[MicroPerf] Inline the free-variable typar foldBacks - #20385
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accFreeInTyparConstraints and accFreeInTypars fold accFreeInTyparConstraint / accFreeTyparRef over a typar's constraint and typar lists during free-variable computation, one of the hottest traversals in the compiler. Passing those top-level functions to List.foldBack allocated a partial- application closure per call, over typically tiny (often empty) lists where the closure is the entire cost. Switch both folds to ListInline.foldBack (added in the parent change), whose InlineIfLambda folder inlines the top-level partial application, so no closure is allocated. Fold order is unchanged; compiler output is byte-identical under --deterministic+. Measured (dotnet-trace gc-verbose, 6 self-compiles of a 120-file corpus): accFreeInTyparConstraints closure 147.8 MB -> 0, accFreeTyparRef closure 238.8 MB -> 0. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: c6610fae-a96e-4421-a920-e73de4fc94dc
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Stacked on #20384 — depends on its
ListInlinemodule; the base auto-retargets tomainwhen #20384 merges.Free-variable computation is one of the hottest compiler traversals.
accFreeInTyparConstraintsandaccFreeInTyparsfold the top-levelaccFreeInTyparConstraint/accFreeTyparRefover a typar's constraint and typar lists — usually tiny or empty. Passed toList.foldBack, each call allocated a partial-application closure; sincefoldBackbuilds no result list, that closure is the entire allocation.ListInline.foldBackinlines the folder (InlineIfLambda) and the top-level partial application fuses, so nothing is allocated.Closures eliminated (dotnet-trace
gc-verbose, 6 self-compiles of a 120-file corpus):accFreeInTyparConstraint opts(foldBack)accFreeTyparRef opts(foldBack)Fold order is unchanged, so free-variable results are identical; compiler output is byte-identical under
--deterministic+(SHA-256 match vs base), and tests pass.