[Tarantool-patches] [PATCH 1/3] cmake: ignore warnings on alignof() and offsetof()

[Cyrill Gorcunov <gorcunov@gmail.com>]

From: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>

Warning about invalid offsetof() (used on non-POD types) was set
for g++, but wasn't for clang++.

Warning about invalid alignof() (when expression is passed to it
instead of a type) wasn't ignored, but is going to be very
useful in upcoming unaligned memory access patches. That allows
to write something like:

    struct some_long_type *object = region_aligned_alloc(
            region, size, alignof(*object));

This will work even if type of 'object' will change in future,
and so it is safer. And shorter.

Part of #4609
---
 cmake/compiler.cmake | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/cmake/compiler.cmake b/cmake/compiler.cmake
index 56429dc20..b0908f3b3 100644
--- a/cmake/compiler.cmake
+++ b/cmake/compiler.cmake
@@ -276,11 +276,17 @@ macro(enable_tnt_compile_flags)
         add_compile_flags("C;CXX" "-Wno-format-truncation")
     endif()
 
-    if (CMAKE_COMPILER_IS_GNUCXX)
+    if (CMAKE_COMPILER_IS_CLANG OR CMAKE_COMPILER_IS_GNUCXX)
         # G++ bug. http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31488
+        # Also offsetof() is widely used in Tarantool source code
+        # for classes and structs to implement intrusive lists and
+        # some other data structures. G++ and clang++ both
+        # complain about classes, having a virtual table. They
+        # complain fair, but this can't be fixed for now.
         add_compile_flags("CXX"
             "-Wno-invalid-offsetof"
         )
+        add_compile_flags("C;CXX" "-Wno-gnu-alignof-expression")
     endif()
 
     if (CMAKE_COMPILER_IS_GNUCC)
-- 
2.26.2