Add support for easily declaring static inline functions

We already had those, but they forced modules to spell out the function
bodies twice.  Eliminate some duplicates we had already grown.

Extracted from a somewhat larger patch from Andres Freund.

src/backend/nodes/list.c

@@ -15,6 +15,9 @@
  */
 #include "postgres.h"
 
+/* see pg_list.h */
+#define PG_LIST_INCLUDE_DEFINITIONS
+
 #include "nodes/pg_list.h"
 
 
@@ -1223,31 +1226,6 @@ list_copy_tail(const List *oldlist, int nskip)
 	return newlist;
 }
 
-/*
- * pg_list.h defines inline versions of these functions if allowed by the
- * compiler; in which case the definitions below are skipped.
- */
-#ifndef USE_INLINE
-
-ListCell *
-list_head(const List *l)
-{
-	return l ? l->head : NULL;
-}
-
-ListCell *
-list_tail(List *l)
-{
-	return l ? l->tail : NULL;
-}
-
-int
-list_length(const List *l)
-{
-	return l ? l->length : 0;
-}
-#endif   /* ! USE_INLINE */
-
 /*
  * Temporary compatibility functions
  *

src/backend/utils/mmgr/mcxt.c

@@ -21,6 +21,9 @@
 
 #include "postgres.h"
 
+/* see palloc.h */
+#define MCXT_INCLUDE_DEFINITIONS
+
 #include "utils/memutils.h"
 
 
@@ -695,28 +698,6 @@ repalloc(void *pointer, Size size)
 												 pointer, size);
 }
 
-/*
- * MemoryContextSwitchTo
- *		Returns the current context; installs the given context.
- *
- * palloc.h defines an inline version of this function if allowed by the
- * compiler; in which case the definition below is skipped.
- */
-#ifndef USE_INLINE
-
-MemoryContext
-MemoryContextSwitchTo(MemoryContext context)
-{
-	MemoryContext old;
-
-	AssertArg(MemoryContextIsValid(context));
-
-	old = CurrentMemoryContext;
-	CurrentMemoryContext = context;
-	return old;
-}
-#endif   /* ! USE_INLINE */
-
 /*
  * MemoryContextStrdup
  *		Like strdup(), but allocate from the specified context

src/backend/utils/sort/sortsupport.c

@@ -15,6 +15,9 @@
 
 #include "postgres.h"
 
+/* See sortsupport.h */
+#define SORTSUPPORT_INCLUDE_DEFINITIONS
+
 #include "fmgr.h"
 #include "utils/lsyscache.h"
 #include "utils/sortsupport.h"
@@ -28,50 +31,6 @@ typedef struct
 } SortShimExtra;
 
 
-/*
- * sortsupport.h defines inline versions of these functions if allowed by the
- * compiler; in which case the definitions below are skipped.
- */
-#ifndef USE_INLINE
-
-/*
- * Apply a sort comparator function and return a 3-way comparison result.
- * This takes care of handling reverse-sort and NULLs-ordering properly.
- */
-int
-ApplySortComparator(Datum datum1, bool isNull1,
-					Datum datum2, bool isNull2,
-					SortSupport ssup)
-{
-	int			compare;
-
-	if (isNull1)
-	{
-		if (isNull2)
-			compare = 0;		/* NULL "=" NULL */
-		else if (ssup->ssup_nulls_first)
-			compare = -1;		/* NULL "<" NOT_NULL */
-		else
-			compare = 1;		/* NULL ">" NOT_NULL */
-	}
-	else if (isNull2)
-	{
-		if (ssup->ssup_nulls_first)
-			compare = 1;		/* NOT_NULL ">" NULL */
-		else
-			compare = -1;		/* NOT_NULL "<" NULL */
-	}
-	else
-	{
-		compare = (*ssup->comparator) (datum1, datum2, ssup);
-		if (ssup->ssup_reverse)
-			compare = -compare;
-	}
-
-	return compare;
-}
-#endif   /* ! USE_INLINE */
-
 /*
  * Shim function for calling an old-style comparator
  *

src/include/c.h

@@ -748,6 +748,24 @@ typedef NameData *Name;
 #endif /* HAVE__BUILTIN_TYPES_COMPATIBLE_P */
 
 
+/*
+ * Function inlining support -- Allow modules to define functions that may be
+ * inlined, if the compiler supports it.
+ *
+ * The function bodies must be defined in the module header prefixed by
+ * STATIC_IF_INLINE, protected by a cpp symbol that the module's .c file must
+ * define.  If the compiler doesn't support inline functions, the function
+ * definitions are pulled in by the .c file as regular (not inline) symbols.
+ *
+ * The header must also declare the functions' prototypes, protected by
+ * !USE_INLINE.
+ */
+#ifdef USE_INLINE
+#define STATIC_IF_INLINE static inline
+#else
+#define STATIC_IF_INLINE
+#endif	/* USE_INLINE */
+
 /* ----------------------------------------------------------------
  *				Section 7:	random stuff
  * ----------------------------------------------------------------

src/include/nodes/pg_list.h

@@ -73,32 +73,32 @@ struct ListCell
  * them as macros, since we want to avoid double-evaluation of macro
  * arguments. Therefore, we implement them using static inline functions
  * if supported by the compiler, or as regular functions otherwise.
+ * See STATIC_IF_INLINE in c.h.
  */
-#ifdef USE_INLINE
-
-static inline ListCell *
+#ifndef USE_INLINE
+extern ListCell *list_head(const List *l);
+extern ListCell *list_tail(List *l);
+extern int	list_length(const List *l);
+#endif   /* USE_INLINE */
+#if defined(USE_INLINE) || defined(PG_LIST_INCLUDE_DEFINITIONS)
+STATIC_IF_INLINE ListCell *
 list_head(const List *l)
 {
 	return l ? l->head : NULL;
 }
 
-static inline ListCell *
+STATIC_IF_INLINE ListCell *
 list_tail(List *l)
 {
 	return l ? l->tail : NULL;
 }
 
-static inline int
+STATIC_IF_INLINE int
 list_length(const List *l)
 {
 	return l ? l->length : 0;
 }
-#else
-
-extern ListCell *list_head(const List *l);
-extern ListCell *list_tail(List *l);
-extern int	list_length(const List *l);
-#endif   /* USE_INLINE */
+#endif	/* USE_INLINE || PG_LIST_INCLUDE_DEFINITIONS */
 
 /*
  * NB: There is an unfortunate legacy from a previous incarnation of

src/include/utils/palloc.h

@@ -73,14 +73,19 @@ extern void *repalloc(void *pointer, Size size);
 /*
  * MemoryContextSwitchTo can't be a macro in standard C compilers.
  * But we can make it an inline function if the compiler supports it.
+ * See STATIC_IF_INLINE in c.h.
  *
  * This file has to be includable by some non-backend code such as
  * pg_resetxlog, so don't expose the CurrentMemoryContext reference
  * if FRONTEND is defined.
  */
-#if defined(USE_INLINE) && !defined(FRONTEND)
+#ifndef FRONTEND
 
-static inline MemoryContext
+#ifndef USE_INLINE
+extern MemoryContext MemoryContextSwitchTo(MemoryContext context);
+#endif   /* !USE_INLINE */
+#if defined(USE_INLINE) || defined(MCXT_INCLUDE_DEFINITIONS)
+STATIC_IF_INLINE MemoryContext
 MemoryContextSwitchTo(MemoryContext context)
 {
 	MemoryContext old = CurrentMemoryContext;
@@ -88,10 +93,9 @@ MemoryContextSwitchTo(MemoryContext context)
 	CurrentMemoryContext = context;
 	return old;
 }
-#else
+#endif
 
-extern MemoryContext MemoryContextSwitchTo(MemoryContext context);
-#endif   /* USE_INLINE && !FRONTEND */
+#endif /* !FRONTEND */
 
 /*
  * These are like standard strdup() except the copied string is

src/include/utils/sortsupport.h

@@ -101,14 +101,21 @@ typedef struct SortSupportData
 } SortSupportData;
 
 
-/* ApplySortComparator should be inlined if possible */
-#ifdef USE_INLINE
-
+/*
+ * ApplySortComparator should be inlined if possible.  See STATIC_IF_INLINE
+ * in c.h.
+ */
+#ifndef USE_INLINE
+extern int ApplySortComparator(Datum datum1, bool isNull1,
+					Datum datum2, bool isNull2,
+					SortSupport ssup);
+#endif   /* !USE_INLINE */
+#if defined(USE_INLINE) || defined(SORTSUPPORT_INCLUDE_DEFINITIONS)
 /*
  * Apply a sort comparator function and return a 3-way comparison result.
  * This takes care of handling reverse-sort and NULLs-ordering properly.
  */
-static inline int
+STATIC_IF_INLINE int
 ApplySortComparator(Datum datum1, bool isNull1,
 					Datum datum2, bool isNull2,
 					SortSupport ssup)
@@ -140,12 +147,7 @@ ApplySortComparator(Datum datum1, bool isNull1,
 
 	return compare;
 }
-#else
-
-extern int ApplySortComparator(Datum datum1, bool isNull1,
-					Datum datum2, bool isNull2,
-					SortSupport ssup);
-#endif   /* USE_INLINE */
+#endif	/* USE_INLINE || SORTSUPPORT_INCLUDE_DEFINITIONS */
 
 /* Other functions in utils/sort/sortsupport.c */
 extern void PrepareSortSupportComparisonShim(Oid cmpFunc, SortSupport ssup);