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perf(python): index importlib alias rebind checks instead of rescanning - #848
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importlibAliases checked every distinct alias against every statement in the file, building regexes per alias and statement, so the cost grew with aliases times statements. Repeated `import importlib as ilN` took 102ms at 100 aliases, 1.5s at 500 and 5.3s at 1000 (about 26KB, far under the size cap). A statement can only rebind a name it mentions, so index identifiers to statements once and check each alias against only the statements that contain it. The same checks run on those statements, so which aliases are dropped is unchanged. 1000 aliases now take about 20ms. The new test fails before this change (5.8s against a 1.5s budget) and also checks that a rebound alias is still dropped. Fixes #847
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The importlib alias check compared every distinct alias against every statement in the file, building regexes each time, so the cost grew with aliases times statements. A file with many
import importlib as ilNlines took 102ms at 100 aliases, 1.5s at 500 and 5.3s at 1000, about 26KB and well under the size cap.I now index identifiers to statements once, and each alias only checks the statements that mention it. The same checks run on those statements, so which aliases get dropped is unchanged. 1000 aliases take about 20ms now.
The new test builds 1000 aliases, checks the right dynamic imports are credited and a rebound alias is still dropped, and has a 1.5s budget. On main it took 8.5s on my run and failed; with the change the Python adapter suite passes, 274/274.
Fixes #847.