[cfe-dev] clang-cl and _Interlocked* intrinsics

[Hans Wennborg via cfe-dev]

On Wed, May 23, 2018 at 3:53 PM, Hans Wennborg <hans at chromium.org> wrote:
> Hi Ethan,
>
> On Wed, May 23, 2018 at 1:37 AM, Ethan Smith via cfe-dev
> <cfe-dev at lists.llvm.org> wrote:
>> I am working on porting CPython to build with clang-cl on Windows, since I
>> expect things like labels as values and other optimizations could provide a
>> significant speedup. I am currently running into a strange issue, and was
>> directed here from IRC. When I have, for example,
>>
>> #include <intrin.h>
>> #include <immintrin.h>
>>
>> int main() {
>>     _InterlockedCompareExchange64_HLEAcquire(4L, 5L, 6L);
>> }
>>
>> building with cl is fine (minus obvious warnings about long to pointer
>> conversion). However, if I build with clang-cl, I get "unresolved external
>> symbol _InterlockedCompareExchange64_HLEAcquire referenced in function
>> main". When I build this in a Visual Studio solution I also get that
>> _InterlockedCompareExchange64_HLEAcquire is implicitly declared, and the
>> same link error.
>>
>> Any advice on something I am doing wrong or ways to fix this would be
>> appreciated. For the curious, full branch of CPython is
>> https://github.com/ethanhs/cpython/tree/clang-cl . The usage of these
>> intrinsics is in pyatomic.h.
>
> You're not doing anything wrong. It's we who haven't implemented those
> intrinsics yet.
>
> If you want to work around this until we fix it, you can probably just
> use the InterlockedCompareExchange variants without the _HLE* part in
> pyatomic.h.
>
> (And if you want to consider contributing a patch for this, it should
> be fairly simple to add support based on grepping for
> InterlockedCompareExchange64 :-)

For anyone following along, Ethan submitted a patch here:
https://reviews.llvm.org/D47672