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[libc++] Make _LIBCPP_ASSUME usable when it is appropriate #91801

Merged
merged 2 commits into from
Sep 17, 2024
Merged

[libc++] Make _LIBCPP_ASSUME usable when it is appropriate #91801

merged 2 commits into from
Sep 17, 2024

Commits on Sep 17, 2024

  1. Make _LIBCPP_ASSUME usable when it is appropriate 

    libc++ turned off _LIBCPP_ASSUME because turning every debug assert into
__builtin_assume tripped
https://discourse.llvm.org/t/llvm-assume-blocks-optimization/71609

However, this means we can't use _LIBCPP_ASSUME when there is a clear
optimization intent. See
llvm#78929 (comment)
for discussion of a place where _LIBCPP_ASSUME would be valuable.

Go ahead and fix this now, and adjust the comments. I don't think we
want _LIBCPP_ASSUME in disabled asserts anyway, at least not in any of
the hardened modes. This PR should have no impact on libc++ right
now, since _LIBCPP_ASSUME is currently never called standalone, but I
figure I can do this as a standalone PR since it's pretty
straightforward.
    @davidben
    davidben committed Sep 17, 2024
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  2. Remove comment

    @davidben
    davidben committed Sep 17, 2024
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