This PR resolves the issue of the SPIR-V specification, requiring
Shader-coupled capabilities to read/write images in the OpenCL SPIR-V
environment, from the perspective of the LLVM SPIR-V backend. See
https://github.com/KhronosGroup/SPIRV-Headers/issues/487 for details and
discussion.
Current implementation correctly reproduces requirements of the SPIR-V
specification, however, since the requirements are problematic, out
current implementation blocks generation of valid SPIR-V code for
compute environments. This PR is to implement a solution discussed at
the SPIR-V WG to allow proceeding with generation of valid SPIR-V code
for the OpenCL environment and do not impact Vulkan environment at the
same time.
This commit adds an intrinsic that will read from an image buffer. We
chose to match the name of the DXIL intrinsic for simplicity in clang.
We cannot reuse the existing openCL readimage function because that is
not a reserved name in HLSL.
I considered trying to refactor generateReadImageInst, so that we could
share code between the two implementations. However, most of the code in
generateReadImageInst is concerned with trying to figure out which type
of image read is being done. Once we factor out the code that will be
common, then we end up with just a single call to the MIRBuilder being
common.
