re PR c++/51587 (ICE with struct vs. enum clash)

	PR c++/51587
	* decl.c (start_enum): Avoid using ENUM_UNDERLYING_TYPE on a
	non-enum.

From-SVN: r182441

gcc/cp/ChangeLog

+2011-12-17  Jason Merrill  <jason@redhat.com>
+
+	PR c++/51587
+	* decl.c (start_enum): Avoid using ENUM_UNDERLYING_TYPE on a
+	non-enum.
+
 2011-12-16  Jason Merrill  <jason@redhat.com>
 
 	PR c++/51416

gcc/cp/decl.c

@@ -12069,6 +12069,7 @@ start_enum (tree name, tree enumtype, tree underlying_type,
       /* Do not push the decl more than once, unless we need to
 	 compare underlying types at instantiation time */
       if (!enumtype
+	  || TREE_CODE (enumtype) != ENUMERAL_TYPE
 	  || (underlying_type
 	      && dependent_type_p (underlying_type))
 	  || (ENUM_UNDERLYING_TYPE (enumtype)

gcc/testsuite/ChangeLog

+2011-12-17  Jason Merrill  <jason@redhat.com>
+
+	PR c++/51587
+	* g++.dg/parse/enum6.C: New.
+
 2011-12-17  Tom de Vries  <tom@codesourcery.com>
 
 	PR tree-optimization/51491

gcc/testsuite/g++.dg/parse/enum6.C

+// PR c++/51587
+
+namespace N
+{
+  struct X;			// { dg-message "previous declaration" }
+}
+
+enum N::X {};			// { dg-error "conflicting declaration" }