[cfe-commits] [PATCH] First OpenMP patch

[Dmitri Gribenko]

On Wed, Dec 19, 2012 at 10:53 PM, Douglas Gregor <dgregor at apple.com> wrote:
>
> On Dec 19, 2012, at 3:30 AM, Dmitri Gribenko <gribozavr at gmail.com> wrote:
>
>> On Wed, Dec 19, 2012 at 1:02 PM, Alexey Bataev <a.bataev at gmx.com> wrote:
>>> Dmitry, thanks for a good advice about :option:. Fixed patch is in the
>>> attach.
>>
>> LGTM.  I think that there is a consensus about command line flags and
>> warnings, so this can go in.
>
> Sorry to come late to the party, but I think this is the wrong approach for our users. Our current behavior is that we simply drop "-fopenmp". If we change that behavior to
>
>         warning: Experimental OpenMP support enabled
>
> how have we helped the user? At best, it does nothing and they ignore the warning. At worst, it opens up a ton of questions: should I depend on the experimental implementation? What does it actually do? What was it doing before? How do I shut this warning off? This is especially important to consider for options like -fopenmp that currently exist for GNU compatibility. Changing the behavior in any way other than actually implementing that functionality is not a net win for users.
>
> All we need for OpenMP at this stage is a new LangOpt for OpenMP (which is part of the patch) and a -cc1 option "-fopenmp" that turns on that LangOpt. It also makes sense to define _OPENMP when that LangOpt is true, so that we can write a test for -fopenmp.
>
> It is very important that "-fopenmp" still be dropped by the driver. The -fopenmp at the -cc1 level will be separate, and used for our testing. Once OpenMP is actually usable, we can wire the driver's -fopenmp up to the -cc1 -fopenmp.

That's a good point.  But in order to test the implementation on some
real OpenMP programs easily, we might still want to introduce a
frontend option, just a different one -- like '-fexperimental-openmp'.
 We can also drop the warning then.

Dmitri

-- 
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/