[libcxx-commits] [libcxx] [libc++][hardening] Enable comparator checks for safe mode too (PR #66458)

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zmodem wrote:

> @nico or @zmodem, do you have any input on whether this would affect Chromium's use of this build mode?

I think @nico has followed this more closely, but IIUC we used to ship the old asserts mode (`_LIBCPP_ENABLE_ASSERTIONS`) and have now switched to the new safe mode (`_LIBCPP_ENABLE_SAFE_MODE`) . It sounds like in that transition we lost these comparator checks in production builds. 

What are the implications of a bad comparator? Could it cause an algorithm to go off the rails in an unsafe way, e.g. returning an out-of-bounds element, or would it "just" lead to returning an incorrect result (or fail to return)?

https://github.com/llvm/llvm-project/pull/66458