[CMake] CMake misidentifies xlc++ as Clang

[Robert Maynard]

Just to roundtrip this for posterity. The fix for incorrect
identification of XLC will be in CMake 3.11.0-rc3

On Thu, Mar 8, 2018 at 11:17 AM, Robert Maynard
<robert.maynard at kitware.com> wrote:
> Hi.
>
> 1. You can report this issue on the CMake gitlab (
> https://gitlab.kitware.com/cmake/cmake/issues ). You will want to
> attach the result of dumping all defines from the compiler ( xlc++ -dD
> -E - < /dev/null  or xlc++ -dM -E ).  Currently it looks like we are
> using '__IBMCPP__' to detect xlc++, and that might not be defined on
> the power pc platform.
>
> 2. If my guess about about 1 is correct, You can try setting the
> environment variable CXX_FLAGS to -qxlcompatmacros and see if that
> works ( https://www.ibm.com/support/knowledgecenter/SSXVZZ_13.1.3/com.ibm.xlcpp1313.lelinux.doc/compiler_ref/xlmacros.html#xlmacros__suplink1
> )
>
> On Wed, Mar 7, 2018 at 4:22 PM, Thompson, KT <kgt at lanl.gov> wrote:
>> Hi,
>>
>>
>>
>> I am using cmake-3.9.4 on a power9 system with CXX=xlc++ (IBM XL C++) and
>> CMake is misidentifying the compiler as "clang".
>>
>>
>>
>> % uname -a
>>
>> Linux cn2021 4.11.0-44.4.1.el7a.ppc64le #1 SMP Sat Dec 9 02:17:51 EST 2017
>> ppc64le ppc64le ppc64le GNU/Linux
>>
>>
>>
>> % echo $CXX
>>
>> xlc++
>>
>>
>>
>> % $CXX --version
>>
>> IBM XL C/C++ for Linux, V13.1.6 (Community Edition)
>>
>> Version: 13.01.0006.0001
>>
>>
>>
>> % cmake ..
>>
>> -- The CXX compiler identification is Clang 4.0.1
>>
>> -- Check for working CXX compiler:
>> /projects/opt/ppc64le/ibm/xlc-13.1.6/xlC/13.1.6/bin/xlc++
>>
>> -- Check for working CXX compiler:
>> /projects/opt/ppc64le/ibm/xlc-13.1.6/xlC/13.1.6/bin/xlc++ -- works
>>
>> …
>>
>>
>>
>> Because, the compiler_ID is misidentified, inappropriate compiler options
>> are added when CXX_CXX_STANDARD is set (along with other issues).
>>
>>
>>
>> Question 1: How do I report this as a bug? What additional information is
>> needed to characterize the failure mode?
>>
>>
>>
>> Question 2: Is there a way to force the compiler ID to be "XL" as a
>> temporary work around until the bug is fixed?
>>
>>
>>
>> Thank you,
>>
>>
>>
>> -kt
>>
>>
>>
>>
>> --
>>
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