re PR c++/87582 (Returning a reference to a data member via structured bindings dangles)

	PR c++/87582
	* typeck.c (maybe_warn_about_returning_address_of_local): If
	whats_returned is a structured binding identifier and the structured
	binding is a reference, recurse on its initializer.

	* g++.dg/cpp1z/decomp48.C: New test.

From-SVN: r265041

gcc/cp/ChangeLog

 2018-10-11  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/87582
+	* typeck.c (maybe_warn_about_returning_address_of_local): If
+	whats_returned is a structured binding identifier and the structured
+	binding is a reference, recurse on its initializer.
+
 	PR c++/87547
 	* rtti.c (get_tinfo_decl_dynamic): Use unlowered_expr_type instead
 	of TREE_TYPE.

gcc/cp/typeck.c

@@ -9096,6 +9096,22 @@ maybe_warn_about_returning_address_of_local (tree retval)
       && !(TREE_STATIC (whats_returned)
 	   || TREE_PUBLIC (whats_returned)))
     {
+      if (VAR_P (whats_returned)
+	  && DECL_DECOMPOSITION_P (whats_returned)
+	  && DECL_DECOMP_BASE (whats_returned)
+	  && DECL_HAS_VALUE_EXPR_P (whats_returned))
+	{
+	  /* When returning address of a structured binding, if the structured
+	     binding is not a reference, continue normally, if it is a
+	     reference, recurse on the initializer of the structured
+	     binding.  */
+	  tree base = DECL_DECOMP_BASE (whats_returned);
+	  if (TYPE_REF_P (TREE_TYPE (base)))
+	    {
+	      tree init = DECL_INITIAL (base);
+	      return maybe_warn_about_returning_address_of_local (init);
+	    }
+	}
       bool w = false;
       auto_diagnostic_group d;
       if (TYPE_REF_P (valtype))

gcc/testsuite/ChangeLog

+2018-10-11  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/87582
+	* g++.dg/cpp1z/decomp48.C: New test.
+
 2018-10-11  David Malcolm  <dmalcolm@redhat.com>
 
 	* g++.dg/diagnostic/macro-arg-count.C: Move to...

gcc/testsuite/g++.dg/cpp1z/decomp48.C

+// PR c++/87582
+// { dg-do run { target c++11 } }
+// { dg-options "-Wreturn-local-addr" }
+
+struct S { int s, t; };
+S v {1, 2};
+int a[3] = {1, 2, 3};
+
+int &
+f1 ()
+{
+  auto& [s, t] = v;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return s;		// { dg-bogus "reference to local variable '.' returned" }
+}
+
+int &
+f2 ()
+{
+  S v {1, 2};
+  auto& [s, t] = v;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return s;		// { dg-warning "reference to local variable 'v' returned" }
+}
+
+int &
+f3 ()
+{
+  auto& [s, t, u] = a;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return s;		// { dg-bogus "reference to local variable '.' returned" }
+}
+
+int &
+f4 ()
+{
+  int a[3] = {1, 2, 3};
+  auto& [s, t, u] = a;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return s;		// { dg-warning "reference to local variable 'a' returned" }
+}
+
+int &
+f5 ()
+{
+  auto [s, t] = v;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return s;		// { dg-warning "reference to local variable 's' returned" }
+}
+
+int &
+f6 ()
+{
+  S v {1, 2};
+  auto [s, t] = v;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return s;		// { dg-warning "reference to local variable 's' returned" }
+}
+
+int &
+f7 ()
+{
+  auto [s, t, u] = a;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return s;		// { dg-warning "reference to local variable 's' returned" }
+}
+
+int &
+f8 ()
+{
+  int a[3] = {1, 2, 3};
+  auto [s, t, u] = a;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return s;		// { dg-warning "reference to local variable 's' returned" }
+}
+
+int *
+f9 ()
+{
+  auto& [s, t] = v;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return &s;		// { dg-bogus "address of local variable '.' returned" }
+}
+
+int *
+f10 ()
+{
+  S v {1, 2};
+  auto& [s, t] = v;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return &s;		// { dg-warning "address of local variable 'v' returned" }
+}
+
+int *
+f11 ()
+{
+  auto& [s, t, u] = a;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return &s;		// { dg-bogus "address of local variable '.' returned" }
+}
+
+int *
+f12 ()
+{
+  int a[3] = {1, 2, 3};
+  auto& [s, t, u] = a;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return &s;		// { dg-warning "address of local variable 'a' returned" }
+}
+
+int *
+f13 ()
+{
+  auto [s, t] = v;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return &s;		// { dg-warning "address of local variable 's' returned" }
+}
+
+int *
+f14 ()
+{
+  S v {1, 2};
+  auto [s, t] = v;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return &s;		// { dg-warning "address of local variable 's' returned" }
+}
+
+int *
+f15 ()
+{
+  auto [s, t, u] = a;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return &s;		// { dg-warning "address of local variable 's' returned" }
+}
+
+int *
+f16 ()
+{
+  int a[3] = {1, 2, 3};
+  auto [s, t, u] = a;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return &s;		// { dg-warning "address of local variable 's' returned" }
+}
+
+int
+main ()
+{
+  if (&f1 () != &v.s || &f3 () != &a[0] || f9 () != &v.s || f11 () != &a[0])
+    __builtin_abort ();
+}