PR c++/87145 - bogus error converting class type in template arg list.

	* pt.c (convert_nontype_argument): Don't call
	build_converted_constant_expr if it could involve calling a conversion
	function with a instantiation-dependent constructor as its argument.

	* g++.dg/cpp0x/constexpr-conv3.C: New test.
	* g++.dg/cpp0x/constexpr-conv4.C: New test.

From-SVN: r270178

gcc/cp/ChangeLog

+2019-04-05  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/87145 - bogus error converting class type in template arg list.
+	* pt.c (convert_nontype_argument): Don't call
+	build_converted_constant_expr if it could involve calling a conversion
+	function with a instantiation-dependent constructor as its argument.
+
 2019-04-05  Martin Sebor  <msebor@redhat.com>
 
 	PR bootstrap/89980

gcc/cp/pt.c

@@ -6837,6 +6837,19 @@ convert_nontype_argument (tree type, tree expr, tsubst_flags_t complain)
       else if (INTEGRAL_OR_ENUMERATION_TYPE_P (type)
 	       || cxx_dialect >= cxx17)
 	{
+	  /* Calling build_converted_constant_expr might create a call to
+	     a conversion function with a value-dependent argument, which
+	     could invoke taking the address of a temporary representing
+	     the result of the conversion.  */
+	  if (COMPOUND_LITERAL_P (expr)
+	      && CONSTRUCTOR_IS_DEPENDENT (expr)
+	      && MAYBE_CLASS_TYPE_P (expr_type)
+	      && TYPE_HAS_CONVERSION (expr_type))
+	    {
+	      expr = build1 (IMPLICIT_CONV_EXPR, type, expr);
+	      IMPLICIT_CONV_EXPR_NONTYPE_ARG (expr) = true;
+	      return expr;
+	    }
 	  /* C++17: A template-argument for a non-type template-parameter shall
 	     be a converted constant expression (8.20) of the type of the
 	     template-parameter.  */

gcc/testsuite/ChangeLog

+2019-04-05  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/87145 - bogus error converting class type in template arg list.
+	* g++.dg/cpp0x/constexpr-conv3.C: New test.
+	* g++.dg/cpp0x/constexpr-conv4.C: New test.
+
 2019-04-05  Martin Sebor  <msebor@redhat.com>
 
 	PR bootstrap/89980

gcc/testsuite/g++.dg/cpp0x/constexpr-conv3.C

+// PR c++/87145
+// { dg-do compile { target c++11 } }
+
+template<typename T, T t> struct integral_constant {
+  static constexpr T value = t;
+};
+
+enum class Enum : unsigned {};
+
+struct Pod {
+  unsigned val;
+
+  constexpr operator Enum() const {
+    return static_cast<Enum>(val);
+  }
+};
+
+template<unsigned N>
+constexpr void foo() {
+  using Foo = integral_constant<Enum, Pod{N}>;
+}
+
+int main() {
+  foo<2>();
+}

gcc/testsuite/g++.dg/cpp0x/constexpr-conv4.C

+// PR c++/87145
+// { dg-do compile { target c++11 } }
+
+struct S {
+  int val;
+
+  constexpr operator int() const {
+    return static_cast<int>(val);
+  }
+};
+
+template<int N>
+struct F { };
+
+template<unsigned N>
+constexpr void foo() {
+  F<int{N}> f;
+  F<S{N}> f2;
+}
+
+int
+main()
+{
+  foo<2>();
+}