Change function call information to be variable length.

Before this change FunctionCallInfoData, the struct arguments etc for
V1 function calls are stored in, always had space for
FUNC_MAX_ARGS/100 arguments, storing datums and their nullness in two
arrays.  For nearly every function call 100 arguments is far more than
needed, therefore wasting memory. Arg and argnull being two separate
arrays also guarantees that to access a single argument, two
cachelines have to be touched.

Change the layout so there's a single variable-length array with pairs
of value / isnull. That drastically reduces memory consumption for
most function calls (on x86-64 a two argument function now uses
64bytes, previously 936 bytes), and makes it very likely that argument
value and its nullness are on the same cacheline.

Arguments are stored in a new NullableDatum struct, which, due to
padding, needs more memory per argument than before. But as usually
far fewer arguments are stored, and individual arguments are cheaper
to access, that's still a clear win.  It's likely that there's other
places where conversion to NullableDatum arrays would make sense,
e.g. TupleTableSlots, but that's for another commit.

Because the function call information is now variable-length
allocations have to take the number of arguments into account. For
heap allocations that can be done with SizeForFunctionCallInfoData(),
for on-stack allocations there's a new LOCAL_FCINFO(name, nargs) macro
that helps to allocate an appropriately sized and aligned variable.

Some places with stack allocation function call information don't know
the number of arguments at compile time, and currently variably sized
stack allocations aren't allowed in postgres. Therefore allow for
FUNC_MAX_ARGS space in these cases. They're not that common, so for
now that seems acceptable.

Because of the need to allocate FunctionCallInfo of the appropriate
size, older extensions may need to update their code. To avoid subtle
breakages, the FunctionCallInfoData struct has been renamed to
FunctionCallInfoBaseData. Most code only references FunctionCallInfo,
so that shouldn't cause much collateral damage.

This change is also a prerequisite for more efficient expression JIT
compilation (by allocating the function call information on the stack,
allowing LLVM to optimize it away); previously the size of the call
information caused problems inside LLVM's optimizer.

Author: Andres Freund
Reviewed-By: Tom Lane
Discussion: https://postgr.es/m/20180605172952.x34m5uz6ju6enaem@alap3.anarazel.de

4 files changed, 22 insertions, 21 deletions

diff --git a/src/backend/commands/event_trigger.c b/src/backend/commands/event_trigger.c
index 8adc2cadaf4..adb77d8f692 100644
--- a/src/backend/commands/event_trigger.c
+++ b/src/backend/commands/event_trigger.c
@@ -1055,9 +1055,9 @@ EventTriggerInvoke(List *fn_oid_list, EventTriggerData *trigdata)
 	/* Call each event trigger. */
 	foreach(lc, fn_oid_list)
 	{
+		LOCAL_FCINFO(fcinfo, 0);
 		Oid			fnoid = lfirst_oid(lc);
 		FmgrInfo	flinfo;
-		FunctionCallInfoData fcinfo;
 		PgStat_FunctionCallUsage fcusage;
 
 		elog(DEBUG1, "EventTriggerInvoke %u", fnoid);
@@ -1077,10 +1077,10 @@ EventTriggerInvoke(List *fn_oid_list, EventTriggerData *trigdata)
 		fmgr_info(fnoid, &flinfo);
 
 		/* Call the function, passing no arguments but setting a context. */
-		InitFunctionCallInfoData(fcinfo, &flinfo, 0,
+		InitFunctionCallInfoData(*fcinfo, &flinfo, 0,
 								 InvalidOid, (Node *) trigdata, NULL);
-		pgstat_init_function_usage(&fcinfo, &fcusage);
-		FunctionCallInvoke(&fcinfo);
+		pgstat_init_function_usage(fcinfo, &fcusage);
+		FunctionCallInvoke(fcinfo);
 		pgstat_end_function_usage(&fcusage, true);
 
 		/* Reclaim memory. */
diff --git a/src/backend/commands/functioncmds.c b/src/backend/commands/functioncmds.c
index eae2b09830b..ac401689c82 100644
--- a/src/backend/commands/functioncmds.c
+++ b/src/backend/commands/functioncmds.c
@@ -2216,13 +2216,13 @@ ExecuteDoStmt(DoStmt *stmt, bool atomic)
 void
 ExecuteCallStmt(CallStmt *stmt, ParamListInfo params, bool atomic, DestReceiver *dest)
 {
+	LOCAL_FCINFO(fcinfo, FUNC_MAX_ARGS);
 	ListCell   *lc;
 	FuncExpr   *fexpr;
 	int			nargs;
 	int			i;
 	AclResult	aclresult;
 	FmgrInfo	flinfo;
-	FunctionCallInfoData fcinfo;
 	CallContext *callcontext;
 	EState	   *estate;
 	ExprContext *econtext;
@@ -2297,7 +2297,8 @@ ExecuteCallStmt(CallStmt *stmt, ParamListInfo params, bool atomic, DestReceiver
 	InvokeFunctionExecuteHook(fexpr->funcid);
 	fmgr_info(fexpr->funcid, &flinfo);
 	fmgr_info_set_expr((Node *) fexpr, &flinfo);
-	InitFunctionCallInfoData(fcinfo, &flinfo, nargs, fexpr->inputcollid, (Node *) callcontext, NULL);
+	InitFunctionCallInfoData(*fcinfo, &flinfo, nargs, fexpr->inputcollid,
+							 (Node *) callcontext, NULL);
 
 	/*
 	 * Evaluate procedure arguments inside a suitable execution context.  Note
@@ -2318,14 +2319,14 @@ ExecuteCallStmt(CallStmt *stmt, ParamListInfo params, bool atomic, DestReceiver
 
 		val = ExecEvalExprSwitchContext(exprstate, econtext, &isnull);
 
-		fcinfo.arg[i] = val;
-		fcinfo.argnull[i] = isnull;
+		fcinfo->args[i].value = val;
+		fcinfo->args[i].isnull = isnull;
 
 		i++;
 	}
 
-	pgstat_init_function_usage(&fcinfo, &fcusage);
-	retval = FunctionCallInvoke(&fcinfo);
+	pgstat_init_function_usage(fcinfo, &fcusage);
+	retval = FunctionCallInvoke(fcinfo);
 	pgstat_end_function_usage(&fcusage, true);
 
 	if (fexpr->funcresulttype == VOIDOID)
@@ -2346,7 +2347,7 @@ ExecuteCallStmt(CallStmt *stmt, ParamListInfo params, bool atomic, DestReceiver
 		TupOutputState *tstate;
 		TupleTableSlot *slot;
 
-		if (fcinfo.isnull)
+		if (fcinfo->isnull)
 			elog(ERROR, "procedure returned null record");
 
 		td = DatumGetHeapTupleHeader(retval);
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 9daf3e6588f..ff764991379 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -8879,7 +8879,7 @@ validateForeignKeyConstraint(char *conname,
 
 	while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
 	{
-		FunctionCallInfoData fcinfo;
+		LOCAL_FCINFO(fcinfo, 0);
 		TriggerData trigdata;
 
 		/*
@@ -8887,7 +8887,7 @@ validateForeignKeyConstraint(char *conname,
 		 *
 		 * No parameters are passed, but we do set a context
 		 */
-		MemSet(&fcinfo, 0, sizeof(fcinfo));
+		MemSet(fcinfo, 0, SizeForFunctionCallInfo(0));
 
 		/*
 		 * We assume RI_FKey_check_ins won't look at flinfo...
@@ -8901,9 +8901,9 @@ validateForeignKeyConstraint(char *conname,
 		trigdata.tg_trigtuplebuf = scan->rs_cbuf;
 		trigdata.tg_newtuplebuf = InvalidBuffer;
 
-		fcinfo.context = (Node *) &trigdata;
+		fcinfo->context = (Node *) &trigdata;
 
-		RI_FKey_check_ins(&fcinfo);
+		RI_FKey_check_ins(fcinfo);
 	}
 
 	heap_endscan(scan);
diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index 7ffaeaffc67..499030c4455 100644
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -2357,7 +2357,7 @@ ExecCallTriggerFunc(TriggerData *trigdata,
 					Instrumentation *instr,
 					MemoryContext per_tuple_context)
 {
-	FunctionCallInfoData fcinfo;
+	LOCAL_FCINFO(fcinfo, 0);
 	PgStat_FunctionCallUsage fcusage;
 	Datum		result;
 	MemoryContext oldContext;
@@ -2402,15 +2402,15 @@ ExecCallTriggerFunc(TriggerData *trigdata,
 	/*
 	 * Call the function, passing no arguments but setting a context.
 	 */
-	InitFunctionCallInfoData(fcinfo, finfo, 0,
+	InitFunctionCallInfoData(*fcinfo, finfo, 0,
 							 InvalidOid, (Node *) trigdata, NULL);
 
-	pgstat_init_function_usage(&fcinfo, &fcusage);
+	pgstat_init_function_usage(fcinfo, &fcusage);
 
 	MyTriggerDepth++;
 	PG_TRY();
 	{
-		result = FunctionCallInvoke(&fcinfo);
+		result = FunctionCallInvoke(fcinfo);
 	}
 	PG_CATCH();
 	{
@@ -2428,11 +2428,11 @@ ExecCallTriggerFunc(TriggerData *trigdata,
 	 * Trigger protocol allows function to return a null pointer, but NOT to
 	 * set the isnull result flag.
 	 */
-	if (fcinfo.isnull)
+	if (fcinfo->isnull)
 		ereport(ERROR,
 				(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
 				 errmsg("trigger function %u returned null value",
-						fcinfo.flinfo->fn_oid)));
+						fcinfo->flinfo->fn_oid)));
 
 	/*
 	 * If doing EXPLAIN ANALYZE, stop charging time to this trigger, and count