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::{IntegerExt, PrimitiveExt, TyAndLayout};
11 use rustc_middle::ty::print::{FmtPrinter, PrettyPrinter, Printer};
12 use rustc_middle::ty::Ty;
13 use rustc_middle::{mir, ty};
14 use rustc_target::abi::{Abi, DiscriminantKind, HasDataLayout, Integer, LayoutOf, Size};
15 use rustc_target::abi::{VariantIdx, Variants};
18 from_known_layout, sign_extend, truncate, ConstValue, GlobalId, InterpCx, InterpResult,
19 MPlaceTy, Machine, MemPlace, Place, PlaceTy, Pointer, Scalar, ScalarMaybeUninit,
22 /// An `Immediate` represents a single immediate self-contained Rust value.
24 /// For optimization of a few very common cases, there is also a representation for a pair of
25 /// primitive values (`ScalarPair`). It allows Miri to avoid making allocations for checked binary
26 /// operations and wide pointers. This idea was taken from rustc's codegen.
27 /// In particular, thanks to `ScalarPair`, arithmetic operations and casts can be entirely
28 /// defined on `Immediate`, and do not have to work with a `Place`.
29 #[derive(Copy, Clone, Debug, PartialEq, Eq, HashStable, Hash)]
30 pub enum Immediate<Tag = ()> {
31 Scalar(ScalarMaybeUninit<Tag>),
32 ScalarPair(ScalarMaybeUninit<Tag>, ScalarMaybeUninit<Tag>),
35 impl<Tag> From<ScalarMaybeUninit<Tag>> for Immediate<Tag> {
37 fn from(val: ScalarMaybeUninit<Tag>) -> Self {
38 Immediate::Scalar(val)
42 impl<Tag> From<Scalar<Tag>> for Immediate<Tag> {
44 fn from(val: Scalar<Tag>) -> Self {
45 Immediate::Scalar(val.into())
49 impl<Tag> From<Pointer<Tag>> for Immediate<Tag> {
51 fn from(val: Pointer<Tag>) -> Self {
52 Immediate::Scalar(Scalar::from(val).into())
56 impl<'tcx, Tag> Immediate<Tag> {
57 pub fn new_slice(val: Scalar<Tag>, len: u64, cx: &impl HasDataLayout) -> Self {
58 Immediate::ScalarPair(val.into(), Scalar::from_machine_usize(len, cx).into())
61 pub fn new_dyn_trait(val: Scalar<Tag>, vtable: Pointer<Tag>) -> Self {
62 Immediate::ScalarPair(val.into(), vtable.into())
66 pub fn to_scalar_or_undef(self) -> ScalarMaybeUninit<Tag> {
68 Immediate::Scalar(val) => val,
69 Immediate::ScalarPair(..) => bug!("Got a wide pointer where a scalar was expected"),
74 pub fn to_scalar(self) -> InterpResult<'tcx, Scalar<Tag>> {
75 self.to_scalar_or_undef().not_undef()
79 pub fn to_scalar_pair(self) -> InterpResult<'tcx, (Scalar<Tag>, Scalar<Tag>)> {
81 Immediate::Scalar(..) => bug!("Got a thin pointer where a scalar pair was expected"),
82 Immediate::ScalarPair(a, b) => Ok((a.not_undef()?, b.not_undef()?)),
87 // ScalarPair needs a type to interpret, so we often have an immediate and a type together
88 // as input for binary and cast operations.
89 #[derive(Copy, Clone, Debug)]
90 pub struct ImmTy<'tcx, Tag = ()> {
92 pub layout: TyAndLayout<'tcx>,
95 impl<Tag: Copy> std::fmt::Display for ImmTy<'tcx, Tag> {
96 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
97 /// Helper function for printing a scalar to a FmtPrinter
98 fn p<'a, 'tcx, F: std::fmt::Write, Tag>(
99 cx: FmtPrinter<'a, 'tcx, F>,
100 s: ScalarMaybeUninit<Tag>,
102 ) -> Result<FmtPrinter<'a, 'tcx, F>, std::fmt::Error> {
104 ScalarMaybeUninit::Scalar(s) => {
105 cx.pretty_print_const_scalar(s.erase_tag(), ty, true)
107 ScalarMaybeUninit::Uninit => cx.typed_value(
109 this.write_str("{undef ")?;
112 |this| this.print_type(ty),
117 ty::tls::with(|tcx| {
119 Immediate::Scalar(s) => {
120 if let Some(ty) = tcx.lift(&self.layout.ty) {
121 let cx = FmtPrinter::new(tcx, f, Namespace::ValueNS);
125 write!(f, "{}: {}", s.erase_tag(), self.layout.ty)
127 Immediate::ScalarPair(a, b) => {
128 // FIXME(oli-obk): at least print tuples and slices nicely
129 write!(f, "({}, {}): {}", a.erase_tag(), b.erase_tag(), self.layout.ty,)
136 impl<'tcx, Tag> ::std::ops::Deref for ImmTy<'tcx, Tag> {
137 type Target = Immediate<Tag>;
139 fn deref(&self) -> &Immediate<Tag> {
144 /// An `Operand` is the result of computing a `mir::Operand`. It can be immediate,
145 /// or still in memory. The latter is an optimization, to delay reading that chunk of
146 /// memory and to avoid having to store arbitrary-sized data here.
147 #[derive(Copy, Clone, Debug, PartialEq, Eq, HashStable, Hash)]
148 pub enum Operand<Tag = ()> {
149 Immediate(Immediate<Tag>),
150 Indirect(MemPlace<Tag>),
153 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
154 pub struct OpTy<'tcx, Tag = ()> {
155 op: Operand<Tag>, // Keep this private; it helps enforce invariants.
156 pub layout: TyAndLayout<'tcx>,
159 impl<'tcx, Tag> ::std::ops::Deref for OpTy<'tcx, Tag> {
160 type Target = Operand<Tag>;
162 fn deref(&self) -> &Operand<Tag> {
167 impl<'tcx, Tag: Copy> From<MPlaceTy<'tcx, Tag>> for OpTy<'tcx, Tag> {
169 fn from(mplace: MPlaceTy<'tcx, Tag>) -> Self {
170 OpTy { op: Operand::Indirect(*mplace), layout: mplace.layout }
174 impl<'tcx, Tag> From<ImmTy<'tcx, Tag>> for OpTy<'tcx, Tag> {
176 fn from(val: ImmTy<'tcx, Tag>) -> Self {
177 OpTy { op: Operand::Immediate(val.imm), layout: val.layout }
181 impl<'tcx, Tag: Copy> ImmTy<'tcx, Tag> {
183 pub fn from_scalar(val: Scalar<Tag>, layout: TyAndLayout<'tcx>) -> Self {
184 ImmTy { imm: val.into(), layout }
188 pub fn from_immediate(imm: Immediate<Tag>, layout: TyAndLayout<'tcx>) -> Self {
189 ImmTy { imm, layout }
193 pub fn try_from_uint(i: impl Into<u128>, layout: TyAndLayout<'tcx>) -> Option<Self> {
194 Some(Self::from_scalar(Scalar::try_from_uint(i, layout.size)?, layout))
197 pub fn from_uint(i: impl Into<u128>, layout: TyAndLayout<'tcx>) -> Self {
198 Self::from_scalar(Scalar::from_uint(i, layout.size), layout)
202 pub fn try_from_int(i: impl Into<i128>, layout: TyAndLayout<'tcx>) -> Option<Self> {
203 Some(Self::from_scalar(Scalar::try_from_int(i, layout.size)?, layout))
207 pub fn from_int(i: impl Into<i128>, layout: TyAndLayout<'tcx>) -> Self {
208 Self::from_scalar(Scalar::from_int(i, layout.size), layout)
212 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
213 /// Normalice `place.ptr` to a `Pointer` if this is a place and not a ZST.
214 /// Can be helpful to avoid lots of `force_ptr` calls later, if this place is used a lot.
218 op: OpTy<'tcx, M::PointerTag>,
219 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
220 match op.try_as_mplace(self) {
221 Ok(mplace) => Ok(self.force_mplace_ptr(mplace)?.into()),
222 Err(imm) => Ok(imm.into()), // Nothing to cast/force
226 /// Try reading an immediate in memory; this is interesting particularly for `ScalarPair`.
227 /// Returns `None` if the layout does not permit loading this as a value.
228 fn try_read_immediate_from_mplace(
230 mplace: MPlaceTy<'tcx, M::PointerTag>,
231 ) -> InterpResult<'tcx, Option<ImmTy<'tcx, M::PointerTag>>> {
232 if mplace.layout.is_unsized() {
233 // Don't touch unsized
238 .check_mplace_access(mplace, None)
239 .expect("places should be checked on creation")
243 if let Scalar::Ptr(ptr) = mplace.ptr {
244 // We may be reading from a static.
245 // In order to ensure that `static FOO: Type = FOO;` causes a cycle error
246 // instead of magically pulling *any* ZST value from the ether, we need to
247 // actually access the referenced allocation.
248 self.memory.get_raw(ptr.alloc_id)?;
250 return Ok(Some(ImmTy {
252 imm: Scalar::zst().into(),
253 layout: mplace.layout,
258 let alloc = self.memory.get_raw(ptr.alloc_id)?;
260 match mplace.layout.abi {
262 let scalar = alloc.read_scalar(self, ptr, mplace.layout.size)?;
263 Ok(Some(ImmTy { imm: scalar.into(), layout: mplace.layout }))
265 Abi::ScalarPair(ref a, ref b) => {
266 // We checked `ptr_align` above, so all fields will have the alignment they need.
267 // We would anyway check against `ptr_align.restrict_for_offset(b_offset)`,
268 // which `ptr.offset(b_offset)` cannot possibly fail to satisfy.
269 let (a, b) = (&a.value, &b.value);
270 let (a_size, b_size) = (a.size(self), b.size(self));
272 let b_offset = a_size.align_to(b.align(self).abi);
273 assert!(b_offset.bytes() > 0); // we later use the offset to tell apart the fields
274 let b_ptr = ptr.offset(b_offset, self)?;
275 let a_val = alloc.read_scalar(self, a_ptr, a_size)?;
276 let b_val = alloc.read_scalar(self, b_ptr, b_size)?;
277 Ok(Some(ImmTy { imm: Immediate::ScalarPair(a_val, b_val), layout: mplace.layout }))
283 /// Try returning an immediate for the operand.
284 /// If the layout does not permit loading this as an immediate, return where in memory
285 /// we can find the data.
286 /// Note that for a given layout, this operation will either always fail or always
287 /// succeed! Whether it succeeds depends on whether the layout can be represented
288 /// in a `Immediate`, not on which data is stored there currently.
289 pub(crate) fn try_read_immediate(
291 src: OpTy<'tcx, M::PointerTag>,
292 ) -> InterpResult<'tcx, Result<ImmTy<'tcx, M::PointerTag>, MPlaceTy<'tcx, M::PointerTag>>> {
293 Ok(match src.try_as_mplace(self) {
295 if let Some(val) = self.try_read_immediate_from_mplace(mplace)? {
305 /// Read an immediate from a place, asserting that that is possible with the given layout.
307 pub fn read_immediate(
309 op: OpTy<'tcx, M::PointerTag>,
310 ) -> InterpResult<'tcx, ImmTy<'tcx, M::PointerTag>> {
311 if let Ok(imm) = self.try_read_immediate(op)? {
314 bug!("primitive read failed for type: {:?}", op.layout.ty);
318 /// Read a scalar from a place
321 op: OpTy<'tcx, M::PointerTag>,
322 ) -> InterpResult<'tcx, ScalarMaybeUninit<M::PointerTag>> {
323 Ok(self.read_immediate(op)?.to_scalar_or_undef())
326 // Turn the wide MPlace into a string (must already be dereferenced!)
327 pub fn read_str(&self, mplace: MPlaceTy<'tcx, M::PointerTag>) -> InterpResult<'tcx, &str> {
328 let len = mplace.len(self)?;
329 let bytes = self.memory.read_bytes(mplace.ptr, Size::from_bytes(len))?;
330 let str = ::std::str::from_utf8(bytes).map_err(|err| err_ub!(InvalidStr(err)))?;
334 /// Projection functions
335 pub fn operand_field(
337 op: OpTy<'tcx, M::PointerTag>,
339 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
340 let base = match op.try_as_mplace(self) {
342 // We can reuse the mplace field computation logic for indirect operands.
343 let field = self.mplace_field(mplace, field)?;
344 return Ok(field.into());
349 let field_layout = op.layout.field(self, field)?;
350 if field_layout.is_zst() {
351 let immediate = Scalar::zst().into();
352 return Ok(OpTy { op: Operand::Immediate(immediate), layout: field_layout });
354 let offset = op.layout.fields.offset(field);
355 let immediate = match *base {
356 // the field covers the entire type
357 _ if offset.bytes() == 0 && field_layout.size == op.layout.size => *base,
358 // extract fields from types with `ScalarPair` ABI
359 Immediate::ScalarPair(a, b) => {
360 let val = if offset.bytes() == 0 { a } else { b };
363 Immediate::Scalar(val) => {
364 bug!("field access on non aggregate {:#?}, {:#?}", val, op.layout)
367 Ok(OpTy { op: Operand::Immediate(immediate), layout: field_layout })
370 pub fn operand_index(
372 op: OpTy<'tcx, M::PointerTag>,
374 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
375 if let Ok(index) = usize::try_from(index) {
376 // We can just treat this as a field.
377 self.operand_field(op, index)
379 // Indexing into a big array. This must be an mplace.
380 let mplace = op.assert_mem_place(self);
381 Ok(self.mplace_index(mplace, index)?.into())
385 pub fn operand_downcast(
387 op: OpTy<'tcx, M::PointerTag>,
389 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
390 // Downcasts only change the layout
391 Ok(match op.try_as_mplace(self) {
392 Ok(mplace) => self.mplace_downcast(mplace, variant)?.into(),
394 let layout = op.layout.for_variant(self, variant);
395 OpTy { layout, ..op }
400 pub fn operand_projection(
402 base: OpTy<'tcx, M::PointerTag>,
403 proj_elem: &mir::PlaceElem<'tcx>,
404 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
405 use rustc_middle::mir::ProjectionElem::*;
406 Ok(match *proj_elem {
407 Field(field, _) => self.operand_field(base, field.index())?,
408 Downcast(_, variant) => self.operand_downcast(base, variant)?,
409 Deref => self.deref_operand(base)?.into(),
410 Subslice { .. } | ConstantIndex { .. } | Index(_) => {
411 // The rest should only occur as mplace, we do not use Immediates for types
412 // allowing such operations. This matches place_projection forcing an allocation.
413 let mplace = base.assert_mem_place(self);
414 self.mplace_projection(mplace, proj_elem)?.into()
419 /// This is used by [priroda](https://github.com/oli-obk/priroda) to get an OpTy from a local
422 frame: &super::Frame<'mir, 'tcx, M::PointerTag, M::FrameExtra>,
424 layout: Option<TyAndLayout<'tcx>>,
425 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
426 let layout = self.layout_of_local(frame, local, layout)?;
427 let op = if layout.is_zst() {
428 // Do not read from ZST, they might not be initialized
429 Operand::Immediate(Scalar::zst().into())
431 M::access_local(&self, frame, local)?
433 Ok(OpTy { op, layout })
436 /// Every place can be read from, so we can turn them into an operand.
437 /// This will definitely return `Indirect` if the place is a `Ptr`, i.e., this
438 /// will never actually read from memory.
442 place: PlaceTy<'tcx, M::PointerTag>,
443 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
444 let op = match *place {
445 Place::Ptr(mplace) => Operand::Indirect(mplace),
446 Place::Local { frame, local } => {
447 *self.access_local(&self.stack()[frame], local, None)?
450 Ok(OpTy { op, layout: place.layout })
453 // Evaluate a place with the goal of reading from it. This lets us sometimes
454 // avoid allocations.
455 pub fn eval_place_to_op(
457 place: mir::Place<'tcx>,
458 layout: Option<TyAndLayout<'tcx>>,
459 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
460 // Do not use the layout passed in as argument if the base we are looking at
461 // here is not the entire place.
462 let layout = if place.projection.is_empty() { layout } else { None };
464 let base_op = self.access_local(self.frame(), place.local, layout)?;
469 .try_fold(base_op, |op, elem| self.operand_projection(op, elem))?;
471 trace!("eval_place_to_op: got {:?}", *op);
475 /// Evaluate the operand, returning a place where you can then find the data.
476 /// If you already know the layout, you can save two table lookups
477 /// by passing it in here.
480 mir_op: &mir::Operand<'tcx>,
481 layout: Option<TyAndLayout<'tcx>>,
482 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
483 use rustc_middle::mir::Operand::*;
484 let op = match *mir_op {
485 // FIXME: do some more logic on `move` to invalidate the old location
486 Copy(place) | Move(place) => self.eval_place_to_op(place, layout)?,
488 Constant(ref constant) => {
490 self.subst_from_current_frame_and_normalize_erasing_regions(constant.literal);
491 self.eval_const_to_op(val, layout)?
494 trace!("{:?}: {:?}", mir_op, *op);
498 /// Evaluate a bunch of operands at once
499 pub(super) fn eval_operands(
501 ops: &[mir::Operand<'tcx>],
502 ) -> InterpResult<'tcx, Vec<OpTy<'tcx, M::PointerTag>>> {
503 ops.iter().map(|op| self.eval_operand(op, None)).collect()
506 // Used when the miri-engine runs into a constant and for extracting information from constants
507 // in patterns via the `const_eval` module
508 /// The `val` and `layout` are assumed to already be in our interpreter
509 /// "universe" (param_env).
510 crate fn eval_const_to_op(
512 val: &ty::Const<'tcx>,
513 layout: Option<TyAndLayout<'tcx>>,
514 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
515 let tag_scalar = |scalar| match scalar {
516 Scalar::Ptr(ptr) => Scalar::Ptr(self.tag_global_base_pointer(ptr)),
517 Scalar::Raw { data, size } => Scalar::Raw { data, size },
519 // Early-return cases.
520 let val_val = match val.val {
521 ty::ConstKind::Param(_) => throw_inval!(TooGeneric),
522 ty::ConstKind::Error => throw_inval!(TypeckError(ErrorReported)),
523 ty::ConstKind::Unevaluated(def_id, substs, promoted) => {
524 let instance = self.resolve(def_id, substs)?;
525 // We use `const_eval` here and `const_eval_raw` elsewhere in mir interpretation.
526 // The reason we use `const_eval_raw` everywhere else is to prevent cycles during
527 // validation, because validation automatically reads through any references, thus
528 // potentially requiring the current static to be evaluated again. This is not a
529 // problem here, because we are building an operand which means an actual read is
532 // The machine callback `adjust_global_const` below is guaranteed to
533 // be called for all constants because `const_eval` calls
534 // `eval_const_to_op` recursively.
535 return Ok(self.const_eval(GlobalId { instance, promoted }, val.ty)?);
537 ty::ConstKind::Infer(..)
538 | ty::ConstKind::Bound(..)
539 | ty::ConstKind::Placeholder(..) => {
540 bug!("eval_const_to_op: Unexpected ConstKind {:?}", val)
542 ty::ConstKind::Value(val_val) => val_val,
544 // This call allows the machine to create fresh allocation ids for
545 // thread-local statics (see the `adjust_global_const` function
547 let val_val = M::adjust_global_const(self, val_val)?;
548 // Other cases need layout.
549 let layout = from_known_layout(self.tcx, layout, || self.layout_of(val.ty))?;
550 let op = match val_val {
551 ConstValue::ByRef { alloc, offset } => {
552 let id = self.tcx.alloc_map.lock().create_memory_alloc(alloc);
553 // We rely on mutability being set correctly in that allocation to prevent writes
554 // where none should happen.
555 let ptr = self.tag_global_base_pointer(Pointer::new(id, offset));
556 Operand::Indirect(MemPlace::from_ptr(ptr, layout.align.abi))
558 ConstValue::Scalar(x) => Operand::Immediate(tag_scalar(x).into()),
559 ConstValue::Slice { data, start, end } => {
560 // We rely on mutability being set correctly in `data` to prevent writes
561 // where none should happen.
562 let ptr = Pointer::new(
563 self.tcx.alloc_map.lock().create_memory_alloc(data),
564 Size::from_bytes(start), // offset: `start`
566 Operand::Immediate(Immediate::new_slice(
567 self.tag_global_base_pointer(ptr).into(),
568 u64::try_from(end.checked_sub(start).unwrap()).unwrap(), // len: `end - start`
573 Ok(OpTy { op, layout })
576 /// Read discriminant, return the runtime value as well as the variant index.
577 pub fn read_discriminant(
579 rval: OpTy<'tcx, M::PointerTag>,
580 ) -> InterpResult<'tcx, (u128, VariantIdx)> {
581 trace!("read_discriminant_value {:#?}", rval.layout);
583 let (discr_layout, discr_kind, discr_index) = match rval.layout.variants {
584 Variants::Single { index } => {
588 .discriminant_for_variant(*self.tcx, index)
589 .map_or(u128::from(index.as_u32()), |discr| discr.val);
590 return Ok((discr_val, index));
592 Variants::Multiple { discr: ref discr_layout, ref discr_kind, discr_index, .. } => {
593 (discr_layout, discr_kind, discr_index)
597 // read raw discriminant value
598 let discr_op = self.operand_field(rval, discr_index)?;
599 let discr_val = self.read_immediate(discr_op)?;
600 let raw_discr = discr_val.to_scalar_or_undef();
601 trace!("discr value: {:?}", raw_discr);
603 Ok(match *discr_kind {
604 DiscriminantKind::Tag => {
605 let bits_discr = raw_discr
607 .and_then(|raw_discr| self.force_bits(raw_discr, discr_val.layout.size))
608 .map_err(|_| err_ub!(InvalidDiscriminant(raw_discr.erase_tag())))?;
609 let real_discr = if discr_val.layout.abi.is_signed() {
610 // going from layout tag type to typeck discriminant type
611 // requires first sign extending with the discriminant layout
612 let sexted = sign_extend(bits_discr, discr_val.layout.size);
613 // and then zeroing with the typeck discriminant type
618 .expect("tagged layout corresponds to adt")
621 let size = Integer::from_attr(self, discr_ty).size();
622 truncate(sexted, size)
626 // Make sure we catch invalid discriminants
627 let index = match rval.layout.ty.kind {
629 adt.discriminants(self.tcx.tcx).find(|(_, var)| var.val == real_discr)
631 ty::Generator(def_id, substs, _) => {
632 let substs = substs.as_generator();
634 .discriminants(def_id, self.tcx.tcx)
635 .find(|(_, var)| var.val == real_discr)
637 _ => bug!("tagged layout for non-adt non-generator"),
639 .ok_or_else(|| err_ub!(InvalidDiscriminant(raw_discr.erase_tag())))?;
640 (real_discr, index.0)
642 DiscriminantKind::Niche { dataful_variant, ref niche_variants, niche_start } => {
643 let variants_start = niche_variants.start().as_u32();
644 let variants_end = niche_variants.end().as_u32();
645 let raw_discr = raw_discr
647 .map_err(|_| err_ub!(InvalidDiscriminant(ScalarMaybeUninit::Uninit)))?;
648 match raw_discr.to_bits_or_ptr(discr_val.layout.size, self) {
650 // The niche must be just 0 (which an inbounds pointer value never is)
651 let ptr_valid = niche_start == 0
652 && variants_start == variants_end
653 && !self.memory.ptr_may_be_null(ptr);
655 throw_ub!(InvalidDiscriminant(raw_discr.erase_tag().into()))
657 (u128::from(dataful_variant.as_u32()), dataful_variant)
660 // We need to use machine arithmetic to get the relative variant idx:
661 // variant_index_relative = discr_val - niche_start_val
663 self.layout_of(discr_layout.value.to_int_ty(*self.tcx))?;
664 let discr_val = ImmTy::from_uint(raw_discr, discr_layout);
665 let niche_start_val = ImmTy::from_uint(niche_start, discr_layout);
666 let variant_index_relative_val =
667 self.binary_op(mir::BinOp::Sub, discr_val, niche_start_val)?;
668 let variant_index_relative = variant_index_relative_val
670 .assert_bits(discr_val.layout.size);
671 // Check if this is in the range that indicates an actual discriminant.
672 if variant_index_relative <= u128::from(variants_end - variants_start) {
673 let variant_index_relative = u32::try_from(variant_index_relative)
674 .expect("we checked that this fits into a u32");
675 // Then computing the absolute variant idx should not overflow any more.
676 let variant_index = variants_start
677 .checked_add(variant_index_relative)
678 .expect("overflow computing absolute variant idx");
679 let variants_len = rval
683 .expect("tagged layout for non adt")
686 assert!(usize::try_from(variant_index).unwrap() < variants_len);
687 (u128::from(variant_index), VariantIdx::from_u32(variant_index))
689 (u128::from(dataful_variant.as_u32()), dataful_variant)