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generate reborrow constraints at type check time

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This commit is contained in:
Niko Matsakis 2018-07-01 10:22:36 -04:00
parent fbb7306347
commit 8fa24bbc57
4 changed files with 154 additions and 152 deletions
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138
src/librustc_mir/borrow_check/nll/constraint_generation.rs
View File

@ -13,14 +13,11 @@ use borrow_check::location::LocationTable;
use borrow_check::nll::ToRegionVid;
use borrow_check::nll::facts::AllFacts;
use borrow_check::nll::region_infer::RegionInferenceContext;
use borrow_check::nll::type_check::AtLocation;
use rustc::hir;
use rustc::infer::InferCtxt;
use rustc::mir::visit::TyContext;
use rustc::mir::visit::Visitor;
use rustc::mir::Place::Projection;
use rustc::mir::{BasicBlock, BasicBlockData, Location, Mir, Place, Rvalue};
use rustc::mir::{Local, PlaceProjection, ProjectionElem, Statement, Terminator};
use rustc::mir::{Local, Statement, Terminator};
use rustc::ty::fold::TypeFoldable;
use rustc::ty::subst::Substs;
use rustc::ty::{self, CanonicalTy, ClosureSubsts, GeneratorSubsts};
@ -41,7 +38,6 @@ pub(super) fn generate_constraints<'cx, 'gcx, 'tcx>(
regioncx,
location_table,
all_facts,
mir,
};
cg.add_region_liveness_constraints_from_type_check(liveness_set_from_typeck);
@ -57,7 +53,6 @@ struct ConstraintGeneration<'cg, 'cx: 'cg, 'gcx: 'tcx, 'tcx: 'cx> {
all_facts: &'cg mut Option<AllFacts>,
location_table: &'cg LocationTable,
regioncx: &'cg mut RegionInferenceContext<'tcx>,
mir: &'cg Mir<'tcx>,
borrow_set: &'cg BorrowSet<'tcx>,
}
@ -184,41 +179,6 @@ impl<'cg, 'cx, 'gcx, 'tcx> Visitor<'tcx> for ConstraintGeneration<'cg, 'cx, 'gcx
self.super_terminator(block, terminator, location);
}
fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
debug!("visit_rvalue(rvalue={:?}, location={:?})", rvalue, location);
match rvalue {
Rvalue::Ref(region, _borrow_kind, borrowed_place) => {
// In some cases, e.g. when borrowing from an unsafe
// place, we don't bother to create a loan, since
// there are no conditions to validate.
if let Some(all_facts) = self.all_facts {
if let Some(borrow_index) = self.borrow_set.location_map.get(&location) {
let region_vid = region.to_region_vid();
all_facts.borrow_region.push((
region_vid,
*borrow_index,
self.location_table.mid_index(location),
));
}
}
// Look for an rvalue like:
//
// & L
//
// where L is the path that is borrowed. In that case, we have
// to add the reborrow constraints (which don't fall out
// naturally from the type-checker).
self.add_reborrow_constraint(location, region, borrowed_place);
}
_ => {}
}
self.super_rvalue(rvalue, location);
}
fn visit_user_assert_ty(
&mut self,
_c_ty: &CanonicalTy<'tcx>,
@ -285,100 +245,4 @@ impl<'cx, 'cg, 'gcx, 'tcx> ConstraintGeneration<'cx, 'cg, 'gcx, 'tcx> {
self.regioncx.add_live_point(vid, location);
});
}
// Add the reborrow constraint at `location` so that `borrowed_place`
// is valid for `borrow_region`.
fn add_reborrow_constraint(
&mut self,
location: Location,
borrow_region: ty::Region<'tcx>,
borrowed_place: &Place<'tcx>,
) {
let mut borrowed_place = borrowed_place;
debug!(
"add_reborrow_constraint({:?}, {:?}, {:?})",
location, borrow_region, borrowed_place
);
while let Projection(box PlaceProjection { base, elem }) = borrowed_place {
debug!("add_reborrow_constraint - iteration {:?}", borrowed_place);
match *elem {
ProjectionElem::Deref => {
let tcx = self.infcx.tcx;
let base_ty = base.ty(self.mir, tcx).to_ty(tcx);
debug!("add_reborrow_constraint - base_ty = {:?}", base_ty);
match base_ty.sty {
ty::TyRef(ref_region, _, mutbl) => {
self.regioncx.add_outlives(
location.boring(),
ref_region.to_region_vid(),
borrow_region.to_region_vid(),
);
if let Some(all_facts) = self.all_facts {
all_facts.outlives.push((
ref_region.to_region_vid(),
borrow_region.to_region_vid(),
self.location_table.mid_index(location),
));
}
match mutbl {
hir::Mutability::MutImmutable => {
// Immutable reference. We don't need the base
// to be valid for the entire lifetime of
// the borrow.
break;
}
hir::Mutability::MutMutable => {
// Mutable reference. We *do* need the base
// to be valid, because after the base becomes
// invalid, someone else can use our mutable deref.
// This is in order to make the following function
// illegal:
// ```
// fn unsafe_deref<'a, 'b>(x: &'a &'b mut T) -> &'b mut T {
// &mut *x
// }
// ```
//
// As otherwise you could clone `&mut T` using the
// following function:
// ```
// fn bad(x: &mut T) -> (&mut T, &mut T) {
// let my_clone = unsafe_deref(&'a x);
// ENDREGION 'a;
// (my_clone, x)
// }
// ```
}
}
}
ty::TyRawPtr(..) => {
// deref of raw pointer, guaranteed to be valid
break;
}
ty::TyAdt(def, _) if def.is_box() => {
// deref of `Box`, need the base to be valid - propagate
}
_ => bug!("unexpected deref ty {:?} in {:?}", base_ty, borrowed_place),
}
}
ProjectionElem::Field(..)
| ProjectionElem::Downcast(..)
| ProjectionElem::Index(..)
| ProjectionElem::ConstantIndex { .. }
| ProjectionElem::Subslice { .. } => {
// other field access
}
}
// The "propagate" case. We need to check that our base is valid
// for the borrow's lifetime.
borrowed_place = base;
}
}
}

1
src/librustc_mir/borrow_check/nll/mod.rs
View File

@ -108,6 +108,7 @@ pub(in borrow_check) fn compute_regions<'cx, 'gcx, 'tcx>(
def_id,
&universal_regions,
location_table,
borrow_set,
&liveness,
&mut all_facts,
flow_inits,

11
src/librustc_mir/borrow_check/nll/region_infer/mod.rs
View File

@ -333,17 +333,6 @@ impl<'tcx> RegionInferenceContext<'tcx> {
self.liveness_constraints.add_element(v, element)
}
/// Indicates that the region variable `sup` must outlive `sub` is live at the point `point`.
pub(super) fn add_outlives(&mut self, locations: Locations, sup: RegionVid, sub: RegionVid) {
assert!(self.inferred_values.is_none(), "values already inferred");
self.constraints.push(OutlivesConstraint {
locations,
sup,
sub,
next: None,
})
}
/// Perform region inference and report errors if we see any
/// unsatisfiable constraints. If this is a closure, returns the
/// region requirements to propagate to our creator, if any.

156
src/librustc_mir/borrow_check/nll/type_check/mod.rs
View File

@ -11,14 +11,17 @@
//! This pass type-checks the MIR to ensure it is not broken.
#![allow(unreachable_code)]
use borrow_check::borrow_set::BorrowSet;
use borrow_check::location::LocationTable;
use borrow_check::nll::constraint_set::ConstraintSet;
use borrow_check::nll::constraint_set::{ConstraintSet, OutlivesConstraint};
use borrow_check::nll::facts::AllFacts;
use borrow_check::nll::region_infer::{ClosureRegionRequirementsExt, TypeTest};
use borrow_check::nll::universal_regions::UniversalRegions;
use borrow_check::nll::ToRegionVid;
use dataflow::move_paths::MoveData;
use dataflow::FlowAtLocation;
use dataflow::MaybeInitializedPlaces;
use rustc::hir;
use rustc::hir::def_id::DefId;
use rustc::infer::canonical::QueryRegionConstraint;
use rustc::infer::region_constraints::GenericKind;
@ -103,6 +106,7 @@ pub(crate) fn type_check<'gcx, 'tcx>(
mir_def_id: DefId,
universal_regions: &UniversalRegions<'tcx>,
location_table: &LocationTable,
borrow_set: &BorrowSet<'tcx>,
liveness: &LivenessResults,
all_facts: &mut Option<AllFacts>,
flow_inits: &mut FlowAtLocation<MaybeInitializedPlaces<'_, 'gcx, 'tcx>>,
@ -119,6 +123,7 @@ pub(crate) fn type_check<'gcx, 'tcx>(
Some(BorrowCheckContext {
universal_regions,
location_table,
borrow_set,
all_facts,
}),
&mut |cx| {
@ -141,6 +146,7 @@ fn type_check_internal<'gcx, 'tcx>(
) -> MirTypeckRegionConstraints<'tcx> {
let mut checker = TypeChecker::new(
infcx,
mir,
mir_def_id,
param_env,
region_bound_pairs,
@ -592,6 +598,7 @@ struct TypeChecker<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
param_env: ty::ParamEnv<'gcx>,
last_span: Span,
mir: &'a Mir<'tcx>,
mir_def_id: DefId,
region_bound_pairs: &'a [(ty::Region<'tcx>, GenericKind<'tcx>)],
implicit_region_bound: Option<ty::Region<'tcx>>,
@ -604,6 +611,7 @@ struct BorrowCheckContext<'a, 'tcx: 'a> {
universal_regions: &'a UniversalRegions<'tcx>,
location_table: &'a LocationTable,
all_facts: &'a mut Option<AllFacts>,
borrow_set: &'a BorrowSet<'tcx>,
}
/// A collection of region constraints that must be satisfied for the
@ -704,6 +712,7 @@ impl Locations {
impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
fn new(
infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
mir: &'a Mir<'tcx>,
mir_def_id: DefId,
param_env: ty::ParamEnv<'gcx>,
region_bound_pairs: &'a [(ty::Region<'tcx>, GenericKind<'tcx>)],
@ -713,6 +722,7 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
TypeChecker {
infcx,
last_span: DUMMY_SP,
mir,
mir_def_id,
param_env,
region_bound_pairs,
@ -857,8 +867,7 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
}
StatementKind::UserAssertTy(ref c_ty, ref local) => {
let local_ty = mir.local_decls()[*local].ty;
let (ty, _) = self
.infcx
let (ty, _) = self.infcx
.instantiate_canonical_with_fresh_inference_vars(stmt.source_info.span, c_ty);
debug!(
"check_stmt: user_assert_ty ty={:?} local_ty={:?}",
@ -1400,9 +1409,12 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
CastKind::Misc => {}
},
Rvalue::Ref(region, _borrow_kind, borrowed_place) => {
self.add_reborrow_constraint(location, region, borrowed_place);
}
// FIXME: These other cases have to be implemented in future PRs
Rvalue::Use(..)
| Rvalue::Ref(..)
| Rvalue::Len(..)
| Rvalue::BinaryOp(..)
| Rvalue::CheckedBinaryOp(..)
@ -1457,6 +1469,142 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
}
}
/// Add the constraints that arise from a borrow expression `&'a P` at the location `L`.
///
/// # Parameters
///
/// - `location`: the location `L` where the borrow expression occurs
/// - `borrow_region`: the region `'a` associated with the borrow
/// - `borrowed_place`: the place `P` being borrowed
fn add_reborrow_constraint(
&mut self,
location: Location,
borrow_region: ty::Region<'tcx>,
borrowed_place: &Place<'tcx>,
) {
// These constraints are only meaningful during borrowck:
let BorrowCheckContext {
borrow_set,
location_table,
all_facts,
..
} = match &mut self.borrowck_context {
Some(borrowck_context) => borrowck_context,
None => return,
};
// In Polonius mode, we also push a `borrow_region` fact
// linking the loan to the region (in some cases, though,
// there is no loan associated with this borrow expression --
// that occurs when we are borrowing an unsafe place, for
// example).
if let Some(all_facts) = all_facts {
if let Some(borrow_index) = borrow_set.location_map.get(&location) {
let region_vid = borrow_region.to_region_vid();
all_facts.borrow_region.push((
region_vid,
*borrow_index,
location_table.mid_index(location),
));
}
}
// If we are reborrowing the referent of another reference, we
// need to add outlives relationships. In a case like `&mut
// *p`, where the `p` has type `&'b mut Foo`, for example, we
// need to ensure that `'b: 'a`.
let mut borrowed_place = borrowed_place;
debug!(
"add_reborrow_constraint({:?}, {:?}, {:?})",
location, borrow_region, borrowed_place
);
while let Place::Projection(box PlaceProjection { base, elem }) = borrowed_place {
debug!("add_reborrow_constraint - iteration {:?}", borrowed_place);
match *elem {
ProjectionElem::Deref => {
let tcx = self.infcx.tcx;
let base_ty = base.ty(self.mir, tcx).to_ty(tcx);
debug!("add_reborrow_constraint - base_ty = {:?}", base_ty);
match base_ty.sty {
ty::TyRef(ref_region, _, mutbl) => {
self.constraints
.outlives_constraints
.push(OutlivesConstraint {
sup: ref_region.to_region_vid(),
sub: borrow_region.to_region_vid(),
locations: location.boring(),
next: None,
});
if let Some(all_facts) = all_facts {
all_facts.outlives.push((
ref_region.to_region_vid(),
borrow_region.to_region_vid(),
location_table.mid_index(location),
));
}
match mutbl {
hir::Mutability::MutImmutable => {
// Immutable reference. We don't need the base
// to be valid for the entire lifetime of
// the borrow.
break;
}
hir::Mutability::MutMutable => {
// Mutable reference. We *do* need the base
// to be valid, because after the base becomes
// invalid, someone else can use our mutable deref.
// This is in order to make the following function
// illegal:
// ```
// fn unsafe_deref<'a, 'b>(x: &'a &'b mut T) -> &'b mut T {
// &mut *x
// }
// ```
//
// As otherwise you could clone `&mut T` using the
// following function:
// ```
// fn bad(x: &mut T) -> (&mut T, &mut T) {
// let my_clone = unsafe_deref(&'a x);
// ENDREGION 'a;
// (my_clone, x)
// }
// ```
}
}
}
ty::TyRawPtr(..) => {
// deref of raw pointer, guaranteed to be valid
break;
}
ty::TyAdt(def, _) if def.is_box() => {
// deref of `Box`, need the base to be valid - propagate
}
_ => bug!("unexpected deref ty {:?} in {:?}", base_ty, borrowed_place),
}
}
ProjectionElem::Field(..)
| ProjectionElem::Downcast(..)
| ProjectionElem::Index(..)
| ProjectionElem::ConstantIndex { .. }
| ProjectionElem::Subslice { .. } => {
// other field access
}
}
// The "propagate" case. We need to check that our base is valid
// for the borrow's lifetime.
borrowed_place = base;
}
}
fn prove_aggregate_predicates(
&mut self,
aggregate_kind: &AggregateKind<'tcx>,