Remove useless entries for aggregate functions from fmgrtab.c.

Gen_fmgrtab.pl treated aggregate functions the same as other built-in
functions, which is wasteful because there is no real need to have
entries for them in the fmgr_builtins[] table.  Suppressing those
entries saves about 3KB in the compiled table on my machine; which
is not a lot but it's not nothing either, considering that that
table is pretty "hot".  The only outside code change needed is
that ExecInitWindowAgg() can't be allowed to call fmgr_info_cxt()
on a plain aggregate function.  But that saves a few cycles anyway.

Having done that, the aggregate_dummy() function is unreferenced
and might as well be dropped.  Using "aggregate_dummy" as the prosrc
value for an aggregate is now just a documentation convention not
something that matters.  There was some discussion of using NULL
instead to save a few bytes in pg_proc, but we'd have to remove
prosrc's BKI_FORCE_NOT_NULL marking which doesn't seem a great idea.
Anyway, it's possible there's client-side code that expects to
see "aggregate_dummy" there, so I'm loath to change it without a
strong reason.

Discussion: https://postgr.es/m/533989.1604263665@sss.pgh.pa.us

src/backend/catalog/pg_aggregate.c

@@ -620,7 +620,7 @@ AggregateCreate(const char *aggName,
 							 GetUserId(),	/* proowner */
 							 INTERNALlanguageId,	/* languageObjectId */
 							 InvalidOid,	/* no validator */
-							 "aggregate_dummy", /* placeholder proc */
+							 "aggregate_dummy", /* placeholder (no such proc) */
 							 NULL,	/* probin */
 							 PROKIND_AGGREGATE,
 							 false, /* security invoker (currently not

src/backend/executor/nodeAgg.c

@@ -4935,24 +4935,6 @@ AggRegisterCallback(FunctionCallInfo fcinfo,
 }
 
 
-/*
- * aggregate_dummy - dummy execution routine for aggregate functions
- *
- * This function is listed as the implementation (prosrc field) of pg_proc
- * entries for aggregate functions.  Its only purpose is to throw an error
- * if someone mistakenly executes such a function in the normal way.
- *
- * Perhaps someday we could assign real meaning to the prosrc field of
- * an aggregate?
- */
-Datum
-aggregate_dummy(PG_FUNCTION_ARGS)
-{
-	elog(ERROR, "aggregate function %u called as normal function",
-		 fcinfo->flinfo->fn_oid);
-	return (Datum) 0;			/* keep compiler quiet */
-}
-
 /* ----------------------------------------------------------------
  *						Parallel Query Support
  * ----------------------------------------------------------------

src/backend/executor/nodeWindowAgg.c

@@ -2446,11 +2446,6 @@ ExecInitWindowAgg(WindowAgg *node, EState *estate, int eflags)
 		perfuncstate->wfuncstate = wfuncstate;
 		perfuncstate->wfunc = wfunc;
 		perfuncstate->numArguments = list_length(wfuncstate->args);
-
-		fmgr_info_cxt(wfunc->winfnoid, &perfuncstate->flinfo,
-					  econtext->ecxt_per_query_memory);
-		fmgr_info_set_expr((Node *) wfunc, &perfuncstate->flinfo);
-
 		perfuncstate->winCollation = wfunc->inputcollid;
 
 		get_typlenbyval(wfunc->wintype,
@@ -2479,6 +2474,11 @@ ExecInitWindowAgg(WindowAgg *node, EState *estate, int eflags)
 			winobj->argstates = wfuncstate->args;
 			winobj->localmem = NULL;
 			perfuncstate->winobj = winobj;
+
+			/* It's a real window function, so set up to call it. */
+			fmgr_info_cxt(wfunc->winfnoid, &perfuncstate->flinfo,
+						  econtext->ecxt_per_query_memory);
+			fmgr_info_set_expr((Node *) wfunc, &perfuncstate->flinfo);
 		}
 	}
 

src/backend/utils/Gen_fmgrtab.pl

@@ -75,6 +75,7 @@ foreach my $row (@{ $catalog_data{pg_proc} })
 		oid    => $bki_values{oid},
 		name   => $bki_values{proname},
 		lang   => $bki_values{prolang},
+		kind   => $bki_values{prokind},
 		strict => $bki_values{proisstrict},
 		retset => $bki_values{proretset},
 		nargs  => $bki_values{pronargs},
@@ -195,8 +196,10 @@ foreach my $s (sort { $a->{oid} <=> $b->{oid} } @fmgr)
 	$sqlname .= "_" . $s->{args} if ($proname_counts{ $s->{name} } > 1);
 	$sqlname =~ s/\s+/_/g;
 	print $ofh "#define F_" . uc $sqlname . " $s->{oid}\n";
-	# We want only one extern per internal-language function
-	if ($s->{lang} eq 'internal' && !$seenit{ $s->{prosrc} })
+	# We want only one extern per internal-language, non-aggregate function
+	if (   $s->{lang} eq 'internal'
+		&& $s->{kind} ne 'a'
+		&& !$seenit{ $s->{prosrc} })
 	{
 		$seenit{ $s->{prosrc} } = 1;
 		print $pfh "extern Datum $s->{prosrc}(PG_FUNCTION_ARGS);\n";
@@ -214,6 +217,8 @@ my $fmgr_count       = 0;
 foreach my $s (sort { $a->{oid} <=> $b->{oid} } @fmgr)
 {
 	next if $s->{lang} ne 'internal';
+	# We do not need entries for aggregate functions
+	next if $s->{kind} eq 'a';
 
 	print $tfh ",\n" if ($fmgr_count > 0);
 	print $tfh