Limit size of kernel args no more than 255

[haonanya]

Minimum limit for OpFunctionCall actual arguments is 255 according to https://www.khronos.org/registry/SPIR-V/specs/unified1/SPIRV.html#_universal_validation_rules

Signed-off-by: Haonan Yang [email protected]

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[lakshmih]

[Qualcomm] Our concern is that this change would affect test behavior even on implementations that don't support SPIR-V. Further discussion is needed.

[bashbaug]

Discussed in the OpenCL teleconference on May 10th. Short summary:

• We update the OpenCL specification to restrict the maximum number of kernel arguments to 255 if it is not restricted to a smaller value (via e.g. the minimum supported value for CL_DEVICE_MAX_PARAMETER_SIZE). This will most likely be done as an update to the description of CL_DEVICE_MAX_PARAMETER_SIZE and as a TBD update to the OpenCL C spec. I will file an issue in OpenCL-Docs to track this.

• I will also file an issue in OpenCL-Docs to track a possible longer-term solution, which may add e.g. an additional query as an extension or as part of a new OpenCL API version.

• Based on the above, we are OK with this change in principle (still needs review approval, though).

[bashbaug]

I don't think we can merge this yet. @haonanya, can you please look at my review comments above?

[haonanya]

I don't think we can merge this yet. @haonanya, can you please look at my review comments above?

Hi, @bashbaug, thanks for your review, I will have a look.

[bashbaug]

I've filed the two issues in OpenCL-Docs described above.

[nikhiljnv]

Apologize for late feedback here. If I am reading it correctly, 255 is the minimum limit for actual function arguments of SPIR-V. Does this mean number of kernel arguments should be no more than 255 or implementations supporting SPIR-V need to support minimum of upto 255 kernel arguments and some implementations can choose to support higher limit?

Also, if we decide to cap max number of kernel arguments to 255, is it fair to say all implementations need to limit CL_DEVICE_MAX_PARAMETER_SIZE to 2048? For implementations already reporting CL_DEVICE_MAX_PARAMETER_SIZE > 2048, possibly there may be applications using >255 arguments which may start to fail with this change and this change may potentially break backward compatibility. We have about 40% of reports on GpuInfo reporting >2048 values for CL_DEVICE_MAX_PARAMETER_SIZE spread across vendors. https://opencl.gpuinfo.org/displaydeviceinfo.php?name=CL_DEVICE_MAX_PARAMETER_SIZE