From 4d5038dd20f2f57b520035242dbb0fcad598c4c6 Mon Sep 17 00:00:00 2001
From: jason <jason@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Thu, 24 May 2018 20:03:18 +0000
Subject: [PATCH] 	PR c++/85842 - -Wreturn-type, constexpr if and generic
 lambda.

	* pt.c (tsubst_lambda_expr): Copy current_function_returns_* to
	generic lambda.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@260685 138bc75d-0d04-0410-961f-82ee72b054a4
---
 gcc/cp/ChangeLog                            |  6 ++++++
 gcc/cp/pt.c                                 | 11 +++++++++++
 gcc/testsuite/g++.dg/cpp1z/constexpr-if23.C | 13 +++++++++++++
 3 files changed, 30 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-if23.C

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index fdf73d182eb..371c8b76fef 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2018-05-24  Jason Merrill  <jason@redhat.com>
+
+	PR c++/85842 - -Wreturn-type, constexpr if and generic lambda.
+	* pt.c (tsubst_lambda_expr): Copy current_function_returns_* to
+	generic lambda.
+
 2018-05-24  Ville Voutilainen  <ville.voutilainen@gmail.com>
 
 	Pedwarn on a non-standard position of a C++ attribute.
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index cfce9a9db62..d0fc9ee51a5 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -17636,6 +17636,17 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 
       register_parameter_specializations (oldfn, fn);
 
+      if (oldtmpl)
+	{
+	  /* We might not partially instantiate some parts of the function, so
+	     copy these flags from the original template.  */
+	  language_function *ol = DECL_STRUCT_FUNCTION (oldfn)->language;
+	  current_function_returns_value = ol->returns_value;
+	  current_function_returns_null = ol->returns_null;
+	  current_function_returns_abnormally = ol->returns_abnormally;
+	  current_function_infinite_loop = ol->infinite_loop;
+	}
+
       tsubst_expr (DECL_SAVED_TREE (oldfn), args, complain, r,
 		   /*constexpr*/false);
 
diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-if23.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-if23.C
new file mode 100644
index 00000000000..8e31db3e863
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-if23.C
@@ -0,0 +1,13 @@
+// PR c++/85842
+// { dg-additional-options -std=c++17 }
+
+template<class T>
+auto f = [](auto&& arg) -> T* {
+    if constexpr (sizeof(arg) == 1) {
+        return nullptr;
+    } else {
+        return static_cast<T*>(&arg);
+    }
+};
+
+auto p = f<int>(0);
-- 
2.11.4.GIT