1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! A classic liveness analysis based on dataflow over the AST. Computes,
12 //! for each local variable in a function, whether that variable is live
13 //! at a given point. Program execution points are identified by their
18 //! The basic model is that each local variable is assigned an index. We
19 //! represent sets of local variables using a vector indexed by this
20 //! index. The value in the vector is either 0, indicating the variable
21 //! is dead, or the id of an expression that uses the variable.
23 //! We conceptually walk over the AST in reverse execution order. If we
24 //! find a use of a variable, we add it to the set of live variables. If
25 //! we find an assignment to a variable, we remove it from the set of live
26 //! variables. When we have to merge two flows, we take the union of
27 //! those two flows---if the variable is live on both paths, we simply
28 //! pick one id. In the event of loops, we continue doing this until a
29 //! fixed point is reached.
31 //! ## Checking initialization
33 //! At the function entry point, all variables must be dead. If this is
34 //! not the case, we can report an error using the id found in the set of
35 //! live variables, which identifies a use of the variable which is not
36 //! dominated by an assignment.
40 //! After each explicit move, the variable must be dead.
42 //! ## Computing last uses
44 //! Any use of the variable where the variable is dead afterwards is a
47 //! # Implementation details
49 //! The actual implementation contains two (nested) walks over the AST.
50 //! The outer walk has the job of building up the ir_maps instance for the
51 //! enclosing function. On the way down the tree, it identifies those AST
52 //! nodes and variable IDs that will be needed for the liveness analysis
53 //! and assigns them contiguous IDs. The liveness id for an AST node is
54 //! called a `live_node` (it's a newtype'd usize) and the id for a variable
55 //! is called a `variable` (another newtype'd usize).
57 //! On the way back up the tree, as we are about to exit from a function
58 //! declaration we allocate a `liveness` instance. Now that we know
59 //! precisely how many nodes and variables we need, we can allocate all
60 //! the various arrays that we will need to precisely the right size. We then
61 //! perform the actual propagation on the `liveness` instance.
63 //! This propagation is encoded in the various `propagate_through_*()`
64 //! methods. It effectively does a reverse walk of the AST; whenever we
65 //! reach a loop node, we iterate until a fixed point is reached.
67 //! ## The `Users` struct
69 //! At each live node `N`, we track three pieces of information for each
70 //! variable `V` (these are encapsulated in the `Users` struct):
72 //! - `reader`: the `LiveNode` ID of some node which will read the value
73 //! that `V` holds on entry to `N`. Formally: a node `M` such
74 //! that there exists a path `P` from `N` to `M` where `P` does not
75 //! write `V`. If the `reader` is `invalid_node()`, then the current
76 //! value will never be read (the variable is dead, essentially).
78 //! - `writer`: the `LiveNode` ID of some node which will write the
79 //! variable `V` and which is reachable from `N`. Formally: a node `M`
80 //! such that there exists a path `P` from `N` to `M` and `M` writes
81 //! `V`. If the `writer` is `invalid_node()`, then there is no writer
82 //! of `V` that follows `N`.
84 //! - `used`: a boolean value indicating whether `V` is *used*. We
85 //! distinguish a *read* from a *use* in that a *use* is some read that
86 //! is not just used to generate a new value. For example, `x += 1` is
87 //! a read but not a use. This is used to generate better warnings.
89 //! ## Special Variables
91 //! We generate various special variables for various, well, special purposes.
92 //! These are described in the `specials` struct:
94 //! - `exit_ln`: a live node that is generated to represent every 'exit' from
95 //! the function, whether it be by explicit return, panic, or other means.
97 //! - `fallthrough_ln`: a live node that represents a fallthrough
99 //! - `no_ret_var`: a synthetic variable that is only 'read' from, the
100 //! fallthrough node. This allows us to detect functions where we fail
101 //! to return explicitly.
102 //! - `clean_exit_var`: a synthetic variable that is only 'read' from the
103 //! fallthrough node. It is only live if the function could converge
104 //! via means other than an explicit `return` expression. That is, it is
105 //! only dead if the end of the function's block can never be reached.
106 //! It is the responsibility of typeck to ensure that there are no
107 //! `return` expressions in a function declared as diverging.
108 use self::LoopKind
::*;
109 use self::LiveNodeKind
::*;
110 use self::VarKind
::*;
113 use middle
::pat_util
;
117 use util
::nodemap
::NodeMap
;
119 use std
::{fmt, usize}
;
120 use std
::io
::prelude
::*;
123 use syntax
::ast
::{self, NodeId, Expr}
;
124 use syntax
::codemap
::{BytePos, original_sp, Span}
;
125 use syntax
::parse
::token
::special_idents
;
126 use syntax
::print
::pprust
::{expr_to_string, block_to_string}
;
128 use syntax
::ast_util
;
129 use syntax
::visit
::{self, Visitor, FnKind}
;
131 /// For use with `propagate_through_loop`.
133 /// An endless `loop` loop.
135 /// A `while` loop, with the given expression as condition.
139 #[derive(Copy, Clone, PartialEq)]
140 struct Variable(usize);
142 #[derive(Copy, PartialEq)]
143 struct LiveNode(usize);
146 fn get(&self) -> usize { let Variable(v) = *self; v }
150 fn get(&self) -> usize { let LiveNode(v) = *self; v }
153 impl Clone
for LiveNode
{
154 fn clone(&self) -> LiveNode
{
159 #[derive(Copy, Clone, PartialEq, Debug)]
167 fn live_node_kind_to_string(lnk
: LiveNodeKind
, cx
: &ty
::ctxt
) -> String
{
168 let cm
= cx
.sess
.codemap();
171 format
!("Free var node [{}]", cm
.span_to_string(s
))
174 format
!("Expr node [{}]", cm
.span_to_string(s
))
177 format
!("Var def node [{}]", cm
.span_to_string(s
))
179 ExitNode
=> "Exit node".to_string(),
183 impl<'a
, 'tcx
, 'v
> Visitor
<'v
> for IrMaps
<'a
, 'tcx
> {
184 fn visit_fn(&mut self, fk
: FnKind
<'v
>, fd
: &'v ast
::FnDecl
,
185 b
: &'v ast
::Block
, s
: Span
, id
: NodeId
) {
186 visit_fn(self, fk
, fd
, b
, s
, id
);
188 fn visit_local(&mut self, l
: &ast
::Local
) { visit_local(self, l); }
189 fn visit_expr(&mut self, ex
: &Expr
) { visit_expr(self, ex); }
190 fn visit_arm(&mut self, a
: &ast
::Arm
) { visit_arm(self, a); }
193 pub fn check_crate(tcx
: &ty
::ctxt
) {
194 visit
::walk_crate(&mut IrMaps
::new(tcx
), tcx
.map
.krate());
195 tcx
.sess
.abort_if_errors();
198 impl fmt
::Debug
for LiveNode
{
199 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
200 write
!(f
, "ln({})", self.get())
204 impl fmt
::Debug
for Variable
{
205 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
206 write
!(f
, "v({})", self.get())
210 // ______________________________________________________________________
213 // This is the first pass and the one that drives the main
214 // computation. It walks up and down the IR once. On the way down,
215 // we count for each function the number of variables as well as
216 // liveness nodes. A liveness node is basically an expression or
217 // capture clause that does something of interest: either it has
218 // interesting control flow or it uses/defines a local variable.
220 // On the way back up, at each function node we create liveness sets
221 // (we now know precisely how big to make our various vectors and so
222 // forth) and then do the data-flow propagation to compute the set
223 // of live variables at each program point.
225 // Finally, we run back over the IR one last time and, using the
226 // computed liveness, check various safety conditions. For example,
227 // there must be no live nodes at the definition site for a variable
228 // unless it has an initializer. Similarly, each non-mutable local
229 // variable must not be assigned if there is some successor
230 // assignment. And so forth.
233 fn is_valid(&self) -> bool
{
234 self.get() != usize::MAX
238 fn invalid_node() -> LiveNode { LiveNode(usize::MAX) }
245 #[derive(Copy, Clone, Debug)]
251 #[derive(Copy, Clone, Debug)]
253 Arg(NodeId
, ast
::Name
),
259 struct IrMaps
<'a
, 'tcx
: 'a
> {
260 tcx
: &'a ty
::ctxt
<'tcx
>,
262 num_live_nodes
: usize,
264 live_node_map
: NodeMap
<LiveNode
>,
265 variable_map
: NodeMap
<Variable
>,
266 capture_info_map
: NodeMap
<Rc
<Vec
<CaptureInfo
>>>,
267 var_kinds
: Vec
<VarKind
>,
268 lnks
: Vec
<LiveNodeKind
>,
271 impl<'a
, 'tcx
> IrMaps
<'a
, 'tcx
> {
272 fn new(tcx
: &'a ty
::ctxt
<'tcx
>) -> IrMaps
<'a
, 'tcx
> {
277 live_node_map
: NodeMap(),
278 variable_map
: NodeMap(),
279 capture_info_map
: NodeMap(),
280 var_kinds
: Vec
::new(),
285 fn add_live_node(&mut self, lnk
: LiveNodeKind
) -> LiveNode
{
286 let ln
= LiveNode(self.num_live_nodes
);
288 self.num_live_nodes
+= 1;
290 debug
!("{:?} is of kind {}", ln
,
291 live_node_kind_to_string(lnk
, self.tcx
));
296 fn add_live_node_for_node(&mut self, node_id
: NodeId
, lnk
: LiveNodeKind
) {
297 let ln
= self.add_live_node(lnk
);
298 self.live_node_map
.insert(node_id
, ln
);
300 debug
!("{:?} is node {}", ln
, node_id
);
303 fn add_variable(&mut self, vk
: VarKind
) -> Variable
{
304 let v
= Variable(self.num_vars
);
305 self.var_kinds
.push(vk
);
309 Local(LocalInfo { id: node_id, .. }
) | Arg(node_id
, _
) => {
310 self.variable_map
.insert(node_id
, v
);
312 ImplicitRet
| CleanExit
=> {}
315 debug
!("{:?} is {:?}", v
, vk
);
320 fn variable(&self, node_id
: NodeId
, span
: Span
) -> Variable
{
321 match self.variable_map
.get(&node_id
) {
326 .span_bug(span
, &format
!("no variable registered for id {}",
332 fn variable_name(&self, var
: Variable
) -> String
{
333 match self.var_kinds
[var
.get()] {
334 Local(LocalInfo { name, .. }
) | Arg(_
, name
) => {
337 ImplicitRet
=> "<implicit-ret>".to_string(),
338 CleanExit
=> "<clean-exit>".to_string()
342 fn set_captures(&mut self, node_id
: NodeId
, cs
: Vec
<CaptureInfo
>) {
343 self.capture_info_map
.insert(node_id
, Rc
::new(cs
));
346 fn lnk(&self, ln
: LiveNode
) -> LiveNodeKind
{
351 impl<'a
, 'tcx
, 'v
> Visitor
<'v
> for Liveness
<'a
, 'tcx
> {
352 fn visit_fn(&mut self, fk
: FnKind
<'v
>, fd
: &'v ast
::FnDecl
,
353 b
: &'v ast
::Block
, s
: Span
, n
: NodeId
) {
354 check_fn(self, fk
, fd
, b
, s
, n
);
356 fn visit_local(&mut self, l
: &ast
::Local
) {
357 check_local(self, l
);
359 fn visit_expr(&mut self, ex
: &Expr
) {
360 check_expr(self, ex
);
362 fn visit_arm(&mut self, a
: &ast
::Arm
) {
367 fn visit_fn(ir
: &mut IrMaps
,
375 // swap in a new set of IR maps for this function body:
376 let mut fn_maps
= IrMaps
::new(ir
.tcx
);
378 debug
!("creating fn_maps: {:?}", &fn_maps
as *const IrMaps
);
380 for arg
in &decl
.inputs
{
381 pat_util
::pat_bindings(&ir
.tcx
.def_map
,
383 |_bm
, arg_id
, _x
, path1
| {
384 debug
!("adding argument {}", arg_id
);
385 let name
= path1
.node
.name
;
386 fn_maps
.add_variable(Arg(arg_id
, name
));
390 // gather up the various local variables, significant expressions,
392 visit
::walk_fn(&mut fn_maps
, fk
, decl
, body
, sp
);
394 // Special nodes and variables:
395 // - exit_ln represents the end of the fn, either by return or panic
396 // - implicit_ret_var is a pseudo-variable that represents
397 // an implicit return
398 let specials
= Specials
{
399 exit_ln
: fn_maps
.add_live_node(ExitNode
),
400 fallthrough_ln
: fn_maps
.add_live_node(ExitNode
),
401 no_ret_var
: fn_maps
.add_variable(ImplicitRet
),
402 clean_exit_var
: fn_maps
.add_variable(CleanExit
)
406 let mut lsets
= Liveness
::new(&mut fn_maps
, specials
);
407 let entry_ln
= lsets
.compute(decl
, body
);
409 // check for various error conditions
410 lsets
.visit_block(body
);
411 lsets
.check_ret(id
, sp
, fk
, entry_ln
, body
);
412 lsets
.warn_about_unused_args(decl
, entry_ln
);
415 fn visit_local(ir
: &mut IrMaps
, local
: &ast
::Local
) {
416 pat_util
::pat_bindings(&ir
.tcx
.def_map
, &*local
.pat
, |_
, p_id
, sp
, path1
| {
417 debug
!("adding local variable {}", p_id
);
418 let name
= path1
.node
.name
;
419 ir
.add_live_node_for_node(p_id
, VarDefNode(sp
));
420 ir
.add_variable(Local(LocalInfo
{
425 visit
::walk_local(ir
, local
);
428 fn visit_arm(ir
: &mut IrMaps
, arm
: &ast
::Arm
) {
429 for pat
in &arm
.pats
{
430 pat_util
::pat_bindings(&ir
.tcx
.def_map
, &**pat
, |bm
, p_id
, sp
, path1
| {
431 debug
!("adding local variable {} from match with bm {:?}",
433 let name
= path1
.node
.name
;
434 ir
.add_live_node_for_node(p_id
, VarDefNode(sp
));
435 ir
.add_variable(Local(LocalInfo
{
441 visit
::walk_arm(ir
, arm
);
444 fn visit_expr(ir
: &mut IrMaps
, expr
: &Expr
) {
446 // live nodes required for uses or definitions of variables:
447 ast
::ExprPath(..) => {
448 let def
= ir
.tcx
.def_map
.borrow().get(&expr
.id
).unwrap().full_def();
449 debug
!("expr {}: path that leads to {:?}", expr
.id
, def
);
450 if let DefLocal(..) = def
{
451 ir
.add_live_node_for_node(expr
.id
, ExprNode(expr
.span
));
453 visit
::walk_expr(ir
, expr
);
455 ast
::ExprClosure(..) => {
456 // Interesting control flow (for loops can contain labeled
457 // breaks or continues)
458 ir
.add_live_node_for_node(expr
.id
, ExprNode(expr
.span
));
460 // Make a live_node for each captured variable, with the span
461 // being the location that the variable is used. This results
462 // in better error messages than just pointing at the closure
463 // construction site.
464 let mut call_caps
= Vec
::new();
465 ir
.tcx
.with_freevars(expr
.id
, |freevars
| {
467 if let DefLocal(rv
) = fv
.def
{
468 let fv_ln
= ir
.add_live_node(FreeVarNode(fv
.span
));
469 call_caps
.push(CaptureInfo
{ln
: fv_ln
,
474 ir
.set_captures(expr
.id
, call_caps
);
476 visit
::walk_expr(ir
, expr
);
479 // live nodes required for interesting control flow:
480 ast
::ExprIf(..) | ast
::ExprMatch(..) | ast
::ExprWhile(..) | ast
::ExprLoop(..) => {
481 ir
.add_live_node_for_node(expr
.id
, ExprNode(expr
.span
));
482 visit
::walk_expr(ir
, expr
);
484 ast
::ExprIfLet(..) => {
485 ir
.tcx
.sess
.span_bug(expr
.span
, "non-desugared ExprIfLet");
487 ast
::ExprWhileLet(..) => {
488 ir
.tcx
.sess
.span_bug(expr
.span
, "non-desugared ExprWhileLet");
490 ast
::ExprForLoop(..) => {
491 ir
.tcx
.sess
.span_bug(expr
.span
, "non-desugared ExprForLoop");
493 ast
::ExprBinary(op
, _
, _
) if ast_util
::lazy_binop(op
.node
) => {
494 ir
.add_live_node_for_node(expr
.id
, ExprNode(expr
.span
));
495 visit
::walk_expr(ir
, expr
);
498 // otherwise, live nodes are not required:
499 ast
::ExprIndex(..) | ast
::ExprField(..) | ast
::ExprTupField(..) |
500 ast
::ExprVec(..) | ast
::ExprCall(..) | ast
::ExprMethodCall(..) |
501 ast
::ExprTup(..) | ast
::ExprBinary(..) | ast
::ExprAddrOf(..) |
502 ast
::ExprCast(..) | ast
::ExprUnary(..) | ast
::ExprBreak(_
) |
503 ast
::ExprAgain(_
) | ast
::ExprLit(_
) | ast
::ExprRet(..) |
504 ast
::ExprBlock(..) | ast
::ExprAssign(..) | ast
::ExprAssignOp(..) |
505 ast
::ExprMac(..) | ast
::ExprStruct(..) | ast
::ExprRepeat(..) |
506 ast
::ExprParen(..) | ast
::ExprInlineAsm(..) | ast
::ExprBox(..) |
507 ast
::ExprRange(..) => {
508 visit
::walk_expr(ir
, expr
);
513 // ______________________________________________________________________
514 // Computing liveness sets
516 // Actually we compute just a bit more than just liveness, but we use
517 // the same basic propagation framework in all cases.
519 #[derive(Clone, Copy)]
526 fn invalid_users() -> Users
{
528 reader
: invalid_node(),
529 writer
: invalid_node(),
534 #[derive(Copy, Clone)]
537 fallthrough_ln
: LiveNode
,
538 no_ret_var
: Variable
,
539 clean_exit_var
: Variable
542 const ACC_READ
: u32 = 1;
543 const ACC_WRITE
: u32 = 2;
544 const ACC_USE
: u32 = 4;
546 struct Liveness
<'a
, 'tcx
: 'a
> {
547 ir
: &'a
mut IrMaps
<'a
, 'tcx
>,
549 successors
: Vec
<LiveNode
>,
551 // The list of node IDs for the nested loop scopes
553 loop_scope
: Vec
<NodeId
>,
554 // mappings from loop node ID to LiveNode
555 // ("break" label should map to loop node ID,
556 // it probably doesn't now)
557 break_ln
: NodeMap
<LiveNode
>,
558 cont_ln
: NodeMap
<LiveNode
>
561 impl<'a
, 'tcx
> Liveness
<'a
, 'tcx
> {
562 fn new(ir
: &'a
mut IrMaps
<'a
, 'tcx
>, specials
: Specials
) -> Liveness
<'a
, 'tcx
> {
563 let num_live_nodes
= ir
.num_live_nodes
;
564 let num_vars
= ir
.num_vars
;
568 successors
: vec
![invalid_node(); num_live_nodes
],
569 users
: vec
![invalid_users(); num_live_nodes
* num_vars
],
570 loop_scope
: Vec
::new(),
576 fn live_node(&self, node_id
: NodeId
, span
: Span
) -> LiveNode
{
577 match self.ir
.live_node_map
.get(&node_id
) {
580 // This must be a mismatch between the ir_map construction
581 // above and the propagation code below; the two sets of
582 // code have to agree about which AST nodes are worth
583 // creating liveness nodes for.
584 self.ir
.tcx
.sess
.span_bug(
586 &format
!("no live node registered for node {}",
592 fn variable(&self, node_id
: NodeId
, span
: Span
) -> Variable
{
593 self.ir
.variable(node_id
, span
)
596 fn pat_bindings
<F
>(&mut self, pat
: &ast
::Pat
, mut f
: F
) where
597 F
: FnMut(&mut Liveness
<'a
, 'tcx
>, LiveNode
, Variable
, Span
, NodeId
),
599 pat_util
::pat_bindings(&self.ir
.tcx
.def_map
, pat
, |_bm
, p_id
, sp
, _n
| {
600 let ln
= self.live_node(p_id
, sp
);
601 let var
= self.variable(p_id
, sp
);
602 f(self, ln
, var
, sp
, p_id
);
606 fn arm_pats_bindings
<F
>(&mut self, pat
: Option
<&ast
::Pat
>, f
: F
) where
607 F
: FnMut(&mut Liveness
<'a
, 'tcx
>, LiveNode
, Variable
, Span
, NodeId
),
611 self.pat_bindings(pat
, f
);
617 fn define_bindings_in_pat(&mut self, pat
: &ast
::Pat
, succ
: LiveNode
)
619 self.define_bindings_in_arm_pats(Some(pat
), succ
)
622 fn define_bindings_in_arm_pats(&mut self, pat
: Option
<&ast
::Pat
>, succ
: LiveNode
)
625 self.arm_pats_bindings(pat
, |this
, ln
, var
, _sp
, _id
| {
626 this
.init_from_succ(ln
, succ
);
627 this
.define(ln
, var
);
633 fn idx(&self, ln
: LiveNode
, var
: Variable
) -> usize {
634 ln
.get() * self.ir
.num_vars
+ var
.get()
637 fn live_on_entry(&self, ln
: LiveNode
, var
: Variable
)
638 -> Option
<LiveNodeKind
> {
639 assert
!(ln
.is_valid());
640 let reader
= self.users
[self.idx(ln
, var
)].reader
;
641 if reader
.is_valid() {Some(self.ir.lnk(reader))}
else {None}
645 Is this variable live on entry to any of its successor nodes?
647 fn live_on_exit(&self, ln
: LiveNode
, var
: Variable
)
648 -> Option
<LiveNodeKind
> {
649 let successor
= self.successors
[ln
.get()];
650 self.live_on_entry(successor
, var
)
653 fn used_on_entry(&self, ln
: LiveNode
, var
: Variable
) -> bool
{
654 assert
!(ln
.is_valid());
655 self.users
[self.idx(ln
, var
)].used
658 fn assigned_on_entry(&self, ln
: LiveNode
, var
: Variable
)
659 -> Option
<LiveNodeKind
> {
660 assert
!(ln
.is_valid());
661 let writer
= self.users
[self.idx(ln
, var
)].writer
;
662 if writer
.is_valid() {Some(self.ir.lnk(writer))}
else {None}
665 fn assigned_on_exit(&self, ln
: LiveNode
, var
: Variable
)
666 -> Option
<LiveNodeKind
> {
667 let successor
= self.successors
[ln
.get()];
668 self.assigned_on_entry(successor
, var
)
671 fn indices2
<F
>(&mut self, ln
: LiveNode
, succ_ln
: LiveNode
, mut op
: F
) where
672 F
: FnMut(&mut Liveness
<'a
, 'tcx
>, usize, usize),
674 let node_base_idx
= self.idx(ln
, Variable(0));
675 let succ_base_idx
= self.idx(succ_ln
, Variable(0));
676 for var_idx
in 0..self.ir
.num_vars
{
677 op(self, node_base_idx
+ var_idx
, succ_base_idx
+ var_idx
);
681 fn write_vars
<F
>(&self,
685 -> io
::Result
<()> where
686 F
: FnMut(usize) -> LiveNode
,
688 let node_base_idx
= self.idx(ln
, Variable(0));
689 for var_idx
in 0..self.ir
.num_vars
{
690 let idx
= node_base_idx
+ var_idx
;
691 if test(idx
).is_valid() {
692 try
!(write
!(wr
, " {:?}", Variable(var_idx
)));
698 fn find_loop_scope(&self,
699 opt_label
: Option
<ast
::Ident
>,
705 // Refers to a labeled loop. Use the results of resolve
707 match self.ir
.tcx
.def_map
.borrow().get(&id
).map(|d
| d
.full_def()) {
708 Some(DefLabel(loop_id
)) => loop_id
,
709 _
=> self.ir
.tcx
.sess
.span_bug(sp
, "label on break/loop \
710 doesn't refer to a loop")
714 // Vanilla 'break' or 'loop', so use the enclosing
716 if self.loop_scope
.is_empty() {
717 self.ir
.tcx
.sess
.span_bug(sp
, "break outside loop");
719 *self.loop_scope
.last().unwrap()
725 #[allow(unused_must_use)]
726 fn ln_str(&self, ln
: LiveNode
) -> String
{
727 let mut wr
= Vec
::new();
729 let wr
= &mut wr
as &mut Write
;
730 write
!(wr
, "[ln({:?}) of kind {:?} reads", ln
.get(), self.ir
.lnk(ln
));
731 self.write_vars(wr
, ln
, |idx
| self.users
[idx
].reader
);
732 write
!(wr
, " writes");
733 self.write_vars(wr
, ln
, |idx
| self.users
[idx
].writer
);
734 write
!(wr
, " precedes {:?}]", self.successors
[ln
.get()]);
736 String
::from_utf8(wr
).unwrap()
739 fn init_empty(&mut self, ln
: LiveNode
, succ_ln
: LiveNode
) {
740 self.successors
[ln
.get()] = succ_ln
;
742 // It is not necessary to initialize the
743 // values to empty because this is the value
744 // they have when they are created, and the sets
745 // only grow during iterations.
747 // self.indices(ln) { |idx|
748 // self.users[idx] = invalid_users();
752 fn init_from_succ(&mut self, ln
: LiveNode
, succ_ln
: LiveNode
) {
753 // more efficient version of init_empty() / merge_from_succ()
754 self.successors
[ln
.get()] = succ_ln
;
756 self.indices2(ln
, succ_ln
, |this
, idx
, succ_idx
| {
757 this
.users
[idx
] = this
.users
[succ_idx
]
759 debug
!("init_from_succ(ln={}, succ={})",
760 self.ln_str(ln
), self.ln_str(succ_ln
));
763 fn merge_from_succ(&mut self,
768 if ln
== succ_ln { return false; }
770 let mut changed
= false;
771 self.indices2(ln
, succ_ln
, |this
, idx
, succ_idx
| {
772 changed
|= copy_if_invalid(this
.users
[succ_idx
].reader
,
773 &mut this
.users
[idx
].reader
);
774 changed
|= copy_if_invalid(this
.users
[succ_idx
].writer
,
775 &mut this
.users
[idx
].writer
);
776 if this
.users
[succ_idx
].used
&& !this
.users
[idx
].used
{
777 this
.users
[idx
].used
= true;
782 debug
!("merge_from_succ(ln={:?}, succ={}, first_merge={}, changed={})",
783 ln
, self.ln_str(succ_ln
), first_merge
, changed
);
786 fn copy_if_invalid(src
: LiveNode
, dst
: &mut LiveNode
) -> bool
{
787 if src
.is_valid() && !dst
.is_valid() {
796 // Indicates that a local variable was *defined*; we know that no
797 // uses of the variable can precede the definition (resolve checks
798 // this) so we just clear out all the data.
799 fn define(&mut self, writer
: LiveNode
, var
: Variable
) {
800 let idx
= self.idx(writer
, var
);
801 self.users
[idx
].reader
= invalid_node();
802 self.users
[idx
].writer
= invalid_node();
804 debug
!("{:?} defines {:?} (idx={}): {}", writer
, var
,
805 idx
, self.ln_str(writer
));
808 // Either read, write, or both depending on the acc bitset
809 fn acc(&mut self, ln
: LiveNode
, var
: Variable
, acc
: u32) {
810 debug
!("{:?} accesses[{:x}] {:?}: {}",
811 ln
, acc
, var
, self.ln_str(ln
));
813 let idx
= self.idx(ln
, var
);
814 let user
= &mut self.users
[idx
];
816 if (acc
& ACC_WRITE
) != 0 {
817 user
.reader
= invalid_node();
821 // Important: if we both read/write, must do read second
822 // or else the write will override.
823 if (acc
& ACC_READ
) != 0 {
827 if (acc
& ACC_USE
) != 0 {
832 // _______________________________________________________________________
834 fn compute(&mut self, decl
: &ast
::FnDecl
, body
: &ast
::Block
) -> LiveNode
{
835 // if there is a `break` or `again` at the top level, then it's
836 // effectively a return---this only occurs in `for` loops,
837 // where the body is really a closure.
839 debug
!("compute: using id for block, {}", block_to_string(body
));
841 let exit_ln
= self.s
.exit_ln
;
842 let entry_ln
: LiveNode
=
843 self.with_loop_nodes(body
.id
, exit_ln
, exit_ln
,
844 |this
| this
.propagate_through_fn_block(decl
, body
));
846 // hack to skip the loop unless debug! is enabled:
847 debug
!("^^ liveness computation results for body {} (entry={:?})",
849 for ln_idx
in 0..self.ir
.num_live_nodes
{
850 debug
!("{:?}", self.ln_str(LiveNode(ln_idx
)));
859 fn propagate_through_fn_block(&mut self, _
: &ast
::FnDecl
, blk
: &ast
::Block
)
861 // the fallthrough exit is only for those cases where we do not
862 // explicitly return:
864 self.init_from_succ(s
.fallthrough_ln
, s
.exit_ln
);
865 if blk
.expr
.is_none() {
866 self.acc(s
.fallthrough_ln
, s
.no_ret_var
, ACC_READ
)
868 self.acc(s
.fallthrough_ln
, s
.clean_exit_var
, ACC_READ
);
870 self.propagate_through_block(blk
, s
.fallthrough_ln
)
873 fn propagate_through_block(&mut self, blk
: &ast
::Block
, succ
: LiveNode
)
875 let succ
= self.propagate_through_opt_expr(blk
.expr
.as_ref().map(|e
| &**e
), succ
);
876 blk
.stmts
.iter().rev().fold(succ
, |succ
, stmt
| {
877 self.propagate_through_stmt(&**stmt
, succ
)
881 fn propagate_through_stmt(&mut self, stmt
: &ast
::Stmt
, succ
: LiveNode
)
884 ast
::StmtDecl(ref decl
, _
) => {
885 self.propagate_through_decl(&**decl
, succ
)
888 ast
::StmtExpr(ref expr
, _
) | ast
::StmtSemi(ref expr
, _
) => {
889 self.propagate_through_expr(&**expr
, succ
)
892 ast
::StmtMac(..) => {
893 self.ir
.tcx
.sess
.span_bug(stmt
.span
, "unexpanded macro");
898 fn propagate_through_decl(&mut self, decl
: &ast
::Decl
, succ
: LiveNode
)
901 ast
::DeclLocal(ref local
) => {
902 self.propagate_through_local(&**local
, succ
)
904 ast
::DeclItem(_
) => succ
,
908 fn propagate_through_local(&mut self, local
: &ast
::Local
, succ
: LiveNode
)
910 // Note: we mark the variable as defined regardless of whether
911 // there is an initializer. Initially I had thought to only mark
912 // the live variable as defined if it was initialized, and then we
913 // could check for uninit variables just by scanning what is live
914 // at the start of the function. But that doesn't work so well for
915 // immutable variables defined in a loop:
916 // loop { let x; x = 5; }
917 // because the "assignment" loops back around and generates an error.
919 // So now we just check that variables defined w/o an
920 // initializer are not live at the point of their
921 // initialization, which is mildly more complex than checking
922 // once at the func header but otherwise equivalent.
924 let succ
= self.propagate_through_opt_expr(local
.init
.as_ref().map(|e
| &**e
), succ
);
925 self.define_bindings_in_pat(&*local
.pat
, succ
)
928 fn propagate_through_exprs(&mut self, exprs
: &[P
<Expr
>], succ
: LiveNode
)
930 exprs
.iter().rev().fold(succ
, |succ
, expr
| {
931 self.propagate_through_expr(&**expr
, succ
)
935 fn propagate_through_opt_expr(&mut self,
936 opt_expr
: Option
<&Expr
>,
939 opt_expr
.map_or(succ
, |expr
| self.propagate_through_expr(expr
, succ
))
942 fn propagate_through_expr(&mut self, expr
: &Expr
, succ
: LiveNode
)
944 debug
!("propagate_through_expr: {}", expr_to_string(expr
));
947 // Interesting cases with control flow or which gen/kill
949 ast
::ExprPath(..) => {
950 self.access_path(expr
, succ
, ACC_READ
| ACC_USE
)
953 ast
::ExprField(ref e
, _
) => {
954 self.propagate_through_expr(&**e
, succ
)
957 ast
::ExprTupField(ref e
, _
) => {
958 self.propagate_through_expr(&**e
, succ
)
961 ast
::ExprClosure(_
, _
, ref blk
) => {
962 debug
!("{} is an ExprClosure",
963 expr_to_string(expr
));
966 The next-node for a break is the successor of the entire
967 loop. The next-node for a continue is the top of this loop.
969 let node
= self.live_node(expr
.id
, expr
.span
);
970 self.with_loop_nodes(blk
.id
, succ
, node
, |this
| {
972 // the construction of a closure itself is not important,
973 // but we have to consider the closed over variables.
974 let caps
= match this
.ir
.capture_info_map
.get(&expr
.id
) {
975 Some(caps
) => caps
.clone(),
977 this
.ir
.tcx
.sess
.span_bug(expr
.span
, "no registered caps");
980 caps
.iter().rev().fold(succ
, |succ
, cap
| {
981 this
.init_from_succ(cap
.ln
, succ
);
982 let var
= this
.variable(cap
.var_nid
, expr
.span
);
983 this
.acc(cap
.ln
, var
, ACC_READ
| ACC_USE
);
989 ast
::ExprIf(ref cond
, ref then
, ref els
) => {
1003 let else_ln
= self.propagate_through_opt_expr(els
.as_ref().map(|e
| &**e
), succ
);
1004 let then_ln
= self.propagate_through_block(&**then
, succ
);
1005 let ln
= self.live_node(expr
.id
, expr
.span
);
1006 self.init_from_succ(ln
, else_ln
);
1007 self.merge_from_succ(ln
, then_ln
, false);
1008 self.propagate_through_expr(&**cond
, ln
)
1011 ast
::ExprIfLet(..) => {
1012 self.ir
.tcx
.sess
.span_bug(expr
.span
, "non-desugared ExprIfLet");
1015 ast
::ExprWhile(ref cond
, ref blk
, _
) => {
1016 self.propagate_through_loop(expr
, WhileLoop(&**cond
), &**blk
, succ
)
1019 ast
::ExprWhileLet(..) => {
1020 self.ir
.tcx
.sess
.span_bug(expr
.span
, "non-desugared ExprWhileLet");
1023 ast
::ExprForLoop(..) => {
1024 self.ir
.tcx
.sess
.span_bug(expr
.span
, "non-desugared ExprForLoop");
1027 // Note that labels have been resolved, so we don't need to look
1028 // at the label ident
1029 ast
::ExprLoop(ref blk
, _
) => {
1030 self.propagate_through_loop(expr
, LoopLoop
, &**blk
, succ
)
1033 ast
::ExprMatch(ref e
, ref arms
, _
) => {
1048 let ln
= self.live_node(expr
.id
, expr
.span
);
1049 self.init_empty(ln
, succ
);
1050 let mut first_merge
= true;
1053 self.propagate_through_expr(&*arm
.body
, succ
);
1055 self.propagate_through_opt_expr(arm
.guard
.as_ref().map(|e
| &**e
), body_succ
);
1056 // only consider the first pattern; any later patterns must have
1057 // the same bindings, and we also consider the first pattern to be
1058 // the "authoritative" set of ids
1060 self.define_bindings_in_arm_pats(arm
.pats
.first().map(|p
| &**p
),
1062 self.merge_from_succ(ln
, arm_succ
, first_merge
);
1063 first_merge
= false;
1065 self.propagate_through_expr(&**e
, ln
)
1068 ast
::ExprRet(ref o_e
) => {
1069 // ignore succ and subst exit_ln:
1070 let exit_ln
= self.s
.exit_ln
;
1071 self.propagate_through_opt_expr(o_e
.as_ref().map(|e
| &**e
), exit_ln
)
1074 ast
::ExprBreak(opt_label
) => {
1075 // Find which label this break jumps to
1076 let sc
= self.find_loop_scope(opt_label
, expr
.id
, expr
.span
);
1078 // Now that we know the label we're going to,
1079 // look it up in the break loop nodes table
1081 match self.break_ln
.get(&sc
) {
1083 None
=> self.ir
.tcx
.sess
.span_bug(expr
.span
,
1084 "break to unknown label")
1088 ast
::ExprAgain(opt_label
) => {
1089 // Find which label this expr continues to
1090 let sc
= self.find_loop_scope(opt_label
, expr
.id
, expr
.span
);
1092 // Now that we know the label we're going to,
1093 // look it up in the continue loop nodes table
1095 match self.cont_ln
.get(&sc
) {
1097 None
=> self.ir
.tcx
.sess
.span_bug(expr
.span
,
1098 "loop to unknown label")
1102 ast
::ExprAssign(ref l
, ref r
) => {
1103 // see comment on lvalues in
1104 // propagate_through_lvalue_components()
1105 let succ
= self.write_lvalue(&**l
, succ
, ACC_WRITE
);
1106 let succ
= self.propagate_through_lvalue_components(&**l
, succ
);
1107 self.propagate_through_expr(&**r
, succ
)
1110 ast
::ExprAssignOp(_
, ref l
, ref r
) => {
1111 // see comment on lvalues in
1112 // propagate_through_lvalue_components()
1113 let succ
= self.write_lvalue(&**l
, succ
, ACC_WRITE
|ACC_READ
);
1114 let succ
= self.propagate_through_expr(&**r
, succ
);
1115 self.propagate_through_lvalue_components(&**l
, succ
)
1118 // Uninteresting cases: just propagate in rev exec order
1120 ast
::ExprVec(ref exprs
) => {
1121 self.propagate_through_exprs(&exprs
[..], succ
)
1124 ast
::ExprRepeat(ref element
, ref count
) => {
1125 let succ
= self.propagate_through_expr(&**count
, succ
);
1126 self.propagate_through_expr(&**element
, succ
)
1129 ast
::ExprStruct(_
, ref fields
, ref with_expr
) => {
1130 let succ
= self.propagate_through_opt_expr(with_expr
.as_ref().map(|e
| &**e
), succ
);
1131 fields
.iter().rev().fold(succ
, |succ
, field
| {
1132 self.propagate_through_expr(&*field
.expr
, succ
)
1136 ast
::ExprCall(ref f
, ref args
) => {
1137 let diverges
= !self.ir
.tcx
.is_method_call(expr
.id
) &&
1138 self.ir
.tcx
.expr_ty_adjusted(&**f
).fn_ret().diverges();
1139 let succ
= if diverges
{
1144 let succ
= self.propagate_through_exprs(&args
[..], succ
);
1145 self.propagate_through_expr(&**f
, succ
)
1148 ast
::ExprMethodCall(_
, _
, ref args
) => {
1149 let method_call
= ty
::MethodCall
::expr(expr
.id
);
1150 let method_ty
= self.ir
.tcx
.tables
.borrow().method_map
[&method_call
].ty
;
1151 let succ
= if method_ty
.fn_ret().diverges() {
1156 self.propagate_through_exprs(&args
[..], succ
)
1159 ast
::ExprTup(ref exprs
) => {
1160 self.propagate_through_exprs(&exprs
[..], succ
)
1163 ast
::ExprBinary(op
, ref l
, ref r
) if ast_util
::lazy_binop(op
.node
) => {
1164 let r_succ
= self.propagate_through_expr(&**r
, succ
);
1166 let ln
= self.live_node(expr
.id
, expr
.span
);
1167 self.init_from_succ(ln
, succ
);
1168 self.merge_from_succ(ln
, r_succ
, false);
1170 self.propagate_through_expr(&**l
, ln
)
1173 ast
::ExprIndex(ref l
, ref r
) |
1174 ast
::ExprBinary(_
, ref l
, ref r
) |
1175 ast
::ExprBox(Some(ref l
), ref r
) => {
1176 let r_succ
= self.propagate_through_expr(&**r
, succ
);
1177 self.propagate_through_expr(&**l
, r_succ
)
1180 ast
::ExprRange(ref e1
, ref e2
) => {
1181 let succ
= e2
.as_ref().map_or(succ
, |e
| self.propagate_through_expr(&**e
, succ
));
1182 e1
.as_ref().map_or(succ
, |e
| self.propagate_through_expr(&**e
, succ
))
1185 ast
::ExprBox(None
, ref e
) |
1186 ast
::ExprAddrOf(_
, ref e
) |
1187 ast
::ExprCast(ref e
, _
) |
1188 ast
::ExprUnary(_
, ref e
) |
1189 ast
::ExprParen(ref e
) => {
1190 self.propagate_through_expr(&**e
, succ
)
1193 ast
::ExprInlineAsm(ref ia
) => {
1195 let succ
= ia
.outputs
.iter().rev().fold(succ
, |succ
, &(_
, ref expr
, _
)| {
1196 // see comment on lvalues
1197 // in propagate_through_lvalue_components()
1198 let succ
= self.write_lvalue(&**expr
, succ
, ACC_WRITE
);
1199 self.propagate_through_lvalue_components(&**expr
, succ
)
1201 // Inputs are executed first. Propagate last because of rev order
1202 ia
.inputs
.iter().rev().fold(succ
, |succ
, &(_
, ref expr
)| {
1203 self.propagate_through_expr(&**expr
, succ
)
1207 ast
::ExprLit(..) => {
1211 ast
::ExprBlock(ref blk
) => {
1212 self.propagate_through_block(&**blk
, succ
)
1215 ast
::ExprMac(..) => {
1216 self.ir
.tcx
.sess
.span_bug(expr
.span
, "unexpanded macro");
1221 fn propagate_through_lvalue_components(&mut self,
1227 // In general, the full flow graph structure for an
1228 // assignment/move/etc can be handled in one of two ways,
1229 // depending on whether what is being assigned is a "tracked
1230 // value" or not. A tracked value is basically a local
1231 // variable or argument.
1233 // The two kinds of graphs are:
1235 // Tracked lvalue Untracked lvalue
1236 // ----------------------++-----------------------
1240 // (rvalue) || (rvalue)
1243 // (write of lvalue) || (lvalue components)
1248 // ----------------------++-----------------------
1250 // I will cover the two cases in turn:
1252 // # Tracked lvalues
1254 // A tracked lvalue is a local variable/argument `x`. In
1255 // these cases, the link_node where the write occurs is linked
1256 // to node id of `x`. The `write_lvalue()` routine generates
1257 // the contents of this node. There are no subcomponents to
1260 // # Non-tracked lvalues
1262 // These are lvalues like `x[5]` or `x.f`. In that case, we
1263 // basically ignore the value which is written to but generate
1264 // reads for the components---`x` in these two examples. The
1265 // components reads are generated by
1266 // `propagate_through_lvalue_components()` (this fn).
1268 // # Illegal lvalues
1270 // It is still possible to observe assignments to non-lvalues;
1271 // these errors are detected in the later pass borrowck. We
1272 // just ignore such cases and treat them as reads.
1275 ast
::ExprPath(..) => succ
,
1276 ast
::ExprField(ref e
, _
) => self.propagate_through_expr(&**e
, succ
),
1277 ast
::ExprTupField(ref e
, _
) => self.propagate_through_expr(&**e
, succ
),
1278 _
=> self.propagate_through_expr(expr
, succ
)
1282 // see comment on propagate_through_lvalue()
1283 fn write_lvalue(&mut self, expr
: &Expr
, succ
: LiveNode
, acc
: u32)
1286 ast
::ExprPath(..) => {
1287 self.access_path(expr
, succ
, acc
)
1290 // We do not track other lvalues, so just propagate through
1291 // to their subcomponents. Also, it may happen that
1292 // non-lvalues occur here, because those are detected in the
1293 // later pass borrowck.
1298 fn access_path(&mut self, expr
: &Expr
, succ
: LiveNode
, acc
: u32)
1300 match self.ir
.tcx
.def_map
.borrow().get(&expr
.id
).unwrap().full_def() {
1302 let ln
= self.live_node(expr
.id
, expr
.span
);
1304 self.init_from_succ(ln
, succ
);
1305 let var
= self.variable(nid
, expr
.span
);
1306 self.acc(ln
, var
, acc
);
1314 fn propagate_through_loop(&mut self,
1323 We model control flow like this:
1341 let mut first_merge
= true;
1342 let ln
= self.live_node(expr
.id
, expr
.span
);
1343 self.init_empty(ln
, succ
);
1347 // If this is not a `loop` loop, then it's possible we bypass
1348 // the body altogether. Otherwise, the only way is via a `break`
1349 // in the loop body.
1350 self.merge_from_succ(ln
, succ
, first_merge
);
1351 first_merge
= false;
1354 debug
!("propagate_through_loop: using id for loop body {} {}",
1355 expr
.id
, block_to_string(body
));
1357 let cond_ln
= match kind
{
1359 WhileLoop(ref cond
) => self.propagate_through_expr(&**cond
, ln
),
1361 let body_ln
= self.with_loop_nodes(expr
.id
, succ
, ln
, |this
| {
1362 this
.propagate_through_block(body
, cond_ln
)
1365 // repeat until fixed point is reached:
1366 while self.merge_from_succ(ln
, body_ln
, first_merge
) {
1367 first_merge
= false;
1369 let new_cond_ln
= match kind
{
1371 WhileLoop(ref cond
) => {
1372 self.propagate_through_expr(&**cond
, ln
)
1375 assert
!(cond_ln
== new_cond_ln
);
1376 assert
!(body_ln
== self.with_loop_nodes(expr
.id
, succ
, ln
,
1377 |this
| this
.propagate_through_block(body
, cond_ln
)));
1383 fn with_loop_nodes
<R
, F
>(&mut self,
1384 loop_node_id
: NodeId
,
1389 F
: FnOnce(&mut Liveness
<'a
, 'tcx
>) -> R
,
1391 debug
!("with_loop_nodes: {} {}", loop_node_id
, break_ln
.get());
1392 self.loop_scope
.push(loop_node_id
);
1393 self.break_ln
.insert(loop_node_id
, break_ln
);
1394 self.cont_ln
.insert(loop_node_id
, cont_ln
);
1396 self.loop_scope
.pop();
1401 // _______________________________________________________________________
1402 // Checking for error conditions
1404 fn check_local(this
: &mut Liveness
, local
: &ast
::Local
) {
1407 this
.warn_about_unused_or_dead_vars_in_pat(&*local
.pat
);
1410 this
.pat_bindings(&*local
.pat
, |this
, ln
, var
, sp
, id
| {
1411 this
.warn_about_unused(sp
, id
, ln
, var
);
1416 visit
::walk_local(this
, local
);
1419 fn check_arm(this
: &mut Liveness
, arm
: &ast
::Arm
) {
1420 // only consider the first pattern; any later patterns must have
1421 // the same bindings, and we also consider the first pattern to be
1422 // the "authoritative" set of ids
1423 this
.arm_pats_bindings(arm
.pats
.first().map(|p
| &**p
), |this
, ln
, var
, sp
, id
| {
1424 this
.warn_about_unused(sp
, id
, ln
, var
);
1426 visit
::walk_arm(this
, arm
);
1429 fn check_expr(this
: &mut Liveness
, expr
: &Expr
) {
1431 ast
::ExprAssign(ref l
, ref r
) => {
1432 this
.check_lvalue(&**l
);
1433 this
.visit_expr(&**r
);
1435 visit
::walk_expr(this
, expr
);
1438 ast
::ExprAssignOp(_
, ref l
, _
) => {
1439 this
.check_lvalue(&**l
);
1441 visit
::walk_expr(this
, expr
);
1444 ast
::ExprInlineAsm(ref ia
) => {
1445 for &(_
, ref input
) in &ia
.inputs
{
1446 this
.visit_expr(&**input
);
1449 // Output operands must be lvalues
1450 for &(_
, ref out
, _
) in &ia
.outputs
{
1451 this
.check_lvalue(&**out
);
1452 this
.visit_expr(&**out
);
1455 visit
::walk_expr(this
, expr
);
1458 // no correctness conditions related to liveness
1459 ast
::ExprCall(..) | ast
::ExprMethodCall(..) | ast
::ExprIf(..) |
1460 ast
::ExprMatch(..) | ast
::ExprWhile(..) | ast
::ExprLoop(..) |
1461 ast
::ExprIndex(..) | ast
::ExprField(..) | ast
::ExprTupField(..) |
1462 ast
::ExprVec(..) | ast
::ExprTup(..) | ast
::ExprBinary(..) |
1463 ast
::ExprCast(..) | ast
::ExprUnary(..) | ast
::ExprRet(..) |
1464 ast
::ExprBreak(..) | ast
::ExprAgain(..) | ast
::ExprLit(_
) |
1465 ast
::ExprBlock(..) | ast
::ExprMac(..) | ast
::ExprAddrOf(..) |
1466 ast
::ExprStruct(..) | ast
::ExprRepeat(..) | ast
::ExprParen(..) |
1467 ast
::ExprClosure(..) | ast
::ExprPath(..) | ast
::ExprBox(..) |
1468 ast
::ExprRange(..) => {
1469 visit
::walk_expr(this
, expr
);
1471 ast
::ExprIfLet(..) => {
1472 this
.ir
.tcx
.sess
.span_bug(expr
.span
, "non-desugared ExprIfLet");
1474 ast
::ExprWhileLet(..) => {
1475 this
.ir
.tcx
.sess
.span_bug(expr
.span
, "non-desugared ExprWhileLet");
1477 ast
::ExprForLoop(..) => {
1478 this
.ir
.tcx
.sess
.span_bug(expr
.span
, "non-desugared ExprForLoop");
1483 fn check_fn(_v
: &Liveness
,
1485 _decl
: &ast
::FnDecl
,
1489 // do not check contents of nested fns
1492 impl<'a
, 'tcx
> Liveness
<'a
, 'tcx
> {
1493 fn fn_ret(&self, id
: NodeId
) -> ty
::PolyFnOutput
<'tcx
> {
1494 let fn_ty
= self.ir
.tcx
.node_id_to_type(id
);
1496 ty
::TyClosure(closure_def_id
, ref substs
) =>
1497 self.ir
.tcx
.closure_type(closure_def_id
, substs
).sig
.output(),
1509 // within the fn body, late-bound regions are liberated:
1511 self.ir
.tcx
.liberate_late_bound_regions(
1512 region
::DestructionScopeData
::new(body
.id
),
1516 ty
::FnConverging(t_ret
)
1517 if self.live_on_entry(entry_ln
, self.s
.no_ret_var
).is_some() => {
1520 // for nil return types, it is ok to not return a value expl.
1522 let ends_with_stmt
= match body
.expr
{
1523 None
if !body
.stmts
.is_empty() =>
1524 match body
.stmts
.first().unwrap().node
{
1525 ast
::StmtSemi(ref e
, _
) => {
1526 self.ir
.tcx
.expr_ty(&**e
) == t_ret
1532 span_err
!(self.ir
.tcx
.sess
, sp
, E0269
, "not all control paths return a value");
1534 let last_stmt
= body
.stmts
.first().unwrap();
1535 let original_span
= original_sp(self.ir
.tcx
.sess
.codemap(),
1536 last_stmt
.span
, sp
);
1537 let span_semicolon
= Span
{
1538 lo
: original_span
.hi
- BytePos(1),
1539 hi
: original_span
.hi
,
1540 expn_id
: original_span
.expn_id
1542 self.ir
.tcx
.sess
.span_help(
1543 span_semicolon
, "consider removing this semicolon:");
1548 if self.live_on_entry(entry_ln
, self.s
.clean_exit_var
).is_some() => {
1549 span_err
!(self.ir
.tcx
.sess
, sp
, E0270
,
1550 "computation may converge in a function marked as diverging");
1557 fn check_lvalue(&mut self, expr
: &Expr
) {
1559 ast
::ExprPath(..) => {
1560 if let DefLocal(nid
) = self.ir
.tcx
.def_map
.borrow().get(&expr
.id
)
1563 // Assignment to an immutable variable or argument: only legal
1564 // if there is no later assignment. If this local is actually
1565 // mutable, then check for a reassignment to flag the mutability
1567 let ln
= self.live_node(expr
.id
, expr
.span
);
1568 let var
= self.variable(nid
, expr
.span
);
1569 self.warn_about_dead_assign(expr
.span
, expr
.id
, ln
, var
);
1573 // For other kinds of lvalues, no checks are required,
1574 // and any embedded expressions are actually rvalues
1575 visit
::walk_expr(self, expr
);
1580 fn should_warn(&self, var
: Variable
) -> Option
<String
> {
1581 let name
= self.ir
.variable_name(var
);
1582 if name
.is_empty() || name
.as_bytes()[0] == ('_'
as u8) {
1589 fn warn_about_unused_args(&self, decl
: &ast
::FnDecl
, entry_ln
: LiveNode
) {
1590 for arg
in &decl
.inputs
{
1591 pat_util
::pat_bindings(&self.ir
.tcx
.def_map
,
1593 |_bm
, p_id
, sp
, path1
| {
1594 let var
= self.variable(p_id
, sp
);
1595 // Ignore unused self.
1596 let ident
= path1
.node
;
1597 if ident
.name
!= special_idents
::self_
.name
{
1598 self.warn_about_unused(sp
, p_id
, entry_ln
, var
);
1604 fn warn_about_unused_or_dead_vars_in_pat(&mut self, pat
: &ast
::Pat
) {
1605 self.pat_bindings(pat
, |this
, ln
, var
, sp
, id
| {
1606 if !this
.warn_about_unused(sp
, id
, ln
, var
) {
1607 this
.warn_about_dead_assign(sp
, id
, ln
, var
);
1612 fn warn_about_unused(&self,
1618 if !self.used_on_entry(ln
, var
) {
1619 let r
= self.should_warn(var
);
1620 if let Some(name
) = r
{
1622 // annoying: for parameters in funcs like `fn(x: int)
1623 // {ret}`, there is only one node, so asking about
1624 // assigned_on_exit() is not meaningful.
1625 let is_assigned
= if ln
== self.s
.exit_ln
{
1628 self.assigned_on_exit(ln
, var
).is_some()
1632 self.ir
.tcx
.sess
.add_lint(lint
::builtin
::UNUSED_VARIABLES
, id
, sp
,
1633 format
!("variable `{}` is assigned to, but never used",
1636 self.ir
.tcx
.sess
.add_lint(lint
::builtin
::UNUSED_VARIABLES
, id
, sp
,
1637 format
!("unused variable: `{}`", name
));
1646 fn warn_about_dead_assign(&self,
1651 if self.live_on_exit(ln
, var
).is_none() {
1652 let r
= self.should_warn(var
);
1653 if let Some(name
) = r
{
1654 self.ir
.tcx
.sess
.add_lint(lint
::builtin
::UNUSED_ASSIGNMENTS
, id
, sp
,
1655 format
!("value assigned to `{}` is never read", name
));