[SPIR-V][Feature Request][SM6.7] Implement GatherRaw in the SPIR-V backend about directxshadercompiler HOT 4 OPEN

I don't think this can be implemented in a straight forward way. The problem is that the new instruction retrieves "a single value that represents a raw, bitwise copy of all of the element’s channels without any conversion of texture contents." As far a I can tell, no existing Vulkan instruction will do that.

from directxshadercompiler.

FYI: https://docs.vulkan.org/spec/latest/chapters/textures.html#textures-format-conversion

from directxshadercompiler.

When we talked about that, it seemed we'd need to to 4 OpImageGather calls to recombine the N components. But I saw the GatherRaw limits thew formats of the textures to single channels, or worst case, 2 channels textures. So doesn't this means in most cases, we would have a single OpImageGather to do? And in a very few cases 2?

from directxshadercompiler.

The issue the the bitwise copy. AFAIK, all of the existing instructions will do a format conversion. The point of RawGather is to avoid the format conversion.

from directxshadercompiler.