Merge branch 'feature/force-inline' into 'master'

Add preprocessor macro DUNE_FORCE_INLINE

See merge request !1502

CHANGELOG.md

@@ -25,6 +25,8 @@ SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
 
 ## C++: Changelog
 
+- Add preprocessor macro `DUNE_FORCE_INLINE` as a portable attribute to force inlining of functions (if supported).
+
 - Add `bit_width` and `countl_zero` overloads for `bigunsignedint` objects.
 
 - `DUNE_THROW` no longer prevents functions from being used in `constexpr` contexts,

dune/common/CMakeLists.txt

@@ -55,6 +55,7 @@ install(FILES
         float_cmp.hh
         fmatrix.hh
         fmatrixev.hh
+        forceinline.hh
         ftraits.hh
         fvector.hh
         genericiterator.hh

dune/common/forceinline.hh

+// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+// vi: set et ts=4 sw=2 sts=2:
+// SPDX-FileCopyrightInfo: Copyright © DUNE Project contributors, see file LICENSE.md in module root
+// SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
+#ifndef DUNE_COMMON_FORCEINLINE_HH
+#define DUNE_COMMON_FORCEINLINE_HH
+
+/**
+ * \file Provide the  macro `DUNE_FORCE_INLINE` that expands to attribute `always_inline`
+ * or similar depending on the compiler (version). Some information is extracted from
+ * https://meghprkh.github.io/blog/posts/c++-force-inline.
+ *
+ * The effect of DUNE_FORCE_INLINE is typically as follows:
+ * - Inlining heuristics are disabled and inlining is always attempted regardless
+ *   of optimization level.
+ * - Ignore `-fno-inline`
+ * - Ignore the inlining limits hence inlining the function regardless. It also
+ *   inlines functions with allocation calls, which `inline` keyword never does.
+ *
+ * Even when marked with DUNE_FORCE_INLINE, the compiler cannot always inline a
+ * function. Examples for such exceptions are
+ * - The function is virtual and is called virtually.
+ * - The program calls a function indirectly via a pointer to the function.
+ * - The function uses a variable argument list.
+ *
+ * \b Example:
+ * \code{.cpp}
+   DUNE_FORCE_INLINE int maxInt (int a, int b) { return a < b ? b : a; }
+ * \endcode
+ **/
+
+#if defined(__clang__)
+  // Clang does not generate an error for non-inlinable `always_inline` functions.
+  #define DUNE_FORCE_INLINE __attribute__((always_inline)) inline
+
+#elif defined(__GNUC__)
+  // GCC would generate an error if it can't always_inline
+  #define DUNE_FORCE_INLINE __attribute__((always_inline)) inline
+
+#elif defined(_MSC_VER)
+  // MSVC generates a warning for for non-inlinable `__forceinline` functions. But
+  // only if compiled with any "inline expansion" optimization (`/Ob<n>`). This is
+  // present with `/O1` or `/O2`. We promote this warning to an error.
+  #pragma warning(error: 4714)
+  #define DUNE_FORCE_INLINE [[msvc::forceinline]]
+
+#else
+  // fallback to `inline` in case the compiler cannot be detected.
+  #define DUNE_FORCE_INLINE inline
+#endif
+
+#endif // DUNE_COMMON_FORCEINLINE_HH

dune/common/test/CMakeLists.txt

@@ -169,6 +169,9 @@ dune_add_test(SOURCES fmatrixtest.cc
               LABELS quick)
 add_dune_vc_flags(fmatrixtest)
 
+dune_add_test(SOURCES forceinlinetest.cc
+              LABELS quick)
+
 dune_add_test(SOURCES fvectortest.cc
               LABELS quick)
 

dune/common/test/forceinlinetest.cc

+// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+// vi: set et ts=4 sw=2 sts=2:
+// SPDX-FileCopyrightInfo: Copyright © DUNE Project contributors, see file LICENSE.md in module root
+// SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
+
+#include <dune/common/forceinline.hh>
+#include <dune/common/test/testsuite.hh>
+
+template <unsigned int n>
+DUNE_FORCE_INLINE int compute_sum ()
+{
+  if constexpr (n <= 1)
+    return n;
+  else
+    return n + compute_sum<n-1>();
+}
+
+int main ()
+{
+  Dune::TestSuite test;
+
+  test.check(compute_sum<100>() == (100 * 101)/2);
+
+  return test.exit();
+}
\ No newline at end of file