C++ PATCH for c++/86099, ICE with NSDMI

[Jason Merrill]

In this testcase, the compiler is trying to evaluate a
constant-expression which involves a trivial defaulted copy
constructor.  My patch for CWG 1581 had us instantiate any function
that appears in a potential constant expression, but that's not what
we want for a trivial constructor like this.

Tested x86_64-pc-linux-gnu, applying to trunk.

commit b71b855538a05716e704d02f636b8820faec3e62
Author: Jason Merrill <ja...@redhat.com>
Date:   Wed Jun 13 17:51:44 2018 -0400

            PR c++/86099 - ICE with trivial copy and non-trivial default ctor.
    
            * constexpr.c (instantiate_cx_fn_r): Don't synthesize trivial
            constructors.

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 97a338535db..93de6162c04 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -4841,6 +4841,7 @@ instantiate_cx_fn_r (tree *tp, int *walk_subtrees, void */*data*/)
   if (TREE_CODE (*tp) == FUNCTION_DECL
       && DECL_DECLARED_CONSTEXPR_P (*tp)
       && !DECL_INITIAL (*tp)
+      && !trivial_fn_p (*tp)
       && DECL_TEMPLOID_INSTANTIATION (*tp))
     {
       ++function_depth;
diff --git a/gcc/testsuite/g++.dg/cpp0x/nsdmi-template18.C b/gcc/testsuite/g++.dg/cpp0x/nsdmi-template18.C
new file mode 100644
index 00000000000..e3520bc6b44
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/nsdmi-template18.C
@@ -0,0 +1,43 @@
+// PR c++/86099
+// { dg-do compile { target c++11 } }
+
+template <int a> struct e { static constexpr int c = a; };
+template <bool a> using d = e<a>;
+template <bool, typename> struct aa;
+template <typename...> struct j;
+template <typename f, typename g> struct j<f, g> : aa<f::c, g>::h {};
+template <typename i> struct n : d<i::c> {};
+template <typename k, typename l = k> l m(int);
+template <typename k> auto ab() -> decltype(m<k>(0));
+template <typename...> struct p;
+template <typename k, typename o> struct p<k, o> : e<noexcept(k(ab<o>()))> {};
+template <typename> struct r;
+class s;
+template <typename, typename... q>
+struct ac : j<d<true>, p<r<s>, q...>> {};
+template <typename k> struct ae : ac<k, k> {};
+template <bool, typename ad> struct aa { typedef ad h; };
+template <typename k> struct w : j<n<ae<k>>, d<true>> {};
+template <typename t> struct r {
+  t f;
+  int af;
+  r(r &&) = default;
+};
+template <typename k, typename = typename aa<w<k>::c, k>::h> void v(k *);
+template <typename ag, typename ah, typename ai> ah aj(ag x, ah, ai) { v(x); return 0; }
+template <typename> struct y { typedef int ak; };
+template <typename, typename = int> class z {
+public:
+  template <typename...> void al();
+};
+template <typename k, typename am> template <typename...> void z<k, am>::al() {
+  r<s> *u;
+  typename y<am>::ak a = aj(u, a, int());
+}
+class s {
+  char *an = nullptr;
+};
+void ao() {
+  z<int> b;
+  b.al();
+}