re PR c++/39415 (static_cast used as downcast can silently lose const)

	PR c++/39415
	* typeck.c (build_static_cast_1): Convert to the target type
	when doing static_cast<cv Derived*>(Base*).

From-SVN: r166667

gcc/cp/ChangeLog

+2010-11-12  James Dennett <jdennett@google.com>
+
+	PR/39415
+	* typeck.c (build_static_cast_1): Convert to the target type
+	when doing static_cast<cv Derived*>(Base*).
+
 2010-11-10  Jason Merrill  <jason@redhat.com>
 
 	PR c++/46420

gcc/cp/typeck.c

@@ -5884,7 +5884,8 @@ build_static_cast_1 (tree type, tree expr, bool c_cast_p,
       base = lookup_base (TREE_TYPE (type), TREE_TYPE (intype),
 			  c_cast_p ? ba_unique : ba_check,
 			  NULL);
-      return build_base_path (MINUS_EXPR, expr, base, /*nonnull=*/false);
+      expr = build_base_path (MINUS_EXPR, expr, base, /*nonnull=*/false);
+      return cp_fold_convert(type, expr);
     }
 
   if ((TYPE_PTRMEM_P (type) && TYPE_PTRMEM_P (intype))

gcc/testsuite/ChangeLog

+2010-11-12  James Dennett <jdennett@google.com>
+
+	PR c++/39415
+	* g++.dg/expr/static_cast7.C: New.
+
 2010-11-12  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
 
 	* lib/prune.exp (prune_gcc_output): Ignore IRIX 6 linker multiline

gcc/testsuite/g++.dg/expr/static_cast7.C

+// Regression test for bug 39415 (and its duplicate 44916).
+struct S {};
+struct T : S {};
+int f(const T*) {}
+void f(T*);
+int main() {
+  S* s(0);
+  int a = f(static_cast<const T*>(s));
+  int b = f(static_cast<const T*>(0));
+}