[swift-dev] Code that uses the is-Swift metadata bit

Greg Parker gparker at apple.com
Fri Sep 29 20:28:04 CDT 2017

I'm looking for all code that uses the is-Swift bit in class metadata.

Uses that I know of:
* Compiler-generated class metadata (addClassDataPointer() in GenMeta.cpp)
* Runtime metadata checks (isTypeMetadata() inMetadata.h)
* Stuff in lldb and other debugging tools
* Stuff in the Objective-C runtime

Is there any other code that reads or writes this bit? Does compiler-generated code ever do so? Or maybe something in reflection that I haven't found?

(Backstory: The forthcoming stable Swift ABI will need to use a different bit to avoid collisions with existing pre-stable-ABI Swift apps. We will need to find all of these locations and change them.)

Greg Parker     gparker at apple.com <mailto:gparker at apple.com>     Runtime Wrangler

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