Apparently we didn't use those yet. MSL seems to be able to alias struct
types and variable types to a degree, so that's why it has escaped
testing until now.
In the past, SPIRV-Cross threw an error in this case because it couldn't
work out which swizzle from the auxiliary buffer needs to be passed.
Now, we pass the swizzle around with the texture object, like a combined
image-sampler and its associated sampler.
If not enough components are provided in the shader,
the shader MSL compiler throws an error rather than make components
undefined. This hurts portability, so we need to add explicit padding
here.
MSL does not support value semantics for arrays (sigh), so we need to
force constant references and deal with copies if we have a different
address space than what we end up guessing.
Opt-in, since user need to know about a cbuffer.
Conflicts a bit with the GLSL option for base instance,
since that one is enabled by default, but the HLSL one isn't (because
user needs to know about a magic cbuffer, whereas GLSL can only get
default initialized uniform).
The arrays are incredibly sparse for the most part as we only need
entires per basic block.
For a small shader with ID bound of 8 million, we now have about 30x
uplift.
A flat array was consuming way too much memory and was far too slow to
initialize properly with a very large ID bound (8 million IDs, showed up as #1 hotspot in perf).
Meta struct does not have to be in-order as we never iterate over it in
a meaningful way, so using a hashmap here is reasonable. Very few IDs
should need decorations or meta-data, so this should also be a quite
decent memory save.
For the pathological case, a 6x uplift was observed.
This is a fairly fundamental change on how IDs are handled.
It serves many purposes:
- Improve performance. We only need to iterate over IDs which are
relevant at any one time.
- Makes sure we iterate through IDs in SPIR-V module declaration order
rather than ID space. IDs don't have to be monotonically increasing,
which was an assumption SPIRV-Cross used to have. It has apparently
never been a problem until now.
- Support LUTs of structs. We do this by interleaving declaration of
constants and struct types in SPIR-V module order.
To support this, the ParsedIR interface needed to change slightly.
Before setting any ID with variant_set<T> we let ParsedIR know
that an ID with a specific type has been added. The surface for change
should be minimal.
ParsedIR will maintain a per-type list of IDs which the cross-compiler
will need to consider for later.
Instead of looping over ir.ids[] (which can be extremely large), we loop
over types now, using:
ir.for_each_typed_id<SPIRVariable>([&](uint32_t id, SPIRVariable &var) {
handle_variable(var);
});
Now we make sure that we're never looking at irrelevant types.
