diff options
| -rw-r--r-- | compiler/rustc_const_eval/src/interpret/terminator.rs | 15 | ||||
| -rw-r--r-- | compiler/rustc_middle/src/mir/syntax.rs | 15 | ||||
| -rw-r--r-- | src/tools/miri/tests/fail/stacked_borrows/drop_in_place_retag.rs | 4 |
3 files changed, 21 insertions, 13 deletions
diff --git a/compiler/rustc_const_eval/src/interpret/terminator.rs b/compiler/rustc_const_eval/src/interpret/terminator.rs index 0e7ffcdffc9..550c7a44c41 100644 --- a/compiler/rustc_const_eval/src/interpret/terminator.rs +++ b/compiler/rustc_const_eval/src/interpret/terminator.rs @@ -119,11 +119,20 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> { } Drop { place, target, unwind } => { + let frame = self.frame(); + let ty = place.ty(&frame.body.local_decls, *self.tcx).ty; + let ty = self.subst_from_frame_and_normalize_erasing_regions(frame, ty)?; + let instance = Instance::resolve_drop_in_place(*self.tcx, ty); + if let ty::InstanceDef::DropGlue(_, None) = instance.def { + // This is the branch we enter if and only if the dropped type has no drop glue + // whatsoever. This can happen as a result of monomorphizing a drop of a + // generic. In order to make sure that generic and non-generic code behaves + // roughly the same (and in keeping with Mir semantics) we do nothing here. + self.go_to_block(target); + return Ok(()); + } let place = self.eval_place(place)?; - let ty = place.layout.ty; trace!("TerminatorKind::drop: {:?}, type {}", place, ty); - - let instance = Instance::resolve_drop_in_place(*self.tcx, ty); self.drop_in_place(&place, instance, target, unwind)?; } diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs index 99e59c770d7..6e7d84410da 100644 --- a/compiler/rustc_middle/src/mir/syntax.rs +++ b/compiler/rustc_middle/src/mir/syntax.rs @@ -562,14 +562,13 @@ pub enum TerminatorKind<'tcx> { Unreachable, /// The behavior of this statement differs significantly before and after drop elaboration. - /// After drop elaboration, `Drop` executes the drop glue for the specified place, after which - /// it continues execution/unwinds at the given basic blocks. It is possible that executing drop - /// glue is special - this would be part of Rust's memory model. (**FIXME**: due we have an - /// issue tracking if drop glue has any interesting semantics in addition to those of a function - /// call?) - /// - /// `Drop` before drop elaboration is a *conditional* execution of the drop glue. Specifically, the - /// `Drop` will be executed if... + /// + /// After drop elaboration: `Drop` terminators are a complete nop for types that have no drop + /// glue. For other types, `Drop` terminators behave exactly like a call to + /// `core::mem::drop_in_place` with a pointer to the given place. + /// + /// `Drop` before drop elaboration is a *conditional* execution of the drop glue. Specifically, + /// the `Drop` will be executed if... /// /// **Needs clarification**: End of that sentence. This in effect should document the exact /// behavior of drop elaboration. The following sounds vaguely right, but I'm not quite sure: diff --git a/src/tools/miri/tests/fail/stacked_borrows/drop_in_place_retag.rs b/src/tools/miri/tests/fail/stacked_borrows/drop_in_place_retag.rs index e7d256b686d..8180e2f03a7 100644 --- a/src/tools/miri/tests/fail/stacked_borrows/drop_in_place_retag.rs +++ b/src/tools/miri/tests/fail/stacked_borrows/drop_in_place_retag.rs @@ -1,5 +1,5 @@ -//! Test that drop_in_place mutably retags the entire place, -//! ensuring it is writeable +//! Test that drop_in_place mutably retags the entire place, even for a type that does not need +//! dropping, ensuring among other things that it is writeable //@error-pattern: /retag .* for Unique permission .* only grants SharedReadOnly permission/ |