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 rustc_hir::def::Namespace;
5 use rustc_middle::ty::layout::{LayoutOf, PrimitiveExt, TyAndLayout};
6 use rustc_middle::ty::print::{FmtPrinter, PrettyPrinter};
7 use rustc_middle::ty::{ConstInt, Ty};
8 use rustc_middle::{mir, ty};
9 use rustc_target::abi::{self, Abi, Align, HasDataLayout, Size, TagEncoding};
10 use rustc_target::abi::{VariantIdx, Variants};
13 alloc_range, from_known_layout, mir_assign_valid_types, AllocId, ConstValue, Frame, GlobalId,
14 InterpCx, InterpResult, MPlaceTy, Machine, MemPlace, MemPlaceMeta, Place, PlaceTy, Pointer,
18 /// An `Immediate` represents a single immediate self-contained Rust value.
20 /// For optimization of a few very common cases, there is also a representation for a pair of
21 /// primitive values (`ScalarPair`). It allows Miri to avoid making allocations for checked binary
22 /// operations and wide pointers. This idea was taken from rustc's codegen.
23 /// In particular, thanks to `ScalarPair`, arithmetic operations and casts can be entirely
24 /// defined on `Immediate`, and do not have to work with a `Place`.
25 #[derive(Copy, Clone, Debug)]
26 pub enum Immediate<Prov: Provenance = AllocId> {
27 /// A single scalar value (must have *initialized* `Scalar` ABI).
29 /// A pair of two scalar value (must have `ScalarPair` ABI where both fields are
30 /// `Scalar::Initialized`).
31 ScalarPair(Scalar<Prov>, Scalar<Prov>),
32 /// A value of fully uninitialized memory. Can have and size and layout.
36 impl<Prov: Provenance> From<Scalar<Prov>> for Immediate<Prov> {
38 fn from(val: Scalar<Prov>) -> Self {
39 Immediate::Scalar(val.into())
43 impl<Prov: Provenance> Immediate<Prov> {
44 pub fn from_pointer(p: Pointer<Prov>, cx: &impl HasDataLayout) -> Self {
45 Immediate::Scalar(Scalar::from_pointer(p, cx))
48 pub fn from_maybe_pointer(p: Pointer<Option<Prov>>, cx: &impl HasDataLayout) -> Self {
49 Immediate::Scalar(Scalar::from_maybe_pointer(p, cx))
52 pub fn new_slice(val: Scalar<Prov>, len: u64, cx: &impl HasDataLayout) -> Self {
53 Immediate::ScalarPair(val.into(), Scalar::from_machine_usize(len, cx).into())
58 vtable: Pointer<Option<Prov>>,
59 cx: &impl HasDataLayout,
61 Immediate::ScalarPair(val.into(), Scalar::from_maybe_pointer(vtable, cx))
65 #[cfg_attr(debug_assertions, track_caller)] // only in debug builds due to perf (see #98980)
66 pub fn to_scalar(self) -> Scalar<Prov> {
68 Immediate::Scalar(val) => val,
69 Immediate::ScalarPair(..) => bug!("Got a scalar pair where a scalar was expected"),
70 Immediate::Uninit => bug!("Got uninit where a scalar was expected"),
75 #[cfg_attr(debug_assertions, track_caller)] // only in debug builds due to perf (see #98980)
76 pub fn to_scalar_pair(self) -> (Scalar<Prov>, Scalar<Prov>) {
78 Immediate::ScalarPair(val1, val2) => (val1, val2),
79 Immediate::Scalar(..) => bug!("Got a scalar where a scalar pair was expected"),
80 Immediate::Uninit => bug!("Got uninit where a scalar pair was expected"),
85 // ScalarPair needs a type to interpret, so we often have an immediate and a type together
86 // as input for binary and cast operations.
87 #[derive(Clone, Debug)]
88 pub struct ImmTy<'tcx, Prov: Provenance = AllocId> {
90 pub layout: TyAndLayout<'tcx>,
93 impl<Prov: Provenance> std::fmt::Display for ImmTy<'_, Prov> {
94 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
95 /// Helper function for printing a scalar to a FmtPrinter
96 fn p<'a, 'tcx, Prov: Provenance>(
97 cx: FmtPrinter<'a, 'tcx>,
100 ) -> Result<FmtPrinter<'a, 'tcx>, std::fmt::Error> {
102 Scalar::Int(int) => cx.pretty_print_const_scalar_int(int, ty, true),
103 Scalar::Ptr(ptr, _sz) => {
104 // Just print the ptr value. `pretty_print_const_scalar_ptr` would also try to
105 // print what is points to, which would fail since it has no access to the local
107 cx.pretty_print_const_pointer(ptr, ty, true)
111 ty::tls::with(|tcx| {
113 Immediate::Scalar(s) => {
114 if let Some(ty) = tcx.lift(self.layout.ty) {
115 let cx = FmtPrinter::new(tcx, Namespace::ValueNS);
116 f.write_str(&p(cx, s, ty)?.into_buffer())?;
119 write!(f, "{:x}: {}", s, self.layout.ty)
121 Immediate::ScalarPair(a, b) => {
122 // FIXME(oli-obk): at least print tuples and slices nicely
123 write!(f, "({:x}, {:x}): {}", a, b, self.layout.ty)
125 Immediate::Uninit => {
126 write!(f, "uninit: {}", self.layout.ty)
133 impl<'tcx, Prov: Provenance> std::ops::Deref for ImmTy<'tcx, Prov> {
134 type Target = Immediate<Prov>;
136 fn deref(&self) -> &Immediate<Prov> {
141 /// An `Operand` is the result of computing a `mir::Operand`. It can be immediate,
142 /// or still in memory. The latter is an optimization, to delay reading that chunk of
143 /// memory and to avoid having to store arbitrary-sized data here.
144 #[derive(Copy, Clone, Debug)]
145 pub enum Operand<Prov: Provenance = AllocId> {
146 Immediate(Immediate<Prov>),
147 Indirect(MemPlace<Prov>),
150 #[derive(Clone, Debug)]
151 pub struct OpTy<'tcx, Prov: Provenance = AllocId> {
152 op: Operand<Prov>, // Keep this private; it helps enforce invariants.
153 pub layout: TyAndLayout<'tcx>,
154 /// rustc does not have a proper way to represent the type of a field of a `repr(packed)` struct:
155 /// it needs to have a different alignment than the field type would usually have.
156 /// So we represent this here with a separate field that "overwrites" `layout.align`.
157 /// This means `layout.align` should never be used for an `OpTy`!
158 /// `None` means "alignment does not matter since this is a by-value operand"
159 /// (`Operand::Immediate`); this field is only relevant for `Operand::Indirect`.
160 /// Also CTFE ignores alignment anyway, so this is for Miri only.
161 pub align: Option<Align>,
164 impl<'tcx, Prov: Provenance> std::ops::Deref for OpTy<'tcx, Prov> {
165 type Target = Operand<Prov>;
167 fn deref(&self) -> &Operand<Prov> {
172 impl<'tcx, Prov: Provenance> From<MPlaceTy<'tcx, Prov>> for OpTy<'tcx, Prov> {
174 fn from(mplace: MPlaceTy<'tcx, Prov>) -> Self {
175 OpTy { op: Operand::Indirect(*mplace), layout: mplace.layout, align: Some(mplace.align) }
179 impl<'tcx, Prov: Provenance> From<&'_ MPlaceTy<'tcx, Prov>> for OpTy<'tcx, Prov> {
181 fn from(mplace: &MPlaceTy<'tcx, Prov>) -> Self {
182 OpTy { op: Operand::Indirect(**mplace), layout: mplace.layout, align: Some(mplace.align) }
186 impl<'tcx, Prov: Provenance> From<&'_ mut MPlaceTy<'tcx, Prov>> for OpTy<'tcx, Prov> {
188 fn from(mplace: &mut MPlaceTy<'tcx, Prov>) -> Self {
189 OpTy { op: Operand::Indirect(**mplace), layout: mplace.layout, align: Some(mplace.align) }
193 impl<'tcx, Prov: Provenance> From<ImmTy<'tcx, Prov>> for OpTy<'tcx, Prov> {
195 fn from(val: ImmTy<'tcx, Prov>) -> Self {
196 OpTy { op: Operand::Immediate(val.imm), layout: val.layout, align: None }
200 impl<'tcx, Prov: Provenance> ImmTy<'tcx, Prov> {
202 pub fn from_scalar(val: Scalar<Prov>, layout: TyAndLayout<'tcx>) -> Self {
203 ImmTy { imm: val.into(), layout }
207 pub fn from_immediate(imm: Immediate<Prov>, layout: TyAndLayout<'tcx>) -> Self {
208 ImmTy { imm, layout }
212 pub fn uninit(layout: TyAndLayout<'tcx>) -> Self {
213 ImmTy { imm: Immediate::Uninit, layout }
217 pub fn try_from_uint(i: impl Into<u128>, layout: TyAndLayout<'tcx>) -> Option<Self> {
218 Some(Self::from_scalar(Scalar::try_from_uint(i, layout.size)?, layout))
221 pub fn from_uint(i: impl Into<u128>, layout: TyAndLayout<'tcx>) -> Self {
222 Self::from_scalar(Scalar::from_uint(i, layout.size), layout)
226 pub fn try_from_int(i: impl Into<i128>, layout: TyAndLayout<'tcx>) -> Option<Self> {
227 Some(Self::from_scalar(Scalar::try_from_int(i, layout.size)?, layout))
231 pub fn from_int(i: impl Into<i128>, layout: TyAndLayout<'tcx>) -> Self {
232 Self::from_scalar(Scalar::from_int(i, layout.size), layout)
236 pub fn to_const_int(self) -> ConstInt {
237 assert!(self.layout.ty.is_integral());
238 let int = self.to_scalar().assert_int();
239 ConstInt::new(int, self.layout.ty.is_signed(), self.layout.ty.is_ptr_sized_integral())
243 impl<'tcx, Prov: Provenance> OpTy<'tcx, Prov> {
244 pub fn len(&self, cx: &impl HasDataLayout) -> InterpResult<'tcx, u64> {
245 if self.layout.is_unsized() {
246 // There are no unsized immediates.
247 self.assert_mem_place().len(cx)
249 match self.layout.fields {
250 abi::FieldsShape::Array { count, .. } => Ok(count),
251 _ => bug!("len not supported on sized type {:?}", self.layout.ty),
256 pub fn offset_with_meta(
259 meta: MemPlaceMeta<Prov>,
260 layout: TyAndLayout<'tcx>,
261 cx: &impl HasDataLayout,
262 ) -> InterpResult<'tcx, Self> {
263 match self.try_as_mplace() {
264 Ok(mplace) => Ok(mplace.offset_with_meta(offset, meta, layout, cx)?.into()),
267 matches!(*imm, Immediate::Uninit),
268 "Scalar/ScalarPair cannot be offset into"
270 assert!(!meta.has_meta()); // no place to store metadata here
271 // Every part of an uninit is uninit.
272 Ok(ImmTy::uninit(layout).into())
280 layout: TyAndLayout<'tcx>,
281 cx: &impl HasDataLayout,
282 ) -> InterpResult<'tcx, Self> {
283 assert!(!layout.is_unsized());
284 self.offset_with_meta(offset, MemPlaceMeta::None, layout, cx)
288 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
289 /// Try reading an immediate in memory; this is interesting particularly for `ScalarPair`.
290 /// Returns `None` if the layout does not permit loading this as a value.
292 /// This is an internal function; call `read_immediate` instead.
293 fn read_immediate_from_mplace_raw(
295 mplace: &MPlaceTy<'tcx, M::Provenance>,
296 ) -> InterpResult<'tcx, Option<ImmTy<'tcx, M::Provenance>>> {
297 if mplace.layout.is_unsized() {
298 // Don't touch unsized
302 let Some(alloc) = self.get_place_alloc(mplace)? else {
303 // zero-sized type can be left uninit
304 return Ok(Some(ImmTy::uninit(mplace.layout)));
307 // It may seem like all types with `Scalar` or `ScalarPair` ABI are fair game at this point.
308 // However, `MaybeUninit<u64>` is considered a `Scalar` as far as its layout is concerned --
309 // and yet cannot be represented by an interpreter `Scalar`, since we have to handle the
310 // case where some of the bytes are initialized and others are not. So, we need an extra
311 // check that walks over the type of `mplace` to make sure it is truly correct to treat this
312 // like a `Scalar` (or `ScalarPair`).
313 Ok(match mplace.layout.abi {
314 Abi::Scalar(abi::Scalar::Initialized { value: s, .. }) => {
315 let size = s.size(self);
316 assert_eq!(size, mplace.layout.size, "abi::Scalar size does not match layout size");
317 let scalar = alloc.read_scalar(
318 alloc_range(Size::ZERO, size),
319 /*read_provenance*/ s.is_ptr(),
321 Some(ImmTy { imm: scalar.into(), layout: mplace.layout })
324 abi::Scalar::Initialized { value: a, .. },
325 abi::Scalar::Initialized { value: b, .. },
327 // We checked `ptr_align` above, so all fields will have the alignment they need.
328 // We would anyway check against `ptr_align.restrict_for_offset(b_offset)`,
329 // which `ptr.offset(b_offset)` cannot possibly fail to satisfy.
330 let (a_size, b_size) = (a.size(self), b.size(self));
331 let b_offset = a_size.align_to(b.align(self).abi);
332 assert!(b_offset.bytes() > 0); // in `operand_field` we use the offset to tell apart the fields
333 let a_val = alloc.read_scalar(
334 alloc_range(Size::ZERO, a_size),
335 /*read_provenance*/ a.is_ptr(),
337 let b_val = alloc.read_scalar(
338 alloc_range(b_offset, b_size),
339 /*read_provenance*/ b.is_ptr(),
342 imm: Immediate::ScalarPair(a_val.into(), b_val.into()),
343 layout: mplace.layout,
347 // Neither a scalar nor scalar pair.
353 /// Try returning an immediate for the operand. If the layout does not permit loading this as an
354 /// immediate, return where in memory we can find the data.
355 /// Note that for a given layout, this operation will either always fail or always
356 /// succeed! Whether it succeeds depends on whether the layout can be represented
357 /// in an `Immediate`, not on which data is stored there currently.
359 /// This is an internal function that should not usually be used; call `read_immediate` instead.
360 /// ConstProp needs it, though.
361 pub fn read_immediate_raw(
363 src: &OpTy<'tcx, M::Provenance>,
364 ) -> InterpResult<'tcx, Result<ImmTy<'tcx, M::Provenance>, MPlaceTy<'tcx, M::Provenance>>> {
365 Ok(match src.try_as_mplace() {
367 if let Some(val) = self.read_immediate_from_mplace_raw(mplace)? {
377 /// Read an immediate from a place, asserting that that is possible with the given layout.
379 /// If this suceeds, the `ImmTy` is never `Uninit`.
381 pub fn read_immediate(
383 op: &OpTy<'tcx, M::Provenance>,
384 ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
387 Abi::Scalar(abi::Scalar::Initialized { .. })
388 | Abi::ScalarPair(abi::Scalar::Initialized { .. }, abi::Scalar::Initialized { .. })
390 span_bug!(self.cur_span(), "primitive read not possible for type: {:?}", op.layout.ty);
392 let imm = self.read_immediate_raw(op)?.unwrap();
393 if matches!(*imm, Immediate::Uninit) {
394 throw_ub!(InvalidUninitBytes(None));
399 /// Read a scalar from a place
402 op: &OpTy<'tcx, M::Provenance>,
403 ) -> InterpResult<'tcx, Scalar<M::Provenance>> {
404 Ok(self.read_immediate(op)?.to_scalar())
407 /// Read a pointer from a place.
410 op: &OpTy<'tcx, M::Provenance>,
411 ) -> InterpResult<'tcx, Pointer<Option<M::Provenance>>> {
412 self.read_scalar(op)?.to_pointer(self)
415 /// Turn the wide MPlace into a string (must already be dereferenced!)
416 pub fn read_str(&self, mplace: &MPlaceTy<'tcx, M::Provenance>) -> InterpResult<'tcx, &str> {
417 let len = mplace.len(self)?;
418 let bytes = self.read_bytes_ptr_strip_provenance(mplace.ptr, Size::from_bytes(len))?;
419 let str = std::str::from_utf8(bytes).map_err(|err| err_ub!(InvalidStr(err)))?;
423 /// Converts a repr(simd) operand into an operand where `place_index` accesses the SIMD elements.
424 /// Also returns the number of elements.
426 /// Can (but does not always) trigger UB if `op` is uninitialized.
427 pub fn operand_to_simd(
429 op: &OpTy<'tcx, M::Provenance>,
430 ) -> InterpResult<'tcx, (MPlaceTy<'tcx, M::Provenance>, u64)> {
431 // Basically we just transmute this place into an array following simd_size_and_type.
432 // This only works in memory, but repr(simd) types should never be immediates anyway.
433 assert!(op.layout.ty.is_simd());
434 match op.try_as_mplace() {
435 Ok(mplace) => self.mplace_to_simd(&mplace),
436 Err(imm) => match *imm {
437 Immediate::Uninit => {
438 throw_ub!(InvalidUninitBytes(None))
440 Immediate::Scalar(..) | Immediate::ScalarPair(..) => {
441 bug!("arrays/slices can never have Scalar/ScalarPair layout")
447 /// Read from a local.
448 /// Will not access memory, instead an indirect `Operand` is returned.
450 /// This is public because it is used by [priroda](https://github.com/oli-obk/priroda) to get an
451 /// OpTy from a local.
454 frame: &Frame<'mir, 'tcx, M::Provenance, M::FrameExtra>,
456 layout: Option<TyAndLayout<'tcx>>,
457 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
458 let layout = self.layout_of_local(frame, local, layout)?;
459 let op = *frame.locals[local].access()?;
460 Ok(OpTy { op, layout, align: Some(layout.align.abi) })
463 /// Every place can be read from, so we can turn them into an operand.
464 /// This will definitely return `Indirect` if the place is a `Ptr`, i.e., this
465 /// will never actually read from memory.
469 place: &PlaceTy<'tcx, M::Provenance>,
470 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
471 let op = match **place {
472 Place::Ptr(mplace) => Operand::Indirect(mplace),
473 Place::Local { frame, local } => {
474 *self.local_to_op(&self.stack()[frame], local, None)?
477 Ok(OpTy { op, layout: place.layout, align: Some(place.align) })
480 /// Evaluate a place with the goal of reading from it. This lets us sometimes
481 /// avoid allocations.
482 pub fn eval_place_to_op(
484 mir_place: mir::Place<'tcx>,
485 layout: Option<TyAndLayout<'tcx>>,
486 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
487 // Do not use the layout passed in as argument if the base we are looking at
488 // here is not the entire place.
489 let layout = if mir_place.projection.is_empty() { layout } else { None };
491 let mut op = self.local_to_op(self.frame(), mir_place.local, layout)?;
492 // Using `try_fold` turned out to be bad for performance, hence the loop.
493 for elem in mir_place.projection.iter() {
494 op = self.operand_projection(&op, elem)?
497 trace!("eval_place_to_op: got {:?}", *op);
498 // Sanity-check the type we ended up with.
500 mir_assign_valid_types(
503 self.layout_of(self.subst_from_current_frame_and_normalize_erasing_regions(
504 mir_place.ty(&self.frame().body.local_decls, *self.tcx).ty
508 "eval_place of a MIR place with type {:?} produced an interpreter operand with type {:?}",
509 mir_place.ty(&self.frame().body.local_decls, *self.tcx).ty,
515 /// Evaluate the operand, returning a place where you can then find the data.
516 /// If you already know the layout, you can save two table lookups
517 /// by passing it in here.
521 mir_op: &mir::Operand<'tcx>,
522 layout: Option<TyAndLayout<'tcx>>,
523 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
524 use rustc_middle::mir::Operand::*;
525 let op = match *mir_op {
526 // FIXME: do some more logic on `move` to invalidate the old location
527 Copy(place) | Move(place) => self.eval_place_to_op(place, layout)?,
529 Constant(ref constant) => {
531 self.subst_from_current_frame_and_normalize_erasing_regions(constant.literal)?;
533 // This can still fail:
534 // * During ConstProp, with `TooGeneric` or since the `required_consts` were not all
536 // * During CTFE, since promoteds in `const`/`static` initializer bodies can fail.
537 self.const_to_op(&val, layout)?
540 trace!("{:?}: {:?}", mir_op, *op);
544 /// Evaluate a bunch of operands at once
545 pub(super) fn eval_operands(
547 ops: &[mir::Operand<'tcx>],
548 ) -> InterpResult<'tcx, Vec<OpTy<'tcx, M::Provenance>>> {
549 ops.iter().map(|op| self.eval_operand(op, None)).collect()
554 val: &mir::ConstantKind<'tcx>,
555 layout: Option<TyAndLayout<'tcx>>,
556 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
557 // FIXME(const_prop): normalization needed b/c const prop lint in
558 // `mir_drops_elaborated_and_const_checked`, which happens before
559 // optimized MIR. Only after optimizing the MIR can we guarantee
560 // that the `RevealAll` pass has happened and that the body's consts
561 // are normalized, so any call to resolve before that needs to be
562 // manually normalized.
563 let val = self.tcx.normalize_erasing_regions(self.param_env, *val);
565 mir::ConstantKind::Ty(ct) => {
567 ty::ConstKind::Param(_) | ty::ConstKind::Placeholder(..) => {
568 throw_inval!(TooGeneric)
570 ty::ConstKind::Error(reported) => {
571 throw_inval!(AlreadyReported(reported))
573 ty::ConstKind::Unevaluated(uv) => {
574 // NOTE: We evaluate to a `ValTree` here as a check to ensure
575 // we're working with valid constants, even though we never need it.
576 let instance = self.resolve(uv.def, uv.substs)?;
577 let cid = GlobalId { instance, promoted: None };
580 .eval_to_valtree(self.param_env.and(cid))?
581 .unwrap_or_else(|| bug!("unable to create ValTree for {uv:?}"));
583 Ok(self.eval_to_allocation(cid)?.into())
585 ty::ConstKind::Bound(..) | ty::ConstKind::Infer(..) => {
586 span_bug!(self.cur_span(), "unexpected ConstKind in ctfe: {ct:?}")
588 ty::ConstKind::Value(valtree) => {
590 let const_val = self.tcx.valtree_to_const_val((ty, valtree));
591 self.const_val_to_op(const_val, ty, layout)
595 mir::ConstantKind::Val(val, ty) => self.const_val_to_op(val, ty, layout),
596 mir::ConstantKind::Unevaluated(uv, _) => {
597 let instance = self.resolve(uv.def, uv.substs)?;
598 Ok(self.eval_to_allocation(GlobalId { instance, promoted: uv.promoted })?.into())
603 pub(crate) fn const_val_to_op(
605 val_val: ConstValue<'tcx>,
607 layout: Option<TyAndLayout<'tcx>>,
608 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
609 // Other cases need layout.
610 let adjust_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()))
625 ConstValue::Scalar(x) => Operand::Immediate(adjust_scalar(x)?.into()),
626 ConstValue::ZeroSized => Operand::Immediate(Immediate::Uninit),
627 ConstValue::Slice { data, start, end } => {
628 // We rely on mutability being set correctly in `data` to prevent writes
629 // where none should happen.
630 let ptr = Pointer::new(
631 self.tcx.create_memory_alloc(data),
632 Size::from_bytes(start), // offset: `start`
634 Operand::Immediate(Immediate::new_slice(
635 Scalar::from_pointer(self.global_base_pointer(ptr)?, &*self.tcx),
636 u64::try_from(end.checked_sub(start).unwrap()).unwrap(), // len: `end - start`
641 Ok(OpTy { op, layout, align: Some(layout.align.abi) })
644 /// Read discriminant, return the runtime value as well as the variant index.
645 /// Can also legally be called on non-enums (e.g. through the discriminant_value intrinsic)!
646 pub fn read_discriminant(
648 op: &OpTy<'tcx, M::Provenance>,
649 ) -> InterpResult<'tcx, (Scalar<M::Provenance>, VariantIdx)> {
650 trace!("read_discriminant_value {:#?}", op.layout);
651 // Get type and layout of the discriminant.
652 let discr_layout = self.layout_of(op.layout.ty.discriminant_ty(*self.tcx))?;
653 trace!("discriminant type: {:?}", discr_layout.ty);
655 // We use "discriminant" to refer to the value associated with a particular enum variant.
656 // This is not to be confused with its "variant index", which is just determining its position in the
657 // declared list of variants -- they can differ with explicitly assigned discriminants.
658 // We use "tag" to refer to how the discriminant is encoded in memory, which can be either
659 // straight-forward (`TagEncoding::Direct`) or with a niche (`TagEncoding::Niche`).
660 let (tag_scalar_layout, tag_encoding, tag_field) = match op.layout.variants {
661 Variants::Single { index } => {
662 let discr = match op.layout.ty.discriminant_for_variant(*self.tcx, index) {
664 // This type actually has discriminants.
665 assert_eq!(discr.ty, discr_layout.ty);
666 Scalar::from_uint(discr.val, discr_layout.size)
669 // On a type without actual discriminants, variant is 0.
670 assert_eq!(index.as_u32(), 0);
671 Scalar::from_uint(index.as_u32(), discr_layout.size)
674 return Ok((discr, index));
676 Variants::Multiple { tag, ref tag_encoding, tag_field, .. } => {
677 (tag, tag_encoding, tag_field)
681 // There are *three* layouts that come into play here:
682 // - The discriminant has a type for typechecking. This is `discr_layout`, and is used for
683 // the `Scalar` we return.
684 // - The tag (encoded discriminant) has layout `tag_layout`. This is always an integer type,
685 // and used to interpret the value we read from the tag field.
686 // For the return value, a cast to `discr_layout` is performed.
687 // - The field storing the tag has a layout, which is very similar to `tag_layout` but
688 // may be a pointer. This is `tag_val.layout`; we just use it for sanity checks.
690 // Get layout for tag.
691 let tag_layout = self.layout_of(tag_scalar_layout.primitive().to_int_ty(*self.tcx))?;
693 // Read tag and sanity-check `tag_layout`.
694 let tag_val = self.read_immediate(&self.operand_field(op, tag_field)?)?;
695 assert_eq!(tag_layout.size, tag_val.layout.size);
696 assert_eq!(tag_layout.abi.is_signed(), tag_val.layout.abi.is_signed());
697 trace!("tag value: {}", tag_val);
699 // Figure out which discriminant and variant this corresponds to.
700 Ok(match *tag_encoding {
701 TagEncoding::Direct => {
702 let scalar = tag_val.to_scalar();
703 // Generate a specific error if `tag_val` is not an integer.
704 // (`tag_bits` itself is only used for error messages below.)
705 let tag_bits = scalar
707 .map_err(|dbg_val| err_ub!(InvalidTag(dbg_val)))?
708 .assert_bits(tag_layout.size);
709 // Cast bits from tag layout to discriminant layout.
710 // After the checks we did above, this cannot fail, as
711 // discriminants are int-like.
713 self.cast_from_int_like(scalar, tag_val.layout, discr_layout.ty).unwrap();
714 let discr_bits = discr_val.assert_bits(discr_layout.size);
715 // Convert discriminant to variant index, and catch invalid discriminants.
716 let index = match *op.layout.ty.kind() {
718 adt.discriminants(*self.tcx).find(|(_, var)| var.val == discr_bits)
720 ty::Generator(def_id, substs, _) => {
721 let substs = substs.as_generator();
723 .discriminants(def_id, *self.tcx)
724 .find(|(_, var)| var.val == discr_bits)
726 _ => span_bug!(self.cur_span(), "tagged layout for non-adt non-generator"),
728 .ok_or_else(|| err_ub!(InvalidTag(Scalar::from_uint(tag_bits, tag_layout.size))))?;
729 // Return the cast value, and the index.
732 TagEncoding::Niche { untagged_variant, ref niche_variants, niche_start } => {
733 let tag_val = tag_val.to_scalar();
734 // Compute the variant this niche value/"tag" corresponds to. With niche layout,
735 // discriminant (encoded in niche/tag) and variant index are the same.
736 let variants_start = niche_variants.start().as_u32();
737 let variants_end = niche_variants.end().as_u32();
738 let variant = match tag_val.try_to_int() {
740 // So this is a pointer then, and casting to an int failed.
741 // Can only happen during CTFE.
742 // The niche must be just 0, and the ptr not null, then we know this is
743 // okay. Everything else, we conservatively reject.
744 let ptr_valid = niche_start == 0
745 && variants_start == variants_end
746 && !self.scalar_may_be_null(tag_val)?;
748 throw_ub!(InvalidTag(dbg_val))
753 let tag_bits = tag_bits.assert_bits(tag_layout.size);
754 // We need to use machine arithmetic to get the relative variant idx:
755 // variant_index_relative = tag_val - niche_start_val
756 let tag_val = ImmTy::from_uint(tag_bits, tag_layout);
757 let niche_start_val = ImmTy::from_uint(niche_start, tag_layout);
758 let variant_index_relative_val =
759 self.binary_op(mir::BinOp::Sub, &tag_val, &niche_start_val)?;
760 let variant_index_relative =
761 variant_index_relative_val.to_scalar().assert_bits(tag_val.layout.size);
762 // Check if this is in the range that indicates an actual discriminant.
763 if variant_index_relative <= u128::from(variants_end - variants_start) {
764 let variant_index_relative = u32::try_from(variant_index_relative)
765 .expect("we checked that this fits into a u32");
766 // Then computing the absolute variant idx should not overflow any more.
767 let variant_index = variants_start
768 .checked_add(variant_index_relative)
769 .expect("overflow computing absolute variant idx");
770 let variants_len = op
774 .expect("tagged layout for non adt")
777 assert!(usize::try_from(variant_index).unwrap() < variants_len);
778 VariantIdx::from_u32(variant_index)
784 // Compute the size of the scalar we need to return.
785 // No need to cast, because the variant index directly serves as discriminant and is
786 // encoded in the tag.
787 (Scalar::from_uint(variant.as_u32(), discr_layout.size), variant)
793 // Some nodes are used a lot. Make sure they don't unintentionally get bigger.
794 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
797 use rustc_data_structures::static_assert_size;
798 // tidy-alphabetical-start
799 static_assert_size!(Immediate, 48);
800 static_assert_size!(ImmTy<'_>, 64);
801 static_assert_size!(Operand, 56);
802 static_assert_size!(OpTy<'_>, 80);
803 // tidy-alphabetical-end