Replace the switching function ExecEvalExpr() with a macro that jumps

directly to the appropriate per-node execution function, using a function
pointer stored by ExecInitExpr.  This speeds things up by eliminating one
level of function call.  The function-pointer technique also enables further
small improvements such as only making one-time tests once (and then
changing the function pointer).  Overall this seems to gain about 10%
on evaluation of simple expressions, which isn't earthshaking but seems
a worthwhile gain for a relatively small hack.  Per recent discussion
on pghackers.

1 files changed, 13 insertions, 6 deletions

diff --git a/src/include/executor/executor.h b/src/include/executor/executor.h
index cc2e49efafc..1eb158440b1 100644
--- a/src/include/executor/executor.h
+++ b/src/include/executor/executor.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/executor/executor.h,v 1.107 2004/03/02 18:56:15 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/executor/executor.h,v 1.108 2004/03/17 01:02:24 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -17,17 +17,26 @@
 #include "executor/execdesc.h"
 
 
-/* ----------------
- *		TupIsNull
+/*
+ * TupIsNull
  *
  *		This is used mainly to detect when there are no more
  *		tuples to process.
- * ----------------
  */
 /* return: true if tuple in slot is NULL, slot is slot to test */
 #define TupIsNull(slot) \
 	((slot) == NULL || (slot)->val == NULL)
 
+
+/*
+ * ExecEvalExpr was formerly a function containing a switch statement;
+ * now it's just a macro invoking the function pointed to by an ExprState
+ * node.  Beware of double evaluation of the ExprState argument!
+ */
+#define ExecEvalExpr(expr, econtext, isNull, isDone) \
+	((*(expr)->evalfunc) (expr, econtext, isNull, isDone))
+
+
 /*
  * prototypes from functions in execAmi.c
  */
@@ -125,8 +134,6 @@ extern Tuplestorestate *ExecMakeTableFunctionResult(ExprState *funcexpr,
 							ExprContext *econtext,
 							TupleDesc expectedDesc,
 							TupleDesc *returnDesc);
-extern Datum ExecEvalExpr(ExprState *expression, ExprContext *econtext,
-			 bool *isNull, ExprDoneCond *isDone);
 extern Datum ExecEvalExprSwitchContext(ExprState *expression, ExprContext *econtext,
 						  bool *isNull, ExprDoneCond *isDone);
 extern ExprState *ExecInitExpr(Expr *node, PlanState *parent);