General optimisations for dict lookup/insert performance

Proposal:

There's room for tiny refactorings in the Objects/dictobject.c that may allow speedups, for example via better CPU cache behavior, compiler hints, cheap checks & fast exits for common cases. In my guess-timation, they may bring about upto 10% overall lookup/insert performance gains. That's more of an un-scientific intuition at best right now, but I'm laying some ideas out here:

• compare_unicode_unicode(): can benefit from pointer-equality and branch prediction, and reducing unnecessary function calls

• compare_generic(): can use early rejections on hash-mismatch, avoiding RichCompareBool calls

• unicodekeys_lookup_unicode(): pointer-equality for the common case can precede do_lookup which today is invoked everytime for all cases

• find_empty_slot(): early termination / separate path for first iteration can speed up insertions, especially for lightly-populated dicts

• build_indices_generic / build_indices_unicode (): breaking out the first-probe success case may speed up dict resize operations

I welcome feedback on how to raise this proposal differently, but otherwise I'd like to work on these ideas and quantify them. I feel modern CPUs have deep pipelines and these optimizations may help us avoid some cache-thrashing. These changes are purely performance oriented and don't change functionality / API / ABI and should be thread-safe too.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Bắt đầu trong Objects/dictobject.c và kiểm tra các hàm được nêu tên liên quan đến tra cứu, so sánh, slot trống và xây dựng chỉ mục. Định lượng từng tối ưu hóa được đề xuất bằng các phép đo hiệu năng, đồng thời xác nhận rằng chức năng của dictionary cũng như hành vi của API, ABI và tính an toàn luồng vẫn không thay đổi.