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);
140 #[deriving(PartialEq)]
141 struct LiveNode(uint);
144 fn get(&self) -> uint { let Variable(v) = *self; v }
148 fn get(&self) -> uint { let LiveNode(v) = *self; v }
151 impl Clone for LiveNode {
152 fn clone(&self) -> LiveNode {
157 #[deriving(PartialEq, Show)]
165 fn live_node_kind_to_string(lnk: LiveNodeKind, cx: &ty::ctxt) -> String {
166 let cm = cx.sess.codemap();
169 format!("Free var node [{}]", cm.span_to_string(s))
172 format!("Expr node [{}]", cm.span_to_string(s))
175 format!("Var def node [{}]", cm.span_to_string(s))
177 ExitNode => "Exit node".to_string(),
181 impl<'a, 'tcx, 'v> Visitor<'v> for IrMaps<'a, 'tcx> {
182 fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v ast::FnDecl,
183 b: &'v ast::Block, s: Span, id: NodeId) {
184 visit_fn(self, fk, fd, b, s, id);
186 fn visit_local(&mut self, l: &ast::Local) { visit_local(self, l); }
187 fn visit_expr(&mut self, ex: &Expr) { visit_expr(self, ex); }
188 fn visit_arm(&mut self, a: &ast::Arm) { visit_arm(self, a); }
191 pub fn check_crate(tcx: &ty::ctxt) {
192 visit::walk_crate(&mut IrMaps::new(tcx), tcx.map.krate());
193 tcx.sess.abort_if_errors();
196 impl fmt::Show for LiveNode {
197 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
198 write!(f, "ln({})", self.get())
202 impl fmt::Show for Variable {
203 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
204 write!(f, "v({})", self.get())
208 // ______________________________________________________________________
211 // This is the first pass and the one that drives the main
212 // computation. It walks up and down the IR once. On the way down,
213 // we count for each function the number of variables as well as
214 // liveness nodes. A liveness node is basically an expression or
215 // capture clause that does something of interest: either it has
216 // interesting control flow or it uses/defines a local variable.
218 // On the way back up, at each function node we create liveness sets
219 // (we now know precisely how big to make our various vectors and so
220 // forth) and then do the data-flow propagation to compute the set
221 // of live variables at each program point.
223 // Finally, we run back over the IR one last time and, using the
224 // computed liveness, check various safety conditions. For example,
225 // there must be no live nodes at the definition site for a variable
226 // unless it has an initializer. Similarly, each non-mutable local
227 // variable must not be assigned if there is some successor
228 // assignment. And so forth.
231 fn is_valid(&self) -> bool {
232 self.get() != uint::MAX
236 fn invalid_node() -> LiveNode { LiveNode(uint::MAX) }
251 Arg(NodeId, ast::Ident),
257 struct IrMaps<'a, 'tcx: 'a> {
258 tcx: &'a ty::ctxt<'tcx>,
260 num_live_nodes: uint,
262 live_node_map: NodeMap<LiveNode>,
263 variable_map: NodeMap<Variable>,
264 capture_info_map: NodeMap<Rc<Vec<CaptureInfo>>>,
265 var_kinds: Vec<VarKind>,
266 lnks: Vec<LiveNodeKind>,
269 impl<'a, 'tcx> IrMaps<'a, 'tcx> {
270 fn new(tcx: &'a ty::ctxt<'tcx>) -> IrMaps<'a, 'tcx> {
275 live_node_map: NodeMap::new(),
276 variable_map: NodeMap::new(),
277 capture_info_map: NodeMap::new(),
278 var_kinds: Vec::new(),
283 fn add_live_node(&mut self, lnk: LiveNodeKind) -> LiveNode {
284 let ln = LiveNode(self.num_live_nodes);
286 self.num_live_nodes += 1;
288 debug!("{} is of kind {}", ln.to_string(),
289 live_node_kind_to_string(lnk, self.tcx));
294 fn add_live_node_for_node(&mut self, node_id: NodeId, lnk: LiveNodeKind) {
295 let ln = self.add_live_node(lnk);
296 self.live_node_map.insert(node_id, ln);
298 debug!("{} is node {}", ln.to_string(), node_id);
301 fn add_variable(&mut self, vk: VarKind) -> Variable {
302 let v = Variable(self.num_vars);
303 self.var_kinds.push(vk);
307 Local(LocalInfo { id: node_id, .. }) | Arg(node_id, _) => {
308 self.variable_map.insert(node_id, v);
310 ImplicitRet | CleanExit => {}
313 debug!("{} is {}", v.to_string(), vk);
318 fn variable(&self, node_id: NodeId, span: Span) -> Variable {
319 match self.variable_map.get(&node_id) {
324 .span_bug(span, format!("no variable registered for id {}",
325 node_id).as_slice());
330 fn variable_name(&self, var: Variable) -> String {
331 match self.var_kinds[var.get()] {
332 Local(LocalInfo { ident: nm, .. }) | Arg(_, nm) => {
333 token::get_ident(nm).get().to_string()
335 ImplicitRet => "<implicit-ret>".to_string(),
336 CleanExit => "<clean-exit>".to_string()
340 fn set_captures(&mut self, node_id: NodeId, cs: Vec<CaptureInfo>) {
341 self.capture_info_map.insert(node_id, Rc::new(cs));
344 fn lnk(&self, ln: LiveNode) -> LiveNodeKind {
349 impl<'a, 'tcx, 'v> Visitor<'v> for Liveness<'a, 'tcx> {
350 fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v ast::FnDecl,
351 b: &'v ast::Block, s: Span, n: NodeId) {
352 check_fn(self, fk, fd, b, s, n);
354 fn visit_local(&mut self, l: &ast::Local) {
355 check_local(self, l);
357 fn visit_expr(&mut self, ex: &Expr) {
358 check_expr(self, ex);
360 fn visit_arm(&mut self, a: &ast::Arm) {
365 fn visit_fn(ir: &mut IrMaps,
373 // swap in a new set of IR maps for this function body:
374 let mut fn_maps = IrMaps::new(ir.tcx);
376 debug!("creating fn_maps: {}", &fn_maps as *const IrMaps);
378 for arg in decl.inputs.iter() {
379 pat_util::pat_bindings(&ir.tcx.def_map,
381 |_bm, arg_id, _x, path1| {
382 debug!("adding argument {}", arg_id);
383 let ident = path1.node;
384 fn_maps.add_variable(Arg(arg_id, ident));
388 // gather up the various local variables, significant expressions,
390 visit::walk_fn(&mut fn_maps, fk, decl, body, sp);
392 // Special nodes and variables:
393 // - exit_ln represents the end of the fn, either by return or panic
394 // - implicit_ret_var is a pseudo-variable that represents
395 // an implicit return
396 let specials = Specials {
397 exit_ln: fn_maps.add_live_node(ExitNode),
398 fallthrough_ln: fn_maps.add_live_node(ExitNode),
399 no_ret_var: fn_maps.add_variable(ImplicitRet),
400 clean_exit_var: fn_maps.add_variable(CleanExit)
404 let mut lsets = Liveness::new(&mut fn_maps, specials);
405 let entry_ln = lsets.compute(decl, body);
407 // check for various error conditions
408 lsets.visit_block(body);
409 lsets.check_ret(id, sp, fk, entry_ln, body);
410 lsets.warn_about_unused_args(decl, entry_ln);
413 fn visit_local(ir: &mut IrMaps, local: &ast::Local) {
414 pat_util::pat_bindings(&ir.tcx.def_map, &*local.pat, |_, p_id, sp, path1| {
415 debug!("adding local variable {}", p_id);
416 let name = path1.node;
417 ir.add_live_node_for_node(p_id, VarDefNode(sp));
418 ir.add_variable(Local(LocalInfo {
423 visit::walk_local(ir, local);
426 fn visit_arm(ir: &mut IrMaps, arm: &ast::Arm) {
427 for pat in arm.pats.iter() {
428 pat_util::pat_bindings(&ir.tcx.def_map, &**pat, |bm, p_id, sp, path1| {
429 debug!("adding local variable {} from match with bm {}",
431 let name = path1.node;
432 ir.add_live_node_for_node(p_id, VarDefNode(sp));
433 ir.add_variable(Local(LocalInfo {
439 visit::walk_arm(ir, arm);
442 fn visit_expr(ir: &mut IrMaps, expr: &Expr) {
444 // live nodes required for uses or definitions of variables:
445 ast::ExprPath(_) => {
446 let def = ir.tcx.def_map.borrow()[expr.id].clone();
447 debug!("expr {}: path that leads to {}", expr.id, def);
448 if let DefLocal(..) = def {
449 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
451 visit::walk_expr(ir, expr);
453 ast::ExprClosure(..) | ast::ExprProc(..) => {
454 // Interesting control flow (for loops can contain labeled
455 // breaks or continues)
456 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
458 // Make a live_node for each captured variable, with the span
459 // being the location that the variable is used. This results
460 // in better error messages than just pointing at the closure
461 // construction site.
462 let mut call_caps = Vec::new();
463 ty::with_freevars(ir.tcx, expr.id, |freevars| {
464 for fv in freevars.iter() {
465 if let DefLocal(rv) = fv.def {
466 let fv_ln = ir.add_live_node(FreeVarNode(fv.span));
467 call_caps.push(CaptureInfo {ln: fv_ln,
472 ir.set_captures(expr.id, call_caps);
474 visit::walk_expr(ir, expr);
477 // live nodes required for interesting control flow:
478 ast::ExprIf(..) | ast::ExprMatch(..) | ast::ExprWhile(..) | ast::ExprLoop(..) => {
479 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
480 visit::walk_expr(ir, expr);
482 ast::ExprIfLet(..) => {
483 ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
485 ast::ExprWhileLet(..) => {
486 ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet");
488 ast::ExprForLoop(ref pat, _, _, _) => {
489 pat_util::pat_bindings(&ir.tcx.def_map, &**pat, |bm, p_id, sp, path1| {
490 debug!("adding local variable {} from for loop with bm {}",
492 let name = path1.node;
493 ir.add_live_node_for_node(p_id, VarDefNode(sp));
494 ir.add_variable(Local(LocalInfo {
499 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
500 visit::walk_expr(ir, expr);
502 ast::ExprBinary(op, _, _) if ast_util::lazy_binop(op) => {
503 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
504 visit::walk_expr(ir, expr);
507 // otherwise, live nodes are not required:
508 ast::ExprIndex(..) | ast::ExprField(..) | ast::ExprTupField(..) |
509 ast::ExprVec(..) | ast::ExprCall(..) | ast::ExprMethodCall(..) |
510 ast::ExprTup(..) | ast::ExprBinary(..) | ast::ExprAddrOf(..) |
511 ast::ExprCast(..) | ast::ExprUnary(..) | ast::ExprBreak(_) |
512 ast::ExprAgain(_) | ast::ExprLit(_) | ast::ExprRet(..) |
513 ast::ExprBlock(..) | ast::ExprAssign(..) | ast::ExprAssignOp(..) |
514 ast::ExprMac(..) | ast::ExprStruct(..) | ast::ExprRepeat(..) |
515 ast::ExprParen(..) | ast::ExprInlineAsm(..) | ast::ExprBox(..) |
516 ast::ExprSlice(..) => {
517 visit::walk_expr(ir, expr);
522 // ______________________________________________________________________
523 // Computing liveness sets
525 // Actually we compute just a bit more than just liveness, but we use
526 // the same basic propagation framework in all cases.
535 fn invalid_users() -> Users {
537 reader: invalid_node(),
538 writer: invalid_node(),
545 fallthrough_ln: LiveNode,
546 no_ret_var: Variable,
547 clean_exit_var: Variable
550 static ACC_READ: uint = 1u;
551 static ACC_WRITE: uint = 2u;
552 static ACC_USE: uint = 4u;
554 struct Liveness<'a, 'tcx: 'a> {
555 ir: &'a mut IrMaps<'a, 'tcx>,
557 successors: Vec<LiveNode>,
559 // The list of node IDs for the nested loop scopes
561 loop_scope: Vec<NodeId>,
562 // mappings from loop node ID to LiveNode
563 // ("break" label should map to loop node ID,
564 // it probably doesn't now)
565 break_ln: NodeMap<LiveNode>,
566 cont_ln: NodeMap<LiveNode>
569 impl<'a, 'tcx> Liveness<'a, 'tcx> {
570 fn new(ir: &'a mut IrMaps<'a, 'tcx>, specials: Specials) -> Liveness<'a, 'tcx> {
571 let num_live_nodes = ir.num_live_nodes;
572 let num_vars = ir.num_vars;
576 successors: Vec::from_elem(num_live_nodes, invalid_node()),
577 users: Vec::from_elem(num_live_nodes * num_vars, invalid_users()),
578 loop_scope: Vec::new(),
579 break_ln: NodeMap::new(),
580 cont_ln: NodeMap::new(),
584 fn live_node(&self, node_id: NodeId, span: Span) -> LiveNode {
585 match self.ir.live_node_map.get(&node_id) {
588 // This must be a mismatch between the ir_map construction
589 // above and the propagation code below; the two sets of
590 // code have to agree about which AST nodes are worth
591 // creating liveness nodes for.
592 self.ir.tcx.sess.span_bug(
594 format!("no live node registered for node {}",
595 node_id).as_slice());
600 fn variable(&self, node_id: NodeId, span: Span) -> Variable {
601 self.ir.variable(node_id, span)
604 fn pat_bindings(&mut self,
606 f: |&mut Liveness<'a, 'tcx>, LiveNode, Variable, Span, NodeId|) {
607 pat_util::pat_bindings(&self.ir.tcx.def_map, pat, |_bm, p_id, sp, _n| {
608 let ln = self.live_node(p_id, sp);
609 let var = self.variable(p_id, sp);
610 f(self, ln, var, sp, p_id);
614 fn arm_pats_bindings(&mut self,
615 pat: Option<&ast::Pat>,
616 f: |&mut Liveness<'a, 'tcx>, LiveNode, Variable, Span, NodeId|) {
619 self.pat_bindings(pat, f);
625 fn define_bindings_in_pat(&mut self, pat: &ast::Pat, succ: LiveNode)
627 self.define_bindings_in_arm_pats(Some(pat), succ)
630 fn define_bindings_in_arm_pats(&mut self, pat: Option<&ast::Pat>, succ: LiveNode)
633 self.arm_pats_bindings(pat, |this, ln, var, _sp, _id| {
634 this.init_from_succ(ln, succ);
635 this.define(ln, var);
641 fn idx(&self, ln: LiveNode, var: Variable) -> uint {
642 ln.get() * self.ir.num_vars + var.get()
645 fn live_on_entry(&self, ln: LiveNode, var: Variable)
646 -> Option<LiveNodeKind> {
647 assert!(ln.is_valid());
648 let reader = self.users[self.idx(ln, var)].reader;
649 if reader.is_valid() {Some(self.ir.lnk(reader))} else {None}
653 Is this variable live on entry to any of its successor nodes?
655 fn live_on_exit(&self, ln: LiveNode, var: Variable)
656 -> Option<LiveNodeKind> {
657 let successor = self.successors[ln.get()];
658 self.live_on_entry(successor, var)
661 fn used_on_entry(&self, ln: LiveNode, var: Variable) -> bool {
662 assert!(ln.is_valid());
663 self.users[self.idx(ln, var)].used
666 fn assigned_on_entry(&self, ln: LiveNode, var: Variable)
667 -> Option<LiveNodeKind> {
668 assert!(ln.is_valid());
669 let writer = self.users[self.idx(ln, var)].writer;
670 if writer.is_valid() {Some(self.ir.lnk(writer))} else {None}
673 fn assigned_on_exit(&self, ln: LiveNode, var: Variable)
674 -> Option<LiveNodeKind> {
675 let successor = self.successors[ln.get()];
676 self.assigned_on_entry(successor, var)
679 fn indices2(&mut self,
682 op: |&mut Liveness<'a, 'tcx>, uint, uint|) {
683 let node_base_idx = self.idx(ln, Variable(0u));
684 let succ_base_idx = self.idx(succ_ln, Variable(0u));
685 for var_idx in range(0u, self.ir.num_vars) {
686 op(self, node_base_idx + var_idx, succ_base_idx + var_idx);
693 test: |uint| -> LiveNode) -> io::IoResult<()> {
694 let node_base_idx = self.idx(ln, Variable(0));
695 for var_idx in range(0u, self.ir.num_vars) {
696 let idx = node_base_idx + var_idx;
697 if test(idx).is_valid() {
698 try!(write!(wr, " {}", Variable(var_idx).to_string()));
704 fn find_loop_scope(&self,
705 opt_label: Option<ast::Ident>,
711 // Refers to a labeled loop. Use the results of resolve
713 match self.ir.tcx.def_map.borrow().get(&id) {
714 Some(&DefLabel(loop_id)) => loop_id,
715 _ => self.ir.tcx.sess.span_bug(sp, "label on break/loop \
716 doesn't refer to a loop")
720 // Vanilla 'break' or 'loop', so use the enclosing
722 if self.loop_scope.len() == 0 {
723 self.ir.tcx.sess.span_bug(sp, "break outside loop");
725 *self.loop_scope.last().unwrap()
731 #[allow(unused_must_use)]
732 fn ln_str(&self, ln: LiveNode) -> String {
733 let mut wr = Vec::new();
735 let wr = &mut wr as &mut io::Writer;
736 write!(wr, "[ln({}) of kind {} reads", ln.get(), self.ir.lnk(ln));
737 self.write_vars(wr, ln, |idx| self.users[idx].reader);
738 write!(wr, " writes");
739 self.write_vars(wr, ln, |idx| self.users[idx].writer);
740 write!(wr, " precedes {}]", self.successors[ln.get()].to_string());
742 String::from_utf8(wr).unwrap()
745 fn init_empty(&mut self, ln: LiveNode, succ_ln: LiveNode) {
746 self.successors[ln.get()] = succ_ln;
748 // It is not necessary to initialize the
749 // values to empty because this is the value
750 // they have when they are created, and the sets
751 // only grow during iterations.
753 // self.indices(ln) { |idx|
754 // self.users[idx] = invalid_users();
758 fn init_from_succ(&mut self, ln: LiveNode, succ_ln: LiveNode) {
759 // more efficient version of init_empty() / merge_from_succ()
760 self.successors[ln.get()] = succ_ln;
762 self.indices2(ln, succ_ln, |this, idx, succ_idx| {
763 this.users[idx] = this.users[succ_idx]
765 debug!("init_from_succ(ln={}, succ={})",
766 self.ln_str(ln), self.ln_str(succ_ln));
769 fn merge_from_succ(&mut self,
774 if ln == succ_ln { return false; }
776 let mut changed = false;
777 self.indices2(ln, succ_ln, |this, idx, succ_idx| {
778 changed |= copy_if_invalid(this.users[succ_idx].reader,
779 &mut this.users[idx].reader);
780 changed |= copy_if_invalid(this.users[succ_idx].writer,
781 &mut this.users[idx].writer);
782 if this.users[succ_idx].used && !this.users[idx].used {
783 this.users[idx].used = true;
788 debug!("merge_from_succ(ln={}, succ={}, first_merge={}, changed={})",
789 ln.to_string(), self.ln_str(succ_ln), first_merge, changed);
792 fn copy_if_invalid(src: LiveNode, dst: &mut LiveNode) -> bool {
793 if src.is_valid() && !dst.is_valid() {
802 // Indicates that a local variable was *defined*; we know that no
803 // uses of the variable can precede the definition (resolve checks
804 // this) so we just clear out all the data.
805 fn define(&mut self, writer: LiveNode, var: Variable) {
806 let idx = self.idx(writer, var);
807 self.users[idx].reader = invalid_node();
808 self.users[idx].writer = invalid_node();
810 debug!("{} defines {} (idx={}): {}", writer.to_string(), var.to_string(),
811 idx, self.ln_str(writer));
814 // Either read, write, or both depending on the acc bitset
815 fn acc(&mut self, ln: LiveNode, var: Variable, acc: uint) {
816 debug!("{} accesses[{:x}] {}: {}",
817 ln.to_string(), acc, var.to_string(), self.ln_str(ln));
819 let idx = self.idx(ln, var);
820 let user = &mut self.users[idx];
822 if (acc & ACC_WRITE) != 0 {
823 user.reader = invalid_node();
827 // Important: if we both read/write, must do read second
828 // or else the write will override.
829 if (acc & ACC_READ) != 0 {
833 if (acc & ACC_USE) != 0 {
838 // _______________________________________________________________________
840 fn compute(&mut self, decl: &ast::FnDecl, body: &ast::Block) -> LiveNode {
841 // if there is a `break` or `again` at the top level, then it's
842 // effectively a return---this only occurs in `for` loops,
843 // where the body is really a closure.
845 debug!("compute: using id for block, {}", block_to_string(body));
847 let exit_ln = self.s.exit_ln;
848 let entry_ln: LiveNode =
849 self.with_loop_nodes(body.id, exit_ln, exit_ln,
850 |this| this.propagate_through_fn_block(decl, body));
852 // hack to skip the loop unless debug! is enabled:
853 debug!("^^ liveness computation results for body {} (entry={})",
855 for ln_idx in range(0u, self.ir.num_live_nodes) {
856 debug!("{}", self.ln_str(LiveNode(ln_idx)));
860 entry_ln.to_string());
865 fn propagate_through_fn_block(&mut self, _: &ast::FnDecl, blk: &ast::Block)
867 // the fallthrough exit is only for those cases where we do not
868 // explicitly return:
870 self.init_from_succ(s.fallthrough_ln, s.exit_ln);
871 if blk.expr.is_none() {
872 self.acc(s.fallthrough_ln, s.no_ret_var, ACC_READ)
874 self.acc(s.fallthrough_ln, s.clean_exit_var, ACC_READ);
876 self.propagate_through_block(blk, s.fallthrough_ln)
879 fn propagate_through_block(&mut self, blk: &ast::Block, succ: LiveNode)
881 let succ = self.propagate_through_opt_expr(blk.expr.as_ref().map(|e| &**e), succ);
882 blk.stmts.iter().rev().fold(succ, |succ, stmt| {
883 self.propagate_through_stmt(&**stmt, succ)
887 fn propagate_through_stmt(&mut self, stmt: &ast::Stmt, succ: LiveNode)
890 ast::StmtDecl(ref decl, _) => {
891 self.propagate_through_decl(&**decl, succ)
894 ast::StmtExpr(ref expr, _) | ast::StmtSemi(ref expr, _) => {
895 self.propagate_through_expr(&**expr, succ)
898 ast::StmtMac(..) => {
899 self.ir.tcx.sess.span_bug(stmt.span, "unexpanded macro");
904 fn propagate_through_decl(&mut self, decl: &ast::Decl, succ: LiveNode)
907 ast::DeclLocal(ref local) => {
908 self.propagate_through_local(&**local, succ)
910 ast::DeclItem(_) => succ,
914 fn propagate_through_local(&mut self, local: &ast::Local, succ: LiveNode)
916 // Note: we mark the variable as defined regardless of whether
917 // there is an initializer. Initially I had thought to only mark
918 // the live variable as defined if it was initialized, and then we
919 // could check for uninit variables just by scanning what is live
920 // at the start of the function. But that doesn't work so well for
921 // immutable variables defined in a loop:
922 // loop { let x; x = 5; }
923 // because the "assignment" loops back around and generates an error.
925 // So now we just check that variables defined w/o an
926 // initializer are not live at the point of their
927 // initialization, which is mildly more complex than checking
928 // once at the func header but otherwise equivalent.
930 let succ = self.propagate_through_opt_expr(local.init.as_ref().map(|e| &**e), succ);
931 self.define_bindings_in_pat(&*local.pat, succ)
934 fn propagate_through_exprs(&mut self, exprs: &[P<Expr>], succ: LiveNode)
936 exprs.iter().rev().fold(succ, |succ, expr| {
937 self.propagate_through_expr(&**expr, succ)
941 fn propagate_through_opt_expr(&mut self,
942 opt_expr: Option<&Expr>,
945 opt_expr.map_or(succ, |expr| self.propagate_through_expr(expr, succ))
948 fn propagate_through_expr(&mut self, expr: &Expr, succ: LiveNode)
950 debug!("propagate_through_expr: {}", expr_to_string(expr));
953 // Interesting cases with control flow or which gen/kill
955 ast::ExprPath(_) => {
956 self.access_path(expr, succ, ACC_READ | ACC_USE)
959 ast::ExprField(ref e, _) => {
960 self.propagate_through_expr(&**e, succ)
963 ast::ExprTupField(ref e, _) => {
964 self.propagate_through_expr(&**e, succ)
967 ast::ExprClosure(_, _, _, ref blk) |
968 ast::ExprProc(_, ref blk) => {
969 debug!("{} is an ExprClosure or ExprProc",
970 expr_to_string(expr));
973 The next-node for a break is the successor of the entire
974 loop. The next-node for a continue is the top of this loop.
976 let node = self.live_node(expr.id, expr.span);
977 self.with_loop_nodes(blk.id, succ, node, |this| {
979 // the construction of a closure itself is not important,
980 // but we have to consider the closed over variables.
981 let caps = match this.ir.capture_info_map.get(&expr.id) {
982 Some(caps) => caps.clone(),
984 this.ir.tcx.sess.span_bug(expr.span, "no registered caps");
987 caps.iter().rev().fold(succ, |succ, cap| {
988 this.init_from_succ(cap.ln, succ);
989 let var = this.variable(cap.var_nid, expr.span);
990 this.acc(cap.ln, var, ACC_READ | ACC_USE);
996 ast::ExprIf(ref cond, ref then, ref els) => {
1010 let else_ln = self.propagate_through_opt_expr(els.as_ref().map(|e| &**e), succ);
1011 let then_ln = self.propagate_through_block(&**then, succ);
1012 let ln = self.live_node(expr.id, expr.span);
1013 self.init_from_succ(ln, else_ln);
1014 self.merge_from_succ(ln, then_ln, false);
1015 self.propagate_through_expr(&**cond, ln)
1018 ast::ExprIfLet(..) => {
1019 self.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
1022 ast::ExprWhile(ref cond, ref blk, _) => {
1023 self.propagate_through_loop(expr, WhileLoop(&**cond), &**blk, succ)
1026 ast::ExprWhileLet(..) => {
1027 self.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet");
1030 ast::ExprForLoop(ref pat, ref head, ref blk, _) => {
1031 let ln = self.propagate_through_loop(expr, ForLoop(&**pat), &**blk, succ);
1032 self.propagate_through_expr(&**head, ln)
1035 // Note that labels have been resolved, so we don't need to look
1036 // at the label ident
1037 ast::ExprLoop(ref blk, _) => {
1038 self.propagate_through_loop(expr, LoopLoop, &**blk, succ)
1041 ast::ExprMatch(ref e, ref arms, _) => {
1056 let ln = self.live_node(expr.id, expr.span);
1057 self.init_empty(ln, succ);
1058 let mut first_merge = true;
1059 for arm in arms.iter() {
1061 self.propagate_through_expr(&*arm.body, succ);
1063 self.propagate_through_opt_expr(arm.guard.as_ref().map(|e| &**e), body_succ);
1064 // only consider the first pattern; any later patterns must have
1065 // the same bindings, and we also consider the first pattern to be
1066 // the "authoritative" set of ids
1068 self.define_bindings_in_arm_pats(arm.pats.head().map(|p| &**p),
1070 self.merge_from_succ(ln, arm_succ, first_merge);
1071 first_merge = false;
1073 self.propagate_through_expr(&**e, ln)
1076 ast::ExprRet(ref o_e) => {
1077 // ignore succ and subst exit_ln:
1078 let exit_ln = self.s.exit_ln;
1079 self.propagate_through_opt_expr(o_e.as_ref().map(|e| &**e), exit_ln)
1082 ast::ExprBreak(opt_label) => {
1083 // Find which label this break jumps to
1084 let sc = self.find_loop_scope(opt_label, expr.id, expr.span);
1086 // Now that we know the label we're going to,
1087 // look it up in the break loop nodes table
1089 match self.break_ln.get(&sc) {
1091 None => self.ir.tcx.sess.span_bug(expr.span,
1092 "break to unknown label")
1096 ast::ExprAgain(opt_label) => {
1097 // Find which label this expr continues to
1098 let sc = self.find_loop_scope(opt_label, expr.id, expr.span);
1100 // Now that we know the label we're going to,
1101 // look it up in the continue loop nodes table
1103 match self.cont_ln.get(&sc) {
1105 None => self.ir.tcx.sess.span_bug(expr.span,
1106 "loop to unknown label")
1110 ast::ExprAssign(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);
1114 let succ = self.propagate_through_lvalue_components(&**l, succ);
1115 self.propagate_through_expr(&**r, succ)
1118 ast::ExprAssignOp(_, ref l, ref r) => {
1119 // see comment on lvalues in
1120 // propagate_through_lvalue_components()
1121 let succ = self.write_lvalue(&**l, succ, ACC_WRITE|ACC_READ);
1122 let succ = self.propagate_through_expr(&**r, succ);
1123 self.propagate_through_lvalue_components(&**l, succ)
1126 // Uninteresting cases: just propagate in rev exec order
1128 ast::ExprVec(ref exprs) => {
1129 self.propagate_through_exprs(exprs.as_slice(), succ)
1132 ast::ExprRepeat(ref element, ref count) => {
1133 let succ = self.propagate_through_expr(&**count, succ);
1134 self.propagate_through_expr(&**element, succ)
1137 ast::ExprStruct(_, ref fields, ref with_expr) => {
1138 let succ = self.propagate_through_opt_expr(with_expr.as_ref().map(|e| &**e), succ);
1139 fields.iter().rev().fold(succ, |succ, field| {
1140 self.propagate_through_expr(&*field.expr, succ)
1144 ast::ExprCall(ref f, ref args) => {
1145 let diverges = !self.ir.tcx.is_method_call(expr.id) && {
1146 let t_ret = ty::ty_fn_ret(ty::expr_ty(self.ir.tcx, &**f));
1147 t_ret == ty::FnDiverging
1149 let succ = if diverges {
1154 let succ = self.propagate_through_exprs(args.as_slice(), succ);
1155 self.propagate_through_expr(&**f, succ)
1158 ast::ExprMethodCall(_, _, ref args) => {
1159 let method_call = ty::MethodCall::expr(expr.id);
1160 let method_ty = self.ir.tcx.method_map.borrow().get(&method_call).unwrap().ty;
1161 let diverges = ty::ty_fn_ret(method_ty) == ty::FnDiverging;
1162 let succ = if diverges {
1167 self.propagate_through_exprs(args.as_slice(), succ)
1170 ast::ExprTup(ref exprs) => {
1171 self.propagate_through_exprs(exprs.as_slice(), succ)
1174 ast::ExprBinary(op, ref l, ref r) if ast_util::lazy_binop(op) => {
1175 let r_succ = self.propagate_through_expr(&**r, succ);
1177 let ln = self.live_node(expr.id, expr.span);
1178 self.init_from_succ(ln, succ);
1179 self.merge_from_succ(ln, r_succ, false);
1181 self.propagate_through_expr(&**l, ln)
1184 ast::ExprIndex(ref l, ref r) |
1185 ast::ExprBinary(_, ref l, ref r) |
1186 ast::ExprBox(ref l, ref r) => {
1187 let r_succ = self.propagate_through_expr(&**r, succ);
1188 self.propagate_through_expr(&**l, r_succ)
1191 ast::ExprSlice(ref e1, ref e2, ref e3, _) => {
1192 let succ = e3.as_ref().map_or(succ, |e| self.propagate_through_expr(&**e, succ));
1193 let succ = e2.as_ref().map_or(succ, |e| self.propagate_through_expr(&**e, succ));
1194 self.propagate_through_expr(&**e1, succ)
1197 ast::ExprAddrOf(_, ref e) |
1198 ast::ExprCast(ref e, _) |
1199 ast::ExprUnary(_, ref e) |
1200 ast::ExprParen(ref e) => {
1201 self.propagate_through_expr(&**e, succ)
1204 ast::ExprInlineAsm(ref ia) => {
1206 let succ = ia.outputs.iter().rev().fold(succ, |succ, &(_, ref expr, _)| {
1207 // see comment on lvalues
1208 // in propagate_through_lvalue_components()
1209 let succ = self.write_lvalue(&**expr, succ, ACC_WRITE);
1210 self.propagate_through_lvalue_components(&**expr, succ)
1212 // Inputs are executed first. Propagate last because of rev order
1213 ia.inputs.iter().rev().fold(succ, |succ, &(_, ref expr)| {
1214 self.propagate_through_expr(&**expr, succ)
1218 ast::ExprLit(..) => {
1222 ast::ExprBlock(ref blk) => {
1223 self.propagate_through_block(&**blk, succ)
1226 ast::ExprMac(..) => {
1227 self.ir.tcx.sess.span_bug(expr.span, "unexpanded macro");
1232 fn propagate_through_lvalue_components(&mut self,
1238 // In general, the full flow graph structure for an
1239 // assignment/move/etc can be handled in one of two ways,
1240 // depending on whether what is being assigned is a "tracked
1241 // value" or not. A tracked value is basically a local
1242 // variable or argument.
1244 // The two kinds of graphs are:
1246 // Tracked lvalue Untracked lvalue
1247 // ----------------------++-----------------------
1251 // (rvalue) || (rvalue)
1254 // (write of lvalue) || (lvalue components)
1259 // ----------------------++-----------------------
1261 // I will cover the two cases in turn:
1263 // # Tracked lvalues
1265 // A tracked lvalue is a local variable/argument `x`. In
1266 // these cases, the link_node where the write occurs is linked
1267 // to node id of `x`. The `write_lvalue()` routine generates
1268 // the contents of this node. There are no subcomponents to
1271 // # Non-tracked lvalues
1273 // These are lvalues like `x[5]` or `x.f`. In that case, we
1274 // basically ignore the value which is written to but generate
1275 // reads for the components---`x` in these two examples. The
1276 // components reads are generated by
1277 // `propagate_through_lvalue_components()` (this fn).
1279 // # Illegal lvalues
1281 // It is still possible to observe assignments to non-lvalues;
1282 // these errors are detected in the later pass borrowck. We
1283 // just ignore such cases and treat them as reads.
1286 ast::ExprPath(_) => succ,
1287 ast::ExprField(ref e, _) => self.propagate_through_expr(&**e, succ),
1288 ast::ExprTupField(ref e, _) => self.propagate_through_expr(&**e, succ),
1289 _ => self.propagate_through_expr(expr, succ)
1293 // see comment on propagate_through_lvalue()
1294 fn write_lvalue(&mut self, expr: &Expr, succ: LiveNode, acc: uint)
1297 ast::ExprPath(_) => self.access_path(expr, succ, acc),
1299 // We do not track other lvalues, so just propagate through
1300 // to their subcomponents. Also, it may happen that
1301 // non-lvalues occur here, because those are detected in the
1302 // later pass borrowck.
1307 fn access_path(&mut self, expr: &Expr, succ: LiveNode, acc: uint)
1309 match self.ir.tcx.def_map.borrow()[expr.id].clone() {
1311 let ln = self.live_node(expr.id, expr.span);
1313 self.init_from_succ(ln, succ);
1314 let var = self.variable(nid, expr.span);
1315 self.acc(ln, var, acc);
1323 fn propagate_through_loop(&mut self,
1332 We model control flow like this:
1350 let mut first_merge = true;
1351 let ln = self.live_node(expr.id, expr.span);
1352 self.init_empty(ln, succ);
1356 // If this is not a `loop` loop, then it's possible we bypass
1357 // the body altogether. Otherwise, the only way is via a `break`
1358 // in the loop body.
1359 self.merge_from_succ(ln, succ, first_merge);
1360 first_merge = false;
1363 debug!("propagate_through_loop: using id for loop body {} {}",
1364 expr.id, block_to_string(body));
1366 let cond_ln = match kind {
1368 ForLoop(ref pat) => self.define_bindings_in_pat(*pat, ln),
1369 WhileLoop(ref cond) => self.propagate_through_expr(&**cond, ln),
1371 let body_ln = self.with_loop_nodes(expr.id, succ, ln, |this| {
1372 this.propagate_through_block(body, cond_ln)
1375 // repeat until fixed point is reached:
1376 while self.merge_from_succ(ln, body_ln, first_merge) {
1377 first_merge = false;
1379 let new_cond_ln = match kind {
1381 ForLoop(ref pat) => {
1382 self.define_bindings_in_pat(*pat, ln)
1384 WhileLoop(ref cond) => {
1385 self.propagate_through_expr(&**cond, ln)
1388 assert!(cond_ln == new_cond_ln);
1389 assert!(body_ln == self.with_loop_nodes(expr.id, succ, ln,
1390 |this| this.propagate_through_block(body, cond_ln)));
1396 fn with_loop_nodes<R>(&mut self,
1397 loop_node_id: NodeId,
1400 f: |&mut Liveness<'a, 'tcx>| -> R)
1402 debug!("with_loop_nodes: {} {}", loop_node_id, break_ln.get());
1403 self.loop_scope.push(loop_node_id);
1404 self.break_ln.insert(loop_node_id, break_ln);
1405 self.cont_ln.insert(loop_node_id, cont_ln);
1407 self.loop_scope.pop();
1412 // _______________________________________________________________________
1413 // Checking for error conditions
1415 fn check_local(this: &mut Liveness, local: &ast::Local) {
1418 this.warn_about_unused_or_dead_vars_in_pat(&*local.pat);
1421 this.pat_bindings(&*local.pat, |this, ln, var, sp, id| {
1422 this.warn_about_unused(sp, id, ln, var);
1427 visit::walk_local(this, local);
1430 fn check_arm(this: &mut Liveness, arm: &ast::Arm) {
1431 // only consider the first pattern; any later patterns must have
1432 // the same bindings, and we also consider the first pattern to be
1433 // the "authoritative" set of ids
1434 this.arm_pats_bindings(arm.pats.head().map(|p| &**p), |this, ln, var, sp, id| {
1435 this.warn_about_unused(sp, id, ln, var);
1437 visit::walk_arm(this, arm);
1440 fn check_expr(this: &mut Liveness, expr: &Expr) {
1442 ast::ExprAssign(ref l, ref r) => {
1443 this.check_lvalue(&**l);
1444 this.visit_expr(&**r);
1446 visit::walk_expr(this, expr);
1449 ast::ExprAssignOp(_, ref l, _) => {
1450 this.check_lvalue(&**l);
1452 visit::walk_expr(this, expr);
1455 ast::ExprInlineAsm(ref ia) => {
1456 for &(_, ref input) in ia.inputs.iter() {
1457 this.visit_expr(&**input);
1460 // Output operands must be lvalues
1461 for &(_, ref out, _) in ia.outputs.iter() {
1462 this.check_lvalue(&**out);
1463 this.visit_expr(&**out);
1466 visit::walk_expr(this, expr);
1469 ast::ExprForLoop(ref pat, _, _, _) => {
1470 this.pat_bindings(&**pat, |this, ln, var, sp, id| {
1471 this.warn_about_unused(sp, id, ln, var);
1474 visit::walk_expr(this, expr);
1477 // no correctness conditions related to liveness
1478 ast::ExprCall(..) | ast::ExprMethodCall(..) | ast::ExprIf(..) |
1479 ast::ExprMatch(..) | ast::ExprWhile(..) | ast::ExprLoop(..) |
1480 ast::ExprIndex(..) | ast::ExprField(..) | ast::ExprTupField(..) |
1481 ast::ExprVec(..) | ast::ExprTup(..) | ast::ExprBinary(..) |
1482 ast::ExprCast(..) | ast::ExprUnary(..) | ast::ExprRet(..) |
1483 ast::ExprBreak(..) | ast::ExprAgain(..) | ast::ExprLit(_) |
1484 ast::ExprBlock(..) | ast::ExprMac(..) | ast::ExprAddrOf(..) |
1485 ast::ExprStruct(..) | ast::ExprRepeat(..) | ast::ExprParen(..) |
1486 ast::ExprClosure(..) | ast::ExprProc(..) |
1487 ast::ExprPath(..) | ast::ExprBox(..) | ast::ExprSlice(..) => {
1488 visit::walk_expr(this, expr);
1490 ast::ExprIfLet(..) => {
1491 this.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
1493 ast::ExprWhileLet(..) => {
1494 this.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet");
1499 fn check_fn(_v: &Liveness,
1501 _decl: &ast::FnDecl,
1505 // do not check contents of nested fns
1508 impl<'a, 'tcx> Liveness<'a, 'tcx> {
1509 fn fn_ret(&self, id: NodeId) -> ty::FnOutput<'tcx> {
1510 let fn_ty = ty::node_id_to_type(self.ir.tcx, id);
1512 ty::ty_unboxed_closure(closure_def_id, _, _) =>
1513 self.ir.tcx.unboxed_closures()
1515 .get(&closure_def_id)
1520 _ => ty::ty_fn_ret(fn_ty)
1529 body: &ast::Block) {
1530 match self.fn_ret(id) {
1531 ty::FnConverging(t_ret)
1532 if self.live_on_entry(entry_ln, self.s.no_ret_var).is_some() => {
1534 if ty::type_is_nil(t_ret) {
1535 // for nil return types, it is ok to not return a value expl.
1537 let ends_with_stmt = match body.expr {
1538 None if body.stmts.len() > 0 =>
1539 match body.stmts.last().unwrap().node {
1540 ast::StmtSemi(ref e, _) => {
1541 ty::expr_ty(self.ir.tcx, &**e) == t_ret
1547 self.ir.tcx.sess.span_err(
1548 sp, "not all control paths return a value");
1550 let last_stmt = body.stmts.last().unwrap();
1551 let original_span = original_sp(self.ir.tcx.sess.codemap(),
1552 last_stmt.span, sp);
1553 let span_semicolon = Span {
1554 lo: original_span.hi - BytePos(1),
1555 hi: original_span.hi,
1556 expn_id: original_span.expn_id
1558 self.ir.tcx.sess.span_help(
1559 span_semicolon, "consider removing this semicolon:");
1564 if self.live_on_entry(entry_ln, self.s.clean_exit_var).is_some() => {
1565 self.ir.tcx.sess.span_err(sp,
1566 "computation may converge in a function marked as diverging");
1573 fn check_lvalue(&mut self, expr: &Expr) {
1575 ast::ExprPath(_) => {
1576 if let DefLocal(nid) = self.ir.tcx.def_map.borrow()[expr.id].clone() {
1577 // Assignment to an immutable variable or argument: only legal
1578 // if there is no later assignment. If this local is actually
1579 // mutable, then check for a reassignment to flag the mutability
1581 let ln = self.live_node(expr.id, expr.span);
1582 let var = self.variable(nid, expr.span);
1583 self.warn_about_dead_assign(expr.span, expr.id, ln, var);
1587 // For other kinds of lvalues, no checks are required,
1588 // and any embedded expressions are actually rvalues
1589 visit::walk_expr(self, expr);
1594 fn should_warn(&self, var: Variable) -> Option<String> {
1595 let name = self.ir.variable_name(var);
1596 if name.len() == 0 || name.as_bytes()[0] == ('_' as u8) {
1603 fn warn_about_unused_args(&self, decl: &ast::FnDecl, entry_ln: LiveNode) {
1604 for arg in decl.inputs.iter() {
1605 pat_util::pat_bindings(&self.ir.tcx.def_map,
1607 |_bm, p_id, sp, path1| {
1608 let var = self.variable(p_id, sp);
1609 // Ignore unused self.
1610 let ident = path1.node;
1611 if ident.name != special_idents::self_.name {
1612 self.warn_about_unused(sp, p_id, entry_ln, var);
1618 fn warn_about_unused_or_dead_vars_in_pat(&mut self, pat: &ast::Pat) {
1619 self.pat_bindings(pat, |this, ln, var, sp, id| {
1620 if !this.warn_about_unused(sp, id, ln, var) {
1621 this.warn_about_dead_assign(sp, id, ln, var);
1626 fn warn_about_unused(&self,
1632 if !self.used_on_entry(ln, var) {
1633 let r = self.should_warn(var);
1634 for name in r.iter() {
1636 // annoying: for parameters in funcs like `fn(x: int)
1637 // {ret}`, there is only one node, so asking about
1638 // assigned_on_exit() is not meaningful.
1639 let is_assigned = if ln == self.s.exit_ln {
1642 self.assigned_on_exit(ln, var).is_some()
1646 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_VARIABLES, id, sp,
1647 format!("variable `{}` is assigned to, but never used",
1650 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_VARIABLES, id, sp,
1651 format!("unused variable: `{}`", *name));
1660 fn warn_about_dead_assign(&self,
1665 if self.live_on_exit(ln, var).is_none() {
1666 let r = self.should_warn(var);
1667 for name in r.iter() {
1668 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_ASSIGNMENTS, id, sp,
1669 format!("value assigned to `{}` is never read", *name));