From 6253f9de6702fa73101997034b4fec038d547f6d Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 29 Aug 2008 22:49:07 +0000
Subject: [PATCH] In GCC-based builds, use a better newNode() macro that relies
on GCC-specific syntax to avoid a useless store into a global variable. Per
experimentation, this works better than my original thought of trying to push
the code into an out-of-line subroutine.
---
src/backend/nodes/nodes.c | 6 +++++-
src/include/nodes/nodes.h | 21 ++++++++++++++++++++-
2 files changed, 25 insertions(+), 2 deletions(-)
diff --git a/src/backend/nodes/nodes.c b/src/backend/nodes/nodes.c
index a2ced5f945..30cbeb8e1d 100644
--- a/src/backend/nodes/nodes.c
+++ b/src/backend/nodes/nodes.c
@@ -9,7 +9,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/nodes/nodes.c,v 1.28 2008/01/01 19:45:50 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/nodes/nodes.c,v 1.29 2008/08/29 22:49:07 tgl Exp $
*
* HISTORY
* Andrew Yu Oct 20, 1994 file creation
@@ -22,6 +22,10 @@
/*
* Support for newNode() macro
+ *
+ * In a GCC build there is no need for the global variable newNodeMacroHolder.
+ * However, we create it anyway, to support the case of a non-GCC-built
+ * loadable module being loaded into a GCC-built backend.
*/
Node *newNodeMacroHolder;
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index b9e00bfdde..78dd917ecf 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $PostgreSQL: pgsql/src/include/nodes/nodes.h,v 1.209 2008/08/22 00:16:04 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/nodes.h,v 1.210 2008/08/29 22:49:07 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -384,6 +384,23 @@ typedef struct Node
* !WARNING!: Avoid using newNode directly. You should be using the
* macro makeNode. eg. to create a Query node, use makeNode(Query)
*
+ * Note: the size argument should always be a compile-time constant, so the
+ * apparent risk of multiple evaluation doesn't matter in practice.
+ */
+#ifdef __GNUC__
+
+/* With GCC, we can use a compound statement within an expression */
+#define newNode(size, tag) \
+({ Node *_result; \
+ AssertMacro((size) >= sizeof(Node)); /* need the tag, at least */ \
+ _result = (Node *) palloc0fast(size); \
+ _result->type = (tag); \
+ _result; \
+})
+
+#else
+
+/*
* There is no way to dereference the palloc'ed pointer to assign the
* tag, and also return the pointer itself, so we need a holder variable.
* Fortunately, this macro isn't recursive so we just define
@@ -399,6 +416,8 @@ extern PGDLLIMPORT Node *newNodeMacroHolder;
newNodeMacroHolder \
)
+#endif /* __GNUC__ */
+
#define makeNode(_type_) ((_type_ *) newNode(sizeof(_type_),T_##_type_))
#define NodeSetTag(nodeptr,t) (((Node*)(nodeptr))->type = (t))
--
2.49.0