[mypyc] feat: further optimize equality check with string literals [1/1] #19883
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BobTheBuidler
commented
Oct 1, 2025
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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BobTheBuidler
commented
Oct 13, 2025
| Py_ssize_t str1_length = PyUnicode_GET_LENGTH(str1); | ||
| if (str1_length != str2_length) | ||
| return 0; | ||
| int kind = PyUnicode_KIND(str1); |
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Can we deduce a literal's kind at compile time as well?
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Looks like there isn't a good way to reliably do this
JukkaL
reviewed
Oct 14, 2025
| if is_string_literal(lhs): | ||
| if is_string_literal(rhs): | ||
| # we can optimize out the check entirely in some constant-folded cases | ||
| return self.true() if lhs.value == rhs.value else self.false() |
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Add a irbuild test cases for constant folding.
| return self.true() if lhs.value == rhs.value else self.false() | ||
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| # if lhs argument is string literal, switch sides to match specializer C api | ||
| lhs, rhs = rhs, lhs |
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Add irbuild test case for string literal as the lhs.
JukkaL
approved these changes
Oct 14, 2025
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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?