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

[Howard Hinnant]

Hi Rich,

I recommend filing a bug against clang on this.  I am hesitant to commit the libc++ fix due to David Chisnall's concerns.  If the clang team reassigns the bug to libc++, then I will commit the libc++ solution.

Howard

On May 21, 2013, at 12:12 AM, Rich E <reakinator at gmail.com> wrote:

> Thank you to all for addressing this, I must say that you are very much considered awesome in the eyes of those who use the tools you are creating.
> 
> While I can't justly review the code in this patch, I would like to test if the issue I ran into is indeed solved with it, however I ran into difficulties when applyinng the patch to my local git clone (http://llvm.org/git/libcxx.git).  Nonetheless, it's pretty clear the problem is understood and thank you again for addressing it.  I will continue to test and report any issues I come across.
> 
> cheers,
> Rich
> 
> 
> On Mon, May 20, 2013 at 8:55 PM, Howard Hinnant <hhinnant at apple.com> wrote:
> 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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