Rollup merge of #52859 - ljedrz:smallvec_true_extend, r=Mark-Simulacrum

Use Vec::extend in SmallVec::extend when applicable

As calculated in #52738, `Vec::extend` is much faster than `push`ing to it in a loop. We can take advantage of this method in `SmallVec` too - at least in cases when its underlying object is an `AccumulateVec::Heap`.

~~This approach also accidentally improves the `push` loop of the `AccumulateVec::Array` variant, because it doesn't utilize `SmallVec::push` which performs `self.reserve(1)` with every iteration; this is unnecessary, because we're already reserving the whole space we will be needing by performing `self.reserve(iter.size_hint().0)` at the beginning.~~

0 files changed, 0 insertions, 0 deletions