re PR c++/20746 ([4.0 only] Incorrect return value for covariant return function returning null ptr)

cp:
	PR c++/20746
	* method.c (use_thunk): Protect covariant pointer return
	adjustments from NULL pointers.
testsuite:
	PR c++/20746
	* g++.dg/abi/covariant5.C: New.

From-SVN: r97557

4 files changed, 81 insertions, 3 deletions

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index c50d7d2..f38b03d 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2005-04-04  Nathan Sidwell  <nathan@codesourcery.com>
+
+	PR c++/20746
+	* method.c (use_thunk): Protect covariant pointer return
+	adjustments from NULL pointers.
+
 2005-04-04  Jan Hubicka  <jh@suse.cz>
 
 	* decl2.c (finish_objects): Revert my previous patch.
diff --git a/gcc/cp/method.c b/gcc/cp/method.c
index 70d6642..9036f64 100644
--- a/gcc/cp/method.c
+++ b/gcc/cp/method.c
@@ -470,10 +470,27 @@ use_thunk (tree thunk_fndecl, bool emit_p)
 	finish_expr_stmt (t);
       else
 	{
-	  t = force_target_expr (TREE_TYPE (t), t);
 	  if (!this_adjusting)
-	    t = thunk_adjust (t, /*this_adjusting=*/0,
-			      fixed_offset, virtual_offset);
+	    {
+	      tree cond = NULL_TREE;
+
+	      if (TREE_CODE (TREE_TYPE (t)) == POINTER_TYPE)
+		{
+		  /* If the return type is a pointer, we need to
+		     protect against NULL.  We know there will be an
+		     adjustment, because that's why we're emitting a
+		     thunk.  */
+		  t = save_expr (t);
+		  cond = cp_convert (boolean_type_node, t);
+		}
+	      
+	      t = thunk_adjust (t, /*this_adjusting=*/0,
+				fixed_offset, virtual_offset);
+	      if (cond)
+		t = build3 (COND_EXPR, TREE_TYPE (t), cond, t,
+			    cp_convert (TREE_TYPE (t), integer_zero_node));
+	    }
+	  t = force_target_expr (TREE_TYPE (t), t);
 	  finish_return_stmt (t);
 	}
 
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 507f14a..ddb7ae2 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,8 @@
 2005-04-04  Nathan Sidwell  <nathan@codesourcery.com>
 
+	PR c++/20746
+	* g++.dg/abi/covariant5.C: New.
+
 	PR debug/20505
 	* g++.dg/debug/const2.C: New.
 
diff --git a/gcc/testsuite/g++.dg/abi/covariant5.C b/gcc/testsuite/g++.dg/abi/covariant5.C
new file mode 100644
index 0000000..03e55583
--- /dev/null
+++ b/gcc/testsuite/g++.dg/abi/covariant5.C
@@ -0,0 +1,52 @@
+// Copyright (C) 2005 Free Software Foundation, Inc.
+// Contributed by Nathan Sidwell 4 Apr 2005 <nathan@codesourcery.com>
+
+// { dg-do run }
+
+// PR 20746: Covariant return pointer could be null.
+
+// Origin: yanliu@ca.ibm.com
+//         nathan@codesourcery.com
+
+struct A {
+  virtual void One ();
+};
+struct B  { 
+  virtual B *Two ();
+  virtual B &Three ();
+};
+
+struct C : A, B
+{
+  virtual C *Two (); 
+  virtual C &Three (); 
+};
+void A::One () {}
+B *B::Two()    {return this;}
+B &B::Three()    {return *this;}
+C *C::Two ()   {return 0;}
+C &C::Three ()   {return *(C *)0;}
+
+B *Foo (B *b)
+{
+  return b->Two ();
+}
+
+B &Bar (B *b)
+{
+  return b->Three ();
+}
+
+int main ()
+{
+  C c;
+
+  /* We should not adjust a null pointer.  */
+  if (Foo (&c))
+    return 1;
+  /* But we should adjust a (bogus) null reference.  */
+  if (!&Bar (&c))
+    return 2;
+
+  return 0;
+}