PR c++/78373 - ICE with TREE_CONSTANT reference

	* decl.c (cp_finish_decl): Don't set TREE_CONSTANT on a reference.
	* typeck2.c (store_init_value): Likewise.

From-SVN: r242523

gcc/cp/ChangeLog

 2016-11-16  Jason Merrill  <jason@redhat.com>
 
+	PR c++/78373
+	* decl.c (cp_finish_decl): Don't set TREE_CONSTANT on a reference.
+	* typeck2.c (store_init_value): Likewise.
+
 	* decl.c (store_decomp_type, lookup_decomp_type): New.
 	(cp_finish_decomp): Call store_decomp_type.
 	* semantics.c (finish_decltype_type): Call lookup_decomp_type.

gcc/cp/decl.c

@@ -6839,7 +6839,9 @@ cp_finish_decl (tree decl, tree init, bool init_const_expr_p,
 	  /* Set these flags now for templates.  We'll update the flags in
 	     store_init_value for instantiations.  */
 	  DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (decl) = 1;
-	  if (decl_maybe_constant_var_p (decl))
+	  if (decl_maybe_constant_var_p (decl)
+	      /* FIXME setting TREE_CONSTANT on refs breaks the back end.  */
+	      && TREE_CODE (type) != REFERENCE_TYPE)
 	    TREE_CONSTANT (decl) = 1;
 	}
     }

gcc/cp/typeck2.c

@@ -824,7 +824,9 @@ store_init_value (tree decl, tree init, vec<tree, va_gc>** cleanups, int flags)
       const_init = (reduced_constant_expression_p (value)
 		    || error_operand_p (value));
       DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (decl) = const_init;
-      TREE_CONSTANT (decl) = const_init && decl_maybe_constant_var_p (decl);
+      /* FIXME setting TREE_CONSTANT on refs breaks the back end.  */
+      if (TREE_CODE (type) != REFERENCE_TYPE)
+	TREE_CONSTANT (decl) = const_init && decl_maybe_constant_var_p (decl);
     }
   value = cp_fully_fold (value);
 

gcc/testsuite/g++.dg/opt/pr78373.C

+// PR c++/78373
+// { dg-do compile { target c++11 } }
+
+struct A {
+  static A singleton;
+};
+struct B {
+  void m_fn2();
+  virtual int m_fn1();
+};
+struct D : B {
+  static int m_fn3(int, int, int, A) {
+    D &self = singleton;
+    self.m_fn2();
+  }
+  static D singleton;
+};
+template <typename, typename> struct C { bool m_fn4() const; };
+template <typename Base, typename Traits> bool C<Base, Traits>::m_fn4() const {
+  Traits::m_fn3(0, 0, 0, Base::singleton);
+}
+template struct C<A, D>;