[swift-dev] Moving generic metadata pattern cache out-of-line

Joe Groff jgroff at apple.com
Tue Jan 26 18:39:56 CST 2016

We currently emit generic metadata templates with space statically allocated inline for the runtime to emplace its metadata cache. This would prevent generic metadata patterns from being mapped read-only if we eliminate the relocations from the rest of the compiler-emitted structure. Now that we're putting an accessor function in front of the raw metadata runtime calls, I think we could allocate this space separately in the data segment and pass it as a separate parameter to swift_getGenericMetadata alongside the pattern pointer. Any objections?

On a similar note, we also emit a one-word invasive uniquing cache in nonuniqued metadata objects, used for things like metadata for imported C types where we don't have a single Swift TU to associate with the type. Could this also be moved out-of-line?


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