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::{TryInto, TryFrom};
7 use rustc::ty::layout::{
8 self, Size, LayoutOf, TyLayout, HasDataLayout, IntegerExt, PrimitiveExt, VariantIdx,
11 use rustc::mir::interpret::{
13 ConstValue, Pointer, Scalar,
14 InterpResult, sign_extend, truncate,
18 MemPlace, MPlaceTy, PlaceTy, Place,
20 pub use rustc::mir::interpret::ScalarMaybeUndef;
21 use rustc_macros::HashStable;
24 /// An `Immediate` represents a single immediate self-contained Rust value.
26 /// For optimization of a few very common cases, there is also a representation for a pair of
27 /// primitive values (`ScalarPair`). It allows Miri to avoid making allocations for checked binary
28 /// operations and wide pointers. This idea was taken from rustc's codegen.
29 /// In particular, thanks to `ScalarPair`, arithmetic operations and casts can be entirely
30 /// defined on `Immediate`, and do not have to work with a `Place`.
31 #[derive(Copy, Clone, Debug, PartialEq, Eq, HashStable, Hash)]
32 pub enum Immediate<Tag=(), Id=AllocId> {
33 Scalar(ScalarMaybeUndef<Tag, Id>),
34 ScalarPair(ScalarMaybeUndef<Tag, Id>, ScalarMaybeUndef<Tag, Id>),
37 impl<Tag> From<ScalarMaybeUndef<Tag>> for Immediate<Tag> {
39 fn from(val: ScalarMaybeUndef<Tag>) -> Self {
40 Immediate::Scalar(val)
44 impl<Tag> From<Scalar<Tag>> for Immediate<Tag> {
46 fn from(val: Scalar<Tag>) -> Self {
47 Immediate::Scalar(val.into())
51 impl<Tag> From<Pointer<Tag>> for Immediate<Tag> {
53 fn from(val: Pointer<Tag>) -> Self {
54 Immediate::Scalar(Scalar::from(val).into())
58 impl<'tcx, Tag> Immediate<Tag> {
62 cx: &impl HasDataLayout
64 Immediate::ScalarPair(
66 Scalar::from_uint(len, cx.data_layout().pointer_size).into(),
70 pub fn new_dyn_trait(val: Scalar<Tag>, vtable: Pointer<Tag>) -> Self {
71 Immediate::ScalarPair(val.into(), vtable.into())
75 pub fn to_scalar_or_undef(self) -> ScalarMaybeUndef<Tag> {
77 Immediate::Scalar(val) => val,
78 Immediate::ScalarPair(..) => bug!("Got a wide pointer where a scalar was expected"),
83 pub fn to_scalar(self) -> InterpResult<'tcx, Scalar<Tag>> {
84 self.to_scalar_or_undef().not_undef()
88 pub fn to_scalar_pair(self) -> InterpResult<'tcx, (Scalar<Tag>, Scalar<Tag>)> {
90 Immediate::Scalar(..) => bug!("Got a thin pointer where a scalar pair was expected"),
91 Immediate::ScalarPair(a, b) => Ok((a.not_undef()?, b.not_undef()?))
96 // ScalarPair needs a type to interpret, so we often have an immediate and a type together
97 // as input for binary and cast operations.
98 #[derive(Copy, Clone, Debug)]
99 pub struct ImmTy<'tcx, Tag=()> {
100 pub(crate) imm: Immediate<Tag>,
101 pub layout: TyLayout<'tcx>,
104 // `Tag: Copy` because some methods on `Scalar` consume them by value
105 impl<Tag: Copy> std::fmt::Display for ImmTy<'tcx, Tag> {
106 fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
108 Immediate::Scalar(ScalarMaybeUndef::Scalar(s)) => match s.to_bits(self.layout.size) {
110 match self.layout.ty.kind {
111 ty::Int(_) => return write!(
113 super::sign_extend(s, self.layout.size) as i128,
115 ty::Uint(_) => return write!(fmt, "{}", s),
116 ty::Bool if s == 0 => return fmt.write_str("false"),
117 ty::Bool if s == 1 => return fmt.write_str("true"),
118 ty::Char => if let Some(c) =
119 u32::try_from(s).ok().and_then(std::char::from_u32) {
120 return write!(fmt, "{}", c);
122 ty::Float(ast::FloatTy::F32) => if let Ok(u) = u32::try_from(s) {
123 return write!(fmt, "{}", f32::from_bits(u));
125 ty::Float(ast::FloatTy::F64) => if let Ok(u) = u64::try_from(s) {
126 return write!(fmt, "{}", f64::from_bits(u));
130 write!(fmt, "{:x}", s)
132 Err(_) => fmt.write_str("{pointer}"),
134 Immediate::Scalar(ScalarMaybeUndef::Undef) => fmt.write_str("{undef}"),
135 Immediate::ScalarPair(..) => fmt.write_str("{wide pointer or tuple}"),
140 impl<'tcx, Tag> ::std::ops::Deref for ImmTy<'tcx, Tag> {
141 type Target = Immediate<Tag>;
143 fn deref(&self) -> &Immediate<Tag> {
148 /// An `Operand` is the result of computing a `mir::Operand`. It can be immediate,
149 /// or still in memory. The latter is an optimization, to delay reading that chunk of
150 /// memory and to avoid having to store arbitrary-sized data here.
151 #[derive(Copy, Clone, Debug, PartialEq, Eq, HashStable, Hash)]
152 pub enum Operand<Tag=(), Id=AllocId> {
153 Immediate(Immediate<Tag, Id>),
154 Indirect(MemPlace<Tag, Id>),
157 impl<Tag> Operand<Tag> {
159 pub fn assert_mem_place(self) -> MemPlace<Tag>
160 where Tag: ::std::fmt::Debug
163 Operand::Indirect(mplace) => mplace,
164 _ => bug!("assert_mem_place: expected Operand::Indirect, got {:?}", self),
170 pub fn assert_immediate(self) -> Immediate<Tag>
171 where Tag: ::std::fmt::Debug
174 Operand::Immediate(imm) => imm,
175 _ => bug!("assert_immediate: expected Operand::Immediate, got {:?}", self),
181 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
182 pub struct OpTy<'tcx, Tag=()> {
183 op: Operand<Tag>, // Keep this private; it helps enforce invariants.
184 pub layout: TyLayout<'tcx>,
187 impl<'tcx, Tag> ::std::ops::Deref for OpTy<'tcx, Tag> {
188 type Target = Operand<Tag>;
190 fn deref(&self) -> &Operand<Tag> {
195 impl<'tcx, Tag: Copy> From<MPlaceTy<'tcx, Tag>> for OpTy<'tcx, Tag> {
197 fn from(mplace: MPlaceTy<'tcx, Tag>) -> Self {
199 op: Operand::Indirect(*mplace),
200 layout: mplace.layout
205 impl<'tcx, Tag> From<ImmTy<'tcx, Tag>> for OpTy<'tcx, Tag> {
207 fn from(val: ImmTy<'tcx, Tag>) -> Self {
209 op: Operand::Immediate(val.imm),
215 impl<'tcx, Tag: Copy> ImmTy<'tcx, Tag> {
217 pub fn from_scalar(val: Scalar<Tag>, layout: TyLayout<'tcx>) -> Self {
218 ImmTy { imm: val.into(), layout }
222 pub fn try_from_uint(i: impl Into<u128>, layout: TyLayout<'tcx>) -> Option<Self> {
223 Some(Self::from_scalar(Scalar::try_from_uint(i, layout.size)?, layout))
226 pub fn from_uint(i: impl Into<u128>, layout: TyLayout<'tcx>) -> Self {
227 Self::from_scalar(Scalar::from_uint(i, layout.size), layout)
231 pub fn try_from_int(i: impl Into<i128>, layout: TyLayout<'tcx>) -> Option<Self> {
232 Some(Self::from_scalar(Scalar::try_from_int(i, layout.size)?, layout))
236 pub fn from_int(i: impl Into<i128>, layout: TyLayout<'tcx>) -> Self {
237 Self::from_scalar(Scalar::from_int(i, layout.size), layout)
241 pub fn to_bits(self) -> InterpResult<'tcx, u128> {
242 self.to_scalar()?.to_bits(self.layout.size)
246 // Use the existing layout if given (but sanity check in debug mode),
247 // or compute the layout.
249 pub(super) fn from_known_layout<'tcx>(
250 layout: Option<TyLayout<'tcx>>,
251 compute: impl FnOnce() -> InterpResult<'tcx, TyLayout<'tcx>>
252 ) -> InterpResult<'tcx, TyLayout<'tcx>> {
256 if cfg!(debug_assertions) {
257 let layout2 = compute()?;
258 assert_eq!(layout.details, layout2.details,
259 "mismatch in layout of supposedly equal-layout types {:?} and {:?}",
260 layout.ty, layout2.ty);
267 impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
268 /// Normalice `place.ptr` to a `Pointer` if this is a place and not a ZST.
269 /// Can be helpful to avoid lots of `force_ptr` calls later, if this place is used a lot.
273 op: OpTy<'tcx, M::PointerTag>,
274 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
275 match op.try_as_mplace() {
276 Ok(mplace) => Ok(self.force_mplace_ptr(mplace)?.into()),
277 Err(imm) => Ok(imm.into()), // Nothing to cast/force
281 /// Try reading an immediate in memory; this is interesting particularly for `ScalarPair`.
282 /// Returns `None` if the layout does not permit loading this as a value.
283 fn try_read_immediate_from_mplace(
285 mplace: MPlaceTy<'tcx, M::PointerTag>,
286 ) -> InterpResult<'tcx, Option<ImmTy<'tcx, M::PointerTag>>> {
287 if mplace.layout.is_unsized() {
288 // Don't touch unsized
292 let ptr = match self.check_mplace_access(mplace, None)
293 .expect("places should be checked on creation")
296 None => return Ok(Some(ImmTy { // zero-sized type
297 imm: Scalar::zst().into(),
298 layout: mplace.layout,
302 match mplace.layout.abi {
303 layout::Abi::Scalar(..) => {
304 let scalar = self.memory
305 .get_raw(ptr.alloc_id)?
306 .read_scalar(self, ptr, mplace.layout.size)?;
309 layout: mplace.layout,
312 layout::Abi::ScalarPair(ref a, ref b) => {
313 // We checked `ptr_align` above, so all fields will have the alignment they need.
314 // We would anyway check against `ptr_align.restrict_for_offset(b_offset)`,
315 // which `ptr.offset(b_offset)` cannot possibly fail to satisfy.
316 let (a, b) = (&a.value, &b.value);
317 let (a_size, b_size) = (a.size(self), b.size(self));
319 let b_offset = a_size.align_to(b.align(self).abi);
320 assert!(b_offset.bytes() > 0); // we later use the offset to tell apart the fields
321 let b_ptr = ptr.offset(b_offset, self)?;
322 let a_val = self.memory
323 .get_raw(ptr.alloc_id)?
324 .read_scalar(self, a_ptr, a_size)?;
325 let b_val = self.memory
326 .get_raw(ptr.alloc_id)?
327 .read_scalar(self, b_ptr, b_size)?;
329 imm: Immediate::ScalarPair(a_val, b_val),
330 layout: mplace.layout,
337 /// Try returning an immediate for the operand.
338 /// If the layout does not permit loading this as an immediate, return where in memory
339 /// we can find the data.
340 /// Note that for a given layout, this operation will either always fail or always
341 /// succeed! Whether it succeeds depends on whether the layout can be represented
342 /// in a `Immediate`, not on which data is stored there currently.
343 pub(crate) fn try_read_immediate(
345 src: OpTy<'tcx, M::PointerTag>,
346 ) -> InterpResult<'tcx, Result<ImmTy<'tcx, M::PointerTag>, MPlaceTy<'tcx, M::PointerTag>>> {
347 Ok(match src.try_as_mplace() {
349 if let Some(val) = self.try_read_immediate_from_mplace(mplace)? {
359 /// Read an immediate from a place, asserting that that is possible with the given layout.
361 pub fn read_immediate(
363 op: OpTy<'tcx, M::PointerTag>
364 ) -> InterpResult<'tcx, ImmTy<'tcx, M::PointerTag>> {
365 if let Ok(imm) = self.try_read_immediate(op)? {
368 bug!("primitive read failed for type: {:?}", op.layout.ty);
372 /// Read a scalar from a place
375 op: OpTy<'tcx, M::PointerTag>
376 ) -> InterpResult<'tcx, ScalarMaybeUndef<M::PointerTag>> {
377 Ok(self.read_immediate(op)?.to_scalar_or_undef())
380 // Turn the wide MPlace into a string (must already be dereferenced!)
383 mplace: MPlaceTy<'tcx, M::PointerTag>,
384 ) -> InterpResult<'tcx, &str> {
385 let len = mplace.len(self)?;
386 let bytes = self.memory.read_bytes(mplace.ptr, Size::from_bytes(len as u64))?;
387 let str = ::std::str::from_utf8(bytes).map_err(|err| {
388 err_unsup!(ValidationFailure(err.to_string()))
393 /// Projection functions
394 pub fn operand_field(
396 op: OpTy<'tcx, M::PointerTag>,
398 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
399 let base = match op.try_as_mplace() {
402 let field = self.mplace_field(mplace, field)?;
403 return Ok(field.into());
408 let field = field.try_into().unwrap();
409 let field_layout = op.layout.field(self, field)?;
410 if field_layout.is_zst() {
411 let immediate = Scalar::zst().into();
412 return Ok(OpTy { op: Operand::Immediate(immediate), layout: field_layout });
414 let offset = op.layout.fields.offset(field);
415 let immediate = match *base {
416 // the field covers the entire type
417 _ if offset.bytes() == 0 && field_layout.size == op.layout.size => *base,
418 // extract fields from types with `ScalarPair` ABI
419 Immediate::ScalarPair(a, b) => {
420 let val = if offset.bytes() == 0 { a } else { b };
423 Immediate::Scalar(val) =>
424 bug!("field access on non aggregate {:#?}, {:#?}", val, op.layout),
426 Ok(OpTy { op: Operand::Immediate(immediate), layout: field_layout })
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() {
437 self.mplace_downcast(mplace, variant)?.into()
440 let layout = op.layout.for_variant(self, variant);
441 OpTy { layout, ..op }
446 pub fn operand_projection(
448 base: OpTy<'tcx, M::PointerTag>,
449 proj_elem: &mir::PlaceElem<'tcx>,
450 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
451 use rustc::mir::ProjectionElem::*;
452 Ok(match *proj_elem {
453 Field(field, _) => self.operand_field(base, field.index() as u64)?,
454 Downcast(_, variant) => self.operand_downcast(base, variant)?,
455 Deref => self.deref_operand(base)?.into(),
456 ConstantIndex { .. } | Index(_) if base.layout.is_zst() => {
458 op: Operand::Immediate(Scalar::zst().into()),
459 // the actual index doesn't matter, so we just pick a convenient one like 0
460 layout: base.layout.field(self, 0)?,
463 Subslice { from, to, from_end } if base.layout.is_zst() => {
464 let elem_ty = if let ty::Array(elem_ty, _) = base.layout.ty.kind {
467 bug!("slices shouldn't be zero-sized");
469 assert!(!from_end, "arrays shouldn't be subsliced from the end");
472 op: Operand::Immediate(Scalar::zst().into()),
473 layout: self.layout_of(self.tcx.mk_array(elem_ty, (to - from) as u64))?,
476 Subslice { .. } | ConstantIndex { .. } | Index(_) => {
477 // The rest should only occur as mplace, we do not use Immediates for types
478 // allowing such operations. This matches place_projection forcing an allocation.
479 let mplace = base.assert_mem_place();
480 self.mplace_projection(mplace, proj_elem)?.into()
485 /// This is used by [priroda](https://github.com/oli-obk/priroda) to get an OpTy from a local
488 frame: &super::Frame<'mir, 'tcx, M::PointerTag, M::FrameExtra>,
490 layout: Option<TyLayout<'tcx>>,
491 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
492 assert_ne!(local, mir::RETURN_PLACE);
493 let layout = self.layout_of_local(frame, local, layout)?;
494 let op = if layout.is_zst() {
495 // Do not read from ZST, they might not be initialized
496 Operand::Immediate(Scalar::zst().into())
498 M::access_local(&self, frame, local)?
500 Ok(OpTy { op, layout })
503 /// Every place can be read from, so we can turn them into an operand
507 place: PlaceTy<'tcx, M::PointerTag>
508 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
509 let op = match *place {
510 Place::Ptr(mplace) => {
511 Operand::Indirect(mplace)
513 Place::Local { frame, local } =>
514 *self.access_local(&self.stack[frame], local, None)?
516 Ok(OpTy { op, layout: place.layout })
519 // Evaluate a place with the goal of reading from it. This lets us sometimes
520 // avoid allocations.
521 pub fn eval_place_to_op(
523 place: &mir::Place<'tcx>,
524 layout: Option<TyLayout<'tcx>>,
525 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
526 use rustc::mir::PlaceBase;
528 let base_op = match &place.base {
529 PlaceBase::Local(mir::RETURN_PLACE) =>
530 throw_unsup!(ReadFromReturnPointer),
531 PlaceBase::Local(local) => {
532 // Do not use the layout passed in as argument if the base we are looking at
533 // here is not the entire place.
534 // FIXME use place_projection.is_empty() when is available
535 let layout = if place.projection.is_empty() {
541 self.access_local(self.frame(), *local, layout)?
543 PlaceBase::Static(place_static) => {
544 self.eval_static_to_mplace(&place_static)?.into()
548 let op = place.projection.iter().try_fold(
550 |op, elem| self.operand_projection(op, elem)
553 trace!("eval_place_to_op: got {:?}", *op);
557 /// Evaluate the operand, returning a place where you can then find the data.
558 /// If you already know the layout, you can save two table lookups
559 /// by passing it in here.
562 mir_op: &mir::Operand<'tcx>,
563 layout: Option<TyLayout<'tcx>>,
564 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
565 use rustc::mir::Operand::*;
566 let op = match *mir_op {
567 // FIXME: do some more logic on `move` to invalidate the old location
570 self.eval_place_to_op(place, layout)?,
572 Constant(ref constant) => {
573 let val = self.subst_from_frame_and_normalize_erasing_regions(constant.literal);
574 self.eval_const_to_op(val, layout)?
577 trace!("{:?}: {:?}", mir_op, *op);
581 /// Evaluate a bunch of operands at once
582 pub(super) fn eval_operands(
584 ops: &[mir::Operand<'tcx>],
585 ) -> InterpResult<'tcx, Vec<OpTy<'tcx, M::PointerTag>>> {
587 .map(|op| self.eval_operand(op, None))
591 // Used when the miri-engine runs into a constant and for extracting information from constants
592 // in patterns via the `const_eval` module
593 /// The `val` and `layout` are assumed to already be in our interpreter
594 /// "universe" (param_env).
595 crate fn eval_const_to_op(
597 val: &'tcx ty::Const<'tcx>,
598 layout: Option<TyLayout<'tcx>>,
599 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
600 let tag_scalar = |scalar| match scalar {
601 Scalar::Ptr(ptr) => Scalar::Ptr(self.tag_static_base_pointer(ptr)),
602 Scalar::Raw { data, size } => Scalar::Raw { data, size },
604 // Early-return cases.
605 let val_val = match val.val {
606 ty::ConstKind::Param(_) =>
607 throw_inval!(TooGeneric),
608 ty::ConstKind::Unevaluated(def_id, substs) => {
609 let instance = self.resolve(def_id, substs)?;
610 return Ok(OpTy::from(self.const_eval_raw(GlobalId {
615 ty::ConstKind::Infer(..) |
616 ty::ConstKind::Bound(..) |
617 ty::ConstKind::Placeholder(..) =>
618 bug!("eval_const_to_op: Unexpected ConstKind {:?}", val),
619 ty::ConstKind::Value(val_val) => val_val,
621 // Other cases need layout.
622 let layout = from_known_layout(layout, || {
623 self.layout_of(val.ty)
625 let op = match val_val {
626 ConstValue::ByRef { alloc, offset } => {
627 let id = self.tcx.alloc_map.lock().create_memory_alloc(alloc);
628 // We rely on mutability being set correctly in that allocation to prevent writes
629 // where none should happen.
630 let ptr = self.tag_static_base_pointer(Pointer::new(id, offset));
631 Operand::Indirect(MemPlace::from_ptr(ptr, layout.align.abi))
633 ConstValue::Scalar(x) => Operand::Immediate(tag_scalar(x).into()),
634 ConstValue::Slice { data, start, end } => {
635 // We rely on mutability being set correctly in `data` to prevent writes
636 // where none should happen.
637 let ptr = Pointer::new(
638 self.tcx.alloc_map.lock().create_memory_alloc(data),
639 Size::from_bytes(start as u64), // offset: `start`
641 Operand::Immediate(Immediate::new_slice(
642 self.tag_static_base_pointer(ptr).into(),
643 (end - start) as u64, // len: `end - start`
648 Ok(OpTy { op, layout })
651 /// Read discriminant, return the runtime value as well as the variant index.
652 pub fn read_discriminant(
654 rval: OpTy<'tcx, M::PointerTag>,
655 ) -> InterpResult<'tcx, (u128, VariantIdx)> {
656 trace!("read_discriminant_value {:#?}", rval.layout);
658 let (discr_layout, discr_kind, discr_index) = match rval.layout.variants {
659 layout::Variants::Single { index } => {
660 let discr_val = rval.layout.ty.discriminant_for_variant(*self.tcx, index).map_or(
661 index.as_u32() as u128,
663 return Ok((discr_val, index));
665 layout::Variants::Multiple {
666 discr: ref discr_layout,
671 (discr_layout, discr_kind, discr_index),
674 // read raw discriminant value
675 let discr_op = self.operand_field(rval, discr_index as u64)?;
676 let discr_val = self.read_immediate(discr_op)?;
677 let raw_discr = discr_val.to_scalar_or_undef();
678 trace!("discr value: {:?}", raw_discr);
680 Ok(match *discr_kind {
681 layout::DiscriminantKind::Tag => {
682 let bits_discr = raw_discr
684 .and_then(|raw_discr| self.force_bits(raw_discr, discr_val.layout.size))
685 .map_err(|_| err_ub!(InvalidDiscriminant(raw_discr.erase_tag())))?;
686 let real_discr = if discr_val.layout.ty.is_signed() {
687 // going from layout tag type to typeck discriminant type
688 // requires first sign extending with the discriminant layout
689 let sexted = sign_extend(bits_discr, discr_val.layout.size) as i128;
690 // and then zeroing with the typeck discriminant type
691 let discr_ty = rval.layout.ty
692 .ty_adt_def().expect("tagged layout corresponds to adt")
695 let size = layout::Integer::from_attr(self, discr_ty).size();
696 let truncatee = sexted as u128;
697 truncate(truncatee, size)
701 // Make sure we catch invalid discriminants
702 let index = match rval.layout.ty.kind {
703 ty::Adt(adt, _) => adt
704 .discriminants(self.tcx.tcx)
705 .find(|(_, var)| var.val == real_discr),
706 ty::Generator(def_id, substs, _) => {
707 let substs = substs.as_generator();
709 .discriminants(def_id, self.tcx.tcx)
710 .find(|(_, var)| var.val == real_discr)
712 _ => bug!("tagged layout for non-adt non-generator"),
715 || err_ub!(InvalidDiscriminant(raw_discr.erase_tag()))
717 (real_discr, index.0)
719 layout::DiscriminantKind::Niche {
724 let variants_start = niche_variants.start().as_u32();
725 let variants_end = niche_variants.end().as_u32();
726 let raw_discr = raw_discr.not_undef().map_err(|_| {
727 err_ub!(InvalidDiscriminant(ScalarMaybeUndef::Undef))
729 match raw_discr.to_bits_or_ptr(discr_val.layout.size, self) {
731 // The niche must be just 0 (which an inbounds pointer value never is)
732 let ptr_valid = niche_start == 0 && variants_start == variants_end &&
733 !self.memory.ptr_may_be_null(ptr);
735 throw_ub!(InvalidDiscriminant(raw_discr.erase_tag().into()))
737 (dataful_variant.as_u32() as u128, dataful_variant)
740 // We need to use machine arithmetic to get the relative variant idx:
741 // variant_index_relative = discr_val - niche_start_val
742 let discr_layout = self.layout_of(discr_layout.value.to_int_ty(*self.tcx))?;
743 let discr_val = ImmTy::from_uint(raw_discr, discr_layout);
744 let niche_start_val = ImmTy::from_uint(niche_start, discr_layout);
745 let variant_index_relative_val = self.binary_op(
750 let variant_index_relative = variant_index_relative_val
752 .assert_bits(discr_val.layout.size);
753 // Check if this is in the range that indicates an actual discriminant.
754 if variant_index_relative <= u128::from(variants_end - variants_start) {
755 let variant_index_relative = u32::try_from(variant_index_relative)
756 .expect("we checked that this fits into a u32");
757 // Then computing the absolute variant idx should not overflow any more.
758 let variant_index = variants_start
759 .checked_add(variant_index_relative)
760 .expect("oveflow computing absolute variant idx");
761 assert!((variant_index as usize) < rval.layout.ty
763 .expect("tagged layout for non adt")
765 (u128::from(variant_index), VariantIdx::from_u32(variant_index))
767 (u128::from(dataful_variant.as_u32()), dataful_variant)