Re: [PATCH v4 2/3] target/riscv: Use float64_to_int64_modulo for fcvtmod.w.d

[Richard Henderson]

On 6/30/23 11:13, Christoph Muellner wrote:
> From: Christoph Müllner <christoph.muellner@vrull.eu>
>
> For the most part we can use the new generic routine,
> though exceptions need some post-processing.
>
> Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
> ---
>   target/riscv/fpu_helper.c | 78 ++++++++++++++-------------------------
>   1 file changed, 27 insertions(+), 51 deletions(-)
>
> diff --git a/target/riscv/fpu_helper.c b/target/riscv/fpu_helper.c
> index 289b3bbea5..0f897cf072 100644
> --- a/target/riscv/fpu_helper.c
> +++ b/target/riscv/fpu_helper.c
> @@ -482,70 +482,46 @@ target_ulong helper_fcvt_w_d(CPURISCVState *env, uint64_t 
> frs1)
>       return float64_to_int32(frs1, &env->fp_status);
>   }
>   
> +/* T floating (double) */
> +static inline float64 t_to_float64(uint64_t a)
> +{
> +    /* Memory format is the same as float64 */
> +    CPU_DoubleU r;
> +    r.ll = a;
> +    return r.d;
> +}

You don't need this.  Nor does Alpha anymore, come to that.
float64 is uint64_t now, always.

> +    int64_t ret;
> +    int32_t ret32;
> +    uint32_t e_old, e_new;
> +    float64 fvalue;
> +
> +    e_old = get_float_exception_flags(status);
> +    set_float_exception_flags(0, status);
> +    fvalue = t_to_float64(value);
> +    ret = float64_to_int32_modulo(fvalue, float_round_to_zero, status);
> +    e_new = get_float_exception_flags(status);
> +
> +    /* Map the flags to the specified ones. */
> +    if (e_new & float_flag_inexact) {
> +        e_new = float_flag_inexact;
> +    } else if (e_new) {
> +        e_new = float_flag_invalid;
>       }

Why?  Generic code will not set both inexact and invalid.
So this is a nop.

Removing that, all of your fp flags handling can go away.


>       /* Truncate to 32-bits. */
> -    int32_t ret32 = (int32_t)ret;
> +    ret32 = (int32_t)ret;
>   
>       /* If the truncation drops bits then raise NV. */
>       if ((uint64_t)ret32 != ret)

This will never fail, because you used float64_to_int32_modulo, which already 
returns int32_t.

But we have already raised invalid for overflow, so this can go away as well.

Finally, this patch must be merged with the previous, which introduced this 
function.


r~