ALD input data
** ALD.I data is valid at shader start -- until ASTs overwrite it
** ALD.O data is undefined before the relevant AST 

[-input]
    vtg shader:   shows shader input data using ALD.I
    pixel shader: shows shader input data using IPA

[-output]
    vtg shader: shows shader output data using ALD.O

[-vertexIndex=<vertex index>]n    vertex shaders have exactly one vertex
    tesselation/geometry shaders have multiple vertices
    <vertex index> applies to -input/-output

[-patch]
    tesselation/geometry shader: shows patch attribute data

[-pixld]
    pixel shaders: shows PIXLD attribute data

[-ldtram]
    pixel shaders: shows LDTRAM (vertex attribute) data, i.e. barycentric data at <vertex index={0=A, 1=B, 2=C}

references:
* https://p4viewer.nvidia.com/get/hw/doc/gpu/maxwell/maxwell/design/IAS/SM/ISA/opcodes/opALD.htm
* https://p4viewer.nvidia.com/get/hw/doc/gpu/maxwell/maxwell/design/IAS/SM/ISA/opcodes/opAL2P.htm
* https://p4viewer.nvidia.com/get///hw/doc/gpu/volta/volta/design/IAS/SM/ISA/opcodes/opALD.htm
* https://p4viewer.nvidia.com/get///hw/doc/gpu/volta/volta/design/IAS/SM/ISA/opcodes/opAL2P.htm
* https://p4viewer.nvidia.com/get///hw/doc/gpu/turing/turing/design/IAS/SM/ISA/opcodes/opALD.htm
* https://p4viewer.nvidia.com/get///hw/doc/gpu/turing/turing/design/IAS/SM/ISA/opcodes/opAL2P.htm
* https://p4viewer.nvidia.com/get///hw/doc/gpu/ampere/ampere/design/IAS/SM/ISA/opcodes/opALD.htm
* https://p4viewer.nvidia.com/get///hw/doc/gpu/ampere/ampere/design/IAS/SM/ISA/opcodes/opAL2P.htm
* https://p4viewer.nvidia.com/get/hw/doc/gpu/maxwell/maxwell/design/IAS/SM/ISA/IAS_Maxwell_ISA.htm#SM_Attribute_Access
* https://p4viewer.nvidia.com/get///hw/doc/gpu/volta/volta/design/IAS/SM/ISA/IAS_Volta_ISA.htm#Architecture_State__Attributes
* https://p4viewer.nvidia.com/get///hw/doc/gpu/turing/turing/design/IAS/SM/ISA/IAS_Turing_ISA.htm#Architecture_State__Attributes
* https://p4viewer.nvidia.com/get///hw/doc/gpu/ampere/ampere/design/IAS/SM/ISA/IAS_Ampere_ISA.htm#Architecture_State__Attributes