3 //! The job of the categorization module is to analyze an expression to
4 //! determine what kind of memory is used in evaluating it (for example,
5 //! where dereferences occur and what kind of pointer is dereferenced;
6 //! whether the memory is mutable, etc.).
8 //! Categorization effectively transforms all of our expressions into
9 //! expressions of the following forms (the actual enum has many more
10 //! possibilities, naturally, but they are all variants of these base
13 //! E = rvalue // some computed rvalue
14 //! | x // address of a local variable or argument
15 //! | *E // deref of a ptr
16 //! | E.comp // access to an interior component
18 //! Imagine a routine ToAddr(Expr) that evaluates an expression and returns an
19 //! address where the result is to be found. If Expr is a place, then this
20 //! is the address of the place. If `Expr` is an rvalue, this is the address of
21 //! some temporary spot in memory where the result is stored.
23 //! Now, `cat_expr()` classifies the expression `Expr` and the address `A = ToAddr(Expr)`
26 //! - `cat`: what kind of expression was this? This is a subset of the
27 //! full expression forms which only includes those that we care about
28 //! for the purpose of the analysis.
29 //! - `mutbl`: mutability of the address `A`.
30 //! - `ty`: the type of data found at the address `A`.
32 //! The resulting categorization tree differs somewhat from the expressions
33 //! themselves. For example, auto-derefs are explicit. Also, an index a[b] is
34 //! decomposed into two operations: a dereference to reach the array data and
35 //! then an index to jump forward to the relevant item.
37 //! ## By-reference upvars
39 //! One part of the codegen which may be non-obvious is that we translate
40 //! closure upvars into the dereference of a borrowed pointer; this more closely
41 //! resembles the runtime codegen. So, for example, if we had:
45 //! let inc = || x += y;
47 //! Then when we categorize `x` (*within* the closure) we would yield a
48 //! result of `*x'`, effectively, where `x'` is a `Categorization::Upvar` reference
49 //! tied to `x`. The type of `x'` will be a borrowed pointer.
52 use rustc::hir::PatKind;
53 use rustc::hir::def_id::DefId;
54 use rustc::hir::def::{Res, DefKind};
55 use rustc::infer::InferCtxt;
56 use rustc::ty::adjustment;
57 use rustc::ty::{self, Ty, TyCtxt};
58 use rustc::ty::fold::TypeFoldable;
62 use rustc_data_structures::fx::FxIndexMap;
64 #[derive(Clone, Debug)]
66 /// A temporary variable
68 /// A named `static` item
70 /// A named local variable
72 /// An upvar referenced by closure env
76 #[derive(Clone, Debug)]
77 pub enum Projection<'tcx> {
78 /// A dereference of a pointer, reference or `Box<T>` of the given type
80 /// An index or a field
84 /// A `Place` represents how a value is located in memory.
86 /// This is an HIR version of `mir::Place`
87 #[derive(Clone, Debug)]
88 pub struct Place<'tcx> {
89 /// `HirId` of the expression or pattern producing this value.
90 pub hir_id: hir::HirId,
91 /// The `Span` of the expression or pattern producing this value.
93 /// The type of the `Place`
95 /// The "outermost" place that holds this value.
97 /// How this place is derived from the base place.
98 pub projections: Vec<Projection<'tcx>>,
101 impl<'tcx> Place<'tcx> {
102 /// Returns an iterator of the types that have to be dereferenced to access
105 /// The types are in the reverse order that they are applied. So if
106 /// `x: &*const u32` and the `Place` is `**x`, then the types returned are
107 ///`*const u32` then `&*const u32`.
108 crate fn deref_tys(&self) -> impl Iterator<Item=Ty<'tcx>> + '_ {
109 self.projections.iter().rev().filter_map(|proj| if let Projection::Deref(deref_ty) = *proj {
117 crate trait HirNode {
118 fn hir_id(&self) -> hir::HirId;
119 fn span(&self) -> Span;
122 impl HirNode for hir::Expr {
123 fn hir_id(&self) -> hir::HirId { self.hir_id }
124 fn span(&self) -> Span { self.span }
127 impl HirNode for hir::Pat {
128 fn hir_id(&self) -> hir::HirId { self.hir_id }
129 fn span(&self) -> Span { self.span }
133 crate struct MemCategorizationContext<'a, 'tcx> {
134 crate tables: &'a ty::TypeckTables<'tcx>,
135 infcx: &'a InferCtxt<'a, 'tcx>,
136 param_env: ty::ParamEnv<'tcx>,
138 upvars: Option<&'tcx FxIndexMap<hir::HirId, hir::Upvar>>,
141 crate type McResult<T> = Result<T, ()>;
143 impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
144 /// Creates a `MemCategorizationContext`.
146 infcx: &'a InferCtxt<'a, 'tcx>,
147 param_env: ty::ParamEnv<'tcx>,
149 tables: &'a ty::TypeckTables<'tcx>,
150 ) -> MemCategorizationContext<'a, 'tcx> {
151 MemCategorizationContext {
156 upvars: infcx.tcx.upvars(body_owner),
160 crate fn tcx(&self) -> TyCtxt<'tcx> {
164 crate fn type_is_copy_modulo_regions(
169 self.infcx.type_is_copy_modulo_regions(self.param_env, ty, span)
172 fn resolve_vars_if_possible<T>(&self, value: &T) -> T
173 where T: TypeFoldable<'tcx>
175 self.infcx.resolve_vars_if_possible(value)
178 fn is_tainted_by_errors(&self) -> bool {
179 self.infcx.is_tainted_by_errors()
182 fn resolve_type_vars_or_error(&self,
184 ty: Option<Ty<'tcx>>)
185 -> McResult<Ty<'tcx>> {
188 let ty = self.resolve_vars_if_possible(&ty);
189 if ty.references_error() || ty.is_ty_var() {
190 debug!("resolve_type_vars_or_error: error from {:?}", ty);
197 None if self.is_tainted_by_errors() => Err(()),
199 bug!("no type for node {}: {} in mem_categorization",
200 id, self.tcx().hir().node_to_string(id));
205 crate fn node_ty(&self, hir_id: hir::HirId) -> McResult<Ty<'tcx>> {
206 self.resolve_type_vars_or_error(hir_id, self.tables.node_type_opt(hir_id))
209 fn expr_ty(&self, expr: &hir::Expr) -> McResult<Ty<'tcx>> {
210 self.resolve_type_vars_or_error(expr.hir_id, self.tables.expr_ty_opt(expr))
213 crate fn expr_ty_adjusted(&self, expr: &hir::Expr) -> McResult<Ty<'tcx>> {
214 self.resolve_type_vars_or_error(expr.hir_id, self.tables.expr_ty_adjusted_opt(expr))
217 /// Returns the type of value that this pattern matches against.
218 /// Some non-obvious cases:
220 /// - a `ref x` binding matches against a value of type `T` and gives
221 /// `x` the type `&T`; we return `T`.
222 /// - a pattern with implicit derefs (thanks to default binding
223 /// modes #42640) may look like `Some(x)` but in fact have
224 /// implicit deref patterns attached (e.g., it is really
225 /// `&Some(x)`). In that case, we return the "outermost" type
226 /// (e.g., `&Option<T>).
227 crate fn pat_ty_adjusted(&self, pat: &hir::Pat) -> McResult<Ty<'tcx>> {
228 // Check for implicit `&` types wrapping the pattern; note
229 // that these are never attached to binding patterns, so
230 // actually this is somewhat "disjoint" from the code below
231 // that aims to account for `ref x`.
232 if let Some(vec) = self.tables.pat_adjustments().get(pat.hir_id) {
233 if let Some(first_ty) = vec.first() {
234 debug!("pat_ty(pat={:?}) found adjusted ty `{:?}`", pat, first_ty);
239 self.pat_ty_unadjusted(pat)
243 /// Like `pat_ty`, but ignores implicit `&` patterns.
244 fn pat_ty_unadjusted(&self, pat: &hir::Pat) -> McResult<Ty<'tcx>> {
245 let base_ty = self.node_ty(pat.hir_id)?;
246 debug!("pat_ty(pat={:?}) base_ty={:?}", pat, base_ty);
248 // This code detects whether we are looking at a `ref x`,
249 // and if so, figures out what the type *being borrowed* is.
250 let ret_ty = match pat.kind {
251 PatKind::Binding(..) => {
252 let bm = *self.tables
255 .expect("missing binding mode");
257 if let ty::BindByReference(_) = bm {
258 // a bind-by-ref means that the base_ty will be the type of the ident itself,
259 // but what we want here is the type of the underlying value being borrowed.
260 // So peel off one-level, turning the &T into T.
261 match base_ty.builtin_deref(false) {
264 debug!("By-ref binding of non-derefable type {:?}", base_ty);
274 debug!("pat_ty(pat={:?}) ret_ty={:?}", pat, ret_ty);
279 crate fn cat_expr(&self, expr: &hir::Expr) -> McResult<Place<'tcx>> {
280 // This recursion helper avoids going through *too many*
281 // adjustments, since *only* non-overloaded deref recurses.
283 mc: &MemCategorizationContext<'a, 'tcx>,
285 adjustments: &[adjustment::Adjustment<'tcx>],
286 ) -> McResult<Place<'tcx>> {
287 match adjustments.split_last() {
288 None => mc.cat_expr_unadjusted(expr),
289 Some((adjustment, previous)) => {
290 mc.cat_expr_adjusted_with(expr, || helper(mc, expr, previous), adjustment)
295 helper(self, expr, self.tables.expr_adjustments(expr))
298 crate fn cat_expr_adjusted(&self, expr: &hir::Expr,
299 previous: Place<'tcx>,
300 adjustment: &adjustment::Adjustment<'tcx>)
301 -> McResult<Place<'tcx>> {
302 self.cat_expr_adjusted_with(expr, || Ok(previous), adjustment)
305 fn cat_expr_adjusted_with<F>(&self, expr: &hir::Expr,
307 adjustment: &adjustment::Adjustment<'tcx>)
308 -> McResult<Place<'tcx>>
309 where F: FnOnce() -> McResult<Place<'tcx>>
311 debug!("cat_expr_adjusted_with({:?}): {:?}", adjustment, expr);
312 let target = self.resolve_vars_if_possible(&adjustment.target);
313 match adjustment.kind {
314 adjustment::Adjust::Deref(overloaded) => {
315 // Equivalent to *expr or something similar.
316 let base = if let Some(deref) = overloaded {
317 let ref_ty = self.tcx().mk_ref(deref.region, ty::TypeAndMut {
321 self.cat_rvalue(expr.hir_id, expr.span, ref_ty)
325 self.cat_deref(expr, base)
328 adjustment::Adjust::NeverToAny |
329 adjustment::Adjust::Pointer(_) |
330 adjustment::Adjust::Borrow(_) => {
331 // Result is an rvalue.
332 Ok(self.cat_rvalue(expr.hir_id, expr.span, target))
337 crate fn cat_expr_unadjusted(&self, expr: &hir::Expr) -> McResult<Place<'tcx>> {
338 debug!("cat_expr: id={} expr={:?}", expr.hir_id, expr);
340 let expr_ty = self.expr_ty(expr)?;
342 hir::ExprKind::Unary(hir::UnDeref, ref e_base) => {
343 if self.tables.is_method_call(expr) {
344 self.cat_overloaded_place(expr, e_base)
346 let base = self.cat_expr(&e_base)?;
347 self.cat_deref(expr, base)
351 hir::ExprKind::Field(ref base, _) => {
352 let base = self.cat_expr(&base)?;
353 debug!("cat_expr(cat_field): id={} expr={:?} base={:?}",
357 Ok(self.cat_projection(expr, base, expr_ty))
360 hir::ExprKind::Index(ref base, _) => {
361 if self.tables.is_method_call(expr) {
362 // If this is an index implemented by a method call, then it
363 // will include an implicit deref of the result.
364 // The call to index() returns a `&T` value, which
365 // is an rvalue. That is what we will be
367 self.cat_overloaded_place(expr, base)
369 let base = self.cat_expr(&base)?;
370 Ok(self.cat_projection(expr, base, expr_ty))
374 hir::ExprKind::Path(ref qpath) => {
375 let res = self.tables.qpath_res(qpath, expr.hir_id);
376 self.cat_res(expr.hir_id, expr.span, expr_ty, res)
379 hir::ExprKind::Type(ref e, _) => {
383 hir::ExprKind::AddrOf(..) | hir::ExprKind::Call(..) |
384 hir::ExprKind::Assign(..) | hir::ExprKind::AssignOp(..) |
385 hir::ExprKind::Closure(..) | hir::ExprKind::Ret(..) |
386 hir::ExprKind::Unary(..) | hir::ExprKind::Yield(..) |
387 hir::ExprKind::MethodCall(..) | hir::ExprKind::Cast(..) | hir::ExprKind::DropTemps(..) |
388 hir::ExprKind::Array(..) | hir::ExprKind::Tup(..) |
389 hir::ExprKind::Binary(..) |
390 hir::ExprKind::Block(..) | hir::ExprKind::Loop(..) | hir::ExprKind::Match(..) |
391 hir::ExprKind::Lit(..) | hir::ExprKind::Break(..) |
392 hir::ExprKind::Continue(..) | hir::ExprKind::Struct(..) | hir::ExprKind::Repeat(..) |
393 hir::ExprKind::InlineAsm(..) | hir::ExprKind::Box(..) | hir::ExprKind::Err => {
394 Ok(self.cat_rvalue(expr.hir_id, expr.span, expr_ty))
399 crate fn cat_res(&self,
404 -> McResult<Place<'tcx>> {
405 debug!("cat_res: id={:?} expr={:?} def={:?}",
406 hir_id, expr_ty, res);
409 Res::Def(DefKind::Ctor(..), _)
410 | Res::Def(DefKind::Const, _)
411 | Res::Def(DefKind::ConstParam, _)
412 | Res::Def(DefKind::AssocConst, _)
413 | Res::Def(DefKind::Fn, _)
414 | Res::Def(DefKind::Method, _)
415 | Res::SelfCtor(..) => {
416 Ok(self.cat_rvalue(hir_id, span, expr_ty))
419 Res::Def(DefKind::Static, _) => {
424 base: PlaceBase::StaticItem,
425 projections: Vec::new(),
429 Res::Local(var_id) => {
430 if self.upvars.map_or(false, |upvars| upvars.contains_key(&var_id)) {
431 self.cat_upvar(hir_id, span, var_id)
437 base: PlaceBase::Local(var_id),
438 projections: Vec::new(),
443 def => span_bug!(span, "unexpected definition in memory categorization: {:?}", def)
447 /// Categorize an upvar.
449 /// Note: the actual upvar access contains invisible derefs of closure
450 /// environment and upvar reference as appropriate. Only regionck cares
451 /// about these dereferences, so we let it compute them as needed.
457 ) -> McResult<Place<'tcx>> {
458 let closure_expr_def_id = self.body_owner;
460 let upvar_id = ty::UpvarId {
461 var_path: ty::UpvarPath { hir_id: var_id },
462 closure_expr_id: closure_expr_def_id.to_local(),
464 let var_ty = self.node_ty(var_id)?;
470 base: PlaceBase::Upvar(upvar_id),
471 projections: Vec::new(),
474 debug!("cat_upvar ret={:?}", ret);
478 crate fn cat_rvalue(&self, hir_id: hir::HirId, span: Span, expr_ty: Ty<'tcx>) -> Place<'tcx> {
479 debug!("cat_rvalue hir_id={:?}, expr_ty={:?}, span={:?}", hir_id, expr_ty, span);
483 base: PlaceBase::Rvalue,
484 projections: Vec::new(),
487 debug!("cat_rvalue ret={:?}", ret);
491 crate fn cat_projection<N: HirNode>(
494 base_place: Place<'tcx>,
497 let mut projections = base_place.projections;
498 projections.push(Projection::Other);
500 hir_id: node.hir_id(),
503 base: base_place.base,
506 debug!("cat_field ret {:?}", ret);
510 fn cat_overloaded_place(
514 ) -> McResult<Place<'tcx>> {
515 debug!("cat_overloaded_place(expr={:?}, base={:?})", expr, base);
517 // Reconstruct the output assuming it's a reference with the
518 // same region and mutability as the receiver. This holds for
519 // `Deref(Mut)::Deref(_mut)` and `Index(Mut)::index(_mut)`.
520 let place_ty = self.expr_ty(expr)?;
521 let base_ty = self.expr_ty_adjusted(base)?;
523 let (region, mutbl) = match base_ty.kind {
524 ty::Ref(region, _, mutbl) => (region, mutbl),
525 _ => span_bug!(expr.span, "cat_overloaded_place: base is not a reference")
527 let ref_ty = self.tcx().mk_ref(region, ty::TypeAndMut {
532 let base = self.cat_rvalue(expr.hir_id, expr.span, ref_ty);
533 self.cat_deref(expr, base)
539 base_place: Place<'tcx>,
540 ) -> McResult<Place<'tcx>> {
541 debug!("cat_deref: base_place={:?}", base_place);
543 let base_ty = base_place.ty;
544 let deref_ty = match base_ty.builtin_deref(true) {
547 debug!("explicit deref of non-derefable type: {:?}", base_ty);
551 let mut projections = base_place.projections;
552 projections.push(Projection::Deref(base_ty));
555 hir_id: node.hir_id(),
558 base: base_place.base,
561 debug!("cat_deref ret {:?}", ret);
565 crate fn cat_pattern<F>(&self, place: Place<'tcx>, pat: &hir::Pat, mut op: F) -> McResult<()>
566 where F: FnMut(&Place<'tcx>, &hir::Pat),
568 self.cat_pattern_(place, pat, &mut op)
571 // FIXME(#19596) This is a workaround, but there should be a better way to do this
572 fn cat_pattern_<F>(&self, mut place: Place<'tcx>, pat: &hir::Pat, op: &mut F) -> McResult<()>
573 where F: FnMut(&Place<'tcx>, &hir::Pat)
575 // Here, `place` is the `Place` being matched and pat is the pattern it
576 // is being matched against.
578 // In general, the way that this works is that we walk down the pattern,
579 // constructing a `Place` that represents the path that will be taken
580 // to reach the value being matched.
582 debug!("cat_pattern(pat={:?}, place={:?})", pat, place);
584 // If (pattern) adjustments are active for this pattern, adjust the `Place` correspondingly.
585 // `Place`s are constructed differently from patterns. For example, in
589 // &&Some(x, ) => { ... },
594 // the pattern `&&Some(x,)` is represented as `Ref { Ref { TupleStruct }}`. To build the
595 // corresponding `Place` we start with the `Place` for `foo`, and then, by traversing the
596 // pattern, try to answer the question: given the address of `foo`, how is `x` reached?
598 // `&&Some(x,)` `place_foo`
599 // `&Some(x,)` `deref { place_foo}`
600 // `Some(x,)` `deref { deref { place_foo }}`
601 // (x,)` `field0 { deref { deref { place_foo }}}` <- resulting place
603 // The above example has no adjustments. If the code were instead the (after adjustments,
604 // equivalent) version
608 // Some(x, ) => { ... },
613 // Then we see that to get the same result, we must start with
614 // `deref { deref { place_foo }}` instead of `place_foo` since the pattern is now `Some(x,)`
615 // and not `&&Some(x,)`, even though its assigned type is that of `&&Some(x,)`.
616 for _ in 0..self.tables
622 debug!("cat_pattern: applying adjustment to place={:?}", place);
623 place = self.cat_deref(pat, place)?;
625 let place = place; // lose mutability
626 debug!("cat_pattern: applied adjustment derefs to get place={:?}", place);
628 // Invoke the callback, but only now, after the `place` has adjusted.
630 // To see that this makes sense, consider `match &Some(3) { Some(x) => { ... }}`. In that
631 // case, the initial `place` will be that for `&Some(3)` and the pattern is `Some(x)`. We
632 // don't want to call `op` with these incompatible values. As written, what happens instead
633 // is that `op` is called with the adjusted place (that for `*&Some(3)`) and the pattern
634 // `Some(x)` (which matches). Recursing once more, `*&Some(3)` and the pattern `Some(x)`
635 // result in the place `Downcast<Some>(*&Some(3)).0` associated to `x` and invoke `op` with
636 // that (where the `ref` on `x` is implied).
640 PatKind::TupleStruct(_, ref subpats, _)
641 | PatKind::Tuple(ref subpats, _) => {
642 // S(p1, ..., pN) or (p1, ..., pN)
643 for subpat in subpats.iter() {
644 let subpat_ty = self.pat_ty_adjusted(&subpat)?;
645 let sub_place = self.cat_projection(pat, place.clone(), subpat_ty);
646 self.cat_pattern_(sub_place, &subpat, op)?;
650 PatKind::Struct(_, ref field_pats, _) => {
651 // S { f1: p1, ..., fN: pN }
652 for fp in field_pats {
653 let field_ty = self.pat_ty_adjusted(&fp.pat)?;
654 let field_place = self.cat_projection(pat, place.clone(), field_ty);
655 self.cat_pattern_(field_place, &fp.pat, op)?;
659 PatKind::Or(ref pats) => {
661 self.cat_pattern_(place.clone(), &pat, op)?;
665 PatKind::Binding(.., Some(ref subpat)) => {
666 self.cat_pattern_(place, &subpat, op)?;
669 PatKind::Box(ref subpat) | PatKind::Ref(ref subpat, _) => {
670 // box p1, &p1, &mut p1. we can ignore the mutability of
671 // PatKind::Ref since that information is already contained
673 let subplace = self.cat_deref(pat, place)?;
674 self.cat_pattern_(subplace, &subpat, op)?;
677 PatKind::Slice(ref before, ref slice, ref after) => {
678 let element_ty = match place.ty.builtin_index() {
681 debug!("explicit index of non-indexable type {:?}", place);
685 let elt_place = self.cat_projection(pat, place.clone(), element_ty);
686 for before_pat in before {
687 self.cat_pattern_(elt_place.clone(), &before_pat, op)?;
689 if let Some(ref slice_pat) = *slice {
690 let slice_pat_ty = self.pat_ty_adjusted(&slice_pat)?;
691 let slice_place = self.cat_projection(pat, place, slice_pat_ty);
692 self.cat_pattern_(slice_place, &slice_pat, op)?;
694 for after_pat in after {
695 self.cat_pattern_(elt_place.clone(), &after_pat, op)?;
699 PatKind::Path(_) | PatKind::Binding(.., None) |
700 PatKind::Lit(..) | PatKind::Range(..) | PatKind::Wild => {