Use multi-key tree search for {map, set}::{count, equal_range}

Patch from ngolovliov@gmail.com
Reviewed as: https://reviews.llvm.org/D42344

As described in llvm.org/PR30959, the current
implementation of std::{map, key}::{count, equal_range} in libcxx is
non-conforming. Quoting the C++14 standard [associative.reqmts]p3

> The phrase “equivalence of keys” means the equivalence relation imposed by
> the comparison and not the operator== on keys. That is, two keys k1 and k2 are
> considered to be equivalent if for the comparison object comp,
> comp(k1, k2) == false && comp(k2, k1) == false.

In the same section, the requirements table states the following:

> a.equal_range(k) equivalent to make_pair(a.lower_bound(k), a.upper_bound(k))
> a.count(k) returns the number of elements with key equivalent to k

The behaviour of libstdc++ seems to conform to the standard here.

llvm-svn: 324799

0 files changed, 0 insertions, 0 deletions