rustc_const_eval/interpret/
cast.rs

1use std::assert_matches::assert_matches;
2
3use rustc_abi::{FieldIdx, Integer};
4use rustc_apfloat::ieee::{Double, Half, Quad, Single};
5use rustc_apfloat::{Float, FloatConvert};
6use rustc_middle::mir::CastKind;
7use rustc_middle::mir::interpret::{InterpResult, PointerArithmetic, Scalar};
8use rustc_middle::ty::adjustment::PointerCoercion;
9use rustc_middle::ty::layout::{IntegerExt, TyAndLayout};
10use rustc_middle::ty::{self, FloatTy, Ty};
11use rustc_middle::{bug, span_bug};
12use tracing::trace;
13
14use super::util::ensure_monomorphic_enough;
15use super::{
16    FnVal, ImmTy, Immediate, InterpCx, Machine, OpTy, PlaceTy, err_inval, interp_ok, throw_ub,
17    throw_ub_custom,
18};
19use crate::fluent_generated as fluent;
20
21impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
22    pub fn cast(
23        &mut self,
24        src: &OpTy<'tcx, M::Provenance>,
25        cast_kind: CastKind,
26        cast_ty: Ty<'tcx>,
27        dest: &PlaceTy<'tcx, M::Provenance>,
28    ) -> InterpResult<'tcx> {
29        // `cast_ty` will often be the same as `dest.ty`, but not always, since subtyping is still
30        // possible.
31        let cast_layout =
32            if cast_ty == dest.layout.ty { dest.layout } else { self.layout_of(cast_ty)? };
33        // FIXME: In which cases should we trigger UB when the source is uninit?
34        match cast_kind {
35            CastKind::PointerCoercion(PointerCoercion::Unsize, _) => {
36                self.unsize_into(src, cast_layout, dest)?;
37            }
38
39            CastKind::PointerExposeProvenance => {
40                let src = self.read_immediate(src)?;
41                let res = self.pointer_expose_provenance_cast(&src, cast_layout)?;
42                self.write_immediate(*res, dest)?;
43            }
44
45            CastKind::PointerWithExposedProvenance => {
46                let src = self.read_immediate(src)?;
47                let res = self.pointer_with_exposed_provenance_cast(&src, cast_layout)?;
48                self.write_immediate(*res, dest)?;
49            }
50
51            CastKind::IntToInt | CastKind::IntToFloat => {
52                let src = self.read_immediate(src)?;
53                let res = self.int_to_int_or_float(&src, cast_layout)?;
54                self.write_immediate(*res, dest)?;
55            }
56
57            CastKind::FloatToFloat | CastKind::FloatToInt => {
58                let src = self.read_immediate(src)?;
59                let res = self.float_to_float_or_int(&src, cast_layout)?;
60                self.write_immediate(*res, dest)?;
61            }
62
63            CastKind::FnPtrToPtr | CastKind::PtrToPtr => {
64                let src = self.read_immediate(src)?;
65                let res = self.ptr_to_ptr(&src, cast_layout)?;
66                self.write_immediate(*res, dest)?;
67            }
68
69            CastKind::PointerCoercion(
70                PointerCoercion::MutToConstPointer | PointerCoercion::ArrayToPointer,
71                _,
72            ) => {
73                bug!("{cast_kind:?} casts are for borrowck only, not runtime MIR");
74            }
75
76            CastKind::PointerCoercion(PointerCoercion::ReifyFnPointer, _) => {
77                // All reifications must be monomorphic, bail out otherwise.
78                ensure_monomorphic_enough(*self.tcx, src.layout.ty)?;
79
80                // The src operand does not matter, just its type
81                match *src.layout.ty.kind() {
82                    ty::FnDef(def_id, args) => {
83                        let instance = ty::Instance::resolve_for_fn_ptr(
84                            *self.tcx,
85                            self.typing_env,
86                            def_id,
87                            args,
88                        )
89                        .ok_or_else(|| err_inval!(TooGeneric))?;
90
91                        let fn_ptr = self.fn_ptr(FnVal::Instance(instance));
92                        self.write_pointer(fn_ptr, dest)?;
93                    }
94                    _ => span_bug!(self.cur_span(), "reify fn pointer on {}", src.layout.ty),
95                }
96            }
97
98            CastKind::PointerCoercion(PointerCoercion::UnsafeFnPointer, _) => {
99                let src = self.read_immediate(src)?;
100                match cast_ty.kind() {
101                    ty::FnPtr(..) => {
102                        // No change to value
103                        self.write_immediate(*src, dest)?;
104                    }
105                    _ => span_bug!(self.cur_span(), "fn to unsafe fn cast on {}", cast_ty),
106                }
107            }
108
109            CastKind::PointerCoercion(PointerCoercion::ClosureFnPointer(_), _) => {
110                // All reifications must be monomorphic, bail out otherwise.
111                ensure_monomorphic_enough(*self.tcx, src.layout.ty)?;
112
113                // The src operand does not matter, just its type
114                match *src.layout.ty.kind() {
115                    ty::Closure(def_id, args) => {
116                        let instance = ty::Instance::resolve_closure(
117                            *self.tcx,
118                            def_id,
119                            args,
120                            ty::ClosureKind::FnOnce,
121                        );
122                        let fn_ptr = self.fn_ptr(FnVal::Instance(instance));
123                        self.write_pointer(fn_ptr, dest)?;
124                    }
125                    _ => span_bug!(self.cur_span(), "closure fn pointer on {}", src.layout.ty),
126                }
127            }
128
129            CastKind::Transmute => {
130                assert!(src.layout.is_sized());
131                assert!(dest.layout.is_sized());
132                assert_eq!(cast_ty, dest.layout.ty); // we otherwise ignore `cast_ty` enirely...
133                if src.layout.size != dest.layout.size {
134                    throw_ub_custom!(
135                        fluent::const_eval_invalid_transmute,
136                        src_bytes = src.layout.size.bytes(),
137                        dest_bytes = dest.layout.size.bytes(),
138                        src = src.layout.ty,
139                        dest = dest.layout.ty,
140                    );
141                }
142
143                self.copy_op_allow_transmute(src, dest)?;
144            }
145        }
146        interp_ok(())
147    }
148
149    /// Handles 'IntToInt' and 'IntToFloat' casts.
150    pub fn int_to_int_or_float(
151        &self,
152        src: &ImmTy<'tcx, M::Provenance>,
153        cast_to: TyAndLayout<'tcx>,
154    ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
155        assert!(src.layout.ty.is_integral() || src.layout.ty.is_char() || src.layout.ty.is_bool());
156        assert!(cast_to.ty.is_floating_point() || cast_to.ty.is_integral() || cast_to.ty.is_char());
157
158        interp_ok(ImmTy::from_scalar(
159            self.cast_from_int_like(src.to_scalar(), src.layout, cast_to.ty)?,
160            cast_to,
161        ))
162    }
163
164    /// Handles 'FloatToFloat' and 'FloatToInt' casts.
165    pub fn float_to_float_or_int(
166        &self,
167        src: &ImmTy<'tcx, M::Provenance>,
168        cast_to: TyAndLayout<'tcx>,
169    ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
170        let ty::Float(fty) = src.layout.ty.kind() else {
171            bug!("FloatToFloat/FloatToInt cast: source type {} is not a float type", src.layout.ty)
172        };
173        let val = match fty {
174            FloatTy::F16 => self.cast_from_float(src.to_scalar().to_f16()?, cast_to.ty),
175            FloatTy::F32 => self.cast_from_float(src.to_scalar().to_f32()?, cast_to.ty),
176            FloatTy::F64 => self.cast_from_float(src.to_scalar().to_f64()?, cast_to.ty),
177            FloatTy::F128 => self.cast_from_float(src.to_scalar().to_f128()?, cast_to.ty),
178        };
179        interp_ok(ImmTy::from_scalar(val, cast_to))
180    }
181
182    /// Handles 'FnPtrToPtr' and 'PtrToPtr' casts.
183    pub fn ptr_to_ptr(
184        &self,
185        src: &ImmTy<'tcx, M::Provenance>,
186        cast_to: TyAndLayout<'tcx>,
187    ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
188        assert!(src.layout.ty.is_any_ptr());
189        assert!(cast_to.ty.is_raw_ptr());
190        // Handle casting any ptr to raw ptr (might be a wide ptr).
191        if cast_to.size == src.layout.size {
192            // Thin or wide pointer that just has the ptr kind of target type changed.
193            return interp_ok(ImmTy::from_immediate(**src, cast_to));
194        } else {
195            // Casting the metadata away from a wide ptr.
196            assert_eq!(src.layout.size, 2 * self.pointer_size());
197            assert_eq!(cast_to.size, self.pointer_size());
198            assert!(src.layout.ty.is_raw_ptr());
199            return match **src {
200                Immediate::ScalarPair(data, _) => interp_ok(ImmTy::from_scalar(data, cast_to)),
201                Immediate::Scalar(..) => span_bug!(
202                    self.cur_span(),
203                    "{:?} input to a fat-to-thin cast ({} -> {})",
204                    *src,
205                    src.layout.ty,
206                    cast_to.ty
207                ),
208                Immediate::Uninit => throw_ub!(InvalidUninitBytes(None)),
209            };
210        }
211    }
212
213    pub fn pointer_expose_provenance_cast(
214        &mut self,
215        src: &ImmTy<'tcx, M::Provenance>,
216        cast_to: TyAndLayout<'tcx>,
217    ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
218        assert_matches!(src.layout.ty.kind(), ty::RawPtr(_, _) | ty::FnPtr(..));
219        assert!(cast_to.ty.is_integral());
220
221        let scalar = src.to_scalar();
222        let ptr = scalar.to_pointer(self)?;
223        match ptr.into_pointer_or_addr() {
224            Ok(ptr) => M::expose_provenance(self, ptr.provenance)?,
225            Err(_) => {} // Do nothing, exposing an invalid pointer (`None` provenance) is a NOP.
226        };
227        interp_ok(ImmTy::from_scalar(
228            self.cast_from_int_like(scalar, src.layout, cast_to.ty)?,
229            cast_to,
230        ))
231    }
232
233    pub fn pointer_with_exposed_provenance_cast(
234        &self,
235        src: &ImmTy<'tcx, M::Provenance>,
236        cast_to: TyAndLayout<'tcx>,
237    ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
238        assert!(src.layout.ty.is_integral());
239        assert_matches!(cast_to.ty.kind(), ty::RawPtr(_, _));
240
241        // First cast to usize.
242        let scalar = src.to_scalar();
243        let addr = self.cast_from_int_like(scalar, src.layout, self.tcx.types.usize)?;
244        let addr = addr.to_target_usize(self)?;
245
246        // Then turn address into pointer.
247        let ptr = M::ptr_from_addr_cast(self, addr)?;
248        interp_ok(ImmTy::from_scalar(Scalar::from_maybe_pointer(ptr, self), cast_to))
249    }
250
251    /// Low-level cast helper function. This works directly on scalars and can take 'int-like' input
252    /// type (basically everything with a scalar layout) to int/float/char types.
253    fn cast_from_int_like(
254        &self,
255        scalar: Scalar<M::Provenance>, // input value (there is no ScalarTy so we separate data+layout)
256        src_layout: TyAndLayout<'tcx>,
257        cast_ty: Ty<'tcx>,
258    ) -> InterpResult<'tcx, Scalar<M::Provenance>> {
259        // Let's make sure v is sign-extended *if* it has a signed type.
260        let signed = src_layout.backend_repr.is_signed(); // Also asserts that abi is `Scalar`.
261
262        let v = match src_layout.ty.kind() {
263            ty::Uint(_) | ty::RawPtr(..) | ty::FnPtr(..) => scalar.to_uint(src_layout.size)?,
264            ty::Int(_) => scalar.to_int(src_layout.size)? as u128, // we will cast back to `i128` below if the sign matters
265            ty::Bool => scalar.to_bool()?.into(),
266            ty::Char => scalar.to_char()?.into(),
267            _ => span_bug!(self.cur_span(), "invalid int-like cast from {}", src_layout.ty),
268        };
269
270        interp_ok(match *cast_ty.kind() {
271            // int -> int
272            ty::Int(_) | ty::Uint(_) => {
273                let size = match *cast_ty.kind() {
274                    ty::Int(t) => Integer::from_int_ty(self, t).size(),
275                    ty::Uint(t) => Integer::from_uint_ty(self, t).size(),
276                    _ => bug!(),
277                };
278                let v = size.truncate(v);
279                Scalar::from_uint(v, size)
280            }
281
282            // signed int -> float
283            ty::Float(fty) if signed => {
284                let v = v as i128;
285                match fty {
286                    FloatTy::F16 => Scalar::from_f16(Half::from_i128(v).value),
287                    FloatTy::F32 => Scalar::from_f32(Single::from_i128(v).value),
288                    FloatTy::F64 => Scalar::from_f64(Double::from_i128(v).value),
289                    FloatTy::F128 => Scalar::from_f128(Quad::from_i128(v).value),
290                }
291            }
292            // unsigned int -> float
293            ty::Float(fty) => match fty {
294                FloatTy::F16 => Scalar::from_f16(Half::from_u128(v).value),
295                FloatTy::F32 => Scalar::from_f32(Single::from_u128(v).value),
296                FloatTy::F64 => Scalar::from_f64(Double::from_u128(v).value),
297                FloatTy::F128 => Scalar::from_f128(Quad::from_u128(v).value),
298            },
299
300            // u8 -> char
301            ty::Char => Scalar::from_u32(u8::try_from(v).unwrap().into()),
302
303            // Casts to bool are not permitted by rustc, no need to handle them here.
304            _ => span_bug!(self.cur_span(), "invalid int to {} cast", cast_ty),
305        })
306    }
307
308    /// Low-level cast helper function. Converts an apfloat `f` into int or float types.
309    fn cast_from_float<F>(&self, f: F, dest_ty: Ty<'tcx>) -> Scalar<M::Provenance>
310    where
311        F: Float
312            + Into<Scalar<M::Provenance>>
313            + FloatConvert<Half>
314            + FloatConvert<Single>
315            + FloatConvert<Double>
316            + FloatConvert<Quad>,
317    {
318        match *dest_ty.kind() {
319            // float -> uint
320            ty::Uint(t) => {
321                let size = Integer::from_uint_ty(self, t).size();
322                // `to_u128` is a saturating cast, which is what we need
323                // (https://doc.rust-lang.org/nightly/nightly-rustc/rustc_apfloat/trait.Float.html#method.to_i128_r).
324                let v = f.to_u128(size.bits_usize()).value;
325                // This should already fit the bit width
326                Scalar::from_uint(v, size)
327            }
328            // float -> int
329            ty::Int(t) => {
330                let size = Integer::from_int_ty(self, t).size();
331                // `to_i128` is a saturating cast, which is what we need
332                // (https://doc.rust-lang.org/nightly/nightly-rustc/rustc_apfloat/trait.Float.html#method.to_i128_r).
333                let v = f.to_i128(size.bits_usize()).value;
334                Scalar::from_int(v, size)
335            }
336            // float -> float
337            ty::Float(fty) => match fty {
338                FloatTy::F16 => {
339                    Scalar::from_f16(self.adjust_nan(f.convert(&mut false).value, &[f]))
340                }
341                FloatTy::F32 => {
342                    Scalar::from_f32(self.adjust_nan(f.convert(&mut false).value, &[f]))
343                }
344                FloatTy::F64 => {
345                    Scalar::from_f64(self.adjust_nan(f.convert(&mut false).value, &[f]))
346                }
347                FloatTy::F128 => {
348                    Scalar::from_f128(self.adjust_nan(f.convert(&mut false).value, &[f]))
349                }
350            },
351            // That's it.
352            _ => span_bug!(self.cur_span(), "invalid float to {} cast", dest_ty),
353        }
354    }
355
356    /// `src` is a *pointer to* a `source_ty`, and in `dest` we should store a pointer to th same
357    /// data at type `cast_ty`.
358    fn unsize_into_ptr(
359        &mut self,
360        src: &OpTy<'tcx, M::Provenance>,
361        dest: &PlaceTy<'tcx, M::Provenance>,
362        // The pointee types
363        source_ty: Ty<'tcx>,
364        cast_ty: Ty<'tcx>,
365    ) -> InterpResult<'tcx> {
366        // A<Struct> -> A<Trait> conversion
367        let (src_pointee_ty, dest_pointee_ty) =
368            self.tcx.struct_lockstep_tails_for_codegen(source_ty, cast_ty, self.typing_env);
369
370        match (src_pointee_ty.kind(), dest_pointee_ty.kind()) {
371            (&ty::Array(_, length), &ty::Slice(_)) => {
372                let ptr = self.read_pointer(src)?;
373                let val = Immediate::new_slice(
374                    ptr,
375                    length
376                        .try_to_target_usize(*self.tcx)
377                        .expect("expected monomorphic const in const eval"),
378                    self,
379                );
380                self.write_immediate(val, dest)
381            }
382            (ty::Dynamic(data_a, _, ty::Dyn), ty::Dynamic(data_b, _, ty::Dyn)) => {
383                let val = self.read_immediate(src)?;
384                // MIR building generates odd NOP casts, prevent them from causing unexpected trouble.
385                // See <https://github.com/rust-lang/rust/issues/128880>.
386                // FIXME: ideally we wouldn't have to do this.
387                if data_a == data_b {
388                    return self.write_immediate(*val, dest);
389                }
390                // Take apart the old pointer, and find the dynamic type.
391                let (old_data, old_vptr) = val.to_scalar_pair();
392                let old_data = old_data.to_pointer(self)?;
393                let old_vptr = old_vptr.to_pointer(self)?;
394                let ty = self.get_ptr_vtable_ty(old_vptr, Some(data_a))?;
395
396                // Sanity-check that `supertrait_vtable_slot` in this type's vtable indeed produces
397                // our destination trait.
398                let vptr_entry_idx =
399                    self.tcx.supertrait_vtable_slot((src_pointee_ty, dest_pointee_ty));
400                let vtable_entries = self.vtable_entries(data_a.principal(), ty);
401                if let Some(entry_idx) = vptr_entry_idx {
402                    let Some(&ty::VtblEntry::TraitVPtr(upcast_trait_ref)) =
403                        vtable_entries.get(entry_idx)
404                    else {
405                        span_bug!(
406                            self.cur_span(),
407                            "invalid vtable entry index in {} -> {} upcast",
408                            src_pointee_ty,
409                            dest_pointee_ty
410                        );
411                    };
412                    let erased_trait_ref =
413                        ty::ExistentialTraitRef::erase_self_ty(*self.tcx, upcast_trait_ref);
414                    assert_eq!(
415                        data_b.principal().map(|b| {
416                            self.tcx.normalize_erasing_late_bound_regions(self.typing_env, b)
417                        }),
418                        Some(erased_trait_ref),
419                    );
420                } else {
421                    // In this case codegen would keep using the old vtable. We don't want to do
422                    // that as it has the wrong trait. The reason codegen can do this is that
423                    // one vtable is a prefix of the other, so we double-check that.
424                    let vtable_entries_b = self.vtable_entries(data_b.principal(), ty);
425                    assert!(&vtable_entries[..vtable_entries_b.len()] == vtable_entries_b);
426                };
427
428                // Get the destination trait vtable and return that.
429                let new_vptr = self.get_vtable_ptr(ty, data_b)?;
430                self.write_immediate(Immediate::new_dyn_trait(old_data, new_vptr, self), dest)
431            }
432            (_, &ty::Dynamic(data, _, ty::Dyn)) => {
433                // Initial cast from sized to dyn trait
434                let vtable = self.get_vtable_ptr(src_pointee_ty, data)?;
435                let ptr = self.read_pointer(src)?;
436                let val = Immediate::new_dyn_trait(ptr, vtable, &*self.tcx);
437                self.write_immediate(val, dest)
438            }
439            _ => {
440                // Do not ICE if we are not monomorphic enough.
441                ensure_monomorphic_enough(*self.tcx, src.layout.ty)?;
442                ensure_monomorphic_enough(*self.tcx, cast_ty)?;
443
444                span_bug!(
445                    self.cur_span(),
446                    "invalid pointer unsizing {} -> {}",
447                    src.layout.ty,
448                    cast_ty
449                )
450            }
451        }
452    }
453
454    pub fn unsize_into(
455        &mut self,
456        src: &OpTy<'tcx, M::Provenance>,
457        cast_ty: TyAndLayout<'tcx>,
458        dest: &PlaceTy<'tcx, M::Provenance>,
459    ) -> InterpResult<'tcx> {
460        trace!("Unsizing {:?} of type {} into {}", *src, src.layout.ty, cast_ty.ty);
461        match (src.layout.ty.kind(), cast_ty.ty.kind()) {
462            (&ty::Ref(_, s, _), &ty::Ref(_, c, _) | &ty::RawPtr(c, _))
463            | (&ty::RawPtr(s, _), &ty::RawPtr(c, _)) => self.unsize_into_ptr(src, dest, s, c),
464            (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => {
465                assert_eq!(def_a, def_b); // implies same number of fields
466
467                // Unsizing of generic struct with pointer fields, like `Arc<T>` -> `Arc<Trait>`.
468                // There can be extra fields as long as they don't change their type or are 1-ZST.
469                // There might also be no field that actually needs unsizing.
470                let mut found_cast_field = false;
471                for i in 0..src.layout.fields.count() {
472                    let cast_ty_field = cast_ty.field(self, i);
473                    let i = FieldIdx::from_usize(i);
474                    let src_field = self.project_field(src, i)?;
475                    let dst_field = self.project_field(dest, i)?;
476                    if src_field.layout.is_1zst() && cast_ty_field.is_1zst() {
477                        // Skip 1-ZST fields.
478                    } else if src_field.layout.ty == cast_ty_field.ty {
479                        self.copy_op(&src_field, &dst_field)?;
480                    } else {
481                        if found_cast_field {
482                            span_bug!(self.cur_span(), "unsize_into: more than one field to cast");
483                        }
484                        found_cast_field = true;
485                        self.unsize_into(&src_field, cast_ty_field, &dst_field)?;
486                    }
487                }
488                interp_ok(())
489            }
490            _ => {
491                // Do not ICE if we are not monomorphic enough.
492                ensure_monomorphic_enough(*self.tcx, src.layout.ty)?;
493                ensure_monomorphic_enough(*self.tcx, cast_ty.ty)?;
494
495                span_bug!(
496                    self.cur_span(),
497                    "unsize_into: invalid conversion: {:?} -> {:?}",
498                    src.layout,
499                    dest.layout
500                )
501            }
502        }
503    }
504}
rustc_const_eval/interpret/cast.rs

rustc_const_eval/interpret/
cast.rs
