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interpret: Drop: always evaluate place #124720

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May 4, 2024
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interpret: Drop: always evaluate place #124720

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86a933a
interpret: Drop: always evaluate place
RalfJung May 4, 2024
f0dee6b
some comments or dynamic drop handling
RalfJung May 4, 2024
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4 changes: 2 additions & 2 deletions compiler/rustc_codegen_ssa/src/mir/block.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -540,7 +540,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
// \-------/
//
let virtual_drop = Instance {
def: ty::InstanceDef::Virtual(drop_fn.def_id(), 0),
def: ty::InstanceDef::Virtual(drop_fn.def_id(), 0), // idx 0: the drop function
args: drop_fn.args,
};
debug!("ty = {:?}", ty);
Expand Down Expand Up @@ -581,7 +581,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
//
// SO THEN WE CAN USE THE ABOVE CODE.
let virtual_drop = Instance {
def: ty::InstanceDef::Virtual(drop_fn.def_id(), 0),
def: ty::InstanceDef::Virtual(drop_fn.def_id(), 0), // idx 0: the drop function
args: drop_fn.args,
};
debug!("ty = {:?}", ty);
Expand Down
15 changes: 9 additions & 6 deletions compiler/rustc_const_eval/src/interpret/terminator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -169,10 +169,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
}

Drop { place, target, unwind, replace: _ } => {
let frame = self.frame();
let ty = place.ty(&frame.body.local_decls, *self.tcx).ty;
let ty = self.instantiate_from_frame_and_normalize_erasing_regions(frame, ty)?;
let instance = Instance::resolve_drop_in_place(*self.tcx, ty);
let place = self.eval_place(place)?;
let instance = Instance::resolve_drop_in_place(*self.tcx, place.layout.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
Expand All @@ -181,8 +179,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
self.go_to_block(target);
return Ok(());
}
let place = self.eval_place(place)?;
trace!("TerminatorKind::drop: {:?}, type {}", place, ty);
trace!("TerminatorKind::drop: {:?}, type {}", place, place.layout.ty);
self.drop_in_place(&place, instance, target, unwind)?;
}

Expand Down Expand Up @@ -952,6 +949,12 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
// implementation fail -- a problem shared by rustc.
let place = self.force_allocation(place)?;

// We behave a bit different from codegen here.
// Codegen creates an `InstanceDef::Virtual` with index 0 (the slot of the drop method) and
// then dispatches that to the normal call machinery. However, our call machinery currently
// only supports calling `VtblEntry::Method`; it would choke on a `MetadataDropInPlace`. So
// instead we do the virtual call stuff ourselves. It's easier here than in `eval_fn_call`
// since we can just get a place of the underlying type and use `mplace_to_ref`.
let place = match place.layout.ty.kind() {
ty::Dynamic(data, _, ty::Dyn) => {
// Dropping a trait object. Need to find actual drop fn.
Expand Down
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