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Define pg_attribute_cold and pg_attribute_hot macros

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For compilers supporting __has_attribute and __has_attribute (hot/cold).

__has_attribute is supported on gcc >= 5, clang >= 2.9 and icc >= 17.

A followup commit will implement some usages of these macros.

Author: David Rowley
Reviewed-by: Andres Freund, Peter Eisentraut
Discussion: https://postgr.es/m/CAApHDvrVpasrEzLL2er7p9iwZFZ%3DJj6WisePcFeunwfrV0js_A%40mail.gmail.com
This commit is contained in:
David Rowley 2020-11-24 11:29:28 +13:00
parent 3b9b01f75d
commit 697e1d02f5
1 changed files with 16 additions and 0 deletions
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16
src/include/c.h
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@ -191,6 +191,22 @@
#define pg_noinline #define pg_noinline
#endif #endif
/*
* Marking certain functions as "hot" or "cold" can be useful to assist the
* compiler in arranging the assembly code in a more efficient way.
*/
#if defined(__has_attribute) && __has_attribute (cold)
#define pg_attribute_cold __attribute__((cold))
#else
#define pg_attribute_cold
#endif
#if defined(__has_attribute) && __has_attribute (hot)
#define pg_attribute_hot __attribute__((hot))
#else
#define pg_attribute_hot
#endif
/* /*
* Mark a point as unreachable in a portable fashion. This should preferably * Mark a point as unreachable in a portable fashion. This should preferably
* be something that the compiler understands, to aid code generation. * be something that the compiler understands, to aid code generation.