[C++ Patch / RFC] Change DERIVED_FROM_P to use tf_none?!?

[Paolo Carlini]

Hi,

On 07/23/2013 05:27 PM, Jason Merrill wrote:
> Hmm, I suppose this could still end up doing unnecessary completions 
> if both types are incomplete.  What happens if X is also incomplete?
Indeed, it fails and shouldn't. I thought I had tested this case but 
didn't. Thus I extended a bit the testcase.
> The version that returns false if either is incomplete would give the 
> wrong answer if the types are the same.
>
> I think a better way would be to use COMPARE_STRICT if either type is 
> incomplete.
I see. Just don't bother looking for inheritance in all such cases, can 
only cause troubles. Thus shall we implement this like in the below? It 
passes testing.

Thanks!
Paolo.

////////////////////
-------------- next part --------------
Index: cp/cp-tree.h
===================================================================
--- cp/cp-tree.h	(revision 201148)
+++ cp/cp-tree.h	(working copy)
@@ -6022,7 +6022,7 @@ extern tree convert_for_initialization		(tree, tre
 extern int comp_ptr_ttypes			(tree, tree);
 extern bool comp_ptr_ttypes_const		(tree, tree);
 extern bool error_type_p			(const_tree);
-extern int ptr_reasonably_similar		(const_tree, const_tree);
+extern bool ptr_reasonably_similar		(const_tree, const_tree);
 extern tree build_ptrmemfunc			(tree, tree, int, bool,
 						 tsubst_flags_t);
 extern int cp_type_quals			(const_tree);
Index: cp/typeck.c
===================================================================
--- cp/typeck.c	(revision 201148)
+++ cp/typeck.c	(working copy)
@@ -8599,10 +8599,10 @@ error_type_p (const_tree type)
     }
 }
 
-/* Returns 1 if to and from are (possibly multi-level) pointers to the same
+/* Returns true if to and from are (possibly multi-level) pointers to the same
    type or inheritance-related types, regardless of cv-quals.  */
 
-int
+bool
 ptr_reasonably_similar (const_tree to, const_tree from)
 {
   for (; ; to = TREE_TYPE (to), from = TREE_TYPE (from))
@@ -8614,7 +8614,7 @@ ptr_reasonably_similar (const_tree to, const_tree
 	return !error_type_p (to);
 
       if (TREE_CODE (to) != TREE_CODE (from))
-	return 0;
+	return false;
 
       if (TREE_CODE (from) == OFFSET_TYPE
 	  && comptypes (TYPE_OFFSET_BASETYPE (to),
@@ -8624,19 +8624,24 @@ ptr_reasonably_similar (const_tree to, const_tree
 
       if (TREE_CODE (to) == VECTOR_TYPE
 	  && vector_types_convertible_p (to, from, false))
-	return 1;
+	return true;
 
       if (TREE_CODE (to) == INTEGER_TYPE
 	  && TYPE_PRECISION (to) == TYPE_PRECISION (from))
-	return 1;
+	return true;
 
       if (TREE_CODE (to) == FUNCTION_TYPE)
 	return !error_type_p (to) && !error_type_p (from);
 
       if (!TYPE_PTR_P (to))
-	return comptypes
-	  (TYPE_MAIN_VARIANT (to), TYPE_MAIN_VARIANT (from),
-	   COMPARE_BASE | COMPARE_DERIVED);
+	{
+	  /* When either type is incomplete avoid DERIVED_FROM_P,
+	     which may call complete_type (c++/57942).  */
+	  bool b = !COMPLETE_TYPE_P (to) || !COMPLETE_TYPE_P (from);
+	  return comptypes
+	    (TYPE_MAIN_VARIANT (to), TYPE_MAIN_VARIANT (from),
+	     b ? COMPARE_STRICT : COMPARE_BASE | COMPARE_DERIVED);
+	}
     }
 }
 
Index: testsuite/g++.dg/inherit/pr57942.C
===================================================================
--- testsuite/g++.dg/inherit/pr57942.C	(revision 0)
+++ testsuite/g++.dg/inherit/pr57942.C	(working copy)
@@ -0,0 +1,9 @@
+// PR c++/57942
+
+template<typename T> struct S { typename T::error type; };
+struct X {};
+void f(S<int>*);
+void f(...);
+void g() { f((X*)0); }
+struct Y;
+void h() { f((Y*)0); }