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Use a visitor that could be reused by opaque type capture check later
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163 changes: 163 additions & 0 deletions
163
compiler/rustc_infer/src/infer/outlives/for_liveness.rs
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,163 @@ | ||
| use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor}; | ||
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| use std::ops::ControlFlow; | ||
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| use crate::infer::outlives::test_type_match; | ||
| use crate::infer::region_constraints::VerifyIfEq; | ||
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| /// Visits free regions in the type that are relevant for liveness computation. | ||
| /// These regions are passed to `OP`. | ||
| /// | ||
| /// Specifically, we visit all of the regions of types recursively, except: | ||
| /// | ||
| /// 1. If the type is an alias, we look at the outlives bounds in the param-env | ||
| /// and alias's item bounds. If there is a unique outlives bound, then visit | ||
| /// that instead. If there is not a unique but there is a `'static` outlives | ||
| /// bound, then don't visit anything. Otherwise, walk through the opaque's | ||
| /// regions structurally. | ||
| /// | ||
| /// 2. If the type is a closure, only walk through the signature of the closure | ||
| /// and the upvars. Similarly, if the type is a generator, walk through the | ||
| /// three "signature" types (yield/resume/return) and its upvars. All generator | ||
| /// interior regions are bound regions, so ther is no need to walk through | ||
| /// that type. | ||
| /// | ||
| /// # How does this differ from other region visitors? | ||
| /// | ||
| /// We cannot use `push_outlives_components` because regions in closure | ||
| /// signatures are not included in their outlives components. We need to | ||
| /// ensure all regions outlive the given bound so that we don't end up with, | ||
| /// say, `ReVar` appearing in a return type and causing ICEs when other | ||
| /// functions end up with region constraints involving regions from other | ||
| /// functions. | ||
| /// | ||
| /// We also cannot use `for_each_free_region` because for closures it includes | ||
| /// the regions parameters from the enclosing item, which we know are always | ||
| /// universal, so we don't particularly care about since they're not relevant | ||
| /// for opaque type captures or computing liveness. | ||
| pub struct FreeRegionsVisitor<'tcx, OP: FnMut(ty::Region<'tcx>)> { | ||
| pub tcx: TyCtxt<'tcx>, | ||
| pub param_env: ty::ParamEnv<'tcx>, | ||
| pub op: OP, | ||
| } | ||
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| impl<'tcx, OP> TypeVisitor<TyCtxt<'tcx>> for FreeRegionsVisitor<'tcx, OP> | ||
| where | ||
| OP: FnMut(ty::Region<'tcx>), | ||
| { | ||
| fn visit_binder<T: TypeVisitable<TyCtxt<'tcx>>>( | ||
| &mut self, | ||
| t: &ty::Binder<'tcx, T>, | ||
| ) -> ControlFlow<Self::BreakTy> { | ||
| t.super_visit_with(self); | ||
| ControlFlow::Continue(()) | ||
| } | ||
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| fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> { | ||
| match *r { | ||
| // ignore bound regions, keep visiting | ||
| ty::ReLateBound(_, _) => ControlFlow::Continue(()), | ||
| _ => { | ||
| (self.op)(r); | ||
| ControlFlow::Continue(()) | ||
| } | ||
| } | ||
| } | ||
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| fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> { | ||
| // We're only interested in types involving regions | ||
| if !ty.flags().intersects(ty::TypeFlags::HAS_FREE_REGIONS) { | ||
| return ControlFlow::Continue(()); | ||
| } | ||
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| match ty.kind() { | ||
| ty::Closure(_, ref args) => { | ||
| // Skip lifetime parameters of the enclosing item(s) | ||
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| for upvar in args.as_closure().upvar_tys() { | ||
| upvar.visit_with(self); | ||
| } | ||
| args.as_closure().sig_as_fn_ptr_ty().visit_with(self); | ||
| } | ||
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| ty::Generator(_, ref args, _) => { | ||
| // Skip lifetime parameters of the enclosing item(s) | ||
| // Also skip the witness type, because that has no free regions. | ||
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| for upvar in args.as_generator().upvar_tys() { | ||
| upvar.visit_with(self); | ||
| } | ||
| args.as_generator().return_ty().visit_with(self); | ||
| args.as_generator().yield_ty().visit_with(self); | ||
| args.as_generator().resume_ty().visit_with(self); | ||
| } | ||
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| // We can prove that an alias is live two ways: | ||
| // 1. All the components are live. | ||
| // | ||
| // 2. There is a known outlives bound or where-clause, and that | ||
| // region is live. | ||
| // | ||
| // We search through the item bounds and where clauses for | ||
| // either `'static` or a unique outlives region, and if one is | ||
| // found, we just need to prove that that region is still live. | ||
| // If one is not found, then we continue to walk through the alias. | ||
| ty::Alias(kind, ty::AliasTy { def_id, args, .. }) => { | ||
| let tcx = self.tcx; | ||
| let param_env = self.param_env; | ||
| let outlives_bounds: Vec<_> = tcx | ||
| .item_bounds(def_id) | ||
| .iter_instantiated(tcx, args) | ||
| .chain(param_env.caller_bounds()) | ||
| .filter_map(|clause| { | ||
| let outlives = clause.as_type_outlives_clause()?; | ||
| if let Some(outlives) = outlives.no_bound_vars() | ||
| && outlives.0 == ty | ||
| { | ||
| Some(outlives.1) | ||
| } else { | ||
| test_type_match::extract_verify_if_eq( | ||
| tcx, | ||
| param_env, | ||
| &outlives.map_bound(|ty::OutlivesPredicate(ty, bound)| { | ||
| VerifyIfEq { ty, bound } | ||
| }), | ||
| ty, | ||
| ) | ||
| } | ||
| }) | ||
| .collect(); | ||
| // If we find `'static`, then we know the alias doesn't capture *any* regions. | ||
| // Otherwise, all of the outlives regions should be equal -- if they're not, | ||
| // we don't really know how to proceed, so we continue recursing through the | ||
| // alias. | ||
| if outlives_bounds.contains(&tcx.lifetimes.re_static) { | ||
| // no | ||
| } else if let Some(r) = outlives_bounds.first() | ||
| && outlives_bounds[1..].iter().all(|other_r| other_r == r) | ||
| { | ||
| assert!(r.type_flags().intersects(ty::TypeFlags::HAS_FREE_REGIONS)); | ||
| r.visit_with(self)?; | ||
| } else { | ||
| // Skip lifetime parameters that are not captures. | ||
| let variances = match kind { | ||
| ty::Opaque => Some(self.tcx.variances_of(*def_id)), | ||
| _ => None, | ||
| }; | ||
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| for (idx, s) in args.iter().enumerate() { | ||
| if variances.map(|variances| variances[idx]) != Some(ty::Variance::Bivariant) { | ||
| s.visit_with(self)?; | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| _ => { | ||
| ty.super_visit_with(self)?; | ||
| } | ||
| } | ||
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| ControlFlow::Continue(()) | ||
| } | ||
| } |
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