What tag does LBC_TYPE_TAGGED_USERDATA_BASE map to?

[jackdotink]

It would make sense for it to map to 0 or 1, so I'm wondering which it actually is.

[vegorov-rbx]

In the compilation options, you specify the array of userdata type names that you wish to detect later in CodeGen lowering.

From the compilation options struct:

// null-terminated array of userdata types that will be included in the type information
const char* const* userdataTypes;

Example use:

static const char* kUserdataCompileTypes[] = {"vec2", "color", "mat3", nullptr};
copts.userdataTypes = kUserdataCompileTypes;

Later, you provide a re-mapper to provide type indices you need at runtime using Luau::CodeGen::setUserdataRemapper.
This is needed because bytecode and runtime might be out of sync (runtime optimizing for new types that bytecode wasn't compiled for or the other way around).

This mapping is separate from the actual userdata tags used at runtime, you can still have color have a tag of any value, even different in different VMs.

In this example and if we imagine that kUserdataCompileTypes is in sync between bytecode and runtime, vec2 will have a value of LBC_TYPE_TAGGED_USERDATA_BASE, color will be LBC_TYPE_TAGGED_USERDATA_BASE + 1 and so on.

userdataTypes can also be provided in CodeGen compilation options for better IR/assembly output.