1 //! Functions concerning immediate values and operands, and reading from operands.
2 //! All high-level functions to read from memory work on operands as sources.
4 use std::convert::TryFrom;
7 use rustc_errors::ErrorReported;
8 use rustc_hir::def::Namespace;
9 use rustc_macros::HashStable;
10 use rustc_middle::ty::layout::{PrimitiveExt, TyAndLayout};
11 use rustc_middle::ty::print::{FmtPrinter, PrettyPrinter, Printer};
12 use rustc_middle::ty::{ConstInt, Ty};
13 use rustc_middle::{mir, ty};
14 use rustc_target::abi::{Abi, HasDataLayout, LayoutOf, Size, TagEncoding};
15 use rustc_target::abi::{VariantIdx, Variants};
18 alloc_range, from_known_layout, mir_assign_valid_types, AllocId, ConstValue, GlobalId,
19 InterpCx, InterpResult, MPlaceTy, Machine, MemPlace, Place, PlaceTy, Pointer, Provenance,
20 Scalar, ScalarMaybeUninit,
23 /// An `Immediate` represents a single immediate self-contained Rust value.
25 /// For optimization of a few very common cases, there is also a representation for a pair of
26 /// primitive values (`ScalarPair`). It allows Miri to avoid making allocations for checked binary
27 /// operations and wide pointers. This idea was taken from rustc's codegen.
28 /// In particular, thanks to `ScalarPair`, arithmetic operations and casts can be entirely
29 /// defined on `Immediate`, and do not have to work with a `Place`.
30 #[derive(Copy, Clone, PartialEq, Eq, HashStable, Hash)]
31 pub enum Immediate<Tag = AllocId> {
32 Scalar(ScalarMaybeUninit<Tag>),
33 ScalarPair(ScalarMaybeUninit<Tag>, ScalarMaybeUninit<Tag>),
36 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
37 rustc_data_structures::static_assert_size!(Immediate, 56);
39 impl<Tag: Provenance> std::fmt::Debug for Immediate<Tag> {
40 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
43 Scalar(s) => f.debug_tuple("Scalar").field(s).finish(),
44 ScalarPair(s1, s2) => f.debug_tuple("ScalarPair").field(s1).field(s2).finish(),
49 impl<Tag> From<ScalarMaybeUninit<Tag>> for Immediate<Tag> {
51 fn from(val: ScalarMaybeUninit<Tag>) -> Self {
52 Immediate::Scalar(val)
56 impl<Tag> From<Scalar<Tag>> for Immediate<Tag> {
58 fn from(val: Scalar<Tag>) -> Self {
59 Immediate::Scalar(val.into())
63 impl<'tcx, Tag> Immediate<Tag> {
64 pub fn from_pointer(p: Pointer<Tag>, cx: &impl HasDataLayout) -> Self {
65 Immediate::Scalar(ScalarMaybeUninit::from_pointer(p, cx))
68 pub fn from_maybe_pointer(p: Pointer<Option<Tag>>, cx: &impl HasDataLayout) -> Self {
69 Immediate::Scalar(ScalarMaybeUninit::from_maybe_pointer(p, cx))
72 pub fn new_slice(val: Scalar<Tag>, len: u64, cx: &impl HasDataLayout) -> Self {
73 Immediate::ScalarPair(val.into(), Scalar::from_machine_usize(len, cx).into())
76 pub fn new_dyn_trait(val: Scalar<Tag>, vtable: Pointer<Tag>, cx: &impl HasDataLayout) -> Self {
77 Immediate::ScalarPair(val.into(), ScalarMaybeUninit::from_pointer(vtable, cx))
81 pub fn to_scalar_or_uninit(self) -> ScalarMaybeUninit<Tag> {
83 Immediate::Scalar(val) => val,
84 Immediate::ScalarPair(..) => bug!("Got a wide pointer where a scalar was expected"),
89 pub fn to_scalar(self) -> InterpResult<'tcx, Scalar<Tag>> {
90 self.to_scalar_or_uninit().check_init()
94 // ScalarPair needs a type to interpret, so we often have an immediate and a type together
95 // as input for binary and cast operations.
96 #[derive(Copy, Clone)]
97 pub struct ImmTy<'tcx, Tag = AllocId> {
99 pub layout: TyAndLayout<'tcx>,
102 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
103 rustc_data_structures::static_assert_size!(ImmTy<'_>, 72);
105 impl<'tcx, Tag: Provenance> std::fmt::Debug for ImmTy<'tcx, Tag> {
106 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
107 let ImmTy { imm, layout } = self;
108 f.debug_struct("ImmTy").field("imm", imm).field("layout", layout).finish()
112 impl<Tag: Provenance> std::fmt::Display for ImmTy<'tcx, Tag> {
113 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
114 /// Helper function for printing a scalar to a FmtPrinter
115 fn p<'a, 'tcx, F: std::fmt::Write, Tag: Provenance>(
116 cx: FmtPrinter<'a, 'tcx, F>,
117 s: ScalarMaybeUninit<Tag>,
119 ) -> Result<FmtPrinter<'a, 'tcx, F>, std::fmt::Error> {
121 ScalarMaybeUninit::Scalar(Scalar::Int(int)) => {
122 cx.pretty_print_const_scalar_int(int, ty, true)
124 ScalarMaybeUninit::Scalar(Scalar::Ptr(ptr, _sz)) => {
125 // Just print the ptr value. `pretty_print_const_scalar_ptr` would also try to
126 // print what is points to, which would fail since it has no access to the local
128 cx.pretty_print_const_pointer(ptr, ty, true)
130 ScalarMaybeUninit::Uninit => cx.typed_value(
132 this.write_str("uninit ")?;
135 |this| this.print_type(ty),
140 ty::tls::with(|tcx| {
142 Immediate::Scalar(s) => {
143 if let Some(ty) = tcx.lift(self.layout.ty) {
144 let cx = FmtPrinter::new(tcx, f, Namespace::ValueNS);
148 write!(f, "{}: {}", s, self.layout.ty)
150 Immediate::ScalarPair(a, b) => {
151 // FIXME(oli-obk): at least print tuples and slices nicely
152 write!(f, "({}, {}): {}", a, b, self.layout.ty,)
159 impl<'tcx, Tag> std::ops::Deref for ImmTy<'tcx, Tag> {
160 type Target = Immediate<Tag>;
162 fn deref(&self) -> &Immediate<Tag> {
167 /// An `Operand` is the result of computing a `mir::Operand`. It can be immediate,
168 /// or still in memory. The latter is an optimization, to delay reading that chunk of
169 /// memory and to avoid having to store arbitrary-sized data here.
170 #[derive(Copy, Clone, PartialEq, Eq, HashStable, Hash)]
171 pub enum Operand<Tag = AllocId> {
172 Immediate(Immediate<Tag>),
173 Indirect(MemPlace<Tag>),
176 impl<Tag: Provenance> std::fmt::Debug for Operand<Tag> {
177 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
180 Immediate(i) => f.debug_tuple("Immediate").field(i).finish(),
181 Indirect(p) => f.debug_tuple("Indirect").field(p).finish(),
186 #[derive(Copy, Clone, PartialEq, Eq, Hash)]
187 pub struct OpTy<'tcx, Tag = AllocId> {
188 op: Operand<Tag>, // Keep this private; it helps enforce invariants.
189 pub layout: TyAndLayout<'tcx>,
192 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
193 rustc_data_structures::static_assert_size!(OpTy<'_, ()>, 80);
195 impl<'tcx, Tag: Provenance> std::fmt::Debug for OpTy<'tcx, Tag> {
196 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
197 let OpTy { op, layout } = self;
198 f.debug_struct("OpTy").field("op", op).field("layout", layout).finish()
202 impl<'tcx, Tag> std::ops::Deref for OpTy<'tcx, Tag> {
203 type Target = Operand<Tag>;
205 fn deref(&self) -> &Operand<Tag> {
210 impl<'tcx, Tag: Copy> From<MPlaceTy<'tcx, Tag>> for OpTy<'tcx, Tag> {
212 fn from(mplace: MPlaceTy<'tcx, Tag>) -> Self {
213 OpTy { op: Operand::Indirect(*mplace), layout: mplace.layout }
217 impl<'tcx, Tag: Copy> From<&'_ MPlaceTy<'tcx, Tag>> for OpTy<'tcx, Tag> {
219 fn from(mplace: &MPlaceTy<'tcx, Tag>) -> Self {
220 OpTy { op: Operand::Indirect(**mplace), layout: mplace.layout }
224 impl<'tcx, Tag> From<ImmTy<'tcx, Tag>> for OpTy<'tcx, Tag> {
226 fn from(val: ImmTy<'tcx, Tag>) -> Self {
227 OpTy { op: Operand::Immediate(val.imm), layout: val.layout }
231 impl<'tcx, Tag: Copy> ImmTy<'tcx, Tag> {
233 pub fn from_scalar(val: Scalar<Tag>, layout: TyAndLayout<'tcx>) -> Self {
234 ImmTy { imm: val.into(), layout }
238 pub fn from_immediate(imm: Immediate<Tag>, layout: TyAndLayout<'tcx>) -> Self {
239 ImmTy { imm, layout }
243 pub fn try_from_uint(i: impl Into<u128>, layout: TyAndLayout<'tcx>) -> Option<Self> {
244 Some(Self::from_scalar(Scalar::try_from_uint(i, layout.size)?, layout))
247 pub fn from_uint(i: impl Into<u128>, layout: TyAndLayout<'tcx>) -> Self {
248 Self::from_scalar(Scalar::from_uint(i, layout.size), layout)
252 pub fn try_from_int(i: impl Into<i128>, layout: TyAndLayout<'tcx>) -> Option<Self> {
253 Some(Self::from_scalar(Scalar::try_from_int(i, layout.size)?, layout))
257 pub fn from_int(i: impl Into<i128>, layout: TyAndLayout<'tcx>) -> Self {
258 Self::from_scalar(Scalar::from_int(i, layout.size), layout)
262 pub fn to_const_int(self) -> ConstInt
266 assert!(self.layout.ty.is_integral());
267 let int = self.to_scalar().expect("to_const_int doesn't work on scalar pairs").assert_int();
268 ConstInt::new(int, self.layout.ty.is_signed(), self.layout.ty.is_ptr_sized_integral())
272 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
273 /// Try reading an immediate in memory; this is interesting particularly for `ScalarPair`.
274 /// Returns `None` if the layout does not permit loading this as a value.
275 fn try_read_immediate_from_mplace(
277 mplace: &MPlaceTy<'tcx, M::PointerTag>,
278 ) -> InterpResult<'tcx, Option<ImmTy<'tcx, M::PointerTag>>> {
279 if mplace.layout.is_unsized() {
280 // Don't touch unsized
284 let alloc = match self.get_alloc(mplace)? {
287 return Ok(Some(ImmTy {
289 imm: Scalar::ZST.into(),
290 layout: mplace.layout,
295 match mplace.layout.abi {
297 let scalar = alloc.read_scalar(alloc_range(Size::ZERO, mplace.layout.size))?;
298 Ok(Some(ImmTy { imm: scalar.into(), layout: mplace.layout }))
300 Abi::ScalarPair(ref a, ref b) => {
301 // We checked `ptr_align` above, so all fields will have the alignment they need.
302 // We would anyway check against `ptr_align.restrict_for_offset(b_offset)`,
303 // which `ptr.offset(b_offset)` cannot possibly fail to satisfy.
304 let (a, b) = (&a.value, &b.value);
305 let (a_size, b_size) = (a.size(self), b.size(self));
306 let b_offset = a_size.align_to(b.align(self).abi);
307 assert!(b_offset.bytes() > 0); // we later use the offset to tell apart the fields
308 let a_val = alloc.read_scalar(alloc_range(Size::ZERO, a_size))?;
309 let b_val = alloc.read_scalar(alloc_range(b_offset, b_size))?;
310 Ok(Some(ImmTy { imm: Immediate::ScalarPair(a_val, b_val), layout: mplace.layout }))
316 /// Try returning an immediate for the operand.
317 /// If the layout does not permit loading this as an immediate, return where in memory
318 /// we can find the data.
319 /// Note that for a given layout, this operation will either always fail or always
320 /// succeed! Whether it succeeds depends on whether the layout can be represented
321 /// in a `Immediate`, not on which data is stored there currently.
322 pub(crate) fn try_read_immediate(
324 src: &OpTy<'tcx, M::PointerTag>,
325 ) -> InterpResult<'tcx, Result<ImmTy<'tcx, M::PointerTag>, MPlaceTy<'tcx, M::PointerTag>>> {
326 Ok(match src.try_as_mplace() {
328 if let Some(val) = self.try_read_immediate_from_mplace(mplace)? {
338 /// Read an immediate from a place, asserting that that is possible with the given layout.
340 pub fn read_immediate(
342 op: &OpTy<'tcx, M::PointerTag>,
343 ) -> InterpResult<'tcx, ImmTy<'tcx, M::PointerTag>> {
344 if let Ok(imm) = self.try_read_immediate(op)? {
347 span_bug!(self.cur_span(), "primitive read failed for type: {:?}", op.layout.ty);
351 /// Read a scalar from a place
354 op: &OpTy<'tcx, M::PointerTag>,
355 ) -> InterpResult<'tcx, ScalarMaybeUninit<M::PointerTag>> {
356 Ok(self.read_immediate(op)?.to_scalar_or_uninit())
359 /// Read a pointer from a place.
362 op: &OpTy<'tcx, M::PointerTag>,
363 ) -> InterpResult<'tcx, Pointer<Option<M::PointerTag>>> {
364 Ok(self.scalar_to_ptr(self.read_scalar(op)?.check_init()?))
367 // Turn the wide MPlace into a string (must already be dereferenced!)
368 pub fn read_str(&self, mplace: &MPlaceTy<'tcx, M::PointerTag>) -> InterpResult<'tcx, &str> {
369 let len = mplace.len(self)?;
370 let bytes = self.memory.read_bytes(mplace.ptr, Size::from_bytes(len))?;
371 let str = std::str::from_utf8(bytes).map_err(|err| err_ub!(InvalidStr(err)))?;
375 /// Projection functions
376 pub fn operand_field(
378 op: &OpTy<'tcx, M::PointerTag>,
380 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
381 let base = match op.try_as_mplace() {
383 // We can reuse the mplace field computation logic for indirect operands.
384 let field = self.mplace_field(mplace, field)?;
385 return Ok(field.into());
390 let field_layout = op.layout.field(self, field)?;
391 if field_layout.is_zst() {
392 let immediate = Scalar::ZST.into();
393 return Ok(OpTy { op: Operand::Immediate(immediate), layout: field_layout });
395 let offset = op.layout.fields.offset(field);
396 let immediate = match *base {
397 // the field covers the entire type
398 _ if offset.bytes() == 0 && field_layout.size == op.layout.size => *base,
399 // extract fields from types with `ScalarPair` ABI
400 Immediate::ScalarPair(a, b) => {
401 let val = if offset.bytes() == 0 { a } else { b };
404 Immediate::Scalar(val) => span_bug!(
406 "field access on non aggregate {:#?}, {:#?}",
411 Ok(OpTy { op: Operand::Immediate(immediate), layout: field_layout })
414 pub fn operand_index(
416 op: &OpTy<'tcx, M::PointerTag>,
418 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
419 if let Ok(index) = usize::try_from(index) {
420 // We can just treat this as a field.
421 self.operand_field(op, index)
423 // Indexing into a big array. This must be an mplace.
424 let mplace = op.assert_mem_place();
425 Ok(self.mplace_index(&mplace, index)?.into())
429 pub fn operand_downcast(
431 op: &OpTy<'tcx, M::PointerTag>,
433 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
434 // Downcasts only change the layout
435 Ok(match op.try_as_mplace() {
436 Ok(ref mplace) => self.mplace_downcast(mplace, variant)?.into(),
438 let layout = op.layout.for_variant(self, variant);
439 OpTy { layout, ..*op }
444 pub fn operand_projection(
446 base: &OpTy<'tcx, M::PointerTag>,
447 proj_elem: mir::PlaceElem<'tcx>,
448 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
449 use rustc_middle::mir::ProjectionElem::*;
451 Field(field, _) => self.operand_field(base, field.index())?,
452 Downcast(_, variant) => self.operand_downcast(base, variant)?,
453 Deref => self.deref_operand(base)?.into(),
454 Subslice { .. } | ConstantIndex { .. } | Index(_) => {
455 // The rest should only occur as mplace, we do not use Immediates for types
456 // allowing such operations. This matches place_projection forcing an allocation.
457 let mplace = base.assert_mem_place();
458 self.mplace_projection(&mplace, proj_elem)?.into()
463 /// Read from a local. Will not actually access the local if reading from a ZST.
464 /// Will not access memory, instead an indirect `Operand` is returned.
466 /// This is public because it is used by [priroda](https://github.com/oli-obk/priroda) to get an
467 /// OpTy from a local
470 frame: &super::Frame<'mir, 'tcx, M::PointerTag, M::FrameExtra>,
472 layout: Option<TyAndLayout<'tcx>>,
473 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
474 let layout = self.layout_of_local(frame, local, layout)?;
475 let op = if layout.is_zst() {
476 // Do not read from ZST, they might not be initialized
477 Operand::Immediate(Scalar::ZST.into())
479 M::access_local(&self, frame, local)?
481 Ok(OpTy { op, layout })
484 /// Every place can be read from, so we can turn them into an operand.
485 /// This will definitely return `Indirect` if the place is a `Ptr`, i.e., this
486 /// will never actually read from memory.
490 place: &PlaceTy<'tcx, M::PointerTag>,
491 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
492 let op = match **place {
493 Place::Ptr(mplace) => Operand::Indirect(mplace),
494 Place::Local { frame, local } => {
495 *self.access_local(&self.stack()[frame], local, None)?
498 Ok(OpTy { op, layout: place.layout })
501 // Evaluate a place with the goal of reading from it. This lets us sometimes
502 // avoid allocations.
503 pub fn eval_place_to_op(
505 place: mir::Place<'tcx>,
506 layout: Option<TyAndLayout<'tcx>>,
507 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
508 // Do not use the layout passed in as argument if the base we are looking at
509 // here is not the entire place.
510 let layout = if place.projection.is_empty() { layout } else { None };
512 let base_op = self.access_local(self.frame(), place.local, layout)?;
517 .try_fold(base_op, |op, elem| self.operand_projection(&op, elem))?;
519 trace!("eval_place_to_op: got {:?}", *op);
520 // Sanity-check the type we ended up with.
521 debug_assert!(mir_assign_valid_types(
524 self.layout_of(self.subst_from_current_frame_and_normalize_erasing_regions(
525 place.ty(&self.frame().body.local_decls, *self.tcx).ty
532 /// Evaluate the operand, returning a place where you can then find the data.
533 /// If you already know the layout, you can save two table lookups
534 /// by passing it in here.
538 mir_op: &mir::Operand<'tcx>,
539 layout: Option<TyAndLayout<'tcx>>,
540 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
541 use rustc_middle::mir::Operand::*;
542 let op = match *mir_op {
543 // FIXME: do some more logic on `move` to invalidate the old location
544 Copy(place) | Move(place) => self.eval_place_to_op(place, layout)?,
546 Constant(ref constant) => {
548 self.subst_from_current_frame_and_normalize_erasing_regions(constant.literal);
549 // This can still fail:
550 // * During ConstProp, with `TooGeneric` or since the `requried_consts` were not all
552 // * During CTFE, since promoteds in `const`/`static` initializer bodies can fail.
554 self.mir_const_to_op(&val, layout)?
557 trace!("{:?}: {:?}", mir_op, *op);
561 /// Evaluate a bunch of operands at once
562 pub(super) fn eval_operands(
564 ops: &[mir::Operand<'tcx>],
565 ) -> InterpResult<'tcx, Vec<OpTy<'tcx, M::PointerTag>>> {
566 ops.iter().map(|op| self.eval_operand(op, None)).collect()
569 // Used when the miri-engine runs into a constant and for extracting information from constants
570 // in patterns via the `const_eval` module
571 /// The `val` and `layout` are assumed to already be in our interpreter
572 /// "universe" (param_env).
573 crate fn const_to_op(
575 val: &ty::Const<'tcx>,
576 layout: Option<TyAndLayout<'tcx>>,
577 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
579 ty::ConstKind::Param(_) | ty::ConstKind::Bound(..) => throw_inval!(TooGeneric),
580 ty::ConstKind::Error(_) => throw_inval!(AlreadyReported(ErrorReported)),
581 ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }) => {
582 let instance = self.resolve(def, substs)?;
583 Ok(self.eval_to_allocation(GlobalId { instance, promoted })?.into())
585 ty::ConstKind::Infer(..) | ty::ConstKind::Placeholder(..) => {
586 span_bug!(self.cur_span(), "const_to_op: Unexpected ConstKind {:?}", val)
588 ty::ConstKind::Value(val_val) => self.const_val_to_op(val_val, val.ty, layout),
592 crate fn mir_const_to_op(
594 val: &mir::ConstantKind<'tcx>,
595 layout: Option<TyAndLayout<'tcx>>,
596 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
598 mir::ConstantKind::Ty(ct) => self.const_to_op(ct, layout),
599 mir::ConstantKind::Val(val, ty) => self.const_val_to_op(*val, ty, layout),
603 crate fn const_val_to_op(
605 val_val: ConstValue<'tcx>,
607 layout: Option<TyAndLayout<'tcx>>,
608 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
609 // Other cases need layout.
610 let tag_scalar = |scalar| -> InterpResult<'tcx, _> {
612 Scalar::Ptr(ptr, size) => Scalar::Ptr(self.global_base_pointer(ptr)?, size),
613 Scalar::Int(int) => Scalar::Int(int),
616 let layout = from_known_layout(self.tcx, self.param_env, layout, || self.layout_of(ty))?;
617 let op = match val_val {
618 ConstValue::ByRef { alloc, offset } => {
619 let id = self.tcx.create_memory_alloc(alloc);
620 // We rely on mutability being set correctly in that allocation to prevent writes
621 // where none should happen.
622 let ptr = self.global_base_pointer(Pointer::new(id, offset))?;
623 Operand::Indirect(MemPlace::from_ptr(ptr.into(), layout.align.abi))
625 ConstValue::Scalar(x) => Operand::Immediate(tag_scalar(x.into())?.into()),
626 ConstValue::Slice { data, start, end } => {
627 // We rely on mutability being set correctly in `data` to prevent writes
628 // where none should happen.
629 let ptr = Pointer::new(
630 self.tcx.create_memory_alloc(data),
631 Size::from_bytes(start), // offset: `start`
633 Operand::Immediate(Immediate::new_slice(
634 Scalar::from_pointer(self.global_base_pointer(ptr)?, &*self.tcx),
635 u64::try_from(end.checked_sub(start).unwrap()).unwrap(), // len: `end - start`
640 Ok(OpTy { op, layout })
643 /// Read discriminant, return the runtime value as well as the variant index.
644 pub fn read_discriminant(
646 op: &OpTy<'tcx, M::PointerTag>,
647 ) -> InterpResult<'tcx, (Scalar<M::PointerTag>, VariantIdx)> {
648 trace!("read_discriminant_value {:#?}", op.layout);
649 // Get type and layout of the discriminant.
650 let discr_layout = self.layout_of(op.layout.ty.discriminant_ty(*self.tcx))?;
651 trace!("discriminant type: {:?}", discr_layout.ty);
653 // We use "discriminant" to refer to the value associated with a particular enum variant.
654 // This is not to be confused with its "variant index", which is just determining its position in the
655 // declared list of variants -- they can differ with explicitly assigned discriminants.
656 // We use "tag" to refer to how the discriminant is encoded in memory, which can be either
657 // straight-forward (`TagEncoding::Direct`) or with a niche (`TagEncoding::Niche`).
658 let (tag_scalar_layout, tag_encoding, tag_field) = match op.layout.variants {
659 Variants::Single { index } => {
660 let discr = match op.layout.ty.discriminant_for_variant(*self.tcx, index) {
662 // This type actually has discriminants.
663 assert_eq!(discr.ty, discr_layout.ty);
664 Scalar::from_uint(discr.val, discr_layout.size)
667 // On a type without actual discriminants, variant is 0.
668 assert_eq!(index.as_u32(), 0);
669 Scalar::from_uint(index.as_u32(), discr_layout.size)
672 return Ok((discr, index));
674 Variants::Multiple { ref tag, ref tag_encoding, tag_field, .. } => {
675 (tag, tag_encoding, tag_field)
679 // There are *three* layouts that come into play here:
680 // - The discriminant has a type for typechecking. This is `discr_layout`, and is used for
681 // the `Scalar` we return.
682 // - The tag (encoded discriminant) has layout `tag_layout`. This is always an integer type,
683 // and used to interpret the value we read from the tag field.
684 // For the return value, a cast to `discr_layout` is performed.
685 // - The field storing the tag has a layout, which is very similar to `tag_layout` but
686 // may be a pointer. This is `tag_val.layout`; we just use it for sanity checks.
688 // Get layout for tag.
689 let tag_layout = self.layout_of(tag_scalar_layout.value.to_int_ty(*self.tcx))?;
691 // Read tag and sanity-check `tag_layout`.
692 let tag_val = self.read_immediate(&self.operand_field(op, tag_field)?)?;
693 assert_eq!(tag_layout.size, tag_val.layout.size);
694 assert_eq!(tag_layout.abi.is_signed(), tag_val.layout.abi.is_signed());
695 let tag_val = tag_val.to_scalar()?;
696 trace!("tag value: {:?}", tag_val);
698 // Figure out which discriminant and variant this corresponds to.
699 Ok(match *tag_encoding {
700 TagEncoding::Direct => {
701 let tag_bits = tag_val
703 .map_err(|dbg_val| err_ub!(InvalidTag(dbg_val)))?
704 .assert_bits(tag_layout.size);
705 // Cast bits from tag layout to discriminant layout.
706 let discr_val = self.cast_from_scalar(tag_bits, tag_layout, discr_layout.ty);
707 let discr_bits = discr_val.assert_bits(discr_layout.size);
708 // Convert discriminant to variant index, and catch invalid discriminants.
709 let index = match *op.layout.ty.kind() {
711 adt.discriminants(*self.tcx).find(|(_, var)| var.val == discr_bits)
713 ty::Generator(def_id, substs, _) => {
714 let substs = substs.as_generator();
716 .discriminants(def_id, *self.tcx)
717 .find(|(_, var)| var.val == discr_bits)
719 _ => span_bug!(self.cur_span(), "tagged layout for non-adt non-generator"),
721 .ok_or_else(|| err_ub!(InvalidTag(Scalar::from_uint(tag_bits, tag_layout.size))))?;
722 // Return the cast value, and the index.
725 TagEncoding::Niche { dataful_variant, ref niche_variants, niche_start } => {
726 // Compute the variant this niche value/"tag" corresponds to. With niche layout,
727 // discriminant (encoded in niche/tag) and variant index are the same.
728 let variants_start = niche_variants.start().as_u32();
729 let variants_end = niche_variants.end().as_u32();
730 let variant = match tag_val.try_to_int() {
732 // So this is a pointer then, and casting to an int failed.
733 // Can only happen during CTFE.
734 let ptr = self.scalar_to_ptr(tag_val);
735 // The niche must be just 0, and the ptr not null, then we know this is
736 // okay. Everything else, we conservatively reject.
737 let ptr_valid = niche_start == 0
738 && variants_start == variants_end
739 && !self.memory.ptr_may_be_null(ptr);
741 throw_ub!(InvalidTag(dbg_val))
746 let tag_bits = tag_bits.assert_bits(tag_layout.size);
747 // We need to use machine arithmetic to get the relative variant idx:
748 // variant_index_relative = tag_val - niche_start_val
749 let tag_val = ImmTy::from_uint(tag_bits, tag_layout);
750 let niche_start_val = ImmTy::from_uint(niche_start, tag_layout);
751 let variant_index_relative_val =
752 self.binary_op(mir::BinOp::Sub, &tag_val, &niche_start_val)?;
753 let variant_index_relative = variant_index_relative_val
755 .assert_bits(tag_val.layout.size);
756 // Check if this is in the range that indicates an actual discriminant.
757 if variant_index_relative <= u128::from(variants_end - variants_start) {
758 let variant_index_relative = u32::try_from(variant_index_relative)
759 .expect("we checked that this fits into a u32");
760 // Then computing the absolute variant idx should not overflow any more.
761 let variant_index = variants_start
762 .checked_add(variant_index_relative)
763 .expect("overflow computing absolute variant idx");
764 let variants_len = op
768 .expect("tagged layout for non adt")
771 assert!(usize::try_from(variant_index).unwrap() < variants_len);
772 VariantIdx::from_u32(variant_index)
778 // Compute the size of the scalar we need to return.
779 // No need to cast, because the variant index directly serves as discriminant and is
780 // encoded in the tag.
781 (Scalar::from_uint(variant.as_u32(), discr_layout.size), variant)