rnk added a comment. I think the main user-facing feature here to think about is `__attribute__((used))`. I see that it's currently listed as Undocumented. We should fix that while we're rehashing how this is supposed to work, and clarify what it does on each platform. As I understand it, `__attribute__((used))` globals will be GC roots on Mac/Win, but not ELF targets. The mismatch in behavior is unfortunate, but it matches the dominant system compilers on those platforms.
Here are all the existing addUsedGlobal call sites: https://reviews.llvm.org/P8257 I categorize them as: - ObjC/blocks: this wants GC root semantics, since ObjC mainly runs on Mac. - MS C++ ABI stuff: wants GC root semantics, no change - OpenMP: unsure, but GC root semantics probably don't hurt - CodeGenModule: affected in this patch to *not* use GC root semantics so that `__attribute__((used))` behavior remains the same on ELF, plus two other minor use cases that don't want GC semantics - Coverage: Probably want GC root semantics - CGExpr.cpp: refers to LTO, wants GC root - CGDeclCXX.cpp: one is MS ABI specific, so yes GC root, one is some other C++ init functionality, which should form GC roots (C++ initializers can have side effects and must run) - CGDecl.cpp: Changed in this patch for `__attribute__((used))` So, looks good, I think you spotted all the things that should change. ================ Comment at: clang/lib/CodeGen/CodeGenModule.cpp:1829 VD->getStorageDuration() == SD_Static) - addUsedGlobal(GV); + addUsedOrCompilerUsedGlobal(GV); } ---------------- Should -fkeep-static-consts be getting GC root semantics on Mac/Win? We can leave this as behavior preserving, I don't think -fkeep-static-consts is a very important feature. ================ Comment at: clang/lib/CodeGen/CodeGenModule.cpp:5924 if (Val && !getModule().getNamedValue(Name->getName())) - addUsedGlobal(llvm::GlobalAlias::create(Name->getName(), Val)); + addUsedOrCompilerUsedGlobal( + llvm::GlobalAlias::create(Name->getName(), Val)); ---------------- This probably doesn't need GC semantics, and should always used llvm.compiler.used on all platforms. This alias will be internal, this factory function it takes the linkage from the aliasee. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D97446/new/ https://reviews.llvm.org/D97446 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
