Memoize SafetyEvaluator type evaluations - #2976
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SafetyEvaluator re-evaluates the transitive safety of a referenced type at every reference site, so evaluation cost is proportional to the number of paths through the type graph rather than its size. On large, dense conjure definitions this dominates java codegen: a real-world 3.2MB IR spends ~350s in objects generation, with all sampled stacks inside SafetyEvaluator; the same IR generates in ~35s with this cache, with byte-identical output. Results are memoized per TypeName, respecting the recursive-type cycle guard: values computed after hitting the in-progress set are substituted with SAFE and therefore context-dependent, so only cycle-free subtree results and outermost (canonical) evaluations enter the cache.
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Before this PR
SafetyEvaluatorre-evaluates the transitive log-safety of a referenced type at every reference site:FieldSafetyVisitor#visitReferencedescends into the referenced type's full definition each time, so evaluation cost is proportional to the number of paths through the type graph rather than the number of types. On large, dense conjure definitions this dominates codegen wall-clock.Measured on real-world IRs (conjure-java 8.70.0, objects flavor, single run each):
During the slow runs, 20/20 thread-dump samples were inside the
SafetyEvaluatorrecursion. Generated output with the cache is byte-identical on both IRs (318/318 and 2371/2371 files).After this PR
Safety results are memoized per
TypeNamein a cache scoped to theSafetyEvaluatorinstance, shared across the visitor instances it creates. The cache respects the recursive-type cycle guard: values computed after hitting theinProgressset embed the SAFE cycle substitution and are context-dependent, so only results computed from a cycle-free subtree — or at the outermost evaluation of a type, which is canonical by definition — are cached.Two tests added: repeated evaluations on a shared evaluator agree with fresh evaluators, and a
Foo ↔ Barcycle where onlyFoocarries unsafe data verifies thatBar's within-cycle value (SAFE by substitution) is not reused for its standalone evaluation (UNSAFE).Possible downsides?
The cache retains one entry per named type for the lifetime of the
SafetyEvaluator— negligible next to theConjureDefinitionit already holds.SafetyEvaluatorwas not thread-safe before this change (callers construct per-generation instances) and remains so.