Consolidate ItemPointer to Datum conversion functions

Instead of defining the same set of macros several times, define it
once in an appropriate header file.  In passing, convert to inline
functions.

Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Discussion: https://www.postgresql.org/message-id/flat/844dd4c5-e5a1-3df1-bfaf-d1e1c2a16e45%40enterprisedb.com

contrib/pageinspect/btreefuncs.c

@@ -50,8 +50,6 @@ PG_FUNCTION_INFO_V1(bt_multi_page_stats);
 
 #define IS_INDEX(r) ((r)->rd_rel->relkind == RELKIND_INDEX)
 #define IS_BTREE(r) ((r)->rd_rel->relam == BTREE_AM_OID)
-#define DatumGetItemPointer(X)	 ((ItemPointer) DatumGetPointer(X))
-#define ItemPointerGetDatum(X)	 PointerGetDatum(X)
 
 /* ------------------------------------------------
  * structure for single btree page statistics

contrib/pageinspect/ginfuncs.c

@@ -21,9 +21,6 @@
 #include "utils/builtins.h"
 #include "utils/rel.h"
 
-#define DatumGetItemPointer(X)	 ((ItemPointer) DatumGetPointer(X))
-#define ItemPointerGetDatum(X)	 PointerGetDatum(X)
-
 
 PG_FUNCTION_INFO_V1(gin_metapage_info);
 PG_FUNCTION_INFO_V1(gin_page_opaque_info);

contrib/pageinspect/gistfuncs.c

@@ -31,8 +31,6 @@ PG_FUNCTION_INFO_V1(gist_page_items_bytea);
 
 #define IS_GIST(r) ((r)->rd_rel->relam == GIST_AM_OID)
 
-#define ItemPointerGetDatum(X)	 PointerGetDatum(X)
-
 
 Datum
 gist_page_opaque_info(PG_FUNCTION_ARGS)

src/backend/utils/adt/tid.c

@@ -37,11 +37,6 @@
 #include "utils/varlena.h"
 
 
-#define DatumGetItemPointer(X)	 ((ItemPointer) DatumGetPointer(X))
-#define ItemPointerGetDatum(X)	 PointerGetDatum(X)
-#define PG_GETARG_ITEMPOINTER(n) DatumGetItemPointer(PG_GETARG_DATUM(n))
-#define PG_RETURN_ITEMPOINTER(x) return ItemPointerGetDatum(x)
-
 #define LDELIM			'('
 #define RDELIM			')'
 #define DELIM			','

src/include/storage/itemptr.h

@@ -222,4 +222,24 @@ extern int32 ItemPointerCompare(ItemPointer arg1, ItemPointer arg2);
 extern void ItemPointerInc(ItemPointer pointer);
 extern void ItemPointerDec(ItemPointer pointer);
 
+/* ----------------
+ *		Datum conversion functions
+ * ----------------
+ */
+
+static inline ItemPointer
+DatumGetItemPointer(Datum X)
+{
+	return (ItemPointer) DatumGetPointer(X);
+}
+
+static inline Datum
+ItemPointerGetDatum(const ItemPointerData *X)
+{
+	return PointerGetDatum(X);
+}
+
+#define PG_GETARG_ITEMPOINTER(n) DatumGetItemPointer(PG_GETARG_DATUM(n))
+#define PG_RETURN_ITEMPOINTER(x) return ItemPointerGetDatum(x)
+
 #endif							/* ITEMPTR_H */