[Openmp-dev] Bug in clang/openmp: max-reduction fails if data type is "long double"

[Alexey Bataev via Openmp-dev]

Could you do it one more time but with -fopenmp option added? Your LLVM 
IR does not have any OpenMP code. Seems to me you compiled it wihtout 
-fopenmp

Best regards,
Alexey Bataev
=============
Software Engineer
Intel Compiler Team

15.03.2016 16:48, Stefan Illy пишет:
> Here it comes!
>
> Regards,
>
> Stefan
>
> Am 15.03.2016 um 13:38 schrieb Alexey Bataev:
>> Hi, could please send llvm ir for your example?
>> you can do it like this: clang -c -S -emit-llvm -o openmpbug.ll 
>> openmpbug.cc
>> and attach openmpbug.ll file.
>>
>> Best regards,
>> Alexey Bataev
>> =============
>> Software Engineer
>> Intel Compiler Team
>>
>> 15.03.2016 12:43, Cownie, James H via Openmp-dev пишет:
>>> This looks like an inconsistency in our knowledge of LLVM/Clang.
>>>
>>> Historically LLVM did not support 16 byte floating point, so the 
>>> OpenMP runtime does not have support for them when compiled with 
>>> clang (because the necessary routines couldn't be compiled!).
>>>
>>> If your code really is using 16 byte floating point numbers, then 
>>> the tests in the runtime that don't compile those routines need to 
>>> be enabled.
>>>
>>> It'd be worth checking, though, that the "long double" really is 16 
>>> bytes, so maybe you could just check sizeof(real_t).
>>>
>>> p.s. You don't need to initialize max_val; whatever value you put 
>>> there will be ignored anyway, since the OpenMP standard says that 
>>> the per-thread reduction values are initialized with the most 
>>> negative value of the type.
>>>
>>> -- Jim
>>>
>>> James Cownie <james.h.cownie at intel.com>
>>> SSG/DPD/TCAR (Technical Computing, Analyzers and Runtimes)
>>> Tel: +44 117 9071438
>>>
>>> -----Original Message-----
>>> From: Openmp-dev [mailto:openmp-dev-bounces at lists.llvm.org] On 
>>> Behalf Of Stefan Illy via Openmp-dev
>>> Sent: Friday, March 11, 2016 7:36 AM
>>> To: openmp-dev at lists.llvm.org
>>> Subject: [Openmp-dev] Bug in clang/openmp: max-reduction fails if 
>>> data type is "long double"
>>>
>>> Hello everybody,
>>>
>>> When I compile the simple test program attached below I get the
>>> following error message:
>>>
>>> openmpbug.cc:(.text+0x2de): undefined reference to
>>> `__sync_val_compare_and_swap_16'
>>> openmpbug.cc:(.text+0x3a7): undefined reference to
>>> `__sync_val_compare_and_swap_16'
>>> clang-3.8: error: linker command failed with exit code 1 (use -v to see
>>> invocation)
>>>
>>> This is caused by the OMP max-reduction statement. It also fails if I
>>> switch from "max" to "min".
>>> I use version 3.8 of clang on an Ubuntu 14.04 LTS system. It also fails
>>> with version 3.9 (trunk, self-compiled).
>>> If I switch the floating point data type (real_t) from "long double" to
>>> "double" or "float", the code compiles and runs without problems.
>>>
>>> I hope this helps to make clang+openmp even better!
>>>
>>>
>>> Here comes the simple test program:
>>> ---------------------------------------SNIP------------------------------------------- 
>>>
>>> #include <iostream>
>>>
>>> using namespace std;
>>>
>>> //typedef float real_t;
>>> //typedef double real_t;
>>> typedef long double real_t;
>>>
>>> int
>>> main()
>>> {
>>>      real_t maxval = -1.0e-10;
>>> #pragma omp parallel for reduction(max: maxval)
>>>      for (int i = 1; i <= 1000; i++) maxval = max(maxval, real_t(i));
>>>      cout << maxval << endl;
>>>      return 0;
>>> }
>>> ------------------------------------SNIP------------------------------------------------ 
>>>
>>>
>>> ---------------------------------------------------------------------
>>> Intel Corporation (UK) Limited
>>> Registered No. 1134945 (England)
>>> Registered Office: Pipers Way, Swindon SN3 1RJ
>>> VAT No: 860 2173 47
>>>
>>> This e-mail and any attachments may contain confidential material for
>>> the sole use of the intended recipient(s). Any review or distribution
>>> by others is strictly prohibited. If you are not the intended
>>> recipient, please contact the sender and delete all copies.
>>>
>>> _______________________________________________
>>> Openmp-dev mailing list
>>> Openmp-dev at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/openmp-dev
>