From fe0604d349c4d9eb18b17dd018383d591eed67c7 Mon Sep 17 00:00:00 2001
From: Marek Polacek <polacek@redhat.com>
Date: Wed, 11 Apr 2018 13:10:16 +0000
Subject: [PATCH] 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                            |  6 ++++++
 gcc/cp/constexpr.c                          | 19 ++++++++++++++++++
 gcc/testsuite/ChangeLog                     |  6 ++++++
 gcc/testsuite/g++.dg/cpp0x/pr51225.C        |  2 +-
 gcc/testsuite/g++.dg/cpp1z/constexpr-if21.C | 22 +++++++++++++++++++++
 5 files changed, 54 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-if21.C

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 78e7ed77b45..e9a32b0d204 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+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
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 3cc196b4d17..75f56df4465 100644
--- a/gcc/cp/constexpr.c
+++ b/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));
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 8deaeb95974..186986aafe4 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+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
diff --git a/gcc/testsuite/g++.dg/cpp0x/pr51225.C b/gcc/testsuite/g++.dg/cpp0x/pr51225.C
index f80bd0e778e..5b4e432f7ed 100644
--- a/gcc/testsuite/g++.dg/cpp0x/pr51225.C
+++ b/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
diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-if21.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-if21.C
new file mode 100644
index 00000000000..56e108be4ad
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-if21.C
@@ -0,0 +1,22 @@
+// 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>();
+}
-- 
2.30.2