microsoft/compiler: Compute correct usage masks

This starts actually updating the always-read/never-written
masks while processing the shader. Note that we follow DXC's
lead here and treat "always read" as "sometimes read."

This isn't strictly required, but might help drivers out.

Reviewed-by: Enrico Galli <enrico.galli@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17603>
1 file changed