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 uint) and the id for a variable
55 //! is called a `variable` (another newtype'd uint).
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::mem_categorization::Typer;
114 use middle::{pat_util, ty};
116 use util::nodemap::NodeMap;
118 use std::{fmt, io, uint};
120 use syntax::ast::{mod, NodeId, Expr};
121 use syntax::codemap::{BytePos, original_sp, Span};
122 use syntax::parse::token::{mod, special_idents};
123 use syntax::print::pprust::{expr_to_string, block_to_string};
125 use syntax::ast_util;
126 use syntax::visit::{mod, Visitor, FnKind};
128 /// For use with `propagate_through_loop`.
130 /// An endless `loop` loop.
132 /// A `while` loop, with the given expression as condition.
134 /// A `for` loop, with the given pattern to bind.
135 ForLoop(&'a ast::Pat),
138 #[deriving(PartialEq)]
139 struct Variable(uint);
141 impl Copy for Variable {}
143 #[deriving(PartialEq)]
144 struct LiveNode(uint);
146 impl Copy for LiveNode {}
149 fn get(&self) -> uint { let Variable(v) = *self; v }
153 fn get(&self) -> uint { let LiveNode(v) = *self; v }
156 impl Clone for LiveNode {
157 fn clone(&self) -> LiveNode {
162 #[deriving(PartialEq, Show)]
170 impl Copy for LiveNodeKind {}
172 fn live_node_kind_to_string(lnk: LiveNodeKind, cx: &ty::ctxt) -> String {
173 let cm = cx.sess.codemap();
176 format!("Free var node [{}]", cm.span_to_string(s))
179 format!("Expr node [{}]", cm.span_to_string(s))
182 format!("Var def node [{}]", cm.span_to_string(s))
184 ExitNode => "Exit node".to_string(),
188 impl<'a, 'tcx, 'v> Visitor<'v> for IrMaps<'a, 'tcx> {
189 fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v ast::FnDecl,
190 b: &'v ast::Block, s: Span, id: NodeId) {
191 visit_fn(self, fk, fd, b, s, id);
193 fn visit_local(&mut self, l: &ast::Local) { visit_local(self, l); }
194 fn visit_expr(&mut self, ex: &Expr) { visit_expr(self, ex); }
195 fn visit_arm(&mut self, a: &ast::Arm) { visit_arm(self, a); }
198 pub fn check_crate(tcx: &ty::ctxt) {
199 visit::walk_crate(&mut IrMaps::new(tcx), tcx.map.krate());
200 tcx.sess.abort_if_errors();
203 impl fmt::Show for LiveNode {
204 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
205 write!(f, "ln({})", self.get())
209 impl fmt::Show for Variable {
210 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
211 write!(f, "v({})", self.get())
215 // ______________________________________________________________________
218 // This is the first pass and the one that drives the main
219 // computation. It walks up and down the IR once. On the way down,
220 // we count for each function the number of variables as well as
221 // liveness nodes. A liveness node is basically an expression or
222 // capture clause that does something of interest: either it has
223 // interesting control flow or it uses/defines a local variable.
225 // On the way back up, at each function node we create liveness sets
226 // (we now know precisely how big to make our various vectors and so
227 // forth) and then do the data-flow propagation to compute the set
228 // of live variables at each program point.
230 // Finally, we run back over the IR one last time and, using the
231 // computed liveness, check various safety conditions. For example,
232 // there must be no live nodes at the definition site for a variable
233 // unless it has an initializer. Similarly, each non-mutable local
234 // variable must not be assigned if there is some successor
235 // assignment. And so forth.
238 fn is_valid(&self) -> bool {
239 self.get() != uint::MAX
243 fn invalid_node() -> LiveNode { LiveNode(uint::MAX) }
256 impl Copy for LocalInfo {}
260 Arg(NodeId, ast::Ident),
266 impl Copy for VarKind {}
268 struct IrMaps<'a, 'tcx: 'a> {
269 tcx: &'a ty::ctxt<'tcx>,
271 num_live_nodes: uint,
273 live_node_map: NodeMap<LiveNode>,
274 variable_map: NodeMap<Variable>,
275 capture_info_map: NodeMap<Rc<Vec<CaptureInfo>>>,
276 var_kinds: Vec<VarKind>,
277 lnks: Vec<LiveNodeKind>,
280 impl<'a, 'tcx> IrMaps<'a, 'tcx> {
281 fn new(tcx: &'a ty::ctxt<'tcx>) -> IrMaps<'a, 'tcx> {
286 live_node_map: NodeMap::new(),
287 variable_map: NodeMap::new(),
288 capture_info_map: NodeMap::new(),
289 var_kinds: Vec::new(),
294 fn add_live_node(&mut self, lnk: LiveNodeKind) -> LiveNode {
295 let ln = LiveNode(self.num_live_nodes);
297 self.num_live_nodes += 1;
299 debug!("{} is of kind {}", ln.to_string(),
300 live_node_kind_to_string(lnk, self.tcx));
305 fn add_live_node_for_node(&mut self, node_id: NodeId, lnk: LiveNodeKind) {
306 let ln = self.add_live_node(lnk);
307 self.live_node_map.insert(node_id, ln);
309 debug!("{} is node {}", ln.to_string(), node_id);
312 fn add_variable(&mut self, vk: VarKind) -> Variable {
313 let v = Variable(self.num_vars);
314 self.var_kinds.push(vk);
318 Local(LocalInfo { id: node_id, .. }) | Arg(node_id, _) => {
319 self.variable_map.insert(node_id, v);
321 ImplicitRet | CleanExit => {}
324 debug!("{} is {}", v.to_string(), vk);
329 fn variable(&self, node_id: NodeId, span: Span) -> Variable {
330 match self.variable_map.get(&node_id) {
335 .span_bug(span, format!("no variable registered for id {}",
336 node_id).as_slice());
341 fn variable_name(&self, var: Variable) -> String {
342 match self.var_kinds[var.get()] {
343 Local(LocalInfo { ident: nm, .. }) | Arg(_, nm) => {
344 token::get_ident(nm).get().to_string()
346 ImplicitRet => "<implicit-ret>".to_string(),
347 CleanExit => "<clean-exit>".to_string()
351 fn set_captures(&mut self, node_id: NodeId, cs: Vec<CaptureInfo>) {
352 self.capture_info_map.insert(node_id, Rc::new(cs));
355 fn lnk(&self, ln: LiveNode) -> LiveNodeKind {
360 impl<'a, 'tcx, 'v> Visitor<'v> for Liveness<'a, 'tcx> {
361 fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v ast::FnDecl,
362 b: &'v ast::Block, s: Span, n: NodeId) {
363 check_fn(self, fk, fd, b, s, n);
365 fn visit_local(&mut self, l: &ast::Local) {
366 check_local(self, l);
368 fn visit_expr(&mut self, ex: &Expr) {
369 check_expr(self, ex);
371 fn visit_arm(&mut self, a: &ast::Arm) {
376 fn visit_fn(ir: &mut IrMaps,
384 // swap in a new set of IR maps for this function body:
385 let mut fn_maps = IrMaps::new(ir.tcx);
387 debug!("creating fn_maps: {}", &fn_maps as *const IrMaps);
389 for arg in decl.inputs.iter() {
390 pat_util::pat_bindings(&ir.tcx.def_map,
392 |_bm, arg_id, _x, path1| {
393 debug!("adding argument {}", arg_id);
394 let ident = path1.node;
395 fn_maps.add_variable(Arg(arg_id, ident));
399 // gather up the various local variables, significant expressions,
401 visit::walk_fn(&mut fn_maps, fk, decl, body, sp);
403 // Special nodes and variables:
404 // - exit_ln represents the end of the fn, either by return or panic
405 // - implicit_ret_var is a pseudo-variable that represents
406 // an implicit return
407 let specials = Specials {
408 exit_ln: fn_maps.add_live_node(ExitNode),
409 fallthrough_ln: fn_maps.add_live_node(ExitNode),
410 no_ret_var: fn_maps.add_variable(ImplicitRet),
411 clean_exit_var: fn_maps.add_variable(CleanExit)
415 let mut lsets = Liveness::new(&mut fn_maps, specials);
416 let entry_ln = lsets.compute(decl, body);
418 // check for various error conditions
419 lsets.visit_block(body);
420 lsets.check_ret(id, sp, fk, entry_ln, body);
421 lsets.warn_about_unused_args(decl, entry_ln);
424 fn visit_local(ir: &mut IrMaps, local: &ast::Local) {
425 pat_util::pat_bindings(&ir.tcx.def_map, &*local.pat, |_, p_id, sp, path1| {
426 debug!("adding local variable {}", p_id);
427 let name = path1.node;
428 ir.add_live_node_for_node(p_id, VarDefNode(sp));
429 ir.add_variable(Local(LocalInfo {
434 visit::walk_local(ir, local);
437 fn visit_arm(ir: &mut IrMaps, arm: &ast::Arm) {
438 for pat in arm.pats.iter() {
439 pat_util::pat_bindings(&ir.tcx.def_map, &**pat, |bm, p_id, sp, path1| {
440 debug!("adding local variable {} from match with bm {}",
442 let name = path1.node;
443 ir.add_live_node_for_node(p_id, VarDefNode(sp));
444 ir.add_variable(Local(LocalInfo {
450 visit::walk_arm(ir, arm);
453 fn visit_expr(ir: &mut IrMaps, expr: &Expr) {
455 // live nodes required for uses or definitions of variables:
456 ast::ExprPath(_) => {
457 let def = ir.tcx.def_map.borrow()[expr.id].clone();
458 debug!("expr {}: path that leads to {}", expr.id, def);
459 if let DefLocal(..) = def {
460 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
462 visit::walk_expr(ir, expr);
464 ast::ExprClosure(..) | ast::ExprProc(..) => {
465 // Interesting control flow (for loops can contain labeled
466 // breaks or continues)
467 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
469 // Make a live_node for each captured variable, with the span
470 // being the location that the variable is used. This results
471 // in better error messages than just pointing at the closure
472 // construction site.
473 let mut call_caps = Vec::new();
474 ty::with_freevars(ir.tcx, expr.id, |freevars| {
475 for fv in freevars.iter() {
476 if let DefLocal(rv) = fv.def {
477 let fv_ln = ir.add_live_node(FreeVarNode(fv.span));
478 call_caps.push(CaptureInfo {ln: fv_ln,
483 ir.set_captures(expr.id, call_caps);
485 visit::walk_expr(ir, expr);
488 // live nodes required for interesting control flow:
489 ast::ExprIf(..) | ast::ExprMatch(..) | ast::ExprWhile(..) | ast::ExprLoop(..) => {
490 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
491 visit::walk_expr(ir, expr);
493 ast::ExprIfLet(..) => {
494 ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
496 ast::ExprWhileLet(..) => {
497 ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet");
499 ast::ExprForLoop(ref pat, _, _, _) => {
500 pat_util::pat_bindings(&ir.tcx.def_map, &**pat, |bm, p_id, sp, path1| {
501 debug!("adding local variable {} from for loop with bm {}",
503 let name = path1.node;
504 ir.add_live_node_for_node(p_id, VarDefNode(sp));
505 ir.add_variable(Local(LocalInfo {
510 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
511 visit::walk_expr(ir, expr);
513 ast::ExprBinary(op, _, _) if ast_util::lazy_binop(op) => {
514 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
515 visit::walk_expr(ir, expr);
518 // otherwise, live nodes are not required:
519 ast::ExprIndex(..) | ast::ExprField(..) | ast::ExprTupField(..) |
520 ast::ExprVec(..) | ast::ExprCall(..) | ast::ExprMethodCall(..) |
521 ast::ExprTup(..) | ast::ExprBinary(..) | ast::ExprAddrOf(..) |
522 ast::ExprCast(..) | ast::ExprUnary(..) | ast::ExprBreak(_) |
523 ast::ExprAgain(_) | ast::ExprLit(_) | ast::ExprRet(..) |
524 ast::ExprBlock(..) | ast::ExprAssign(..) | ast::ExprAssignOp(..) |
525 ast::ExprMac(..) | ast::ExprStruct(..) | ast::ExprRepeat(..) |
526 ast::ExprParen(..) | ast::ExprInlineAsm(..) | ast::ExprBox(..) |
527 ast::ExprSlice(..) => {
528 visit::walk_expr(ir, expr);
533 // ______________________________________________________________________
534 // Computing liveness sets
536 // Actually we compute just a bit more than just liveness, but we use
537 // the same basic propagation framework in all cases.
546 impl Copy for Users {}
548 fn invalid_users() -> Users {
550 reader: invalid_node(),
551 writer: invalid_node(),
558 fallthrough_ln: LiveNode,
559 no_ret_var: Variable,
560 clean_exit_var: Variable
563 impl Copy for Specials {}
565 static ACC_READ: uint = 1u;
566 static ACC_WRITE: uint = 2u;
567 static ACC_USE: uint = 4u;
569 struct Liveness<'a, 'tcx: 'a> {
570 ir: &'a mut IrMaps<'a, 'tcx>,
572 successors: Vec<LiveNode>,
574 // The list of node IDs for the nested loop scopes
576 loop_scope: Vec<NodeId>,
577 // mappings from loop node ID to LiveNode
578 // ("break" label should map to loop node ID,
579 // it probably doesn't now)
580 break_ln: NodeMap<LiveNode>,
581 cont_ln: NodeMap<LiveNode>
584 impl<'a, 'tcx> Liveness<'a, 'tcx> {
585 fn new(ir: &'a mut IrMaps<'a, 'tcx>, specials: Specials) -> Liveness<'a, 'tcx> {
586 let num_live_nodes = ir.num_live_nodes;
587 let num_vars = ir.num_vars;
591 successors: Vec::from_elem(num_live_nodes, invalid_node()),
592 users: Vec::from_elem(num_live_nodes * num_vars, invalid_users()),
593 loop_scope: Vec::new(),
594 break_ln: NodeMap::new(),
595 cont_ln: NodeMap::new(),
599 fn live_node(&self, node_id: NodeId, span: Span) -> LiveNode {
600 match self.ir.live_node_map.get(&node_id) {
603 // This must be a mismatch between the ir_map construction
604 // above and the propagation code below; the two sets of
605 // code have to agree about which AST nodes are worth
606 // creating liveness nodes for.
607 self.ir.tcx.sess.span_bug(
609 format!("no live node registered for node {}",
610 node_id).as_slice());
615 fn variable(&self, node_id: NodeId, span: Span) -> Variable {
616 self.ir.variable(node_id, span)
619 fn pat_bindings(&mut self,
621 f: |&mut Liveness<'a, 'tcx>, LiveNode, Variable, Span, NodeId|) {
622 pat_util::pat_bindings(&self.ir.tcx.def_map, pat, |_bm, p_id, sp, _n| {
623 let ln = self.live_node(p_id, sp);
624 let var = self.variable(p_id, sp);
625 f(self, ln, var, sp, p_id);
629 fn arm_pats_bindings(&mut self,
630 pat: Option<&ast::Pat>,
631 f: |&mut Liveness<'a, 'tcx>, LiveNode, Variable, Span, NodeId|) {
634 self.pat_bindings(pat, f);
640 fn define_bindings_in_pat(&mut self, pat: &ast::Pat, succ: LiveNode)
642 self.define_bindings_in_arm_pats(Some(pat), succ)
645 fn define_bindings_in_arm_pats(&mut self, pat: Option<&ast::Pat>, succ: LiveNode)
648 self.arm_pats_bindings(pat, |this, ln, var, _sp, _id| {
649 this.init_from_succ(ln, succ);
650 this.define(ln, var);
656 fn idx(&self, ln: LiveNode, var: Variable) -> uint {
657 ln.get() * self.ir.num_vars + var.get()
660 fn live_on_entry(&self, ln: LiveNode, var: Variable)
661 -> Option<LiveNodeKind> {
662 assert!(ln.is_valid());
663 let reader = self.users[self.idx(ln, var)].reader;
664 if reader.is_valid() {Some(self.ir.lnk(reader))} else {None}
668 Is this variable live on entry to any of its successor nodes?
670 fn live_on_exit(&self, ln: LiveNode, var: Variable)
671 -> Option<LiveNodeKind> {
672 let successor = self.successors[ln.get()];
673 self.live_on_entry(successor, var)
676 fn used_on_entry(&self, ln: LiveNode, var: Variable) -> bool {
677 assert!(ln.is_valid());
678 self.users[self.idx(ln, var)].used
681 fn assigned_on_entry(&self, ln: LiveNode, var: Variable)
682 -> Option<LiveNodeKind> {
683 assert!(ln.is_valid());
684 let writer = self.users[self.idx(ln, var)].writer;
685 if writer.is_valid() {Some(self.ir.lnk(writer))} else {None}
688 fn assigned_on_exit(&self, ln: LiveNode, var: Variable)
689 -> Option<LiveNodeKind> {
690 let successor = self.successors[ln.get()];
691 self.assigned_on_entry(successor, var)
694 fn indices2(&mut self,
697 op: |&mut Liveness<'a, 'tcx>, uint, uint|) {
698 let node_base_idx = self.idx(ln, Variable(0u));
699 let succ_base_idx = self.idx(succ_ln, Variable(0u));
700 for var_idx in range(0u, self.ir.num_vars) {
701 op(self, node_base_idx + var_idx, succ_base_idx + var_idx);
708 test: |uint| -> LiveNode) -> io::IoResult<()> {
709 let node_base_idx = self.idx(ln, Variable(0));
710 for var_idx in range(0u, self.ir.num_vars) {
711 let idx = node_base_idx + var_idx;
712 if test(idx).is_valid() {
713 try!(write!(wr, " {}", Variable(var_idx).to_string()));
719 fn find_loop_scope(&self,
720 opt_label: Option<ast::Ident>,
726 // Refers to a labeled loop. Use the results of resolve
728 match self.ir.tcx.def_map.borrow().get(&id) {
729 Some(&DefLabel(loop_id)) => loop_id,
730 _ => self.ir.tcx.sess.span_bug(sp, "label on break/loop \
731 doesn't refer to a loop")
735 // Vanilla 'break' or 'loop', so use the enclosing
737 if self.loop_scope.len() == 0 {
738 self.ir.tcx.sess.span_bug(sp, "break outside loop");
740 *self.loop_scope.last().unwrap()
746 #[allow(unused_must_use)]
747 fn ln_str(&self, ln: LiveNode) -> String {
748 let mut wr = Vec::new();
750 let wr = &mut wr as &mut io::Writer;
751 write!(wr, "[ln({}) of kind {} reads", ln.get(), self.ir.lnk(ln));
752 self.write_vars(wr, ln, |idx| self.users[idx].reader);
753 write!(wr, " writes");
754 self.write_vars(wr, ln, |idx| self.users[idx].writer);
755 write!(wr, " precedes {}]", self.successors[ln.get()].to_string());
757 String::from_utf8(wr).unwrap()
760 fn init_empty(&mut self, ln: LiveNode, succ_ln: LiveNode) {
761 self.successors[ln.get()] = succ_ln;
763 // It is not necessary to initialize the
764 // values to empty because this is the value
765 // they have when they are created, and the sets
766 // only grow during iterations.
768 // self.indices(ln) { |idx|
769 // self.users[idx] = invalid_users();
773 fn init_from_succ(&mut self, ln: LiveNode, succ_ln: LiveNode) {
774 // more efficient version of init_empty() / merge_from_succ()
775 self.successors[ln.get()] = succ_ln;
777 self.indices2(ln, succ_ln, |this, idx, succ_idx| {
778 this.users[idx] = this.users[succ_idx]
780 debug!("init_from_succ(ln={}, succ={})",
781 self.ln_str(ln), self.ln_str(succ_ln));
784 fn merge_from_succ(&mut self,
789 if ln == succ_ln { return false; }
791 let mut changed = false;
792 self.indices2(ln, succ_ln, |this, idx, succ_idx| {
793 changed |= copy_if_invalid(this.users[succ_idx].reader,
794 &mut this.users[idx].reader);
795 changed |= copy_if_invalid(this.users[succ_idx].writer,
796 &mut this.users[idx].writer);
797 if this.users[succ_idx].used && !this.users[idx].used {
798 this.users[idx].used = true;
803 debug!("merge_from_succ(ln={}, succ={}, first_merge={}, changed={})",
804 ln.to_string(), self.ln_str(succ_ln), first_merge, changed);
807 fn copy_if_invalid(src: LiveNode, dst: &mut LiveNode) -> bool {
808 if src.is_valid() && !dst.is_valid() {
817 // Indicates that a local variable was *defined*; we know that no
818 // uses of the variable can precede the definition (resolve checks
819 // this) so we just clear out all the data.
820 fn define(&mut self, writer: LiveNode, var: Variable) {
821 let idx = self.idx(writer, var);
822 self.users[idx].reader = invalid_node();
823 self.users[idx].writer = invalid_node();
825 debug!("{} defines {} (idx={}): {}", writer.to_string(), var.to_string(),
826 idx, self.ln_str(writer));
829 // Either read, write, or both depending on the acc bitset
830 fn acc(&mut self, ln: LiveNode, var: Variable, acc: uint) {
831 debug!("{} accesses[{:x}] {}: {}",
832 ln.to_string(), acc, var.to_string(), self.ln_str(ln));
834 let idx = self.idx(ln, var);
835 let user = &mut self.users[idx];
837 if (acc & ACC_WRITE) != 0 {
838 user.reader = invalid_node();
842 // Important: if we both read/write, must do read second
843 // or else the write will override.
844 if (acc & ACC_READ) != 0 {
848 if (acc & ACC_USE) != 0 {
853 // _______________________________________________________________________
855 fn compute(&mut self, decl: &ast::FnDecl, body: &ast::Block) -> LiveNode {
856 // if there is a `break` or `again` at the top level, then it's
857 // effectively a return---this only occurs in `for` loops,
858 // where the body is really a closure.
860 debug!("compute: using id for block, {}", block_to_string(body));
862 let exit_ln = self.s.exit_ln;
863 let entry_ln: LiveNode =
864 self.with_loop_nodes(body.id, exit_ln, exit_ln,
865 |this| this.propagate_through_fn_block(decl, body));
867 // hack to skip the loop unless debug! is enabled:
868 debug!("^^ liveness computation results for body {} (entry={})",
870 for ln_idx in range(0u, self.ir.num_live_nodes) {
871 debug!("{}", self.ln_str(LiveNode(ln_idx)));
875 entry_ln.to_string());
880 fn propagate_through_fn_block(&mut self, _: &ast::FnDecl, blk: &ast::Block)
882 // the fallthrough exit is only for those cases where we do not
883 // explicitly return:
885 self.init_from_succ(s.fallthrough_ln, s.exit_ln);
886 if blk.expr.is_none() {
887 self.acc(s.fallthrough_ln, s.no_ret_var, ACC_READ)
889 self.acc(s.fallthrough_ln, s.clean_exit_var, ACC_READ);
891 self.propagate_through_block(blk, s.fallthrough_ln)
894 fn propagate_through_block(&mut self, blk: &ast::Block, succ: LiveNode)
896 let succ = self.propagate_through_opt_expr(blk.expr.as_ref().map(|e| &**e), succ);
897 blk.stmts.iter().rev().fold(succ, |succ, stmt| {
898 self.propagate_through_stmt(&**stmt, succ)
902 fn propagate_through_stmt(&mut self, stmt: &ast::Stmt, succ: LiveNode)
905 ast::StmtDecl(ref decl, _) => {
906 self.propagate_through_decl(&**decl, succ)
909 ast::StmtExpr(ref expr, _) | ast::StmtSemi(ref expr, _) => {
910 self.propagate_through_expr(&**expr, succ)
913 ast::StmtMac(..) => {
914 self.ir.tcx.sess.span_bug(stmt.span, "unexpanded macro");
919 fn propagate_through_decl(&mut self, decl: &ast::Decl, succ: LiveNode)
922 ast::DeclLocal(ref local) => {
923 self.propagate_through_local(&**local, succ)
925 ast::DeclItem(_) => succ,
929 fn propagate_through_local(&mut self, local: &ast::Local, succ: LiveNode)
931 // Note: we mark the variable as defined regardless of whether
932 // there is an initializer. Initially I had thought to only mark
933 // the live variable as defined if it was initialized, and then we
934 // could check for uninit variables just by scanning what is live
935 // at the start of the function. But that doesn't work so well for
936 // immutable variables defined in a loop:
937 // loop { let x; x = 5; }
938 // because the "assignment" loops back around and generates an error.
940 // So now we just check that variables defined w/o an
941 // initializer are not live at the point of their
942 // initialization, which is mildly more complex than checking
943 // once at the func header but otherwise equivalent.
945 let succ = self.propagate_through_opt_expr(local.init.as_ref().map(|e| &**e), succ);
946 self.define_bindings_in_pat(&*local.pat, succ)
949 fn propagate_through_exprs(&mut self, exprs: &[P<Expr>], succ: LiveNode)
951 exprs.iter().rev().fold(succ, |succ, expr| {
952 self.propagate_through_expr(&**expr, succ)
956 fn propagate_through_opt_expr(&mut self,
957 opt_expr: Option<&Expr>,
960 opt_expr.map_or(succ, |expr| self.propagate_through_expr(expr, succ))
963 fn propagate_through_expr(&mut self, expr: &Expr, succ: LiveNode)
965 debug!("propagate_through_expr: {}", expr_to_string(expr));
968 // Interesting cases with control flow or which gen/kill
970 ast::ExprPath(_) => {
971 self.access_path(expr, succ, ACC_READ | ACC_USE)
974 ast::ExprField(ref e, _) => {
975 self.propagate_through_expr(&**e, succ)
978 ast::ExprTupField(ref e, _) => {
979 self.propagate_through_expr(&**e, succ)
982 ast::ExprClosure(_, _, _, ref blk) |
983 ast::ExprProc(_, ref blk) => {
984 debug!("{} is an ExprClosure or ExprProc",
985 expr_to_string(expr));
988 The next-node for a break is the successor of the entire
989 loop. The next-node for a continue is the top of this loop.
991 let node = self.live_node(expr.id, expr.span);
992 self.with_loop_nodes(blk.id, succ, node, |this| {
994 // the construction of a closure itself is not important,
995 // but we have to consider the closed over variables.
996 let caps = match this.ir.capture_info_map.get(&expr.id) {
997 Some(caps) => caps.clone(),
999 this.ir.tcx.sess.span_bug(expr.span, "no registered caps");
1002 caps.iter().rev().fold(succ, |succ, cap| {
1003 this.init_from_succ(cap.ln, succ);
1004 let var = this.variable(cap.var_nid, expr.span);
1005 this.acc(cap.ln, var, ACC_READ | ACC_USE);
1011 ast::ExprIf(ref cond, ref then, ref els) => {
1025 let else_ln = self.propagate_through_opt_expr(els.as_ref().map(|e| &**e), succ);
1026 let then_ln = self.propagate_through_block(&**then, succ);
1027 let ln = self.live_node(expr.id, expr.span);
1028 self.init_from_succ(ln, else_ln);
1029 self.merge_from_succ(ln, then_ln, false);
1030 self.propagate_through_expr(&**cond, ln)
1033 ast::ExprIfLet(..) => {
1034 self.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
1037 ast::ExprWhile(ref cond, ref blk, _) => {
1038 self.propagate_through_loop(expr, WhileLoop(&**cond), &**blk, succ)
1041 ast::ExprWhileLet(..) => {
1042 self.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet");
1045 ast::ExprForLoop(ref pat, ref head, ref blk, _) => {
1046 let ln = self.propagate_through_loop(expr, ForLoop(&**pat), &**blk, succ);
1047 self.propagate_through_expr(&**head, ln)
1050 // Note that labels have been resolved, so we don't need to look
1051 // at the label ident
1052 ast::ExprLoop(ref blk, _) => {
1053 self.propagate_through_loop(expr, LoopLoop, &**blk, succ)
1056 ast::ExprMatch(ref e, ref arms, _) => {
1071 let ln = self.live_node(expr.id, expr.span);
1072 self.init_empty(ln, succ);
1073 let mut first_merge = true;
1074 for arm in arms.iter() {
1076 self.propagate_through_expr(&*arm.body, succ);
1078 self.propagate_through_opt_expr(arm.guard.as_ref().map(|e| &**e), body_succ);
1079 // only consider the first pattern; any later patterns must have
1080 // the same bindings, and we also consider the first pattern to be
1081 // the "authoritative" set of ids
1083 self.define_bindings_in_arm_pats(arm.pats.head().map(|p| &**p),
1085 self.merge_from_succ(ln, arm_succ, first_merge);
1086 first_merge = false;
1088 self.propagate_through_expr(&**e, ln)
1091 ast::ExprRet(ref o_e) => {
1092 // ignore succ and subst exit_ln:
1093 let exit_ln = self.s.exit_ln;
1094 self.propagate_through_opt_expr(o_e.as_ref().map(|e| &**e), exit_ln)
1097 ast::ExprBreak(opt_label) => {
1098 // Find which label this break jumps to
1099 let sc = self.find_loop_scope(opt_label, expr.id, expr.span);
1101 // Now that we know the label we're going to,
1102 // look it up in the break loop nodes table
1104 match self.break_ln.get(&sc) {
1106 None => self.ir.tcx.sess.span_bug(expr.span,
1107 "break to unknown label")
1111 ast::ExprAgain(opt_label) => {
1112 // Find which label this expr continues to
1113 let sc = self.find_loop_scope(opt_label, expr.id, expr.span);
1115 // Now that we know the label we're going to,
1116 // look it up in the continue loop nodes table
1118 match self.cont_ln.get(&sc) {
1120 None => self.ir.tcx.sess.span_bug(expr.span,
1121 "loop to unknown label")
1125 ast::ExprAssign(ref l, ref r) => {
1126 // see comment on lvalues in
1127 // propagate_through_lvalue_components()
1128 let succ = self.write_lvalue(&**l, succ, ACC_WRITE);
1129 let succ = self.propagate_through_lvalue_components(&**l, succ);
1130 self.propagate_through_expr(&**r, succ)
1133 ast::ExprAssignOp(_, ref l, ref r) => {
1134 // see comment on lvalues in
1135 // propagate_through_lvalue_components()
1136 let succ = self.write_lvalue(&**l, succ, ACC_WRITE|ACC_READ);
1137 let succ = self.propagate_through_expr(&**r, succ);
1138 self.propagate_through_lvalue_components(&**l, succ)
1141 // Uninteresting cases: just propagate in rev exec order
1143 ast::ExprVec(ref exprs) => {
1144 self.propagate_through_exprs(exprs.as_slice(), succ)
1147 ast::ExprRepeat(ref element, ref count) => {
1148 let succ = self.propagate_through_expr(&**count, succ);
1149 self.propagate_through_expr(&**element, succ)
1152 ast::ExprStruct(_, ref fields, ref with_expr) => {
1153 let succ = self.propagate_through_opt_expr(with_expr.as_ref().map(|e| &**e), succ);
1154 fields.iter().rev().fold(succ, |succ, field| {
1155 self.propagate_through_expr(&*field.expr, succ)
1159 ast::ExprCall(ref f, ref args) => {
1160 let diverges = !self.ir.tcx.is_method_call(expr.id) && {
1161 let t_ret = ty::ty_fn_ret(ty::expr_ty(self.ir.tcx, &**f));
1162 t_ret == ty::FnDiverging
1164 let succ = if diverges {
1169 let succ = self.propagate_through_exprs(args.as_slice(), succ);
1170 self.propagate_through_expr(&**f, succ)
1173 ast::ExprMethodCall(_, _, ref args) => {
1174 let method_call = ty::MethodCall::expr(expr.id);
1175 let method_ty = self.ir.tcx.method_map.borrow().get(&method_call).unwrap().ty;
1176 let diverges = ty::ty_fn_ret(method_ty) == ty::FnDiverging;
1177 let succ = if diverges {
1182 self.propagate_through_exprs(args.as_slice(), succ)
1185 ast::ExprTup(ref exprs) => {
1186 self.propagate_through_exprs(exprs.as_slice(), succ)
1189 ast::ExprBinary(op, ref l, ref r) if ast_util::lazy_binop(op) => {
1190 let r_succ = self.propagate_through_expr(&**r, succ);
1192 let ln = self.live_node(expr.id, expr.span);
1193 self.init_from_succ(ln, succ);
1194 self.merge_from_succ(ln, r_succ, false);
1196 self.propagate_through_expr(&**l, ln)
1199 ast::ExprIndex(ref l, ref r) |
1200 ast::ExprBinary(_, ref l, ref r) |
1201 ast::ExprBox(ref l, ref r) => {
1202 let r_succ = self.propagate_through_expr(&**r, succ);
1203 self.propagate_through_expr(&**l, r_succ)
1206 ast::ExprSlice(ref e1, ref e2, ref e3, _) => {
1207 let succ = e3.as_ref().map_or(succ, |e| self.propagate_through_expr(&**e, succ));
1208 let succ = e2.as_ref().map_or(succ, |e| self.propagate_through_expr(&**e, succ));
1209 self.propagate_through_expr(&**e1, succ)
1212 ast::ExprAddrOf(_, ref e) |
1213 ast::ExprCast(ref e, _) |
1214 ast::ExprUnary(_, ref e) |
1215 ast::ExprParen(ref e) => {
1216 self.propagate_through_expr(&**e, succ)
1219 ast::ExprInlineAsm(ref ia) => {
1221 let succ = ia.outputs.iter().rev().fold(succ, |succ, &(_, ref expr, _)| {
1222 // see comment on lvalues
1223 // in propagate_through_lvalue_components()
1224 let succ = self.write_lvalue(&**expr, succ, ACC_WRITE);
1225 self.propagate_through_lvalue_components(&**expr, succ)
1227 // Inputs are executed first. Propagate last because of rev order
1228 ia.inputs.iter().rev().fold(succ, |succ, &(_, ref expr)| {
1229 self.propagate_through_expr(&**expr, succ)
1233 ast::ExprLit(..) => {
1237 ast::ExprBlock(ref blk) => {
1238 self.propagate_through_block(&**blk, succ)
1241 ast::ExprMac(..) => {
1242 self.ir.tcx.sess.span_bug(expr.span, "unexpanded macro");
1247 fn propagate_through_lvalue_components(&mut self,
1253 // In general, the full flow graph structure for an
1254 // assignment/move/etc can be handled in one of two ways,
1255 // depending on whether what is being assigned is a "tracked
1256 // value" or not. A tracked value is basically a local
1257 // variable or argument.
1259 // The two kinds of graphs are:
1261 // Tracked lvalue Untracked lvalue
1262 // ----------------------++-----------------------
1266 // (rvalue) || (rvalue)
1269 // (write of lvalue) || (lvalue components)
1274 // ----------------------++-----------------------
1276 // I will cover the two cases in turn:
1278 // # Tracked lvalues
1280 // A tracked lvalue is a local variable/argument `x`. In
1281 // these cases, the link_node where the write occurs is linked
1282 // to node id of `x`. The `write_lvalue()` routine generates
1283 // the contents of this node. There are no subcomponents to
1286 // # Non-tracked lvalues
1288 // These are lvalues like `x[5]` or `x.f`. In that case, we
1289 // basically ignore the value which is written to but generate
1290 // reads for the components---`x` in these two examples. The
1291 // components reads are generated by
1292 // `propagate_through_lvalue_components()` (this fn).
1294 // # Illegal lvalues
1296 // It is still possible to observe assignments to non-lvalues;
1297 // these errors are detected in the later pass borrowck. We
1298 // just ignore such cases and treat them as reads.
1301 ast::ExprPath(_) => succ,
1302 ast::ExprField(ref e, _) => self.propagate_through_expr(&**e, succ),
1303 ast::ExprTupField(ref e, _) => self.propagate_through_expr(&**e, succ),
1304 _ => self.propagate_through_expr(expr, succ)
1308 // see comment on propagate_through_lvalue()
1309 fn write_lvalue(&mut self, expr: &Expr, succ: LiveNode, acc: uint)
1312 ast::ExprPath(_) => self.access_path(expr, succ, acc),
1314 // We do not track other lvalues, so just propagate through
1315 // to their subcomponents. Also, it may happen that
1316 // non-lvalues occur here, because those are detected in the
1317 // later pass borrowck.
1322 fn access_path(&mut self, expr: &Expr, succ: LiveNode, acc: uint)
1324 match self.ir.tcx.def_map.borrow()[expr.id].clone() {
1326 let ln = self.live_node(expr.id, expr.span);
1328 self.init_from_succ(ln, succ);
1329 let var = self.variable(nid, expr.span);
1330 self.acc(ln, var, acc);
1338 fn propagate_through_loop(&mut self,
1347 We model control flow like this:
1365 let mut first_merge = true;
1366 let ln = self.live_node(expr.id, expr.span);
1367 self.init_empty(ln, succ);
1371 // If this is not a `loop` loop, then it's possible we bypass
1372 // the body altogether. Otherwise, the only way is via a `break`
1373 // in the loop body.
1374 self.merge_from_succ(ln, succ, first_merge);
1375 first_merge = false;
1378 debug!("propagate_through_loop: using id for loop body {} {}",
1379 expr.id, block_to_string(body));
1381 let cond_ln = match kind {
1383 ForLoop(ref pat) => self.define_bindings_in_pat(*pat, ln),
1384 WhileLoop(ref cond) => self.propagate_through_expr(&**cond, ln),
1386 let body_ln = self.with_loop_nodes(expr.id, succ, ln, |this| {
1387 this.propagate_through_block(body, cond_ln)
1390 // repeat until fixed point is reached:
1391 while self.merge_from_succ(ln, body_ln, first_merge) {
1392 first_merge = false;
1394 let new_cond_ln = match kind {
1396 ForLoop(ref pat) => {
1397 self.define_bindings_in_pat(*pat, ln)
1399 WhileLoop(ref cond) => {
1400 self.propagate_through_expr(&**cond, ln)
1403 assert!(cond_ln == new_cond_ln);
1404 assert!(body_ln == self.with_loop_nodes(expr.id, succ, ln,
1405 |this| this.propagate_through_block(body, cond_ln)));
1411 fn with_loop_nodes<R>(&mut self,
1412 loop_node_id: NodeId,
1415 f: |&mut Liveness<'a, 'tcx>| -> R)
1417 debug!("with_loop_nodes: {} {}", loop_node_id, break_ln.get());
1418 self.loop_scope.push(loop_node_id);
1419 self.break_ln.insert(loop_node_id, break_ln);
1420 self.cont_ln.insert(loop_node_id, cont_ln);
1422 self.loop_scope.pop();
1427 // _______________________________________________________________________
1428 // Checking for error conditions
1430 fn check_local(this: &mut Liveness, local: &ast::Local) {
1433 this.warn_about_unused_or_dead_vars_in_pat(&*local.pat);
1436 this.pat_bindings(&*local.pat, |this, ln, var, sp, id| {
1437 this.warn_about_unused(sp, id, ln, var);
1442 visit::walk_local(this, local);
1445 fn check_arm(this: &mut Liveness, arm: &ast::Arm) {
1446 // only consider the first pattern; any later patterns must have
1447 // the same bindings, and we also consider the first pattern to be
1448 // the "authoritative" set of ids
1449 this.arm_pats_bindings(arm.pats.head().map(|p| &**p), |this, ln, var, sp, id| {
1450 this.warn_about_unused(sp, id, ln, var);
1452 visit::walk_arm(this, arm);
1455 fn check_expr(this: &mut Liveness, expr: &Expr) {
1457 ast::ExprAssign(ref l, ref r) => {
1458 this.check_lvalue(&**l);
1459 this.visit_expr(&**r);
1461 visit::walk_expr(this, expr);
1464 ast::ExprAssignOp(_, ref l, _) => {
1465 this.check_lvalue(&**l);
1467 visit::walk_expr(this, expr);
1470 ast::ExprInlineAsm(ref ia) => {
1471 for &(_, ref input) in ia.inputs.iter() {
1472 this.visit_expr(&**input);
1475 // Output operands must be lvalues
1476 for &(_, ref out, _) in ia.outputs.iter() {
1477 this.check_lvalue(&**out);
1478 this.visit_expr(&**out);
1481 visit::walk_expr(this, expr);
1484 ast::ExprForLoop(ref pat, _, _, _) => {
1485 this.pat_bindings(&**pat, |this, ln, var, sp, id| {
1486 this.warn_about_unused(sp, id, ln, var);
1489 visit::walk_expr(this, expr);
1492 // no correctness conditions related to liveness
1493 ast::ExprCall(..) | ast::ExprMethodCall(..) | ast::ExprIf(..) |
1494 ast::ExprMatch(..) | ast::ExprWhile(..) | ast::ExprLoop(..) |
1495 ast::ExprIndex(..) | ast::ExprField(..) | ast::ExprTupField(..) |
1496 ast::ExprVec(..) | ast::ExprTup(..) | ast::ExprBinary(..) |
1497 ast::ExprCast(..) | ast::ExprUnary(..) | ast::ExprRet(..) |
1498 ast::ExprBreak(..) | ast::ExprAgain(..) | ast::ExprLit(_) |
1499 ast::ExprBlock(..) | ast::ExprMac(..) | ast::ExprAddrOf(..) |
1500 ast::ExprStruct(..) | ast::ExprRepeat(..) | ast::ExprParen(..) |
1501 ast::ExprClosure(..) | ast::ExprProc(..) |
1502 ast::ExprPath(..) | ast::ExprBox(..) | ast::ExprSlice(..) => {
1503 visit::walk_expr(this, expr);
1505 ast::ExprIfLet(..) => {
1506 this.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
1508 ast::ExprWhileLet(..) => {
1509 this.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet");
1514 fn check_fn(_v: &Liveness,
1516 _decl: &ast::FnDecl,
1520 // do not check contents of nested fns
1523 impl<'a, 'tcx> Liveness<'a, 'tcx> {
1524 fn fn_ret(&self, id: NodeId) -> ty::FnOutput<'tcx> {
1525 let fn_ty = ty::node_id_to_type(self.ir.tcx, id);
1527 ty::ty_unboxed_closure(closure_def_id, _, _) =>
1528 self.ir.tcx.unboxed_closures()
1530 .get(&closure_def_id)
1535 _ => ty::ty_fn_ret(fn_ty)
1544 body: &ast::Block) {
1545 match self.fn_ret(id) {
1546 ty::FnConverging(t_ret)
1547 if self.live_on_entry(entry_ln, self.s.no_ret_var).is_some() => {
1549 if ty::type_is_nil(t_ret) {
1550 // for nil return types, it is ok to not return a value expl.
1552 let ends_with_stmt = match body.expr {
1553 None if body.stmts.len() > 0 =>
1554 match body.stmts.last().unwrap().node {
1555 ast::StmtSemi(ref e, _) => {
1556 ty::expr_ty(self.ir.tcx, &**e) == t_ret
1562 self.ir.tcx.sess.span_err(
1563 sp, "not all control paths return a value");
1565 let last_stmt = body.stmts.last().unwrap();
1566 let original_span = original_sp(self.ir.tcx.sess.codemap(),
1567 last_stmt.span, sp);
1568 let span_semicolon = Span {
1569 lo: original_span.hi - BytePos(1),
1570 hi: original_span.hi,
1571 expn_id: original_span.expn_id
1573 self.ir.tcx.sess.span_help(
1574 span_semicolon, "consider removing this semicolon:");
1579 if self.live_on_entry(entry_ln, self.s.clean_exit_var).is_some() => {
1580 self.ir.tcx.sess.span_err(sp,
1581 "computation may converge in a function marked as diverging");
1588 fn check_lvalue(&mut self, expr: &Expr) {
1590 ast::ExprPath(_) => {
1591 if let DefLocal(nid) = self.ir.tcx.def_map.borrow()[expr.id].clone() {
1592 // Assignment to an immutable variable or argument: only legal
1593 // if there is no later assignment. If this local is actually
1594 // mutable, then check for a reassignment to flag the mutability
1596 let ln = self.live_node(expr.id, expr.span);
1597 let var = self.variable(nid, expr.span);
1598 self.warn_about_dead_assign(expr.span, expr.id, ln, var);
1602 // For other kinds of lvalues, no checks are required,
1603 // and any embedded expressions are actually rvalues
1604 visit::walk_expr(self, expr);
1609 fn should_warn(&self, var: Variable) -> Option<String> {
1610 let name = self.ir.variable_name(var);
1611 if name.len() == 0 || name.as_bytes()[0] == ('_' as u8) {
1618 fn warn_about_unused_args(&self, decl: &ast::FnDecl, entry_ln: LiveNode) {
1619 for arg in decl.inputs.iter() {
1620 pat_util::pat_bindings(&self.ir.tcx.def_map,
1622 |_bm, p_id, sp, path1| {
1623 let var = self.variable(p_id, sp);
1624 // Ignore unused self.
1625 let ident = path1.node;
1626 if ident.name != special_idents::self_.name {
1627 self.warn_about_unused(sp, p_id, entry_ln, var);
1633 fn warn_about_unused_or_dead_vars_in_pat(&mut self, pat: &ast::Pat) {
1634 self.pat_bindings(pat, |this, ln, var, sp, id| {
1635 if !this.warn_about_unused(sp, id, ln, var) {
1636 this.warn_about_dead_assign(sp, id, ln, var);
1641 fn warn_about_unused(&self,
1647 if !self.used_on_entry(ln, var) {
1648 let r = self.should_warn(var);
1649 for name in r.iter() {
1651 // annoying: for parameters in funcs like `fn(x: int)
1652 // {ret}`, there is only one node, so asking about
1653 // assigned_on_exit() is not meaningful.
1654 let is_assigned = if ln == self.s.exit_ln {
1657 self.assigned_on_exit(ln, var).is_some()
1661 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_VARIABLES, id, sp,
1662 format!("variable `{}` is assigned to, but never used",
1665 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_VARIABLES, id, sp,
1666 format!("unused variable: `{}`", *name));
1675 fn warn_about_dead_assign(&self,
1680 if self.live_on_exit(ln, var).is_none() {
1681 let r = self.should_warn(var);
1682 for name in r.iter() {
1683 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_ASSIGNMENTS, id, sp,
1684 format!("value assigned to `{}` is never read", *name));