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Narrowing analysis builds a map from each affected place to the constraint contributed by an expression or pattern. These results are cached, but once construction finishes we only read them; retaining each result as an FxHashMap therefore keeps hash-table storage that the cached value no longer needs.
This keeps FxHashMap in NarrowingConstraintsBuilder for efficient construction, then converts each completed result to a FrozenMap, whose sorted boxed slice provides binary-search lookup without retaining hash-table capacity.
In the memory report, this reduced retained memory for all_narrowing_constraints_for_expression by 40.1–45.6% across Flake8, Trio, Sphinx, and Prefect, reducing total retained memory by 0.2–1.1%. The typing-conformance and ecosystem comparisons reported no diagnostic changes.
Current numbers
The percentage of diagnostics emitted that were expected errors held steady at 94.36%. The percentage of expected errors that received a diagnostic held steady at 88.82%. The number of fully passing files held steady at 93/134.
charliermarsh
changed the title
[ty] Reduce memory for narrowing constraints
[ty] Use compact frozen representation for narrowing constraints
Jun 14, 2026
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performancePotential performance improvementtyMulti-file analysis & type inference
2 participants
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Summary
Narrowing analysis builds a map from each affected place to the constraint contributed by an expression or pattern. These results are cached, but once construction finishes we only read them; retaining each result as an
FxHashMaptherefore keeps hash-table storage that the cached value no longer needs.This keeps
FxHashMapinNarrowingConstraintsBuilderfor efficient construction, then converts each completed result to aFrozenMap, whose sorted boxed slice provides binary-search lookup without retaining hash-table capacity.In the memory report, this reduced retained memory for
all_narrowing_constraints_for_expressionby 40.1–45.6% across Flake8, Trio, Sphinx, and Prefect, reducing total retained memory by 0.2–1.1%. The typing-conformance and ecosystem comparisons reported no diagnostic changes.