Improved performance and arguably simpler code for dictionaries by changing the keys layout

Current layout

Currently the _dictkeysobject struct is laid out like this:

ptr ---->  +--------------+
           |     header   |
           +--------------+
           |    indices   |
           +--------------+
           |     keys     |
           +--------------+

which requires some relatively expensive calculation to find the start of the keys, as the indices are not only variable in number, but variable in size also.

Proposed layout

If instead it is laid out as follows:

           +--------------+
           |    indices   |
ptr ---->  +--------------+
           |     header   |
           +--------------+
           |     keys     |
           +--------------+

and the indices laid from highest to lowest with 0 just before ptr, finding the start of the keys is as simple as ptr->keys . Accessing an index is no slower, and the code barely any more complex.

Linked PRs

• gh-145097
• gh-150640

首先查看提議的 _dictkeysobject 配置以及連結的 PR gh-145097 和 gh-150640，因為工作已移至那裡。比較目前和提議的 index、header 與 keys 排列；要完成這項工作，需要實作新配置，並透過效能或正確性驗證來支援它。