RFA PATCH to get_narrower for c++/48106 (ICE with scoped enum)

[Jason Merrill <jason@redhat.com>]

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C++0x scoped enums don't implicitly convert to an integral type, so we 
need to be careful about throwing away explicit conversions.  In this 
case, the static_cast<int>(e) creates a NOP_EXPR which get_narrower 
throws away, but 'e' itself is not a valid argument for &, so we need to 
replace the NOP_EXPR with a different one.

Tested x86_64-pc-linux-gnu.  OK for trunk?

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commit 8f9cf5d22de2418bdb2ab9cb79ae878f809299ec
Author: Jason Merrill <jason@redhat.com>
Date:   Sun May 22 15:21:19 2011 -0400

    	PR c++/48106
    	* tree.c (get_narrower): Handle scoped enum.

diff --git a/gcc/testsuite/g++.dg/cpp0x/enum14.C b/gcc/testsuite/g++.dg/cpp0x/enum14.C
new file mode 100644
index 0000000..709b201
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/enum14.C
@@ -0,0 +1,12 @@
+// PR c++/48106
+// { dg-options -std=c++0x }
+
+enum class E : char
+{
+  e
+};
+
+bool operator&(E e, char m)
+{
+  return static_cast<int>(e) & m;
+}
diff --git a/gcc/tree.c b/gcc/tree.c
index 3357d84..99402e8 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -8117,6 +8117,17 @@ get_narrower (tree op, int *unsignedp_ptr)
 	  win = fold_convert (type, op);
 	}
     }
+  else if (TREE_CODE (TREE_TYPE (op)) == ENUMERAL_TYPE
+	   && ENUM_IS_SCOPED (TREE_TYPE (op)))
+    {
+      /* C++0x scoped enumerations don't implicitly convert to integral
+	 type, so if we stripped an explicit conversion to a larger type we
+	 need to replace it.  */
+      tree type = (lang_hooks.types.type_for_size
+		   (TYPE_PRECISION (TREE_TYPE (op)),
+		    TYPE_UNSIGNED (TREE_TYPE (op))));
+      win = fold_convert (type, op);
+    }
 
   *unsignedp_ptr = uns;
   return win;