Henri Verbeet 8700e3a5bd vkd3d-shader/dxil: Allow returning signed types from vsir_data_type_from_dxil(). ...

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().

2025-09-16 15:46:23 +02:00

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