c++: ICE with MODIFY_EXPR in constexpr [PR118169]

Here, cxx_eval_outermost_expression gets a sequence of initialization
statements:

  D.2912.t = TARGET_EXPR <...>;
  TARGET_EXPR <D.2922, 1>;
  D.2922 = 0;

the last of which wasn't converted to void and so we, since r15-6369,
do not take the "if (VOID_TYPE_P (type))" path, and try to set
D.2912 to false.

The last statement comes from build_disable_temp_cleanup.
convert_to_void is typically called from finish_expr_stmt, but we are
adding the cleanup statement via add_stmt which doesn't convert to void.
So I think we can use finish_expr_stmt instead.

	PR c++/118169

gcc/cp/ChangeLog:

	* typeck2.cc (split_nonconstant_init): Call finish_expr_stmt instead
	of add_stmt.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1y/constexpr-prvalue2.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>

2 files changed, 14 insertions, 1 deletions

diff --git a/gcc/cp/typeck2.cc b/gcc/cp/typeck2.cc
index 381f198..5dae7fc 100644
--- a/gcc/cp/typeck2.cc
+++ b/gcc/cp/typeck2.cc
@@ -757,7 +757,7 @@ split_nonconstant_init (tree dest, tree init)
 	init = NULL_TREE;
 
       for (tree f : flags)
-	add_stmt (build_disable_temp_cleanup (f));
+	finish_expr_stmt (build_disable_temp_cleanup (f));
       release_tree_vector (flags);
 
       code = pop_stmt_list (code);
diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-prvalue2.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-prvalue2.C
new file mode 100644
index 0000000..7076c65
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-prvalue2.C
@@ -0,0 +1,13 @@
+// PR c++/118169
+// { dg-do compile { target c++14 } }
+// { dg-options "-O" }
+
+struct A { constexpr A (int *x) : s(x) {} ~A (); int *s; };
+struct B { A t; int u = 0; };
+void foo (B &&);
+
+void
+bar (int &x)
+{
+  foo ({ &x });
+}