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bpo-45116: Py_DEBUG ignores Py_ALWAYS_INLINE #28419

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Merged
merged 1 commit into from
Sep 17, 2021
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bpo-45116: Py_DEBUG ignores Py_ALWAYS_INLINE #28419

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3 changes: 3 additions & 0 deletions Doc/c-api/intro.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -124,6 +124,9 @@ complete listing.
worse performances (due to increased code size for example). The compiler is
usually smarter than the developer for the cost/benefit analysis.

If Python is :ref:`built in debug mode <debug-build>` (if the ``Py_DEBUG``
macro is defined), the :c:macro:`Py_ALWAYS_INLINE` macro does nothing.

It must be specified before the function return type. Usage::

static inline Py_ALWAYS_INLINE int random(void) { return 4; }
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11 changes: 10 additions & 1 deletion Include/pyport.h
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Expand Up @@ -568,10 +568,19 @@ extern "C" {
// worse performances (due to increased code size for example). The compiler is
// usually smarter than the developer for the cost/benefit analysis.
//
// If Python is built in debug mode (if the Py_DEBUG macro is defined), the
// Py_ALWAYS_INLINE macro does nothing.
//
// 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)
#if defined(Py_DEBUG)
// If Python is built in debug mode, usually compiler optimizations are
// disabled. In this case, Py_ALWAYS_INLINE can increase a lot the stack
// memory usage. For example, forcing inlining using gcc -O0 increases the
// stack usage from 6 KB to 15 KB per Python function call.
# define Py_ALWAYS_INLINE
#elif defined(__GNUC__) || defined(__clang__) || defined(__INTEL_COMPILER)
# define Py_ALWAYS_INLINE __attribute__((always_inline))
#elif defined(_MSC_VER)
# define Py_ALWAYS_INLINE __forceinline
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