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;
20use crate::interpret::Writeable;
21
22impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
23    pub fn cast(
24        &mut self,
25        src: &OpTy<'tcx, M::Provenance>,
26        cast_kind: CastKind,
27        cast_ty: Ty<'tcx>,
28        dest: &PlaceTy<'tcx, M::Provenance>,
29    ) -> InterpResult<'tcx> {
30        // `cast_ty` will often be the same as `dest.ty`, but not always, since subtyping is still
31        // possible.
32        let cast_layout =
33            if cast_ty == dest.layout.ty { dest.layout } else { self.layout_of(cast_ty)? };
34        // FIXME: In which cases should we trigger UB when the source is uninit?
35        match cast_kind {
36            CastKind::PointerCoercion(PointerCoercion::Unsize, _) => {
37                self.unsize_into(src, cast_layout, dest)?;
38            }
39
40            CastKind::PointerExposeProvenance => {
41                let src = self.read_immediate(src)?;
42                let res = self.pointer_expose_provenance_cast(&src, cast_layout)?;
43                self.write_immediate(*res, dest)?;
44            }
45
46            CastKind::PointerWithExposedProvenance => {
47                let src = self.read_immediate(src)?;
48                let res = self.pointer_with_exposed_provenance_cast(&src, cast_layout)?;
49                self.write_immediate(*res, dest)?;
50            }
51
52            CastKind::IntToInt | CastKind::IntToFloat => {
53                let src = self.read_immediate(src)?;
54                let res = self.int_to_int_or_float(&src, cast_layout)?;
55                self.write_immediate(*res, dest)?;
56            }
57
58            CastKind::FloatToFloat | CastKind::FloatToInt => {
59                let src = self.read_immediate(src)?;
60                let res = self.float_to_float_or_int(&src, cast_layout)?;
61                self.write_immediate(*res, dest)?;
62            }
63
64            CastKind::FnPtrToPtr | CastKind::PtrToPtr => {
65                let src = self.read_immediate(src)?;
66                let res = self.ptr_to_ptr(&src, cast_layout)?;
67                self.write_immediate(*res, dest)?;
68            }
69
70            CastKind::PointerCoercion(
71                PointerCoercion::MutToConstPointer | PointerCoercion::ArrayToPointer,
72                _,
73            ) => {
74                bug!("{cast_kind:?} casts are for borrowck only, not runtime MIR");
75            }
76
77            CastKind::PointerCoercion(PointerCoercion::ReifyFnPointer, _) => {
78                // All reifications must be monomorphic, bail out otherwise.
79                ensure_monomorphic_enough(*self.tcx, src.layout.ty)?;
80
81                // The src operand does not matter, just its type
82                match *src.layout.ty.kind() {
83                    ty::FnDef(def_id, args) => {
84                        let instance = ty::Instance::resolve_for_fn_ptr(
85                            *self.tcx,
86                            self.typing_env,
87                            def_id,
88                            args,
89                        )
90                        .ok_or_else(|| err_inval!(TooGeneric))?;
91
92                        let fn_ptr = self.fn_ptr(FnVal::Instance(instance));
93                        self.write_pointer(fn_ptr, dest)?;
94                    }
95                    _ => span_bug!(self.cur_span(), "reify fn pointer on {}", src.layout.ty),
96                }
97            }
98
99            CastKind::PointerCoercion(PointerCoercion::UnsafeFnPointer, _) => {
100                let src = self.read_immediate(src)?;
101                match cast_ty.kind() {
102                    ty::FnPtr(..) => {
103                        // No change to value
104                        self.write_immediate(*src, dest)?;
105                    }
106                    _ => span_bug!(self.cur_span(), "fn to unsafe fn cast on {}", cast_ty),
107                }
108            }
109
110            CastKind::PointerCoercion(PointerCoercion::ClosureFnPointer(_), _) => {
111                // All reifications must be monomorphic, bail out otherwise.
112                ensure_monomorphic_enough(*self.tcx, src.layout.ty)?;
113
114                // The src operand does not matter, just its type
115                match *src.layout.ty.kind() {
116                    ty::Closure(def_id, args) => {
117                        let instance = ty::Instance::resolve_closure(
118                            *self.tcx,
119                            def_id,
120                            args,
121                            ty::ClosureKind::FnOnce,
122                        );
123                        let fn_ptr = self.fn_ptr(FnVal::Instance(instance));
124                        self.write_pointer(fn_ptr, dest)?;
125                    }
126                    _ => span_bug!(self.cur_span(), "closure fn pointer on {}", src.layout.ty),
127                }
128            }
129
130            CastKind::Transmute => {
131                assert!(src.layout.is_sized());
132                assert!(dest.layout.is_sized());
133                assert_eq!(cast_ty, dest.layout.ty); // we otherwise ignore `cast_ty` enirely...
134                if src.layout.size != dest.layout.size {
135                    throw_ub_custom!(
136                        fluent::const_eval_invalid_transmute,
137                        src_bytes = src.layout.size.bytes(),
138                        dest_bytes = dest.layout.size.bytes(),
139                        src = src.layout.ty,
140                        dest = dest.layout.ty,
141                    );
142                }
143
144                self.copy_op_allow_transmute(src, dest)?;
145            }
146        }
147        interp_ok(())
148    }
149
150    /// Handles 'IntToInt' and 'IntToFloat' casts.
151    pub fn int_to_int_or_float(
152        &self,
153        src: &ImmTy<'tcx, M::Provenance>,
154        cast_to: TyAndLayout<'tcx>,
155    ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
156        assert!(src.layout.ty.is_integral() || src.layout.ty.is_char() || src.layout.ty.is_bool());
157        assert!(cast_to.ty.is_floating_point() || cast_to.ty.is_integral() || cast_to.ty.is_char());
158
159        interp_ok(ImmTy::from_scalar(
160            self.cast_from_int_like(src.to_scalar(), src.layout, cast_to.ty)?,
161            cast_to,
162        ))
163    }
164
165    /// Handles 'FloatToFloat' and 'FloatToInt' casts.
166    pub fn float_to_float_or_int(
167        &self,
168        src: &ImmTy<'tcx, M::Provenance>,
169        cast_to: TyAndLayout<'tcx>,
170    ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
171        let ty::Float(fty) = src.layout.ty.kind() else {
172            bug!("FloatToFloat/FloatToInt cast: source type {} is not a float type", src.layout.ty)
173        };
174        let val = match fty {
175            FloatTy::F16 => self.cast_from_float(src.to_scalar().to_f16()?, cast_to.ty),
176            FloatTy::F32 => self.cast_from_float(src.to_scalar().to_f32()?, cast_to.ty),
177            FloatTy::F64 => self.cast_from_float(src.to_scalar().to_f64()?, cast_to.ty),
178            FloatTy::F128 => self.cast_from_float(src.to_scalar().to_f128()?, cast_to.ty),
179        };
180        interp_ok(ImmTy::from_scalar(val, cast_to))
181    }
182
183    /// Handles 'FnPtrToPtr' and 'PtrToPtr' casts.
184    pub fn ptr_to_ptr(
185        &self,
186        src: &ImmTy<'tcx, M::Provenance>,
187        cast_to: TyAndLayout<'tcx>,
188    ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
189        assert!(src.layout.ty.is_any_ptr());
190        assert!(cast_to.ty.is_raw_ptr());
191        // Handle casting any ptr to raw ptr (might be a wide ptr).
192        if cast_to.size == src.layout.size {
193            // Thin or wide pointer that just has the ptr kind of target type changed.
194            return interp_ok(ImmTy::from_immediate(**src, cast_to));
195        } else {
196            // Casting the metadata away from a wide ptr.
197            assert_eq!(src.layout.size, 2 * self.pointer_size());
198            assert_eq!(cast_to.size, self.pointer_size());
199            assert!(src.layout.ty.is_raw_ptr());
200            return match **src {
201                Immediate::ScalarPair(data, _) => interp_ok(ImmTy::from_scalar(data, cast_to)),
202                Immediate::Scalar(..) => span_bug!(
203                    self.cur_span(),
204                    "{:?} input to a fat-to-thin cast ({} -> {})",
205                    *src,
206                    src.layout.ty,
207                    cast_to.ty
208                ),
209                Immediate::Uninit => throw_ub!(InvalidUninitBytes(None)),
210            };
211        }
212    }
213
214    pub fn pointer_expose_provenance_cast(
215        &mut self,
216        src: &ImmTy<'tcx, M::Provenance>,
217        cast_to: TyAndLayout<'tcx>,
218    ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
219        assert_matches!(src.layout.ty.kind(), ty::RawPtr(_, _) | ty::FnPtr(..));
220        assert!(cast_to.ty.is_integral());
221
222        let scalar = src.to_scalar();
223        let ptr = scalar.to_pointer(self)?;
224        match ptr.into_pointer_or_addr() {
225            Ok(ptr) => M::expose_provenance(self, ptr.provenance)?,
226            Err(_) => {} // Do nothing, exposing an invalid pointer (`None` provenance) is a NOP.
227        };
228        interp_ok(ImmTy::from_scalar(
229            self.cast_from_int_like(scalar, src.layout, cast_to.ty)?,
230            cast_to,
231        ))
232    }
233
234    pub fn pointer_with_exposed_provenance_cast(
235        &self,
236        src: &ImmTy<'tcx, M::Provenance>,
237        cast_to: TyAndLayout<'tcx>,
238    ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
239        assert!(src.layout.ty.is_integral());
240        assert_matches!(cast_to.ty.kind(), ty::RawPtr(_, _));
241
242        // First cast to usize.
243        let scalar = src.to_scalar();
244        let addr = self.cast_from_int_like(scalar, src.layout, self.tcx.types.usize)?;
245        let addr = addr.to_target_usize(self)?;
246
247        // Then turn address into pointer.
248        let ptr = M::ptr_from_addr_cast(self, addr)?;
249        interp_ok(ImmTy::from_scalar(Scalar::from_maybe_pointer(ptr, self), cast_to))
250    }
251
252    /// Low-level cast helper function. This works directly on scalars and can take 'int-like' input
253    /// type (basically everything with a scalar layout) to int/float/char types.
254    fn cast_from_int_like(
255        &self,
256        scalar: Scalar<M::Provenance>, // input value (there is no ScalarTy so we separate data+layout)
257        src_layout: TyAndLayout<'tcx>,
258        cast_ty: Ty<'tcx>,
259    ) -> InterpResult<'tcx, Scalar<M::Provenance>> {
260        // Let's make sure v is sign-extended *if* it has a signed type.
261        let signed = src_layout.backend_repr.is_signed(); // Also asserts that abi is `Scalar`.
262
263        let v = match src_layout.ty.kind() {
264            ty::Uint(_) | ty::RawPtr(..) | ty::FnPtr(..) => scalar.to_uint(src_layout.size)?,
265            ty::Int(_) => scalar.to_int(src_layout.size)? as u128, // we will cast back to `i128` below if the sign matters
266            ty::Bool => scalar.to_bool()?.into(),
267            ty::Char => scalar.to_char()?.into(),
268            _ => span_bug!(self.cur_span(), "invalid int-like cast from {}", src_layout.ty),
269        };
270
271        interp_ok(match *cast_ty.kind() {
272            // int -> int
273            ty::Int(_) | ty::Uint(_) => {
274                let size = match *cast_ty.kind() {
275                    ty::Int(t) => Integer::from_int_ty(self, t).size(),
276                    ty::Uint(t) => Integer::from_uint_ty(self, t).size(),
277                    _ => bug!(),
278                };
279                let v = size.truncate(v);
280                Scalar::from_uint(v, size)
281            }
282
283            // signed int -> float
284            ty::Float(fty) if signed => {
285                let v = v as i128;
286                match fty {
287                    FloatTy::F16 => Scalar::from_f16(Half::from_i128(v).value),
288                    FloatTy::F32 => Scalar::from_f32(Single::from_i128(v).value),
289                    FloatTy::F64 => Scalar::from_f64(Double::from_i128(v).value),
290                    FloatTy::F128 => Scalar::from_f128(Quad::from_i128(v).value),
291                }
292            }
293            // unsigned int -> float
294            ty::Float(fty) => match fty {
295                FloatTy::F16 => Scalar::from_f16(Half::from_u128(v).value),
296                FloatTy::F32 => Scalar::from_f32(Single::from_u128(v).value),
297                FloatTy::F64 => Scalar::from_f64(Double::from_u128(v).value),
298                FloatTy::F128 => Scalar::from_f128(Quad::from_u128(v).value),
299            },
300
301            // u8 -> char
302            ty::Char => Scalar::from_u32(u8::try_from(v).unwrap().into()),
303
304            // Casts to bool are not permitted by rustc, no need to handle them here.
305            _ => span_bug!(self.cur_span(), "invalid int to {} cast", cast_ty),
306        })
307    }
308
309    /// Low-level cast helper function. Converts an apfloat `f` into int or float types.
310    fn cast_from_float<F>(&self, f: F, dest_ty: Ty<'tcx>) -> Scalar<M::Provenance>
311    where
312        F: Float
313            + Into<Scalar<M::Provenance>>
314            + FloatConvert<Half>
315            + FloatConvert<Single>
316            + FloatConvert<Double>
317            + FloatConvert<Quad>,
318    {
319        match *dest_ty.kind() {
320            // float -> uint
321            ty::Uint(t) => {
322                let size = Integer::from_uint_ty(self, t).size();
323                // `to_u128` is a saturating cast, which is what we need
324                // (https://doc.rust-lang.org/nightly/nightly-rustc/rustc_apfloat/trait.Float.html#method.to_i128_r).
325                let v = f.to_u128(size.bits_usize()).value;
326                // This should already fit the bit width
327                Scalar::from_uint(v, size)
328            }
329            // float -> int
330            ty::Int(t) => {
331                let size = Integer::from_int_ty(self, t).size();
332                // `to_i128` is a saturating cast, which is what we need
333                // (https://doc.rust-lang.org/nightly/nightly-rustc/rustc_apfloat/trait.Float.html#method.to_i128_r).
334                let v = f.to_i128(size.bits_usize()).value;
335                Scalar::from_int(v, size)
336            }
337            // float -> float
338            ty::Float(fty) => match fty {
339                FloatTy::F16 => {
340                    Scalar::from_f16(self.adjust_nan(f.convert(&mut false).value, &[f]))
341                }
342                FloatTy::F32 => {
343                    Scalar::from_f32(self.adjust_nan(f.convert(&mut false).value, &[f]))
344                }
345                FloatTy::F64 => {
346                    Scalar::from_f64(self.adjust_nan(f.convert(&mut false).value, &[f]))
347                }
348                FloatTy::F128 => {
349                    Scalar::from_f128(self.adjust_nan(f.convert(&mut false).value, &[f]))
350                }
351            },
352            // That's it.
353            _ => span_bug!(self.cur_span(), "invalid float to {} cast", dest_ty),
354        }
355    }
356
357    /// `src` is a *pointer to* a `source_ty`, and in `dest` we should store a pointer to th same
358    /// data at type `cast_ty`.
359    fn unsize_into_ptr(
360        &mut self,
361        src: &OpTy<'tcx, M::Provenance>,
362        dest: &impl Writeable<'tcx, M::Provenance>,
363        // The pointee types
364        source_ty: Ty<'tcx>,
365        cast_ty: Ty<'tcx>,
366    ) -> InterpResult<'tcx> {
367        // A<Struct> -> A<Trait> conversion
368        let (src_pointee_ty, dest_pointee_ty) =
369            self.tcx.struct_lockstep_tails_for_codegen(source_ty, cast_ty, self.typing_env);
370
371        match (src_pointee_ty.kind(), dest_pointee_ty.kind()) {
372            (&ty::Array(_, length), &ty::Slice(_)) => {
373                let ptr = self.read_pointer(src)?;
374                let val = Immediate::new_slice(
375                    ptr,
376                    length
377                        .try_to_target_usize(*self.tcx)
378                        .expect("expected monomorphic const in const eval"),
379                    self,
380                );
381                self.write_immediate(val, dest)
382            }
383            (ty::Dynamic(data_a, _, ty::Dyn), ty::Dynamic(data_b, _, ty::Dyn)) => {
384                let val = self.read_immediate(src)?;
385                // MIR building generates odd NOP casts, prevent them from causing unexpected trouble.
386                // See <https://github.com/rust-lang/rust/issues/128880>.
387                // FIXME: ideally we wouldn't have to do this.
388                if data_a == data_b {
389                    return self.write_immediate(*val, dest);
390                }
391                // Take apart the old pointer, and find the dynamic type.
392                let (old_data, old_vptr) = val.to_scalar_pair();
393                let old_data = old_data.to_pointer(self)?;
394                let old_vptr = old_vptr.to_pointer(self)?;
395                let ty = self.get_ptr_vtable_ty(old_vptr, Some(data_a))?;
396
397                // Sanity-check that `supertrait_vtable_slot` in this type's vtable indeed produces
398                // our destination trait.
399                let vptr_entry_idx =
400                    self.tcx.supertrait_vtable_slot((src_pointee_ty, dest_pointee_ty));
401                let vtable_entries = self.vtable_entries(data_a.principal(), ty);
402                if let Some(entry_idx) = vptr_entry_idx {
403                    let Some(&ty::VtblEntry::TraitVPtr(upcast_trait_ref)) =
404                        vtable_entries.get(entry_idx)
405                    else {
406                        span_bug!(
407                            self.cur_span(),
408                            "invalid vtable entry index in {} -> {} upcast",
409                            src_pointee_ty,
410                            dest_pointee_ty
411                        );
412                    };
413                    let erased_trait_ref =
414                        ty::ExistentialTraitRef::erase_self_ty(*self.tcx, upcast_trait_ref);
415                    assert_eq!(
416                        data_b.principal().map(|b| {
417                            self.tcx.normalize_erasing_late_bound_regions(self.typing_env, b)
418                        }),
419                        Some(erased_trait_ref),
420                    );
421                } else {
422                    // In this case codegen would keep using the old vtable. We don't want to do
423                    // that as it has the wrong trait. The reason codegen can do this is that
424                    // one vtable is a prefix of the other, so we double-check that.
425                    let vtable_entries_b = self.vtable_entries(data_b.principal(), ty);
426                    assert!(&vtable_entries[..vtable_entries_b.len()] == vtable_entries_b);
427                };
428
429                // Get the destination trait vtable and return that.
430                let new_vptr = self.get_vtable_ptr(ty, data_b)?;
431                self.write_immediate(Immediate::new_dyn_trait(old_data, new_vptr, self), dest)
432            }
433            (_, &ty::Dynamic(data, _, ty::Dyn)) => {
434                // Initial cast from sized to dyn trait
435                let vtable = self.get_vtable_ptr(src_pointee_ty, data)?;
436                let ptr = self.read_pointer(src)?;
437                let val = Immediate::new_dyn_trait(ptr, vtable, &*self.tcx);
438                self.write_immediate(val, dest)
439            }
440            _ => {
441                // Do not ICE if we are not monomorphic enough.
442                ensure_monomorphic_enough(*self.tcx, src.layout.ty)?;
443                ensure_monomorphic_enough(*self.tcx, cast_ty)?;
444
445                span_bug!(
446                    self.cur_span(),
447                    "invalid pointer unsizing {} -> {}",
448                    src.layout.ty,
449                    cast_ty
450                )
451            }
452        }
453    }
454
455    pub fn unsize_into(
456        &mut self,
457        src: &OpTy<'tcx, M::Provenance>,
458        cast_ty: TyAndLayout<'tcx>,
459        dest: &impl Writeable<'tcx, M::Provenance>,
460    ) -> InterpResult<'tcx> {
461        trace!("Unsizing {:?} of type {} into {}", *src, src.layout.ty, cast_ty.ty);
462        match (src.layout.ty.kind(), cast_ty.ty.kind()) {
463            (&ty::Ref(_, s, _), &ty::Ref(_, c, _) | &ty::RawPtr(c, _))
464            | (&ty::RawPtr(s, _), &ty::RawPtr(c, _)) => self.unsize_into_ptr(src, dest, s, c),
465            (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => {
466                assert_eq!(def_a, def_b); // implies same number of fields
467
468                // Unsizing of generic struct with pointer fields, like `Arc<T>` -> `Arc<Trait>`.
469                // There can be extra fields as long as they don't change their type or are 1-ZST.
470                // There might also be no field that actually needs unsizing.
471                let mut found_cast_field = false;
472                for i in 0..src.layout.fields.count() {
473                    let cast_ty_field = cast_ty.field(self, i);
474                    let i = FieldIdx::from_usize(i);
475                    let src_field = self.project_field(src, i)?;
476                    let dst_field = self.project_field(dest, i)?;
477                    if src_field.layout.is_1zst() && cast_ty_field.is_1zst() {
478                        // Skip 1-ZST fields.
479                    } else if src_field.layout.ty == cast_ty_field.ty {
480                        self.copy_op(&src_field, &dst_field)?;
481                    } else {
482                        if found_cast_field {
483                            span_bug!(self.cur_span(), "unsize_into: more than one field to cast");
484                        }
485                        found_cast_field = true;
486                        self.unsize_into(&src_field, cast_ty_field, &dst_field)?;
487                    }
488                }
489                interp_ok(())
490            }
491            _ => {
492                // Do not ICE if we are not monomorphic enough.
493                ensure_monomorphic_enough(*self.tcx, src.layout.ty)?;
494                ensure_monomorphic_enough(*self.tcx, cast_ty.ty)?;
495
496                span_bug!(
497                    self.cur_span(),
498                    "unsize_into: invalid conversion: {:?} -> {:?}",
499                    src.layout,
500                    dest.layout()
501                )
502            }
503        }
504    }
505}
rustc_const_eval/interpret/cast.rs

rustc_const_eval/interpret/
cast.rs
