re PR c++/85032 (Wrong non-constant condition for static assertion)

	PR c++/85032
	* constexpr.c (potential_constant_expression_1): Consider conversions
	from classes to literal types potentially constant.

	* g++.dg/cpp0x/pr51225.C: Adjust error message.
	* g++.dg/cpp1z/constexpr-if21.C: New test.

From-SVN: r259318

gcc/cp/ChangeLog

+2018-04-11  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/85032
+	* constexpr.c (potential_constant_expression_1): Consider conversions
+	from classes to literal types potentially constant.
+
 2018-04-10  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/70808

gcc/cp/constexpr.c

@@ -5777,6 +5777,25 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
 		      TREE_TYPE (t));
 	  return false;
 	}
+      /* This might be a conversion from a class to a (potentially) literal
+	 type.  Let's consider it potentially constant since the conversion
+	 might be a constexpr user-defined conversion.  */
+      else if (cxx_dialect >= cxx11
+	       && (dependent_type_p (TREE_TYPE (t))
+		   || !COMPLETE_TYPE_P (TREE_TYPE (t))
+		   || literal_type_p (TREE_TYPE (t)))
+	       && TREE_OPERAND (t, 0))
+	{
+	  tree type = TREE_TYPE (TREE_OPERAND (t, 0));
+	  /* If this is a dependent type, it could end up being a class
+	     with conversions.  */
+	  if (type == NULL_TREE || WILDCARD_TYPE_P (type))
+	    return true;
+	  /* Or a non-dependent class which has conversions.  */
+	  else if (CLASS_TYPE_P (type)
+		   && (TYPE_HAS_CONVERSION (type) || dependent_scope_p (type)))
+	    return true;
+	}
 
       return (RECUR (TREE_OPERAND (t, 0),
 		     TREE_CODE (TREE_TYPE (t)) != REFERENCE_TYPE));

gcc/testsuite/ChangeLog

+2018-04-11  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/85032
+	* g++.dg/cpp0x/pr51225.C: Adjust error message.
+	* g++.dg/cpp1z/constexpr-if21.C: New test.
+
 2018-04-11  Jakub Jelinek  <jakub@redhat.com>
 
 	PR target/85281

gcc/testsuite/g++.dg/cpp0x/pr51225.C

@@ -5,7 +5,7 @@ template<int> struct A {};
 
 template<typename> void foo()
 {
-  A<int(x)> a; // { dg-error "not declared|invalid type" }
+  A<int(x)> a; // { dg-error "not declared|could not convert" }
 }
 
 template<typename> struct bar

gcc/testsuite/g++.dg/cpp1z/constexpr-if21.C

+// PR c++/85032
+// { dg-options -std=c++17 }
+
+struct A
+{
+  constexpr operator bool () { return true; }
+  int i;
+};
+
+A a;
+
+template <class T>
+void f()
+{
+  constexpr bool b = a;
+  static_assert (a);
+}
+
+int main()
+{
+  f<int>();
+}