tree 6038b79fb1f25f58e5827930561e7d3b6ffc4f2b
parent bf9653d85f05b945ed5e2a79f1c93b16e064e054
author Eric Fiselier <eric@efcs.ca> 1427820859 +0000
committer Eric Fiselier <eric@efcs.ca> 1427820859 +0000

[libcxx] Optimize vectors uninitialized construction of trivial types from an iterator range.

Summary:
In certain cases vector can use memcpy to construct a range of elements at the back of the vector. We currently don't do this resulting in terrible code gen in non-optimized mode and a
very large slowdown compared to libstdc++. 

This patch adds a `__construct_forward_range(Allocator, Iter, Iter, _Ptr&)` and `__construct_forward_range(Allocator, Tp*, Tp*, Tp*&)` functions to `allocator_traits` which act similarly to the existing `__construct_forward(...)` functions.

This patch also changes vectors `__construct_at_end(Iter, Iter)` to be `__construct_at_end(Iter, Iter, SizeType)` where SizeType is the size of the range. `__construct_at_end(Iter, Iter, SizeType)` now calls `allocator_traits<Tp>::__construct_forward_range(...)`. 

This patch is based off the design of `__swap_out_circular_buffer(...)` which uses `allocator_traits<Tp>::__construct_forward(...)`.

On my machine this code performs 4x better than the current implementation when tested against `std::vector<int>`. 


Reviewers: howard.hinnant, titus, kcc, mclow.lists

Reviewed By: mclow.lists

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D8109

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@233711 91177308-0d34-0410-b5e6-96231b3b80d8