Mingming Liu 6faf17b762 [ThinLTO]Supports declaration import for global variables in distributed ThinLTO (#117616) ...

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](fe3c23b439/clang/lib/CodeGen/CodeGenModule.cpp (L1730-L1746)).
This optimizes the global variable access as shown by
https://gcc.godbolt.org/z/vMzWcKdh3

2024-12-02 16:15:52 -08:00

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