From 675ce5cc59f6b28cb54b3789dca339bc703f120c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Steffen=20M=C3=BCthing?= <muething@dune-project.org>
Date: Fri, 18 Aug 2017 19:56:30 +0200
Subject: [PATCH] [cmake] Add test for inline variables
Inline variables are a C++17 feature that gives variables the same
type of linkage as inline functions, which avoids object file bloat
and linker problems.
For us, this is mostly interesting in the context of constexpr
variables like the partition sets provided in dune-grid: Right now,
a separate copy of those objects is emitted by each translation unit,
and those copies do not get merged by the linker. This has created
problems in the past and forced us to place the variables in an
anonymous namespace, which creates unique symbol names for each
translation unit.
With inline variables, the problem will eventually go away.
---
cmake/modules/CheckCXXFeatures.cmake | 12 ++++++++++++
config.h.cmake | 3 +++
2 files changed, 15 insertions(+)
diff --git a/cmake/modules/CheckCXXFeatures.cmake b/cmake/modules/CheckCXXFeatures.cmake
index 5c4bd828c..d8f922837 100644
--- a/cmake/modules/CheckCXXFeatures.cmake
+++ b/cmake/modules/CheckCXXFeatures.cmake
@@ -481,3 +481,15 @@ check_cxx_source_compiles("
}
" DUNE_SUPPORTS_CXX_THROW_IN_CONSTEXPR
)
+
+
+# Check whether the compiler supports inline variables
+check_cxx_source_compiles("
+ inline int foo = 42;
+
+ int main()
+ {
+ return not (foo == 42);
+ }
+" DUNE_HAVE_CXX_INLINE_VARIABLES
+ )
diff --git a/config.h.cmake b/config.h.cmake
index fa6b9d211..a15ab8a8d 100644
--- a/config.h.cmake
+++ b/config.h.cmake
@@ -35,6 +35,9 @@
/* does the compiler support conditionally throwing exceptions in constexpr context? */
#cmakedefine DUNE_SUPPORTS_CXX_THROW_IN_CONSTEXPR 1
+/* does the compiler support inline variables? */
+#cmakedefine DUNE_HAVE_CXX_INLINE_VARIABLES 1
+
/* Define if you have a BLAS library. */
#cmakedefine HAVE_BLAS 1
--
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