Use a linked list to eliminate imemo tmp bufs for managing local tables

This patch changes local table memory to be managed by a linked list
rather than via the garbage collector.  It reduces allocations from the
GC and also fixes a use-after-free bug in the concurrent-with-sweep
compactor I'm working on.

node.c

@@ -1144,6 +1144,7 @@ typedef struct {
 struct node_buffer_struct {
     node_buffer_list_t unmarkable;
     node_buffer_list_t markable;
+    ID *local_tables;
     VALUE mark_hash;
 };
 
@@ -1169,6 +1170,7 @@ rb_node_buffer_new(void)
     node_buffer_t *nb = ruby_xmalloc(alloc_size);
     init_node_buffer_list(&nb->unmarkable, (node_buffer_elem_t*)&nb[1]);
     init_node_buffer_list(&nb->markable, (node_buffer_elem_t*)((size_t)nb->unmarkable.head + bucket_size));
+    nb->local_tables = 0;
     nb->mark_hash = Qnil;
     return nb;
 }
@@ -1190,6 +1192,13 @@ rb_node_buffer_free(node_buffer_t *nb)
 {
     node_buffer_list_free(&nb->unmarkable);
     node_buffer_list_free(&nb->markable);
+    ID * local_table = nb->local_tables;
+    while (local_table) {
+        unsigned int size = (unsigned int)*local_table;
+        ID * next_table = (ID *)local_table[size + 1];
+        xfree(local_table);
+        local_table = next_table;
+    }
     xfree(nb);
 }
 
@@ -1223,7 +1232,6 @@ rb_ast_newnode(rb_ast_t *ast, enum node_type type)
       case NODE_DREGX:
       case NODE_DSYM:
       case NODE_ARGS:
-      case NODE_SCOPE:
       case NODE_ARYPTN:
       case NODE_FNDPTN:
         return ast_newnode_in_bucket(&nb->markable);
@@ -1232,6 +1240,14 @@ rb_ast_newnode(rb_ast_t *ast, enum node_type type)
     }
 }
 
+void
+rb_ast_add_local_table(rb_ast_t *ast, ID *buf)
+{
+    unsigned int size = (unsigned int)*buf;
+    buf[size + 1] = (ID)ast->node_buffer->local_tables;
+    ast->node_buffer->local_tables = buf;
+}
+
 void
 rb_ast_delete_node(rb_ast_t *ast, NODE *n)
 {
@@ -1278,15 +1294,6 @@ static void
 mark_ast_value(void *ctx, NODE * node)
 {
     switch (nd_type(node)) {
-      case NODE_SCOPE:
-        {
-            ID *buf = node->nd_tbl;
-            if (buf) {
-                unsigned int size = (unsigned int)*buf;
-                rb_gc_mark_movable((VALUE)buf[size + 1]);
-            }
-            break;
-        }
       case NODE_ARYPTN:
         {
             struct rb_ary_pattern_info *apinfo = node->nd_apinfo;
@@ -1324,15 +1331,6 @@ static void
 update_ast_value(void *ctx, NODE * node)
 {
     switch (nd_type(node)) {
-      case NODE_SCOPE:
-        {
-            ID *buf = node->nd_tbl;
-            if (buf) {
-                unsigned int size = (unsigned int)*buf;
-                buf[size + 1] = rb_gc_location((VALUE)buf[size + 1]);
-            }
-            break;
-        }
       case NODE_ARYPTN:
         {
             struct rb_ary_pattern_info *apinfo = node->nd_apinfo;

node.h

@@ -401,11 +401,13 @@ typedef struct rb_ast_body_struct {
 typedef struct rb_ast_struct {
     VALUE flags;
     node_buffer_t *node_buffer;
+    ID *local_lists;
     rb_ast_body_t body;
 } rb_ast_t;
 rb_ast_t *rb_ast_new(void);
 void rb_ast_mark(rb_ast_t*);
 void rb_ast_update_references(rb_ast_t*);
+void rb_ast_add_local_table(rb_ast_t*, ID *buf);
 void rb_ast_dispose(rb_ast_t*);
 void rb_ast_free(rb_ast_t*);
 size_t rb_ast_memsize(const rb_ast_t*);

parse.y

@@ -3050,11 +3050,9 @@ primary		: literal
 			ID id = internal_id(p);
 			NODE *m = NEW_ARGS_AUX(0, 0, &NULL_LOC);
 			NODE *args, *scope, *internal_var = NEW_DVAR(id, &@2);
-			VALUE tmpbuf = rb_imemo_tmpbuf_auto_free_pointer();
 			ID *tbl = ALLOC_N(ID, 3);
-			rb_imemo_tmpbuf_set_ptr(tmpbuf, tbl);
 			tbl[0] = 1 /* length of local var table */; tbl[1] = id /* internal id */;
-                        tbl[2] = tmpbuf;
+                        rb_ast_add_local_table(p->ast, tbl);
 
 			switch (nd_type($2)) {
 			  case NODE_LASGN:
@@ -3074,7 +3072,6 @@ primary		: literal
 			/* {|*internal_id| <m> = internal_id; ... } */
 			args = new_args(p, m, 0, id, 0, new_args_tail(p, 0, 0, 0, &@2), &@2);
 			scope = NEW_NODE(NODE_SCOPE, tbl, $5, args, &@$);
-                        RB_OBJ_WRITTEN(p->ast, Qnil, tmpbuf);
 			$$ = NEW_FOR($4, scope, &@$);
 			fixpos($$, $2);
 		    /*% %*/
@@ -12037,12 +12034,9 @@ local_tbl(struct parser_params *p)
     int cnt = cnt_args + cnt_vars;
     int i, j;
     ID *buf;
-    VALUE tbl = 0;
 
     if (cnt <= 0) return 0;
-    tbl = rb_imemo_tmpbuf_auto_free_pointer();
     buf = ALLOC_N(ID, cnt + 2);
-    rb_imemo_tmpbuf_set_ptr(tbl, buf);
     MEMCPY(buf+1, p->lvtbl->args->tbl, ID, cnt_args);
     /* remove IDs duplicated to warn shadowing */
     for (i = 0, j = cnt_args+1; i < cnt_vars; ++i) {
@@ -12053,11 +12047,9 @@ local_tbl(struct parser_params *p)
     }
     if (--j < cnt) {
 	REALLOC_N(buf, ID, (cnt = j) + 2);
-	rb_imemo_tmpbuf_set_ptr(tbl, buf);
     }
     buf[0] = cnt;
-    buf[cnt + 1] = (ID)tbl;
+    rb_ast_add_local_table(p->ast, buf);
-    RB_OBJ_WRITTEN(p->ast, Qnil, tbl);
 
     return buf;
 }