re PR sanitizer/87095 (UndefinedBehaviorSanitizer vptr false positive with…

re PR sanitizer/87095 (UndefinedBehaviorSanitizer vptr false positive with virtual inheritance only with -fno-sanitize-recover)

	PR c++/87095
	* decl.c (begin_destructor_body): If current_class_type has
	virtual bases and the primary base is nearly empty virtual base,
	voidify clearing of vptr and make it conditional on in-charge
	argument.

	* g++.dg/ubsan/vptr-13.C: New test.

From-SVN: r263967

gcc/cp/ChangeLog

+2018-08-29  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/87095
+	* decl.c (begin_destructor_body): If current_class_type has
+	virtual bases and the primary base is nearly empty virtual base,
+	voidify clearing of vptr and make it conditional on in-charge
+	argument.
+
 2018-08-29  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/85265

gcc/cp/decl.c

@@ -15698,6 +15698,18 @@ begin_destructor_body (void)
 	    tree stmt = cp_build_modify_expr (input_location, vtbl_ptr,
 					      NOP_EXPR, vtbl,
 					      tf_warning_or_error);
+	    /* If the vptr is shared with some virtual nearly empty base,
+	       don't clear it if not in charge, the dtor of the virtual
+	       nearly empty base will do that later.  */
+	    if (CLASSTYPE_VBASECLASSES (current_class_type)
+		&& CLASSTYPE_PRIMARY_BINFO (current_class_type)
+		&& BINFO_VIRTUAL_P
+			  (CLASSTYPE_PRIMARY_BINFO (current_class_type)))
+	      {
+		stmt = convert_to_void (stmt, ICV_STATEMENT,
+					tf_warning_or_error);
+		stmt = build_if_in_charge (stmt);
+	      }
 	    finish_decl_cleanup (NULL_TREE, stmt);
 	  }
 	else

gcc/testsuite/ChangeLog

+2018-08-29  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/87095
+	* g++.dg/ubsan/vptr-13.C: New test.
+
 2018-08-29  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/85265

gcc/testsuite/g++.dg/ubsan/vptr-13.C

+// PR c++/87095
+// { dg-do run }
+// { dg-options "-fsanitize=vptr -fno-sanitize-recover=vptr" }
+
+struct A
+{
+  virtual ~A () {}
+};
+
+struct B : virtual A {};
+
+struct C : B {};
+
+int
+main ()
+{
+  C c;
+  return 0;
+}