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author | Szabolcs Nagy <nsz@port70.net> | 2018-11-29 23:33:40 +0000 |
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committer | Rich Felker <dalias@aerifal.cx> | 2019-04-17 13:12:08 -0400 |
commit | 3c3763fc529114e209aea08336a420c5d5be4dc2 (patch) | |
tree | 6ab36f16fb49fa0b92c433b5a9fe080237326f1a /src | |
parent | 4f8acf953ccf1a978a3378db7fb1e8d5a7afbca1 (diff) | |
download | musl-3c3763fc529114e209aea08336a420c5d5be4dc2.tar.gz musl-3c3763fc529114e209aea08336a420c5d5be4dc2.tar.bz2 musl-3c3763fc529114e209aea08336a420c5d5be4dc2.tar.xz musl-3c3763fc529114e209aea08336a420c5d5be4dc2.zip |
math: add macros for static branch prediction hints
These don't have an effectw with -Os so not useful with default settings
other than documenting the expectation.
With --enable-optimize=internal,malloc,string,math the libc.so code size
increases by 18K on x86_64 and performance varies in -2% .. +10%.
Diffstat (limited to 'src')
-rw-r--r-- | src/internal/libm.h | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/src/internal/libm.h b/src/internal/libm.h index 62da4bdb..28537603 100644 --- a/src/internal/libm.h +++ b/src/internal/libm.h @@ -59,6 +59,15 @@ union ldshape { #error Unsupported long double representation #endif +/* Helps static branch prediction so hot path can be better optimized. */ +#ifdef __GNUC__ +#define predict_true(x) __builtin_expect(!!(x), 1) +#define predict_false(x) __builtin_expect(x, 0) +#else +#define predict_true(x) (x) +#define predict_false(x) (x) +#endif + /* Evaluate an expression as the specified type. With standard excess precision handling a type cast or assignment is enough (with -ffloat-store an assignment is required, in old compilers argument |