forked from OSchip/llvm-project
3c24fae398
Apple Clang in Xcode 14 introduced a new feature for reducing the overhead of objc_msgSend calls by deduplicating the setup calls for each individual selector. This works by clang adding undefined symbols for each selector called in a translation unit, such as `_objc_msgSend$foo` for calling the `foo` method on any `NSObject`. There are 2 different modes for this behavior, the default directly does the setup for `_objc_msgSend` and calls it, and the smaller option does the selector setup, and then calls the standard `_objc_msgSend` stub function. The general overview of how this works is: - Undefined symbols with the given prefix are collected - The suffix of each matching undefined symbol is added as a string to `__objc_methname` - A pointer is added for every method name in the `__objc_selrefs` section - A `got` entry is emitted for `_objc_msgSend` - Stubs are emitting pointing to the synthesized locations Notes: - Both `__objc_methname` and `__objc_selrefs` can also exist from object files, so their contents are merged with our synthesized contents - The compiler emits method names for defined methods, but not for undefined symbols you call, but stubs are used for both - This only implements the default "fast" mode currently just to reduce the diff, I also doubt many folks will care to swap modes - This only implements this for arm64 and x86_64, we don't need to implement this for 32 bit iOS archs, but we should implement it for watchOS archs in a later diff Differential Revision: https://reviews.llvm.org/D128108 |
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| .. | ||
| Arch | ||
| CMakeLists.txt | ||
| ConcatOutputSection.cpp | ||
| ConcatOutputSection.h | ||
| Config.h | ||
| Driver.cpp | ||
| Driver.h | ||
| DriverUtils.cpp | ||
| Dwarf.cpp | ||
| Dwarf.h | ||
| EhFrame.cpp | ||
| EhFrame.h | ||
| ExportTrie.cpp | ||
| ExportTrie.h | ||
| ICF.cpp | ||
| ICF.h | ||
| InputFiles.cpp | ||
| InputFiles.h | ||
| InputSection.cpp | ||
| InputSection.h | ||
| LTO.cpp | ||
| LTO.h | ||
| MachOStructs.h | ||
| MapFile.cpp | ||
| MapFile.h | ||
| MarkLive.cpp | ||
| MarkLive.h | ||
| ObjC.cpp | ||
| ObjC.h | ||
| Options.td | ||
| OutputSection.cpp | ||
| OutputSection.h | ||
| OutputSegment.cpp | ||
| OutputSegment.h | ||
| Relocations.cpp | ||
| Relocations.h | ||
| SectionPriorities.cpp | ||
| SectionPriorities.h | ||
| SymbolTable.cpp | ||
| SymbolTable.h | ||
| Symbols.cpp | ||
| Symbols.h | ||
| SyntheticSections.cpp | ||
| SyntheticSections.h | ||
| Target.cpp | ||
| Target.h | ||
| UnwindInfoSection.cpp | ||
| UnwindInfoSection.h | ||
| Writer.cpp | ||
| Writer.h | ||
| ld64-vs-lld.rst | ||