When we have a debug map we have an executable with a bunch of STAB symbols and each source file has a N_SO symbol which scopes a bunch of symbols inside of it. We can use this to our advantage here when looking for the complete definition of an objective C class by looking for a symbol whose name matches the class name and whose type is eSymbolTypeObjCClass. If we find one, that symbol will be contained within a N_SO symbol. This symbol gets turned into a symbol whose type is eSymbolTypeSourceFile and that symbol will contain the eSymbolTypeObjCClass which helps us to locate the correct .o file and allows us to only look in that file.
To further accelerate things, if we are looking for the implementation, we can avoid looking at all .o files if we don't find a matching symbol because we have a debug map, which means the objective C symbol for the class can't have been stripped, so we can safely not search all remaining .o files. This will save us lots of time when trying to look for "NSObject" and any other AppKit and Foundation classes that we never have implementation definitions for.
<rdar://problem/19234225>
llvm-svn: 230562
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