[ty] Shrink reachability constraints#19410
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MichaReiser merged 1 commit intomainfrom Jul 18, 2025
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This is a follow-on to #19410 that further reduces the memory usage of our reachability constraints. When finishing the building of a use-def map, we walk through all of the "final" states and mark only those reachability constraints as "used". We then throw away the interior TDD nodes of any reachability constraints that weren't marked as used. (This helps because we build up quite a few intermediate TDD nodes when constructing complex reachability constraints. These nodes can never be accessed if they were _only_ used as an intermediate TDD node. The marking step ensures that we keep any nodes that ended up being referred to in some accessible use-def map state.)
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Summary
Shrink the reachability constraints before storing them in the
UseDefMap.This reduces memory usage on a large project for UseDefMaps by about 400mb or around 8%
Test Plan
cargo test