We have a number of vsir operations which should take a signed type, but
which the DXIL parser currently emits unsigned types for. For example,
ISHR.
In the SPIR-V backend, we translate ISHR to OpShiftRightArithmetic,
which is specified as filling the most-significant bits of the result
with the sign bit of the "Base" operand. For an unsigned type, that
would technically be 0. In practice, implementations like radv/Mesa seem
to fill with the most-significant bit of the "Base" operand for unsigned
types, but arguably that could be considered a bug. Alternatively, the
wording in the specification is just unfortunate; SPIR-V does generally
take the position that signedness of operands should be irrelevant for
almost all operations. Either way, it seems best to avoid using
OpShiftRightArithmetic with unsigned types.
For a target like MSL, allowing ISHR to take an unsigned source operand
is just inconvenient; we'd have to introduce bitcasts to achieve the
desired behaviour, instead of simply using msl_binop().
This works around an issue introduced by commit
66cb2815f0. SV_PRIMITIVE_ID inputs in
geometry shaders use VKD3DSPR_PRIMID registers, and we create the
corresponding SPIR-V inputs using spirv_compiler_emit_io_register().
Unfortunately we also have an input signature element for the same
input, and simply creating another PrimitiveId input would run into
VUID-StandaloneSpirv-OpEntryPoint-09658.
Before the commit mentioned above, we'd use DCL_INPUT instructions to
emit input declarations, and these would help to distinguish whether
VKD3DSPR_INPUT or VKD3DSPR_PRIMID registers were used for primitive ID
inputs. Note that we can't simply ignore input signature element with
SIGNATURE_TARGET_LOCATION_UNUSED; the DXIL parser emits SV_SAMPLE_INDEX
inputs with that target location, but does require them to use a
VKD3DSPR_INPUT register.
The change in vsir_program_iterator_next() is necessary to allow us to
introduce instructions before the iterator using:
vsir_program_iterator_prev(&it);
vsir_program_iterator_inset_after(&it, n);
vsir_program_iterator_next(&it);
This since (it.idx == SIZE_MAX) is equivalent to the iterator being
before the beginning of the list.
