[PATCH] D74751: [ThinLTO] Drop dso_local if a GlobalVariable satisfies isDeclarationForLinker()

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: evgeny777, pcc, tejohnson.
Herald added subscribers: llvm-commits, dang, arphaman, dexonsmith, steven_wu, hiraditya, inglorion.
Herald added a project: LLVM.

dso_local leads to direct access even if the definition is not within this compilation unit (it is
still in the same linkage unit). On ELF, such a relocation (e.g. R_X86_64_PC32) referencing a
STB_GLOBAL STV_DEFAULT object can cause a linker error in a -shared link.

If the linkage is changed to available_externally, the dso_local flag should be dropped, so that no
direct access will be generated.

The current behavior is benign, because -fpic does not assume dso_local
(clang/lib/CodeGen/CodeGenModule.cpp:shouldAssumeDSOLocal).
If we do that for -fno-semantic-interposition, there will be an
R_X86_64_PC32 linker error without this patch.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D74751

Files:
  llvm/include/llvm/Transforms/IPO/FunctionImport.h
  llvm/include/llvm/Transforms/Utils/FunctionImportUtils.h
  llvm/lib/LTO/LTOBackend.cpp
  llvm/lib/LTO/ThinLTOCodeGenerator.cpp
  llvm/lib/Transforms/IPO/FunctionImport.cpp
  llvm/lib/Transforms/Utils/FunctionImportUtils.cpp
  llvm/test/LTO/Resolution/X86/local-def-dllimport.ll
  llvm/test/ThinLTO/X86/funcimport_alwaysinline.ll
  llvm/test/ThinLTO/X86/index-const-prop-alias.ll
  llvm/test/ThinLTO/X86/index-const-prop-comdat.ll
  llvm/test/ThinLTO/X86/index-const-prop-dead.ll
  llvm/test/ThinLTO/X86/index-const-prop-full-lto.ll
  llvm/test/ThinLTO/X86/index-const-prop-gvref-pie.ll
  llvm/test/ThinLTO/X86/index-const-prop-gvref.ll
  llvm/test/ThinLTO/X86/index-const-prop-ldst.ll
  llvm/test/ThinLTO/X86/index-const-prop-linkage.ll
  llvm/test/ThinLTO/X86/index-const-prop2.ll
  llvm/tools/llvm-link/llvm-link.cpp

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