[all-commits] [llvm/llvm-project] adeae9: [libc++] Make _LIBCPP_ASSUME usable when it is app...

[David Benjamin via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: adeae925dcd7db0d49256f687c66a662d6604128
      https://github.com/llvm/llvm-project/commit/adeae925dcd7db0d49256f687c66a662d6604128
  Author: David Benjamin <davidben at google.com>
  Date:   2024-09-17 (Tue, 17 Sep 2024)

  Changed paths:
    M libcxx/include/__assert

  Log Message:
  -----------
  [libc++] Make _LIBCPP_ASSUME usable when it is appropriate (#91801)

libc++ turned off _LIBCPP_ASSUME because turning every debug assert into
__builtin_assume tripped [1]. However, this means we can't use _LIBCPP_ASSUME
when there is a clear optimization intent. See [2] for discussion of a place 
where _LIBCPP_ASSUME would be valuable.

This patch fixes this by not undefining the definition of _LIBCPP_ASSUME and
making sure that we don't attempt to `_LIBCPP_ASSSUME` every assertion in
the library.

[1]: https://discourse.llvm.org/t/llvm-assume-blocks-optimization/71609
[2]: https://github.com/llvm/llvm-project/pull/78929#issuecomment-1936582711



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