Commits on Sep 4, 2026

1. Cache IL method parameter attributes during overload resolution (#20353) …

   MethInfo.GetParamAttribs rebuilt the full per-parameter attribute list
   (custom-attr decoding, well-known-attr probes, OptionalArgInfo) from IL
   metadata on every call and was never cached. On an overload-heavy compile
   it was called 2.17M times against only 137 distinct underlying methods.
   
   Memoize the decode with the existing MemoizationTable, held per compilation
   via WeakMap.getOrCreate keyed on the ImportMap. The key is the method's
   physical ILMethodDef plus extension-member use (the C#-style extension view
   drops the object argument from ParamMetadata, so the two views must not share
   an entry); canMemoize restricts caching to monomorphic declaring types (an
   optional arg's default can otherwise depend on the instantiation), matching
   InfoReader's monomorphic-only caches.
   
   Add a regression test covering an IL extension method used with both instance
   and static call syntax, which shares one ILMethodDef across both views.
   
   Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

   

   T-Gro and Copilot authored Sep 4, 2026
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2. Avoid per-call closure allocation in type-hierarchy traversal (#20384) …

   FoldHierarchyOfTypeAux runs on a hot path (InfoReader member/property/field
   lookup and type inference). Its inner 'let rec loop' was handed to
   List.foldBack / Option.foldBack / List.exists as a partial application, so a
   fresh closure was allocated on every traversal.
   
   Add a ListInline module (illib.fs) with exists / foldBack whose function
   argument is inlined at the call site via InlineIfLambda, so the closure never
   materializes. foldBack folds lists up to length five directly (no allocation)
   and only copies to an array for longer lists, so it stays stack-safe. Length
   five is measured: over a real compile GetImmediateInterfacesOfType returns
   <=5 elements ~96% of the time (81% are empty), so short interface lists
   allocate nothing at all.
   
   At the call sites the top-level 'typeEquiv g ty' stays partially applied (the
   optimizer fuses it after inlining), but the local 'loop' is passed as a lambda
   so InlineIfLambda inlines it rather than allocating it as a closure.
   
   Fold order is unchanged, so visit order, dedup and the ndeep>100 error are
   preserved; compiler output is byte-identical under --deterministic+.
   
   Co-authored-by: perf-bundle <perf@local>
   Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
   Co-authored-by: Copilot <copilot@github.com>
   Copilot-Session: c6610fae-a96e-4421-a920-e73de4fc94dc

   

   4 people authored Sep 4, 2026
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3. Remove always-on language feature flag OverloadsForCustomOperations (#… …

   …20427)
   
   Flatten the permanently-enabled LanguageFeature.OverloadsForCustomOperations:
   delete the DU case, features-map entry, GetFeatureString arm and FSComp string,
   regenerate xlf, and collapse every enforcement gate to its always-on path.
   Drops the now-dead customOperationMethodsIndexedByMethodName field and its
   overload-rejection branch.
   
   Co-authored-by: Copilot <copilot@github.com>
   Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

   

   3 people authored Sep 4, 2026
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4. Remove always-on ExtendedFixedBindings language feature flag (#20429) …

   The ExtendedFixedBindings feature shipped in F# 8.0, the minimum accepted
   --langversion, so its flag can never be disabled and is dead configuration.
   Remove the LanguageFeature case, its feature-map entry, GetFeatureString arm,
   and FSComp resource string, and collapse both guarded paths in
   TcAndBuildFixedExpr to their always-on behaviour. Regenerated xlf files.
   
   Fixes #20194
   
   Co-authored-by: Copilot <copilot@github.com>
   Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

   

   3 people authored Sep 4, 2026
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5. Remove the ArithmeticInLiterals language feature flag (#20430) …

   * Collapse ArithmeticInLiterals enforcement site
   
   Remove the always-true suppressLangFeatureCheck threading and checkFeature helper from EvalAttribArgExpr, and delete the now-unused SuppressLanguageFeatureCheck type.
   
   Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
   
   * Remove the ArithmeticInLiterals language feature flag and its resources
   
   The feature shipped in F# 8.0 and the minimum selectable --langversion is now
   8.0, so the flag is permanently enabled dead configuration (#20176).
   Delete the LanguageFeature DU case, its features-map entry and GetFeatureString
   arm, the featureArithmeticInLiterals resource string, and regenerate the xlf
   translation files.
   
   Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
   
   ---------
   
   Co-authored-by: Copilot <copilot@github.com>
   Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

   

   3 people authored Sep 4, 2026
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