[Alvaro Herrera <alvherre@2ndquadrant.com>]

I noticed while going over the multirange types patch that it adds a
pointless typiofunc cached OID to a struct used for I/O functions'
fn_extra.  It seems to go completely unused, so I checked range types
(which this was cribbed from) and indeed, it is completely unused there
either.  My guess is that it was in turn cribbed from array's
ArrayMetaState, which is considerably more sophisticated; I suspect
nobody noticed that caching it was pointless.

Here's a patch to remove it from rangetypes.c.  It doesn't really waste
much memory anyway, but removing it lessens the cognitive load by one or
two bits.

-- 
Álvaro Herrera

Attachments:

  [text/x-diff] range-typiofunc-cleanup.patch (1.5K, ../20200304215711.GA8732@alvherre.pgsql/2-range-typiofunc-cleanup.patch)
  download | inline diff:
diff --git a/src/backend/utils/adt/rangetypes.c b/src/backend/utils/adt/rangetypes.c
index 490bc2ae81..412322c6fa 100644
--- a/src/backend/utils/adt/rangetypes.c
+++ b/src/backend/utils/adt/rangetypes.c
@@ -49,7 +49,6 @@
 typedef struct RangeIOData
 {
 	TypeCacheEntry *typcache;	/* range type's typcache entry */
-	Oid			typiofunc;		/* element type's I/O function */
 	Oid			typioparam;		/* element type's I/O parameter */
 	FmgrInfo	proc;			/* lookup result for typiofunc */
 } RangeIOData;
@@ -309,6 +308,7 @@ get_range_io_data(FunctionCallInfo fcinfo, Oid rngtypid, IOFuncSelector func)
 		bool		typbyval;
 		char		typalign;
 		char		typdelim;
+		Oid			typiofunc;
 
 		cache = (RangeIOData *) MemoryContextAlloc(fcinfo->flinfo->fn_mcxt,
 												   sizeof(RangeIOData));
@@ -324,9 +324,9 @@ get_range_io_data(FunctionCallInfo fcinfo, Oid rngtypid, IOFuncSelector func)
 						 &typalign,
 						 &typdelim,
 						 &cache->typioparam,
-						 &cache->typiofunc);
+						 &typiofunc);
 
-		if (!OidIsValid(cache->typiofunc))
+		if (!OidIsValid(typiofunc))
 		{
 			/* this could only happen for receive or send */
 			if (func == IOFunc_receive)
@@ -340,7 +340,7 @@ get_range_io_data(FunctionCallInfo fcinfo, Oid rngtypid, IOFuncSelector func)
 						 errmsg("no binary output function available for type %s",
 								format_type_be(cache->typcache->rngelemtype->type_id))));
 		}
-		fmgr_info_cxt(cache->typiofunc, &cache->proc,
+		fmgr_info_cxt(typiofunc, &cache->proc,
 					  fcinfo->flinfo->fn_mcxt);
 
 		fcinfo->flinfo->fn_extra = (void *) cache;