hasattr() performance is bad on a slot that has no value

Bug report

Bug description:

Compare these two timeit invocations:

$ python3.14 -m timeit -s 'class Test: pass' -s 't = Test()' 'hasattr(t,"x")'
10000000 loops, best of 5: 33.5 nsec per loop
$ python3.14 -m timeit -s 'class Test: __slots__ = ("x",)' -s 't = Test()' 'hasattr(t,"x")'
1000000 loops, best of 5: 241 nsec per loop

Observe that in the case where Test.x is a slot, hasattr takes 241 ns to return False while it only takes 33.5 ns when there is no Test.x slot.

Peter Bierma advised me to file an issue when I asked about this in Discourse.

CPython versions tested on:

3.14, 3.13, 3.12

Operating systems tested on:

Linux

首先复现 issue 中的两个 Python 3.14 timeit 命令，并比较缺少属性的情况与未赋值 slot 的情况。跟踪导致差异的 slot 查找和 hasattr 路径。完成的标准是未赋值 slot 的情况得到可测量的改进，同时不改变 hasattr 的 False 结果或现有行为。