The semantic variables from a patch parameter are split as usual, with
the difference being that the semantic variable being added is a patch
variable itself, with the type being the split variable type, and its
number of control points being equal to the original patch variable's
number of control points. It is then stored in the original patch
variable as follows:
for (i = 0; i < n; ++i)
patch[i][f] := <inputpatch-sem-var>[i]
where n is the number of control points of "patch", and f is the field
index in patch corresponding to "<inputpatch-sem-var>".
We use special prefixes, "inputpatch-" or "outputpatch-", when adding
the semantic patch variables, in order to distinguish them from
non-patch semantic variables of the same name.
In anticipation of the need for is_patch_constant_func in
sm4_generate_vsir_reg_from_deref(), in order to generate vsir
registers from InputPatch/OutputPatch dereferences.
If the parameter is HLSL_STORAGE_IN, we add a cast from the arg to the
param type so that it can enter the function, however this cast should
not be considered part of the lhs on the implicit assignment that happens
if the var is also HLSL_STORAGE_OUT.
