[cfe-dev] [PATCH] libc++: help diagnosing the following std::atomic compile error

[Howard Hinnant]

Please review:

I've enclosed a proposed patch for fixing <atomic>.  This patch changes us from using _Atomic(T) for the stored type, to just T, but aligned to _Atomic(T).  It also switches from the __c11_atomic intrinsics to the gcc __atomic intrinsics.  This change exposed several silly bugs in the test suite.  But most importantly it is meant to allow std::atomic to be instantiated with trivially copyable class types.

The enclosed patch passes all (modified) tests on Apple's Mountain Lion except one:

passed 1 tests in /Users/hhinnant/Development/temp_libcxx/test/atomics
passed 2 tests in /Users/hhinnant/Development/temp_libcxx/test/atomics/atomics.fences
passed 11 tests in /Users/hhinnant/Development/temp_libcxx/test/atomics/atomics.flag
passed 1 tests in /Users/hhinnant/Development/temp_libcxx/test/atomics/atomics.general
passed 1 tests in /Users/hhinnant/Development/temp_libcxx/test/atomics/atomics.lockfree
passed 2 tests in /Users/hhinnant/Development/temp_libcxx/test/atomics/atomics.order
passed 1 tests in /Users/hhinnant/Development/temp_libcxx/test/atomics/atomics.syn
passed 5 tests in /Users/hhinnant/Development/temp_libcxx/test/atomics/atomics.types.generic
passed 1 tests in /Users/hhinnant/Development/temp_libcxx/test/atomics/atomics.types.operations
passed 1 tests in /Users/hhinnant/Development/temp_libcxx/test/atomics/atomics.types.operations/atomics.types.operations.arith
passed 1 tests in /Users/hhinnant/Development/temp_libcxx/test/atomics/atomics.types.operations/atomics.types.operations.general
passed 1 tests in /Users/hhinnant/Development/temp_libcxx/test/atomics/atomics.types.operations/atomics.types.operations.pointer
Undefined symbols for architecture x86_64:
  "___atomic_is_lock_free", referenced from:
      void test<A>() in atomic_is_lock_free-cA4Y5d.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
/Users/hhinnant/Development/temp_libcxx/test/atomics/atomics.types.operations/atomics.types.operations.req/atomic_is_lock_free.pass.cpp failed to compile
Compile line was: xcrun clang++ -stdlib=libc++ -std=c++11 -I/Users/hhinnant/Development/temp_libcxx/test/support -I/Users/hhinnant/Development/temp_libcxx/include -L/Users/hhinnant/Development/temp_libcxx/lib -D_LIBCPP_STD_VER=13 -I/Users/hhinnant/Development/temp_libcxx/test/support -I/Users/hhinnant/Development/temp_libcxx/include -L/Users/hhinnant/Development/temp_libcxx/lib atomic_is_lock_free.pass.cpp
failed 1 tests in /Users/hhinnant/Development/temp_libcxx/test/atomics/atomics.types.operations/atomics.types.operations.req
passed 22 tests in /Users/hhinnant/Development/temp_libcxx/test/atomics/atomics.types.operations/atomics.types.operations.req
passed 1 tests in /Users/hhinnant/Development/temp_libcxx/test/atomics/atomics.types.operations/atomics.types.operations.templ
****************************************************
Results for /Users/hhinnant/Development/temp_libcxx/test/atomics:
using Apple LLVM version 4.2 (clang-425.1.16) (based on LLVM 3.2svn)
Target: x86_64-apple-darwin12.3.0
Thread model: posix
with -stdlib=libc++ -std=c++11 -I/Users/hhinnant/Development/temp_libcxx/test/support -I/Users/hhinnant/Development/temp_libcxx/include -L/Users/hhinnant/Development/temp_libcxx/lib -D_LIBCPP_STD_VER=13 -I/Users/hhinnant/Development/temp_libcxx/test/support -I/Users/hhinnant/Development/temp_libcxx/include -L/Users/hhinnant/Development/temp_libcxx/lib
----------------------------------------------------
sections without tests   : 0
sections with failures   : 1
sections without failures: 13
                       +   ----
total number of sections : 14
----------------------------------------------------
number of tests failed   : 1
number of tests passed   : 51
                       +   ----
total number of tests    : 52
****************************************************

Comments welcomed.  We need more clang expertise here than libc++ expertise.

Howard
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