[Vulkan] Broke out implicit device requirements into SPIRVSupport

[Lunderberg]

Codifies the current requirements that are implicit in the shaders
built by CodeGenSPIRV (e.g. can read from 8-bit buffers). The next
steps for this development are (1) to query driver/device support
information from the device, (2) to pass these query parameters
through the Target, and (3) to ensure correct shader generation even
when features are not supported.

Step (3) will require exposing the target properties to relay
optimization passes.

[Lunderberg]

Potential reviewers: @masahi @tqchen

[Lunderberg]

@masahi In the new SPIRVSupport struct, there's a field that will hold the subgroup operation support. Can you confirm that this is the appropriate parameter you'll need for the prefix sum improvements?

[tqchen]

note: stl_style to be consistent with the rest of the codebase

[Lunderberg]

Thank you, and I will change the names. I had been attempting to have the names here mimic the names of the spirv/vulkan features that they enable, but I can see how that would be inconsistent elsewhere.

[Lunderberg]

Member variable names have been updated, along with adding additional documentation on where they should be derived from on the vulkan side.

[tqchen]

One thing to keep in mind is the need of cross compilation, e.g. the machine that runs compilation may not be the machine that executes the program. So we cannot do simple live query on the driver on the same machine.

It would be good to list the some attributes of interest and register them directly in the vulkan.

[Lunderberg]

Agreed, and that is my plan for the next steps. My plan is to have many of these parameters be added to the TVM_REGISTER_TARGET_KIND for vulkan, both to pass them through to the codegen, and in the future to expose them to the optimization passes.

[masahi]

@masahi In the new SPIRVSupport struct, there's a field that will hold the subgroup operation support. Can you confirm that this is the appropriate parameter you'll need for the prefix sum improvements?

Probably we need more fine-grained information than yes/no result. Vulkan has (surprisingly) wide variety of subgroup op support as described in https://www.khronos.org/blog/vulkan-subgroup-tutorial. For prefix scan, it is probably enough to have GL_KHR_shader_subgroup_arithmetic, since it literally has subgroupExclusiveAdd. I'm also planning to do FFT at some point, for that I probably want explicit shuffle ops as provided by GL_KHR_shader_subgroup_shuffle extension.

Since this is a complicated issue, we can add support for them on a need basis later. So feel free to drop supported_subgroup_operations from this PR.

[Lunderberg]

Probably we need more fine-grained information than yes/no result. Vulkan has (surprisingly) wide variety of subgroup op support as described in https://www.khronos.org/blog/vulkan-subgroup-tutorial.

I think the bitflags from the supportedOperations member of VkPhysicalDeviceSubgroupProperties should give that more fine-grained information. The supported_subgroup_operations is intended to be a copy of the bitflags from supportedOperations, which can then be checked by the codegen. In the case of the subgroup arithmetic operations, that should be doable by checking the VK_SUBGROUP_FEATURE_ARITHMETIC_BIT of supported_subgroup_operations.

[masahi]

Thanks, there was a CI issue, please retrigger