charon_lib/ast/
expressions.rs

1//! Implements expressions: paths, operands, rvalues, lvalues
2
3use crate::ast::*;
4use derive_generic_visitor::{Drive, DriveMut};
5use macros::{EnumAsGetters, EnumIsA, EnumToGetters, VariantIndexArity, VariantName};
6use serde::{Deserialize, Serialize};
7use std::vec::Vec;
8
9#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize, Drive, DriveMut)]
10pub struct Place {
11    pub kind: PlaceKind,
12    pub ty: Ty,
13}
14
15#[derive(
16    Debug,
17    PartialEq,
18    Eq,
19    Clone,
20    EnumIsA,
21    EnumAsGetters,
22    EnumToGetters,
23    Serialize,
24    Deserialize,
25    Drive,
26    DriveMut,
27)]
28#[charon::variants_prefix("Place")]
29pub enum PlaceKind {
30    Local(LocalId),
31    Projection(Box<Place>, ProjectionElem),
32}
33
34/// Note that we don't have the equivalent of "downcasts".
35/// Downcasts are actually necessary, for instance when initializing enumeration
36/// values: the value is initially `Bottom`, and we need a way of knowing the
37/// variant.
38/// For example:
39/// `((_0 as Right).0: T2) = move _1;`
40/// In MIR, downcasts always happen before field projections: in our internal
41/// language, we thus merge downcasts and field projections.
42#[derive(
43    Debug,
44    PartialEq,
45    Eq,
46    Clone,
47    EnumIsA,
48    EnumAsGetters,
49    EnumToGetters,
50    VariantName,
51    Serialize,
52    Deserialize,
53    Drive,
54    DriveMut,
55)]
56pub enum ProjectionElem {
57    /// Dereference a shared/mutable reference, a box, or a raw pointer.
58    Deref,
59    /// Projection from ADTs (variants, structures).
60    /// We allow projections to be used as left-values and right-values.
61    /// We should never have projections to fields of symbolic variants (they
62    /// should have been expanded before through a match).
63    Field(FieldProjKind, FieldId),
64    /// MIR imposes that the argument to an index projection be a local variable, meaning
65    /// that even constant indices into arrays are let-bound as separate variables.
66    /// We **eliminate** this variant in a micro-pass.
67    #[charon::opaque]
68    Index {
69        offset: Box<Operand>,
70        #[drive(skip)]
71        from_end: bool,
72    },
73    /// Take a subslice of a slice or array. If `from_end` is `true` this is
74    /// `slice[from..slice.len() - to]`, otherwise this is `slice[from..to]`.
75    /// We **eliminate** this variant in a micro-pass.
76    #[charon::opaque]
77    Subslice {
78        from: Box<Operand>,
79        to: Box<Operand>,
80        #[drive(skip)]
81        from_end: bool,
82    },
83}
84
85#[derive(
86    Debug,
87    PartialEq,
88    Eq,
89    Copy,
90    Clone,
91    EnumIsA,
92    EnumAsGetters,
93    Serialize,
94    Deserialize,
95    Drive,
96    DriveMut,
97)]
98#[charon::variants_prefix("Proj")]
99pub enum FieldProjKind {
100    Adt(TypeDeclId, Option<VariantId>),
101    /// If we project from a tuple, the projection kind gives the arity of the tuple.
102    #[drive(skip)]
103    Tuple(usize),
104    /// Access to a field in a closure state.
105    /// We eliminate this in a micro-pass ([crate::update_closure_signatures]).
106    #[charon::opaque]
107    ClosureState,
108}
109
110#[derive(
111    Debug,
112    PartialEq,
113    Eq,
114    Copy,
115    Clone,
116    EnumIsA,
117    EnumAsGetters,
118    Serialize,
119    Deserialize,
120    Drive,
121    DriveMut,
122)]
123#[charon::variants_prefix("B")]
124pub enum BorrowKind {
125    Shared,
126    Mut,
127    /// See <https://doc.rust-lang.org/beta/nightly-rustc/rustc_middle/mir/enum.MutBorrowKind.html#variant.TwoPhaseBorrow>
128    /// and <https://rustc-dev-guide.rust-lang.org/borrow_check/two_phase_borrows.html>
129    TwoPhaseMut,
130    /// Those are typically introduced when using guards in matches, to make sure guards don't
131    /// change the variant of an enum value while me match over it.
132    ///
133    /// See <https://doc.rust-lang.org/beta/nightly-rustc/rustc_middle/mir/enum.FakeBorrowKind.html#variant.Shallow>.
134    Shallow,
135    /// Data must be immutable but not aliasable. In other words you can't mutate the data but you
136    /// can mutate *through it*, e.g. if it points to a `&mut T`. This is only used in closure
137    /// captures, e.g.
138    /// ```rust,ignore
139    /// let mut z = 3;
140    /// let x: &mut isize = &mut z;
141    /// let y = || *x += 5;
142    /// ```
143    /// Here the captured variable can't be `&mut &mut x` since the `x` binding is not mutable, yet
144    /// we must be able to mutate what it points to.
145    ///
146    /// See <https://doc.rust-lang.org/beta/nightly-rustc/rustc_middle/mir/enum.MutBorrowKind.html#variant.ClosureCapture>.
147    UniqueImmutable,
148}
149
150/// Unary operation
151#[derive(
152    Debug, PartialEq, Eq, Clone, EnumIsA, VariantName, Serialize, Deserialize, Drive, DriveMut,
153)]
154#[charon::rename("Unop")]
155pub enum UnOp {
156    Not,
157    /// This can overflow. In practice, rust introduces an assert before
158    /// (in debug mode) to check that it is not equal to the minimum integer
159    /// value (for the proper type).
160    Neg,
161    /// Retreive the metadata part of a fat pointer. For slices, this retreives their length.
162    PtrMetadata,
163    /// Casts are rvalues in MIR, but we treat them as unops.
164    Cast(CastKind),
165    /// Coercion from array (i.e., [T; N]) to slice.
166    ///
167    /// **Remark:** We introduce this unop when translating from MIR, **then transform**
168    /// it to a function call in a micro pass. The type and the scalar value are not
169    /// *necessary* as we can retrieve them from the context, but storing them here is
170    /// very useful. The [RefKind] argument states whethere we operate on a mutable
171    /// or a shared borrow to an array.
172    #[charon::opaque]
173    ArrayToSlice(RefKind, Ty, ConstGeneric),
174}
175
176/// Nullary operation
177#[derive(
178    Debug, PartialEq, Eq, Clone, EnumIsA, VariantName, Serialize, Deserialize, Drive, DriveMut,
179)]
180#[charon::rename("Nullop")]
181pub enum NullOp {
182    SizeOf,
183    AlignOf,
184    #[drive(skip)]
185    OffsetOf(Vec<(usize, FieldId)>),
186    UbChecks,
187}
188
189/// For all the variants: the first type gives the source type, the second one gives
190/// the destination type.
191#[derive(
192    Debug, PartialEq, Eq, Clone, EnumIsA, VariantName, Serialize, Deserialize, Drive, DriveMut,
193)]
194#[charon::variants_prefix("Cast")]
195pub enum CastKind {
196    /// Conversion between types in {Integer, Bool}
197    /// Remark: for now we don't support conversions with Char.
198    Scalar(LiteralTy, LiteralTy),
199    RawPtr(Ty, Ty),
200    FnPtr(Ty, Ty),
201    /// [Unsize coercion](https://doc.rust-lang.org/std/ops/trait.CoerceUnsized.html). This is
202    /// either `[T; N]` -> `[T]` or `T: Trait` -> `dyn Trait` coercions, behind a pointer
203    /// (reference, `Box`, or other type that implements `CoerceUnsized`).
204    ///
205    /// The special case of `&[T; N]` -> `&[T]` coercion is caught by `UnOp::ArrayToSlice`.
206    Unsize(Ty, Ty),
207    /// Reinterprets the bits of a value of one type as another type, i.e. exactly what
208    /// [`std::mem::transmute`] does.
209    Transmute(Ty, Ty),
210}
211
212/// Binary operations.
213#[derive(
214    Debug, PartialEq, Eq, Copy, Clone, EnumIsA, VariantName, Serialize, Deserialize, Drive, DriveMut,
215)]
216#[charon::rename("Binop")]
217pub enum BinOp {
218    BitXor,
219    BitAnd,
220    BitOr,
221    Eq,
222    Lt,
223    Le,
224    Ne,
225    Ge,
226    Gt,
227    /// Fails if the divisor is 0, or if the operation is `int::MIN / -1`.
228    Div,
229    /// Fails if the divisor is 0, or if the operation is `int::MIN % -1`.
230    Rem,
231    /// Fails on overflow.
232    Add,
233    /// Fails on overflow.
234    Sub,
235    /// Fails on overflow.
236    Mul,
237    /// Returns `(result, did_overflow)`, where `result` is the result of the operation with
238    /// wrapping semantics, and `did_overflow` is a boolean that indicates whether the operation
239    /// overflowed. This operation does not fail.
240    CheckedAdd,
241    /// Like `CheckedAdd`.
242    CheckedSub,
243    /// Like `CheckedAdd`.
244    CheckedMul,
245    /// Fails if the shift is bigger than the bit-size of the type.
246    Shl,
247    /// Fails if the shift is bigger than the bit-size of the type.
248    Shr,
249    /// `BinOp(Offset, ptr, n)` for `ptr` a pointer to type `T` offsets `ptr` by `n * size_of::<T>()`.
250    Offset,
251    /// `BinOp(Cmp, a, b)` returns `-1u8` if `a < b`, `0u8` if `a == b`, and `1u8` if `a > b`.
252    Cmp,
253}
254
255#[derive(
256    Debug,
257    PartialEq,
258    Eq,
259    Clone,
260    EnumIsA,
261    EnumToGetters,
262    EnumAsGetters,
263    VariantName,
264    Serialize,
265    Deserialize,
266    Drive,
267    DriveMut,
268)]
269pub enum Operand {
270    Copy(Place),
271    Move(Place),
272    /// Constant value (including constant and static variables)
273    #[charon::rename("Constant")]
274    Const(ConstantExpr),
275}
276
277/// A function identifier. See [crate::ullbc_ast::Terminator]
278#[derive(
279    Debug,
280    Clone,
281    PartialEq,
282    Eq,
283    EnumIsA,
284    EnumAsGetters,
285    VariantName,
286    Serialize,
287    Deserialize,
288    Drive,
289    DriveMut,
290)]
291#[charon::variants_prefix("F")]
292pub enum FunId {
293    /// A "regular" function (function local to the crate, external function
294    /// not treated as a primitive one).
295    Regular(FunDeclId),
296    /// A primitive function, coming from a standard library (for instance:
297    /// `alloc::boxed::Box::new`).
298    /// TODO: rename to "Primitive"
299    #[charon::rename("FBuiltin")]
300    Builtin(BuiltinFunId),
301}
302
303/// An built-in function identifier, identifying a function coming from a
304/// standard library.
305#[derive(
306    Debug,
307    Clone,
308    Copy,
309    PartialEq,
310    Eq,
311    EnumIsA,
312    EnumAsGetters,
313    VariantName,
314    Serialize,
315    Deserialize,
316    Drive,
317    DriveMut,
318)]
319pub enum BuiltinFunId {
320    /// `alloc::boxed::Box::new`
321    BoxNew,
322    /// Cast an array as a slice.
323    ///
324    /// Converted from [UnOp::ArrayToSlice]
325    ArrayToSliceShared,
326    /// Cast an array as a slice.
327    ///
328    /// Converted from [UnOp::ArrayToSlice]
329    ArrayToSliceMut,
330    /// `repeat(n, x)` returns an array where `x` has been replicated `n` times.
331    ///
332    /// We introduce this when desugaring the [ArrayRepeat] rvalue.
333    ArrayRepeat,
334    /// Converted from indexing `ProjectionElem`s. The signature depends on the parameters. It
335    /// could look like:
336    /// - `fn ArrayIndexShared<T,N>(&[T;N], usize) -> &T`
337    /// - `fn SliceIndexShared<T>(&[T], usize) -> &T`
338    /// - `fn ArraySubSliceShared<T,N>(&[T;N], usize, usize) -> &[T]`
339    /// - `fn SliceSubSliceMut<T>(&mut [T], usize, usize) -> &mut [T]`
340    /// - etc
341    Index(BuiltinIndexOp),
342    /// Build a raw pointer, from a data pointer and metadata. The metadata can be unit, if
343    /// building a thin pointer.
344    ///
345    /// Converted from [AggregateKind::RawPtr]
346    PtrFromParts(RefKind),
347}
348
349/// One of 8 built-in indexing operations.
350#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Drive, DriveMut)]
351pub struct BuiltinIndexOp {
352    /// Whether this is a slice or array.
353    #[drive(skip)]
354    pub is_array: bool,
355    /// Whether we're indexing mutably or not. Determines the type ofreference of the input and
356    /// output.
357    pub mutability: RefKind,
358    /// Whether we're indexing a single element or a subrange. If `true`, the function takes
359    /// two indices and the output is a slice; otherwise, the function take one index and the
360    /// output is a reference to a single element.
361    #[drive(skip)]
362    pub is_range: bool,
363}
364
365#[derive(Debug, Clone, PartialEq, Eq, EnumAsGetters, Serialize, Deserialize, Drive, DriveMut)]
366pub enum FunIdOrTraitMethodRef {
367    #[charon::rename("FunId")]
368    Fun(FunId),
369    /// If a trait: the reference to the trait and the id of the trait method.
370    /// The fun decl id is not really necessary - we put it here for convenience
371    /// purposes.
372    #[charon::rename("TraitMethod")]
373    Trait(TraitRef, TraitItemName, FunDeclId),
374}
375
376#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize, Drive, DriveMut)]
377pub struct FnPtr {
378    pub func: FunIdOrTraitMethodRef,
379    pub generics: GenericArgs,
380}
381
382/// A constant expression.
383///
384/// Only the [Literal] and [Var] cases are left in the final LLBC.
385///
386/// The other cases come from a straight translation from the MIR:
387///
388/// [Adt] case:
389/// It is a bit annoying, but rustc treats some ADT and tuple instances as
390/// constants when generating MIR:
391/// - an enumeration with one variant and no fields is a constant.
392/// - a structure with no field is a constant.
393/// - sometimes, Rust stores the initialization of an ADT as a constant
394///   (if all the fields are constant) rather than as an aggregated value
395/// We later desugar those to regular ADTs, see [regularize_constant_adts.rs].
396///
397/// [Global] case: access to a global variable. We later desugar it to
398/// a separate statement.
399///
400/// [Ref] case: reference to a constant value. We later desugar it to a separate
401/// statement.
402///
403/// [FnPtr] case: a function pointer (to a top-level function).
404///
405/// Remark:
406/// MIR seems to forbid more complex expressions like paths. For instance,
407/// reading the constant `a.b` is translated to `{ _1 = const a; _2 = (_1.0) }`.
408#[derive(
409    Debug,
410    PartialEq,
411    Eq,
412    Clone,
413    VariantName,
414    EnumIsA,
415    EnumAsGetters,
416    Serialize,
417    Deserialize,
418    Drive,
419    DriveMut,
420)]
421#[charon::variants_prefix("C")]
422pub enum RawConstantExpr {
423    Literal(Literal),
424    ///
425    /// In most situations:
426    /// Enumeration with one variant with no fields, structure with
427    /// no fields, unit (encoded as a 0-tuple).
428    ///
429    /// Less frequently: arbitrary ADT values.
430    ///
431    /// We eliminate this case in a micro-pass.
432    #[charon::opaque]
433    Adt(Option<VariantId>, Vec<ConstantExpr>),
434    #[charon::opaque]
435    Array(Vec<ConstantExpr>),
436    /// The value is a top-level constant/static.
437    ///
438    /// We eliminate this case in a micro-pass.
439    ///
440    /// Remark: constants can actually have generic parameters.
441    /// ```text
442    /// struct V<const N: usize, T> {
443    ///   x: [T; N],
444    /// }
445    ///
446    /// impl<const N: usize, T> V<N, T> {
447    ///   const LEN: usize = N; // This has generics <N, T>
448    /// }
449    ///
450    /// fn use_v<const N: usize, T>(v: V<N, T>) {
451    ///   let l = V::<N, T>::LEN; // We need to provided a substitution here
452    /// }
453    /// ```
454    #[charon::opaque]
455    Global(GlobalDeclRef),
456    ///
457    /// A trait constant.
458    ///
459    /// Ex.:
460    /// ```text
461    /// impl Foo for Bar {
462    ///   const C : usize = 32; // <-
463    /// }
464    /// ```
465    ///
466    /// Remark: trait constants can not be used in types, they are necessarily
467    /// values.
468    TraitConst(TraitRef, TraitItemName),
469    /// A shared reference to a constant value.
470    ///
471    /// We eliminate this case in a micro-pass.
472    #[charon::opaque]
473    Ref(Box<ConstantExpr>),
474    /// A mutable pointer to a mutable static.
475    ///
476    /// We eliminate this case in a micro-pass.
477    #[charon::opaque]
478    MutPtr(Box<ConstantExpr>),
479    /// A const generic var
480    Var(ConstGenericDbVar),
481    /// Function pointer
482    FnPtr(FnPtr),
483    /// Raw memory value obtained from constant evaluation. Used when a more structured
484    /// representation isn't possible (e.g. for unions) or just isn't implemented yet.
485    #[drive(skip)]
486    RawMemory(Vec<u8>),
487    /// A constant expression that Charon still doesn't handle, along with the reason why.
488    #[drive(skip)]
489    Opaque(String),
490}
491
492#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize, Drive, DriveMut)]
493pub struct ConstantExpr {
494    pub value: RawConstantExpr,
495    pub ty: Ty,
496}
497
498/// TODO: we could factor out [Rvalue] and function calls (for LLBC, not ULLBC).
499/// We can also factor out the unops, binops with the function calls.
500/// TODO: move the aggregate kind to operands
501/// TODO: we should prefix the type variants with "R" or "Rv", this would avoid collisions
502#[derive(
503    Debug, Clone, EnumToGetters, EnumAsGetters, EnumIsA, Serialize, Deserialize, Drive, DriveMut,
504)]
505pub enum Rvalue {
506    /// Lifts an operand as an rvalue.
507    Use(Operand),
508    /// Takes a reference to the given place.
509    #[charon::rename("RvRef")]
510    Ref(Place, BorrowKind),
511    /// Takes a raw pointer with the given mutability to the given place. This is generated by
512    /// pointer casts like `&v as *const _` or raw borrow expressions like `&raw const v.`
513    RawPtr(Place, RefKind),
514    /// Binary operations (note that we merge "checked" and "unchecked" binops)
515    BinaryOp(BinOp, Operand, Operand),
516    /// Unary operation (e.g. not, neg)
517    UnaryOp(UnOp, Operand),
518    /// Nullary operation (e.g. `size_of`)
519    NullaryOp(NullOp, Ty),
520    /// Discriminant (for enumerations).
521    /// Note that discriminant values have type isize. We also store the identifier
522    /// of the type from which we read the discriminant.
523    ///
524    /// This case is filtered in [crate::remove_read_discriminant]
525    Discriminant(Place, TypeDeclId),
526    /// Creates an aggregate value, like a tuple, a struct or an enum:
527    /// ```text
528    /// l = List::Cons { value:x, tail:tl };
529    /// ```
530    /// Note that in some MIR passes (like optimized MIR), aggregate values are
531    /// decomposed, like below:
532    /// ```text
533    /// (l as List::Cons).value = x;
534    /// (l as List::Cons).tail = tl;
535    /// ```
536    /// Because we may want to plug our translation mechanism at various
537    /// places, we need to take both into accounts in the translation and in
538    /// our semantics. Aggregate value initialization is easy, you might want
539    /// to have a look at expansion of `Bottom` values for explanations about the
540    /// other case.
541    ///
542    /// Remark: in case of closures, the aggregated value groups the closure id
543    /// together with its state.
544    Aggregate(AggregateKind, Vec<Operand>),
545    /// Copy the value of the referenced global.
546    /// Not present in MIR; introduced in [simplify_constants.rs].
547    Global(GlobalDeclRef),
548    /// Reference the value of the global. This has type `&T` or `*mut T` depending on desired
549    /// mutability.
550    /// Not present in MIR; introduced in [simplify_constants.rs].
551    GlobalRef(GlobalDeclRef, RefKind),
552    /// Length of a memory location. The run-time length of e.g. a vector or a slice is
553    /// represented differently (but pretty-prints the same, FIXME).
554    /// Should be seen as a function of signature:
555    /// - `fn<T;N>(&[T;N]) -> usize`
556    /// - `fn<T>(&[T]) -> usize`
557    ///
558    /// We store the type argument and the const generic (the latter only for arrays).
559    ///
560    /// [Len] is automatically introduced by rustc, notably for the bound checks:
561    /// we eliminate it together with the bounds checks whenever possible.
562    /// There are however occurrences that we don't eliminate (yet).
563    /// For instance, for the following Rust code:
564    /// ```text
565    /// fn slice_pattern_4(x: &[()]) {
566    ///     match x {
567    ///         [_named] => (),
568    ///         _ => (),
569    ///     }
570    /// }
571    /// ```
572    /// rustc introduces a check that the length of the slice is exactly equal
573    /// to 1 and that we preserve.
574    Len(Place, Ty, Option<ConstGeneric>),
575    /// [Repeat(x, n)] creates an array where [x] is copied [n] times.
576    ///
577    /// We translate this to a function call.
578    #[charon::opaque]
579    Repeat(Operand, Ty, ConstGeneric),
580    /// Transmutes a `*mut u8` (obtained from `malloc`) into shallow-initialized `Box<T>`. This
581    /// only appears as part of lowering `Box::new()` in some cases. We reconstruct the original
582    /// `Box::new()` call.
583    #[charon::opaque]
584    ShallowInitBox(Operand, Ty),
585}
586
587/// An aggregated ADT.
588///
589/// Note that ADTs are desaggregated at some point in MIR. For instance, if
590/// we have in Rust:
591/// ```ignore
592///   let ls = Cons(hd, tl);
593/// ```
594///
595/// In MIR we have (yes, the discriminant update happens *at the end* for some
596/// reason):
597/// ```text
598///   (ls as Cons).0 = move hd;
599///   (ls as Cons).1 = move tl;
600///   discriminant(ls) = 0; // assuming `Cons` is the variant of index 0
601/// ```
602///
603/// Rem.: in the Aeneas semantics, both cases are handled (in case of desaggregated
604/// initialization, `ls` is initialized to `⊥`, then this `⊥` is expanded to
605/// `Cons (⊥, ⊥)` upon the first assignment, at which point we can initialize
606/// the field 0, etc.).
607#[derive(Debug, Clone, VariantIndexArity, Serialize, Deserialize, Drive, DriveMut)]
608#[charon::variants_prefix("Aggregated")]
609pub enum AggregateKind {
610    /// A struct, enum or union aggregate. The `VariantId`, if present, indicates this is an enum
611    /// and the aggregate uses that variant. The `FieldId`, if present, indicates this is a union
612    /// and the aggregate writes into that field. Otherwise this is a struct.
613    Adt(TypeId, Option<VariantId>, Option<FieldId>, GenericArgs),
614    /// We don't put this with the ADT cas because this is the only built-in type
615    /// with aggregates, and it is a primitive type. In particular, it makes
616    /// sense to treat it differently because it has a variable number of fields.
617    Array(Ty, ConstGeneric),
618    /// Aggregated values for closures group the function id together with its
619    /// state.
620    Closure(FunDeclId, GenericArgs),
621    /// Construct a raw pointer from a pointer value, and its metadata (can be unit, if building
622    /// a thin pointer). The type is the type of the pointee.
623    /// We lower this to a builtin function call in [crate::ops_to_function_calls].
624    #[charon::opaque]
625    RawPtr(Ty, RefKind),
626}
charon_lib/ast/expressions.rs

charon_lib/ast/
expressions.rs
