Inline ginCompareItemPointers function for speed.

ginCompareItemPointers function is called heavily in gin index scans -
inlining it speeds up some kind of queries a lot.

src/backend/access/gin/gindatapage.c

@@ -17,25 +17,6 @@
 #include "access/gin_private.h"
 #include "utils/rel.h"
 
-int
-ginCompareItemPointers(ItemPointer a, ItemPointer b)
-{
-	BlockNumber ba = GinItemPointerGetBlockNumber(a);
-	BlockNumber bb = GinItemPointerGetBlockNumber(b);
-
-	if (ba == bb)
-	{
-		OffsetNumber oa = GinItemPointerGetOffsetNumber(a);
-		OffsetNumber ob = GinItemPointerGetOffsetNumber(b);
-
-		if (oa == ob)
-			return 0;
-		return (oa > ob) ? 1 : -1;
-	}
-
-	return (ba > bb) ? 1 : -1;
-}
-
 /*
  * Merge two ordered arrays of itempointers, eliminating any duplicates.
  * Returns the number of items in the result.

src/include/access/gin_private.h

@@ -530,7 +530,6 @@ extern void ginEntryFillRoot(GinBtree btree, Buffer root, Buffer lbuf, Buffer rb
 extern IndexTuple ginPageGetLinkItup(Buffer buf);
 
 /* gindatapage.c */
-extern int	ginCompareItemPointers(ItemPointer a, ItemPointer b);
 extern uint32 ginMergeItemPointers(ItemPointerData *dst,
 					 ItemPointerData *a, uint32 na,
 					 ItemPointerData *b, uint32 nb);
@@ -724,4 +723,28 @@ extern void ginHeapTupleFastCollect(GinState *ginstate,
 extern void ginInsertCleanup(GinState *ginstate,
 				 bool vac_delay, IndexBulkDeleteResult *stats);
 
+/*
+ * Merging the results of several gin scans compares item pointers a lot,
+ * so we want this to be inlined. But if the compiler doesn't support that,
+ * fall back on the non-inline version from itemptr.c. See STATIC_IF_INLINE in
+ * c.h.
+ */
+#ifdef PG_USE_INLINE
+static inline int
+ginCompareItemPointers(ItemPointer a, ItemPointer b)
+{
+	uint64 ia = (uint64) a->ip_blkid.bi_hi << 32 | (uint64) a->ip_blkid.bi_lo << 16 | a->ip_posid;
+	uint64 ib = (uint64) b->ip_blkid.bi_hi << 32 | (uint64) b->ip_blkid.bi_lo << 16 | b->ip_posid;
+
+	if (ia == ib)
+		return 0;
+	else if (ia > ib)
+		return 1;
+	else
+		return -1;
+}
+#else
+#define ginCompareItemPointers(a, b) ItemPointerCompare(a, b)
+#endif   /* PG_USE_INLINE */
+
 #endif   /* GIN_PRIVATE_H */