[mypyc] feat: further optimize equality check with string literals [1/1] #19883
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BobTheBuidler
commented
Oct 1, 2025
| } | ||
| Py_ssize_t len = PyUnicode_GET_LENGTH(str1); | ||
| if (PyUnicode_GET_LENGTH(str2) != len) | ||
| static char _CPyStr_Equal_NoIdentCheck(PyObject *str1, PyObject *str2, Py_ssize_t str2_length) { |
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I'm not sure if it makes sense to re-duplicate the code and get rid of this helper
how much does an extra C call slow things down? The de-duplicated functions aren't exactly clean even with the helper so I don't really have a strong opinion either way
BobTheBuidler
commented
Oct 1, 2025
mypyc/irbuild/ll_builder.py
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| return self.primitive_op(str_eq, [lhs, rhs], line) | ||
| elif op == "!=": | ||
| eq = self.primitive_op(str_eq, [lhs, rhs], line) | ||
| if is_string_literal(lhs): |
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looking at this again, I think we can just refactor this whole block for "!=" into:
return self.add(ComparisonOp(compare_strings(lhs, rhs, line), self.false(), ComparisonOp.EQ, line)
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BobTheBuidler
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This PR further optimizes string equality checks against literals by getting rid of the PyUnicode_GET_LENGTH call against the literal value, which is not necessary since the value is known at compile-time
I think this optimization will be helpful in cases where the non-literal string DOES match but is actually a subtype of string (actual strings instances that match would be caught by the identity check), or in cases where an exact string does NOT match. But we can also extend this implementation to use c-strings in certain cases where we know at compile-time that the literal value is compact ascii. Actually, maybe I should do that now? Thoughts?