ArrayLengthFromUniform is needed for correct bounds checks on
dynamic storage buffers on D3D12. The intrinsic GetDimensions does
not return the actual size of the buffer binding.
ArrayLengthFromUniform is updated to output the indices of the
uniform buffer that are statically used. This allows Dawn to minimize
the amount of data needed to upload into the uniform buffer.
These output indices are returned on the HLSL/MSL generator result.
ArrayLengthFromUniform is also updated to allow only some of the
arrayLength calls to be replaced with uniform buffer loads. For HLSL
output, the remaining arrayLength computations will continue to use
GetDimensions(). For MSL, it is invalid to not specify an index into
the uniform buffer for all storage buffers.
After Dawn is updated to use the array_length_from_uniform option in the
Metal backend, the buffer_size_ubo_index member for MSL output may be
removed.
Bug: dawn:429
Change-Id: I9da4ec4a20882e9f1bfa5bb026725d72529eff26
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/69301
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: James Price <jrprice@google.com>
Commit-Queue: Austin Eng <enga@chromium.org>
38fa643702