diff options
Diffstat (limited to 'compiler/rustc_mir/src/interpret/operand.rs')
| -rw-r--r-- | compiler/rustc_mir/src/interpret/operand.rs | 736 |
1 files changed, 736 insertions, 0 deletions
diff --git a/compiler/rustc_mir/src/interpret/operand.rs b/compiler/rustc_mir/src/interpret/operand.rs new file mode 100644 index 00000000000..0b58caef54d --- /dev/null +++ b/compiler/rustc_mir/src/interpret/operand.rs @@ -0,0 +1,736 @@ +//! Functions concerning immediate values and operands, and reading from operands. +//! All high-level functions to read from memory work on operands as sources. + +use std::convert::TryFrom; +use std::fmt::Write; + +use rustc_errors::ErrorReported; +use rustc_hir::def::Namespace; +use rustc_macros::HashStable; +use rustc_middle::ty::layout::{PrimitiveExt, TyAndLayout}; +use rustc_middle::ty::print::{FmtPrinter, PrettyPrinter, Printer}; +use rustc_middle::ty::{ConstInt, Ty}; +use rustc_middle::{mir, ty}; +use rustc_target::abi::{Abi, HasDataLayout, LayoutOf, Size, TagEncoding}; +use rustc_target::abi::{VariantIdx, Variants}; + +use super::{ + from_known_layout, mir_assign_valid_types, ConstValue, GlobalId, InterpCx, InterpResult, + MPlaceTy, Machine, MemPlace, Place, PlaceTy, Pointer, Scalar, ScalarMaybeUninit, +}; + +/// An `Immediate` represents a single immediate self-contained Rust value. +/// +/// For optimization of a few very common cases, there is also a representation for a pair of +/// primitive values (`ScalarPair`). It allows Miri to avoid making allocations for checked binary +/// operations and wide pointers. This idea was taken from rustc's codegen. +/// In particular, thanks to `ScalarPair`, arithmetic operations and casts can be entirely +/// defined on `Immediate`, and do not have to work with a `Place`. +#[derive(Copy, Clone, Debug, PartialEq, Eq, HashStable, Hash)] +pub enum Immediate<Tag = ()> { + Scalar(ScalarMaybeUninit<Tag>), + ScalarPair(ScalarMaybeUninit<Tag>, ScalarMaybeUninit<Tag>), +} + +impl<Tag> From<ScalarMaybeUninit<Tag>> for Immediate<Tag> { + #[inline(always)] + fn from(val: ScalarMaybeUninit<Tag>) -> Self { + Immediate::Scalar(val) + } +} + +impl<Tag> From<Scalar<Tag>> for Immediate<Tag> { + #[inline(always)] + fn from(val: Scalar<Tag>) -> Self { + Immediate::Scalar(val.into()) + } +} + +impl<Tag> From<Pointer<Tag>> for Immediate<Tag> { + #[inline(always)] + fn from(val: Pointer<Tag>) -> Self { + Immediate::Scalar(Scalar::from(val).into()) + } +} + +impl<'tcx, Tag> Immediate<Tag> { + pub fn new_slice(val: Scalar<Tag>, len: u64, cx: &impl HasDataLayout) -> Self { + Immediate::ScalarPair(val.into(), Scalar::from_machine_usize(len, cx).into()) + } + + pub fn new_dyn_trait(val: Scalar<Tag>, vtable: Pointer<Tag>) -> Self { + Immediate::ScalarPair(val.into(), vtable.into()) + } + + #[inline] + pub fn to_scalar_or_uninit(self) -> ScalarMaybeUninit<Tag> { + match self { + Immediate::Scalar(val) => val, + Immediate::ScalarPair(..) => bug!("Got a wide pointer where a scalar was expected"), + } + } + + #[inline] + pub fn to_scalar(self) -> InterpResult<'tcx, Scalar<Tag>> { + self.to_scalar_or_uninit().check_init() + } + + #[inline] + pub fn to_scalar_pair(self) -> InterpResult<'tcx, (Scalar<Tag>, Scalar<Tag>)> { + match self { + Immediate::Scalar(..) => bug!("Got a thin pointer where a scalar pair was expected"), + Immediate::ScalarPair(a, b) => Ok((a.check_init()?, b.check_init()?)), + } + } +} + +// ScalarPair needs a type to interpret, so we often have an immediate and a type together +// as input for binary and cast operations. +#[derive(Copy, Clone, Debug)] +pub struct ImmTy<'tcx, Tag = ()> { + imm: Immediate<Tag>, + pub layout: TyAndLayout<'tcx>, +} + +impl<Tag: Copy> std::fmt::Display for ImmTy<'tcx, Tag> { + fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { + /// Helper function for printing a scalar to a FmtPrinter + fn p<'a, 'tcx, F: std::fmt::Write, Tag>( + cx: FmtPrinter<'a, 'tcx, F>, + s: ScalarMaybeUninit<Tag>, + ty: Ty<'tcx>, + ) -> Result<FmtPrinter<'a, 'tcx, F>, std::fmt::Error> { + match s { + ScalarMaybeUninit::Scalar(s) => { + cx.pretty_print_const_scalar(s.erase_tag(), ty, true) + } + ScalarMaybeUninit::Uninit => cx.typed_value( + |mut this| { + this.write_str("{uninit ")?; + Ok(this) + }, + |this| this.print_type(ty), + " ", + ), + } + } + ty::tls::with(|tcx| { + match self.imm { + Immediate::Scalar(s) => { + if let Some(ty) = tcx.lift(&self.layout.ty) { + let cx = FmtPrinter::new(tcx, f, Namespace::ValueNS); + p(cx, s, ty)?; + return Ok(()); + } + write!(f, "{}: {}", s.erase_tag(), self.layout.ty) + } + Immediate::ScalarPair(a, b) => { + // FIXME(oli-obk): at least print tuples and slices nicely + write!(f, "({}, {}): {}", a.erase_tag(), b.erase_tag(), self.layout.ty,) + } + } + }) + } +} + +impl<'tcx, Tag> ::std::ops::Deref for ImmTy<'tcx, Tag> { + type Target = Immediate<Tag>; + #[inline(always)] + fn deref(&self) -> &Immediate<Tag> { + &self.imm + } +} + +/// An `Operand` is the result of computing a `mir::Operand`. It can be immediate, +/// or still in memory. The latter is an optimization, to delay reading that chunk of +/// memory and to avoid having to store arbitrary-sized data here. +#[derive(Copy, Clone, Debug, PartialEq, Eq, HashStable, Hash)] +pub enum Operand<Tag = ()> { + Immediate(Immediate<Tag>), + Indirect(MemPlace<Tag>), +} + +#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)] +pub struct OpTy<'tcx, Tag = ()> { + op: Operand<Tag>, // Keep this private; it helps enforce invariants. + pub layout: TyAndLayout<'tcx>, +} + +impl<'tcx, Tag> ::std::ops::Deref for OpTy<'tcx, Tag> { + type Target = Operand<Tag>; + #[inline(always)] + fn deref(&self) -> &Operand<Tag> { + &self.op + } +} + +impl<'tcx, Tag: Copy> From<MPlaceTy<'tcx, Tag>> for OpTy<'tcx, Tag> { + #[inline(always)] + fn from(mplace: MPlaceTy<'tcx, Tag>) -> Self { + OpTy { op: Operand::Indirect(*mplace), layout: mplace.layout } + } +} + +impl<'tcx, Tag> From<ImmTy<'tcx, Tag>> for OpTy<'tcx, Tag> { + #[inline(always)] + fn from(val: ImmTy<'tcx, Tag>) -> Self { + OpTy { op: Operand::Immediate(val.imm), layout: val.layout } + } +} + +impl<'tcx, Tag: Copy> ImmTy<'tcx, Tag> { + #[inline] + pub fn from_scalar(val: Scalar<Tag>, layout: TyAndLayout<'tcx>) -> Self { + ImmTy { imm: val.into(), layout } + } + + #[inline] + pub fn from_immediate(imm: Immediate<Tag>, layout: TyAndLayout<'tcx>) -> Self { + ImmTy { imm, layout } + } + + #[inline] + pub fn try_from_uint(i: impl Into<u128>, layout: TyAndLayout<'tcx>) -> Option<Self> { + Some(Self::from_scalar(Scalar::try_from_uint(i, layout.size)?, layout)) + } + #[inline] + pub fn from_uint(i: impl Into<u128>, layout: TyAndLayout<'tcx>) -> Self { + Self::from_scalar(Scalar::from_uint(i, layout.size), layout) + } + + #[inline] + pub fn try_from_int(i: impl Into<i128>, layout: TyAndLayout<'tcx>) -> Option<Self> { + Some(Self::from_scalar(Scalar::try_from_int(i, layout.size)?, layout)) + } + + #[inline] + pub fn from_int(i: impl Into<i128>, layout: TyAndLayout<'tcx>) -> Self { + Self::from_scalar(Scalar::from_int(i, layout.size), layout) + } + + #[inline] + pub fn to_const_int(self) -> ConstInt { + assert!(self.layout.ty.is_integral()); + ConstInt::new( + self.to_scalar() + .expect("to_const_int doesn't work on scalar pairs") + .assert_bits(self.layout.size), + self.layout.size, + self.layout.ty.is_signed(), + self.layout.ty.is_ptr_sized_integral(), + ) + } +} + +impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> { + /// Normalice `place.ptr` to a `Pointer` if this is a place and not a ZST. + /// Can be helpful to avoid lots of `force_ptr` calls later, if this place is used a lot. + #[inline] + pub fn force_op_ptr( + &self, + op: OpTy<'tcx, M::PointerTag>, + ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> { + match op.try_as_mplace(self) { + Ok(mplace) => Ok(self.force_mplace_ptr(mplace)?.into()), + Err(imm) => Ok(imm.into()), // Nothing to cast/force + } + } + + /// Try reading an immediate in memory; this is interesting particularly for `ScalarPair`. + /// Returns `None` if the layout does not permit loading this as a value. + fn try_read_immediate_from_mplace( + &self, + mplace: MPlaceTy<'tcx, M::PointerTag>, + ) -> InterpResult<'tcx, Option<ImmTy<'tcx, M::PointerTag>>> { + if mplace.layout.is_unsized() { + // Don't touch unsized + return Ok(None); + } + + let ptr = match self + .check_mplace_access(mplace, None) + .expect("places should be checked on creation") + { + Some(ptr) => ptr, + None => { + if let Scalar::Ptr(ptr) = mplace.ptr { + // We may be reading from a static. + // In order to ensure that `static FOO: Type = FOO;` causes a cycle error + // instead of magically pulling *any* ZST value from the ether, we need to + // actually access the referenced allocation. + self.memory.get_raw(ptr.alloc_id)?; + } + return Ok(Some(ImmTy { + // zero-sized type + imm: Scalar::zst().into(), + layout: mplace.layout, + })); + } + }; + + let alloc = self.memory.get_raw(ptr.alloc_id)?; + + match mplace.layout.abi { + Abi::Scalar(..) => { + let scalar = alloc.read_scalar(self, ptr, mplace.layout.size)?; + Ok(Some(ImmTy { imm: scalar.into(), layout: mplace.layout })) + } + Abi::ScalarPair(ref a, ref b) => { + // We checked `ptr_align` above, so all fields will have the alignment they need. + // We would anyway check against `ptr_align.restrict_for_offset(b_offset)`, + // which `ptr.offset(b_offset)` cannot possibly fail to satisfy. + let (a, b) = (&a.value, &b.value); + let (a_size, b_size) = (a.size(self), b.size(self)); + let a_ptr = ptr; + let b_offset = a_size.align_to(b.align(self).abi); + assert!(b_offset.bytes() > 0); // we later use the offset to tell apart the fields + let b_ptr = ptr.offset(b_offset, self)?; + let a_val = alloc.read_scalar(self, a_ptr, a_size)?; + let b_val = alloc.read_scalar(self, b_ptr, b_size)?; + Ok(Some(ImmTy { imm: Immediate::ScalarPair(a_val, b_val), layout: mplace.layout })) + } + _ => Ok(None), + } + } + + /// Try returning an immediate for the operand. + /// If the layout does not permit loading this as an immediate, return where in memory + /// we can find the data. + /// Note that for a given layout, this operation will either always fail or always + /// succeed! Whether it succeeds depends on whether the layout can be represented + /// in a `Immediate`, not on which data is stored there currently. + pub(crate) fn try_read_immediate( + &self, + src: OpTy<'tcx, M::PointerTag>, + ) -> InterpResult<'tcx, Result<ImmTy<'tcx, M::PointerTag>, MPlaceTy<'tcx, M::PointerTag>>> { + Ok(match src.try_as_mplace(self) { + Ok(mplace) => { + if let Some(val) = self.try_read_immediate_from_mplace(mplace)? { + Ok(val) + } else { + Err(mplace) + } + } + Err(val) => Ok(val), + }) + } + + /// Read an immediate from a place, asserting that that is possible with the given layout. + #[inline(always)] + pub fn read_immediate( + &self, + op: OpTy<'tcx, M::PointerTag>, + ) -> InterpResult<'tcx, ImmTy<'tcx, M::PointerTag>> { + if let Ok(imm) = self.try_read_immediate(op)? { + Ok(imm) + } else { + span_bug!(self.cur_span(), "primitive read failed for type: {:?}", op.layout.ty); + } + } + + /// Read a scalar from a place + pub fn read_scalar( + &self, + op: OpTy<'tcx, M::PointerTag>, + ) -> InterpResult<'tcx, ScalarMaybeUninit<M::PointerTag>> { + Ok(self.read_immediate(op)?.to_scalar_or_uninit()) + } + + // Turn the wide MPlace into a string (must already be dereferenced!) + pub fn read_str(&self, mplace: MPlaceTy<'tcx, M::PointerTag>) -> InterpResult<'tcx, &str> { + let len = mplace.len(self)?; + let bytes = self.memory.read_bytes(mplace.ptr, Size::from_bytes(len))?; + let str = ::std::str::from_utf8(bytes).map_err(|err| err_ub!(InvalidStr(err)))?; + Ok(str) + } + + /// Projection functions + pub fn operand_field( + &self, + op: OpTy<'tcx, M::PointerTag>, + field: usize, + ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> { + let base = match op.try_as_mplace(self) { + Ok(mplace) => { + // We can reuse the mplace field computation logic for indirect operands. + let field = self.mplace_field(mplace, field)?; + return Ok(field.into()); + } + Err(value) => value, + }; + + let field_layout = op.layout.field(self, field)?; + if field_layout.is_zst() { + let immediate = Scalar::zst().into(); + return Ok(OpTy { op: Operand::Immediate(immediate), layout: field_layout }); + } + let offset = op.layout.fields.offset(field); + let immediate = match *base { + // the field covers the entire type + _ if offset.bytes() == 0 && field_layout.size == op.layout.size => *base, + // extract fields from types with `ScalarPair` ABI + Immediate::ScalarPair(a, b) => { + let val = if offset.bytes() == 0 { a } else { b }; + Immediate::from(val) + } + Immediate::Scalar(val) => span_bug!( + self.cur_span(), + "field access on non aggregate {:#?}, {:#?}", + val, + op.layout + ), + }; + Ok(OpTy { op: Operand::Immediate(immediate), layout: field_layout }) + } + + pub fn operand_index( + &self, + op: OpTy<'tcx, M::PointerTag>, + index: u64, + ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> { + if let Ok(index) = usize::try_from(index) { + // We can just treat this as a field. + self.operand_field(op, index) + } else { + // Indexing into a big array. This must be an mplace. + let mplace = op.assert_mem_place(self); + Ok(self.mplace_index(mplace, index)?.into()) + } + } + + pub fn operand_downcast( + &self, + op: OpTy<'tcx, M::PointerTag>, + variant: VariantIdx, + ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> { + // Downcasts only change the layout + Ok(match op.try_as_mplace(self) { + Ok(mplace) => self.mplace_downcast(mplace, variant)?.into(), + Err(..) => { + let layout = op.layout.for_variant(self, variant); + OpTy { layout, ..op } + } + }) + } + + pub fn operand_projection( + &self, + base: OpTy<'tcx, M::PointerTag>, + proj_elem: mir::PlaceElem<'tcx>, + ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> { + use rustc_middle::mir::ProjectionElem::*; + Ok(match proj_elem { + Field(field, _) => self.operand_field(base, field.index())?, + Downcast(_, variant) => self.operand_downcast(base, variant)?, + Deref => self.deref_operand(base)?.into(), + Subslice { .. } | ConstantIndex { .. } | Index(_) => { + // The rest should only occur as mplace, we do not use Immediates for types + // allowing such operations. This matches place_projection forcing an allocation. + let mplace = base.assert_mem_place(self); + self.mplace_projection(mplace, proj_elem)?.into() + } + }) + } + + /// Read from a local. Will not actually access the local if reading from a ZST. + /// Will not access memory, instead an indirect `Operand` is returned. + /// + /// This is public because it is used by [priroda](https://github.com/oli-obk/priroda) to get an + /// OpTy from a local + pub fn access_local( + &self, + frame: &super::Frame<'mir, 'tcx, M::PointerTag, M::FrameExtra>, + local: mir::Local, + layout: Option<TyAndLayout<'tcx>>, + ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> { + let layout = self.layout_of_local(frame, local, layout)?; + let op = if layout.is_zst() { + // Do not read from ZST, they might not be initialized + Operand::Immediate(Scalar::zst().into()) + } else { + M::access_local(&self, frame, local)? + }; + Ok(OpTy { op, layout }) + } + + /// Every place can be read from, so we can turn them into an operand. + /// This will definitely return `Indirect` if the place is a `Ptr`, i.e., this + /// will never actually read from memory. + #[inline(always)] + pub fn place_to_op( + &self, + place: PlaceTy<'tcx, M::PointerTag>, + ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> { + let op = match *place { + Place::Ptr(mplace) => Operand::Indirect(mplace), + Place::Local { frame, local } => { + *self.access_local(&self.stack()[frame], local, None)? + } + }; + Ok(OpTy { op, layout: place.layout }) + } + + // Evaluate a place with the goal of reading from it. This lets us sometimes + // avoid allocations. + pub fn eval_place_to_op( + &self, + place: mir::Place<'tcx>, + layout: Option<TyAndLayout<'tcx>>, + ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> { + // Do not use the layout passed in as argument if the base we are looking at + // here is not the entire place. + let layout = if place.projection.is_empty() { layout } else { None }; + + let base_op = self.access_local(self.frame(), place.local, layout)?; + + let op = place + .projection + .iter() + .try_fold(base_op, |op, elem| self.operand_projection(op, elem))?; + + trace!("eval_place_to_op: got {:?}", *op); + // Sanity-check the type we ended up with. + debug_assert!(mir_assign_valid_types( + *self.tcx, + self.param_env, + self.layout_of(self.subst_from_current_frame_and_normalize_erasing_regions( + place.ty(&self.frame().body.local_decls, *self.tcx).ty + ))?, + op.layout, + )); + Ok(op) + } + + /// Evaluate the operand, returning a place where you can then find the data. + /// If you already know the layout, you can save two table lookups + /// by passing it in here. + pub fn eval_operand( + &self, + mir_op: &mir::Operand<'tcx>, + layout: Option<TyAndLayout<'tcx>>, + ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> { + use rustc_middle::mir::Operand::*; + let op = match *mir_op { + // FIXME: do some more logic on `move` to invalidate the old location + Copy(place) | Move(place) => self.eval_place_to_op(place, layout)?, + + Constant(ref constant) => { + let val = + self.subst_from_current_frame_and_normalize_erasing_regions(constant.literal); + self.const_to_op(val, layout)? + } + }; + trace!("{:?}: {:?}", mir_op, *op); + Ok(op) + } + + /// Evaluate a bunch of operands at once + pub(super) fn eval_operands( + &self, + ops: &[mir::Operand<'tcx>], + ) -> InterpResult<'tcx, Vec<OpTy<'tcx, M::PointerTag>>> { + ops.iter().map(|op| self.eval_operand(op, None)).collect() + } + + // Used when the miri-engine runs into a constant and for extracting information from constants + // in patterns via the `const_eval` module + /// The `val` and `layout` are assumed to already be in our interpreter + /// "universe" (param_env). + crate fn const_to_op( + &self, + val: &ty::Const<'tcx>, + layout: Option<TyAndLayout<'tcx>>, + ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> { + let tag_scalar = |scalar| -> InterpResult<'tcx, _> { + Ok(match scalar { + Scalar::Ptr(ptr) => Scalar::Ptr(self.global_base_pointer(ptr)?), + Scalar::Raw { data, size } => Scalar::Raw { data, size }, + }) + }; + // Early-return cases. + let val_val = match val.val { + ty::ConstKind::Param(_) => throw_inval!(TooGeneric), + ty::ConstKind::Error(_) => throw_inval!(TypeckError(ErrorReported)), + ty::ConstKind::Unevaluated(def, substs, promoted) => { + let instance = self.resolve(def.did, substs)?; + // We use `const_eval` here and `const_eval_raw` elsewhere in mir interpretation. + // The reason we use `const_eval_raw` everywhere else is to prevent cycles during + // validation, because validation automatically reads through any references, thus + // potentially requiring the current static to be evaluated again. This is not a + // problem here, because we are building an operand which means an actual read is + // happening. + return Ok(self.const_eval(GlobalId { instance, promoted }, val.ty)?); + } + ty::ConstKind::Infer(..) + | ty::ConstKind::Bound(..) + | ty::ConstKind::Placeholder(..) => { + span_bug!(self.cur_span(), "const_to_op: Unexpected ConstKind {:?}", val) + } + ty::ConstKind::Value(val_val) => val_val, + }; + // Other cases need layout. + let layout = + from_known_layout(self.tcx, self.param_env, layout, || self.layout_of(val.ty))?; + let op = match val_val { + ConstValue::ByRef { alloc, offset } => { + let id = self.tcx.create_memory_alloc(alloc); + // We rely on mutability being set correctly in that allocation to prevent writes + // where none should happen. + let ptr = self.global_base_pointer(Pointer::new(id, offset))?; + Operand::Indirect(MemPlace::from_ptr(ptr, layout.align.abi)) + } + ConstValue::Scalar(x) => Operand::Immediate(tag_scalar(x)?.into()), + ConstValue::Slice { data, start, end } => { + // We rely on mutability being set correctly in `data` to prevent writes + // where none should happen. + let ptr = Pointer::new( + self.tcx.create_memory_alloc(data), + Size::from_bytes(start), // offset: `start` + ); + Operand::Immediate(Immediate::new_slice( + self.global_base_pointer(ptr)?.into(), + u64::try_from(end.checked_sub(start).unwrap()).unwrap(), // len: `end - start` + self, + )) + } + }; + Ok(OpTy { op, layout }) + } + + /// Read discriminant, return the runtime value as well as the variant index. + pub fn read_discriminant( + &self, + op: OpTy<'tcx, M::PointerTag>, + ) -> InterpResult<'tcx, (Scalar<M::PointerTag>, VariantIdx)> { + trace!("read_discriminant_value {:#?}", op.layout); + // Get type and layout of the discriminant. + let discr_layout = self.layout_of(op.layout.ty.discriminant_ty(*self.tcx))?; + trace!("discriminant type: {:?}", discr_layout.ty); + + // We use "discriminant" to refer to the value associated with a particular enum variant. + // This is not to be confused with its "variant index", which is just determining its position in the + // declared list of variants -- they can differ with explicitly assigned discriminants. + // We use "tag" to refer to how the discriminant is encoded in memory, which can be either + // straight-forward (`TagEncoding::Direct`) or with a niche (`TagEncoding::Niche`). + let (tag_scalar_layout, tag_encoding, tag_field) = match op.layout.variants { + Variants::Single { index } => { + let discr = match op.layout.ty.discriminant_for_variant(*self.tcx, index) { + Some(discr) => { + // This type actually has discriminants. + assert_eq!(discr.ty, discr_layout.ty); + Scalar::from_uint(discr.val, discr_layout.size) + } + None => { + // On a type without actual discriminants, variant is 0. + assert_eq!(index.as_u32(), 0); + Scalar::from_uint(index.as_u32(), discr_layout.size) + } + }; + return Ok((discr, index)); + } + Variants::Multiple { ref tag, ref tag_encoding, tag_field, .. } => { + (tag, tag_encoding, tag_field) + } + }; + + // There are *three* layouts that come into play here: + // - The discriminant has a type for typechecking. This is `discr_layout`, and is used for + // the `Scalar` we return. + // - The tag (encoded discriminant) has layout `tag_layout`. This is always an integer type, + // and used to interpret the value we read from the tag field. + // For the return value, a cast to `discr_layout` is performed. + // - The field storing the tag has a layout, which is very similar to `tag_layout` but + // may be a pointer. This is `tag_val.layout`; we just use it for sanity checks. + + // Get layout for tag. + let tag_layout = self.layout_of(tag_scalar_layout.value.to_int_ty(*self.tcx))?; + + // Read tag and sanity-check `tag_layout`. + let tag_val = self.read_immediate(self.operand_field(op, tag_field)?)?; + assert_eq!(tag_layout.size, tag_val.layout.size); + assert_eq!(tag_layout.abi.is_signed(), tag_val.layout.abi.is_signed()); + let tag_val = tag_val.to_scalar()?; + trace!("tag value: {:?}", tag_val); + + // Figure out which discriminant and variant this corresponds to. + Ok(match *tag_encoding { + TagEncoding::Direct => { + let tag_bits = self + .force_bits(tag_val, tag_layout.size) + .map_err(|_| err_ub!(InvalidTag(tag_val.erase_tag())))?; + // Cast bits from tag layout to discriminant layout. + let discr_val = self.cast_from_scalar(tag_bits, tag_layout, discr_layout.ty); + let discr_bits = discr_val.assert_bits(discr_layout.size); + // Convert discriminant to variant index, and catch invalid discriminants. + let index = match op.layout.ty.kind { + ty::Adt(adt, _) => { + adt.discriminants(*self.tcx).find(|(_, var)| var.val == discr_bits) + } + ty::Generator(def_id, substs, _) => { + let substs = substs.as_generator(); + substs + .discriminants(def_id, *self.tcx) + .find(|(_, var)| var.val == discr_bits) + } + _ => span_bug!(self.cur_span(), "tagged layout for non-adt non-generator"), + } + .ok_or_else(|| err_ub!(InvalidTag(tag_val.erase_tag())))?; + // Return the cast value, and the index. + (discr_val, index.0) + } + TagEncoding::Niche { dataful_variant, ref niche_variants, niche_start } => { + // Compute the variant this niche value/"tag" corresponds to. With niche layout, + // discriminant (encoded in niche/tag) and variant index are the same. + let variants_start = niche_variants.start().as_u32(); + let variants_end = niche_variants.end().as_u32(); + let variant = match tag_val.to_bits_or_ptr(tag_layout.size, self) { + Err(ptr) => { + // The niche must be just 0 (which an inbounds pointer value never is) + let ptr_valid = niche_start == 0 + && variants_start == variants_end + && !self.memory.ptr_may_be_null(ptr); + if !ptr_valid { + throw_ub!(InvalidTag(tag_val.erase_tag())) + } + dataful_variant + } + Ok(tag_bits) => { + // We need to use machine arithmetic to get the relative variant idx: + // variant_index_relative = tag_val - niche_start_val + let tag_val = ImmTy::from_uint(tag_bits, tag_layout); + let niche_start_val = ImmTy::from_uint(niche_start, tag_layout); + let variant_index_relative_val = + self.binary_op(mir::BinOp::Sub, tag_val, niche_start_val)?; + let variant_index_relative = variant_index_relative_val + .to_scalar()? + .assert_bits(tag_val.layout.size); + // Check if this is in the range that indicates an actual discriminant. + if variant_index_relative <= u128::from(variants_end - variants_start) { + let variant_index_relative = u32::try_from(variant_index_relative) + .expect("we checked that this fits into a u32"); + // Then computing the absolute variant idx should not overflow any more. + let variant_index = variants_start + .checked_add(variant_index_relative) + .expect("overflow computing absolute variant idx"); + let variants_len = op + .layout + .ty + .ty_adt_def() + .expect("tagged layout for non adt") + .variants + .len(); + assert!(usize::try_from(variant_index).unwrap() < variants_len); + VariantIdx::from_u32(variant_index) + } else { + dataful_variant + } + } + }; + // Compute the size of the scalar we need to return. + // No need to cast, because the variant index directly serves as discriminant and is + // encoded in the tag. + (Scalar::from_uint(variant.as_u32(), discr_layout.size), variant) + } + }) + } +} |