Simplify newNode() by removing special cases

- Remove MemoryContextAllocZeroAligned(). It was supposed to be a
  faster version of MemoryContextAllocZero(), but modern compilers turn
  the MemSetLoop() into a call to memset() anyway, making it more or
  less identical to MemoryContextAllocZero(). That was the only user of
  MemSetTest, MemSetLoop, so remove those too, as well as palloc0fast().

- Convert newNode() to a static inline function. When this was
  originally originally written, it was written as a macro because
  testing showed that gcc didn't inline the size check as we
  intended. Modern compiler versions do, and now that it just calls
  palloc0() there is no size-check to inline anyway.

One nice effect is that the palloc0() takes one less argument than
MemoryContextAllocZeroAligned(), which saves a few instructions in the
callers of newNode().

Reviewed-by: Peter Eisentraut, Tom Lane, John Naylor, Thomas Munro
Discussion: https://www.postgresql.org/message-id/b51f1fa7-7e6a-4ecc-936d-90a8a1659e7c@iki.fi

src/backend/nodes/Makefile

@@ -23,7 +23,6 @@ OBJS = \
 	makefuncs.o \
 	multibitmapset.o \
 	nodeFuncs.o \
-	nodes.o \
 	outfuncs.o \
 	params.o \
 	print.o \

src/backend/nodes/meson.build

@@ -7,7 +7,6 @@ backend_sources += files(
   'makefuncs.c',
   'multibitmapset.c',
   'nodeFuncs.c',
-  'nodes.c',
   'params.c',
   'print.c',
   'read.c',

src/backend/nodes/nodes.c

@@ -1,31 +0,0 @@
-/*-------------------------------------------------------------------------
- *
- * nodes.c
- *	  support code for nodes (now that we have removed the home-brew
- *	  inheritance system, our support code for nodes is much simpler)
- *
- * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
- * Portions Copyright (c) 1994, Regents of the University of California
- *
- *
- * IDENTIFICATION
- *	  src/backend/nodes/nodes.c
- *
- * HISTORY
- *	  Andrew Yu			Oct 20, 1994	file creation
- *
- *-------------------------------------------------------------------------
- */
-#include "postgres.h"
-
-#include "nodes/nodes.h"
-
-/*
- * 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;

src/backend/utils/mmgr/mcxt.c

@@ -1091,44 +1091,6 @@ MemoryContextAllocZero(MemoryContext context, Size size)
 	return ret;
 }
 
-/*
- * MemoryContextAllocZeroAligned
- *		MemoryContextAllocZero where length is suitable for MemSetLoop
- *
- *	This might seem overly specialized, but it's not because newNode()
- *	is so often called with compile-time-constant sizes.
- */
-void *
-MemoryContextAllocZeroAligned(MemoryContext context, Size size)
-{
-	void	   *ret;
-
-	Assert(MemoryContextIsValid(context));
-	AssertNotInCriticalSection(context);
-
-	if (!AllocSizeIsValid(size))
-		elog(ERROR, "invalid memory alloc request size %zu", size);
-
-	context->isReset = false;
-
-	ret = context->methods->alloc(context, size);
-	if (unlikely(ret == NULL))
-	{
-		MemoryContextStats(TopMemoryContext);
-		ereport(ERROR,
-				(errcode(ERRCODE_OUT_OF_MEMORY),
-				 errmsg("out of memory"),
-				 errdetail("Failed on request of size %zu in memory context \"%s\".",
-						   size, context->name)));
-	}
-
-	VALGRIND_MEMPOOL_ALLOC(context, ret, size);
-
-	MemSetLoop(ret, 0, size);
-
-	return ret;
-}
-
 /*
  * MemoryContextAllocExtended
  *		Allocate space within the specified context using the given flags.

src/include/c.h

@@ -1060,30 +1060,6 @@ extern void ExceptionalCondition(const char *conditionName,
 	} while (0)
 
 
-/*
- * MemSetTest/MemSetLoop are a variant version that allow all the tests in
- * MemSet to be done at compile time in cases where "val" and "len" are
- * constants *and* we know the "start" pointer must be word-aligned.
- * If MemSetTest succeeds, then it is okay to use MemSetLoop, otherwise use
- * MemSetAligned.  Beware of multiple evaluations of the arguments when using
- * this approach.
- */
-#define MemSetTest(val, len) \
-	( ((len) & LONG_ALIGN_MASK) == 0 && \
-	(len) <= MEMSET_LOOP_LIMIT && \
-	MEMSET_LOOP_LIMIT != 0 && \
-	(val) == 0 )
-
-#define MemSetLoop(start, val, len) \
-	do \
-	{ \
-		long * _start = (long *) (start); \
-		long * _stop = (long *) ((char *) _start + (Size) (len)); \
-	\
-		while (_start < _stop) \
-			*_start++ = 0; \
-	} while (0)
-
 /*
  * Macros for range-checking float values before converting to integer.
  * We must be careful here that the boundary values are expressed exactly

src/include/nodes/nodes.h

@@ -139,39 +139,18 @@ 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__
+static inline Node *
+newNode(size_t size, NodeTag tag)
+{
+	Node	   *result;
 
-/* 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
- *	a global variable for this purpose.
- */
-extern PGDLLIMPORT Node *newNodeMacroHolder;
-
-#define newNode(size, tag) \
-( \
-	AssertMacro((size) >= sizeof(Node)),		/* need the tag, at least */ \
-	newNodeMacroHolder = (Node *) palloc0fast(size), \
-	newNodeMacroHolder->type = (tag), \
-	newNodeMacroHolder \
-)
-#endif							/* __GNUC__ */
+	Assert(size >= sizeof(Node));	/* need the tag, at least */
+	result = (Node *) palloc0(size);
+	result->type = tag;
 
+	return result;
+}
 
 #define makeNode(_type_)		((_type_ *) newNode(sizeof(_type_),T_##_type_))
 #define NodeSetTag(nodeptr,t)	(((Node*)(nodeptr))->type = (t))

src/include/utils/palloc.h

@@ -70,7 +70,6 @@ extern PGDLLIMPORT MemoryContext CurrentMemoryContext;
  */
 extern void *MemoryContextAlloc(MemoryContext context, Size size);
 extern void *MemoryContextAllocZero(MemoryContext context, Size size);
-extern void *MemoryContextAllocZeroAligned(MemoryContext context, Size size);
 extern void *MemoryContextAllocExtended(MemoryContext context,
 										Size size, int flags);
 extern void *MemoryContextAllocAligned(MemoryContext context,
@@ -109,19 +108,6 @@ extern void pfree(void *pointer);
 #define repalloc_array(pointer, type, count) ((type *) repalloc(pointer, sizeof(type) * (count)))
 #define repalloc0_array(pointer, type, oldcount, count) ((type *) repalloc0(pointer, sizeof(type) * (oldcount), sizeof(type) * (count)))
 
-/*
- * The result of palloc() is always word-aligned, so we can skip testing
- * alignment of the pointer when deciding which MemSet variant to use.
- * Note that this variant does not offer any advantage, and should not be
- * used, unless its "sz" argument is a compile-time constant; therefore, the
- * issue that it evaluates the argument multiple times isn't a problem in
- * practice.
- */
-#define palloc0fast(sz) \
-	( MemSetTest(0, sz) ? \
-		MemoryContextAllocZeroAligned(CurrentMemoryContext, sz) : \
-		MemoryContextAllocZero(CurrentMemoryContext, sz) )
-
 /* Higher-limit allocators. */
 extern void *MemoryContextAllocHuge(MemoryContext context, Size size);
 extern pg_nodiscard void *repalloc_huge(void *pointer, Size size);