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bpo-45116: Add the Py_ALWAYS_INLINE macro (GH-28390)

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Add the Py_ALWAYS_INLINE macro to ask the compiler to always inline a
static inline function. The compiler can ignore it and decides to not
inline the function.
This commit is contained in:
Victor Stinner 2021-09-17 14:09:14 +02:00 committed by GitHub
parent 064464fc38
commit 6b41355128
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19
Doc/c-api/intro.rst
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@ -111,6 +111,25 @@ complete listing.
.. versionadded:: 3.3
.. c:macro:: Py_ALWAYS_INLINE
Ask the compiler to always inline a static inline function. The compiler can
ignore it and decides to not inline the function.
It can be used to inline performance critical static inline functions when
building Python in debug mode with function inlining disabled. For example,
MSC disables function inlining when building in debug mode.
Marking blindly a static inline function with Py_ALWAYS_INLINE can result in
worse performances (due to increased code size for example). The compiler is
usually smarter than the developer for the cost/benefit analysis.
It must be specified before the function return type. Usage::
static inline Py_ALWAYS_INLINE int random(void) { return 4; }
.. versionadded:: 3.11
.. c:macro:: Py_CHARMASK(c)
Argument must be a character or an integer in the range [-128, 127] or [0,

22
Include/pyport.h
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@ -557,6 +557,28 @@ extern "C" {
#define _Py_HOT_FUNCTION
#endif
// Ask the compiler to always inline a static inline function. The compiler can
// ignore it and decides to not inline the function.
//
// It can be used to inline performance critical static inline functions when
// building Python in debug mode with function inlining disabled. For example,
// MSC disables function inlining when building in debug mode.
//
// Marking blindly a static inline function with Py_ALWAYS_INLINE can result in
// worse performances (due to increased code size for example). The compiler is
// usually smarter than the developer for the cost/benefit analysis.
//
// It must be specified before the function return type. Usage:
//
// static inline Py_ALWAYS_INLINE int random(void) { return 4; }
#if defined(__GNUC__) || defined(__clang__) || defined(__INTEL_COMPILER)
# define Py_ALWAYS_INLINE __attribute__((always_inline))
#elif defined(_MSC_VER)
# define Py_ALWAYS_INLINE __forceinline
#else
# define Py_ALWAYS_INLINE
#endif
// Py_NO_INLINE
// Disable inlining on a function. For example, it reduces the C stack
// consumption: useful on LTO+PGO builds which heavily inline code (see

3
Misc/NEWS.d/next/C API/2021-09-16-18-05-20.bpo-45116.WxXewl.rst Normal file
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@ -0,0 +1,3 @@
Add the :c:macro:`Py_ALWAYS_INLINE` macro to ask the compiler to always
inline a static inline function. The compiler can ignore it and decides to
not inline the function. Patch by Victor Stinner.