r264205 - [CUDA] Don't define __NVCC__.

Hal Finkel via cfe-commits cfe-commits at lists.llvm.org
Thu Mar 24 08:44:08 PDT 2016

----- Original Message -----

> From: "Reid Kleckner via cfe-commits" <cfe-commits at lists.llvm.org>
> To: "David Blaikie" <dblaikie at gmail.com>
> Cc: "cfe-commits" <cfe-commits at lists.llvm.org>
> Sent: Thursday, March 24, 2016 10:39:18 AM
> Subject: Re: r264205 - [CUDA] Don't define __NVCC__.

> On Thu, Mar 24, 2016 at 8:30 AM, David Blaikie via cfe-commits <
> cfe-commits at lists.llvm.org > wrote:
> > This seems like a different tradeoff from the one Clang made for
> > GCC
> > compatibility (we define all the GCC macros, but then also define
> > others so people can detect Clang). If people were just disabling
> > features that NVCC didn't support, that seems fairly harmless -
> > what
> > sort of problems/difficulties did this create?
> I think Clang is aiming for less bug-for-bug compatibility with NVCC
> than with GCC or Clang, so it makes less sense to pretend to be
> them. I also expect that there are fewer checks in the wild for
> __NVCC__ than for _MSC_VER and __GNUC__. If we didn't *have* to
> define these macros to build the world, we wouldn't, and if we can
> get away without defining __NVCC__, that's great.

I don't yet think there is a precedent for other compilers to pretend to be nvcc, and I don't think we should start one if it is not necessary. I'm sure we have some checks for __NVCC__ witin DOE applications, but I'm happy to tell those users to migrate them to __CUDACC__ as appropriate as part of transitioning to supporting Clang as a CUDA compiler. 


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Hal Finkel 
Assistant Computational Scientist 
Leadership Computing Facility 
Argonne National Laboratory 
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