The SPIR-V backend may emit SPIR-V 1.3 if Vulkan 1.1 is available.
Some extensions which provide wave op instructions are available in
SPIR-V 1.0, but these are not sufficient to implement all Shader Model 6
wave op intrinsics. SPIR-V 1.3 has all of the required instructions, but
does not support reading from a quad at a non-constant (but uniform) lane
index, so it may later prove necessary to introduce a Vulkan 1.2
environment.
This codepath path is currently triggered when transpiling d3dbc shaders
that use vPos (or other of these special registers).
While vPos gets added to the input signature and gets assigned an INPUT
register, the registers in the shader instructions are still of
VKD3DSPR_MISCTYPE type and are not propperly mapped yet. This gives
invalid results.
Some SM1 tests must be set back to "todo" but they only work because, by
coincidence, we are assigning vPos the input register with index 0.
Propper mapping of these registers is still required.
