It was originally intended that this structure could hold other information
about the next stage which compilation might depend on. For example, compilation
to GLSL needs to know the type of the next shader in some circumstances.
That was never actualized, and since the API is fixed at this point for 1.9, it
makes the most sense to rename the structure to match its actual scope.
The documentation was written and arranged to imply that the structure would
hold other information about the next shader than the varying map; this is
changed accordingly as well.
In Shader Model 6 each signature element can span a range of register
indices, or 'rows', and system values do not share a register index with
non-system values. Inputs and outputs are referenced by element index
instead of register index. This patch merges multiple signature elements
into a single element under the following conditions:
- The register index in a load or store is specified dynamically by
including a relative address parameter with a base register index. The
dcl_index_range instruction is used to identify these.
- A register declaration is split across multiple elements which declare
different components of the register.
- A patch constant function writes tessellation factors. These are an
array in SPIR-V, but in SM 5.x each factor is declared as a separate
register, and these are dynamically indexed by the fork/join instance
id. Elimination of multiple fork/join phases converts the indices to
constants, but merging the signature elements into a single arrayed
element matches the SPIR-V output.
All references to input/output register indices are converted to element
indices. If a relative address is present, the element index is moved up
a slot so it cannot be confused with a constant offset. Existing code
only handles register index relative addressing for tessellation factors.
This patch adds generic support for it.
