[llvm-dev] cuda __shfl_sync problem

[George K via llvm-dev]

I couldn't find `-target-feature`. I am on llvm 10. Has the interface 
changed maybe?

Fortunately, `-mattr=+ptx60 ` did the trick.

George

On 25-09-2020 17:05, Johannes Doerfert wrote:
> Have you tried `-target-feature +ptx60`?
>
>
> On 9/25/20 3:18 AM, George K wrote:
>> Do you mean in llc? Because i don't see such an option i'm afraid.
>>
>> ~George
>>
>> On 24-09-2020 20:54, Johannes Doerfert wrote:
>>> Not that I am an expert but it looks like it defaults to the minimal 
>>> PTX version that supports the compute capability. You might be able 
>>> to choose PTX 6.0 though.
>>>
>>> ~ Johannes
>>>
>>>
>>> On 9/24/20 1:02 PM, George K via llvm-dev wrote:
>>>> Hi,
>>>>
>>>> First of all, i'm not sure if i should be posting this here or in 
>>>> cfe-dev, but here it goes.
>>>>
>>>> In order to instrument CUDA kernels i first generate device IR with:
>>>>
>>>> clang++ -x cuda --cuda-device-only -emit-llvm --cuda-gpu-arch=sm_52 
>>>> -o device.bc
>>>>
>>>> I also have a library that contains the instrumentation stubs for 
>>>> which i generate IR similarly and i link it with the device IR 
>>>> programmatically with Linker::linkModules(..)
>>>>
>>>> Then after some analysis i use llc to get ptx:
>>>>
>>>> llc device.bc --march=nvptx64 --mcpu=sm_52 --filetype=asm -o 
>>>> device.ptx
>>>>
>>>> This works fine but the problem is that the instrumentation code 
>>>> uses __shfl_sync() and ptxas gives me the following error:
>>>>
>>>> ptxas device.ptx, line 1033; error   : Feature 'shfl.sync' requires 
>>>> PTX ISA .version 6.0 or later
>>>>
>>>> Now according to 
>>>> https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#warp-shuffle-functions,
>>>>
>>>> __shfl_sync is supported by compute capability >= 3 and according 
>>>> to https://developer.nvidia.com/cuda-gpus#compute my GTX950 has 
>>>> Compute Capability 5.2.
>>>>
>>>> Also according to 
>>>> https://docs.nvidia.com/cuda/parallel-thread-execution/index.html#release-notes 
>>>> PTX ISA 6.0 does support sm_52.
>>>>
>>>> However llc generates:
>>>>
>>>> .version 4.1
>>>> .target sm_52, debug
>>>> .address_size 64
>>>>
>>>> Any ideas why this is happening? Or am i doing something wrong?
>>>>
>>>> PS. I'm using CUDA 10, driver 440
>>>>
>>>> ~George
>>>>
>>>>
>>>>
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