[clang] [llvm] [clang][codegen] Prevent inline weak static locals from being placed in .rodata if not formally constant-initialized (PR #226645)

[Eli Friedman via llvm-commits]

https://github.com/efriedma-quic commented:

Missing testcase.  And somehow you mixed in your FROUND patch.

There's a FIXME related to this in CodeGenFunction::EmitVarDecl.

Skipping the guarded init is not threadsafe: if one thread accesses the variable while another thread is performing init, that's a race, even if the stored values are actually equal.

On targets that support comdats, we might be able to emit a guard variable in initialized form; that way, we wouldn't write to the variable even if it isn't constant-folded in some translation unit.

https://github.com/llvm/llvm-project/pull/226645