================
Comment at: lib/Headers/cuda/cuda_builtin_vars.h:89
@@ +88,3 @@
+// architectures have a WARP_SZ value of 32'.
+__CUDA_BUILTIN_VAR int warpSize = 32;
+
----------------
tra wrote:
> rsmith wrote:
> > This is a (strong) definition due to the `extern` in the
> > `__CUDA_BUILTIN_VAR` macro, and will cause a link error if this file is
> > `#include`d into multiple objects in the same binary. You could solve this
> > by removing the `extern` (that'd give the variable internal linkage) or by
> > using `enum { warpSize = 32 };` or similar. I'm not sure exactly what the
> > CUDA spec requires here.
> Those have to be extern because no instances of those special variables can
> ever exist, yet they are referred to as if they do. 'extern' matches this
> functionality best. I've added a weak attribute to make linking work. That
> is, if/when we'll get to do any linking on the GPU code. Currently we produce
> PTX assembly and we don't ever link one PTX file with another.
>
> I've reworked warpSize into a class with the same restrictions on
> construction and access as the other built-in variables.
>
> As for CUDA spec, it does not say much -- 'They [built-in variables] are only
> valid within functions that are executed on the device. [warpSize] is of type
> int and contains the warp size in threads.'
>
>
I was only talking about `warpSize`, not the others. The others seem OK as
(non-weak) `extern` declarations, on the assumption that programs aren't
actually allowed to use the address of these.
Your new approach doesn't satisfy the requirement that "`warpSize` is of type
`int`": this is detectable through template argument deduction, for instance:
template<typename T> T max(T, T)
max(warpSize, 10); // error, T is ambiguous, could be int or
__cuda_builtin_warpSize_t
Using
__attribute__((device)) const int warpSize = 32;
would probably work (that is, drop the `extern` from what you had before).
http://reviews.llvm.org/D9064
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