core: add tree-node comments

As we've moved to 64-bit systems, the padding information has become
conditionally inaccurate.  I also hit cases where invalid tree codes
did not get flagged as invalid.

	gcc/
	* tree-core.h (tree_decl_with_vis, tree_function_decl):
	Note additional padding on 64-bits
	* tree.c (cache_integer_cst): Note why no caching of enum literals.
	(get_tree_code_name): Robustify error case.

1 files changed, 5 insertions, 1 deletions

diff --git a/gcc/tree.c b/gcc/tree.c
index 3d9968f..9102f8d 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -1771,6 +1771,8 @@ cache_integer_cst (tree t)
       break;
 
     case ENUMERAL_TYPE:
+      /* The slot used by TYPE_CACHED_VALUES is used for the enum
+	 members.  */
       break;
 
     default:
@@ -13254,7 +13256,9 @@ get_tree_code_name (enum tree_code code)
 {
   const char *invalid = "<invalid tree code>";
 
-  if (code >= MAX_TREE_CODES)
+  /* The tree_code enum promotes to signed, but we could be getting
+     invalid values, so force an unsigned comparison.  */
+  if (unsigned (code) >= MAX_TREE_CODES)
     {
       if (code == 0xa5a5)
 	return "ggc_freed";