diff options
| author | Emilio G. Cota <cota@braap.org> | 2018-12-25 02:03:05 -0500 |
|---|---|---|
| committer | Alex Bennée <alex.bennee@linaro.org> | 2019-01-22 20:48:17 +0000 |
| commit | f6b3b108a808fe07f8a45f82bc88196f668cf627 (patch) | |
| tree | c25d3a0c91ff44f25e6aa89313fb0da8c58da3f9 /fpu | |
| parent | b343eb462bcf825d60a29269054d54aff95b1722 (diff) | |
| download | qemu-f6b3b108a808fe07f8a45f82bc88196f668cf627.zip qemu-f6b3b108a808fe07f8a45f82bc88196f668cf627.tar.gz qemu-f6b3b108a808fe07f8a45f82bc88196f668cf627.tar.bz2 | |
softfloat: enforce softfloat if the host's FMA is broken
The added branch to the FMA ops is marked as unlikely and therefore
its impact on performance (measured with fp-bench) is within noise range
when measured on an Intel(R) Xeon(R) Gold 6142 CPU @ 2.60GHz.
Reported-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Diffstat (limited to 'fpu')
| -rw-r--r-- | fpu/softfloat.c | 33 |
1 files changed, 33 insertions, 0 deletions
diff --git a/fpu/softfloat.c b/fpu/softfloat.c index 59eac97..9132d7a 100644 --- a/fpu/softfloat.c +++ b/fpu/softfloat.c @@ -1542,6 +1542,8 @@ soft_f64_muladd(float64 a, float64 b, float64 c, int flags, return float64_round_pack_canonical(pr, status); } +static bool force_soft_fma; + float32 QEMU_FLATTEN float32_muladd(float32 xa, float32 xb, float32 xc, int flags, float_status *s) { @@ -1562,6 +1564,11 @@ float32_muladd(float32 xa, float32 xb, float32 xc, int flags, float_status *s) if (unlikely(!f32_is_zon3(ua, ub, uc))) { goto soft; } + + if (unlikely(force_soft_fma)) { + goto soft; + } + /* * When (a || b) == 0, there's no need to check for under/over flow, * since we know the addend is (normal || 0) and the product is 0. @@ -1623,6 +1630,11 @@ float64_muladd(float64 xa, float64 xb, float64 xc, int flags, float_status *s) if (unlikely(!f64_is_zon3(ua, ub, uc))) { goto soft; } + + if (unlikely(force_soft_fma)) { + goto soft; + } + /* * When (a || b) == 0, there's no need to check for under/over flow, * since we know the addend is (normal || 0) and the product is 0. @@ -7974,3 +7986,24 @@ float128 float128_scalbn(float128 a, int n, float_status *status) , status); } + +static void __attribute__((constructor)) softfloat_init(void) +{ + union_float64 ua, ub, uc, ur; + + if (QEMU_NO_HARDFLOAT) { + return; + } + /* + * Test that the host's FMA is not obviously broken. For example, + * glibc < 2.23 can perform an incorrect FMA on certain hosts; see + * https://sourceware.org/bugzilla/show_bug.cgi?id=13304 + */ + ua.s = 0x0020000000000001ULL; + ub.s = 0x3ca0000000000000ULL; + uc.s = 0x0020000000000000ULL; + ur.h = fma(ua.h, ub.h, uc.h); + if (ur.s != 0x0020000000000001ULL) { + force_soft_fma = true; + } +} |