r238389 - [omp] Re-work Clang's handling of -fopenmp and undo r237769.

[İsmail Dönmez]

On Fri, May 29, 2015 at 9:32 PM, Richard Smith <richard at metafoo.co.uk> wrote:
> On Fri, May 29, 2015 at 5:56 AM, İsmail Dönmez <ismail at donmez.ws> wrote:
>>
>> On Thu, May 28, 2015 at 11:48 PM, Chandler Carruth <chandlerc at gmail.com>
>> wrote:
>> > On Thu, May 28, 2015 at 5:09 AM İsmail Dönmez <ismail at donmez.ws> wrote:
>> >>
>> >> Hi,
>> >>
>> >> On Thu, May 28, 2015 at 4:52 AM, Chandler Carruth <chandlerc at gmail.com>
>> >> wrote:
>> >> > Author: chandlerc
>> >> > Date: Wed May 27 20:52:38 2015
>> >> > New Revision: 238389
>> >> >
>> >> > URL: http://llvm.org/viewvc/llvm-project?rev=238389&view=rev
>> >> > Log:
>> >> > [omp] Re-work Clang's handling of -fopenmp and undo r237769.
>> >>
>> >>
>> >> This seems to break openmp tests with
>> >> -DCLANG_DEFAULT_OPENMP_RUNTIME=libiomp5 see:
>> >
>> >
>> > Yea, I wanted to have test coverage of the default, but it doesn't work
>> > well
>> > when the default is overridden.
>> >
>> > I looked into how to actually have test coverage of the default and
>> > track
>> > which default was selected, but its really hard and complex. Yuck.
>> >
>> > I'll look for a way to get at least *some* coverage of the default
>> > without
>> > making it break folks that are overriding it. Sorry for the trouble.
>>
>> Tests pass now but there is still one grave problem. With
>> CLANG_DEFAULT_OPENMP_RUNTIME=libiomp5 if you do:
>>
>> λ clang -fopenmp=libgomp omp_hello.c
>> λ ./a.out
>> Hello World from thread = 0
>> Number of threads = 1
>>
>> No OpenMP, lets go back to defaults:
>>
>> λ clang -fopenmp=libiomp5 omp_hello.c
>> λ ./a.out
>> Hello World from thread = 0
>> Hello World from thread = 4
>> Hello World from thread = 3
>> Hello World from thread = 2
>> Hello World from thread = 6
>> Hello World from thread = 1
>> Hello World from thread = 5
>> Hello World from thread = 7
>> Number of threads = 8
>
>
> OK, and what's the one grave problem?

tl;dr clang -fopenmp=libgomp compiles and links to libgomp but doesn't
enable OpenMP.