Mingming Liu
6faf17b762
When `-import-declaration` option is enabled, declaration import is supported for functions. https://github.com/llvm/llvm-project/pull/88024 has the context for this option. This patch supports declaration import for global variables in distributed ThinLTO. The motivating use case is to propagate `dso_local` attribute of global variables across modules, to optimize global variable access when a binary is built with `-fno-direct-access-external-data`. * With `-fdirect-access-external-data`, non thread-local global variables will [have `dso_local` attributes](https://github.com/llvm/llvm-project/blob/fe3c23b439b9a2d00442d9bc6a4ca86f73066a3d/clang/lib/CodeGen/CodeGenModule.cpp#L1730-L1746). This optimizes the global variable access as shown by https://gcc.godbolt.org/z/vMzWcKdh3