[libcxx-commits] [PATCH] D85420: [libcxx/variant] Introduce `switch`-based mechanism for `std::visit`.

[Michael Park via Phabricator via libcxx-commits]

mpark created this revision.
mpark added reviewers: ldionne, EricWF, mclow.lists.
Herald added subscribers: libcxx-commits, dexonsmith.
Herald added a project: libc++.
Herald added a reviewer: libc++.
mpark requested review of this revision.

This patch introduces mechanism for `std::visit` backed by `switch`.
The dispatching mechansim itself is fully general, and the manual vtable
approach is left in-tact. The benchmarks added shows that for <= 2 variants,
the `switch` approach can be much faster due to better inlining. For 3 variants
and above, it seems to start to perform at par and starts to get worse.

The proposed solution here is to use the `switch`-based mechanism for <= 2
variants and to keep the existing mechanism for 3 variants and above.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D85420

Files:
  libcxx/include/variant

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