[MicroPerf] Reduce Detuple usage-analysis allocation with a mutable Dictionary - #20351
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Detuple.GlobalUsageAnalysis threads a Uses map (Zmap<Val,_>) through a per-file fold; logUse does tryFind+add on every value occurrence, so a value used K times re-inserts at the same key K times, each path-copying the whole balanced tree. This is the largest MapTree.mk allocation source in the optimizer. A per-file mutable Dictionary (BagAdd) removes the churn; Uses is only grown during the sequential per-file fold and read back by point lookup or one enumeration sorted by (valSourceOrderKey, Stamp), so its iteration order never reaches output. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 69e8646f-b2d9-4852-af5c-5f96dc2d36a3
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Detuple
GlobalUsageAnalysis.Uses:Zmap<Val,_>→ per-file mutableDictionary.logUsere-adds the same key on every occurrence; each add path-copied the whole AVL tree before.65k-LOC compile, net11.0 Release:
MapTreeNode<Val, _ list>(this map): 634 MB → 0