PR c++/80084 - wrong C++17 decomposition by reference of parameter.

	* decl.c (cp_finish_decomp): Don't pull out the DECL_INITIAL of a
	reference decomposition.

From-SVN: r246273

gcc/cp/ChangeLog

 2017-03-19  Jason Merrill  <jason@redhat.com>
 
+	PR c++/80084 - wrong C++17 decomposition by reference of parameter.
+	* decl.c (cp_finish_decomp): Don't pull out the DECL_INITIAL of a
+	reference decomposition.
+
 	PR c++/80077 - error with constexpr and -fno-elide-constructors.
 	* constexpr.c (cxx_eval_call_expression): Set ctx->call while
 	expanding trivial constructor.

gcc/cp/decl.c

@@ -7439,9 +7439,6 @@ cp_finish_decomp (tree decl, tree first, unsigned int count)
 
   if (TREE_CODE (type) == REFERENCE_TYPE)
     {
-      /* If e is a constant reference, use the referent directly.  */
-      if (DECL_INITIAL (decl))
-	dexp = DECL_INITIAL (decl);
       dexp = convert_from_reference (dexp);
       type = TREE_TYPE (type);
     }

gcc/testsuite/g++.dg/cpp1z/decomp27.C

+// PR c++/80084
+// { dg-options -std=c++1z }
+// { dg-do run }
+
+struct A
+{
+  A() { }
+  A(const A&) { }
+};
+
+struct B
+{
+  A a;
+};
+
+void f(B b)
+{
+  auto& [a] = b;
+  if (&a != &b.a)
+    __builtin_abort();
+}
+
+int main()
+{
+  f(B());
+}