In the testcase ref11.C below, during deduction for the call f(a),
uses_deducible_template_parms returns false for the dependent
specialization A<V> because the generic template argument V here is
wrapped in an implicit INDIRECT_REF (formed from template_parm_to_arg).
Since uses_deducible_template_parms returns false, unify_one_argument
exits early without ever attempting to deduce 'n' for 'V'. This patch
fixes this by making deducible_expression look through such implicit
INDIRECT_REFs.
gcc/cp/ChangeLog:
PR c++/83476
PR c++/99885
* pt.c (deducible_expression): Look through implicit
INDIRECT_REFs as well.
gcc/testsuite/ChangeLog:
PR c++/83476
PR c++/99885
* g++.dg/cpp1z/class-deduction85.C: New test.
* g++.dg/template/ref11.C: New test.
static bool
deducible_expression (tree expr)
{
- /* Strip implicit conversions. */
- while (CONVERT_EXPR_P (expr) || TREE_CODE (expr) == VIEW_CONVERT_EXPR)
+ /* Strip implicit conversions and implicit INDIRECT_REFs. */
+ while (CONVERT_EXPR_P (expr)
+ || TREE_CODE (expr) == VIEW_CONVERT_EXPR
+ || REFERENCE_REF_P (expr))
expr = TREE_OPERAND (expr, 0);
return (TREE_CODE (expr) == TEMPLATE_PARM_INDEX);
}
--- /dev/null
+// PR c++/99885
+// { dg-do compile { target c++17 } }
+
+template <auto const& A>
+struct Foo {};
+
+template <auto const& A>
+struct Bar {
+ constexpr auto foo() const -> Foo<A> {
+ return {};
+ }
+};
+
+constexpr int a = 1;
+constexpr Bar<a> bar;
+Foo foo = bar.foo(); // <-- CTAD failure
--- /dev/null
+// PR c++/83476
+
+int n;
+template <int& V> struct A {};
+template <int& V> void f(A<V>);
+int main() {
+ A<n> a;
+ f(a);
+}