[PATCH] D71219: Fix conflict value for metadata "Objective-C Garbage Collection" in the mix of swift and Objective-C bitcode

[John McCall via Phabricator via llvm-commits]

rjmccall added a comment.

In D71219#1892512 <https://reviews.llvm.org/D71219#1892512>, @steven_wu wrote:

> > I agree with all of this except that I'm not sure there's any situation where ObjC and Swift translation units should be disagreeing about the ObjC-specific parts of the OBJC_IMAGE_INFO.
>
> The lower bits of the flag is for objc info and here is the definition:
>  #define OBJC_IMAGE_SUPPORTS_GC						(1<<1)
>  #define OBJC_IMAGE_REQUIRES_GC						(1<<2)
>  #define OBJC_IMAGE_OPTIMIZED_BY_DYLD				(1<<3)
>  #define OBJC_IMAGE_SUPPORTS_COMPACTION				(1<<4)
>  #define OBJC_IMAGE_IS_SIMULATED						(1<<5)
>  #define OBJC_IMAGE_HAS_CATEGORY_CLASS_PROPERTIES	(1<<6)
>
> The 0x40 bit is actually OBJC_IMAGE_HAS_CATEGORY_CLASS_PROPERTIES, which probably can differ from translation unit to translation unit even within ObjC. Some of the other bits should not be different. That is why I say you can break the bits down even more if needed.


Clang seems to set it unconditionally.  Presumably it just controls whether category descriptors have a class-properties field; offhand, I don't know why that would need to be set globally.


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  https://reviews.llvm.org/D71219/new/

https://reviews.llvm.org/D71219