c++: template-id dependence wrt local static arg [PR117792]

Here we end up ICEing at instantiation time for the call to
f<local_static> ultimately because we wrongly consider the call to be
non-dependent, and so we specialize f ahead of time and then get
confused when fully substituting this specialization.

The call is dependent due to [temp.dep.temp]/3 and we miss that because
function template-id arguments aren't coerced until overload resolution,
and so the local static template argument lacks an implicit cast to
reference type that value_dependent_expression_p looks for before
considering dependence of the address.  Other kinds of template-ids aren't
affected since they're coerced ahead of time.

So when considering dependence of a function template-id, we need to
conservatively consider dependence of the address of each argument (if
applicable).

	PR c++/117792

gcc/cp/ChangeLog:

	* pt.cc (type_dependent_expression_p): Consider the dependence
	of the address of each template argument of a function
	template-id.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1z/nontype7.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>
(cherry picked from commit 40f0f6ab75a391906bed40cbdc098b0df3a91af7)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index becc7305bfc646754f5cc600aec9fb5932970a0d..56f33a01ed6334a05ae9e045d123de40a55cdc46 100644 (file)
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -28137,9 +28137,15 @@ type_dependent_expression_p (tree expression)
 
       if (TREE_CODE (expression) == TEMPLATE_ID_EXPR)
        {
-         if (any_dependent_template_arguments_p
-             (TREE_OPERAND (expression, 1)))
+         tree args = TREE_OPERAND (expression, 1);
+         if (any_dependent_template_arguments_p (args))
            return true;
+         /* Arguments of a function template-id aren't necessarily coerced
+            yet so we must conservatively assume that the address (and not
+            just value) of the argument matters as per [temp.dep.temp]/3.  */
+         for (int i = 0; i < TREE_VEC_LENGTH (args); i++)
+           if (has_value_dependent_address (TREE_VEC_ELT (args, i)))
+             return true;
          expression = TREE_OPERAND (expression, 0);
          if (identifier_p (expression))
            return true;

diff --git a/gcc/testsuite/g++.dg/cpp1z/nontype7.C b/gcc/testsuite/g++.dg/cpp1z/nontype7.C
new file mode 100644 (file)
index 0000000..f103d5a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/nontype7.C
@@ -0,0 +1,22 @@
+// PR c++/117792
+// { dg-do compile { target c++17 } }
+
+template<const int& N, class T>
+void f(T) { }
+
+template<int N, class T>
+void f(...) = delete;
+
+template<const int& N> int v;
+
+template<const int& N> struct A { };
+
+template<class T>
+void g() {
+  static constexpr int local_static = 0;
+  auto x = v<local_static>; // OK
+  A<local_static> y; // OK
+  f<local_static>(0); // ICE
+}
+
+template void g<int>();