[LLVMdev] JIT on Intel KNC

["C. Bergström"]

On 12/ 3/13 06:38 AM, Dmitry Mikushin wrote:
> Hi,
>
> We have the same difficulties.
>
> KNC (dubbed k1om in compiler utils) is a 64-bit device with 
> 8087-compatible scalar arithmetics and non-standard vector 
> arithmetics. More specifically, the widely used variant of 64-bit ABI 
> implemented by LLVM involves xmm registers, while KNC does not have 
> xmm-s and instead has zmm-s (512-bit wide). This makes standard 64-bit 
> binaries you're trying to compile partially incompatible with KNC. So, 
> even if you'd succeed to compile them somehow, they may fail to run 
> (illegal instruction).
>
> There are two possible solutions I know of.
>
> First one - use KNC in 32-bit mode. KNC can run any 32-bit binary, if 
> 32-bit C runtime is provided and device Linux kernel is compiled with 
> CONFIG_IA32_EMULATION=y. This will not allow to use KNC's vector 
> units, so it will be worth only for massive multi-threading. You do 
> not loose much, because even if k1om-ready LLVM backend would exist, I 
> doubt it could optimize for vector arithmetics well enough without 
> man-year of testing/tuning the exiting vectorizer.
>
> Second one - ask Intel to increase the priority of KNC support in 
> LLVM. As far as I know, they do not plan official KNC support at all, 
> only KNL (Landing, the next one). According to SC13, KNL will appear 
> in 2015...
PathScale has KNC llvm backend and also a non-intel runtime for managing 
the device.

We're missing some SLP vector tuning and a few other performance things, 
but that should improve in the next couple months. We're open to sharing 
our work with researchers, but please contact me off list.