--- /dev/null
+use rustc_hir as hir;
+use rustc_index::bit_set::BitSet;
+use rustc_index::vec::{Idx, IndexVec};
+use rustc_middle::mir::{GeneratorLayout, GeneratorSavedLocal};
+use rustc_middle::ty::layout::{
+ IntegerExt, LayoutCx, LayoutError, LayoutOf, TyAndLayout, MAX_SIMD_LANES,
+};
+use rustc_middle::ty::{
+ self, subst::SubstsRef, EarlyBinder, ReprOptions, Ty, TyCtxt, TypeVisitable,
+};
+use rustc_session::{DataTypeKind, FieldInfo, SizeKind, VariantInfo};
+use rustc_span::symbol::Symbol;
+use rustc_span::DUMMY_SP;
+use rustc_target::abi::*;
+
+use std::cmp::{self, Ordering};
+use std::iter;
+use std::num::NonZeroUsize;
+use std::ops::Bound;
+
+use rand::{seq::SliceRandom, SeedableRng};
+use rand_xoshiro::Xoshiro128StarStar;
+
+use crate::layout_sanity_check::sanity_check_layout;
+
+pub fn provide(providers: &mut ty::query::Providers) {
+ *providers = ty::query::Providers { layout_of, ..*providers };
+}
+
+#[instrument(skip(tcx, query), level = "debug")]
+fn layout_of<'tcx>(
+ tcx: TyCtxt<'tcx>,
+ query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
+) -> Result<TyAndLayout<'tcx>, LayoutError<'tcx>> {
+ let (param_env, ty) = query.into_parts();
+ debug!(?ty);
+
+ let param_env = param_env.with_reveal_all_normalized(tcx);
+ let unnormalized_ty = ty;
+
+ // FIXME: We might want to have two different versions of `layout_of`:
+ // One that can be called after typecheck has completed and can use
+ // `normalize_erasing_regions` here and another one that can be called
+ // before typecheck has completed and uses `try_normalize_erasing_regions`.
+ let ty = match tcx.try_normalize_erasing_regions(param_env, ty) {
+ Ok(t) => t,
+ Err(normalization_error) => {
+ return Err(LayoutError::NormalizationFailure(ty, normalization_error));
+ }
+ };
+
+ if ty != unnormalized_ty {
+ // Ensure this layout is also cached for the normalized type.
+ return tcx.layout_of(param_env.and(ty));
+ }
+
+ let cx = LayoutCx { tcx, param_env };
+
+ let layout = layout_of_uncached(&cx, ty)?;
+ let layout = TyAndLayout { ty, layout };
+
+ record_layout_for_printing(&cx, layout);
+
+ sanity_check_layout(&cx, &layout);
+
+ Ok(layout)
+}
+
+#[derive(Copy, Clone, Debug)]
+enum StructKind {
+ /// A tuple, closure, or univariant which cannot be coerced to unsized.
+ AlwaysSized,
+ /// A univariant, the last field of which may be coerced to unsized.
+ MaybeUnsized,
+ /// A univariant, but with a prefix of an arbitrary size & alignment (e.g., enum tag).
+ Prefixed(Size, Align),
+}
+
+// Invert a bijective mapping, i.e. `invert(map)[y] = x` if `map[x] = y`.
+// This is used to go between `memory_index` (source field order to memory order)
+// and `inverse_memory_index` (memory order to source field order).
+// See also `FieldsShape::Arbitrary::memory_index` for more details.
+// FIXME(eddyb) build a better abstraction for permutations, if possible.
+fn invert_mapping(map: &[u32]) -> Vec<u32> {
+ let mut inverse = vec![0; map.len()];
+ for i in 0..map.len() {
+ inverse[map[i] as usize] = i as u32;
+ }
+ inverse
+}
+
+fn scalar_pair<'tcx>(cx: &LayoutCx<'tcx, TyCtxt<'tcx>>, a: Scalar, b: Scalar) -> LayoutS<'tcx> {
+ let dl = cx.data_layout();
+ let b_align = b.align(dl);
+ let align = a.align(dl).max(b_align).max(dl.aggregate_align);
+ let b_offset = a.size(dl).align_to(b_align.abi);
+ let size = (b_offset + b.size(dl)).align_to(align.abi);
+
+ // HACK(nox): We iter on `b` and then `a` because `max_by_key`
+ // returns the last maximum.
+ let largest_niche = Niche::from_scalar(dl, b_offset, b)
+ .into_iter()
+ .chain(Niche::from_scalar(dl, Size::ZERO, a))
+ .max_by_key(|niche| niche.available(dl));
+
+ LayoutS {
+ variants: Variants::Single { index: VariantIdx::new(0) },
+ fields: FieldsShape::Arbitrary {
+ offsets: vec![Size::ZERO, b_offset],
+ memory_index: vec![0, 1],
+ },
+ abi: Abi::ScalarPair(a, b),
+ largest_niche,
+ align,
+ size,
+ }
+}
+
+fn univariant_uninterned<'tcx>(
+ cx: &LayoutCx<'tcx, TyCtxt<'tcx>>,
+ ty: Ty<'tcx>,
+ fields: &[TyAndLayout<'_>],
+ repr: &ReprOptions,
+ kind: StructKind,
+) -> Result<LayoutS<'tcx>, LayoutError<'tcx>> {
+ let dl = cx.data_layout();
+ let pack = repr.pack;
+ if pack.is_some() && repr.align.is_some() {
+ cx.tcx.sess.delay_span_bug(DUMMY_SP, "struct cannot be packed and aligned");
+ return Err(LayoutError::Unknown(ty));
+ }
+
+ let mut align = if pack.is_some() { dl.i8_align } else { dl.aggregate_align };
+
+ let mut inverse_memory_index: Vec<u32> = (0..fields.len() as u32).collect();
+
+ let optimize = !repr.inhibit_struct_field_reordering_opt();
+ if optimize {
+ let end = if let StructKind::MaybeUnsized = kind { fields.len() - 1 } else { fields.len() };
+ let optimizing = &mut inverse_memory_index[..end];
+ let field_align = |f: &TyAndLayout<'_>| {
+ if let Some(pack) = pack { f.align.abi.min(pack) } else { f.align.abi }
+ };
+
+ // If `-Z randomize-layout` was enabled for the type definition we can shuffle
+ // the field ordering to try and catch some code making assumptions about layouts
+ // we don't guarantee
+ if repr.can_randomize_type_layout() {
+ // `ReprOptions.layout_seed` is a deterministic seed that we can use to
+ // randomize field ordering with
+ let mut rng = Xoshiro128StarStar::seed_from_u64(repr.field_shuffle_seed);
+
+ // Shuffle the ordering of the fields
+ optimizing.shuffle(&mut rng);
+
+ // Otherwise we just leave things alone and actually optimize the type's fields
+ } else {
+ match kind {
+ StructKind::AlwaysSized | StructKind::MaybeUnsized => {
+ optimizing.sort_by_key(|&x| {
+ // Place ZSTs first to avoid "interesting offsets",
+ // especially with only one or two non-ZST fields.
+ let f = &fields[x as usize];
+ (!f.is_zst(), cmp::Reverse(field_align(f)))
+ });
+ }
+
+ StructKind::Prefixed(..) => {
+ // Sort in ascending alignment so that the layout stays optimal
+ // regardless of the prefix
+ optimizing.sort_by_key(|&x| field_align(&fields[x as usize]));
+ }
+ }
+
+ // FIXME(Kixiron): We can always shuffle fields within a given alignment class
+ // regardless of the status of `-Z randomize-layout`
+ }
+ }
+
+ // inverse_memory_index holds field indices by increasing memory offset.
+ // That is, if field 5 has offset 0, the first element of inverse_memory_index is 5.
+ // We now write field offsets to the corresponding offset slot;
+ // field 5 with offset 0 puts 0 in offsets[5].
+ // At the bottom of this function, we invert `inverse_memory_index` to
+ // produce `memory_index` (see `invert_mapping`).
+
+ let mut sized = true;
+ let mut offsets = vec![Size::ZERO; fields.len()];
+ let mut offset = Size::ZERO;
+ let mut largest_niche = None;
+ let mut largest_niche_available = 0;
+
+ if let StructKind::Prefixed(prefix_size, prefix_align) = kind {
+ let prefix_align =
+ if let Some(pack) = pack { prefix_align.min(pack) } else { prefix_align };
+ align = align.max(AbiAndPrefAlign::new(prefix_align));
+ offset = prefix_size.align_to(prefix_align);
+ }
+
+ for &i in &inverse_memory_index {
+ let field = fields[i as usize];
+ if !sized {
+ cx.tcx.sess.delay_span_bug(
+ DUMMY_SP,
+ &format!(
+ "univariant: field #{} of `{}` comes after unsized field",
+ offsets.len(),
+ ty
+ ),
+ );
+ }
+
+ if field.is_unsized() {
+ sized = false;
+ }
+
+ // Invariant: offset < dl.obj_size_bound() <= 1<<61
+ let field_align = if let Some(pack) = pack {
+ field.align.min(AbiAndPrefAlign::new(pack))
+ } else {
+ field.align
+ };
+ offset = offset.align_to(field_align.abi);
+ align = align.max(field_align);
+
+ debug!("univariant offset: {:?} field: {:#?}", offset, field);
+ offsets[i as usize] = offset;
+
+ if let Some(mut niche) = field.largest_niche {
+ let available = niche.available(dl);
+ if available > largest_niche_available {
+ largest_niche_available = available;
+ niche.offset += offset;
+ largest_niche = Some(niche);
+ }
+ }
+
+ offset = offset.checked_add(field.size, dl).ok_or(LayoutError::SizeOverflow(ty))?;
+ }
+
+ if let Some(repr_align) = repr.align {
+ align = align.max(AbiAndPrefAlign::new(repr_align));
+ }
+
+ debug!("univariant min_size: {:?}", offset);
+ let min_size = offset;
+
+ // As stated above, inverse_memory_index holds field indices by increasing offset.
+ // This makes it an already-sorted view of the offsets vec.
+ // To invert it, consider:
+ // If field 5 has offset 0, offsets[0] is 5, and memory_index[5] should be 0.
+ // Field 5 would be the first element, so memory_index is i:
+ // Note: if we didn't optimize, it's already right.
+
+ let memory_index =
+ if optimize { invert_mapping(&inverse_memory_index) } else { inverse_memory_index };
+
+ let size = min_size.align_to(align.abi);
+ let mut abi = Abi::Aggregate { sized };
+
+ // Unpack newtype ABIs and find scalar pairs.
+ if sized && size.bytes() > 0 {
+ // All other fields must be ZSTs.
+ let mut non_zst_fields = fields.iter().enumerate().filter(|&(_, f)| !f.is_zst());
+
+ match (non_zst_fields.next(), non_zst_fields.next(), non_zst_fields.next()) {
+ // We have exactly one non-ZST field.
+ (Some((i, field)), None, None) => {
+ // Field fills the struct and it has a scalar or scalar pair ABI.
+ if offsets[i].bytes() == 0 && align.abi == field.align.abi && size == field.size {
+ match field.abi {
+ // For plain scalars, or vectors of them, we can't unpack
+ // newtypes for `#[repr(C)]`, as that affects C ABIs.
+ Abi::Scalar(_) | Abi::Vector { .. } if optimize => {
+ abi = field.abi;
+ }
+ // But scalar pairs are Rust-specific and get
+ // treated as aggregates by C ABIs anyway.
+ Abi::ScalarPair(..) => {
+ abi = field.abi;
+ }
+ _ => {}
+ }
+ }
+ }
+
+ // Two non-ZST fields, and they're both scalars.
+ (Some((i, a)), Some((j, b)), None) => {
+ match (a.abi, b.abi) {
+ (Abi::Scalar(a), Abi::Scalar(b)) => {
+ // Order by the memory placement, not source order.
+ let ((i, a), (j, b)) = if offsets[i] < offsets[j] {
+ ((i, a), (j, b))
+ } else {
+ ((j, b), (i, a))
+ };
+ let pair = scalar_pair(cx, a, b);
+ let pair_offsets = match pair.fields {
+ FieldsShape::Arbitrary { ref offsets, ref memory_index } => {
+ assert_eq!(memory_index, &[0, 1]);
+ offsets
+ }
+ _ => bug!(),
+ };
+ if offsets[i] == pair_offsets[0]
+ && offsets[j] == pair_offsets[1]
+ && align == pair.align
+ && size == pair.size
+ {
+ // We can use `ScalarPair` only when it matches our
+ // already computed layout (including `#[repr(C)]`).
+ abi = pair.abi;
+ }
+ }
+ _ => {}
+ }
+ }
+
+ _ => {}
+ }
+ }
+
+ if fields.iter().any(|f| f.abi.is_uninhabited()) {
+ abi = Abi::Uninhabited;
+ }
+
+ Ok(LayoutS {
+ variants: Variants::Single { index: VariantIdx::new(0) },
+ fields: FieldsShape::Arbitrary { offsets, memory_index },
+ abi,
+ largest_niche,
+ align,
+ size,
+ })
+}
+
+fn layout_of_uncached<'tcx>(
+ cx: &LayoutCx<'tcx, TyCtxt<'tcx>>,
+ ty: Ty<'tcx>,
+) -> Result<Layout<'tcx>, LayoutError<'tcx>> {
+ let tcx = cx.tcx;
+ let param_env = cx.param_env;
+ let dl = cx.data_layout();
+ let scalar_unit = |value: Primitive| {
+ let size = value.size(dl);
+ assert!(size.bits() <= 128);
+ Scalar::Initialized { value, valid_range: WrappingRange::full(size) }
+ };
+ let scalar = |value: Primitive| tcx.intern_layout(LayoutS::scalar(cx, scalar_unit(value)));
+
+ let univariant = |fields: &[TyAndLayout<'_>], repr: &ReprOptions, kind| {
+ Ok(tcx.intern_layout(univariant_uninterned(cx, ty, fields, repr, kind)?))
+ };
+ debug_assert!(!ty.has_non_region_infer());
+
+ Ok(match *ty.kind() {
+ // Basic scalars.
+ ty::Bool => tcx.intern_layout(LayoutS::scalar(
+ cx,
+ Scalar::Initialized {
+ value: Int(I8, false),
+ valid_range: WrappingRange { start: 0, end: 1 },
+ },
+ )),
+ ty::Char => tcx.intern_layout(LayoutS::scalar(
+ cx,
+ Scalar::Initialized {
+ value: Int(I32, false),
+ valid_range: WrappingRange { start: 0, end: 0x10FFFF },
+ },
+ )),
+ ty::Int(ity) => scalar(Int(Integer::from_int_ty(dl, ity), true)),
+ ty::Uint(ity) => scalar(Int(Integer::from_uint_ty(dl, ity), false)),
+ ty::Float(fty) => scalar(match fty {
+ ty::FloatTy::F32 => F32,
+ ty::FloatTy::F64 => F64,
+ }),
+ ty::FnPtr(_) => {
+ let mut ptr = scalar_unit(Pointer);
+ ptr.valid_range_mut().start = 1;
+ tcx.intern_layout(LayoutS::scalar(cx, ptr))
+ }
+
+ // The never type.
+ ty::Never => tcx.intern_layout(LayoutS {
+ variants: Variants::Single { index: VariantIdx::new(0) },
+ fields: FieldsShape::Primitive,
+ abi: Abi::Uninhabited,
+ largest_niche: None,
+ align: dl.i8_align,
+ size: Size::ZERO,
+ }),
+
+ // Potentially-wide pointers.
+ ty::Ref(_, pointee, _) | ty::RawPtr(ty::TypeAndMut { ty: pointee, .. }) => {
+ let mut data_ptr = scalar_unit(Pointer);
+ if !ty.is_unsafe_ptr() {
+ data_ptr.valid_range_mut().start = 1;
+ }
+
+ let pointee = tcx.normalize_erasing_regions(param_env, pointee);
+ if pointee.is_sized(tcx, param_env) {
+ return Ok(tcx.intern_layout(LayoutS::scalar(cx, data_ptr)));
+ }
+
+ let unsized_part = tcx.struct_tail_erasing_lifetimes(pointee, param_env);
+ let metadata = match unsized_part.kind() {
+ ty::Foreign(..) => {
+ return Ok(tcx.intern_layout(LayoutS::scalar(cx, data_ptr)));
+ }
+ ty::Slice(_) | ty::Str => scalar_unit(Int(dl.ptr_sized_integer(), false)),
+ ty::Dynamic(..) => {
+ let mut vtable = scalar_unit(Pointer);
+ vtable.valid_range_mut().start = 1;
+ vtable
+ }
+ _ => return Err(LayoutError::Unknown(unsized_part)),
+ };
+
+ // Effectively a (ptr, meta) tuple.
+ tcx.intern_layout(scalar_pair(cx, data_ptr, metadata))
+ }
+
+ ty::Dynamic(_, _, ty::DynStar) => {
+ let mut data = scalar_unit(Int(dl.ptr_sized_integer(), false));
+ data.valid_range_mut().start = 0;
+ let mut vtable = scalar_unit(Pointer);
+ vtable.valid_range_mut().start = 1;
+ tcx.intern_layout(scalar_pair(cx, data, vtable))
+ }
+
+ // Arrays and slices.
+ ty::Array(element, mut count) => {
+ if count.has_projections() {
+ count = tcx.normalize_erasing_regions(param_env, count);
+ if count.has_projections() {
+ return Err(LayoutError::Unknown(ty));
+ }
+ }
+
+ let count = count.try_eval_usize(tcx, param_env).ok_or(LayoutError::Unknown(ty))?;
+ let element = cx.layout_of(element)?;
+ let size = element.size.checked_mul(count, dl).ok_or(LayoutError::SizeOverflow(ty))?;
+
+ let abi = if count != 0 && tcx.conservative_is_privately_uninhabited(param_env.and(ty))
+ {
+ Abi::Uninhabited
+ } else {
+ Abi::Aggregate { sized: true }
+ };
+
+ let largest_niche = if count != 0 { element.largest_niche } else { None };
+
+ tcx.intern_layout(LayoutS {
+ variants: Variants::Single { index: VariantIdx::new(0) },
+ fields: FieldsShape::Array { stride: element.size, count },
+ abi,
+ largest_niche,
+ align: element.align,
+ size,
+ })
+ }
+ ty::Slice(element) => {
+ let element = cx.layout_of(element)?;
+ tcx.intern_layout(LayoutS {
+ variants: Variants::Single { index: VariantIdx::new(0) },
+ fields: FieldsShape::Array { stride: element.size, count: 0 },
+ abi: Abi::Aggregate { sized: false },
+ largest_niche: None,
+ align: element.align,
+ size: Size::ZERO,
+ })
+ }
+ ty::Str => tcx.intern_layout(LayoutS {
+ variants: Variants::Single { index: VariantIdx::new(0) },
+ fields: FieldsShape::Array { stride: Size::from_bytes(1), count: 0 },
+ abi: Abi::Aggregate { sized: false },
+ largest_niche: None,
+ align: dl.i8_align,
+ size: Size::ZERO,
+ }),
+
+ // Odd unit types.
+ ty::FnDef(..) => univariant(&[], &ReprOptions::default(), StructKind::AlwaysSized)?,
+ ty::Dynamic(_, _, ty::Dyn) | ty::Foreign(..) => {
+ let mut unit = univariant_uninterned(
+ cx,
+ ty,
+ &[],
+ &ReprOptions::default(),
+ StructKind::AlwaysSized,
+ )?;
+ match unit.abi {
+ Abi::Aggregate { ref mut sized } => *sized = false,
+ _ => bug!(),
+ }
+ tcx.intern_layout(unit)
+ }
+
+ ty::Generator(def_id, substs, _) => generator_layout(cx, ty, def_id, substs)?,
+
+ ty::Closure(_, ref substs) => {
+ let tys = substs.as_closure().upvar_tys();
+ univariant(
+ &tys.map(|ty| cx.layout_of(ty)).collect::<Result<Vec<_>, _>>()?,
+ &ReprOptions::default(),
+ StructKind::AlwaysSized,
+ )?
+ }
+
+ ty::Tuple(tys) => {
+ let kind =
+ if tys.len() == 0 { StructKind::AlwaysSized } else { StructKind::MaybeUnsized };
+
+ univariant(
+ &tys.iter().map(|k| cx.layout_of(k)).collect::<Result<Vec<_>, _>>()?,
+ &ReprOptions::default(),
+ kind,
+ )?
+ }
+
+ // SIMD vector types.
+ ty::Adt(def, substs) if def.repr().simd() => {
+ if !def.is_struct() {
+ // Should have yielded E0517 by now.
+ tcx.sess.delay_span_bug(
+ DUMMY_SP,
+ "#[repr(simd)] was applied to an ADT that is not a struct",
+ );
+ return Err(LayoutError::Unknown(ty));
+ }
+
+ // Supported SIMD vectors are homogeneous ADTs with at least one field:
+ //
+ // * #[repr(simd)] struct S(T, T, T, T);
+ // * #[repr(simd)] struct S { x: T, y: T, z: T, w: T }
+ // * #[repr(simd)] struct S([T; 4])
+ //
+ // where T is a primitive scalar (integer/float/pointer).
+
+ // SIMD vectors with zero fields are not supported.
+ // (should be caught by typeck)
+ if def.non_enum_variant().fields.is_empty() {
+ tcx.sess.fatal(&format!("monomorphising SIMD type `{}` of zero length", ty));
+ }
+
+ // Type of the first ADT field:
+ let f0_ty = def.non_enum_variant().fields[0].ty(tcx, substs);
+
+ // Heterogeneous SIMD vectors are not supported:
+ // (should be caught by typeck)
+ for fi in &def.non_enum_variant().fields {
+ if fi.ty(tcx, substs) != f0_ty {
+ tcx.sess.fatal(&format!("monomorphising heterogeneous SIMD type `{}`", ty));
+ }
+ }
+
+ // The element type and number of elements of the SIMD vector
+ // are obtained from:
+ //
+ // * the element type and length of the single array field, if
+ // the first field is of array type, or
+ //
+ // * the homogeneous field type and the number of fields.
+ let (e_ty, e_len, is_array) = if let ty::Array(e_ty, _) = f0_ty.kind() {
+ // First ADT field is an array:
+
+ // SIMD vectors with multiple array fields are not supported:
+ // (should be caught by typeck)
+ if def.non_enum_variant().fields.len() != 1 {
+ tcx.sess.fatal(&format!(
+ "monomorphising SIMD type `{}` with more than one array field",
+ ty
+ ));
+ }
+
+ // Extract the number of elements from the layout of the array field:
+ let FieldsShape::Array { count, .. } = cx.layout_of(f0_ty)?.layout.fields() else {
+ return Err(LayoutError::Unknown(ty));
+ };
+
+ (*e_ty, *count, true)
+ } else {
+ // First ADT field is not an array:
+ (f0_ty, def.non_enum_variant().fields.len() as _, false)
+ };
+
+ // SIMD vectors of zero length are not supported.
+ // Additionally, lengths are capped at 2^16 as a fixed maximum backends must
+ // support.
+ //
+ // Can't be caught in typeck if the array length is generic.
+ if e_len == 0 {
+ tcx.sess.fatal(&format!("monomorphising SIMD type `{}` of zero length", ty));
+ } else if e_len > MAX_SIMD_LANES {
+ tcx.sess.fatal(&format!(
+ "monomorphising SIMD type `{}` of length greater than {}",
+ ty, MAX_SIMD_LANES,
+ ));
+ }
+
+ // Compute the ABI of the element type:
+ let e_ly = cx.layout_of(e_ty)?;
+ let Abi::Scalar(e_abi) = e_ly.abi else {
+ // This error isn't caught in typeck, e.g., if
+ // the element type of the vector is generic.
+ tcx.sess.fatal(&format!(
+ "monomorphising SIMD type `{}` with a non-primitive-scalar \
+ (integer/float/pointer) element type `{}`",
+ ty, e_ty
+ ))
+ };
+
+ // Compute the size and alignment of the vector:
+ let size = e_ly.size.checked_mul(e_len, dl).ok_or(LayoutError::SizeOverflow(ty))?;
+ let align = dl.vector_align(size);
+ let size = size.align_to(align.abi);
+
+ // Compute the placement of the vector fields:
+ let fields = if is_array {
+ FieldsShape::Arbitrary { offsets: vec![Size::ZERO], memory_index: vec![0] }
+ } else {
+ FieldsShape::Array { stride: e_ly.size, count: e_len }
+ };
+
+ tcx.intern_layout(LayoutS {
+ variants: Variants::Single { index: VariantIdx::new(0) },
+ fields,
+ abi: Abi::Vector { element: e_abi, count: e_len },
+ largest_niche: e_ly.largest_niche,
+ size,
+ align,
+ })
+ }
+
+ // ADTs.
+ ty::Adt(def, substs) => {
+ // Cache the field layouts.
+ let variants = def
+ .variants()
+ .iter()
+ .map(|v| {
+ v.fields
+ .iter()
+ .map(|field| cx.layout_of(field.ty(tcx, substs)))
+ .collect::<Result<Vec<_>, _>>()
+ })
+ .collect::<Result<IndexVec<VariantIdx, _>, _>>()?;
+
+ if def.is_union() {
+ if def.repr().pack.is_some() && def.repr().align.is_some() {
+ cx.tcx.sess.delay_span_bug(
+ tcx.def_span(def.did()),
+ "union cannot be packed and aligned",
+ );
+ return Err(LayoutError::Unknown(ty));
+ }
+
+ let mut align =
+ if def.repr().pack.is_some() { dl.i8_align } else { dl.aggregate_align };
+
+ if let Some(repr_align) = def.repr().align {
+ align = align.max(AbiAndPrefAlign::new(repr_align));
+ }
+
+ let optimize = !def.repr().inhibit_union_abi_opt();
+ let mut size = Size::ZERO;
+ let mut abi = Abi::Aggregate { sized: true };
+ let index = VariantIdx::new(0);
+ for field in &variants[index] {
+ assert!(!field.is_unsized());
+ align = align.max(field.align);
+
+ // If all non-ZST fields have the same ABI, forward this ABI
+ if optimize && !field.is_zst() {
+ // Discard valid range information and allow undef
+ let field_abi = match field.abi {
+ Abi::Scalar(x) => Abi::Scalar(x.to_union()),
+ Abi::ScalarPair(x, y) => Abi::ScalarPair(x.to_union(), y.to_union()),
+ Abi::Vector { element: x, count } => {
+ Abi::Vector { element: x.to_union(), count }
+ }
+ Abi::Uninhabited | Abi::Aggregate { .. } => {
+ Abi::Aggregate { sized: true }
+ }
+ };
+
+ if size == Size::ZERO {
+ // first non ZST: initialize 'abi'
+ abi = field_abi;
+ } else if abi != field_abi {
+ // different fields have different ABI: reset to Aggregate
+ abi = Abi::Aggregate { sized: true };
+ }
+ }
+
+ size = cmp::max(size, field.size);
+ }
+
+ if let Some(pack) = def.repr().pack {
+ align = align.min(AbiAndPrefAlign::new(pack));
+ }
+
+ return Ok(tcx.intern_layout(LayoutS {
+ variants: Variants::Single { index },
+ fields: FieldsShape::Union(
+ NonZeroUsize::new(variants[index].len()).ok_or(LayoutError::Unknown(ty))?,
+ ),
+ abi,
+ largest_niche: None,
+ align,
+ size: size.align_to(align.abi),
+ }));
+ }
+
+ // A variant is absent if it's uninhabited and only has ZST fields.
+ // Present uninhabited variants only require space for their fields,
+ // but *not* an encoding of the discriminant (e.g., a tag value).
+ // See issue #49298 for more details on the need to leave space
+ // for non-ZST uninhabited data (mostly partial initialization).
+ let absent = |fields: &[TyAndLayout<'_>]| {
+ let uninhabited = fields.iter().any(|f| f.abi.is_uninhabited());
+ let is_zst = fields.iter().all(|f| f.is_zst());
+ uninhabited && is_zst
+ };
+ let (present_first, present_second) = {
+ let mut present_variants = variants
+ .iter_enumerated()
+ .filter_map(|(i, v)| if absent(v) { None } else { Some(i) });
+ (present_variants.next(), present_variants.next())
+ };
+ let present_first = match present_first {
+ Some(present_first) => present_first,
+ // Uninhabited because it has no variants, or only absent ones.
+ None if def.is_enum() => {
+ return Ok(tcx.layout_of(param_env.and(tcx.types.never))?.layout);
+ }
+ // If it's a struct, still compute a layout so that we can still compute the
+ // field offsets.
+ None => VariantIdx::new(0),
+ };
+
+ let is_struct = !def.is_enum() ||
+ // Only one variant is present.
+ (present_second.is_none() &&
+ // Representation optimizations are allowed.
+ !def.repr().inhibit_enum_layout_opt());
+ if is_struct {
+ // Struct, or univariant enum equivalent to a struct.
+ // (Typechecking will reject discriminant-sizing attrs.)
+
+ let v = present_first;
+ let kind = if def.is_enum() || variants[v].is_empty() {
+ StructKind::AlwaysSized
+ } else {
+ let param_env = tcx.param_env(def.did());
+ let last_field = def.variant(v).fields.last().unwrap();
+ let always_sized = tcx.type_of(last_field.did).is_sized(tcx, param_env);
+ if !always_sized { StructKind::MaybeUnsized } else { StructKind::AlwaysSized }
+ };
+
+ let mut st = univariant_uninterned(cx, ty, &variants[v], &def.repr(), kind)?;
+ st.variants = Variants::Single { index: v };
+
+ if def.is_unsafe_cell() {
+ let hide_niches = |scalar: &mut _| match scalar {
+ Scalar::Initialized { value, valid_range } => {
+ *valid_range = WrappingRange::full(value.size(dl))
+ }
+ // Already doesn't have any niches
+ Scalar::Union { .. } => {}
+ };
+ match &mut st.abi {
+ Abi::Uninhabited => {}
+ Abi::Scalar(scalar) => hide_niches(scalar),
+ Abi::ScalarPair(a, b) => {
+ hide_niches(a);
+ hide_niches(b);
+ }
+ Abi::Vector { element, count: _ } => hide_niches(element),
+ Abi::Aggregate { sized: _ } => {}
+ }
+ st.largest_niche = None;
+ return Ok(tcx.intern_layout(st));
+ }
+
+ let (start, end) = cx.tcx.layout_scalar_valid_range(def.did());
+ match st.abi {
+ Abi::Scalar(ref mut scalar) | Abi::ScalarPair(ref mut scalar, _) => {
+ // the asserts ensure that we are not using the
+ // `#[rustc_layout_scalar_valid_range(n)]`
+ // attribute to widen the range of anything as that would probably
+ // result in UB somewhere
+ // FIXME(eddyb) the asserts are probably not needed,
+ // as larger validity ranges would result in missed
+ // optimizations, *not* wrongly assuming the inner
+ // value is valid. e.g. unions enlarge validity ranges,
+ // because the values may be uninitialized.
+ if let Bound::Included(start) = start {
+ // FIXME(eddyb) this might be incorrect - it doesn't
+ // account for wrap-around (end < start) ranges.
+ let valid_range = scalar.valid_range_mut();
+ assert!(valid_range.start <= start);
+ valid_range.start = start;
+ }
+ if let Bound::Included(end) = end {
+ // FIXME(eddyb) this might be incorrect - it doesn't
+ // account for wrap-around (end < start) ranges.
+ let valid_range = scalar.valid_range_mut();
+ assert!(valid_range.end >= end);
+ valid_range.end = end;
+ }
+
+ // Update `largest_niche` if we have introduced a larger niche.
+ let niche = Niche::from_scalar(dl, Size::ZERO, *scalar);
+ if let Some(niche) = niche {
+ match st.largest_niche {
+ Some(largest_niche) => {
+ // Replace the existing niche even if they're equal,
+ // because this one is at a lower offset.
+ if largest_niche.available(dl) <= niche.available(dl) {
+ st.largest_niche = Some(niche);
+ }
+ }
+ None => st.largest_niche = Some(niche),
+ }
+ }
+ }
+ _ => assert!(
+ start == Bound::Unbounded && end == Bound::Unbounded,
+ "nonscalar layout for layout_scalar_valid_range type {:?}: {:#?}",
+ def,
+ st,
+ ),
+ }
+
+ return Ok(tcx.intern_layout(st));
+ }
+
+ // At this point, we have handled all unions and
+ // structs. (We have also handled univariant enums
+ // that allow representation optimization.)
+ assert!(def.is_enum());
+
+ // Until we've decided whether to use the tagged or
+ // niche filling LayoutS, we don't want to intern the
+ // variant layouts, so we can't store them in the
+ // overall LayoutS. Store the overall LayoutS
+ // and the variant LayoutSs here until then.
+ struct TmpLayout<'tcx> {
+ layout: LayoutS<'tcx>,
+ variants: IndexVec<VariantIdx, LayoutS<'tcx>>,
+ }
+
+ let calculate_niche_filling_layout =
+ || -> Result<Option<TmpLayout<'tcx>>, LayoutError<'tcx>> {
+ // The current code for niche-filling relies on variant indices
+ // instead of actual discriminants, so enums with
+ // explicit discriminants (RFC #2363) would misbehave.
+ if def.repr().inhibit_enum_layout_opt()
+ || def
+ .variants()
+ .iter_enumerated()
+ .any(|(i, v)| v.discr != ty::VariantDiscr::Relative(i.as_u32()))
+ {
+ return Ok(None);
+ }
+
+ if variants.len() < 2 {
+ return Ok(None);
+ }
+
+ let mut align = dl.aggregate_align;
+ let mut variant_layouts = variants
+ .iter_enumerated()
+ .map(|(j, v)| {
+ let mut st = univariant_uninterned(
+ cx,
+ ty,
+ v,
+ &def.repr(),
+ StructKind::AlwaysSized,
+ )?;
+ st.variants = Variants::Single { index: j };
+
+ align = align.max(st.align);
+
+ Ok(st)
+ })
+ .collect::<Result<IndexVec<VariantIdx, _>, _>>()?;
+
+ let largest_variant_index = match variant_layouts
+ .iter_enumerated()
+ .max_by_key(|(_i, layout)| layout.size.bytes())
+ .map(|(i, _layout)| i)
+ {
+ None => return Ok(None),
+ Some(i) => i,
+ };
+
+ let all_indices = VariantIdx::new(0)..=VariantIdx::new(variants.len() - 1);
+ let needs_disc = |index: VariantIdx| {
+ index != largest_variant_index && !absent(&variants[index])
+ };
+ let niche_variants = all_indices.clone().find(|v| needs_disc(*v)).unwrap()
+ ..=all_indices.rev().find(|v| needs_disc(*v)).unwrap();
+
+ let count = niche_variants.size_hint().1.unwrap() as u128;
+
+ // Find the field with the largest niche
+ let (field_index, niche, (niche_start, niche_scalar)) = match variants
+ [largest_variant_index]
+ .iter()
+ .enumerate()
+ .filter_map(|(j, field)| Some((j, field.largest_niche?)))
+ .max_by_key(|(_, niche)| niche.available(dl))
+ .and_then(|(j, niche)| Some((j, niche, niche.reserve(cx, count)?)))
+ {
+ None => return Ok(None),
+ Some(x) => x,
+ };
+
+ let niche_offset = niche.offset
+ + variant_layouts[largest_variant_index].fields.offset(field_index);
+ let niche_size = niche.value.size(dl);
+ let size = variant_layouts[largest_variant_index].size.align_to(align.abi);
+
+ let all_variants_fit =
+ variant_layouts.iter_enumerated_mut().all(|(i, layout)| {
+ if i == largest_variant_index {
+ return true;
+ }
+
+ layout.largest_niche = None;
+
+ if layout.size <= niche_offset {
+ // This variant will fit before the niche.
+ return true;
+ }
+
+ // Determine if it'll fit after the niche.
+ let this_align = layout.align.abi;
+ let this_offset = (niche_offset + niche_size).align_to(this_align);
+
+ if this_offset + layout.size > size {
+ return false;
+ }
+
+ // It'll fit, but we need to make some adjustments.
+ match layout.fields {
+ FieldsShape::Arbitrary { ref mut offsets, .. } => {
+ for (j, offset) in offsets.iter_mut().enumerate() {
+ if !variants[i][j].is_zst() {
+ *offset += this_offset;
+ }
+ }
+ }
+ _ => {
+ panic!("Layout of fields should be Arbitrary for variants")
+ }
+ }
+
+ // It can't be a Scalar or ScalarPair because the offset isn't 0.
+ if !layout.abi.is_uninhabited() {
+ layout.abi = Abi::Aggregate { sized: true };
+ }
+ layout.size += this_offset;
+
+ true
+ });
+
+ if !all_variants_fit {
+ return Ok(None);
+ }
+
+ let largest_niche = Niche::from_scalar(dl, niche_offset, niche_scalar);
+
+ let others_zst = variant_layouts
+ .iter_enumerated()
+ .all(|(i, layout)| i == largest_variant_index || layout.size == Size::ZERO);
+ let same_size = size == variant_layouts[largest_variant_index].size;
+ let same_align = align == variant_layouts[largest_variant_index].align;
+
+ let abi = if variant_layouts.iter().all(|v| v.abi.is_uninhabited()) {
+ Abi::Uninhabited
+ } else if same_size && same_align && others_zst {
+ match variant_layouts[largest_variant_index].abi {
+ // When the total alignment and size match, we can use the
+ // same ABI as the scalar variant with the reserved niche.
+ Abi::Scalar(_) => Abi::Scalar(niche_scalar),
+ Abi::ScalarPair(first, second) => {
+ // Only the niche is guaranteed to be initialised,
+ // so use union layouts for the other primitive.
+ if niche_offset == Size::ZERO {
+ Abi::ScalarPair(niche_scalar, second.to_union())
+ } else {
+ Abi::ScalarPair(first.to_union(), niche_scalar)
+ }
+ }
+ _ => Abi::Aggregate { sized: true },
+ }
+ } else {
+ Abi::Aggregate { sized: true }
+ };
+
+ let layout = LayoutS {
+ variants: Variants::Multiple {
+ tag: niche_scalar,
+ tag_encoding: TagEncoding::Niche {
+ untagged_variant: largest_variant_index,
+ niche_variants,
+ niche_start,
+ },
+ tag_field: 0,
+ variants: IndexVec::new(),
+ },
+ fields: FieldsShape::Arbitrary {
+ offsets: vec![niche_offset],
+ memory_index: vec![0],
+ },
+ abi,
+ largest_niche,
+ size,
+ align,
+ };
+
+ Ok(Some(TmpLayout { layout, variants: variant_layouts }))
+ };
+
+ let niche_filling_layout = calculate_niche_filling_layout()?;
+
+ let (mut min, mut max) = (i128::MAX, i128::MIN);
+ let discr_type = def.repr().discr_type();
+ let bits = Integer::from_attr(cx, discr_type).size().bits();
+ for (i, discr) in def.discriminants(tcx) {
+ if variants[i].iter().any(|f| f.abi.is_uninhabited()) {
+ continue;
+ }
+ let mut x = discr.val as i128;
+ if discr_type.is_signed() {
+ // sign extend the raw representation to be an i128
+ x = (x << (128 - bits)) >> (128 - bits);
+ }
+ if x < min {
+ min = x;
+ }
+ if x > max {
+ max = x;
+ }
+ }
+ // We might have no inhabited variants, so pretend there's at least one.
+ if (min, max) == (i128::MAX, i128::MIN) {
+ min = 0;
+ max = 0;
+ }
+ assert!(min <= max, "discriminant range is {}...{}", min, max);
+ let (min_ity, signed) = Integer::repr_discr(tcx, ty, &def.repr(), min, max);
+
+ let mut align = dl.aggregate_align;
+ let mut size = Size::ZERO;
+
+ // We're interested in the smallest alignment, so start large.
+ let mut start_align = Align::from_bytes(256).unwrap();
+ assert_eq!(Integer::for_align(dl, start_align), None);
+
+ // repr(C) on an enum tells us to make a (tag, union) layout,
+ // so we need to grow the prefix alignment to be at least
+ // the alignment of the union. (This value is used both for
+ // determining the alignment of the overall enum, and the
+ // determining the alignment of the payload after the tag.)
+ let mut prefix_align = min_ity.align(dl).abi;
+ if def.repr().c() {
+ for fields in &variants {
+ for field in fields {
+ prefix_align = prefix_align.max(field.align.abi);
+ }
+ }
+ }
+
+ // Create the set of structs that represent each variant.
+ let mut layout_variants = variants
+ .iter_enumerated()
+ .map(|(i, field_layouts)| {
+ let mut st = univariant_uninterned(
+ cx,
+ ty,
+ &field_layouts,
+ &def.repr(),
+ StructKind::Prefixed(min_ity.size(), prefix_align),
+ )?;
+ st.variants = Variants::Single { index: i };
+ // Find the first field we can't move later
+ // to make room for a larger discriminant.
+ for field in st.fields.index_by_increasing_offset().map(|j| field_layouts[j]) {
+ if !field.is_zst() || field.align.abi.bytes() != 1 {
+ start_align = start_align.min(field.align.abi);
+ break;
+ }
+ }
+ size = cmp::max(size, st.size);
+ align = align.max(st.align);
+ Ok(st)
+ })
+ .collect::<Result<IndexVec<VariantIdx, _>, _>>()?;
+
+ // Align the maximum variant size to the largest alignment.
+ size = size.align_to(align.abi);
+
+ if size.bytes() >= dl.obj_size_bound() {
+ return Err(LayoutError::SizeOverflow(ty));
+ }
+
+ let typeck_ity = Integer::from_attr(dl, def.repr().discr_type());
+ if typeck_ity < min_ity {
+ // It is a bug if Layout decided on a greater discriminant size than typeck for
+ // some reason at this point (based on values discriminant can take on). Mostly
+ // because this discriminant will be loaded, and then stored into variable of
+ // type calculated by typeck. Consider such case (a bug): typeck decided on
+ // byte-sized discriminant, but layout thinks we need a 16-bit to store all
+ // discriminant values. That would be a bug, because then, in codegen, in order
+ // to store this 16-bit discriminant into 8-bit sized temporary some of the
+ // space necessary to represent would have to be discarded (or layout is wrong
+ // on thinking it needs 16 bits)
+ bug!(
+ "layout decided on a larger discriminant type ({:?}) than typeck ({:?})",
+ min_ity,
+ typeck_ity
+ );
+ // However, it is fine to make discr type however large (as an optimisation)
+ // after this point – we’ll just truncate the value we load in codegen.
+ }
+
+ // Check to see if we should use a different type for the
+ // discriminant. We can safely use a type with the same size
+ // as the alignment of the first field of each variant.
+ // We increase the size of the discriminant to avoid LLVM copying
+ // padding when it doesn't need to. This normally causes unaligned
+ // load/stores and excessive memcpy/memset operations. By using a
+ // bigger integer size, LLVM can be sure about its contents and
+ // won't be so conservative.
+
+ // Use the initial field alignment
+ let mut ity = if def.repr().c() || def.repr().int.is_some() {
+ min_ity
+ } else {
+ Integer::for_align(dl, start_align).unwrap_or(min_ity)
+ };
+
+ // If the alignment is not larger than the chosen discriminant size,
+ // don't use the alignment as the final size.
+ if ity <= min_ity {
+ ity = min_ity;
+ } else {
+ // Patch up the variants' first few fields.
+ let old_ity_size = min_ity.size();
+ let new_ity_size = ity.size();
+ for variant in &mut layout_variants {
+ match variant.fields {
+ FieldsShape::Arbitrary { ref mut offsets, .. } => {
+ for i in offsets {
+ if *i <= old_ity_size {
+ assert_eq!(*i, old_ity_size);
+ *i = new_ity_size;
+ }
+ }
+ // We might be making the struct larger.
+ if variant.size <= old_ity_size {
+ variant.size = new_ity_size;
+ }
+ }
+ _ => bug!(),
+ }
+ }
+ }
+
+ let tag_mask = ity.size().unsigned_int_max();
+ let tag = Scalar::Initialized {
+ value: Int(ity, signed),
+ valid_range: WrappingRange {
+ start: (min as u128 & tag_mask),
+ end: (max as u128 & tag_mask),
+ },
+ };
+ let mut abi = Abi::Aggregate { sized: true };
+
+ if layout_variants.iter().all(|v| v.abi.is_uninhabited()) {
+ abi = Abi::Uninhabited;
+ } else if tag.size(dl) == size {
+ // Make sure we only use scalar layout when the enum is entirely its
+ // own tag (i.e. it has no padding nor any non-ZST variant fields).
+ abi = Abi::Scalar(tag);
+ } else {
+ // Try to use a ScalarPair for all tagged enums.
+ let mut common_prim = None;
+ let mut common_prim_initialized_in_all_variants = true;
+ for (field_layouts, layout_variant) in iter::zip(&variants, &layout_variants) {
+ let FieldsShape::Arbitrary { ref offsets, .. } = layout_variant.fields else {
+ bug!();
+ };
+ let mut fields = iter::zip(field_layouts, offsets).filter(|p| !p.0.is_zst());
+ let (field, offset) = match (fields.next(), fields.next()) {
+ (None, None) => {
+ common_prim_initialized_in_all_variants = false;
+ continue;
+ }
+ (Some(pair), None) => pair,
+ _ => {
+ common_prim = None;
+ break;
+ }
+ };
+ let prim = match field.abi {
+ Abi::Scalar(scalar) => {
+ common_prim_initialized_in_all_variants &=
+ matches!(scalar, Scalar::Initialized { .. });
+ scalar.primitive()
+ }
+ _ => {
+ common_prim = None;
+ break;
+ }
+ };
+ if let Some(pair) = common_prim {
+ // This is pretty conservative. We could go fancier
+ // by conflating things like i32 and u32, or even
+ // realising that (u8, u8) could just cohabit with
+ // u16 or even u32.
+ if pair != (prim, offset) {
+ common_prim = None;
+ break;
+ }
+ } else {
+ common_prim = Some((prim, offset));
+ }
+ }
+ if let Some((prim, offset)) = common_prim {
+ let prim_scalar = if common_prim_initialized_in_all_variants {
+ scalar_unit(prim)
+ } else {
+ // Common prim might be uninit.
+ Scalar::Union { value: prim }
+ };
+ let pair = scalar_pair(cx, tag, prim_scalar);
+ let pair_offsets = match pair.fields {
+ FieldsShape::Arbitrary { ref offsets, ref memory_index } => {
+ assert_eq!(memory_index, &[0, 1]);
+ offsets
+ }
+ _ => bug!(),
+ };
+ if pair_offsets[0] == Size::ZERO
+ && pair_offsets[1] == *offset
+ && align == pair.align
+ && size == pair.size
+ {
+ // We can use `ScalarPair` only when it matches our
+ // already computed layout (including `#[repr(C)]`).
+ abi = pair.abi;
+ }
+ }
+ }
+
+ // If we pick a "clever" (by-value) ABI, we might have to adjust the ABI of the
+ // variants to ensure they are consistent. This is because a downcast is
+ // semantically a NOP, and thus should not affect layout.
+ if matches!(abi, Abi::Scalar(..) | Abi::ScalarPair(..)) {
+ for variant in &mut layout_variants {
+ // We only do this for variants with fields; the others are not accessed anyway.
+ // Also do not overwrite any already existing "clever" ABIs.
+ if variant.fields.count() > 0 && matches!(variant.abi, Abi::Aggregate { .. }) {
+ variant.abi = abi;
+ // Also need to bump up the size and alignment, so that the entire value fits in here.
+ variant.size = cmp::max(variant.size, size);
+ variant.align.abi = cmp::max(variant.align.abi, align.abi);
+ }
+ }
+ }
+
+ let largest_niche = Niche::from_scalar(dl, Size::ZERO, tag);
+
+ let tagged_layout = LayoutS {
+ variants: Variants::Multiple {
+ tag,
+ tag_encoding: TagEncoding::Direct,
+ tag_field: 0,
+ variants: IndexVec::new(),
+ },
+ fields: FieldsShape::Arbitrary { offsets: vec![Size::ZERO], memory_index: vec![0] },
+ largest_niche,
+ abi,
+ align,
+ size,
+ };
+
+ let tagged_layout = TmpLayout { layout: tagged_layout, variants: layout_variants };
+
+ let mut best_layout = match (tagged_layout, niche_filling_layout) {
+ (tl, Some(nl)) => {
+ // Pick the smaller layout; otherwise,
+ // pick the layout with the larger niche; otherwise,
+ // pick tagged as it has simpler codegen.
+ use Ordering::*;
+ let niche_size = |tmp_l: &TmpLayout<'_>| {
+ tmp_l.layout.largest_niche.map_or(0, |n| n.available(dl))
+ };
+ match (
+ tl.layout.size.cmp(&nl.layout.size),
+ niche_size(&tl).cmp(&niche_size(&nl)),
+ ) {
+ (Greater, _) => nl,
+ (Equal, Less) => nl,
+ _ => tl,
+ }
+ }
+ (tl, None) => tl,
+ };
+
+ // Now we can intern the variant layouts and store them in the enum layout.
+ best_layout.layout.variants = match best_layout.layout.variants {
+ Variants::Multiple { tag, tag_encoding, tag_field, .. } => Variants::Multiple {
+ tag,
+ tag_encoding,
+ tag_field,
+ variants: best_layout
+ .variants
+ .into_iter()
+ .map(|layout| tcx.intern_layout(layout))
+ .collect(),
+ },
+ _ => bug!(),
+ };
+
+ tcx.intern_layout(best_layout.layout)
+ }
+
+ // Types with no meaningful known layout.
+ ty::Projection(_) | ty::Opaque(..) => {
+ // NOTE(eddyb) `layout_of` query should've normalized these away,
+ // if that was possible, so there's no reason to try again here.
+ return Err(LayoutError::Unknown(ty));
+ }
+
+ ty::Placeholder(..) | ty::GeneratorWitness(..) | ty::Infer(_) => {
+ bug!("Layout::compute: unexpected type `{}`", ty)
+ }
+
+ ty::Bound(..) | ty::Param(_) | ty::Error(_) => {
+ return Err(LayoutError::Unknown(ty));
+ }
+ })
+}
+
+/// Overlap eligibility and variant assignment for each GeneratorSavedLocal.
+#[derive(Clone, Debug, PartialEq)]
+enum SavedLocalEligibility {
+ Unassigned,
+ Assigned(VariantIdx),
+ // FIXME: Use newtype_index so we aren't wasting bytes
+ Ineligible(Option<u32>),
+}
+
+// When laying out generators, we divide our saved local fields into two
+// categories: overlap-eligible and overlap-ineligible.
+//
+// Those fields which are ineligible for overlap go in a "prefix" at the
+// beginning of the layout, and always have space reserved for them.
+//
+// Overlap-eligible fields are only assigned to one variant, so we lay
+// those fields out for each variant and put them right after the
+// prefix.
+//
+// Finally, in the layout details, we point to the fields from the
+// variants they are assigned to. It is possible for some fields to be
+// included in multiple variants. No field ever "moves around" in the
+// layout; its offset is always the same.
+//
+// Also included in the layout are the upvars and the discriminant.
+// These are included as fields on the "outer" layout; they are not part
+// of any variant.
+
+/// Compute the eligibility and assignment of each local.
+fn generator_saved_local_eligibility<'tcx>(
+ info: &GeneratorLayout<'tcx>,
+) -> (BitSet<GeneratorSavedLocal>, IndexVec<GeneratorSavedLocal, SavedLocalEligibility>) {
+ use SavedLocalEligibility::*;
+
+ let mut assignments: IndexVec<GeneratorSavedLocal, SavedLocalEligibility> =
+ IndexVec::from_elem_n(Unassigned, info.field_tys.len());
+
+ // The saved locals not eligible for overlap. These will get
+ // "promoted" to the prefix of our generator.
+ let mut ineligible_locals = BitSet::new_empty(info.field_tys.len());
+
+ // Figure out which of our saved locals are fields in only
+ // one variant. The rest are deemed ineligible for overlap.
+ for (variant_index, fields) in info.variant_fields.iter_enumerated() {
+ for local in fields {
+ match assignments[*local] {
+ Unassigned => {
+ assignments[*local] = Assigned(variant_index);
+ }
+ Assigned(idx) => {
+ // We've already seen this local at another suspension
+ // point, so it is no longer a candidate.
+ trace!(
+ "removing local {:?} in >1 variant ({:?}, {:?})",
+ local,
+ variant_index,
+ idx
+ );
+ ineligible_locals.insert(*local);
+ assignments[*local] = Ineligible(None);
+ }
+ Ineligible(_) => {}
+ }
+ }
+ }
+
+ // Next, check every pair of eligible locals to see if they
+ // conflict.
+ for local_a in info.storage_conflicts.rows() {
+ let conflicts_a = info.storage_conflicts.count(local_a);
+ if ineligible_locals.contains(local_a) {
+ continue;
+ }
+
+ for local_b in info.storage_conflicts.iter(local_a) {
+ // local_a and local_b are storage live at the same time, therefore they
+ // cannot overlap in the generator layout. The only way to guarantee
+ // this is if they are in the same variant, or one is ineligible
+ // (which means it is stored in every variant).
+ if ineligible_locals.contains(local_b) || assignments[local_a] == assignments[local_b] {
+ continue;
+ }
+
+ // If they conflict, we will choose one to make ineligible.
+ // This is not always optimal; it's just a greedy heuristic that
+ // seems to produce good results most of the time.
+ let conflicts_b = info.storage_conflicts.count(local_b);
+ let (remove, other) =
+ if conflicts_a > conflicts_b { (local_a, local_b) } else { (local_b, local_a) };
+ ineligible_locals.insert(remove);
+ assignments[remove] = Ineligible(None);
+ trace!("removing local {:?} due to conflict with {:?}", remove, other);
+ }
+ }
+
+ // Count the number of variants in use. If only one of them, then it is
+ // impossible to overlap any locals in our layout. In this case it's
+ // always better to make the remaining locals ineligible, so we can
+ // lay them out with the other locals in the prefix and eliminate
+ // unnecessary padding bytes.
+ {
+ let mut used_variants = BitSet::new_empty(info.variant_fields.len());
+ for assignment in &assignments {
+ if let Assigned(idx) = assignment {
+ used_variants.insert(*idx);
+ }
+ }
+ if used_variants.count() < 2 {
+ for assignment in assignments.iter_mut() {
+ *assignment = Ineligible(None);
+ }
+ ineligible_locals.insert_all();
+ }
+ }
+
+ // Write down the order of our locals that will be promoted to the prefix.
+ {
+ for (idx, local) in ineligible_locals.iter().enumerate() {
+ assignments[local] = Ineligible(Some(idx as u32));
+ }
+ }
+ debug!("generator saved local assignments: {:?}", assignments);
+
+ (ineligible_locals, assignments)
+}
+
+/// Compute the full generator layout.
+fn generator_layout<'tcx>(
+ cx: &LayoutCx<'tcx, TyCtxt<'tcx>>,
+ ty: Ty<'tcx>,
+ def_id: hir::def_id::DefId,
+ substs: SubstsRef<'tcx>,
+) -> Result<Layout<'tcx>, LayoutError<'tcx>> {
+ use SavedLocalEligibility::*;
+ let tcx = cx.tcx;
+ let subst_field = |ty: Ty<'tcx>| EarlyBinder(ty).subst(tcx, substs);
+
+ let Some(info) = tcx.generator_layout(def_id) else {
+ return Err(LayoutError::Unknown(ty));
+ };
+ let (ineligible_locals, assignments) = generator_saved_local_eligibility(&info);
+
+ // Build a prefix layout, including "promoting" all ineligible
+ // locals as part of the prefix. We compute the layout of all of
+ // these fields at once to get optimal packing.
+ let tag_index = substs.as_generator().prefix_tys().count();
+
+ // `info.variant_fields` already accounts for the reserved variants, so no need to add them.
+ let max_discr = (info.variant_fields.len() - 1) as u128;
+ let discr_int = Integer::fit_unsigned(max_discr);
+ let discr_int_ty = discr_int.to_ty(tcx, false);
+ let tag = Scalar::Initialized {
+ value: Primitive::Int(discr_int, false),
+ valid_range: WrappingRange { start: 0, end: max_discr },
+ };
+ let tag_layout = cx.tcx.intern_layout(LayoutS::scalar(cx, tag));
+ let tag_layout = TyAndLayout { ty: discr_int_ty, layout: tag_layout };
+
+ let promoted_layouts = ineligible_locals
+ .iter()
+ .map(|local| subst_field(info.field_tys[local]))
+ .map(|ty| tcx.mk_maybe_uninit(ty))
+ .map(|ty| cx.layout_of(ty));
+ let prefix_layouts = substs
+ .as_generator()
+ .prefix_tys()
+ .map(|ty| cx.layout_of(ty))
+ .chain(iter::once(Ok(tag_layout)))
+ .chain(promoted_layouts)
+ .collect::<Result<Vec<_>, _>>()?;
+ let prefix = univariant_uninterned(
+ cx,
+ ty,
+ &prefix_layouts,
+ &ReprOptions::default(),
+ StructKind::AlwaysSized,
+ )?;
+
+ let (prefix_size, prefix_align) = (prefix.size, prefix.align);
+
+ // Split the prefix layout into the "outer" fields (upvars and
+ // discriminant) and the "promoted" fields. Promoted fields will
+ // get included in each variant that requested them in
+ // GeneratorLayout.
+ debug!("prefix = {:#?}", prefix);
+ let (outer_fields, promoted_offsets, promoted_memory_index) = match prefix.fields {
+ FieldsShape::Arbitrary { mut offsets, memory_index } => {
+ let mut inverse_memory_index = invert_mapping(&memory_index);
+
+ // "a" (`0..b_start`) and "b" (`b_start..`) correspond to
+ // "outer" and "promoted" fields respectively.
+ let b_start = (tag_index + 1) as u32;
+ let offsets_b = offsets.split_off(b_start as usize);
+ let offsets_a = offsets;
+
+ // Disentangle the "a" and "b" components of `inverse_memory_index`
+ // by preserving the order but keeping only one disjoint "half" each.
+ // FIXME(eddyb) build a better abstraction for permutations, if possible.
+ let inverse_memory_index_b: Vec<_> =
+ inverse_memory_index.iter().filter_map(|&i| i.checked_sub(b_start)).collect();
+ inverse_memory_index.retain(|&i| i < b_start);
+ let inverse_memory_index_a = inverse_memory_index;
+
+ // Since `inverse_memory_index_{a,b}` each only refer to their
+ // respective fields, they can be safely inverted
+ let memory_index_a = invert_mapping(&inverse_memory_index_a);
+ let memory_index_b = invert_mapping(&inverse_memory_index_b);
+
+ let outer_fields =
+ FieldsShape::Arbitrary { offsets: offsets_a, memory_index: memory_index_a };
+ (outer_fields, offsets_b, memory_index_b)
+ }
+ _ => bug!(),
+ };
+
+ let mut size = prefix.size;
+ let mut align = prefix.align;
+ let variants = info
+ .variant_fields
+ .iter_enumerated()
+ .map(|(index, variant_fields)| {
+ // Only include overlap-eligible fields when we compute our variant layout.
+ let variant_only_tys = variant_fields
+ .iter()
+ .filter(|local| match assignments[**local] {
+ Unassigned => bug!(),
+ Assigned(v) if v == index => true,
+ Assigned(_) => bug!("assignment does not match variant"),
+ Ineligible(_) => false,
+ })
+ .map(|local| subst_field(info.field_tys[*local]));
+
+ let mut variant = univariant_uninterned(
+ cx,
+ ty,
+ &variant_only_tys.map(|ty| cx.layout_of(ty)).collect::<Result<Vec<_>, _>>()?,
+ &ReprOptions::default(),
+ StructKind::Prefixed(prefix_size, prefix_align.abi),
+ )?;
+ variant.variants = Variants::Single { index };
+
+ let FieldsShape::Arbitrary { offsets, memory_index } = variant.fields else {
+ bug!();
+ };
+
+ // Now, stitch the promoted and variant-only fields back together in
+ // the order they are mentioned by our GeneratorLayout.
+ // Because we only use some subset (that can differ between variants)
+ // of the promoted fields, we can't just pick those elements of the
+ // `promoted_memory_index` (as we'd end up with gaps).
+ // So instead, we build an "inverse memory_index", as if all of the
+ // promoted fields were being used, but leave the elements not in the
+ // subset as `INVALID_FIELD_IDX`, which we can filter out later to
+ // obtain a valid (bijective) mapping.
+ const INVALID_FIELD_IDX: u32 = !0;
+ let mut combined_inverse_memory_index =
+ vec![INVALID_FIELD_IDX; promoted_memory_index.len() + memory_index.len()];
+ let mut offsets_and_memory_index = iter::zip(offsets, memory_index);
+ let combined_offsets = variant_fields
+ .iter()
+ .enumerate()
+ .map(|(i, local)| {
+ let (offset, memory_index) = match assignments[*local] {
+ Unassigned => bug!(),
+ Assigned(_) => {
+ let (offset, memory_index) = offsets_and_memory_index.next().unwrap();
+ (offset, promoted_memory_index.len() as u32 + memory_index)
+ }
+ Ineligible(field_idx) => {
+ let field_idx = field_idx.unwrap() as usize;
+ (promoted_offsets[field_idx], promoted_memory_index[field_idx])
+ }
+ };
+ combined_inverse_memory_index[memory_index as usize] = i as u32;
+ offset
+ })
+ .collect();
+
+ // Remove the unused slots and invert the mapping to obtain the
+ // combined `memory_index` (also see previous comment).
+ combined_inverse_memory_index.retain(|&i| i != INVALID_FIELD_IDX);
+ let combined_memory_index = invert_mapping(&combined_inverse_memory_index);
+
+ variant.fields = FieldsShape::Arbitrary {
+ offsets: combined_offsets,
+ memory_index: combined_memory_index,
+ };
+
+ size = size.max(variant.size);
+ align = align.max(variant.align);
+ Ok(tcx.intern_layout(variant))
+ })
+ .collect::<Result<IndexVec<VariantIdx, _>, _>>()?;
+
+ size = size.align_to(align.abi);
+
+ let abi = if prefix.abi.is_uninhabited() || variants.iter().all(|v| v.abi().is_uninhabited()) {
+ Abi::Uninhabited
+ } else {
+ Abi::Aggregate { sized: true }
+ };
+
+ let layout = tcx.intern_layout(LayoutS {
+ variants: Variants::Multiple {
+ tag,
+ tag_encoding: TagEncoding::Direct,
+ tag_field: tag_index,
+ variants,
+ },
+ fields: outer_fields,
+ abi,
+ largest_niche: prefix.largest_niche,
+ size,
+ align,
+ });
+ debug!("generator layout ({:?}): {:#?}", ty, layout);
+ Ok(layout)
+}
+
+/// This is invoked by the `layout_of` query to record the final
+/// layout of each type.
+#[inline(always)]
+fn record_layout_for_printing<'tcx>(cx: &LayoutCx<'tcx, TyCtxt<'tcx>>, layout: TyAndLayout<'tcx>) {
+ // If we are running with `-Zprint-type-sizes`, maybe record layouts
+ // for dumping later.
+ if cx.tcx.sess.opts.unstable_opts.print_type_sizes {
+ record_layout_for_printing_outlined(cx, layout)
+ }
+}
+
+fn record_layout_for_printing_outlined<'tcx>(
+ cx: &LayoutCx<'tcx, TyCtxt<'tcx>>,
+ layout: TyAndLayout<'tcx>,
+) {
+ // Ignore layouts that are done with non-empty environments or
+ // non-monomorphic layouts, as the user only wants to see the stuff
+ // resulting from the final codegen session.
+ if layout.ty.has_non_region_param() || !cx.param_env.caller_bounds().is_empty() {
+ return;
+ }
+
+ // (delay format until we actually need it)
+ let record = |kind, packed, opt_discr_size, variants| {
+ let type_desc = format!("{:?}", layout.ty);
+ cx.tcx.sess.code_stats.record_type_size(
+ kind,
+ type_desc,
+ layout.align.abi,
+ layout.size,
+ packed,
+ opt_discr_size,
+ variants,
+ );
+ };
+
+ let adt_def = match *layout.ty.kind() {
+ ty::Adt(ref adt_def, _) => {
+ debug!("print-type-size t: `{:?}` process adt", layout.ty);
+ adt_def
+ }
+
+ ty::Closure(..) => {
+ debug!("print-type-size t: `{:?}` record closure", layout.ty);
+ record(DataTypeKind::Closure, false, None, vec![]);
+ return;
+ }
+
+ _ => {
+ debug!("print-type-size t: `{:?}` skip non-nominal", layout.ty);
+ return;
+ }
+ };
+
+ let adt_kind = adt_def.adt_kind();
+ let adt_packed = adt_def.repr().pack.is_some();
+
+ let build_variant_info = |n: Option<Symbol>, flds: &[Symbol], layout: TyAndLayout<'tcx>| {
+ let mut min_size = Size::ZERO;
+ let field_info: Vec<_> = flds
+ .iter()
+ .enumerate()
+ .map(|(i, &name)| {
+ let field_layout = layout.field(cx, i);
+ let offset = layout.fields.offset(i);
+ let field_end = offset + field_layout.size;
+ if min_size < field_end {
+ min_size = field_end;
+ }
+ FieldInfo {
+ name,
+ offset: offset.bytes(),
+ size: field_layout.size.bytes(),
+ align: field_layout.align.abi.bytes(),
+ }
+ })
+ .collect();
+
+ VariantInfo {
+ name: n,
+ kind: if layout.is_unsized() { SizeKind::Min } else { SizeKind::Exact },
+ align: layout.align.abi.bytes(),
+ size: if min_size.bytes() == 0 { layout.size.bytes() } else { min_size.bytes() },
+ fields: field_info,
+ }
+ };
+
+ match layout.variants {
+ Variants::Single { index } => {
+ if !adt_def.variants().is_empty() && layout.fields != FieldsShape::Primitive {
+ debug!("print-type-size `{:#?}` variant {}", layout, adt_def.variant(index).name);
+ let variant_def = &adt_def.variant(index);
+ let fields: Vec<_> = variant_def.fields.iter().map(|f| f.name).collect();
+ record(
+ adt_kind.into(),
+ adt_packed,
+ None,
+ vec![build_variant_info(Some(variant_def.name), &fields, layout)],
+ );
+ } else {
+ // (This case arises for *empty* enums; so give it
+ // zero variants.)
+ record(adt_kind.into(), adt_packed, None, vec![]);
+ }
+ }
+
+ Variants::Multiple { tag, ref tag_encoding, .. } => {
+ debug!(
+ "print-type-size `{:#?}` adt general variants def {}",
+ layout.ty,
+ adt_def.variants().len()
+ );
+ let variant_infos: Vec<_> = adt_def
+ .variants()
+ .iter_enumerated()
+ .map(|(i, variant_def)| {
+ let fields: Vec<_> = variant_def.fields.iter().map(|f| f.name).collect();
+ build_variant_info(Some(variant_def.name), &fields, layout.for_variant(cx, i))
+ })
+ .collect();
+ record(
+ adt_kind.into(),
+ adt_packed,
+ match tag_encoding {
+ TagEncoding::Direct => Some(tag.size(cx)),
+ _ => None,
+ },
+ variant_infos,
+ );
+ }
+ }
+}
projects / rustc.git / blobdiff