PyStr's comparison, PyBytesInner's, and the specialized CompareOpStr
instruction all answered == and != by taking Ord::cmp of the two buffers
and asking whether the result was Equal. An ordering has to read the
bytes: it memcmps the common prefix even where the lengths already settle
the question. CompareOpStr bypasses the Comparable slot, so it had also
lost the identity shortcut that slot takes, and a string compared with
itself was read end to end.
Add PyComparisonOp::eval_eq, which settles Eq and Ne from an equality test
and leaves an ordering operator to the caller, and answer through it in the
three places: slice equality checks the length first, and CompareOpStr
answers an object compared with itself the way the slot it specializes does.
n=1,000,000, per comparison:
before after
s == s (the very same object) 23.21us 0.16us
s == a string one shorter 24.63us 0.17us
b == bytes one shorter 25.28us 0.20us
ba == bytearray one shorter 27.68us 0.23us
s == an equal, distinct string 23.78us 24.50us
s < an equal string 29.87us 25.07us
Assisted-by: Claude
Jeong, YunWon