[PATCH] D102583: -fno-semantic-interposition: Don't set dso_local on GlobalVariable

[Fangrui Song via Phabricator via cfe-commits]

MaskRay created this revision.
MaskRay added reviewers: foutrelis, rnk, serge-sans-paille, xbolva00.
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`clang -fpic -fno-semantic-interposition` may set dso_local on variables for -fpic.

GCC folks consider there are 'address interposition' and 'semantic interposition',
and 'disabling semantic interposition' can optimize function calls but
cannot change variable references to use local aliases
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100483).

This patch removes dso_local for variables in
`clang -fpic -fno-semantic-interposition` mode so that the built shared objects can
work with copy relocations.

Example:

  // a.c
  int var;
  int *addr() { return var; }
  
  // old: cannot be interposed
  movslq  .Lvar$local(%rip), %rax
  // new: can be interposed
  movq    var at GOTPCREL(%rip), %rax
  movslq  (%rax), %rax

The local alias lowering for `GlobalVariable`s is kept in case there is a
future option allowing local aliases.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D102583

Files:
  clang/lib/CodeGen/CodeGenModule.cpp
  clang/test/CodeGen/SystemZ/builtins-systemz-zvector-constrained.c
  clang/test/CodeGen/attr-weakref2.c
  clang/test/CodeGen/semantic-interposition.c
  clang/test/CodeGenCUDA/device-stub.cu
  clang/test/CodeGenCUDA/device-var-linkage.cu
  clang/test/CodeGenCUDA/managed-var.cu
  clang/test/CodeGenCUDA/static-device-var-rdc.cu
  clang/test/OpenMP/declare_target_only_one_side_compilation.cpp

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