[mypyc] Add faster primitive for string equality #19402
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This speeds up self check by ~1.4%. String equality is one of the top five most common primitive function calls in self check. We previously used a string comparison primitive that calculated the relative order of two strings. Usually we only care about equality, which we can do quicker since we can fast path using a length check, for example. I checked the CPython implementation of string equality in 3.9 (lowest supported Python version) and 3.13, and both of them had a fast path based on string object kind, and equality checks overall have the same semantics.
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This speeds up self check by ~1.4%. String equality is one of the top
five most common primitive function calls in self check.
We previously used a string comparison primitive that calculated the
relative order of two strings. Usually we only care about equality,
which we can do quicker since we can fast path using a length check,
for example.
I checked the CPython implementation of string equality in 3.9 (lowest
supported Python version) and 3.13, and both of them had a fast path
based on string object kind, and equality checks overall had the same
semantics.
Current CPython implementation:
https://github.com/python/cpython/blob/main/Objects/stringlib/eq.h
Tests for this were added in #19401.