[PATCH] D49317: Move __construct_forward (etc.) out of std::allocator_traits.

[Louis Dionne via Phabricator via cfe-commits]

ldionne requested changes to this revision.
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After thinking about this for some more, I'm not sure this patch is worth doing in its current form. The minimal patch for allowing specializations of `allocator_traits` would be:

1. move the `__move_construct_forward` & friends functions from `allocator_traits` to private static member functions of `std::vector` (because they're only used in `std::vector` right now).
2. keep the SFINAE on the allocator and avoid encoding any `memcpy` decision at the call site.

However, an even better alternative would be to look into adding an overload to `uninitialized_move` & friends that takes an allocator. We could then be clever in how this is implemented. The major benefit I see here is that there would be one common code path to optimize, as opposed to a `std::vector`-specific code path.

Given the small benefit provided by this patch, my opinion is that it's not worth moving forward with it as-is. However, I believe either of the two alternatives suggested above would be welcome, with a preference for the more comprehensive second approach, which requires a paper.

Arthur, what do you think? Do you think the second approach can work?


Repository:
  rCXX libc++

https://reviews.llvm.org/D49317