[PATCH] Fix PR c++/70332 (ICE due to aggregate initialization of NSDMI)

[Patrick Palka <patrick@parcs.ath.cx>]

With c++14 an NSDMI no longer makes a class type non-aggregate so it's
possible to perform aggregate initialization on a class that has an
NSDMI, but tsubst_copy() currently ICEs on a use of 'this' in such
a situation.

This patch makes tsubst_copy() handle a use of 'this' in an NSDMI as
part of an aggregate initialization.  In that case current_class_ref
will be a PLACEHOLDER_EXPR (as set by get_nsdmi()) and this
PLACEHOLDER_EXPR will later get resolved to the true object by
replace_placeholders().

Does this patch look OK to commit after testing?

gcc/cp/ChangeLog:

	PR c++/70332
	* pt.c (tsubst_copy) [PARM_DECL]: Handle the use of 'this' in an
	NSDMI that's part of an aggregrate initialization.

gcc/testsuite/ChangeLog:

	PR c++/70332
	* g++.dg/cpp1y/nsdmi-aggr5.C: New test.
---
 gcc/cp/pt.c                              | 20 ++++++++++++++++----
 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr5.C | 24 ++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr5.C

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index ebfc45b..49ef9d3 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -13878,10 +13878,22 @@ tsubst_copy (tree t, tree args, tsubst_flags_t complain, tree in_decl)
       if (r == NULL_TREE)
 	{
 	  /* We get here for a use of 'this' in an NSDMI.  */
-	  if (DECL_NAME (t) == this_identifier
-	      && current_function_decl
-	      && DECL_CONSTRUCTOR_P (current_function_decl))
-	    return current_class_ptr;
+	  if (DECL_NAME (t) == this_identifier)
+	    {
+	      /* We're processing an NSDMI as part of a constructor call.  */
+	      if (current_function_decl
+		  && DECL_CONSTRUCTOR_P (current_function_decl))
+		return current_class_ptr;
+
+	      /* Or as part of an aggregate initialization.  */
+	      if (cp_unevaluated_operand == 0
+		  && current_class_ref
+		  && TREE_CODE (current_class_ref) == PLACEHOLDER_EXPR)
+		{
+		  gcc_assert (cxx_dialect >= cxx14);
+		  return current_class_ptr;
+		}
+	    }
 
 	  /* This can happen for a parameter name used later in a function
 	     declaration (such as in a late-specified return type).  Just
diff --git a/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr5.C b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr5.C
new file mode 100644
index 0000000..fe377c3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr5.C
@@ -0,0 +1,24 @@
+// PR c++/70332
+// { dg-do run { target c++14 } }
+
+template <class T>
+struct C
+{
+ T m;
+ T *n = &m;
+};
+
+C<int> c { };
+
+int
+main ()
+{
+  *c.n = 5;
+  if (c.m != 5)
+    __builtin_abort ();
+
+  C<int> d { 10 };
+  *d.n = *d.n + 1;
+  if (d.m != 11)
+    __builtin_abort ();
+}
-- 
2.8.0.rc3.27.gade0865