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, NestedVisitorMap, Visitor}
;
94 use rustc_hir
::{Expr, HirId, HirIdMap, HirIdSet}
;
95 use rustc_index
::vec
::IndexVec
;
96 use rustc_middle
::hir
::map
::Map
;
97 use rustc_middle
::ty
::query
::Providers
;
98 use rustc_middle
::ty
::{self, DefIdTree, 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
::*;
108 rustc_index
::newtype_index
! {
109 pub struct Variable
{
110 DEBUG_FORMAT
= "v({})",
114 rustc_index
::newtype_index
! {
115 pub struct LiveNode
{
116 DEBUG_FORMAT
= "ln({})",
120 #[derive(Copy, Clone, PartialEq, Debug)]
129 fn live_node_kind_to_string(lnk
: LiveNodeKind
, tcx
: TyCtxt
<'_
>) -> String
{
130 let sm
= tcx
.sess
.source_map();
132 UpvarNode(s
) => format
!("Upvar node [{}]", sm
.span_to_string(s
)),
133 ExprNode(s
) => format
!("Expr node [{}]", sm
.span_to_string(s
)),
134 VarDefNode(s
) => format
!("Var def node [{}]", sm
.span_to_string(s
)),
135 ClosureNode
=> "Closure node".to_owned(),
136 ExitNode
=> "Exit node".to_owned(),
140 fn check_mod_liveness(tcx
: TyCtxt
<'_
>, module_def_id
: LocalDefId
) {
141 tcx
.hir().visit_item_likes_in_module(module_def_id
, &mut IrMaps
::new(tcx
).as_deep_visitor());
144 pub fn provide(providers
: &mut Providers
) {
145 *providers
= Providers { check_mod_liveness, ..*providers }
;
148 // ______________________________________________________________________
151 // This is the first pass and the one that drives the main
152 // computation. It walks up and down the IR once. On the way down,
153 // we count for each function the number of variables as well as
154 // liveness nodes. A liveness node is basically an expression or
155 // capture clause that does something of interest: either it has
156 // interesting control flow or it uses/defines a local variable.
158 // On the way back up, at each function node we create liveness sets
159 // (we now know precisely how big to make our various vectors and so
160 // forth) and then do the data-flow propagation to compute the set
161 // of live variables at each program point.
163 // Finally, we run back over the IR one last time and, using the
164 // computed liveness, check various safety conditions. For example,
165 // there must be no live nodes at the definition site for a variable
166 // unless it has an initializer. Similarly, each non-mutable local
167 // variable must not be assigned if there is some successor
168 // assignment. And so forth.
175 #[derive(Copy, Clone, Debug)]
182 #[derive(Copy, Clone, Debug)]
184 Param(HirId
, Symbol
),
186 Upvar(HirId
, Symbol
),
189 struct IrMaps
<'tcx
> {
191 live_node_map
: HirIdMap
<LiveNode
>,
192 variable_map
: HirIdMap
<Variable
>,
193 capture_info_map
: HirIdMap
<Rc
<Vec
<CaptureInfo
>>>,
194 var_kinds
: IndexVec
<Variable
, VarKind
>,
195 lnks
: IndexVec
<LiveNode
, LiveNodeKind
>,
199 fn new(tcx
: TyCtxt
<'tcx
>) -> IrMaps
<'tcx
> {
202 live_node_map
: HirIdMap
::default(),
203 variable_map
: HirIdMap
::default(),
204 capture_info_map
: Default
::default(),
205 var_kinds
: IndexVec
::new(),
206 lnks
: IndexVec
::new(),
210 fn add_live_node(&mut self, lnk
: LiveNodeKind
) -> LiveNode
{
211 let ln
= self.lnks
.push(lnk
);
213 debug
!("{:?} is of kind {}", ln
, live_node_kind_to_string(lnk
, self.tcx
));
218 fn add_live_node_for_node(&mut self, hir_id
: HirId
, lnk
: LiveNodeKind
) {
219 let ln
= self.add_live_node(lnk
);
220 self.live_node_map
.insert(hir_id
, ln
);
222 debug
!("{:?} is node {:?}", ln
, hir_id
);
225 fn add_variable(&mut self, vk
: VarKind
) -> Variable
{
226 let v
= self.var_kinds
.push(vk
);
229 Local(LocalInfo { id: node_id, .. }
) | Param(node_id
, _
) | Upvar(node_id
, _
) => {
230 self.variable_map
.insert(node_id
, v
);
234 debug
!("{:?} is {:?}", v
, vk
);
239 fn variable(&self, hir_id
: HirId
, span
: Span
) -> Variable
{
240 match self.variable_map
.get(&hir_id
) {
243 span_bug
!(span
, "no variable registered for id {:?}", hir_id
);
248 fn variable_name(&self, var
: Variable
) -> Symbol
{
249 match self.var_kinds
[var
] {
250 Local(LocalInfo { name, .. }
) | Param(_
, name
) | Upvar(_
, name
) => name
,
254 fn variable_is_shorthand(&self, var
: Variable
) -> bool
{
255 match self.var_kinds
[var
] {
256 Local(LocalInfo { is_shorthand, .. }
) => is_shorthand
,
257 Param(..) | Upvar(..) => false,
261 fn set_captures(&mut self, hir_id
: HirId
, cs
: Vec
<CaptureInfo
>) {
262 self.capture_info_map
.insert(hir_id
, Rc
::new(cs
));
265 fn add_from_pat(&mut self, pat
: &hir
::Pat
<'tcx
>) {
266 // For struct patterns, take note of which fields used shorthand
267 // (`x` rather than `x: x`).
268 let mut shorthand_field_ids
= HirIdSet
::default();
269 let mut pats
= VecDeque
::new();
271 while let Some(pat
) = pats
.pop_front() {
272 use rustc_hir
::PatKind
::*;
274 Binding(.., inner_pat
) => {
275 pats
.extend(inner_pat
.iter());
277 Struct(_
, fields
, _
) => {
278 let ids
= fields
.iter().filter(|f
| f
.is_shorthand
).map(|f
| f
.pat
.hir_id
);
279 shorthand_field_ids
.extend(ids
);
281 Ref(inner_pat
, _
) | Box(inner_pat
) => {
282 pats
.push_back(inner_pat
);
284 TupleStruct(_
, inner_pats
, _
) | Tuple(inner_pats
, _
) | Or(inner_pats
) => {
285 pats
.extend(inner_pats
.iter());
287 Slice(pre_pats
, inner_pat
, post_pats
) => {
288 pats
.extend(pre_pats
.iter());
289 pats
.extend(inner_pat
.iter());
290 pats
.extend(post_pats
.iter());
296 pat
.each_binding(|_
, hir_id
, _
, ident
| {
297 self.add_live_node_for_node(hir_id
, VarDefNode(ident
.span
));
298 self.add_variable(Local(LocalInfo
{
301 is_shorthand
: shorthand_field_ids
.contains(&hir_id
),
307 impl<'tcx
> Visitor
<'tcx
> for IrMaps
<'tcx
> {
308 type Map
= Map
<'tcx
>;
310 fn nested_visit_map(&mut self) -> NestedVisitorMap
<Self::Map
> {
311 NestedVisitorMap
::OnlyBodies(self.tcx
.hir())
314 fn visit_body(&mut self, body
: &'tcx hir
::Body
<'tcx
>) {
315 debug
!("visit_body {:?}", body
.id());
317 // swap in a new set of IR maps for this body
318 let mut maps
= IrMaps
::new(self.tcx
);
319 let hir_id
= maps
.tcx
.hir().body_owner(body
.id());
320 let def_id
= maps
.tcx
.hir().local_def_id(hir_id
);
322 // Don't run unused pass for #[derive()]
323 if let Some(parent
) = self.tcx
.parent(def_id
.to_def_id()) {
324 if let DefKind
::Impl
= self.tcx
.def_kind(parent
.expect_local()) {
325 if self.tcx
.has_attr(parent
, sym
::automatically_derived
) {
331 if let Some(upvars
) = maps
.tcx
.upvars_mentioned(def_id
) {
332 for (&var_hir_id
, _upvar
) in upvars
{
333 let var_name
= maps
.tcx
.hir().name(var_hir_id
);
334 maps
.add_variable(Upvar(var_hir_id
, var_name
));
338 // gather up the various local variables, significant expressions,
340 intravisit
::walk_body(&mut maps
, body
);
343 let mut lsets
= Liveness
::new(&mut maps
, def_id
);
344 let entry_ln
= lsets
.compute(&body
, hir_id
);
345 lsets
.log_liveness(entry_ln
, body
.id().hir_id
);
347 // check for various error conditions
348 lsets
.visit_body(body
);
349 lsets
.warn_about_unused_upvars(entry_ln
);
350 lsets
.warn_about_unused_args(body
, entry_ln
);
353 fn visit_local(&mut self, local
: &'tcx hir
::Local
<'tcx
>) {
354 self.add_from_pat(&local
.pat
);
355 intravisit
::walk_local(self, local
);
358 fn visit_arm(&mut self, arm
: &'tcx hir
::Arm
<'tcx
>) {
359 self.add_from_pat(&arm
.pat
);
360 intravisit
::walk_arm(self, arm
);
363 fn visit_param(&mut self, param
: &'tcx hir
::Param
<'tcx
>) {
364 let is_shorthand
= match param
.pat
.kind
{
365 rustc_hir
::PatKind
::Struct(..) => true,
368 param
.pat
.each_binding(|_bm
, hir_id
, _x
, ident
| {
369 let var
= if is_shorthand
{
370 Local(LocalInfo { id: hir_id, name: ident.name, is_shorthand: true }
)
372 Param(hir_id
, ident
.name
)
374 self.add_variable(var
);
376 intravisit
::walk_param(self, param
);
379 fn visit_expr(&mut self, expr
: &'tcx Expr
<'tcx
>) {
381 // live nodes required for uses or definitions of variables:
382 hir
::ExprKind
::Path(hir
::QPath
::Resolved(_
, ref path
)) => {
383 debug
!("expr {}: path that leads to {:?}", expr
.hir_id
, path
.res
);
384 if let Res
::Local(_var_hir_id
) = path
.res
{
385 self.add_live_node_for_node(expr
.hir_id
, ExprNode(expr
.span
));
387 intravisit
::walk_expr(self, expr
);
389 hir
::ExprKind
::Closure(..) => {
390 // Interesting control flow (for loops can contain labeled
391 // breaks or continues)
392 self.add_live_node_for_node(expr
.hir_id
, ExprNode(expr
.span
));
394 // Make a live_node for each captured variable, with the span
395 // being the location that the variable is used. This results
396 // in better error messages than just pointing at the closure
397 // construction site.
398 let mut call_caps
= Vec
::new();
399 let closure_def_id
= self.tcx
.hir().local_def_id(expr
.hir_id
);
400 if let Some(upvars
) = self.tcx
.upvars_mentioned(closure_def_id
) {
401 call_caps
.extend(upvars
.iter().map(|(&var_id
, upvar
)| {
402 let upvar_ln
= self.add_live_node(UpvarNode(upvar
.span
));
403 CaptureInfo { ln: upvar_ln, var_hid: var_id }
406 self.set_captures(expr
.hir_id
, call_caps
);
407 intravisit
::walk_expr(self, expr
);
410 // live nodes required for interesting control flow:
411 hir
::ExprKind
::Match(..) | hir
::ExprKind
::Loop(..) => {
412 self.add_live_node_for_node(expr
.hir_id
, ExprNode(expr
.span
));
413 intravisit
::walk_expr(self, expr
);
415 hir
::ExprKind
::Binary(op
, ..) if op
.node
.is_lazy() => {
416 self.add_live_node_for_node(expr
.hir_id
, ExprNode(expr
.span
));
417 intravisit
::walk_expr(self, expr
);
420 // otherwise, live nodes are not required:
421 hir
::ExprKind
::Index(..)
422 | hir
::ExprKind
::Field(..)
423 | hir
::ExprKind
::Array(..)
424 | hir
::ExprKind
::Call(..)
425 | hir
::ExprKind
::MethodCall(..)
426 | hir
::ExprKind
::Tup(..)
427 | hir
::ExprKind
::Binary(..)
428 | hir
::ExprKind
::AddrOf(..)
429 | hir
::ExprKind
::Cast(..)
430 | hir
::ExprKind
::DropTemps(..)
431 | hir
::ExprKind
::Unary(..)
432 | hir
::ExprKind
::Break(..)
433 | hir
::ExprKind
::Continue(_
)
434 | hir
::ExprKind
::Lit(_
)
435 | hir
::ExprKind
::ConstBlock(..)
436 | hir
::ExprKind
::Ret(..)
437 | hir
::ExprKind
::Block(..)
438 | hir
::ExprKind
::Assign(..)
439 | hir
::ExprKind
::AssignOp(..)
440 | hir
::ExprKind
::Struct(..)
441 | hir
::ExprKind
::Repeat(..)
442 | hir
::ExprKind
::InlineAsm(..)
443 | hir
::ExprKind
::LlvmInlineAsm(..)
444 | hir
::ExprKind
::Box(..)
445 | hir
::ExprKind
::Yield(..)
446 | hir
::ExprKind
::Type(..)
448 | hir
::ExprKind
::Path(hir
::QPath
::TypeRelative(..))
449 | hir
::ExprKind
::Path(hir
::QPath
::LangItem(..)) => {
450 intravisit
::walk_expr(self, expr
);
456 // ______________________________________________________________________
457 // Computing liveness sets
459 // Actually we compute just a bit more than just liveness, but we use
460 // the same basic propagation framework in all cases.
462 #[derive(Clone, Copy)]
464 reader
: Option
<LiveNode
>,
465 writer
: Option
<LiveNode
>,
469 /// Conceptually, this is like a `Vec<RWU>`. But the number of `RWU`s can get
470 /// very large, so it uses a more compact representation that takes advantage
471 /// of the fact that when the number of `RWU`s is large, most of them have an
472 /// invalid reader and an invalid writer.
474 /// Each entry in `packed_rwus` is either INV_INV_FALSE, INV_INV_TRUE, or
475 /// an index into `unpacked_rwus`. In the common cases, this compacts the
476 /// 65 bits of data into 32; in the uncommon cases, it expands the 65 bits
479 /// More compact representations are possible -- e.g., use only 2 bits per
480 /// packed `RWU` and make the secondary table a HashMap that maps from
481 /// indices to `RWU`s -- but this one strikes a good balance between size
483 packed_rwus
: Vec
<u32>,
484 unpacked_rwus
: Vec
<RWU
>,
487 // A constant representing `RWU { reader: None; writer: None; used: false }`.
488 const INV_INV_FALSE
: u32 = u32::MAX
;
490 // A constant representing `RWU { reader: None; writer: None; used: true }`.
491 const INV_INV_TRUE
: u32 = u32::MAX
- 1;
494 fn new(num_rwus
: usize) -> RWUTable
{
495 Self { packed_rwus: vec![INV_INV_FALSE; num_rwus], unpacked_rwus: vec![] }
498 fn get(&self, idx
: usize) -> RWU
{
499 let packed_rwu
= self.packed_rwus
[idx
];
501 INV_INV_FALSE
=> RWU { reader: None, writer: None, used: false }
,
502 INV_INV_TRUE
=> RWU { reader: None, writer: None, used: true }
,
503 _
=> self.unpacked_rwus
[packed_rwu
as usize],
507 fn get_reader(&self, idx
: usize) -> Option
<LiveNode
> {
508 let packed_rwu
= self.packed_rwus
[idx
];
510 INV_INV_FALSE
| INV_INV_TRUE
=> None
,
511 _
=> self.unpacked_rwus
[packed_rwu
as usize].reader
,
515 fn get_writer(&self, idx
: usize) -> Option
<LiveNode
> {
516 let packed_rwu
= self.packed_rwus
[idx
];
518 INV_INV_FALSE
| INV_INV_TRUE
=> None
,
519 _
=> self.unpacked_rwus
[packed_rwu
as usize].writer
,
523 fn get_used(&self, idx
: usize) -> bool
{
524 let packed_rwu
= self.packed_rwus
[idx
];
526 INV_INV_FALSE
=> false,
527 INV_INV_TRUE
=> true,
528 _
=> self.unpacked_rwus
[packed_rwu
as usize].used
,
533 fn copy_packed(&mut self, dst_idx
: usize, src_idx
: usize) {
534 self.packed_rwus
[dst_idx
] = self.packed_rwus
[src_idx
];
537 fn assign_unpacked(&mut self, idx
: usize, rwu
: RWU
) {
538 if rwu
.reader
== None
&& rwu
.writer
== None
{
539 // When we overwrite an indexing entry in `self.packed_rwus` with
540 // `INV_INV_{TRUE,FALSE}` we don't remove the corresponding entry
541 // from `self.unpacked_rwus`; it's not worth the effort, and we
542 // can't have entries shifting around anyway.
543 self.packed_rwus
[idx
] = if rwu
.used { INV_INV_TRUE }
else { INV_INV_FALSE }
545 // Add a new RWU to `unpacked_rwus` and make `packed_rwus[idx]`
547 self.packed_rwus
[idx
] = self.unpacked_rwus
.len() as u32;
548 self.unpacked_rwus
.push(rwu
);
552 fn assign_inv_inv(&mut self, idx
: usize) {
553 self.packed_rwus
[idx
] = if self.get_used(idx
) { INV_INV_TRUE }
else { INV_INV_FALSE }
;
557 const ACC_READ
: u32 = 1;
558 const ACC_WRITE
: u32 = 2;
559 const ACC_USE
: u32 = 4;
561 struct Liveness
<'a
, 'tcx
> {
562 ir
: &'a
mut IrMaps
<'tcx
>,
563 body_owner
: LocalDefId
,
564 typeck_results
: &'a ty
::TypeckResults
<'tcx
>,
565 param_env
: ty
::ParamEnv
<'tcx
>,
566 upvars
: Option
<&'tcx FxIndexMap
<hir
::HirId
, hir
::Upvar
>>,
567 successors
: IndexVec
<LiveNode
, Option
<LiveNode
>>,
570 /// A live node representing a point of execution before closure entry &
571 /// after closure exit. Used to calculate liveness of captured variables
572 /// through calls to the same closure. Used for Fn & FnMut closures only.
573 closure_ln
: LiveNode
,
574 /// A live node representing every 'exit' from the function, whether it be
575 /// by explicit return, panic, or other means.
578 // mappings from loop node ID to LiveNode
579 // ("break" label should map to loop node ID,
580 // it probably doesn't now)
581 break_ln
: HirIdMap
<LiveNode
>,
582 cont_ln
: HirIdMap
<LiveNode
>,
585 impl<'a
, 'tcx
> Liveness
<'a
, 'tcx
> {
586 fn new(ir
: &'a
mut IrMaps
<'tcx
>, body_owner
: LocalDefId
) -> Liveness
<'a
, 'tcx
> {
587 let typeck_results
= ir
.tcx
.typeck(body_owner
);
588 let param_env
= ir
.tcx
.param_env(body_owner
);
589 let upvars
= ir
.tcx
.upvars_mentioned(body_owner
);
591 let closure_ln
= ir
.add_live_node(ClosureNode
);
592 let exit_ln
= ir
.add_live_node(ExitNode
);
594 let num_live_nodes
= ir
.lnks
.len();
595 let num_vars
= ir
.var_kinds
.len();
603 successors
: IndexVec
::from_elem_n(None
, num_live_nodes
),
604 rwu_table
: RWUTable
::new(num_live_nodes
* num_vars
),
607 break_ln
: Default
::default(),
608 cont_ln
: Default
::default(),
612 fn live_node(&self, hir_id
: HirId
, span
: Span
) -> LiveNode
{
613 match self.ir
.live_node_map
.get(&hir_id
) {
616 // This must be a mismatch between the ir_map construction
617 // above and the propagation code below; the two sets of
618 // code have to agree about which AST nodes are worth
619 // creating liveness nodes for.
620 span_bug
!(span
, "no live node registered for node {:?}", hir_id
);
625 fn variable(&self, hir_id
: HirId
, span
: Span
) -> Variable
{
626 self.ir
.variable(hir_id
, span
)
629 fn define_bindings_in_pat(&mut self, pat
: &hir
::Pat
<'_
>, mut succ
: LiveNode
) -> LiveNode
{
630 // In an or-pattern, only consider the first pattern; any later patterns
631 // must have the same bindings, and we also consider the first pattern
632 // to be the "authoritative" set of ids.
633 pat
.each_binding_or_first(&mut |_
, hir_id
, pat_sp
, ident
| {
634 let ln
= self.live_node(hir_id
, pat_sp
);
635 let var
= self.variable(hir_id
, ident
.span
);
636 self.init_from_succ(ln
, succ
);
637 self.define(ln
, var
);
643 fn idx(&self, ln
: LiveNode
, var
: Variable
) -> usize {
644 ln
.index() * self.ir
.var_kinds
.len() + var
.index()
647 fn live_on_entry(&self, ln
: LiveNode
, var
: Variable
) -> Option
<LiveNodeKind
> {
648 if let Some(reader
) = self.rwu_table
.get_reader(self.idx(ln
, var
)) {
649 Some(self.ir
.lnks
[reader
])
655 // Is this variable live on entry to any of its successor nodes?
656 fn live_on_exit(&self, ln
: LiveNode
, var
: Variable
) -> Option
<LiveNodeKind
> {
657 let successor
= self.successors
[ln
].unwrap();
658 self.live_on_entry(successor
, var
)
661 fn used_on_entry(&self, ln
: LiveNode
, var
: Variable
) -> bool
{
662 self.rwu_table
.get_used(self.idx(ln
, var
))
665 fn assigned_on_entry(&self, ln
: LiveNode
, var
: Variable
) -> Option
<LiveNodeKind
> {
666 if let Some(writer
) = self.rwu_table
.get_writer(self.idx(ln
, var
)) {
667 Some(self.ir
.lnks
[writer
])
673 fn assigned_on_exit(&self, ln
: LiveNode
, var
: Variable
) -> Option
<LiveNodeKind
> {
674 let successor
= self.successors
[ln
].unwrap();
675 self.assigned_on_entry(successor
, var
)
678 fn indices2
<F
>(&mut self, ln
: LiveNode
, succ_ln
: LiveNode
, mut op
: F
)
680 F
: FnMut(&mut Liveness
<'a
, 'tcx
>, usize, usize),
682 let node_base_idx
= self.idx(ln
, Variable
::from(0u32));
683 let succ_base_idx
= self.idx(succ_ln
, Variable
::from(0u32));
684 for var_idx
in 0..self.ir
.var_kinds
.len() {
685 op(self, node_base_idx
+ var_idx
, succ_base_idx
+ var_idx
);
689 fn write_vars
<F
>(&self, wr
: &mut dyn Write
, ln
: LiveNode
, mut test
: F
) -> io
::Result
<()>
691 F
: FnMut(usize) -> bool
,
693 let node_base_idx
= self.idx(ln
, Variable
::from(0u32));
694 for var_idx
in 0..self.ir
.var_kinds
.len() {
695 let idx
= node_base_idx
+ var_idx
;
697 write
!(wr
, " {:?}", Variable
::from(var_idx
))?
;
703 #[allow(unused_must_use)]
704 fn ln_str(&self, ln
: LiveNode
) -> String
{
705 let mut wr
= Vec
::new();
707 let wr
= &mut wr
as &mut dyn Write
;
708 write
!(wr
, "[{:?} of kind {:?} reads", ln
, self.ir
.lnks
[ln
]);
709 self.write_vars(wr
, ln
, |idx
| self.rwu_table
.get_reader(idx
).is_some());
710 write
!(wr
, " writes");
711 self.write_vars(wr
, ln
, |idx
| self.rwu_table
.get_writer(idx
).is_some());
713 self.write_vars(wr
, ln
, |idx
| self.rwu_table
.get_used(idx
));
715 write
!(wr
, " precedes {:?}]", self.successors
[ln
]);
717 String
::from_utf8(wr
).unwrap()
720 fn log_liveness(&self, entry_ln
: LiveNode
, hir_id
: hir
::HirId
) {
721 // hack to skip the loop unless debug! is enabled:
723 "^^ liveness computation results for body {} (entry={:?})",
725 for ln_idx
in 0..self.ir
.lnks
.len() {
726 debug
!("{:?}", self.ln_str(LiveNode
::from(ln_idx
)));
734 fn init_empty(&mut self, ln
: LiveNode
, succ_ln
: LiveNode
) {
735 self.successors
[ln
] = Some(succ_ln
);
737 // It is not necessary to initialize the RWUs here because they are all
738 // set to INV_INV_FALSE when they are created, and the sets only grow
739 // during iterations.
742 fn init_from_succ(&mut self, ln
: LiveNode
, succ_ln
: LiveNode
) {
743 // more efficient version of init_empty() / merge_from_succ()
744 self.successors
[ln
] = Some(succ_ln
);
746 self.indices2(ln
, succ_ln
, |this
, idx
, succ_idx
| {
747 this
.rwu_table
.copy_packed(idx
, succ_idx
);
749 debug
!("init_from_succ(ln={}, succ={})", self.ln_str(ln
), self.ln_str(succ_ln
));
752 fn merge_from_succ(&mut self, ln
: LiveNode
, succ_ln
: LiveNode
, first_merge
: bool
) -> bool
{
757 let mut any_changed
= false;
758 self.indices2(ln
, succ_ln
, |this
, idx
, succ_idx
| {
759 // This is a special case, pulled out from the code below, where we
760 // don't have to do anything. It occurs about 60-70% of the time.
761 if this
.rwu_table
.packed_rwus
[succ_idx
] == INV_INV_FALSE
{
765 let mut changed
= false;
766 let mut rwu
= this
.rwu_table
.get(idx
);
767 let succ_rwu
= this
.rwu_table
.get(succ_idx
);
768 if succ_rwu
.reader
.is_some() && rwu
.reader
.is_none() {
769 rwu
.reader
= succ_rwu
.reader
;
773 if succ_rwu
.writer
.is_some() && rwu
.writer
.is_none() {
774 rwu
.writer
= succ_rwu
.writer
;
778 if succ_rwu
.used
&& !rwu
.used
{
784 this
.rwu_table
.assign_unpacked(idx
, rwu
);
790 "merge_from_succ(ln={:?}, succ={}, first_merge={}, changed={})",
792 self.ln_str(succ_ln
),
799 // Indicates that a local variable was *defined*; we know that no
800 // uses of the variable can precede the definition (resolve checks
801 // this) so we just clear out all the data.
802 fn define(&mut self, writer
: LiveNode
, var
: Variable
) {
803 let idx
= self.idx(writer
, var
);
804 self.rwu_table
.assign_inv_inv(idx
);
806 debug
!("{:?} defines {:?} (idx={}): {}", writer
, var
, idx
, self.ln_str(writer
));
809 // Either read, write, or both depending on the acc bitset
810 fn acc(&mut self, ln
: LiveNode
, var
: Variable
, acc
: u32) {
811 debug
!("{:?} accesses[{:x}] {:?}: {}", ln
, acc
, var
, self.ln_str(ln
));
813 let idx
= self.idx(ln
, var
);
814 let mut rwu
= self.rwu_table
.get(idx
);
816 if (acc
& ACC_WRITE
) != 0 {
818 rwu
.writer
= Some(ln
);
821 // Important: if we both read/write, must do read second
822 // or else the write will override.
823 if (acc
& ACC_READ
) != 0 {
824 rwu
.reader
= Some(ln
);
827 if (acc
& ACC_USE
) != 0 {
831 self.rwu_table
.assign_unpacked(idx
, rwu
);
834 fn compute(&mut self, body
: &hir
::Body
<'_
>, hir_id
: HirId
) -> LiveNode
{
835 debug
!("compute: for body {:?}", body
.id().hir_id
);
837 // # Liveness of captured variables
839 // When computing the liveness for captured variables we take into
840 // account how variable is captured (ByRef vs ByValue) and what is the
841 // closure kind (Generator / FnOnce vs Fn / FnMut).
843 // Variables captured by reference are assumed to be used on the exit
846 // In FnOnce closures, variables captured by value are known to be dead
847 // on exit since it is impossible to call the closure again.
849 // In Fn / FnMut closures, variables captured by value are live on exit
850 // if they are live on the entry to the closure, since only the closure
851 // itself can access them on subsequent calls.
853 if let Some(upvars
) = self.upvars
{
854 // Mark upvars captured by reference as used after closure exits.
855 for (&var_hir_id
, upvar
) in upvars
.iter().rev() {
856 let upvar_id
= ty
::UpvarId
{
857 var_path
: ty
::UpvarPath { hir_id: var_hir_id }
,
858 closure_expr_id
: self.body_owner
,
860 match self.typeck_results
.upvar_capture(upvar_id
) {
861 ty
::UpvarCapture
::ByRef(_
) => {
862 let var
= self.variable(var_hir_id
, upvar
.span
);
863 self.acc(self.exit_ln
, var
, ACC_READ
| ACC_USE
);
865 ty
::UpvarCapture
::ByValue(_
) => {}
870 let succ
= self.propagate_through_expr(&body
.value
, self.exit_ln
);
872 if self.upvars
.is_none() {
873 // Either not a closure, or closure without any captured variables.
874 // No need to determine liveness of captured variables, since there
879 let ty
= self.typeck_results
.node_type(hir_id
);
881 ty
::Closure(_def_id
, substs
) => match substs
.as_closure().kind() {
882 ty
::ClosureKind
::Fn
=> {}
883 ty
::ClosureKind
::FnMut
=> {}
884 ty
::ClosureKind
::FnOnce
=> return succ
,
886 ty
::Generator(..) => return succ
,
890 "{} has upvars so it should have a closure type: {:?}",
897 // Propagate through calls to the closure.
898 let mut first_merge
= true;
900 self.init_from_succ(self.closure_ln
, succ
);
901 for param
in body
.params
{
902 param
.pat
.each_binding(|_bm
, hir_id
, _x
, ident
| {
903 let var
= self.variable(hir_id
, ident
.span
);
904 self.define(self.closure_ln
, var
);
908 if !self.merge_from_succ(self.exit_ln
, self.closure_ln
, first_merge
) {
912 assert_eq
!(succ
, self.propagate_through_expr(&body
.value
, self.exit_ln
));
918 fn propagate_through_block(&mut self, blk
: &hir
::Block
<'_
>, succ
: LiveNode
) -> LiveNode
{
919 if blk
.targeted_by_break
{
920 self.break_ln
.insert(blk
.hir_id
, succ
);
922 let succ
= self.propagate_through_opt_expr(blk
.expr
.as_deref(), succ
);
923 blk
.stmts
.iter().rev().fold(succ
, |succ
, stmt
| self.propagate_through_stmt(stmt
, succ
))
926 fn propagate_through_stmt(&mut self, stmt
: &hir
::Stmt
<'_
>, succ
: LiveNode
) -> LiveNode
{
928 hir
::StmtKind
::Local(ref local
) => {
929 // Note: we mark the variable as defined regardless of whether
930 // there is an initializer. Initially I had thought to only mark
931 // the live variable as defined if it was initialized, and then we
932 // could check for uninit variables just by scanning what is live
933 // at the start of the function. But that doesn't work so well for
934 // immutable variables defined in a loop:
935 // loop { let x; x = 5; }
936 // because the "assignment" loops back around and generates an error.
938 // So now we just check that variables defined w/o an
939 // initializer are not live at the point of their
940 // initialization, which is mildly more complex than checking
941 // once at the func header but otherwise equivalent.
943 let succ
= self.propagate_through_opt_expr(local
.init
.as_deref(), succ
);
944 self.define_bindings_in_pat(&local
.pat
, succ
)
946 hir
::StmtKind
::Item(..) => succ
,
947 hir
::StmtKind
::Expr(ref expr
) | hir
::StmtKind
::Semi(ref expr
) => {
948 self.propagate_through_expr(&expr
, succ
)
953 fn propagate_through_exprs(&mut self, exprs
: &[Expr
<'_
>], succ
: LiveNode
) -> LiveNode
{
954 exprs
.iter().rev().fold(succ
, |succ
, expr
| self.propagate_through_expr(&expr
, succ
))
957 fn propagate_through_opt_expr(
959 opt_expr
: Option
<&Expr
<'_
>>,
962 opt_expr
.map_or(succ
, |expr
| self.propagate_through_expr(expr
, succ
))
965 fn propagate_through_expr(&mut self, expr
: &Expr
<'_
>, succ
: LiveNode
) -> LiveNode
{
966 debug
!("propagate_through_expr: {:?}", expr
);
969 // Interesting cases with control flow or which gen/kill
970 hir
::ExprKind
::Path(hir
::QPath
::Resolved(_
, ref path
)) => {
971 self.access_path(expr
.hir_id
, path
, succ
, ACC_READ
| ACC_USE
)
974 hir
::ExprKind
::Field(ref e
, _
) => self.propagate_through_expr(&e
, succ
),
976 hir
::ExprKind
::Closure(..) => {
977 debug
!("{:?} is an ExprKind::Closure", expr
);
979 // the construction of a closure itself is not important,
980 // but we have to consider the closed over variables.
986 .unwrap_or_else(|| span_bug
!(expr
.span
, "no registered caps"));
988 caps
.iter().rev().fold(succ
, |succ
, cap
| {
989 self.init_from_succ(cap
.ln
, succ
);
990 let var
= self.variable(cap
.var_hid
, expr
.span
);
991 self.acc(cap
.ln
, var
, ACC_READ
| ACC_USE
);
996 // Note that labels have been resolved, so we don't need to look
997 // at the label ident
998 hir
::ExprKind
::Loop(ref blk
, _
, _
) => self.propagate_through_loop(expr
, &blk
, succ
),
1000 hir
::ExprKind
::Match(ref e
, arms
, _
) => {
1015 let ln
= self.live_node(expr
.hir_id
, expr
.span
);
1016 self.init_empty(ln
, succ
);
1017 let mut first_merge
= true;
1019 let body_succ
= self.propagate_through_expr(&arm
.body
, succ
);
1021 let guard_succ
= self.propagate_through_opt_expr(
1022 arm
.guard
.as_ref().map(|hir
::Guard
::If(e
)| *e
),
1025 let arm_succ
= self.define_bindings_in_pat(&arm
.pat
, guard_succ
);
1026 self.merge_from_succ(ln
, arm_succ
, first_merge
);
1027 first_merge
= false;
1029 self.propagate_through_expr(&e
, ln
)
1032 hir
::ExprKind
::Ret(ref o_e
) => {
1033 // Ignore succ and subst exit_ln.
1034 self.propagate_through_opt_expr(o_e
.as_ref().map(|e
| &**e
), self.exit_ln
)
1037 hir
::ExprKind
::Break(label
, ref opt_expr
) => {
1038 // Find which label this break jumps to
1039 let target
= match label
.target_id
{
1040 Ok(hir_id
) => self.break_ln
.get(&hir_id
),
1041 Err(err
) => span_bug
!(expr
.span
, "loop scope error: {}", err
),
1045 // Now that we know the label we're going to,
1046 // look it up in the break loop nodes table
1049 Some(b
) => self.propagate_through_opt_expr(opt_expr
.as_ref().map(|e
| &**e
), b
),
1050 None
=> span_bug
!(expr
.span
, "`break` to unknown label"),
1054 hir
::ExprKind
::Continue(label
) => {
1055 // Find which label this expr continues to
1058 .unwrap_or_else(|err
| span_bug
!(expr
.span
, "loop scope error: {}", err
));
1060 // Now that we know the label we're going to,
1061 // look it up in the continue loop nodes table
1065 .unwrap_or_else(|| span_bug
!(expr
.span
, "continue to unknown label"))
1068 hir
::ExprKind
::Assign(ref l
, ref r
, _
) => {
1069 // see comment on places in
1070 // propagate_through_place_components()
1071 let succ
= self.write_place(&l
, succ
, ACC_WRITE
);
1072 let succ
= self.propagate_through_place_components(&l
, succ
);
1073 self.propagate_through_expr(&r
, succ
)
1076 hir
::ExprKind
::AssignOp(_
, ref l
, ref r
) => {
1077 // an overloaded assign op is like a method call
1078 if self.typeck_results
.is_method_call(expr
) {
1079 let succ
= self.propagate_through_expr(&l
, succ
);
1080 self.propagate_through_expr(&r
, succ
)
1082 // see comment on places in
1083 // propagate_through_place_components()
1084 let succ
= self.write_place(&l
, succ
, ACC_WRITE
| ACC_READ
);
1085 let succ
= self.propagate_through_expr(&r
, succ
);
1086 self.propagate_through_place_components(&l
, succ
)
1090 // Uninteresting cases: just propagate in rev exec order
1091 hir
::ExprKind
::Array(ref exprs
) => self.propagate_through_exprs(exprs
, succ
),
1093 hir
::ExprKind
::Struct(_
, ref fields
, ref with_expr
) => {
1094 let succ
= self.propagate_through_opt_expr(with_expr
.as_ref().map(|e
| &**e
), succ
);
1098 .fold(succ
, |succ
, field
| self.propagate_through_expr(&field
.expr
, succ
))
1101 hir
::ExprKind
::Call(ref f
, ref args
) => {
1102 let m
= self.ir
.tcx
.parent_module(expr
.hir_id
).to_def_id();
1103 let succ
= if self.ir
.tcx
.is_ty_uninhabited_from(
1105 self.typeck_results
.expr_ty(expr
),
1112 let succ
= self.propagate_through_exprs(args
, succ
);
1113 self.propagate_through_expr(&f
, succ
)
1116 hir
::ExprKind
::MethodCall(.., ref args
, _
) => {
1117 let m
= self.ir
.tcx
.parent_module(expr
.hir_id
).to_def_id();
1118 let succ
= if self.ir
.tcx
.is_ty_uninhabited_from(
1120 self.typeck_results
.expr_ty(expr
),
1128 self.propagate_through_exprs(args
, succ
)
1131 hir
::ExprKind
::Tup(ref exprs
) => self.propagate_through_exprs(exprs
, succ
),
1133 hir
::ExprKind
::Binary(op
, ref l
, ref r
) if op
.node
.is_lazy() => {
1134 let r_succ
= self.propagate_through_expr(&r
, succ
);
1136 let ln
= self.live_node(expr
.hir_id
, expr
.span
);
1137 self.init_from_succ(ln
, succ
);
1138 self.merge_from_succ(ln
, r_succ
, false);
1140 self.propagate_through_expr(&l
, ln
)
1143 hir
::ExprKind
::Index(ref l
, ref r
) | hir
::ExprKind
::Binary(_
, ref l
, ref r
) => {
1144 let r_succ
= self.propagate_through_expr(&r
, succ
);
1145 self.propagate_through_expr(&l
, r_succ
)
1148 hir
::ExprKind
::Box(ref e
)
1149 | hir
::ExprKind
::AddrOf(_
, _
, ref e
)
1150 | hir
::ExprKind
::Cast(ref e
, _
)
1151 | hir
::ExprKind
::Type(ref e
, _
)
1152 | hir
::ExprKind
::DropTemps(ref e
)
1153 | hir
::ExprKind
::Unary(_
, ref e
)
1154 | hir
::ExprKind
::Yield(ref e
, _
)
1155 | hir
::ExprKind
::Repeat(ref e
, _
) => self.propagate_through_expr(&e
, succ
),
1157 hir
::ExprKind
::InlineAsm(ref asm
) => {
1158 // Handle non-returning asm
1159 let mut succ
= if asm
.options
.contains(InlineAsmOptions
::NORETURN
) {
1165 // Do a first pass for writing outputs only
1166 for op
in asm
.operands
.iter().rev() {
1168 hir
::InlineAsmOperand
::In { .. }
1169 | hir
::InlineAsmOperand
::Const { .. }
1170 | hir
::InlineAsmOperand
::Sym { .. }
=> {}
1171 hir
::InlineAsmOperand
::Out { expr, .. }
=> {
1172 if let Some(expr
) = expr
{
1173 succ
= self.write_place(expr
, succ
, ACC_WRITE
);
1176 hir
::InlineAsmOperand
::InOut { expr, .. }
=> {
1177 succ
= self.write_place(expr
, succ
, ACC_READ
| ACC_WRITE
| ACC_USE
);
1179 hir
::InlineAsmOperand
::SplitInOut { out_expr, .. }
=> {
1180 if let Some(expr
) = out_expr
{
1181 succ
= self.write_place(expr
, succ
, ACC_WRITE
);
1187 // Then do a second pass for inputs
1188 let mut succ
= succ
;
1189 for op
in asm
.operands
.iter().rev() {
1191 hir
::InlineAsmOperand
::In { expr, .. }
1192 | hir
::InlineAsmOperand
::Const { expr, .. }
1193 | hir
::InlineAsmOperand
::Sym { expr, .. }
=> {
1194 succ
= self.propagate_through_expr(expr
, succ
)
1196 hir
::InlineAsmOperand
::Out { expr, .. }
=> {
1197 if let Some(expr
) = expr
{
1198 succ
= self.propagate_through_place_components(expr
, succ
);
1201 hir
::InlineAsmOperand
::InOut { expr, .. }
=> {
1202 succ
= self.propagate_through_place_components(expr
, succ
);
1204 hir
::InlineAsmOperand
::SplitInOut { in_expr, out_expr, .. }
=> {
1205 if let Some(expr
) = out_expr
{
1206 succ
= self.propagate_through_place_components(expr
, succ
);
1208 succ
= self.propagate_through_expr(in_expr
, succ
);
1215 hir
::ExprKind
::LlvmInlineAsm(ref asm
) => {
1216 let ia
= &asm
.inner
;
1217 let outputs
= asm
.outputs_exprs
;
1218 let inputs
= asm
.inputs_exprs
;
1219 let succ
= ia
.outputs
.iter().zip(outputs
).rev().fold(succ
, |succ
, (o
, output
)| {
1220 // see comment on places
1221 // in propagate_through_place_components()
1223 self.propagate_through_expr(output
, succ
)
1225 let acc
= if o
.is_rw { ACC_WRITE | ACC_READ }
else { ACC_WRITE }
;
1226 let succ
= self.write_place(output
, succ
, acc
);
1227 self.propagate_through_place_components(output
, succ
)
1231 // Inputs are executed first. Propagate last because of rev order
1232 self.propagate_through_exprs(inputs
, succ
)
1235 hir
::ExprKind
::Lit(..)
1236 | hir
::ExprKind
::ConstBlock(..)
1237 | hir
::ExprKind
::Err
1238 | hir
::ExprKind
::Path(hir
::QPath
::TypeRelative(..))
1239 | hir
::ExprKind
::Path(hir
::QPath
::LangItem(..)) => succ
,
1241 // Note that labels have been resolved, so we don't need to look
1242 // at the label ident
1243 hir
::ExprKind
::Block(ref blk
, _
) => self.propagate_through_block(&blk
, succ
),
1247 fn propagate_through_place_components(&mut self, expr
: &Expr
<'_
>, succ
: LiveNode
) -> LiveNode
{
1250 // In general, the full flow graph structure for an
1251 // assignment/move/etc can be handled in one of two ways,
1252 // depending on whether what is being assigned is a "tracked
1253 // value" or not. A tracked value is basically a local
1254 // variable or argument.
1256 // The two kinds of graphs are:
1258 // Tracked place Untracked place
1259 // ----------------------++-----------------------
1263 // (rvalue) || (rvalue)
1266 // (write of place) || (place components)
1271 // ----------------------++-----------------------
1273 // I will cover the two cases in turn:
1277 // A tracked place is a local variable/argument `x`. In
1278 // these cases, the link_node where the write occurs is linked
1279 // to node id of `x`. The `write_place()` routine generates
1280 // the contents of this node. There are no subcomponents to
1283 // # Non-tracked places
1285 // These are places like `x[5]` or `x.f`. In that case, we
1286 // basically ignore the value which is written to but generate
1287 // reads for the components---`x` in these two examples. The
1288 // components reads are generated by
1289 // `propagate_through_place_components()` (this fn).
1293 // It is still possible to observe assignments to non-places;
1294 // these errors are detected in the later pass borrowck. We
1295 // just ignore such cases and treat them as reads.
1298 hir
::ExprKind
::Path(_
) => succ
,
1299 hir
::ExprKind
::Field(ref e
, _
) => self.propagate_through_expr(&e
, succ
),
1300 _
=> self.propagate_through_expr(expr
, succ
),
1304 // see comment on propagate_through_place()
1305 fn write_place(&mut self, expr
: &Expr
<'_
>, succ
: LiveNode
, acc
: u32) -> LiveNode
{
1307 hir
::ExprKind
::Path(hir
::QPath
::Resolved(_
, ref path
)) => {
1308 self.access_path(expr
.hir_id
, path
, succ
, acc
)
1311 // We do not track other places, so just propagate through
1312 // to their subcomponents. Also, it may happen that
1313 // non-places occur here, because those are detected in the
1314 // later pass borrowck.
1327 let ln
= self.live_node(hir_id
, span
);
1329 self.init_from_succ(ln
, succ
);
1330 let var
= self.variable(var_hid
, span
);
1331 self.acc(ln
, var
, acc
);
1339 path
: &hir
::Path
<'_
>,
1344 Res
::Local(hid
) => self.access_var(hir_id
, hid
, succ
, acc
, path
.span
),
1349 fn propagate_through_loop(
1352 body
: &hir
::Block
<'_
>,
1356 We model control flow like this:
1363 Note that a `continue` expression targeting the `loop` will have a successor of `expr`.
1364 Meanwhile, a `break` expression will have a successor of `succ`.
1368 let mut first_merge
= true;
1369 let ln
= self.live_node(expr
.hir_id
, expr
.span
);
1370 self.init_empty(ln
, succ
);
1371 debug
!("propagate_through_loop: using id for loop body {} {:?}", expr
.hir_id
, body
);
1373 self.break_ln
.insert(expr
.hir_id
, succ
);
1375 self.cont_ln
.insert(expr
.hir_id
, ln
);
1377 let body_ln
= self.propagate_through_block(body
, ln
);
1379 // repeat until fixed point is reached:
1380 while self.merge_from_succ(ln
, body_ln
, first_merge
) {
1381 first_merge
= false;
1382 assert_eq
!(body_ln
, self.propagate_through_block(body
, ln
));
1389 // _______________________________________________________________________
1390 // Checking for error conditions
1392 impl<'a
, 'tcx
> Visitor
<'tcx
> for Liveness
<'a
, 'tcx
> {
1393 type Map
= intravisit
::ErasedMap
<'tcx
>;
1395 fn nested_visit_map(&mut self) -> NestedVisitorMap
<Self::Map
> {
1396 NestedVisitorMap
::None
1399 fn visit_local(&mut self, local
: &'tcx hir
::Local
<'tcx
>) {
1400 self.check_unused_vars_in_pat(&local
.pat
, None
, |spans
, hir_id
, ln
, var
| {
1401 if local
.init
.is_some() {
1402 self.warn_about_dead_assign(spans
, hir_id
, ln
, var
);
1406 intravisit
::walk_local(self, local
);
1409 fn visit_expr(&mut self, ex
: &'tcx Expr
<'tcx
>) {
1410 check_expr(self, ex
);
1413 fn visit_arm(&mut self, arm
: &'tcx hir
::Arm
<'tcx
>) {
1414 self.check_unused_vars_in_pat(&arm
.pat
, None
, |_
, _
, _
, _
| {}
);
1415 intravisit
::walk_arm(self, arm
);
1419 fn check_expr
<'tcx
>(this
: &mut Liveness
<'_
, 'tcx
>, expr
: &'tcx Expr
<'tcx
>) {
1421 hir
::ExprKind
::Assign(ref l
, ..) => {
1422 this
.check_place(&l
);
1425 hir
::ExprKind
::AssignOp(_
, ref l
, _
) => {
1426 if !this
.typeck_results
.is_method_call(expr
) {
1427 this
.check_place(&l
);
1431 hir
::ExprKind
::InlineAsm(ref asm
) => {
1432 for op
in asm
.operands
{
1434 hir
::InlineAsmOperand
::Out { expr, .. }
=> {
1435 if let Some(expr
) = expr
{
1436 this
.check_place(expr
);
1439 hir
::InlineAsmOperand
::InOut { expr, .. }
=> {
1440 this
.check_place(expr
);
1442 hir
::InlineAsmOperand
::SplitInOut { out_expr, .. }
=> {
1443 if let Some(out_expr
) = out_expr
{
1444 this
.check_place(out_expr
);
1452 hir
::ExprKind
::LlvmInlineAsm(ref asm
) => {
1453 for input
in asm
.inputs_exprs
{
1454 this
.visit_expr(input
);
1457 // Output operands must be places
1458 for (o
, output
) in asm
.inner
.outputs
.iter().zip(asm
.outputs_exprs
) {
1460 this
.check_place(output
);
1462 this
.visit_expr(output
);
1466 // no correctness conditions related to liveness
1467 hir
::ExprKind
::Call(..)
1468 | hir
::ExprKind
::MethodCall(..)
1469 | hir
::ExprKind
::Match(..)
1470 | hir
::ExprKind
::Loop(..)
1471 | hir
::ExprKind
::Index(..)
1472 | hir
::ExprKind
::Field(..)
1473 | hir
::ExprKind
::Array(..)
1474 | hir
::ExprKind
::Tup(..)
1475 | hir
::ExprKind
::Binary(..)
1476 | hir
::ExprKind
::Cast(..)
1477 | hir
::ExprKind
::DropTemps(..)
1478 | hir
::ExprKind
::Unary(..)
1479 | hir
::ExprKind
::Ret(..)
1480 | hir
::ExprKind
::Break(..)
1481 | hir
::ExprKind
::Continue(..)
1482 | hir
::ExprKind
::Lit(_
)
1483 | hir
::ExprKind
::ConstBlock(..)
1484 | hir
::ExprKind
::Block(..)
1485 | hir
::ExprKind
::AddrOf(..)
1486 | hir
::ExprKind
::Struct(..)
1487 | hir
::ExprKind
::Repeat(..)
1488 | hir
::ExprKind
::Closure(..)
1489 | hir
::ExprKind
::Path(_
)
1490 | hir
::ExprKind
::Yield(..)
1491 | hir
::ExprKind
::Box(..)
1492 | hir
::ExprKind
::Type(..)
1493 | hir
::ExprKind
::Err
=> {}
1496 intravisit
::walk_expr(this
, expr
);
1499 impl<'tcx
> Liveness
<'_
, 'tcx
> {
1500 fn check_place(&mut self, expr
: &'tcx Expr
<'tcx
>) {
1502 hir
::ExprKind
::Path(hir
::QPath
::Resolved(_
, ref path
)) => {
1503 if let Res
::Local(var_hid
) = path
.res
{
1504 // Assignment to an immutable variable or argument: only legal
1505 // if there is no later assignment. If this local is actually
1506 // mutable, then check for a reassignment to flag the mutability
1508 let ln
= self.live_node(expr
.hir_id
, expr
.span
);
1509 let var
= self.variable(var_hid
, expr
.span
);
1510 self.warn_about_dead_assign(vec
![expr
.span
], expr
.hir_id
, ln
, var
);
1514 // For other kinds of places, no checks are required,
1515 // and any embedded expressions are actually rvalues
1516 intravisit
::walk_expr(self, expr
);
1521 fn should_warn(&self, var
: Variable
) -> Option
<String
> {
1522 let name
= self.ir
.variable_name(var
);
1523 if name
== kw
::Invalid
{
1526 let name
: &str = &name
.as_str();
1527 if name
.as_bytes()[0] == b'_'
{
1530 Some(name
.to_owned())
1533 fn warn_about_unused_upvars(&self, entry_ln
: LiveNode
) {
1534 let upvars
= match self.upvars
{
1536 Some(upvars
) => upvars
,
1538 for (&var_hir_id
, upvar
) in upvars
.iter() {
1539 let var
= self.variable(var_hir_id
, upvar
.span
);
1540 let upvar_id
= ty
::UpvarId
{
1541 var_path
: ty
::UpvarPath { hir_id: var_hir_id }
,
1542 closure_expr_id
: self.body_owner
,
1544 match self.typeck_results
.upvar_capture(upvar_id
) {
1545 ty
::UpvarCapture
::ByValue(_
) => {}
1546 ty
::UpvarCapture
::ByRef(..) => continue,
1548 if self.used_on_entry(entry_ln
, var
) {
1549 if self.live_on_entry(entry_ln
, var
).is_none() {
1550 if let Some(name
) = self.should_warn(var
) {
1551 self.ir
.tcx
.struct_span_lint_hir(
1552 lint
::builtin
::UNUSED_ASSIGNMENTS
,
1556 lint
.build(&format
!("value captured by `{}` is never read", name
))
1557 .help("did you mean to capture by reference instead?")
1564 if let Some(name
) = self.should_warn(var
) {
1565 self.ir
.tcx
.struct_span_lint_hir(
1566 lint
::builtin
::UNUSED_VARIABLES
,
1570 lint
.build(&format
!("unused variable: `{}`", name
))
1571 .help("did you mean to capture by reference instead?")
1580 fn warn_about_unused_args(&self, body
: &hir
::Body
<'_
>, entry_ln
: LiveNode
) {
1581 for p
in body
.params
{
1582 self.check_unused_vars_in_pat(&p
.pat
, Some(entry_ln
), |spans
, hir_id
, ln
, var
| {
1583 if self.live_on_entry(ln
, var
).is_none() {
1584 self.report_unsed_assign(hir_id
, spans
, var
, |name
| {
1585 format
!("value passed to `{}` is never read", name
)
1592 fn check_unused_vars_in_pat(
1595 entry_ln
: Option
<LiveNode
>,
1596 on_used_on_entry
: impl Fn(Vec
<Span
>, HirId
, LiveNode
, Variable
),
1598 // In an or-pattern, only consider the variable; any later patterns must have the same
1599 // bindings, and we also consider the first pattern to be the "authoritative" set of ids.
1600 // However, we should take the ids and spans of variables with the same name from the later
1601 // patterns so the suggestions to prefix with underscores will apply to those too.
1602 let mut vars
: FxIndexMap
<Symbol
, (LiveNode
, Variable
, Vec
<(HirId
, Span
)>)> = <_
>::default();
1604 pat
.each_binding(|_
, hir_id
, pat_sp
, ident
| {
1605 let ln
= entry_ln
.unwrap_or_else(|| self.live_node(hir_id
, pat_sp
));
1606 let var
= self.variable(hir_id
, ident
.span
);
1607 let id_and_sp
= (hir_id
, pat_sp
);
1608 vars
.entry(self.ir
.variable_name(var
))
1609 .and_modify(|(.., hir_ids_and_spans
)| hir_ids_and_spans
.push(id_and_sp
))
1610 .or_insert_with(|| (ln
, var
, vec
![id_and_sp
]));
1613 for (_
, (ln
, var
, hir_ids_and_spans
)) in vars
{
1614 if self.used_on_entry(ln
, var
) {
1615 let id
= hir_ids_and_spans
[0].0;
1616 let spans
= hir_ids_and_spans
.into_iter().map(|(_
, sp
)| sp
).collect();
1617 on_used_on_entry(spans
, id
, ln
, var
);
1619 self.report_unused(hir_ids_and_spans
, ln
, var
);
1624 fn report_unused(&self, hir_ids_and_spans
: Vec
<(HirId
, Span
)>, ln
: LiveNode
, var
: Variable
) {
1625 let first_hir_id
= hir_ids_and_spans
[0].0;
1627 if let Some(name
) = self.should_warn(var
).filter(|name
| name
!= "self") {
1628 // annoying: for parameters in funcs like `fn(x: i32)
1629 // {ret}`, there is only one node, so asking about
1630 // assigned_on_exit() is not meaningful.
1632 if ln
== self.exit_ln { false }
else { self.assigned_on_exit(ln, var).is_some() }
;
1635 self.ir
.tcx
.struct_span_lint_hir(
1636 lint
::builtin
::UNUSED_VARIABLES
,
1638 hir_ids_and_spans
.into_iter().map(|(_
, sp
)| sp
).collect
::<Vec
<_
>>(),
1640 lint
.build(&format
!("variable `{}` is assigned to, but never used", name
))
1641 .note(&format
!("consider using `_{}` instead", name
))
1646 self.ir
.tcx
.struct_span_lint_hir(
1647 lint
::builtin
::UNUSED_VARIABLES
,
1649 hir_ids_and_spans
.iter().map(|(_
, sp
)| *sp
).collect
::<Vec
<_
>>(),
1651 let mut err
= lint
.build(&format
!("unused variable: `{}`", name
));
1653 let (shorthands
, non_shorthands
): (Vec
<_
>, Vec
<_
>) =
1654 hir_ids_and_spans
.into_iter().partition(|(hir_id
, span
)| {
1655 let var
= self.variable(*hir_id
, *span
);
1656 self.ir
.variable_is_shorthand(var
)
1659 let mut shorthands
= shorthands
1661 .map(|(_
, span
)| (span
, format
!("{}: _", name
)))
1662 .collect
::<Vec
<_
>>();
1664 // If we have both shorthand and non-shorthand, prefer the "try ignoring
1665 // the field" message, and suggest `_` for the non-shorthands. If we only
1666 // have non-shorthand, then prefix with an underscore instead.
1667 if !shorthands
.is_empty() {
1671 .map(|(_
, span
)| (span
, "_".to_string()))
1672 .collect
::<Vec
<_
>>(),
1675 err
.multipart_suggestion(
1676 "try ignoring the field",
1678 Applicability
::MachineApplicable
,
1681 err
.multipart_suggestion(
1682 "if this is intentional, prefix it with an underscore",
1685 .map(|(_
, span
)| (span
, format
!("_{}", name
)))
1686 .collect
::<Vec
<_
>>(),
1687 Applicability
::MachineApplicable
,
1698 fn warn_about_dead_assign(&self, spans
: Vec
<Span
>, hir_id
: HirId
, ln
: LiveNode
, var
: Variable
) {
1699 if self.live_on_exit(ln
, var
).is_none() {
1700 self.report_unsed_assign(hir_id
, spans
, var
, |name
| {
1701 format
!("value assigned to `{}` is never read", name
)
1706 fn report_unsed_assign(
1711 message
: impl Fn(&str) -> String
,
1713 if let Some(name
) = self.should_warn(var
) {
1714 self.ir
.tcx
.struct_span_lint_hir(
1715 lint
::builtin
::UNUSED_ASSIGNMENTS
,
1719 lint
.build(&message(&name
))
1720 .help("maybe it is overwritten before being read?")