It's currently useless, when there is a failure we drop out of
sm6_parser_function_init() before even checking what the current
instruction or value looks like.
I think the main argument for preallocating instructions and
passing them to helpers is that this simplifies error handling.
However it seems that the simplification is close to negligible,
while the current solution makes it harder to use the iterator
abstraction layer for the instruction array, and it also makes
the code harder to read and check.
The main reason is to avoid making false assumptions in the code.
I don't know how that could be used, say, to introduce a security
bug, but I think validating untrusted input should be done by
default.
Conveniently this also acts as documentation for who needs to know
what fields we indeed expect to find in a well-known structure.
Emission of code into individual block instruction arrays was done to
enable construction of a control flow graph. A graph is constructed from
the flat instruction array in a later pass, so blocks are not needed.
It is possible to emit instructions directly into the array in struct
vsir_program instead of from sm6_function_emit_instructions(), but since
the patch constant function occurs first in DXIL hull shaders, this would
reverse the current order of functions in the flat array. That may be
acceptable, but it is left for a later patch in case any issues arise.
