From 289c0d8489d02c1bc5cb0b091455fe03cd9384bd Mon Sep 17 00:00:00 2001 From: Ralf Jung Date: Sat, 31 Oct 2020 13:57:56 +0100 Subject: [PATCH] Retagging: do not retag 'raw reborrows' --- compiler/rustc_mir/src/transform/add_retag.rs | 26 ++++++++++++++----- 1 file changed, 20 insertions(+), 6 deletions(-) diff --git a/compiler/rustc_mir/src/transform/add_retag.rs b/compiler/rustc_mir/src/transform/add_retag.rs index eec704e6cb775..6fe9f64be32e8 100644 --- a/compiler/rustc_mir/src/transform/add_retag.rs +++ b/compiler/rustc_mir/src/transform/add_retag.rs @@ -73,6 +73,19 @@ impl<'tcx> MirPass<'tcx> for AddRetag { // a temporary and retag on that. is_stable(place.as_ref()) && may_be_reference(place.ty(&*local_decls, tcx).ty) }; + let place_base_raw = |place: &Place<'tcx>| { + // If this is a `Deref`, get the type of what we are deref'ing. + let deref_base = + place.projection.iter().rposition(|p| matches!(p, ProjectionElem::Deref)); + if let Some(deref_base) = deref_base { + let base_proj = &place.projection[..deref_base]; + let ty = Place::ty_from(place.local, base_proj, &*local_decls, tcx).ty; + ty.is_unsafe_ptr() + } else { + // Not a deref, and thus not raw. + false + } + }; // PART 1 // Retag arguments at the beginning of the start block. @@ -136,13 +149,14 @@ impl<'tcx> MirPass<'tcx> for AddRetag { // iterate backwards using indices. for i in (0..block_data.statements.len()).rev() { let (retag_kind, place) = match block_data.statements[i].kind { - // Retag-as-raw after escaping to a raw pointer. - StatementKind::Assign(box (place, Rvalue::AddressOf(..))) => { - (RetagKind::Raw, place) + // Retag-as-raw after escaping to a raw pointer, if the referent + // is not already a raw pointer. + StatementKind::Assign(box (lplace, Rvalue::AddressOf(_, ref rplace))) + if !place_base_raw(rplace) => + { + (RetagKind::Raw, lplace) } - // Assignments of reference or ptr type are the ones where we may have - // to update tags. This includes `x = &[mut] ...` and hence - // we also retag after taking a reference! + // Retag after assignments of reference type. StatementKind::Assign(box (ref place, ref rvalue)) if needs_retag(place) => { let kind = match rvalue { Rvalue::Ref(_, borrow_kind, _)