1 //! A classic liveness analysis based on dataflow over the AST. Computes,
2 //! for each local variable in a function, whether that variable is live
3 //! at a given point. Program execution points are identified by their
8 //! The basic model is that each local variable is assigned an index. We
9 //! represent sets of local variables using a vector indexed by this
10 //! index. The value in the vector is either 0, indicating the variable
11 //! is dead, or the ID of an expression that uses the variable.
13 //! We conceptually walk over the AST in reverse execution order. If we
14 //! find a use of a variable, we add it to the set of live variables. If
15 //! we find an assignment to a variable, we remove it from the set of live
16 //! variables. When we have to merge two flows, we take the union of
17 //! those two flows -- if the variable is live on both paths, we simply
18 //! pick one ID. In the event of loops, we continue doing this until a
19 //! fixed point is reached.
21 //! ## Checking initialization
23 //! At the function entry point, all variables must be dead. If this is
24 //! not the case, we can report an error using the ID found in the set of
25 //! live variables, which identifies a use of the variable which is not
26 //! dominated by an assignment.
30 //! After each explicit move, the variable must be dead.
32 //! ## Computing last uses
34 //! Any use of the variable where the variable is dead afterwards is a
37 //! # Implementation details
39 //! The actual implementation contains two (nested) walks over the AST.
40 //! The outer walk has the job of building up the ir_maps instance for the
41 //! enclosing function. On the way down the tree, it identifies those AST
42 //! nodes and variable IDs that will be needed for the liveness analysis
43 //! and assigns them contiguous IDs. The liveness ID for an AST node is
44 //! called a `live_node` (it's a newtype'd `u32`) and the ID for a variable
45 //! is called a `variable` (another newtype'd `u32`).
47 //! On the way back up the tree, as we are about to exit from a function
48 //! declaration we allocate a `liveness` instance. Now that we know
49 //! precisely how many nodes and variables we need, we can allocate all
50 //! the various arrays that we will need to precisely the right size. We then
51 //! perform the actual propagation on the `liveness` instance.
53 //! This propagation is encoded in the various `propagate_through_*()`
54 //! methods. It effectively does a reverse walk of the AST; whenever we
55 //! reach a loop node, we iterate until a fixed point is reached.
57 //! ## The `RWU` struct
59 //! At each live node `N`, we track three pieces of information for each
60 //! variable `V` (these are encapsulated in the `RWU` struct):
62 //! - `reader`: the `LiveNode` ID of some node which will read the value
63 //! that `V` holds on entry to `N`. Formally: a node `M` such
64 //! that there exists a path `P` from `N` to `M` where `P` does not
65 //! write `V`. If the `reader` is `None`, then the current
66 //! value will never be read (the variable is dead, essentially).
68 //! - `writer`: the `LiveNode` ID of some node which will write the
69 //! variable `V` and which is reachable from `N`. Formally: a node `M`
70 //! such that there exists a path `P` from `N` to `M` and `M` writes
71 //! `V`. If the `writer` is `None`, then there is no writer
72 //! of `V` that follows `N`.
74 //! - `used`: a boolean value indicating whether `V` is *used*. We
75 //! distinguish a *read* from a *use* in that a *use* is some read that
76 //! is not just used to generate a new value. For example, `x += 1` is
77 //! a read but not a use. This is used to generate better warnings.
79 //! ## Special nodes and variables
81 //! We generate various special nodes for various, well, special purposes.
82 //! These are described in the `Liveness` struct.
84 use self::LiveNodeKind
::*;
87 use rustc_ast
::InlineAsmOptions
;
88 use rustc_data_structures
::fx
::FxIndexMap
;
89 use rustc_errors
::Applicability
;
91 use rustc_hir
::def
::*;
92 use rustc_hir
::def_id
::LocalDefId
;
93 use rustc_hir
::intravisit
::{self, Visitor}
;
94 use rustc_hir
::{Expr, HirId, HirIdMap, HirIdSet}
;
95 use rustc_index
::vec
::IndexVec
;
96 use rustc_middle
::hir
::nested_filter
;
97 use rustc_middle
::ty
::query
::Providers
;
98 use rustc_middle
::ty
::{self, DefIdTree, RootVariableMinCaptureList, Ty, TyCtxt}
;
99 use rustc_session
::lint
;
100 use rustc_span
::symbol
::{kw, sym, Symbol}
;
101 use rustc_span
::Span
;
103 use std
::collections
::VecDeque
;
105 use std
::io
::prelude
::*;
110 rustc_index
::newtype_index
! {
111 pub struct Variable
{
112 DEBUG_FORMAT
= "v({})",
116 rustc_index
::newtype_index
! {
117 pub struct LiveNode
{
118 DEBUG_FORMAT
= "ln({})",
122 #[derive(Copy, Clone, PartialEq, Debug)]
125 ExprNode(Span
, HirId
),
126 VarDefNode(Span
, HirId
),
131 fn live_node_kind_to_string(lnk
: LiveNodeKind
, tcx
: TyCtxt
<'_
>) -> String
{
132 let sm
= tcx
.sess
.source_map();
134 UpvarNode(s
) => format
!("Upvar node [{}]", sm
.span_to_diagnostic_string(s
)),
135 ExprNode(s
, _
) => format
!("Expr node [{}]", sm
.span_to_diagnostic_string(s
)),
136 VarDefNode(s
, _
) => format
!("Var def node [{}]", sm
.span_to_diagnostic_string(s
)),
137 ClosureNode
=> "Closure node".to_owned(),
138 ExitNode
=> "Exit node".to_owned(),
142 fn check_mod_liveness(tcx
: TyCtxt
<'_
>, module_def_id
: LocalDefId
) {
143 tcx
.hir().visit_item_likes_in_module(module_def_id
, &mut IrMaps
::new(tcx
).as_deep_visitor());
146 pub fn provide(providers
: &mut Providers
) {
147 *providers
= Providers { check_mod_liveness, ..*providers }
;
150 // ______________________________________________________________________
153 // This is the first pass and the one that drives the main
154 // computation. It walks up and down the IR once. On the way down,
155 // we count for each function the number of variables as well as
156 // liveness nodes. A liveness node is basically an expression or
157 // capture clause that does something of interest: either it has
158 // interesting control flow or it uses/defines a local variable.
160 // On the way back up, at each function node we create liveness sets
161 // (we now know precisely how big to make our various vectors and so
162 // forth) and then do the data-flow propagation to compute the set
163 // of live variables at each program point.
165 // Finally, we run back over the IR one last time and, using the
166 // computed liveness, check various safety conditions. For example,
167 // there must be no live nodes at the definition site for a variable
168 // unless it has an initializer. Similarly, each non-mutable local
169 // variable must not be assigned if there is some successor
170 // assignment. And so forth.
177 #[derive(Copy, Clone, Debug)]
184 #[derive(Copy, Clone, Debug)]
186 Param(HirId
, Symbol
),
188 Upvar(HirId
, Symbol
),
191 struct IrMaps
<'tcx
> {
193 live_node_map
: HirIdMap
<LiveNode
>,
194 variable_map
: HirIdMap
<Variable
>,
195 capture_info_map
: HirIdMap
<Rc
<Vec
<CaptureInfo
>>>,
196 var_kinds
: IndexVec
<Variable
, VarKind
>,
197 lnks
: IndexVec
<LiveNode
, LiveNodeKind
>,
200 impl<'tcx
> IrMaps
<'tcx
> {
201 fn new(tcx
: TyCtxt
<'tcx
>) -> IrMaps
<'tcx
> {
204 live_node_map
: HirIdMap
::default(),
205 variable_map
: HirIdMap
::default(),
206 capture_info_map
: Default
::default(),
207 var_kinds
: IndexVec
::new(),
208 lnks
: IndexVec
::new(),
212 fn add_live_node(&mut self, lnk
: LiveNodeKind
) -> LiveNode
{
213 let ln
= self.lnks
.push(lnk
);
215 debug
!("{:?} is of kind {}", ln
, live_node_kind_to_string(lnk
, self.tcx
));
220 fn add_live_node_for_node(&mut self, hir_id
: HirId
, lnk
: LiveNodeKind
) {
221 let ln
= self.add_live_node(lnk
);
222 self.live_node_map
.insert(hir_id
, ln
);
224 debug
!("{:?} is node {:?}", ln
, hir_id
);
227 fn add_variable(&mut self, vk
: VarKind
) -> Variable
{
228 let v
= self.var_kinds
.push(vk
);
231 Local(LocalInfo { id: node_id, .. }
) | Param(node_id
, _
) | Upvar(node_id
, _
) => {
232 self.variable_map
.insert(node_id
, v
);
236 debug
!("{:?} is {:?}", v
, vk
);
241 fn variable(&self, hir_id
: HirId
, span
: Span
) -> Variable
{
242 match self.variable_map
.get(&hir_id
) {
245 span_bug
!(span
, "no variable registered for id {:?}", hir_id
);
250 fn variable_name(&self, var
: Variable
) -> Symbol
{
251 match self.var_kinds
[var
] {
252 Local(LocalInfo { name, .. }
) | Param(_
, name
) | Upvar(_
, name
) => name
,
256 fn variable_is_shorthand(&self, var
: Variable
) -> bool
{
257 match self.var_kinds
[var
] {
258 Local(LocalInfo { is_shorthand, .. }
) => is_shorthand
,
259 Param(..) | Upvar(..) => false,
263 fn set_captures(&mut self, hir_id
: HirId
, cs
: Vec
<CaptureInfo
>) {
264 self.capture_info_map
.insert(hir_id
, Rc
::new(cs
));
267 fn collect_shorthand_field_ids(&self, pat
: &hir
::Pat
<'tcx
>) -> HirIdSet
{
268 // For struct patterns, take note of which fields used shorthand
269 // (`x` rather than `x: x`).
270 let mut shorthand_field_ids
= HirIdSet
::default();
271 let mut pats
= VecDeque
::new();
274 while let Some(pat
) = pats
.pop_front() {
275 use rustc_hir
::PatKind
::*;
277 Binding(.., inner_pat
) => {
278 pats
.extend(inner_pat
.iter());
280 Struct(_
, fields
, _
) => {
281 let (short
, not_short
): (Vec
<&_
>, Vec
<&_
>) =
282 fields
.iter().partition(|f
| f
.is_shorthand
);
283 shorthand_field_ids
.extend(short
.iter().map(|f
| f
.pat
.hir_id
));
284 pats
.extend(not_short
.iter().map(|f
| f
.pat
));
286 Ref(inner_pat
, _
) | Box(inner_pat
) => {
287 pats
.push_back(inner_pat
);
289 TupleStruct(_
, inner_pats
, _
) | Tuple(inner_pats
, _
) | Or(inner_pats
) => {
290 pats
.extend(inner_pats
.iter());
292 Slice(pre_pats
, inner_pat
, post_pats
) => {
293 pats
.extend(pre_pats
.iter());
294 pats
.extend(inner_pat
.iter());
295 pats
.extend(post_pats
.iter());
301 return shorthand_field_ids
;
304 fn add_from_pat(&mut self, pat
: &hir
::Pat
<'tcx
>) {
305 let shorthand_field_ids
= self.collect_shorthand_field_ids(pat
);
307 pat
.each_binding(|_
, hir_id
, _
, ident
| {
308 self.add_live_node_for_node(hir_id
, VarDefNode(ident
.span
, hir_id
));
309 self.add_variable(Local(LocalInfo
{
312 is_shorthand
: shorthand_field_ids
.contains(&hir_id
),
318 impl<'tcx
> Visitor
<'tcx
> for IrMaps
<'tcx
> {
319 type NestedFilter
= nested_filter
::OnlyBodies
;
321 fn nested_visit_map(&mut self) -> Self::Map
{
325 fn visit_body(&mut self, body
: &'tcx hir
::Body
<'tcx
>) {
326 debug
!("visit_body {:?}", body
.id());
328 // swap in a new set of IR maps for this body
329 let mut maps
= IrMaps
::new(self.tcx
);
330 let hir_id
= maps
.tcx
.hir().body_owner(body
.id());
331 let local_def_id
= maps
.tcx
.hir().local_def_id(hir_id
);
332 let def_id
= local_def_id
.to_def_id();
334 // Don't run unused pass for #[derive()]
335 if let Some(parent
) = self.tcx
.parent(def_id
) {
336 if let DefKind
::Impl
= self.tcx
.def_kind(parent
.expect_local()) {
337 if self.tcx
.has_attr(parent
, sym
::automatically_derived
) {
343 // Don't run unused pass for #[naked]
344 if self.tcx
.has_attr(def_id
, sym
::naked
) {
348 if let Some(upvars
) = maps
.tcx
.upvars_mentioned(def_id
) {
349 for &var_hir_id
in upvars
.keys() {
350 let var_name
= maps
.tcx
.hir().name(var_hir_id
);
351 maps
.add_variable(Upvar(var_hir_id
, var_name
));
355 // gather up the various local variables, significant expressions,
357 intravisit
::walk_body(&mut maps
, body
);
360 let mut lsets
= Liveness
::new(&mut maps
, local_def_id
);
361 let entry_ln
= lsets
.compute(&body
, hir_id
);
362 lsets
.log_liveness(entry_ln
, body
.id().hir_id
);
364 // check for various error conditions
365 lsets
.visit_body(body
);
366 lsets
.warn_about_unused_upvars(entry_ln
);
367 lsets
.warn_about_unused_args(body
, entry_ln
);
370 fn visit_local(&mut self, local
: &'tcx hir
::Local
<'tcx
>) {
371 self.add_from_pat(&local
.pat
);
372 intravisit
::walk_local(self, local
);
375 fn visit_arm(&mut self, arm
: &'tcx hir
::Arm
<'tcx
>) {
376 self.add_from_pat(&arm
.pat
);
377 if let Some(hir
::Guard
::IfLet(ref pat
, _
)) = arm
.guard
{
378 self.add_from_pat(pat
);
380 intravisit
::walk_arm(self, arm
);
383 fn visit_param(&mut self, param
: &'tcx hir
::Param
<'tcx
>) {
384 let shorthand_field_ids
= self.collect_shorthand_field_ids(param
.pat
);
385 param
.pat
.each_binding(|_bm
, hir_id
, _x
, ident
| {
386 let var
= match param
.pat
.kind
{
387 rustc_hir
::PatKind
::Struct(..) => Local(LocalInfo
{
390 is_shorthand
: shorthand_field_ids
.contains(&hir_id
),
392 _
=> Param(hir_id
, ident
.name
),
394 self.add_variable(var
);
396 intravisit
::walk_param(self, param
);
399 fn visit_expr(&mut self, expr
: &'tcx Expr
<'tcx
>) {
401 // live nodes required for uses or definitions of variables:
402 hir
::ExprKind
::Path(hir
::QPath
::Resolved(_
, ref path
)) => {
403 debug
!("expr {}: path that leads to {:?}", expr
.hir_id
, path
.res
);
404 if let Res
::Local(_var_hir_id
) = path
.res
{
405 self.add_live_node_for_node(expr
.hir_id
, ExprNode(expr
.span
, expr
.hir_id
));
407 intravisit
::walk_expr(self, expr
);
409 hir
::ExprKind
::Closure(..) => {
410 // Interesting control flow (for loops can contain labeled
411 // breaks or continues)
412 self.add_live_node_for_node(expr
.hir_id
, ExprNode(expr
.span
, expr
.hir_id
));
414 // Make a live_node for each mentioned variable, with the span
415 // being the location that the variable is used. This results
416 // in better error messages than just pointing at the closure
417 // construction site.
418 let mut call_caps
= Vec
::new();
419 let closure_def_id
= self.tcx
.hir().local_def_id(expr
.hir_id
);
420 if let Some(upvars
) = self.tcx
.upvars_mentioned(closure_def_id
) {
421 call_caps
.extend(upvars
.keys().map(|var_id
| {
422 let upvar
= upvars
[var_id
];
423 let upvar_ln
= self.add_live_node(UpvarNode(upvar
.span
));
424 CaptureInfo { ln: upvar_ln, var_hid: *var_id }
427 self.set_captures(expr
.hir_id
, call_caps
);
428 intravisit
::walk_expr(self, expr
);
431 hir
::ExprKind
::Let(let_expr
) => {
432 self.add_from_pat(let_expr
.pat
);
433 intravisit
::walk_expr(self, expr
);
436 // live nodes required for interesting control flow:
437 hir
::ExprKind
::If(..)
438 | hir
::ExprKind
::Match(..)
439 | hir
::ExprKind
::Loop(..)
440 | hir
::ExprKind
::Yield(..) => {
441 self.add_live_node_for_node(expr
.hir_id
, ExprNode(expr
.span
, expr
.hir_id
));
442 intravisit
::walk_expr(self, expr
);
444 hir
::ExprKind
::Binary(op
, ..) if op
.node
.is_lazy() => {
445 self.add_live_node_for_node(expr
.hir_id
, ExprNode(expr
.span
, expr
.hir_id
));
446 intravisit
::walk_expr(self, expr
);
449 // otherwise, live nodes are not required:
450 hir
::ExprKind
::Index(..)
451 | hir
::ExprKind
::Field(..)
452 | hir
::ExprKind
::Array(..)
453 | hir
::ExprKind
::Call(..)
454 | hir
::ExprKind
::MethodCall(..)
455 | hir
::ExprKind
::Tup(..)
456 | hir
::ExprKind
::Binary(..)
457 | hir
::ExprKind
::AddrOf(..)
458 | hir
::ExprKind
::Cast(..)
459 | hir
::ExprKind
::DropTemps(..)
460 | hir
::ExprKind
::Unary(..)
461 | hir
::ExprKind
::Break(..)
462 | hir
::ExprKind
::Continue(_
)
463 | hir
::ExprKind
::Lit(_
)
464 | hir
::ExprKind
::ConstBlock(..)
465 | hir
::ExprKind
::Ret(..)
466 | hir
::ExprKind
::Block(..)
467 | hir
::ExprKind
::Assign(..)
468 | hir
::ExprKind
::AssignOp(..)
469 | hir
::ExprKind
::Struct(..)
470 | hir
::ExprKind
::Repeat(..)
471 | hir
::ExprKind
::InlineAsm(..)
472 | hir
::ExprKind
::Box(..)
473 | hir
::ExprKind
::Type(..)
475 | hir
::ExprKind
::Path(hir
::QPath
::TypeRelative(..))
476 | hir
::ExprKind
::Path(hir
::QPath
::LangItem(..)) => {
477 intravisit
::walk_expr(self, expr
);
483 // ______________________________________________________________________
484 // Computing liveness sets
486 // Actually we compute just a bit more than just liveness, but we use
487 // the same basic propagation framework in all cases.
489 const ACC_READ
: u32 = 1;
490 const ACC_WRITE
: u32 = 2;
491 const ACC_USE
: u32 = 4;
493 struct Liveness
<'a
, 'tcx
> {
494 ir
: &'a
mut IrMaps
<'tcx
>,
495 typeck_results
: &'a ty
::TypeckResults
<'tcx
>,
496 param_env
: ty
::ParamEnv
<'tcx
>,
497 closure_min_captures
: Option
<&'tcx RootVariableMinCaptureList
<'tcx
>>,
498 successors
: IndexVec
<LiveNode
, Option
<LiveNode
>>,
499 rwu_table
: rwu_table
::RWUTable
,
501 /// A live node representing a point of execution before closure entry &
502 /// after closure exit. Used to calculate liveness of captured variables
503 /// through calls to the same closure. Used for Fn & FnMut closures only.
504 closure_ln
: LiveNode
,
505 /// A live node representing every 'exit' from the function, whether it be
506 /// by explicit return, panic, or other means.
509 // mappings from loop node ID to LiveNode
510 // ("break" label should map to loop node ID,
511 // it probably doesn't now)
512 break_ln
: HirIdMap
<LiveNode
>,
513 cont_ln
: HirIdMap
<LiveNode
>,
516 impl<'a
, 'tcx
> Liveness
<'a
, 'tcx
> {
517 fn new(ir
: &'a
mut IrMaps
<'tcx
>, body_owner
: LocalDefId
) -> Liveness
<'a
, 'tcx
> {
518 let typeck_results
= ir
.tcx
.typeck(body_owner
);
519 let param_env
= ir
.tcx
.param_env(body_owner
);
520 let closure_min_captures
= typeck_results
.closure_min_captures
.get(&body_owner
.to_def_id());
521 let closure_ln
= ir
.add_live_node(ClosureNode
);
522 let exit_ln
= ir
.add_live_node(ExitNode
);
524 let num_live_nodes
= ir
.lnks
.len();
525 let num_vars
= ir
.var_kinds
.len();
531 closure_min_captures
,
532 successors
: IndexVec
::from_elem_n(None
, num_live_nodes
),
533 rwu_table
: rwu_table
::RWUTable
::new(num_live_nodes
, num_vars
),
536 break_ln
: Default
::default(),
537 cont_ln
: Default
::default(),
541 fn live_node(&self, hir_id
: HirId
, span
: Span
) -> LiveNode
{
542 match self.ir
.live_node_map
.get(&hir_id
) {
545 // This must be a mismatch between the ir_map construction
546 // above and the propagation code below; the two sets of
547 // code have to agree about which AST nodes are worth
548 // creating liveness nodes for.
549 span_bug
!(span
, "no live node registered for node {:?}", hir_id
);
554 fn variable(&self, hir_id
: HirId
, span
: Span
) -> Variable
{
555 self.ir
.variable(hir_id
, span
)
558 fn define_bindings_in_pat(&mut self, pat
: &hir
::Pat
<'_
>, mut succ
: LiveNode
) -> LiveNode
{
559 // In an or-pattern, only consider the first pattern; any later patterns
560 // must have the same bindings, and we also consider the first pattern
561 // to be the "authoritative" set of ids.
562 pat
.each_binding_or_first(&mut |_
, hir_id
, pat_sp
, ident
| {
563 let ln
= self.live_node(hir_id
, pat_sp
);
564 let var
= self.variable(hir_id
, ident
.span
);
565 self.init_from_succ(ln
, succ
);
566 self.define(ln
, var
);
572 fn live_on_entry(&self, ln
: LiveNode
, var
: Variable
) -> bool
{
573 self.rwu_table
.get_reader(ln
, var
)
576 // Is this variable live on entry to any of its successor nodes?
577 fn live_on_exit(&self, ln
: LiveNode
, var
: Variable
) -> bool
{
578 let successor
= self.successors
[ln
].unwrap();
579 self.live_on_entry(successor
, var
)
582 fn used_on_entry(&self, ln
: LiveNode
, var
: Variable
) -> bool
{
583 self.rwu_table
.get_used(ln
, var
)
586 fn assigned_on_entry(&self, ln
: LiveNode
, var
: Variable
) -> bool
{
587 self.rwu_table
.get_writer(ln
, var
)
590 fn assigned_on_exit(&self, ln
: LiveNode
, var
: Variable
) -> bool
{
591 let successor
= self.successors
[ln
].unwrap();
592 self.assigned_on_entry(successor
, var
)
595 fn write_vars
<F
>(&self, wr
: &mut dyn Write
, mut test
: F
) -> io
::Result
<()>
597 F
: FnMut(Variable
) -> bool
,
599 for var_idx
in 0..self.ir
.var_kinds
.len() {
600 let var
= Variable
::from(var_idx
);
602 write
!(wr
, " {:?}", var
)?
;
608 #[allow(unused_must_use)]
609 fn ln_str(&self, ln
: LiveNode
) -> String
{
610 let mut wr
= Vec
::new();
612 let wr
= &mut wr
as &mut dyn Write
;
613 write
!(wr
, "[{:?} of kind {:?} reads", ln
, self.ir
.lnks
[ln
]);
614 self.write_vars(wr
, |var
| self.rwu_table
.get_reader(ln
, var
));
615 write
!(wr
, " writes");
616 self.write_vars(wr
, |var
| self.rwu_table
.get_writer(ln
, var
));
618 self.write_vars(wr
, |var
| self.rwu_table
.get_used(ln
, var
));
620 write
!(wr
, " precedes {:?}]", self.successors
[ln
]);
622 String
::from_utf8(wr
).unwrap()
625 fn log_liveness(&self, entry_ln
: LiveNode
, hir_id
: hir
::HirId
) {
626 // hack to skip the loop unless debug! is enabled:
628 "^^ liveness computation results for body {} (entry={:?})",
630 for ln_idx
in 0..self.ir
.lnks
.len() {
631 debug
!("{:?}", self.ln_str(LiveNode
::from(ln_idx
)));
639 fn init_empty(&mut self, ln
: LiveNode
, succ_ln
: LiveNode
) {
640 self.successors
[ln
] = Some(succ_ln
);
642 // It is not necessary to initialize the RWUs here because they are all
643 // empty when created, and the sets only grow during iterations.
646 fn init_from_succ(&mut self, ln
: LiveNode
, succ_ln
: LiveNode
) {
647 // more efficient version of init_empty() / merge_from_succ()
648 self.successors
[ln
] = Some(succ_ln
);
649 self.rwu_table
.copy(ln
, succ_ln
);
650 debug
!("init_from_succ(ln={}, succ={})", self.ln_str(ln
), self.ln_str(succ_ln
));
653 fn merge_from_succ(&mut self, ln
: LiveNode
, succ_ln
: LiveNode
) -> bool
{
658 let changed
= self.rwu_table
.union(ln
, succ_ln
);
659 debug
!("merge_from_succ(ln={:?}, succ={}, changed={})", ln
, self.ln_str(succ_ln
), changed
);
663 // Indicates that a local variable was *defined*; we know that no
664 // uses of the variable can precede the definition (resolve checks
665 // this) so we just clear out all the data.
666 fn define(&mut self, writer
: LiveNode
, var
: Variable
) {
667 let used
= self.rwu_table
.get_used(writer
, var
);
668 self.rwu_table
.set(writer
, var
, rwu_table
::RWU { reader: false, writer: false, used }
);
669 debug
!("{:?} defines {:?}: {}", writer
, var
, self.ln_str(writer
));
672 // Either read, write, or both depending on the acc bitset
673 fn acc(&mut self, ln
: LiveNode
, var
: Variable
, acc
: u32) {
674 debug
!("{:?} accesses[{:x}] {:?}: {}", ln
, acc
, var
, self.ln_str(ln
));
676 let mut rwu
= self.rwu_table
.get(ln
, var
);
678 if (acc
& ACC_WRITE
) != 0 {
683 // Important: if we both read/write, must do read second
684 // or else the write will override.
685 if (acc
& ACC_READ
) != 0 {
689 if (acc
& ACC_USE
) != 0 {
693 self.rwu_table
.set(ln
, var
, rwu
);
696 fn compute(&mut self, body
: &hir
::Body
<'_
>, hir_id
: HirId
) -> LiveNode
{
697 debug
!("compute: for body {:?}", body
.id().hir_id
);
699 // # Liveness of captured variables
701 // When computing the liveness for captured variables we take into
702 // account how variable is captured (ByRef vs ByValue) and what is the
703 // closure kind (Generator / FnOnce vs Fn / FnMut).
705 // Variables captured by reference are assumed to be used on the exit
708 // In FnOnce closures, variables captured by value are known to be dead
709 // on exit since it is impossible to call the closure again.
711 // In Fn / FnMut closures, variables captured by value are live on exit
712 // if they are live on the entry to the closure, since only the closure
713 // itself can access them on subsequent calls.
715 if let Some(closure_min_captures
) = self.closure_min_captures
{
716 // Mark upvars captured by reference as used after closure exits.
717 for (&var_hir_id
, min_capture_list
) in closure_min_captures
{
718 for captured_place
in min_capture_list
{
719 match captured_place
.info
.capture_kind
{
720 ty
::UpvarCapture
::ByRef(_
) => {
721 let var
= self.variable(
723 captured_place
.get_capture_kind_span(self.ir
.tcx
),
725 self.acc(self.exit_ln
, var
, ACC_READ
| ACC_USE
);
727 ty
::UpvarCapture
::ByValue
=> {}
733 let succ
= self.propagate_through_expr(&body
.value
, self.exit_ln
);
735 if self.closure_min_captures
.is_none() {
736 // Either not a closure, or closure without any captured variables.
737 // No need to determine liveness of captured variables, since there
742 let ty
= self.typeck_results
.node_type(hir_id
);
744 ty
::Closure(_def_id
, substs
) => match substs
.as_closure().kind() {
745 ty
::ClosureKind
::Fn
=> {}
746 ty
::ClosureKind
::FnMut
=> {}
747 ty
::ClosureKind
::FnOnce
=> return succ
,
749 ty
::Generator(..) => return succ
,
753 "{} has upvars so it should have a closure type: {:?}",
760 // Propagate through calls to the closure.
762 self.init_from_succ(self.closure_ln
, succ
);
763 for param
in body
.params
{
764 param
.pat
.each_binding(|_bm
, hir_id
, _x
, ident
| {
765 let var
= self.variable(hir_id
, ident
.span
);
766 self.define(self.closure_ln
, var
);
770 if !self.merge_from_succ(self.exit_ln
, self.closure_ln
) {
773 assert_eq
!(succ
, self.propagate_through_expr(&body
.value
, self.exit_ln
));
779 fn propagate_through_block(&mut self, blk
: &hir
::Block
<'_
>, succ
: LiveNode
) -> LiveNode
{
780 if blk
.targeted_by_break
{
781 self.break_ln
.insert(blk
.hir_id
, succ
);
783 let succ
= self.propagate_through_opt_expr(blk
.expr
, succ
);
784 blk
.stmts
.iter().rev().fold(succ
, |succ
, stmt
| self.propagate_through_stmt(stmt
, succ
))
787 fn propagate_through_stmt(&mut self, stmt
: &hir
::Stmt
<'_
>, succ
: LiveNode
) -> LiveNode
{
789 hir
::StmtKind
::Local(ref local
) => {
790 // Note: we mark the variable as defined regardless of whether
791 // there is an initializer. Initially I had thought to only mark
792 // the live variable as defined if it was initialized, and then we
793 // could check for uninit variables just by scanning what is live
794 // at the start of the function. But that doesn't work so well for
795 // immutable variables defined in a loop:
796 // loop { let x; x = 5; }
797 // because the "assignment" loops back around and generates an error.
799 // So now we just check that variables defined w/o an
800 // initializer are not live at the point of their
801 // initialization, which is mildly more complex than checking
802 // once at the func header but otherwise equivalent.
804 let succ
= self.propagate_through_opt_expr(local
.init
, succ
);
805 self.define_bindings_in_pat(&local
.pat
, succ
)
807 hir
::StmtKind
::Item(..) => succ
,
808 hir
::StmtKind
::Expr(ref expr
) | hir
::StmtKind
::Semi(ref expr
) => {
809 self.propagate_through_expr(&expr
, succ
)
814 fn propagate_through_exprs(&mut self, exprs
: &[Expr
<'_
>], succ
: LiveNode
) -> LiveNode
{
815 exprs
.iter().rev().fold(succ
, |succ
, expr
| self.propagate_through_expr(&expr
, succ
))
818 fn propagate_through_opt_expr(
820 opt_expr
: Option
<&Expr
<'_
>>,
823 opt_expr
.map_or(succ
, |expr
| self.propagate_through_expr(expr
, succ
))
826 fn propagate_through_expr(&mut self, expr
: &Expr
<'_
>, succ
: LiveNode
) -> LiveNode
{
827 debug
!("propagate_through_expr: {:?}", expr
);
830 // Interesting cases with control flow or which gen/kill
831 hir
::ExprKind
::Path(hir
::QPath
::Resolved(_
, ref path
)) => {
832 self.access_path(expr
.hir_id
, path
, succ
, ACC_READ
| ACC_USE
)
835 hir
::ExprKind
::Field(ref e
, _
) => self.propagate_through_expr(&e
, succ
),
837 hir
::ExprKind
::Closure(..) => {
838 debug
!("{:?} is an ExprKind::Closure", expr
);
840 // the construction of a closure itself is not important,
841 // but we have to consider the closed over variables.
847 .unwrap_or_else(|| span_bug
!(expr
.span
, "no registered caps"));
849 caps
.iter().rev().fold(succ
, |succ
, cap
| {
850 self.init_from_succ(cap
.ln
, succ
);
851 let var
= self.variable(cap
.var_hid
, expr
.span
);
852 self.acc(cap
.ln
, var
, ACC_READ
| ACC_USE
);
857 hir
::ExprKind
::Let(let_expr
) => {
858 let succ
= self.propagate_through_expr(let_expr
.init
, succ
);
859 self.define_bindings_in_pat(let_expr
.pat
, succ
)
862 // Note that labels have been resolved, so we don't need to look
863 // at the label ident
864 hir
::ExprKind
::Loop(ref blk
, ..) => self.propagate_through_loop(expr
, &blk
, succ
),
866 hir
::ExprKind
::Yield(ref e
, ..) => {
867 let yield_ln
= self.live_node(expr
.hir_id
, expr
.span
);
868 self.init_from_succ(yield_ln
, succ
);
869 self.merge_from_succ(yield_ln
, self.exit_ln
);
870 self.propagate_through_expr(e
, yield_ln
)
873 hir
::ExprKind
::If(ref cond
, ref then
, ref else_opt
) => {
888 self.propagate_through_opt_expr(else_opt
.as_ref().map(|e
| &**e
), succ
);
889 let then_ln
= self.propagate_through_expr(&then
, succ
);
890 let ln
= self.live_node(expr
.hir_id
, expr
.span
);
891 self.init_from_succ(ln
, else_ln
);
892 self.merge_from_succ(ln
, then_ln
);
893 self.propagate_through_expr(&cond
, ln
)
896 hir
::ExprKind
::Match(ref e
, arms
, _
) => {
911 let ln
= self.live_node(expr
.hir_id
, expr
.span
);
912 self.init_empty(ln
, succ
);
914 let body_succ
= self.propagate_through_expr(&arm
.body
, succ
);
916 let guard_succ
= arm
.guard
.as_ref().map_or(body_succ
, |g
| match g
{
917 hir
::Guard
::If(e
) => self.propagate_through_expr(e
, body_succ
),
918 hir
::Guard
::IfLet(pat
, e
) => {
919 let let_bind
= self.define_bindings_in_pat(pat
, body_succ
);
920 self.propagate_through_expr(e
, let_bind
)
923 let arm_succ
= self.define_bindings_in_pat(&arm
.pat
, guard_succ
);
924 self.merge_from_succ(ln
, arm_succ
);
926 self.propagate_through_expr(&e
, ln
)
929 hir
::ExprKind
::Ret(ref o_e
) => {
930 // Ignore succ and subst exit_ln.
931 self.propagate_through_opt_expr(o_e
.as_ref().map(|e
| &**e
), self.exit_ln
)
934 hir
::ExprKind
::Break(label
, ref opt_expr
) => {
935 // Find which label this break jumps to
936 let target
= match label
.target_id
{
937 Ok(hir_id
) => self.break_ln
.get(&hir_id
),
938 Err(err
) => span_bug
!(expr
.span
, "loop scope error: {}", err
),
942 // Now that we know the label we're going to,
943 // look it up in the break loop nodes table
946 Some(b
) => self.propagate_through_opt_expr(opt_expr
.as_ref().map(|e
| &**e
), b
),
947 None
=> span_bug
!(expr
.span
, "`break` to unknown label"),
951 hir
::ExprKind
::Continue(label
) => {
952 // Find which label this expr continues to
955 .unwrap_or_else(|err
| span_bug
!(expr
.span
, "loop scope error: {}", err
));
957 // Now that we know the label we're going to,
958 // look it up in the continue loop nodes table
962 .unwrap_or_else(|| span_bug
!(expr
.span
, "continue to unknown label"))
965 hir
::ExprKind
::Assign(ref l
, ref r
, _
) => {
966 // see comment on places in
967 // propagate_through_place_components()
968 let succ
= self.write_place(&l
, succ
, ACC_WRITE
);
969 let succ
= self.propagate_through_place_components(&l
, succ
);
970 self.propagate_through_expr(&r
, succ
)
973 hir
::ExprKind
::AssignOp(_
, ref l
, ref r
) => {
974 // an overloaded assign op is like a method call
975 if self.typeck_results
.is_method_call(expr
) {
976 let succ
= self.propagate_through_expr(&l
, succ
);
977 self.propagate_through_expr(&r
, succ
)
979 // see comment on places in
980 // propagate_through_place_components()
981 let succ
= self.write_place(&l
, succ
, ACC_WRITE
| ACC_READ
);
982 let succ
= self.propagate_through_expr(&r
, succ
);
983 self.propagate_through_place_components(&l
, succ
)
987 // Uninteresting cases: just propagate in rev exec order
988 hir
::ExprKind
::Array(ref exprs
) => self.propagate_through_exprs(exprs
, succ
),
990 hir
::ExprKind
::Struct(_
, ref fields
, ref with_expr
) => {
991 let succ
= self.propagate_through_opt_expr(with_expr
.as_ref().map(|e
| &**e
), succ
);
995 .fold(succ
, |succ
, field
| self.propagate_through_expr(&field
.expr
, succ
))
998 hir
::ExprKind
::Call(ref f
, ref args
) => {
999 let succ
= self.check_is_ty_uninhabited(expr
, succ
);
1000 let succ
= self.propagate_through_exprs(args
, succ
);
1001 self.propagate_through_expr(&f
, succ
)
1004 hir
::ExprKind
::MethodCall(.., ref args
, _
) => {
1005 let succ
= self.check_is_ty_uninhabited(expr
, succ
);
1006 self.propagate_through_exprs(args
, succ
)
1009 hir
::ExprKind
::Tup(ref exprs
) => self.propagate_through_exprs(exprs
, succ
),
1011 hir
::ExprKind
::Binary(op
, ref l
, ref r
) if op
.node
.is_lazy() => {
1012 let r_succ
= self.propagate_through_expr(&r
, succ
);
1014 let ln
= self.live_node(expr
.hir_id
, expr
.span
);
1015 self.init_from_succ(ln
, succ
);
1016 self.merge_from_succ(ln
, r_succ
);
1018 self.propagate_through_expr(&l
, ln
)
1021 hir
::ExprKind
::Index(ref l
, ref r
) | hir
::ExprKind
::Binary(_
, ref l
, ref r
) => {
1022 let r_succ
= self.propagate_through_expr(&r
, succ
);
1023 self.propagate_through_expr(&l
, r_succ
)
1026 hir
::ExprKind
::Box(ref e
)
1027 | hir
::ExprKind
::AddrOf(_
, _
, ref e
)
1028 | hir
::ExprKind
::Cast(ref e
, _
)
1029 | hir
::ExprKind
::Type(ref e
, _
)
1030 | hir
::ExprKind
::DropTemps(ref e
)
1031 | hir
::ExprKind
::Unary(_
, ref e
)
1032 | hir
::ExprKind
::Repeat(ref e
, _
) => self.propagate_through_expr(&e
, succ
),
1034 hir
::ExprKind
::InlineAsm(ref asm
) => {
1035 // Handle non-returning asm
1036 let mut succ
= if asm
.options
.contains(InlineAsmOptions
::NORETURN
) {
1042 // Do a first pass for writing outputs only
1043 for (op
, _op_sp
) in asm
.operands
.iter().rev() {
1045 hir
::InlineAsmOperand
::In { .. }
1046 | hir
::InlineAsmOperand
::Const { .. }
1047 | hir
::InlineAsmOperand
::Sym { .. }
=> {}
1048 hir
::InlineAsmOperand
::Out { expr, .. }
=> {
1049 if let Some(expr
) = expr
{
1050 succ
= self.write_place(expr
, succ
, ACC_WRITE
);
1053 hir
::InlineAsmOperand
::InOut { expr, .. }
=> {
1054 succ
= self.write_place(expr
, succ
, ACC_READ
| ACC_WRITE
| ACC_USE
);
1056 hir
::InlineAsmOperand
::SplitInOut { out_expr, .. }
=> {
1057 if let Some(expr
) = out_expr
{
1058 succ
= self.write_place(expr
, succ
, ACC_WRITE
);
1064 // Then do a second pass for inputs
1065 let mut succ
= succ
;
1066 for (op
, _op_sp
) in asm
.operands
.iter().rev() {
1068 hir
::InlineAsmOperand
::In { expr, .. }
1069 | hir
::InlineAsmOperand
::Sym { expr, .. }
=> {
1070 succ
= self.propagate_through_expr(expr
, succ
)
1072 hir
::InlineAsmOperand
::Out { expr, .. }
=> {
1073 if let Some(expr
) = expr
{
1074 succ
= self.propagate_through_place_components(expr
, succ
);
1077 hir
::InlineAsmOperand
::InOut { expr, .. }
=> {
1078 succ
= self.propagate_through_place_components(expr
, succ
);
1080 hir
::InlineAsmOperand
::SplitInOut { in_expr, out_expr, .. }
=> {
1081 if let Some(expr
) = out_expr
{
1082 succ
= self.propagate_through_place_components(expr
, succ
);
1084 succ
= self.propagate_through_expr(in_expr
, succ
);
1086 hir
::InlineAsmOperand
::Const { .. }
=> {}
1092 hir
::ExprKind
::Lit(..)
1093 | hir
::ExprKind
::ConstBlock(..)
1094 | hir
::ExprKind
::Err
1095 | hir
::ExprKind
::Path(hir
::QPath
::TypeRelative(..))
1096 | hir
::ExprKind
::Path(hir
::QPath
::LangItem(..)) => succ
,
1098 // Note that labels have been resolved, so we don't need to look
1099 // at the label ident
1100 hir
::ExprKind
::Block(ref blk
, _
) => self.propagate_through_block(&blk
, succ
),
1104 fn propagate_through_place_components(&mut self, expr
: &Expr
<'_
>, succ
: LiveNode
) -> LiveNode
{
1107 // In general, the full flow graph structure for an
1108 // assignment/move/etc can be handled in one of two ways,
1109 // depending on whether what is being assigned is a "tracked
1110 // value" or not. A tracked value is basically a local
1111 // variable or argument.
1113 // The two kinds of graphs are:
1115 // Tracked place Untracked place
1116 // ----------------------++-----------------------
1120 // (rvalue) || (rvalue)
1123 // (write of place) || (place components)
1128 // ----------------------++-----------------------
1130 // I will cover the two cases in turn:
1134 // A tracked place is a local variable/argument `x`. In
1135 // these cases, the link_node where the write occurs is linked
1136 // to node id of `x`. The `write_place()` routine generates
1137 // the contents of this node. There are no subcomponents to
1140 // # Non-tracked places
1142 // These are places like `x[5]` or `x.f`. In that case, we
1143 // basically ignore the value which is written to but generate
1144 // reads for the components---`x` in these two examples. The
1145 // components reads are generated by
1146 // `propagate_through_place_components()` (this fn).
1150 // It is still possible to observe assignments to non-places;
1151 // these errors are detected in the later pass borrowck. We
1152 // just ignore such cases and treat them as reads.
1155 hir
::ExprKind
::Path(_
) => succ
,
1156 hir
::ExprKind
::Field(ref e
, _
) => self.propagate_through_expr(&e
, succ
),
1157 _
=> self.propagate_through_expr(expr
, succ
),
1161 // see comment on propagate_through_place()
1162 fn write_place(&mut self, expr
: &Expr
<'_
>, succ
: LiveNode
, acc
: u32) -> LiveNode
{
1164 hir
::ExprKind
::Path(hir
::QPath
::Resolved(_
, ref path
)) => {
1165 self.access_path(expr
.hir_id
, path
, succ
, acc
)
1168 // We do not track other places, so just propagate through
1169 // to their subcomponents. Also, it may happen that
1170 // non-places occur here, because those are detected in the
1171 // later pass borrowck.
1184 let ln
= self.live_node(hir_id
, span
);
1186 self.init_from_succ(ln
, succ
);
1187 let var
= self.variable(var_hid
, span
);
1188 self.acc(ln
, var
, acc
);
1196 path
: &hir
::Path
<'_
>,
1201 Res
::Local(hid
) => self.access_var(hir_id
, hid
, succ
, acc
, path
.span
),
1206 fn propagate_through_loop(
1209 body
: &hir
::Block
<'_
>,
1213 We model control flow like this:
1220 Note that a `continue` expression targeting the `loop` will have a successor of `expr`.
1221 Meanwhile, a `break` expression will have a successor of `succ`.
1225 let ln
= self.live_node(expr
.hir_id
, expr
.span
);
1226 self.init_empty(ln
, succ
);
1227 debug
!("propagate_through_loop: using id for loop body {} {:?}", expr
.hir_id
, body
);
1229 self.break_ln
.insert(expr
.hir_id
, succ
);
1231 self.cont_ln
.insert(expr
.hir_id
, ln
);
1233 let body_ln
= self.propagate_through_block(body
, ln
);
1235 // repeat until fixed point is reached:
1236 while self.merge_from_succ(ln
, body_ln
) {
1237 assert_eq
!(body_ln
, self.propagate_through_block(body
, ln
));
1243 fn check_is_ty_uninhabited(&mut self, expr
: &Expr
<'_
>, succ
: LiveNode
) -> LiveNode
{
1244 let ty
= self.typeck_results
.expr_ty(expr
);
1245 let m
= self.ir
.tcx
.parent_module(expr
.hir_id
).to_def_id();
1246 if self.ir
.tcx
.is_ty_uninhabited_from(m
, ty
, self.param_env
) {
1247 match self.ir
.lnks
[succ
] {
1248 LiveNodeKind
::ExprNode(succ_span
, succ_id
) => {
1249 self.warn_about_unreachable(expr
.span
, ty
, succ_span
, succ_id
, "expression");
1251 LiveNodeKind
::VarDefNode(succ_span
, succ_id
) => {
1252 self.warn_about_unreachable(expr
.span
, ty
, succ_span
, succ_id
, "definition");
1262 fn warn_about_unreachable(
1270 if !orig_ty
.is_never() {
1271 // Unreachable code warnings are already emitted during type checking.
1272 // However, during type checking, full type information is being
1273 // calculated but not yet available, so the check for diverging
1274 // expressions due to uninhabited result types is pretty crude and
1275 // only checks whether ty.is_never(). Here, we have full type
1276 // information available and can issue warnings for less obviously
1277 // uninhabited types (e.g. empty enums). The check above is used so
1278 // that we do not emit the same warning twice if the uninhabited type
1281 self.ir
.tcx
.struct_span_lint_hir(
1282 lint
::builtin
::UNREACHABLE_CODE
,
1286 let msg
= format
!("unreachable {}", descr
);
1288 .span_label(expr_span
, &msg
)
1289 .span_label(orig_span
, "any code following this expression is unreachable")
1293 "this expression has type `{}`, which is uninhabited",
1304 // _______________________________________________________________________
1305 // Checking for error conditions
1307 impl<'a
, 'tcx
> Visitor
<'tcx
> for Liveness
<'a
, 'tcx
> {
1308 fn visit_local(&mut self, local
: &'tcx hir
::Local
<'tcx
>) {
1309 self.check_unused_vars_in_pat(&local
.pat
, None
, |spans
, hir_id
, ln
, var
| {
1310 if local
.init
.is_some() {
1311 self.warn_about_dead_assign(spans
, hir_id
, ln
, var
);
1315 intravisit
::walk_local(self, local
);
1318 fn visit_expr(&mut self, ex
: &'tcx Expr
<'tcx
>) {
1319 check_expr(self, ex
);
1320 intravisit
::walk_expr(self, ex
);
1323 fn visit_arm(&mut self, arm
: &'tcx hir
::Arm
<'tcx
>) {
1324 self.check_unused_vars_in_pat(&arm
.pat
, None
, |_
, _
, _
, _
| {}
);
1325 intravisit
::walk_arm(self, arm
);
1329 fn check_expr
<'tcx
>(this
: &mut Liveness
<'_
, 'tcx
>, expr
: &'tcx Expr
<'tcx
>) {
1331 hir
::ExprKind
::Assign(ref l
, ..) => {
1332 this
.check_place(&l
);
1335 hir
::ExprKind
::AssignOp(_
, ref l
, _
) => {
1336 if !this
.typeck_results
.is_method_call(expr
) {
1337 this
.check_place(&l
);
1341 hir
::ExprKind
::InlineAsm(ref asm
) => {
1342 for (op
, _op_sp
) in asm
.operands
{
1344 hir
::InlineAsmOperand
::Out { expr, .. }
=> {
1345 if let Some(expr
) = expr
{
1346 this
.check_place(expr
);
1349 hir
::InlineAsmOperand
::InOut { expr, .. }
=> {
1350 this
.check_place(expr
);
1352 hir
::InlineAsmOperand
::SplitInOut { out_expr, .. }
=> {
1353 if let Some(out_expr
) = out_expr
{
1354 this
.check_place(out_expr
);
1362 hir
::ExprKind
::Let(let_expr
) => {
1363 this
.check_unused_vars_in_pat(let_expr
.pat
, None
, |_
, _
, _
, _
| {}
);
1366 // no correctness conditions related to liveness
1367 hir
::ExprKind
::Call(..)
1368 | hir
::ExprKind
::MethodCall(..)
1369 | hir
::ExprKind
::Match(..)
1370 | hir
::ExprKind
::Loop(..)
1371 | hir
::ExprKind
::Index(..)
1372 | hir
::ExprKind
::Field(..)
1373 | hir
::ExprKind
::Array(..)
1374 | hir
::ExprKind
::Tup(..)
1375 | hir
::ExprKind
::Binary(..)
1376 | hir
::ExprKind
::Cast(..)
1377 | hir
::ExprKind
::If(..)
1378 | hir
::ExprKind
::DropTemps(..)
1379 | hir
::ExprKind
::Unary(..)
1380 | hir
::ExprKind
::Ret(..)
1381 | hir
::ExprKind
::Break(..)
1382 | hir
::ExprKind
::Continue(..)
1383 | hir
::ExprKind
::Lit(_
)
1384 | hir
::ExprKind
::ConstBlock(..)
1385 | hir
::ExprKind
::Block(..)
1386 | hir
::ExprKind
::AddrOf(..)
1387 | hir
::ExprKind
::Struct(..)
1388 | hir
::ExprKind
::Repeat(..)
1389 | hir
::ExprKind
::Closure(..)
1390 | hir
::ExprKind
::Path(_
)
1391 | hir
::ExprKind
::Yield(..)
1392 | hir
::ExprKind
::Box(..)
1393 | hir
::ExprKind
::Type(..)
1394 | hir
::ExprKind
::Err
=> {}
1398 impl<'tcx
> Liveness
<'_
, 'tcx
> {
1399 fn check_place(&mut self, expr
: &'tcx Expr
<'tcx
>) {
1401 hir
::ExprKind
::Path(hir
::QPath
::Resolved(_
, ref path
)) => {
1402 if let Res
::Local(var_hid
) = path
.res
{
1403 // Assignment to an immutable variable or argument: only legal
1404 // if there is no later assignment. If this local is actually
1405 // mutable, then check for a reassignment to flag the mutability
1407 let ln
= self.live_node(expr
.hir_id
, expr
.span
);
1408 let var
= self.variable(var_hid
, expr
.span
);
1409 self.warn_about_dead_assign(vec
![expr
.span
], expr
.hir_id
, ln
, var
);
1413 // For other kinds of places, no checks are required,
1414 // and any embedded expressions are actually rvalues
1415 intravisit
::walk_expr(self, expr
);
1420 fn should_warn(&self, var
: Variable
) -> Option
<String
> {
1421 let name
= self.ir
.variable_name(var
);
1422 if name
== kw
::Empty
{
1425 let name
= name
.as_str();
1426 if name
.as_bytes()[0] == b'_'
{
1429 Some(name
.to_owned())
1432 fn warn_about_unused_upvars(&self, entry_ln
: LiveNode
) {
1433 let closure_min_captures
= match self.closure_min_captures
{
1435 Some(closure_min_captures
) => closure_min_captures
,
1438 // If closure_min_captures is Some(), upvars must be Some() too.
1439 for (&var_hir_id
, min_capture_list
) in closure_min_captures
{
1440 for captured_place
in min_capture_list
{
1441 match captured_place
.info
.capture_kind
{
1442 ty
::UpvarCapture
::ByValue
=> {}
1443 ty
::UpvarCapture
::ByRef(..) => continue,
1445 let span
= captured_place
.get_capture_kind_span(self.ir
.tcx
);
1446 let var
= self.variable(var_hir_id
, span
);
1447 if self.used_on_entry(entry_ln
, var
) {
1448 if !self.live_on_entry(entry_ln
, var
) {
1449 if let Some(name
) = self.should_warn(var
) {
1450 self.ir
.tcx
.struct_span_lint_hir(
1451 lint
::builtin
::UNUSED_ASSIGNMENTS
,
1455 lint
.build(&format
!(
1456 "value captured by `{}` is never read",
1459 .help("did you mean to capture by reference instead?")
1466 if let Some(name
) = self.should_warn(var
) {
1467 self.ir
.tcx
.struct_span_lint_hir(
1468 lint
::builtin
::UNUSED_VARIABLES
,
1472 lint
.build(&format
!("unused variable: `{}`", name
))
1473 .help("did you mean to capture by reference instead?")
1483 fn warn_about_unused_args(&self, body
: &hir
::Body
<'_
>, entry_ln
: LiveNode
) {
1484 for p
in body
.params
{
1485 self.check_unused_vars_in_pat(&p
.pat
, Some(entry_ln
), |spans
, hir_id
, ln
, var
| {
1486 if !self.live_on_entry(ln
, var
) {
1487 self.report_unused_assign(hir_id
, spans
, var
, |name
| {
1488 format
!("value passed to `{}` is never read", name
)
1495 fn check_unused_vars_in_pat(
1498 entry_ln
: Option
<LiveNode
>,
1499 on_used_on_entry
: impl Fn(Vec
<Span
>, HirId
, LiveNode
, Variable
),
1501 // In an or-pattern, only consider the variable; any later patterns must have the same
1502 // bindings, and we also consider the first pattern to be the "authoritative" set of ids.
1503 // However, we should take the ids and spans of variables with the same name from the later
1504 // patterns so the suggestions to prefix with underscores will apply to those too.
1505 let mut vars
: FxIndexMap
<Symbol
, (LiveNode
, Variable
, Vec
<(HirId
, Span
, Span
)>)> =
1508 pat
.each_binding(|_
, hir_id
, pat_sp
, ident
| {
1509 let ln
= entry_ln
.unwrap_or_else(|| self.live_node(hir_id
, pat_sp
));
1510 let var
= self.variable(hir_id
, ident
.span
);
1511 let id_and_sp
= (hir_id
, pat_sp
, ident
.span
);
1512 vars
.entry(self.ir
.variable_name(var
))
1513 .and_modify(|(.., hir_ids_and_spans
)| hir_ids_and_spans
.push(id_and_sp
))
1514 .or_insert_with(|| (ln
, var
, vec
![id_and_sp
]));
1517 for (_
, (ln
, var
, hir_ids_and_spans
)) in vars
{
1518 if self.used_on_entry(ln
, var
) {
1519 let id
= hir_ids_and_spans
[0].0;
1521 hir_ids_and_spans
.into_iter().map(|(_
, _
, ident_span
)| ident_span
).collect();
1522 on_used_on_entry(spans
, id
, ln
, var
);
1524 self.report_unused(hir_ids_and_spans
, ln
, var
);
1531 hir_ids_and_spans
: Vec
<(HirId
, Span
, Span
)>,
1535 let first_hir_id
= hir_ids_and_spans
[0].0;
1537 if let Some(name
) = self.should_warn(var
).filter(|name
| name
!= "self") {
1538 // annoying: for parameters in funcs like `fn(x: i32)
1539 // {ret}`, there is only one node, so asking about
1540 // assigned_on_exit() is not meaningful.
1542 if ln
== self.exit_ln { false }
else { self.assigned_on_exit(ln, var) }
;
1545 self.ir
.tcx
.struct_span_lint_hir(
1546 lint
::builtin
::UNUSED_VARIABLES
,
1550 .map(|(_
, _
, ident_span
)| ident_span
)
1551 .collect
::<Vec
<_
>>(),
1553 lint
.build(&format
!("variable `{}` is assigned to, but never used", name
))
1554 .note(&format
!("consider using `_{}` instead", name
))
1559 let (shorthands
, non_shorthands
): (Vec
<_
>, Vec
<_
>) =
1560 hir_ids_and_spans
.iter().copied().partition(|(hir_id
, _
, ident_span
)| {
1561 let var
= self.variable(*hir_id
, *ident_span
);
1562 self.ir
.variable_is_shorthand(var
)
1565 // If we have both shorthand and non-shorthand, prefer the "try ignoring
1566 // the field" message, and suggest `_` for the non-shorthands. If we only
1567 // have non-shorthand, then prefix with an underscore instead.
1568 if !shorthands
.is_empty() {
1569 let shorthands
= shorthands
1571 .map(|(_
, pat_span
, _
)| (pat_span
, format
!("{}: _", name
)))
1575 .map(|(_
, pat_span
, _
)| (pat_span
, "_".to_string())),
1577 .collect
::<Vec
<_
>>();
1579 self.ir
.tcx
.struct_span_lint_hir(
1580 lint
::builtin
::UNUSED_VARIABLES
,
1584 .map(|(_
, pat_span
, _
)| *pat_span
)
1585 .collect
::<Vec
<_
>>(),
1587 let mut err
= lint
.build(&format
!("unused variable: `{}`", name
));
1588 err
.multipart_suggestion(
1589 "try ignoring the field",
1591 Applicability
::MachineApplicable
,
1597 let non_shorthands
= non_shorthands
1599 .map(|(_
, _
, ident_span
)| (ident_span
, format
!("_{}", name
)))
1600 .collect
::<Vec
<_
>>();
1602 self.ir
.tcx
.struct_span_lint_hir(
1603 lint
::builtin
::UNUSED_VARIABLES
,
1607 .map(|(_
, _
, ident_span
)| *ident_span
)
1608 .collect
::<Vec
<_
>>(),
1610 let mut err
= lint
.build(&format
!("unused variable: `{}`", name
));
1611 err
.multipart_suggestion(
1612 "if this is intentional, prefix it with an underscore",
1614 Applicability
::MachineApplicable
,
1624 fn warn_about_dead_assign(&self, spans
: Vec
<Span
>, hir_id
: HirId
, ln
: LiveNode
, var
: Variable
) {
1625 if !self.live_on_exit(ln
, var
) {
1626 self.report_unused_assign(hir_id
, spans
, var
, |name
| {
1627 format
!("value assigned to `{}` is never read", name
)
1632 fn report_unused_assign(
1637 message
: impl Fn(&str) -> String
,
1639 if let Some(name
) = self.should_warn(var
) {
1640 self.ir
.tcx
.struct_span_lint_hir(
1641 lint
::builtin
::UNUSED_ASSIGNMENTS
,
1645 lint
.build(&message(&name
))
1646 .help("maybe it is overwritten before being read?")