[PATCH] D47849: [OpenMP][Clang][NVPTX] Enable math functions called in an OpenMP NVPTX target device region to be resolved as device-native function calls

[Hal Finkel via Phabricator via cfe-commits]

hfinkel added a comment.

In https://reviews.llvm.org/D47849#1184388, @Hahnfeld wrote:

> In https://reviews.llvm.org/D47849#1184367, @hfinkel wrote:
>
> > The problem is that the inline assembly might actually be for the target, instead of the host, because we also have target preprocessor macros defined, and it's going to be hard to tell. I'm not sure that there's a great solution here, and I agree that having something more general than undefining some specific things that happen to matter for math.h would be better. As you point out, this is not just a system-header problem. We might indeed want to undefine all of the target-feature-related macros (although that won't always be sufficient, because we need basic arch macros for the system headers to work at all, and those are generally enough to guard some inline asm).
>
>
> I think there was a reason for pulling in the host defines. I'd have to look at the commit message though...


As I recall, it's mostly to make glibc's bits/wordsize.h work.

> 
> 
>> Maybe the following makes sense: Only define the host macros, minus target-feature ones, when compiling for the target in the context of the system headers. That makes the system headers work while providing a "clean" preprocessor environment for the rest of the code (and, thus, retains our ability to complain about bad inline asm).
> 
> I'm not sure how that's going to help with Eigen: Just including `Eigen/Core` will pull in the other header file I mentioned with inline assembly. That's completely independent of preprocessor macros, I think it's enough the library's build system detected the host architecture during install.

I don't see any good way to satisfy Eigen in that form. I think that we'll need to update it to understand not to use host inline as when compiling for a target.


Repository:
  rC Clang

https://reviews.llvm.org/D47849