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Comments to clarify the working of HasTypeFlagsVisitor.

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This commit is contained in:
Nicholas Nethercote 2023-09-13 10:15:03 +10:00
parent df98a74c32
commit 4d8e50b2d3
1 changed files with 8 additions and 8 deletions
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16
compiler/rustc_middle/src/ty/visit.rs
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@ -33,14 +33,6 @@ 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");
@ -485,11 +477,16 @@ impl std::fmt::Debug for HasTypeFlagsVisitor {
}
}
// Note: this visitor traverses values down to the level of
// `Ty`/`Const`/`Predicate`, but not within those types. This is because the
// type flags at the outer layer are enough. So it's faster than it first
// looks, particular for `Ty`/`Predicate` where it's just a field access.
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for HasTypeFlagsVisitor {
type BreakTy = FoundFlags;
#[inline]
fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
// Note: no `super_visit_with` call.
let flags = t.flags();
if flags.intersects(self.flags) {
ControlFlow::Break(FoundFlags)
@ -500,6 +497,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for HasTypeFlagsVisitor {
#[inline]
fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
// Note: no `super_visit_with` call, as usual for `Region`.
let flags = r.type_flags();
if flags.intersects(self.flags) {
ControlFlow::Break(FoundFlags)
@ -510,6 +508,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for HasTypeFlagsVisitor {
#[inline]
fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
// Note: no `super_visit_with` call.
let flags = FlagComputation::for_const(c);
trace!(r.flags=?flags);
if flags.intersects(self.flags) {
@ -521,6 +520,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for HasTypeFlagsVisitor {
#[inline]
fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
// Note: no `super_visit_with` call.
if predicate.flags().intersects(self.flags) {
ControlFlow::Break(FoundFlags)
} else {