| //! Codegen of the [`PointerCast::Unsize`] operation. |
| //! |
| //! [`PointerCast::Unsize`]: `rustc_middle::ty::adjustment::PointerCast::Unsize` |
| |
| use crate::prelude::*; |
| |
| // Adapted from https://github.com/rust-lang/rust/blob/2a663555ddf36f6b041445894a8c175cd1bc718c/src/librustc_codegen_ssa/base.rs#L159-L307 |
| |
| /// Retrieve the information we are losing (making dynamic) in an unsizing |
| /// adjustment. |
| /// |
| /// The `old_info` argument is a bit funny. It is intended for use |
| /// in an upcast, where the new vtable for an object will be derived |
| /// from the old one. |
| pub(crate) fn unsized_info<'tcx>( |
| fx: &mut FunctionCx<'_, '_, 'tcx>, |
| source: Ty<'tcx>, |
| target: Ty<'tcx>, |
| old_info: Option<Value>, |
| ) -> Value { |
| let (source, target) = |
| fx.tcx.struct_lockstep_tails_erasing_lifetimes(source, target, ParamEnv::reveal_all()); |
| match (&source.kind(), &target.kind()) { |
| (&ty::Array(_, len), &ty::Slice(_)) => fx |
| .bcx |
| .ins() |
| .iconst(fx.pointer_type, len.eval_usize(fx.tcx, ParamEnv::reveal_all()) as i64), |
| (&ty::Dynamic(..), &ty::Dynamic(..)) => { |
| // For now, upcasts are limited to changes in marker |
| // traits, and hence never actually require an actual |
| // change to the vtable. |
| old_info.expect("unsized_info: missing old info for trait upcast") |
| } |
| (_, &ty::Dynamic(ref data, ..)) => { |
| crate::vtable::get_vtable(fx, fx.layout_of(source), data.principal()) |
| } |
| _ => bug!("unsized_info: invalid unsizing {:?} -> {:?}", source, target), |
| } |
| } |
| |
| /// Coerce `src` to `dst_ty`. `src_ty` must be a thin pointer. |
| fn unsize_thin_ptr<'tcx>( |
| fx: &mut FunctionCx<'_, '_, 'tcx>, |
| src: Value, |
| src_layout: TyAndLayout<'tcx>, |
| dst_layout: TyAndLayout<'tcx>, |
| ) -> (Value, Value) { |
| match (&src_layout.ty.kind(), &dst_layout.ty.kind()) { |
| (&ty::Ref(_, a, _), &ty::Ref(_, b, _)) |
| | (&ty::Ref(_, a, _), &ty::RawPtr(ty::TypeAndMut { ty: b, .. })) |
| | (&ty::RawPtr(ty::TypeAndMut { ty: a, .. }), &ty::RawPtr(ty::TypeAndMut { ty: b, .. })) => { |
| assert!(!fx.layout_of(a).is_unsized()); |
| (src, unsized_info(fx, a, b, None)) |
| } |
| (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) if def_a.is_box() && def_b.is_box() => { |
| let (a, b) = (src_layout.ty.boxed_ty(), dst_layout.ty.boxed_ty()); |
| assert!(!fx.layout_of(a).is_unsized()); |
| (src, unsized_info(fx, a, b, None)) |
| } |
| (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => { |
| assert_eq!(def_a, def_b); |
| |
| let mut result = None; |
| for i in 0..src_layout.fields.count() { |
| let src_f = src_layout.field(fx, i); |
| assert_eq!(src_layout.fields.offset(i).bytes(), 0); |
| assert_eq!(dst_layout.fields.offset(i).bytes(), 0); |
| if src_f.is_zst() { |
| continue; |
| } |
| assert_eq!(src_layout.size, src_f.size); |
| |
| let dst_f = dst_layout.field(fx, i); |
| assert_ne!(src_f.ty, dst_f.ty); |
| assert_eq!(result, None); |
| result = Some(unsize_thin_ptr(fx, src, src_f, dst_f)); |
| } |
| result.unwrap() |
| } |
| _ => bug!("unsize_thin_ptr: called on bad types"), |
| } |
| } |
| |
| /// Coerce `src`, which is a reference to a value of type `src_ty`, |
| /// to a value of type `dst_ty` and store the result in `dst` |
| pub(crate) fn coerce_unsized_into<'tcx>( |
| fx: &mut FunctionCx<'_, '_, 'tcx>, |
| src: CValue<'tcx>, |
| dst: CPlace<'tcx>, |
| ) { |
| let src_ty = src.layout().ty; |
| let dst_ty = dst.layout().ty; |
| let mut coerce_ptr = || { |
| let (base, info) = |
| if fx.layout_of(src.layout().ty.builtin_deref(true).unwrap().ty).is_unsized() { |
| // fat-ptr to fat-ptr unsize preserves the vtable |
| // i.e., &'a fmt::Debug+Send => &'a fmt::Debug |
| src.load_scalar_pair(fx) |
| } else { |
| let base = src.load_scalar(fx); |
| unsize_thin_ptr(fx, base, src.layout(), dst.layout()) |
| }; |
| dst.write_cvalue(fx, CValue::by_val_pair(base, info, dst.layout())); |
| }; |
| match (&src_ty.kind(), &dst_ty.kind()) { |
| (&ty::Ref(..), &ty::Ref(..)) |
| | (&ty::Ref(..), &ty::RawPtr(..)) |
| | (&ty::RawPtr(..), &ty::RawPtr(..)) => coerce_ptr(), |
| (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => { |
| assert_eq!(def_a, def_b); |
| |
| for i in 0..def_a.variants[VariantIdx::new(0)].fields.len() { |
| let src_f = src.value_field(fx, mir::Field::new(i)); |
| let dst_f = dst.place_field(fx, mir::Field::new(i)); |
| |
| if dst_f.layout().is_zst() { |
| continue; |
| } |
| |
| if src_f.layout().ty == dst_f.layout().ty { |
| dst_f.write_cvalue(fx, src_f); |
| } else { |
| coerce_unsized_into(fx, src_f, dst_f); |
| } |
| } |
| } |
| _ => bug!("coerce_unsized_into: invalid coercion {:?} -> {:?}", src_ty, dst_ty), |
| } |
| } |
| |
| // Adapted from https://github.com/rust-lang/rust/blob/2a663555ddf36f6b041445894a8c175cd1bc718c/src/librustc_codegen_ssa/glue.rs |
| |
| pub(crate) fn size_and_align_of_dst<'tcx>( |
| fx: &mut FunctionCx<'_, '_, 'tcx>, |
| layout: TyAndLayout<'tcx>, |
| info: Value, |
| ) -> (Value, Value) { |
| if !layout.is_unsized() { |
| let size = fx.bcx.ins().iconst(fx.pointer_type, layout.size.bytes() as i64); |
| let align = fx.bcx.ins().iconst(fx.pointer_type, layout.align.abi.bytes() as i64); |
| return (size, align); |
| } |
| match layout.ty.kind() { |
| ty::Dynamic(..) => { |
| // load size/align from vtable |
| (crate::vtable::size_of_obj(fx, info), crate::vtable::min_align_of_obj(fx, info)) |
| } |
| ty::Slice(_) | ty::Str => { |
| let unit = layout.field(fx, 0); |
| // The info in this case is the length of the str, so the size is that |
| // times the unit size. |
| ( |
| fx.bcx.ins().imul_imm(info, unit.size.bytes() as i64), |
| fx.bcx.ins().iconst(fx.pointer_type, unit.align.abi.bytes() as i64), |
| ) |
| } |
| _ => { |
| // First get the size of all statically known fields. |
| // Don't use size_of because it also rounds up to alignment, which we |
| // want to avoid, as the unsized field's alignment could be smaller. |
| assert!(!layout.ty.is_simd()); |
| |
| let i = layout.fields.count() - 1; |
| let sized_size = layout.fields.offset(i).bytes(); |
| let sized_align = layout.align.abi.bytes(); |
| let sized_align = fx.bcx.ins().iconst(fx.pointer_type, sized_align as i64); |
| |
| // Recurse to get the size of the dynamically sized field (must be |
| // the last field). |
| let field_layout = layout.field(fx, i); |
| let (unsized_size, mut unsized_align) = size_and_align_of_dst(fx, field_layout, info); |
| |
| // FIXME (#26403, #27023): We should be adding padding |
| // to `sized_size` (to accommodate the `unsized_align` |
| // required of the unsized field that follows) before |
| // summing it with `sized_size`. (Note that since #26403 |
| // is unfixed, we do not yet add the necessary padding |
| // here. But this is where the add would go.) |
| |
| // Return the sum of sizes and max of aligns. |
| let size = fx.bcx.ins().iadd_imm(unsized_size, sized_size as i64); |
| |
| // Packed types ignore the alignment of their fields. |
| if let ty::Adt(def, _) = layout.ty.kind() { |
| if def.repr.packed() { |
| unsized_align = sized_align; |
| } |
| } |
| |
| // Choose max of two known alignments (combined value must |
| // be aligned according to more restrictive of the two). |
| let cmp = fx.bcx.ins().icmp(IntCC::UnsignedGreaterThan, sized_align, unsized_align); |
| let align = fx.bcx.ins().select(cmp, sized_align, unsized_align); |
| |
| // Issue #27023: must add any necessary padding to `size` |
| // (to make it a multiple of `align`) before returning it. |
| // |
| // Namely, the returned size should be, in C notation: |
| // |
| // `size + ((size & (align-1)) ? align : 0)` |
| // |
| // emulated via the semi-standard fast bit trick: |
| // |
| // `(size + (align-1)) & -align` |
| let addend = fx.bcx.ins().iadd_imm(align, -1); |
| let add = fx.bcx.ins().iadd(size, addend); |
| let neg = fx.bcx.ins().ineg(align); |
| let size = fx.bcx.ins().band(add, neg); |
| |
| (size, align) |
| } |
| } |
| } |
