Patchwork add -Wdelete-non-virtual-dtor

login
register
mail settings
Submitter Jonathan Wakely
Date June 2, 2011, 9:27 p.m.
Message ID <BANLkTinxuAywtkOsNzSb+Ge6hmPWSm_D4Q@mail.gmail.com>
Download mbox | patch
Permalink /patch/98489/
State New
Headers show

Comments

Jonathan Wakely - June 2, 2011, 9:27 p.m.
-Wnon-virtual-dtor isn't always what you want, defining a polymorphic
object without a virtual destructor is not necessarily a mistake. You
may never delete such an object so instead of warning when the class
is defined it's more useful to warn only when the class is deleted, as
Clang does with -Wdelete-non-virtual-dtor

This patch implements the same warning for G++.

Unlike Clang's, this diagnostic distinguishes the case where the
pointer might refer to a base class from the case where it definitely
does because the static type is abstract.  There's no warning for a
C++0x final class, since the pointer must refer to the most-derived
type.    I'm not entirely happy with the diagnostic text as I don't
think we usually refer to undefined behaviour.  Better suggestions
welcome.

The new test uses -std=gnu++0x in order to test a 'final' class,
should that be split into a separate c++0x test, so the rest uses
gnu++98?

I'm not sure why PR c++/7302 is still open, but I think this would
allow it to be closed, as it issues a warning for the delete
expression in comment 25.

Bootstrapped and tested x86_64-linux

OK for trunk?


c-family/ChangeLog:

        * c.opt: Add -Wdelete-non-virtual-dtor.
        * c-opts.c (c_common_handle_option): Include it in -Wall.

cp/ChangeLog:

        * init.c (build_delete): Warn when deleting type with non-virtual
        destructor.

testsuite/ChangeLog:

        * testsuite/g++.dg/warn/delete-non-virtual-dtor.cc: New.

ChangeLog:

        * doc/invoke.texi: Document -Wdelete-non-virtual-dtor.

Patch

Index: c-family/c.opt
===================================================================
--- c-family/c.opt	(revision 174539)
+++ c-family/c.opt	(working copy)
@@ -331,6 +331,10 @@  Wdeclaration-after-statement
 C ObjC Var(warn_declaration_after_statement) Warning
 Warn when a declaration is found after a statement
 
+Wdelete-non-virtual-dtor
+C++ ObjC++ Var(warn_delnonvdtor) Warning
+Warn about deleting polymorphic objects with non-virtual destructors
+
 Wdeprecated
 C C++ ObjC ObjC++ Var(warn_deprecated) Init(1) Warning
 Warn if a deprecated compiler feature, class, method, or field is used
Index: c-family/c-opts.c
===================================================================
--- c-family/c-opts.c	(revision 174539)
+++ c-family/c-opts.c	(working copy)
@@ -405,6 +405,7 @@  c_common_handle_option (size_t scode, co
           warn_sign_compare = value;
 	  warn_reorder = value;
           warn_cxx0x_compat = value;
+          warn_delnonvdtor = value;
 	}
 
       cpp_opts->warn_trigraphs = value;
Index: cp/init.c
===================================================================
--- cp/init.c	(revision 174539)
+++ cp/init.c	(working copy)
@@ -3421,6 +3421,31 @@  build_delete (tree type, tree addr, spec
 		}
 	      complete_p = false;
 	    }
+          else if (warn_delnonvdtor && MAYBE_CLASS_TYPE_P (type)
+                   && !CLASSTYPE_FINAL (type) && TYPE_POLYMORPHIC_P (type))
+	    {
+	      tree dtor;
+	      dtor = CLASSTYPE_DESTRUCTORS (type);
+	      if (!dtor || !DECL_VINDEX (dtor))
+	        {
+		  tree x;
+		  bool abstract = false;
+		  for (x = TYPE_METHODS (type); x; x = DECL_CHAIN (x))
+		    if (DECL_PURE_VIRTUAL_P (x))
+		      {
+			abstract = true;
+			break;
+		      }
+		  if (abstract)
+		    warning(OPT_Wdelete_non_virtual_dtor, "deleting object of"
+                            " abstract class type %qT which has non-virtual"
+                            " destructor will cause undefined behaviour", type);
+		  else
+		    warning(OPT_Wdelete_non_virtual_dtor, "deleting object of"
+                            " polymorphic class type %qT which has non-virtual"
+                            " destructor may cause undefined behaviour", type);
+		}
+	    }
 	}
       if (VOID_TYPE_P (type) || !complete_p || !MAYBE_CLASS_TYPE_P (type))
 	/* Call the builtin operator delete.  */
Index: doc/invoke.texi
===================================================================
--- doc/invoke.texi	(revision 174539)
+++ doc/invoke.texi	(working copy)
@@ -2331,6 +2331,15 @@  Warn when a class seems unusable because
 destructors in that class are private, and it has neither friends nor
 public static member functions.
 
+@item -Wdelete-non-virtual-dtor @r{(C++ and Objective-C++ only)}
+@opindex Wdelete-non-virtual-dtor
+@opindex Wno-delete-non-virtual-dtor
+Warn when @samp{delete} is used to destroy an instance of a class which
+has virtual functions and non-virtual destructor. It is unsafe to delete
+an instance of a derived class through a pointer to a base class if the
+base class does not have a virtual destructor.  This warning is enabled
+by @option{-Wall}.
+
 @item -Wnoexcept @r{(C++ and Objective-C++ only)}
 @opindex Wnoexcept
 @opindex Wno-noexcept
Index: testsuite/g++.dg/warn/delete-non-virtual-dtor.C
===================================================================
--- testsuite/g++.dg/warn/delete-non-virtual-dtor.C	(revision 0)
+++ testsuite/g++.dg/warn/delete-non-virtual-dtor.C	(revision 0)
@@ -0,0 +1,44 @@ 
+// { dg-options "-std=gnu++0x -Wdelete-non-virtual-dtor"
+// { dg-do compile }
+
+struct polyBase { virtual void f(); };
+
+void f(polyBase* p, polyBase* arr)
+{
+  delete p;      // { dg-warning "non-virtual destructor may" }
+  delete [] arr;
+}
+
+struct polyDerived : polyBase { };
+
+void f(polyDerived* p, polyDerived* arr)
+{
+  delete p;      // { dg-warning "non-virtual destructor may" }
+  delete [] arr;
+}
+
+struct absDerived : polyBase { virtual void g() = 0; };
+
+void f(absDerived* p, absDerived* arr)
+{
+  delete p;      // { dg-warning "non-virtual destructor will" }
+  delete [] arr;
+}
+
+struct finalDerived final : polyBase { };
+
+void f(finalDerived* p, finalDerived* arr)
+{
+  delete p;      // no error for final classes
+  delete [] arr;
+}
+
+struct safeBase { virtual ~safeBase(); };
+struct safeDerived : safeBase { virtual void f(); };
+
+void f(safeDerived* p, safeDerived* arr)
+{
+  delete p;      // no error because base has virtual dtor
+  delete [] arr;
+}
+