Alexander Medvednikov
18f186278c
* transform: reuse proven tree storage at last-use appends * transform: retain recursive tree append proof after type lowering * transform: scope tree factory locals to their block, propagate rejections once A scalar local declared in a nested block stayed in the factory proof's locals after the block ended. A later use of the same name that resolved to a storage-bearing module constant was then accepted as that local, so the caller skipped the append clone and could mutate the constant. Drop a block's bindings (and their use counts) when the block ends. Propagate unsafe callees to their callers through a reverse-edge worklist instead of repeated passes over all dependencies. A caller-first chain of N forwarding wrappers took N passes; each edge is now visited once (4000 wrappers: 29.7G -> 15.3G instructions to compile, identical C).
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Nested storage when appending a local value
The default compiler can avoid recursively cloning nested storage when an array append consumes an immutable local initialized by a proven tree factory or fresh literal in the same block. The append must be the local's only use after initialization. A field path of that local can qualify too, provided it does not traverse a pointer.
The optimization excludes mutable or static locals, aliases initialized from another variable, and locals read before or after the append. It also excludes appends separated from the initializer by loops, closures, deferred work, spawned work, or jumps.
The compiler proves factories before parallel transformation. They must take scalar inputs, read only their parameters and locals, and consume each storage-bearing local at most once. Loops, indirect or foreign calls, and borrowed storage exclude a factory. Recursive factories can qualify, allowing bottom-up tree construction to reuse a finished child's storage.
Calls that can return an argument's storage, literals containing borrowed fields, factories with shared fields, and types with explicit clone methods keep their existing clones. It also preserves the existing cloning of mutable or reused values. Array literals and bulk appends retain their existing storage behavior; this optimization does not make those forms and single-element appends share one copying rule.