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generalize the Deref case and simplify the code

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This commit is contained in:
Niko Matsakis 2018-08-04 09:26:30 +02:00
parent e7d8d651d5
commit 936fa6f67f
1 changed files with 20 additions and 11 deletions
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31
src/librustc_mir/borrow_check/nll/escaping_locals.rs
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@ -44,7 +44,7 @@
use rustc::mir::visit::Visitor;
use rustc::mir::*;
use rustc::ty::{self, TyCtxt};
use rustc::ty::TyCtxt;
use rustc_data_structures::indexed_vec::Idx;
use rustc_data_structures::unify as ut;
@ -178,20 +178,29 @@ impl Visitor<'tcx> for GatherAssignedLocalsVisitor<'_, '_, 'tcx> {
match rvalue {
Rvalue::Use(op) => self.union_locals_if_needed(local, find_local_in_operand(op)),
Rvalue::Ref(_, _, place) => {
// Special case: if you have `X = &*Y` where `Y` is a
// reference, then the outlives relationships should
// ensure that all regions in `Y` are constrained by
// regions in `X`.
if let Place::Projection(proj) = place {
// Special case: if you have `X = &*Y` (or `X = &**Y`
// etc), then the outlives relationships will ensure
// that all regions in `Y` are constrained by regions
// in `X` -- this is because the lifetimes of the
// references we deref through are required to outlive
// the borrow lifetime (which appears in `X`).
//
// (We don't actually need to check the type of `Y`:
// since `ProjectionElem::Deref` represents a built-in
// deref and not an overloaded deref, if the thing we
// deref through is not a reference, then it must be a
// `Box` or `*const`, in which case it contains no
// references.)
let mut place_ref = place;
while let Place::Projection(proj) = place_ref {
if let ProjectionElem::Deref = proj.elem {
if let ty::TyRef(..) = proj.base.ty(self.mir, self.tcx).to_ty(self.tcx).sty
{
self.union_locals_if_needed(local, find_local_in_place(&proj.base));
}
place_ref = &proj.base;
} else {
break;
}
}
self.union_locals_if_needed(local, find_local_in_place(place))
self.union_locals_if_needed(local, find_local_in_place(place_ref))
}
Rvalue::Cast(kind, op, _) => match kind {