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/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.