From 9dc20710e8380bdaf03551b45a2234c6d18c6519 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Fri, 16 Feb 2018 11:44:17 -0500
Subject: [PATCH] PR c++/84421 - type-dependent if constexpr

	* semantics.c (finish_if_stmt_cond): Check
	type_dependent_expression_p.

From-SVN: r257744
---
 gcc/cp/ChangeLog                            |  5 +++++
 gcc/cp/semantics.c                          |  1 +
 gcc/testsuite/g++.dg/cpp1z/constexpr-if14.C | 14 ++++++++++++++
 3 files changed, 20 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-if14.C

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index ee08e689b4e..17af63328ed 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,8 @@
+2018-02-16  Jason Merrill  <jason@redhat.com>
+
+	PR c++/84421 - type-dependent if constexpr
+	* semantics.c (finish_if_stmt_cond): Check type_dependent_expression_p.
+
 2018-02-16  Nathan Sidwell  <nathan@acm.org>
 
 	Deprecate -ffriend-injection.
diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index f0cee68e46f..35569d0cb0d 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -731,6 +731,7 @@ finish_if_stmt_cond (tree cond, tree if_stmt)
 {
   cond = maybe_convert_cond (cond);
   if (IF_STMT_CONSTEXPR_P (if_stmt)
+      && !type_dependent_expression_p (cond)
       && require_constant_expression (cond)
       && !value_dependent_expression_p (cond))
     {
diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-if14.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-if14.C
new file mode 100644
index 00000000000..f6cc39a0c2f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-if14.C
@@ -0,0 +1,14 @@
+// PR c++/84421
+// { dg-options -std=c++17 }
+
+struct A{
+  constexpr operator bool() const { return true; }
+};
+
+int main(){
+  auto f = [](auto v){
+    if constexpr(v){}
+  };
+  A a;
+  f(a);
+}
-- 
2.30.2