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  fpu/softfloat.c | 65 +++++++++++--------------------------------------
>  1 file changed, 14 insertions(+), 51 deletions(-)
>
> diff --git a/fpu/softfloat.c b/fpu/softfloat.c
> index a362bf89ca..5fb4ef75bb 100644
> --- a/fpu/softfloat.c
> +++ b/fpu/softfloat.c
> @@ -339,12 +339,10 @@ static inline bool f64_is_inf(union_float64 a)
>      return float64_is_infinity(a.s);
>  }
>  
> -/* Note: @fast_test and @post can be NULL */
>  static inline float32
>  float32_gen2(float32 xa, float32 xb, float_status *s,
>               hard_f32_op2_fn hard, soft_f32_op2_fn soft,
> -             f32_check_fn pre, f32_check_fn post,
> -             f32_check_fn fast_test, soft_f32_op2_fn fast_op)
> +             f32_check_fn pre, f32_check_fn post)
>  {
>      union_float32 ua, ub, ur;
>  
> @@ -359,17 +357,12 @@ float32_gen2(float32 xa, float32 xb, float_status *s,
>      if (unlikely(!pre(ua, ub))) {
>          goto soft;
>      }
> -    if (fast_test && fast_test(ua, ub)) {
> -        return fast_op(ua.s, ub.s, s);
> -    }
>  
>      ur.h = hard(ua.h, ub.h);
>      if (unlikely(f32_is_inf(ur))) {
>          s->float_exception_flags |= float_flag_overflow;
> -    } else if (unlikely(fabsf(ur.h) <= FLT_MIN)) {
> -        if (post == NULL || post(ua, ub)) {
> -            goto soft;
> -        }
> +    } else if (unlikely(fabsf(ur.h) <= FLT_MIN) && post(ua, ub)) {
> +        goto soft;
>      }
>      return ur.s;
>  
> @@ -380,8 +373,7 @@ float32_gen2(float32 xa, float32 xb, float_status *s,
>  static inline float64
>  float64_gen2(float64 xa, float64 xb, float_status *s,
>               hard_f64_op2_fn hard, soft_f64_op2_fn soft,
> -             f64_check_fn pre, f64_check_fn post,
> -             f64_check_fn fast_test, soft_f64_op2_fn fast_op)
> +             f64_check_fn pre, f64_check_fn post)
>  {
>      union_float64 ua, ub, ur;
>  
> @@ -396,17 +388,12 @@ float64_gen2(float64 xa, float64 xb, float_status *s,
>      if (unlikely(!pre(ua, ub))) {
>          goto soft;
>      }
> -    if (fast_test && fast_test(ua, ub)) {
> -        return fast_op(ua.s, ub.s, s);
> -    }
>  
>      ur.h = hard(ua.h, ub.h);
>      if (unlikely(f64_is_inf(ur))) {
>          s->float_exception_flags |= float_flag_overflow;
> -    } else if (unlikely(fabs(ur.h) <= DBL_MIN)) {
> -        if (post == NULL || post(ua, ub)) {
> -            goto soft;
> -        }
> +    } else if (unlikely(fabs(ur.h) <= DBL_MIN) && post(ua, ub)) {
> +        goto soft;
>      }
>      return ur.s;
>  
> @@ -1115,7 +1102,7 @@ static double hard_f64_sub(double a, double b)
>      return a - b;
>  }
>  
> -static bool f32_addsub_post(union_float32 a, union_float32 b)
> +static bool f32_addsubmul_post(union_float32 a, union_float32 b)
>  {
>      if (QEMU_HARDFLOAT_2F32_USE_FP) {
>          return !(fpclassify(a.h) == FP_ZERO && fpclassify(b.h) == FP_ZERO);
> @@ -1123,7 +1110,7 @@ static bool f32_addsub_post(union_float32 a, union_float32 b)
>      return !(float32_is_zero(a.s) && float32_is_zero(b.s));
>  }
>  
> -static bool f64_addsub_post(union_float64 a, union_float64 b)
> +static bool f64_addsubmul_post(union_float64 a, union_float64 b)
>  {
>      if (QEMU_HARDFLOAT_2F64_USE_FP) {
>          return !(fpclassify(a.h) == FP_ZERO && fpclassify(b.h) == FP_ZERO);
> @@ -1136,14 +1123,14 @@ static float32 float32_addsub(float32 a, float32 b, float_status *s,
>                                hard_f32_op2_fn hard, soft_f32_op2_fn soft)
>  {
>      return float32_gen2(a, b, s, hard, soft,
> -                        f32_is_zon2, f32_addsub_post, NULL, NULL);
> +                        f32_is_zon2, f32_addsubmul_post);
>  }
>  
>  static float64 float64_addsub(float64 a, float64 b, float_status *s,
>                                hard_f64_op2_fn hard, soft_f64_op2_fn soft)
>  {
>      return float64_gen2(a, b, s, hard, soft,
> -                        f64_is_zon2, f64_addsub_post, NULL, NULL);
> +                        f64_is_zon2, f64_addsubmul_post);
>  }
>  
>  float32 QEMU_FLATTEN
> @@ -1258,42 +1245,18 @@ static double hard_f64_mul(double a, double b)
>      return a * b;
>  }
>  
> -static bool f32_mul_fast_test(union_float32 a, union_float32 b)
> -{
> -    return float32_is_zero(a.s) || float32_is_zero(b.s);
> -}
> -
> -static bool f64_mul_fast_test(union_float64 a, union_float64 b)
> -{
> -    return float64_is_zero(a.s) || float64_is_zero(b.s);
> -}
> -
> -static float32 f32_mul_fast_op(float32 a, float32 b, float_status *s)
> -{
> -    bool signbit = float32_is_neg(a) ^ float32_is_neg(b);
> -
> -    return float32_set_sign(float32_zero, signbit);
> -}
> -
> -static float64 f64_mul_fast_op(float64 a, float64 b, float_status *s)
> -{
> -    bool signbit = float64_is_neg(a) ^ float64_is_neg(b);
> -
> -    return float64_set_sign(float64_zero, signbit);
> -}
> -
>  float32 QEMU_FLATTEN
>  float32_mul(float32 a, float32 b, float_status *s)
>  {
>      return float32_gen2(a, b, s, hard_f32_mul, soft_f32_mul,
> -                        f32_is_zon2, NULL, f32_mul_fast_test, f32_mul_fast_op);
> +                        f32_is_zon2, f32_addsubmul_post);
>  }
>  
>  float64 QEMU_FLATTEN
>  float64_mul(float64 a, float64 b, float_status *s)
>  {
>      return float64_gen2(a, b, s, hard_f64_mul, soft_f64_mul,
> -                        f64_is_zon2, NULL, f64_mul_fast_test, f64_mul_fast_op);
> +                        f64_is_zon2, f64_addsubmul_post);
>  }
>  
>  /*
> @@ -1834,14 +1797,14 @@ float32 QEMU_FLATTEN
>  float32_div(float32 a, float32 b, float_status *s)
>  {
>      return float32_gen2(a, b, s, hard_f32_div, soft_f32_div,
> -                        f32_div_pre, f32_div_post, NULL, NULL);
> +                        f32_div_pre, f32_div_post);
>  }
>  
>  float64 QEMU_FLATTEN
>  float64_div(float64 a, float64 b, float_status *s)
>  {
>      return float64_gen2(a, b, s, hard_f64_div, soft_f64_div,
> -                        f64_div_pre, f64_div_post, NULL, NULL);
> +                        f64_div_pre, f64_div_post);
>  }
>  
>  /*


-- 
Alex Bennée