cp-tree.h (THUNK_VCALL_OFFSET): Update documentation.

	* cp-tree.h (THUNK_VCALL_OFFSET): Update documentation.
	* method.c (use_thunk): Correct handling of vcall offsets.

From-SVN: r35064

gcc/cp/cp-tree.h

@@ -3101,10 +3101,10 @@ extern int flag_new_for_scope;
    `this' pointer when this function is called.  */
 #define THUNK_DELTA(DECL) (DECL_CHECK (DECL)->decl.u1.i)
 
-/* An integer indicating how many bytes should be subtracted from the
+/* A tree indicating how many bytes should be subtracted from the
    vtable for the `this' pointer to find the vcall offset.  (The vptr
    is always located at offset zero from the f `this' pointer.)  If
-   zero, then there is no vcall offset.  */
+   NULL, then there is no vcall offset.  */
 #define THUNK_VCALL_OFFSET(DECL) \
   (DECL_LANG_SPECIFIC (DECL)->decl_flags.u2.vcall_offset)
 

gcc/cp/method.c

@@ -2267,7 +2267,7 @@ use_thunk (thunk_fndecl, emit_p)
     t = fold (build (PLUS_EXPR, TREE_TYPE (a), a, t));
     /* If there's a vcall offset, look up that value in the vtable and
        adjust the `this' pointer again.  */
-    if (!integer_zerop (vcall_offset))
+    if (vcall_offset && !integer_zerop (vcall_offset))
       {
 	tree orig_this;