Teach MemoryContext infrastructure not to depend on Node.aset_frontend

There's no real reason why a MemoryContext's type needs to be a
Node type. So use a separate enum instead.

This makes memory contexts less dependent on backend-only
infrastructure.

7 files changed, 49 insertions, 30 deletions

diff --git a/src/backend/utils/mmgr/aset.c b/src/backend/utils/mmgr/aset.c
index 5ac3811212..23ed57c4cf 100644
--- a/src/backend/utils/mmgr/aset.c
+++ b/src/backend/utils/mmgr/aset.c
@@ -459,7 +459,7 @@ AllocSetContextCreateInternal(MemoryContext parent,
 
 			/* Reinitialize its header, installing correct name and parent */
 			MemoryContextCreate((MemoryContext) set,
-								T_AllocSetContext,
+								MemoryContext_AllocSet,
 								&AllocSetMethods,
 								parent,
 								name);
@@ -550,7 +550,7 @@ AllocSetContextCreateInternal(MemoryContext parent,
 
 	/* Finally, do the type-independent part of context creation */
 	MemoryContextCreate((MemoryContext) set,
-						T_AllocSetContext,
+						MemoryContext_AllocSet,
 						&AllocSetMethods,
 						parent,
 						name);
diff --git a/src/backend/utils/mmgr/generation.c b/src/backend/utils/mmgr/generation.c
index b60a19f5a5..c3de3fd3d9 100644
--- a/src/backend/utils/mmgr/generation.c
+++ b/src/backend/utils/mmgr/generation.c
@@ -263,7 +263,7 @@ GenerationContextCreate(MemoryContext parent,
 
 	/* Finally, do the type-independent part of context creation */
 	MemoryContextCreate((MemoryContext) set,
-						T_GenerationContext,
+						MemoryContext_Generation,
 						&GenerationMethods,
 						parent,
 						name);
diff --git a/src/backend/utils/mmgr/mcxt.c b/src/backend/utils/mmgr/mcxt.c
index d52bd2c073..484b84d4d2 100644
--- a/src/backend/utils/mmgr/mcxt.c
+++ b/src/backend/utils/mmgr/mcxt.c
@@ -746,7 +746,7 @@ MemoryContextContains(MemoryContext context, void *pointer)
  */
 void
 MemoryContextCreate(MemoryContext node,
-					NodeTag tag,
+					MemoryContextType type,
 					const MemoryContextMethods *methods,
 					MemoryContext parent,
 					const char *name)
@@ -755,7 +755,7 @@ MemoryContextCreate(MemoryContext node,
 	Assert(CritSectionCount == 0);
 
 	/* Initialize all standard fields of memory context header */
-	node->type = tag;
+	node->type = type;
 	node->isReset = true;
 	node->methods = methods;
 	node->parent = parent;
diff --git a/src/backend/utils/mmgr/slab.c b/src/backend/utils/mmgr/slab.c
index db1dac3022..011577627f 100644
--- a/src/backend/utils/mmgr/slab.c
+++ b/src/backend/utils/mmgr/slab.c
@@ -260,7 +260,7 @@ SlabContextCreate(MemoryContext parent,
 
 	/* Finally, do the type-independent part of context creation */
 	MemoryContextCreate((MemoryContext) slab,
-						T_SlabContext,
+						MemoryContext_Slab,
 						&SlabMethods,
 						parent,
 						name);
@@ -279,7 +279,7 @@ static void
 SlabReset(MemoryContext context)
 {
 	int			i;
-	SlabContext *slab = castNode(SlabContext, context);
+	SlabContext *slab = MemoryContextCast(Slab, context);
 
 	Assert(slab);
 
@@ -335,7 +335,7 @@ SlabDelete(MemoryContext context)
 static void *
 SlabAlloc(MemoryContext context, Size size)
 {
-	SlabContext *slab = castNode(SlabContext, context);
+	SlabContext *slab = MemoryContextCast(Slab, context);
 	SlabBlock  *block;
 	SlabChunk  *chunk;
 	int			idx;
@@ -496,7 +496,7 @@ static void
 SlabFree(MemoryContext context, void *pointer)
 {
 	int			idx;
-	SlabContext *slab = castNode(SlabContext, context);
+	SlabContext *slab = MemoryContextCast(Slab, context);
 	SlabChunk  *chunk = SlabPointerGetChunk(pointer);
 	SlabBlock  *block = chunk->block;
 
@@ -585,7 +585,7 @@ SlabFree(MemoryContext context, void *pointer)
 static void *
 SlabRealloc(MemoryContext context, void *pointer, Size size)
 {
-	SlabContext *slab = castNode(SlabContext, context);
+	SlabContext *slab = MemoryContextCast(Slab, context);
 
 	Assert(slab);
 
@@ -605,7 +605,7 @@ SlabRealloc(MemoryContext context, void *pointer, Size size)
 static Size
 SlabGetChunkSpace(MemoryContext context, void *pointer)
 {
-	SlabContext *slab = castNode(SlabContext, context);
+	SlabContext *slab = MemoryContextCast(Slab, context);
 
 	Assert(slab);
 
@@ -619,7 +619,7 @@ SlabGetChunkSpace(MemoryContext context, void *pointer)
 static bool
 SlabIsEmpty(MemoryContext context)
 {
-	SlabContext *slab = castNode(SlabContext, context);
+	SlabContext *slab = MemoryContextCast(Slab, context);
 
 	Assert(slab);
 
@@ -639,7 +639,7 @@ SlabStats(MemoryContext context,
 		  MemoryStatsPrintFunc printfunc, void *passthru,
 		  MemoryContextCounters *totals)
 {
-	SlabContext *slab = castNode(SlabContext, context);
+	SlabContext *slab = MemoryContextCast(Slab, context);
 	Size		nblocks = 0;
 	Size		freechunks = 0;
 	Size		totalspace;
@@ -699,7 +699,7 @@ static void
 SlabCheck(MemoryContext context)
 {
 	int			i;
-	SlabContext *slab = castNode(SlabContext, context);
+	SlabContext *slab = MemoryContextCast(Slab, context);
 	const char *name = slab->header.name;
 	char	   *freechunks;
 
diff --git a/src/include/nodes/memnodes.h b/src/include/nodes/memnodes.h
index 854bd5d225..37d27032c2 100644
--- a/src/include/nodes/memnodes.h
+++ b/src/include/nodes/memnodes.h
@@ -14,7 +14,15 @@
 #ifndef MEMNODES_H
 #define MEMNODES_H
 
-#include "nodes/nodes.h"
+/*
+ * List of valid memory context types.
+ */
+typedef enum
+{
+	MemoryContext_AllocSet,
+	MemoryContext_Generation,
+	MemoryContext_Slab
+} MemoryContextType;
 
 /*
  * MemoryContextCounters
@@ -75,7 +83,7 @@ typedef struct MemoryContextMethods
 
 typedef struct MemoryContextData
 {
-	NodeTag		type;			/* identifies exact kind of context */
+	char		type;			/* MemoryContextType for this context */
 	/* these two fields are placed here to minimize alignment wastage: */
 	bool		isReset;		/* T = no space alloced since last reset */
 	bool		allowInCritSection; /* allow palloc in critical section */
@@ -99,10 +107,29 @@ typedef struct MemoryContextData
  *
  * Add new context types to the set accepted by this macro.
  */
-#define MemoryContextIsValid(context) \
-	((context) != NULL && \
-	 (IsA((context), AllocSetContext) || \
-	  IsA((context), SlabContext) || \
-	  IsA((context), GenerationContext)))
+static inline bool
+MemoryContextIsValid(MemoryContext context)
+{
+	return context != NULL &&
+		(context->type == MemoryContext_AllocSet ||
+		 context->type == MemoryContext_Slab ||
+		 context->type == MemoryContext_Generation);
+}
+
+/*
+ * MemoryContextCast
+ *		Cast a MemoryContext to a context of a given type, checking the type.
+ *
+ * NB: The static inline function avoids multiple evaluation.
+ */
+static inline MemoryContext
+MemoryContextCastImpl(MemoryContextType type, MemoryContext context)
+{
+	Assert(context == NULL || context->type == type);
+	return context;
+}
+#define MemoryContextCast(_type_, context) \
+	((_type_##Context *) \
+		MemoryContextCastImpl(MemoryContext_##_type_, context))
 
 #endif							/* MEMNODES_H */
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index bce2d59b0d..d4bba8a80c 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -274,14 +274,6 @@ typedef enum NodeTag
 	T_StatisticExtInfo,
 
 	/*
-	 * TAGS FOR MEMORY NODES (memnodes.h)
-	 */
-	T_MemoryContext,
-	T_AllocSetContext,
-	T_SlabContext,
-	T_GenerationContext,
-
-	/*
 	 * TAGS FOR VALUE NODES (value.h)
 	 */
 	T_Value,
diff --git a/src/include/utils/memutils.h b/src/include/utils/memutils.h
index 106c83da45..ad5d1276ac 100644
--- a/src/include/utils/memutils.h
+++ b/src/include/utils/memutils.h
@@ -139,7 +139,7 @@ GetMemoryChunkContext(void *pointer)
  * specific creation routines, and noplace else.
  */
 extern void MemoryContextCreate(MemoryContext node,
-								NodeTag tag,
+								MemoryContextType type,
 								const MemoryContextMethods *methods,
 								MemoryContext parent,
 								const char *name);