DXIL handles are used to represent descriptors. Currently they are
translated to registers of the appropriate type (depending on the
descriptor type) and three indices. The first two indices are used
to represent the descriptor itself (through its signature and array
index), and are filled when the handle itself is created. The last
index is used with constant buffers to address the data inside the
buffer itself, and it goes unused with other descriptor types.
As currently implemented, however, registers for descriptors other
than constant buffers are still created with three indices, even if
the last one is useless and set to -1. In the interest of creating
more sensible VSIR code, this is now removed: DXIL handles are
created with just two indices; a third one is added when accessing
constant buffers, and nothing is changed for other descriptor types.
As the newly added documentation describes, this reroll serves two purposes:
* to allow shader parameters to be used for any target type (which allows using
parameters for things like Direct3D 8-9 alpha test),
* to allow the union in struct vkd3d_shader_parameter to contain types larger
than 32 bits (by specifying them indirectly through a pointer).
