Emilio G. Cota <c...@braap.org> writes:
> From: Kito Cheng <kito.ch...@gmail.com>
>
> Before falling back to softfloat FMA, we do not restore the original
> values of inputs A and C. Fix it.
>
> This bug was caught by running gcc's testsuite on RISC-V qemu.
>
> Note that this change gives a small perf increase for fp-bench:
>
> Host: Intel(R) Core(TM) i7-4790K CPU @ 4.00GHz
> Command: perf stat -r 3 taskset -c 0 ./fp-bench -o mulAdd -p $prec
Queued to for-4.0/testing-and-fpu-fixes, thanks.
>
> - $prec = single:
> - before:
> 101.71 MFlops
> 102.18 MFlops
> 100.96 MFlops
> - after:
> 103.63 MFlops
> 103.05 MFlops
> 102.96 MFlops
>
> - $prec = double:
> - before:
> 173.10 MFlops
> 173.93 MFlops
> 172.11 MFlops
> - after:
> 178.49 MFlops
> 178.88 MFlops
> 178.66 MFlops
>
> Signed-off-by: Kito Cheng <kito.ch...@gmail.com>
> Signed-off-by: Emilio G. Cota <c...@braap.org>
> ---
> fpu/softfloat.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/fpu/softfloat.c b/fpu/softfloat.c
> index 4610738ab1..2ba36ec370 100644
> --- a/fpu/softfloat.c
> +++ b/fpu/softfloat.c
> @@ -1596,6 +1596,9 @@ float32_muladd(float32 xa, float32 xb, float32 xc, int
> flags, float_status *s)
> }
> ur.h = up.h + uc.h;
> } else {
> + union_float32 ua_orig = ua;
> + union_float32 uc_orig = uc;
> +
> if (flags & float_muladd_negate_product) {
> ua.h = -ua.h;
> }
> @@ -1608,6 +1611,8 @@ float32_muladd(float32 xa, float32 xb, float32 xc, int
> flags, float_status *s)
> if (unlikely(f32_is_inf(ur))) {
> s->float_exception_flags |= float_flag_overflow;
> } else if (unlikely(fabsf(ur.h) <= FLT_MIN)) {
> + ua = ua_orig;
> + uc = uc_orig;
> goto soft;
> }
> }
> @@ -1662,6 +1667,9 @@ float64_muladd(float64 xa, float64 xb, float64 xc, int
> flags, float_status *s)
> }
> ur.h = up.h + uc.h;
> } else {
> + union_float64 ua_orig = ua;
> + union_float64 uc_orig = uc;
> +
> if (flags & float_muladd_negate_product) {
> ua.h = -ua.h;
> }
> @@ -1674,6 +1682,8 @@ float64_muladd(float64 xa, float64 xb, float64 xc, int
> flags, float_status *s)
> if (unlikely(f64_is_inf(ur))) {
> s->float_exception_flags |= float_flag_overflow;
> } else if (unlikely(fabs(ur.h) <= FLT_MIN)) {
> + ua = ua_orig;
> + uc = uc_orig;
> goto soft;
> }
> }
--
Alex Bennée
