bpo-45094: Add Py_ALWAYS_INLINE macro

Doc/c-api/intro.rst

@@ -111,6 +111,28 @@ complete listing.
 
    .. versionadded:: 3.3
 
+.. c:macro:: Py_ALWAYS_INLINE
+
+   Ask the compiler to always inline a static inline function. The compiler is
+   free to ignore this "hint".
+
+   This attribute can be used to avoid increasing the stack memory usage when
+   building Python in debug mode with function inlining disabled. For example,
+   MSC disables function inlining when building in debug mode. It should be
+   used on the most commonly used static inline functions.
+
+   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,

Include/object.h

@@ -127,7 +127,7 @@ PyAPI_FUNC(int) Py_Is(PyObject *x, PyObject *y);
 #define Py_Is(x, y) ((x) == (y))
 
 
-static inline Py_ssize_t _Py_REFCNT(const PyObject *ob) {
+static inline Py_ALWAYS_INLINE Py_ssize_t _Py_REFCNT(const PyObject *ob) {
     return ob->ob_refcnt;
 }
 #define Py_REFCNT(ob) _Py_REFCNT(_PyObject_CAST_CONST(ob))
@@ -140,27 +140,27 @@ static inline Py_ssize_t _Py_REFCNT(const PyObject *ob) {
 #define Py_SIZE(ob)             (_PyVarObject_CAST(ob)->ob_size)
 
 
-static inline int _Py_IS_TYPE(const PyObject *ob, const PyTypeObject *type) {
+static inline Py_ALWAYS_INLINE int _Py_IS_TYPE(const PyObject *ob, const PyTypeObject *type) {
     // bpo-44378: Don't use Py_TYPE() since Py_TYPE() requires a non-const
     // object.
     return ob->ob_type == type;
 }
 #define Py_IS_TYPE(ob, type) _Py_IS_TYPE(_PyObject_CAST_CONST(ob), type)
 
 
-static inline void _Py_SET_REFCNT(PyObject *ob, Py_ssize_t refcnt) {
+static inline Py_ALWAYS_INLINE void _Py_SET_REFCNT(PyObject *ob, Py_ssize_t refcnt) {
     ob->ob_refcnt = refcnt;
 }
 #define Py_SET_REFCNT(ob, refcnt) _Py_SET_REFCNT(_PyObject_CAST(ob), refcnt)
 
 
-static inline void _Py_SET_TYPE(PyObject *ob, PyTypeObject *type) {
+static inline Py_ALWAYS_INLINE void _Py_SET_TYPE(PyObject *ob, PyTypeObject *type) {
     ob->ob_type = type;
 }
 #define Py_SET_TYPE(ob, type) _Py_SET_TYPE(_PyObject_CAST(ob), type)
 
 
-static inline void _Py_SET_SIZE(PyVarObject *ob, Py_ssize_t size) {
+static inline Py_ALWAYS_INLINE void _Py_SET_SIZE(PyVarObject *ob, Py_ssize_t size) {
     ob->ob_size = size;
 }
 #define Py_SET_SIZE(ob, size) _Py_SET_SIZE(_PyVarObject_CAST(ob), size)
@@ -462,7 +462,7 @@ PyAPI_FUNC(void) Py_DecRef(PyObject *);
 PyAPI_FUNC(void) _Py_IncRef(PyObject *);
 PyAPI_FUNC(void) _Py_DecRef(PyObject *);
 
-static inline void _Py_INCREF(PyObject *op)
+static inline Py_ALWAYS_INLINE void _Py_INCREF(PyObject *op)
 {
 #if defined(Py_REF_DEBUG) && defined(Py_LIMITED_API) && Py_LIMITED_API+0 >= 0x030A0000
     // Stable ABI for Python 3.10 built in debug mode.
@@ -478,7 +478,7 @@ static inline void _Py_INCREF(PyObject *op)
 }
 #define Py_INCREF(op) _Py_INCREF(_PyObject_CAST(op))
 
-static inline void _Py_DECREF(
+static inline Py_ALWAYS_INLINE void _Py_DECREF(
 #if defined(Py_REF_DEBUG) && !(defined(Py_LIMITED_API) && Py_LIMITED_API+0 >= 0x030A0000)
     const char *filename, int lineno,
 #endif
@@ -556,7 +556,7 @@ static inline void _Py_DECREF(
     } while (0)
 
 /* Function to use in case the object pointer can be NULL: */
-static inline void _Py_XINCREF(PyObject *op)
+static inline Py_ALWAYS_INLINE void _Py_XINCREF(PyObject *op)
 {
     if (op != NULL) {
         Py_INCREF(op);
@@ -565,7 +565,7 @@ static inline void _Py_XINCREF(PyObject *op)
 
 #define Py_XINCREF(op) _Py_XINCREF(_PyObject_CAST(op))
 
-static inline void _Py_XDECREF(PyObject *op)
+static inline Py_ALWAYS_INLINE void _Py_XDECREF(PyObject *op)
 {
     if (op != NULL) {
         Py_DECREF(op);
@@ -581,13 +581,13 @@ PyAPI_FUNC(PyObject*) Py_NewRef(PyObject *obj);
 // Similar to Py_NewRef(), but the object can be NULL.
 PyAPI_FUNC(PyObject*) Py_XNewRef(PyObject *obj);
 
-static inline PyObject* _Py_NewRef(PyObject *obj)
+static inline Py_ALWAYS_INLINE PyObject* _Py_NewRef(PyObject *obj)
 {
     Py_INCREF(obj);
     return obj;
 }
 
-static inline PyObject* _Py_XNewRef(PyObject *obj)
+static inline Py_ALWAYS_INLINE PyObject* _Py_XNewRef(PyObject *obj)
 {
     Py_XINCREF(obj);
     return obj;

Include/pyport.h

@@ -557,6 +557,30 @@ extern "C" {
 #define _Py_HOT_FUNCTION
 #endif
 
+// Ask the compiler to always inline a static inline function. The compiler is
+// free to ignore this "hint". This attribute can be used to avoid increasing
+// the stack memory usage when building Python in debug mode with function
+// inlining disabled. For example, MSC disables function inlining when building
+// in debug mode. It should be used on the most commonly used static inline
+// functions.
+//
+// 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

Misc/NEWS.d/next/C API/2021-09-03-16-52-23.bpo-45094.IrTcnE.rst

@@ -0,0 +1,2 @@
+Add :c:macro:`Py_ALWAYS_INLINE` macro to ask the compiler to always inline a
+static inline function. Patch by Victor Stinner.