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List:       cfe-dev
Subject:    Re: [cfe-dev] [PROPOSAL] Reintroduce guards for Intel intrinsic headers
From:       Vedant Kumar <vsk () apple ! com>
Date:       2015-07-30 20:05:11
Message-ID: 73FD8D3C-452E-41DE-9813-2BA167BFF42A () apple ! com
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> On Thu, Jul 30, 2015 at 11:27 AM Vedant Kumar <vsk@apple.com> wrote:
> > On Jul 30, 2015, at 10:33 AM, Eric Christopher <echristo@gmail.com> wrote:
> > 
> > > I don't see any downsides to reintroducing these guards.
> > 
> > Then you weren't really paying attention to the point of removing them :)
> > 
> > The idea is so that the headers can be used, with appropriate target attributes, for any code.
> 
> Right, I thought about this but wasn't sure if there were benefits to having symbols available for an \
> unsupported target. 
> I.e, is there some reason a project might want to include the header for SSE4 intrinsics if it can't \
> use any of those symbols? 
> 
> I put a code snippet for something to do in the commit, but the general idea is that you can compile a \
> function for a specific target with subtarget features and use the target attribute to add subtarget \
> features and you'll want to be able to use the intrinsics at the same time. It won't work if you block \
> them at the preprocessor level.

Ah ok, I think I understand. If we want the extra granularity, we can't block off some of the symbols in \
the preprocessor because some function could need them.

Sean's suggestion of putting this behind a flag sounds nice, but the details are hairy. We might have to \
provide a separate set of headers for people who want the feature guards.. and it's not clear whether the \
flag would be gcc-compatible.

vedant 
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