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