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Assure everyone that has_type_flags is fast #110465

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Apr 18, 2023
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Assure everyone that has_type_flags is fast #110465

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8 changes: 8 additions & 0 deletions compiler/rustc_middle/src/ty/visit.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,14 @@ pub trait TypeVisitableExt<'tcx>: TypeVisitable<TyCtxt<'tcx>> {
}

fn has_type_flags(&self, flags: TypeFlags) -> bool {
// N.B. Even though this uses a visitor, the visitor does not actually
// recurse through the whole `TypeVisitable` implementor type.
//
// Instead it stops on the first "level", visiting types, regions,
// consts and predicates just fetches their type flags.
//
// Thus this is a lot faster than it might seem and should be
// optimized to a simple field access.
let res =
self.visit_with(&mut HasTypeFlagsVisitor { flags }).break_value() == Some(FoundFlags);
trace!(?self, ?flags, ?res, "has_type_flags");
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