[LLVMdev] Changes to the PTX calling conventions

[Villmow, Micah]

From: Justin Holewinski [mailto:justin.holewinski at gmail.com]
Sent: Tuesday, December 13, 2011 10:50 AM
To: Villmow, Micah
Cc: LLVM Developers Mailing List
Subject: Re: [LLVMdev] Changes to the PTX calling conventions

On Tue, Dec 13, 2011 at 12:54 PM, Villmow, Micah <Micah.Villmow at amd.com<mailto:Micah.Villmow at amd.com>> wrote:


From: Justin Holewinski [mailto:justin.holewinski at gmail.com<mailto:justin.holewinski at gmail.com>]
Sent: Tuesday, December 13, 2011 9:48 AM
To: Villmow, Micah
Cc: LLVM Developers Mailing List
Subject: Re: [LLVMdev] Changes to the PTX calling conventions

On Tue, Dec 13, 2011 at 11:25 AM, Villmow, Micah <Micah.Villmow at amd.com<mailto:Micah.Villmow at amd.com>> wrote:
Currently, PTX has its own calling conventions where they are split into kernel/device.
The AMDIL backend requires very similar calling conventions and I was wondering if
we could change the calling conventions from PTX_* to something more generic?

Maybe just Kernel/Device? Or would it be preferable to add a new calling convention
that is unique for each target, even though it duplicates functionality?

I don't see any reason why a generic calling convention would not work.  We could do something like cl_device/cl_kernel.  I hate to introduce OpenCL terms into a back-end where OpenCL is just one consumer, but it does map cleanly to the architecture model.  Or perhaps something more generic like gpu_device/gpu_global.
[Villmow, Micah] Yeah, but this should apply to more than just gpu's. For example, AMD's OpenCL CPU implementation could utilize the calling conventions, along with projects like ocelot that have the device-only vs host/device differentiation. Maybe just device/host is good enough?

Device/host just seems vague.  Maybe we could create a set of specific conventions, one set for OpenCL: cl_device/cl_kernel, and another set for general accelerators, e.g. accel_device/accel_global.
[Villmow, Micah] Yeah, that is true. What about leaving the calling convention alone for 'device' and just having a calling convention for 'kernel'(i.e. functions callable from another device). The normal calling conventions handle calls from the same device, but there is no calling convention that handles functions that are callable from a seperate device. This would handle the CPU/GPU and accelerator cases. That I believe is the fundamental difference between the two calling conventions that OpenCL uses.



Thanks,
Micah



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--
Thanks,

Justin Holewinski




--
Thanks,

Justin Holewinski

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