Provide generic and safe C++ interfaces for warp shuffle: Issue #2976

[soumikiith]

Description

closes #2976

I have provided generic and safe C++ interface for warp shuffle (shuffle_sync only for now). The safety features include: (1) checking for allowable data types, (2) handling of variables that consists of 4 bytes (32 bits).
Soon, I will post the feature to handle 16 bit and 64 bit data types.

Provide generic and safe C++ interfaces for warp shuffle: Issue #2976

Checklist

• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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[fbusato]

thanks for the contribution, @soumikiith. I have a couple of initial comments.

• cmath provides a set of mathematical operations, while warp shuffles are about data movement. I would create another header cuda/shuffle.
• you don't need to handle all data types one by one, or by size. My suggestion is to create an array of uint32_t and then use memcpy. Even better if you find a way to use bit_cast.

[fbusato]

I updated #2976 to better formalize the features and checks of these functions

[soumikiith]

One Question:

While computing laneid, can I use modulo operator ? Or is the preferable way to fetch it directly from assembly using asm instructions?

Note that my doubt is only in the context of shfl_up and shfl_down.

Also, why does a mask value need to be passed (I know that the default value is assigned) in shfl_xor? Is not passing lanemask sufficient ?

[fbusato]

While computing laneid, can I use modulo operator ? Or is the preferable way to fetch it directly from assembly using asm instructions?

you can use C++ API for PTX, see https://nvidia.github.io/cccl/libcudacxx/ptx/instructions/special_registers.html#laneid

Also, why does a mask value need to be passed (I know that the default value is assigned) in shfl_xor? Is not passing lanemask sufficient ?

Referring to the official documentation, laneMask and mask have different meaning. mask represents the active lanes, while laneMask is the value to apply to the XOR operator, i.e. laneid() ^ laneMask

[soumikiith]

Hi, I have added the checks (I need to fix the assertion statements, though). Please check them and let me know if this is meeting your expected requirements. I will soon commit the casting of different data types using memcpy.

Please let me know of any additional requirements.