[PATCH] D105461: [Support] CommandLine.cpp - Fix thread race condition in addOption

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.

Adding/deleting options is typically done in a separate initialization stage, and just once.
It is easier to ensure a single thread by application but pretty hard by the library.

https://lists.llvm.org/pipermail/llvm-dev/2018-October/127039.html ([RFC] Enable thread specific cl::opt values for multi-threaded support) is a related previous thread.
The patch D53424 <https://reviews.llvm.org/D53424> was abandoned. Folks had concerns like these:

> @mehdi_amini : The consensus at the time was that the cl::opt were only here for debugging / overriding default, but should not be the way any user of "LLVM as a library" set the options.
> zturner: I can't deny that it solves a practical problem, but I'm mildly concerned that this is making a bad problem even worse.

cl::opt (and its friends like cl::list) does have some problems, but we need to figure out the needs and look at the big picture.


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https://reviews.llvm.org/D105461