From: Matthias Maier <tamiko@43-1.org>
Date: Sat, 12 Aug 2017 16:37:41 +0000 (-0500)
Subject: CMake: In case of C++14 support, check whether std::max/min support constexpr
X-Git-Tag: v9.0.0-rc1~1289^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F4787%2Fhead;p=dealii.git

CMake: In case of C++14 support, check whether std::max/min support constexpr
---

diff --git a/cmake/checks/check_01_cxx_features.cmake b/cmake/checks/check_01_cxx_features.cmake
index d1dc5b7914..877438eaf4 100644
--- a/cmake/checks/check_01_cxx_features.cmake
+++ b/cmake/checks/check_01_cxx_features.cmake
@@ -49,6 +49,7 @@ IF(DEFINED DEAL_II_WITH_CXX14 AND NOT DEAL_II_WITH_CXX14)
   SET(DEAL_II_WITH_CXX17 OFF CACHE STRING "" FORCE)
 ENDIF()
 
+#
 # Check the user supplied DEAL_II_CXX_VERSION_FLAG
 #
 
@@ -183,6 +184,22 @@ IF(NOT DEFINED DEAL_II_WITH_CXX14 OR DEAL_II_WITH_CXX14)
       "
       DEAL_II_HAVE_CXX14_MAKE_UNIQUE)
 
+    #
+    # This test checks constexpr std::max/min support. Unfortunately,
+    # gcc-4.9 does claim to support C++14 but fails to provide a constexpr
+    # compatible std::max/min. Disable C++14 support in this case.
+    #
+    CHECK_CXX_SOURCE_COMPILES(
+      "
+      #include <algorithm>
+      int main()
+      {
+          constexpr int max = std::max(0,1);
+      }
+      "
+      DEAL_II_HAVE_CXX14_CONSTEXPR_STDMAXMIN)
+
+
     #
     # Clang-3.5* or older, bail out with a spurious error message in case
     # of an undeduced auto return type.
@@ -207,7 +224,8 @@ IF(NOT DEFINED DEAL_II_WITH_CXX14 OR DEAL_II_WITH_CXX14)
   ENDIF()
 
   IF( DEAL_II_HAVE_CXX14_MAKE_UNIQUE AND
-      DEAL_II_HAVE_CXX14_CLANGAUTODEBUG_BUG_OK )
+      DEAL_II_HAVE_CXX14_CLANGAUTODEBUG_BUG_OK AND
+      DEAL_II_HAVE_CXX14_CONSTEXPR_STDMAXMIN)
     SET(DEAL_II_HAVE_CXX14 TRUE)
   ELSE()
     IF(NOT _user_provided_cxx_version_flag)