[PATCH] D57018: Fix lvm::is_trivially_copyable portability issues

[serge via Phabricator via llvm-commits]

serge-sans-paille created this revision.
serge-sans-paille added reviewers: fedor.sergeev, Anastasia.
Herald added subscribers: kristina, mgorny.

llvm::is_trivially_copyable portability is verified at compile time using `std::is_trivially_copyable` as the reference implementation. Unfortunately, the latter is not available on all platforms, so introduce a proper configure check to detect if it is available on the target platform.

In a similar manner, `std::is_copy_assignable` is not fully supported for gcc4.9. Provide a portable (?) implementation instead.


Repository:
  rL LLVM

https://reviews.llvm.org/D57018

Files:
  cmake/config-ix.cmake
  include/llvm/Config/config.h.cmake
  include/llvm/Support/type_traits.h


Index: include/llvm/Support/type_traits.h
===================================================================
--- include/llvm/Support/type_traits.h
+++ include/llvm/Support/type_traits.h
@@ -119,6 +119,15 @@
 template <typename T>
 struct is_trivially_move_constructible<T &&> : std::true_type {};
 
+template <typename T>
+class is_copy_assignable {
+  template<class F>
+  static std::true_type apply(decltype(std::declval<F>()=std::declval<T>())*);
+  static std::false_type apply(...);
+  public:
+  static constexpr bool value = decltype(apply((T*)nullptr))::value;
+};
+
 // An implementation of `std::is_trivially_copyable` since STL version
 // is not equally supported by all compilers, especially GCC 4.9.
 // Uniform implementation of this trait is important for ABI compatibility
@@ -140,9 +149,9 @@
 
   // copy assign
   static constexpr bool has_trivial_copy_assign =
-      std::is_copy_assignable<detail::trivial_helper<T>>::value;
+      is_copy_assignable<detail::trivial_helper<T>>::value;
   static constexpr bool has_deleted_copy_assign =
-      !std::is_copy_assignable<T>::value;
+      !is_copy_assignable<T>::value;
 
   // move assign
   static constexpr bool has_trivial_move_assign =
@@ -163,8 +172,9 @@
       (has_deleted_copy_assign || has_trivial_copy_assign) &&
       (has_deleted_copy_constructor || has_trivial_copy_constructor);
 
-#if (__has_feature(is_trivially_copyable) || (defined(__GNUC__) && __GNUC__ >= 5))
-  static_assert(value == std::is_trivially_copyable<T>::value, "inconsistent behavior between llvm:: and std:: implementation of is_trivially_copyable");
+#ifdef HAVE_STD_IS_TRIVIALLY_COPYABLE
+  static_assert(value == std::is_trivially_copyable<T>::value,
+                "inconsistent behavior between llvm:: and std:: implementation of is_trivially_copyable");
 #endif
 };
 
Index: include/llvm/Config/config.h.cmake
===================================================================
--- include/llvm/Config/config.h.cmake
+++ include/llvm/Config/config.h.cmake
@@ -338,6 +338,9 @@
 /* Define as the return type of signal handlers (`int' or `void'). */
 #cmakedefine RETSIGTYPE ${RETSIGTYPE}
 
+/* Define if std::is_trivially_copyable is supported */
+#cmakedefine HAVE_STD_IS_TRIVIALLY_COPYABLE ${HAVE_STD_IS_TRIVIALLY_COPYABLE}
+
 /* Define to a function implementing stricmp */
 #cmakedefine stricmp ${stricmp}
 
Index: cmake/config-ix.cmake
===================================================================
--- cmake/config-ix.cmake
+++ cmake/config-ix.cmake
@@ -325,6 +325,14 @@
   unset(HAVE_FFI_CALL CACHE)
 endif( LLVM_ENABLE_FFI )
 
+check_cxx_source_compiles("
+#include <type_traits>
+struct some_type {};
+static_assert(std::is_trivially_copyable<some_type>::value, \"ok\");
+int main() { return 0;}"
+HAVE_STD_IS_TRIVIALLY_COPYABLE)
+
+
 # Define LLVM_HAS_ATOMICS if gcc or MSVC atomic builtins are supported.
 include(CheckAtomic)
 


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