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, typeck, 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);
449 DefLocal(..) => ir.add_live_node_for_node(expr.id, ExprNode(expr.span)),
452 visit::walk_expr(ir, expr);
454 ast::ExprClosure(..) | ast::ExprProc(..) => {
455 // Interesting control flow (for loops can contain labeled
456 // breaks or continues)
457 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
459 // Make a live_node for each captured variable, with the span
460 // being the location that the variable is used. This results
461 // in better error messages than just pointing at the closure
462 // construction site.
463 let mut call_caps = Vec::new();
464 ty::with_freevars(ir.tcx, expr.id, |freevars| {
465 for fv in freevars.iter() {
468 let fv_ln = ir.add_live_node(FreeVarNode(fv.span));
469 call_caps.push(CaptureInfo {ln: fv_ln,
476 ir.set_captures(expr.id, call_caps);
478 visit::walk_expr(ir, expr);
481 // live nodes required for interesting control flow:
482 ast::ExprIf(..) | ast::ExprMatch(..) | ast::ExprWhile(..) | ast::ExprLoop(..) => {
483 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
484 visit::walk_expr(ir, expr);
486 ast::ExprIfLet(..) => {
487 ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
489 ast::ExprWhileLet(..) => {
490 ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet");
492 ast::ExprForLoop(ref pat, _, _, _) => {
493 pat_util::pat_bindings(&ir.tcx.def_map, &**pat, |bm, p_id, sp, path1| {
494 debug!("adding local variable {} from for loop with bm {}",
496 let name = path1.node;
497 ir.add_live_node_for_node(p_id, VarDefNode(sp));
498 ir.add_variable(Local(LocalInfo {
503 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
504 visit::walk_expr(ir, expr);
506 ast::ExprBinary(op, _, _) if ast_util::lazy_binop(op) => {
507 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
508 visit::walk_expr(ir, expr);
511 // otherwise, live nodes are not required:
512 ast::ExprIndex(..) | ast::ExprField(..) | ast::ExprTupField(..) |
513 ast::ExprVec(..) | ast::ExprCall(..) | ast::ExprMethodCall(..) |
514 ast::ExprTup(..) | ast::ExprBinary(..) | ast::ExprAddrOf(..) |
515 ast::ExprCast(..) | ast::ExprUnary(..) | ast::ExprBreak(_) |
516 ast::ExprAgain(_) | ast::ExprLit(_) | ast::ExprRet(..) |
517 ast::ExprBlock(..) | ast::ExprAssign(..) | ast::ExprAssignOp(..) |
518 ast::ExprMac(..) | ast::ExprStruct(..) | ast::ExprRepeat(..) |
519 ast::ExprParen(..) | ast::ExprInlineAsm(..) | ast::ExprBox(..) |
520 ast::ExprSlice(..) => {
521 visit::walk_expr(ir, expr);
526 // ______________________________________________________________________
527 // Computing liveness sets
529 // Actually we compute just a bit more than just liveness, but we use
530 // the same basic propagation framework in all cases.
539 fn invalid_users() -> Users {
541 reader: invalid_node(),
542 writer: invalid_node(),
549 fallthrough_ln: LiveNode,
550 no_ret_var: Variable,
551 clean_exit_var: Variable
554 static ACC_READ: uint = 1u;
555 static ACC_WRITE: uint = 2u;
556 static ACC_USE: uint = 4u;
558 struct Liveness<'a, 'tcx: 'a> {
559 ir: &'a mut IrMaps<'a, 'tcx>,
561 successors: Vec<LiveNode>,
563 // The list of node IDs for the nested loop scopes
565 loop_scope: Vec<NodeId>,
566 // mappings from loop node ID to LiveNode
567 // ("break" label should map to loop node ID,
568 // it probably doesn't now)
569 break_ln: NodeMap<LiveNode>,
570 cont_ln: NodeMap<LiveNode>
573 impl<'a, 'tcx> Liveness<'a, 'tcx> {
574 fn new(ir: &'a mut IrMaps<'a, 'tcx>, specials: Specials) -> Liveness<'a, 'tcx> {
575 let num_live_nodes = ir.num_live_nodes;
576 let num_vars = ir.num_vars;
580 successors: Vec::from_elem(num_live_nodes, invalid_node()),
581 users: Vec::from_elem(num_live_nodes * num_vars, invalid_users()),
582 loop_scope: Vec::new(),
583 break_ln: NodeMap::new(),
584 cont_ln: NodeMap::new(),
588 fn live_node(&self, node_id: NodeId, span: Span) -> LiveNode {
589 match self.ir.live_node_map.get(&node_id) {
592 // This must be a mismatch between the ir_map construction
593 // above and the propagation code below; the two sets of
594 // code have to agree about which AST nodes are worth
595 // creating liveness nodes for.
596 self.ir.tcx.sess.span_bug(
598 format!("no live node registered for node {}",
599 node_id).as_slice());
604 fn variable(&self, node_id: NodeId, span: Span) -> Variable {
605 self.ir.variable(node_id, span)
608 fn pat_bindings(&mut self,
610 f: |&mut Liveness<'a, 'tcx>, LiveNode, Variable, Span, NodeId|) {
611 pat_util::pat_bindings(&self.ir.tcx.def_map, pat, |_bm, p_id, sp, _n| {
612 let ln = self.live_node(p_id, sp);
613 let var = self.variable(p_id, sp);
614 f(self, ln, var, sp, p_id);
618 fn arm_pats_bindings(&mut self,
619 pat: Option<&ast::Pat>,
620 f: |&mut Liveness<'a, 'tcx>, LiveNode, Variable, Span, NodeId|) {
623 self.pat_bindings(pat, f);
629 fn define_bindings_in_pat(&mut self, pat: &ast::Pat, succ: LiveNode)
631 self.define_bindings_in_arm_pats(Some(pat), succ)
634 fn define_bindings_in_arm_pats(&mut self, pat: Option<&ast::Pat>, succ: LiveNode)
637 self.arm_pats_bindings(pat, |this, ln, var, _sp, _id| {
638 this.init_from_succ(ln, succ);
639 this.define(ln, var);
645 fn idx(&self, ln: LiveNode, var: Variable) -> uint {
646 ln.get() * self.ir.num_vars + var.get()
649 fn live_on_entry(&self, ln: LiveNode, var: Variable)
650 -> Option<LiveNodeKind> {
651 assert!(ln.is_valid());
652 let reader = self.users[self.idx(ln, var)].reader;
653 if reader.is_valid() {Some(self.ir.lnk(reader))} else {None}
657 Is this variable live on entry to any of its successor nodes?
659 fn live_on_exit(&self, ln: LiveNode, var: Variable)
660 -> Option<LiveNodeKind> {
661 let successor = self.successors[ln.get()];
662 self.live_on_entry(successor, var)
665 fn used_on_entry(&self, ln: LiveNode, var: Variable) -> bool {
666 assert!(ln.is_valid());
667 self.users[self.idx(ln, var)].used
670 fn assigned_on_entry(&self, ln: LiveNode, var: Variable)
671 -> Option<LiveNodeKind> {
672 assert!(ln.is_valid());
673 let writer = self.users[self.idx(ln, var)].writer;
674 if writer.is_valid() {Some(self.ir.lnk(writer))} else {None}
677 fn assigned_on_exit(&self, ln: LiveNode, var: Variable)
678 -> Option<LiveNodeKind> {
679 let successor = self.successors[ln.get()];
680 self.assigned_on_entry(successor, var)
683 fn indices2(&mut self,
686 op: |&mut Liveness<'a, 'tcx>, uint, uint|) {
687 let node_base_idx = self.idx(ln, Variable(0u));
688 let succ_base_idx = self.idx(succ_ln, Variable(0u));
689 for var_idx in range(0u, self.ir.num_vars) {
690 op(self, node_base_idx + var_idx, succ_base_idx + var_idx);
697 test: |uint| -> LiveNode) -> io::IoResult<()> {
698 let node_base_idx = self.idx(ln, Variable(0));
699 for var_idx in range(0u, self.ir.num_vars) {
700 let idx = node_base_idx + var_idx;
701 if test(idx).is_valid() {
702 try!(write!(wr, " {}", Variable(var_idx).to_string()));
708 fn find_loop_scope(&self,
709 opt_label: Option<ast::Ident>,
715 // Refers to a labeled loop. Use the results of resolve
717 match self.ir.tcx.def_map.borrow().get(&id) {
718 Some(&DefLabel(loop_id)) => loop_id,
719 _ => self.ir.tcx.sess.span_bug(sp, "label on break/loop \
720 doesn't refer to a loop")
724 // Vanilla 'break' or 'loop', so use the enclosing
726 if self.loop_scope.len() == 0 {
727 self.ir.tcx.sess.span_bug(sp, "break outside loop");
729 *self.loop_scope.last().unwrap()
735 #[allow(unused_must_use)]
736 fn ln_str(&self, ln: LiveNode) -> String {
737 let mut wr = Vec::new();
739 let wr = &mut wr as &mut io::Writer;
740 write!(wr, "[ln({}) of kind {} reads", ln.get(), self.ir.lnk(ln));
741 self.write_vars(wr, ln, |idx| self.users[idx].reader);
742 write!(wr, " writes");
743 self.write_vars(wr, ln, |idx| self.users[idx].writer);
744 write!(wr, " precedes {}]", self.successors[ln.get()].to_string());
746 String::from_utf8(wr).unwrap()
749 fn init_empty(&mut self, ln: LiveNode, succ_ln: LiveNode) {
750 self.successors[ln.get()] = succ_ln;
752 // It is not necessary to initialize the
753 // values to empty because this is the value
754 // they have when they are created, and the sets
755 // only grow during iterations.
757 // self.indices(ln) { |idx|
758 // self.users[idx] = invalid_users();
762 fn init_from_succ(&mut self, ln: LiveNode, succ_ln: LiveNode) {
763 // more efficient version of init_empty() / merge_from_succ()
764 self.successors[ln.get()] = succ_ln;
766 self.indices2(ln, succ_ln, |this, idx, succ_idx| {
767 this.users[idx] = this.users[succ_idx]
769 debug!("init_from_succ(ln={}, succ={})",
770 self.ln_str(ln), self.ln_str(succ_ln));
773 fn merge_from_succ(&mut self,
778 if ln == succ_ln { return false; }
780 let mut changed = false;
781 self.indices2(ln, succ_ln, |this, idx, succ_idx| {
782 changed |= copy_if_invalid(this.users[succ_idx].reader,
783 &mut this.users[idx].reader);
784 changed |= copy_if_invalid(this.users[succ_idx].writer,
785 &mut this.users[idx].writer);
786 if this.users[succ_idx].used && !this.users[idx].used {
787 this.users[idx].used = true;
792 debug!("merge_from_succ(ln={}, succ={}, first_merge={}, changed={})",
793 ln.to_string(), self.ln_str(succ_ln), first_merge, changed);
796 fn copy_if_invalid(src: LiveNode, dst: &mut LiveNode) -> bool {
797 if src.is_valid() && !dst.is_valid() {
806 // Indicates that a local variable was *defined*; we know that no
807 // uses of the variable can precede the definition (resolve checks
808 // this) so we just clear out all the data.
809 fn define(&mut self, writer: LiveNode, var: Variable) {
810 let idx = self.idx(writer, var);
811 self.users[idx].reader = invalid_node();
812 self.users[idx].writer = invalid_node();
814 debug!("{} defines {} (idx={}): {}", writer.to_string(), var.to_string(),
815 idx, self.ln_str(writer));
818 // Either read, write, or both depending on the acc bitset
819 fn acc(&mut self, ln: LiveNode, var: Variable, acc: uint) {
820 debug!("{} accesses[{:x}] {}: {}",
821 ln.to_string(), acc, var.to_string(), self.ln_str(ln));
823 let idx = self.idx(ln, var);
824 let user = &mut self.users[idx];
826 if (acc & ACC_WRITE) != 0 {
827 user.reader = invalid_node();
831 // Important: if we both read/write, must do read second
832 // or else the write will override.
833 if (acc & ACC_READ) != 0 {
837 if (acc & ACC_USE) != 0 {
842 // _______________________________________________________________________
844 fn compute(&mut self, decl: &ast::FnDecl, body: &ast::Block) -> LiveNode {
845 // if there is a `break` or `again` at the top level, then it's
846 // effectively a return---this only occurs in `for` loops,
847 // where the body is really a closure.
849 debug!("compute: using id for block, {}", block_to_string(body));
851 let exit_ln = self.s.exit_ln;
852 let entry_ln: LiveNode =
853 self.with_loop_nodes(body.id, exit_ln, exit_ln,
854 |this| this.propagate_through_fn_block(decl, body));
856 // hack to skip the loop unless debug! is enabled:
857 debug!("^^ liveness computation results for body {} (entry={})",
859 for ln_idx in range(0u, self.ir.num_live_nodes) {
860 debug!("{}", self.ln_str(LiveNode(ln_idx)));
864 entry_ln.to_string());
869 fn propagate_through_fn_block(&mut self, _: &ast::FnDecl, blk: &ast::Block)
871 // the fallthrough exit is only for those cases where we do not
872 // explicitly return:
874 self.init_from_succ(s.fallthrough_ln, s.exit_ln);
875 if blk.expr.is_none() {
876 self.acc(s.fallthrough_ln, s.no_ret_var, ACC_READ)
878 self.acc(s.fallthrough_ln, s.clean_exit_var, ACC_READ);
880 self.propagate_through_block(blk, s.fallthrough_ln)
883 fn propagate_through_block(&mut self, blk: &ast::Block, succ: LiveNode)
885 let succ = self.propagate_through_opt_expr(blk.expr.as_ref().map(|e| &**e), succ);
886 blk.stmts.iter().rev().fold(succ, |succ, stmt| {
887 self.propagate_through_stmt(&**stmt, succ)
891 fn propagate_through_stmt(&mut self, stmt: &ast::Stmt, succ: LiveNode)
894 ast::StmtDecl(ref decl, _) => {
895 self.propagate_through_decl(&**decl, succ)
898 ast::StmtExpr(ref expr, _) | ast::StmtSemi(ref expr, _) => {
899 self.propagate_through_expr(&**expr, succ)
902 ast::StmtMac(..) => {
903 self.ir.tcx.sess.span_bug(stmt.span, "unexpanded macro");
908 fn propagate_through_decl(&mut self, decl: &ast::Decl, succ: LiveNode)
911 ast::DeclLocal(ref local) => {
912 self.propagate_through_local(&**local, succ)
914 ast::DeclItem(_) => succ,
918 fn propagate_through_local(&mut self, local: &ast::Local, succ: LiveNode)
920 // Note: we mark the variable as defined regardless of whether
921 // there is an initializer. Initially I had thought to only mark
922 // the live variable as defined if it was initialized, and then we
923 // could check for uninit variables just by scanning what is live
924 // at the start of the function. But that doesn't work so well for
925 // immutable variables defined in a loop:
926 // loop { let x; x = 5; }
927 // because the "assignment" loops back around and generates an error.
929 // So now we just check that variables defined w/o an
930 // initializer are not live at the point of their
931 // initialization, which is mildly more complex than checking
932 // once at the func header but otherwise equivalent.
934 let succ = self.propagate_through_opt_expr(local.init.as_ref().map(|e| &**e), succ);
935 self.define_bindings_in_pat(&*local.pat, succ)
938 fn propagate_through_exprs(&mut self, exprs: &[P<Expr>], succ: LiveNode)
940 exprs.iter().rev().fold(succ, |succ, expr| {
941 self.propagate_through_expr(&**expr, succ)
945 fn propagate_through_opt_expr(&mut self,
946 opt_expr: Option<&Expr>,
949 opt_expr.map_or(succ, |expr| self.propagate_through_expr(expr, succ))
952 fn propagate_through_expr(&mut self, expr: &Expr, succ: LiveNode)
954 debug!("propagate_through_expr: {}", expr_to_string(expr));
957 // Interesting cases with control flow or which gen/kill
959 ast::ExprPath(_) => {
960 self.access_path(expr, succ, ACC_READ | ACC_USE)
963 ast::ExprField(ref e, _) => {
964 self.propagate_through_expr(&**e, succ)
967 ast::ExprTupField(ref e, _) => {
968 self.propagate_through_expr(&**e, succ)
971 ast::ExprClosure(_, _, _, ref blk) |
972 ast::ExprProc(_, ref blk) => {
973 debug!("{} is an ExprClosure or ExprProc",
974 expr_to_string(expr));
977 The next-node for a break is the successor of the entire
978 loop. The next-node for a continue is the top of this loop.
980 let node = self.live_node(expr.id, expr.span);
981 self.with_loop_nodes(blk.id, succ, node, |this| {
983 // the construction of a closure itself is not important,
984 // but we have to consider the closed over variables.
985 let caps = match this.ir.capture_info_map.get(&expr.id) {
986 Some(caps) => caps.clone(),
988 this.ir.tcx.sess.span_bug(expr.span, "no registered caps");
991 caps.iter().rev().fold(succ, |succ, cap| {
992 this.init_from_succ(cap.ln, succ);
993 let var = this.variable(cap.var_nid, expr.span);
994 this.acc(cap.ln, var, ACC_READ | ACC_USE);
1000 ast::ExprIf(ref cond, ref then, ref els) => {
1014 let else_ln = self.propagate_through_opt_expr(els.as_ref().map(|e| &**e), succ);
1015 let then_ln = self.propagate_through_block(&**then, succ);
1016 let ln = self.live_node(expr.id, expr.span);
1017 self.init_from_succ(ln, else_ln);
1018 self.merge_from_succ(ln, then_ln, false);
1019 self.propagate_through_expr(&**cond, ln)
1022 ast::ExprIfLet(..) => {
1023 self.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
1026 ast::ExprWhile(ref cond, ref blk, _) => {
1027 self.propagate_through_loop(expr, WhileLoop(&**cond), &**blk, succ)
1030 ast::ExprWhileLet(..) => {
1031 self.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet");
1034 ast::ExprForLoop(ref pat, ref head, ref blk, _) => {
1035 let ln = self.propagate_through_loop(expr, ForLoop(&**pat), &**blk, succ);
1036 self.propagate_through_expr(&**head, ln)
1039 // Note that labels have been resolved, so we don't need to look
1040 // at the label ident
1041 ast::ExprLoop(ref blk, _) => {
1042 self.propagate_through_loop(expr, LoopLoop, &**blk, succ)
1045 ast::ExprMatch(ref e, ref arms, _) => {
1060 let ln = self.live_node(expr.id, expr.span);
1061 self.init_empty(ln, succ);
1062 let mut first_merge = true;
1063 for arm in arms.iter() {
1065 self.propagate_through_expr(&*arm.body, succ);
1067 self.propagate_through_opt_expr(arm.guard.as_ref().map(|e| &**e), body_succ);
1068 // only consider the first pattern; any later patterns must have
1069 // the same bindings, and we also consider the first pattern to be
1070 // the "authoritative" set of ids
1072 self.define_bindings_in_arm_pats(arm.pats.as_slice().head().map(|p| &**p),
1074 self.merge_from_succ(ln, arm_succ, first_merge);
1075 first_merge = false;
1077 self.propagate_through_expr(&**e, ln)
1080 ast::ExprRet(ref o_e) => {
1081 // ignore succ and subst exit_ln:
1082 let exit_ln = self.s.exit_ln;
1083 self.propagate_through_opt_expr(o_e.as_ref().map(|e| &**e), exit_ln)
1086 ast::ExprBreak(opt_label) => {
1087 // Find which label this break jumps to
1088 let sc = self.find_loop_scope(opt_label, expr.id, expr.span);
1090 // Now that we know the label we're going to,
1091 // look it up in the break loop nodes table
1093 match self.break_ln.get(&sc) {
1095 None => self.ir.tcx.sess.span_bug(expr.span,
1096 "break to unknown label")
1100 ast::ExprAgain(opt_label) => {
1101 // Find which label this expr continues to
1102 let sc = self.find_loop_scope(opt_label, expr.id, expr.span);
1104 // Now that we know the label we're going to,
1105 // look it up in the continue loop nodes table
1107 match self.cont_ln.get(&sc) {
1109 None => self.ir.tcx.sess.span_bug(expr.span,
1110 "loop to unknown label")
1114 ast::ExprAssign(ref l, ref r) => {
1115 // see comment on lvalues in
1116 // propagate_through_lvalue_components()
1117 let succ = self.write_lvalue(&**l, succ, ACC_WRITE);
1118 let succ = self.propagate_through_lvalue_components(&**l, succ);
1119 self.propagate_through_expr(&**r, succ)
1122 ast::ExprAssignOp(_, ref l, ref r) => {
1123 // see comment on lvalues in
1124 // propagate_through_lvalue_components()
1125 let succ = self.write_lvalue(&**l, succ, ACC_WRITE|ACC_READ);
1126 let succ = self.propagate_through_expr(&**r, succ);
1127 self.propagate_through_lvalue_components(&**l, succ)
1130 // Uninteresting cases: just propagate in rev exec order
1132 ast::ExprVec(ref exprs) => {
1133 self.propagate_through_exprs(exprs.as_slice(), succ)
1136 ast::ExprRepeat(ref element, ref count) => {
1137 let succ = self.propagate_through_expr(&**count, succ);
1138 self.propagate_through_expr(&**element, succ)
1141 ast::ExprStruct(_, ref fields, ref with_expr) => {
1142 let succ = self.propagate_through_opt_expr(with_expr.as_ref().map(|e| &**e), succ);
1143 fields.iter().rev().fold(succ, |succ, field| {
1144 self.propagate_through_expr(&*field.expr, succ)
1148 ast::ExprCall(ref f, ref args) => {
1149 let diverges = !self.ir.tcx.is_method_call(expr.id) && {
1150 let t_ret = ty::ty_fn_ret(ty::expr_ty(self.ir.tcx, &**f));
1151 t_ret == ty::FnDiverging
1153 let succ = if diverges {
1158 let succ = self.propagate_through_exprs(args.as_slice(), succ);
1159 self.propagate_through_expr(&**f, succ)
1162 ast::ExprMethodCall(_, _, ref args) => {
1163 let method_call = typeck::MethodCall::expr(expr.id);
1164 let method_ty = self.ir.tcx.method_map.borrow().get(&method_call).unwrap().ty;
1165 let diverges = ty::ty_fn_ret(method_ty) == ty::FnDiverging;
1166 let succ = if diverges {
1171 self.propagate_through_exprs(args.as_slice(), succ)
1174 ast::ExprTup(ref exprs) => {
1175 self.propagate_through_exprs(exprs.as_slice(), succ)
1178 ast::ExprBinary(op, ref l, ref r) if ast_util::lazy_binop(op) => {
1179 let r_succ = self.propagate_through_expr(&**r, succ);
1181 let ln = self.live_node(expr.id, expr.span);
1182 self.init_from_succ(ln, succ);
1183 self.merge_from_succ(ln, r_succ, false);
1185 self.propagate_through_expr(&**l, ln)
1188 ast::ExprIndex(ref l, ref r) |
1189 ast::ExprBinary(_, ref l, ref r) |
1190 ast::ExprBox(ref l, ref r) => {
1191 let r_succ = self.propagate_through_expr(&**r, succ);
1192 self.propagate_through_expr(&**l, r_succ)
1195 ast::ExprSlice(ref e1, ref e2, ref e3, _) => {
1196 let succ = e3.as_ref().map_or(succ, |e| self.propagate_through_expr(&**e, succ));
1197 let succ = e2.as_ref().map_or(succ, |e| self.propagate_through_expr(&**e, succ));
1198 self.propagate_through_expr(&**e1, succ)
1201 ast::ExprAddrOf(_, ref e) |
1202 ast::ExprCast(ref e, _) |
1203 ast::ExprUnary(_, ref e) |
1204 ast::ExprParen(ref e) => {
1205 self.propagate_through_expr(&**e, succ)
1208 ast::ExprInlineAsm(ref ia) => {
1210 let succ = ia.outputs.iter().rev().fold(succ, |succ, &(_, ref expr, _)| {
1211 // see comment on lvalues
1212 // in propagate_through_lvalue_components()
1213 let succ = self.write_lvalue(&**expr, succ, ACC_WRITE);
1214 self.propagate_through_lvalue_components(&**expr, succ)
1216 // Inputs are executed first. Propagate last because of rev order
1217 ia.inputs.iter().rev().fold(succ, |succ, &(_, ref expr)| {
1218 self.propagate_through_expr(&**expr, succ)
1222 ast::ExprLit(..) => {
1226 ast::ExprBlock(ref blk) => {
1227 self.propagate_through_block(&**blk, succ)
1230 ast::ExprMac(..) => {
1231 self.ir.tcx.sess.span_bug(expr.span, "unexpanded macro");
1236 fn propagate_through_lvalue_components(&mut self,
1242 // In general, the full flow graph structure for an
1243 // assignment/move/etc can be handled in one of two ways,
1244 // depending on whether what is being assigned is a "tracked
1245 // value" or not. A tracked value is basically a local
1246 // variable or argument.
1248 // The two kinds of graphs are:
1250 // Tracked lvalue Untracked lvalue
1251 // ----------------------++-----------------------
1255 // (rvalue) || (rvalue)
1258 // (write of lvalue) || (lvalue components)
1263 // ----------------------++-----------------------
1265 // I will cover the two cases in turn:
1267 // # Tracked lvalues
1269 // A tracked lvalue is a local variable/argument `x`. In
1270 // these cases, the link_node where the write occurs is linked
1271 // to node id of `x`. The `write_lvalue()` routine generates
1272 // the contents of this node. There are no subcomponents to
1275 // # Non-tracked lvalues
1277 // These are lvalues like `x[5]` or `x.f`. In that case, we
1278 // basically ignore the value which is written to but generate
1279 // reads for the components---`x` in these two examples. The
1280 // components reads are generated by
1281 // `propagate_through_lvalue_components()` (this fn).
1283 // # Illegal lvalues
1285 // It is still possible to observe assignments to non-lvalues;
1286 // these errors are detected in the later pass borrowck. We
1287 // just ignore such cases and treat them as reads.
1290 ast::ExprPath(_) => succ,
1291 ast::ExprField(ref e, _) => self.propagate_through_expr(&**e, succ),
1292 ast::ExprTupField(ref e, _) => self.propagate_through_expr(&**e, succ),
1293 _ => self.propagate_through_expr(expr, succ)
1297 // see comment on propagate_through_lvalue()
1298 fn write_lvalue(&mut self, expr: &Expr, succ: LiveNode, acc: uint)
1301 ast::ExprPath(_) => self.access_path(expr, succ, acc),
1303 // We do not track other lvalues, so just propagate through
1304 // to their subcomponents. Also, it may happen that
1305 // non-lvalues occur here, because those are detected in the
1306 // later pass borrowck.
1311 fn access_path(&mut self, expr: &Expr, succ: LiveNode, acc: uint)
1313 match self.ir.tcx.def_map.borrow()[expr.id].clone() {
1315 let ln = self.live_node(expr.id, expr.span);
1317 self.init_from_succ(ln, succ);
1318 let var = self.variable(nid, expr.span);
1319 self.acc(ln, var, acc);
1327 fn propagate_through_loop(&mut self,
1336 We model control flow like this:
1354 let mut first_merge = true;
1355 let ln = self.live_node(expr.id, expr.span);
1356 self.init_empty(ln, succ);
1360 // If this is not a `loop` loop, then it's possible we bypass
1361 // the body altogether. Otherwise, the only way is via a `break`
1362 // in the loop body.
1363 self.merge_from_succ(ln, succ, first_merge);
1364 first_merge = false;
1367 debug!("propagate_through_loop: using id for loop body {} {}",
1368 expr.id, block_to_string(body));
1370 let cond_ln = match kind {
1372 ForLoop(ref pat) => self.define_bindings_in_pat(*pat, ln),
1373 WhileLoop(ref cond) => self.propagate_through_expr(&**cond, ln),
1375 let body_ln = self.with_loop_nodes(expr.id, succ, ln, |this| {
1376 this.propagate_through_block(body, cond_ln)
1379 // repeat until fixed point is reached:
1380 while self.merge_from_succ(ln, body_ln, first_merge) {
1381 first_merge = false;
1383 let new_cond_ln = match kind {
1385 ForLoop(ref pat) => {
1386 self.define_bindings_in_pat(*pat, ln)
1388 WhileLoop(ref cond) => {
1389 self.propagate_through_expr(&**cond, ln)
1392 assert!(cond_ln == new_cond_ln);
1393 assert!(body_ln == self.with_loop_nodes(expr.id, succ, ln,
1394 |this| this.propagate_through_block(body, cond_ln)));
1400 fn with_loop_nodes<R>(&mut self,
1401 loop_node_id: NodeId,
1404 f: |&mut Liveness<'a, 'tcx>| -> R)
1406 debug!("with_loop_nodes: {} {}", loop_node_id, break_ln.get());
1407 self.loop_scope.push(loop_node_id);
1408 self.break_ln.insert(loop_node_id, break_ln);
1409 self.cont_ln.insert(loop_node_id, cont_ln);
1411 self.loop_scope.pop();
1416 // _______________________________________________________________________
1417 // Checking for error conditions
1419 fn check_local(this: &mut Liveness, local: &ast::Local) {
1422 this.warn_about_unused_or_dead_vars_in_pat(&*local.pat);
1425 this.pat_bindings(&*local.pat, |this, ln, var, sp, id| {
1426 this.warn_about_unused(sp, id, ln, var);
1431 visit::walk_local(this, local);
1434 fn check_arm(this: &mut Liveness, arm: &ast::Arm) {
1435 // only consider the first pattern; any later patterns must have
1436 // the same bindings, and we also consider the first pattern to be
1437 // the "authoritative" set of ids
1438 this.arm_pats_bindings(arm.pats.as_slice().head().map(|p| &**p), |this, ln, var, sp, id| {
1439 this.warn_about_unused(sp, id, ln, var);
1441 visit::walk_arm(this, arm);
1444 fn check_expr(this: &mut Liveness, expr: &Expr) {
1446 ast::ExprAssign(ref l, ref r) => {
1447 this.check_lvalue(&**l);
1448 this.visit_expr(&**r);
1450 visit::walk_expr(this, expr);
1453 ast::ExprAssignOp(_, ref l, _) => {
1454 this.check_lvalue(&**l);
1456 visit::walk_expr(this, expr);
1459 ast::ExprInlineAsm(ref ia) => {
1460 for &(_, ref input) in ia.inputs.iter() {
1461 this.visit_expr(&**input);
1464 // Output operands must be lvalues
1465 for &(_, ref out, _) in ia.outputs.iter() {
1466 this.check_lvalue(&**out);
1467 this.visit_expr(&**out);
1470 visit::walk_expr(this, expr);
1473 ast::ExprForLoop(ref pat, _, _, _) => {
1474 this.pat_bindings(&**pat, |this, ln, var, sp, id| {
1475 this.warn_about_unused(sp, id, ln, var);
1478 visit::walk_expr(this, expr);
1481 // no correctness conditions related to liveness
1482 ast::ExprCall(..) | ast::ExprMethodCall(..) | ast::ExprIf(..) |
1483 ast::ExprMatch(..) | ast::ExprWhile(..) | ast::ExprLoop(..) |
1484 ast::ExprIndex(..) | ast::ExprField(..) | ast::ExprTupField(..) |
1485 ast::ExprVec(..) | ast::ExprTup(..) | ast::ExprBinary(..) |
1486 ast::ExprCast(..) | ast::ExprUnary(..) | ast::ExprRet(..) |
1487 ast::ExprBreak(..) | ast::ExprAgain(..) | ast::ExprLit(_) |
1488 ast::ExprBlock(..) | ast::ExprMac(..) | ast::ExprAddrOf(..) |
1489 ast::ExprStruct(..) | ast::ExprRepeat(..) | ast::ExprParen(..) |
1490 ast::ExprClosure(..) | ast::ExprProc(..) |
1491 ast::ExprPath(..) | ast::ExprBox(..) | ast::ExprSlice(..) => {
1492 visit::walk_expr(this, expr);
1494 ast::ExprIfLet(..) => {
1495 this.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
1497 ast::ExprWhileLet(..) => {
1498 this.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet");
1503 fn check_fn(_v: &Liveness,
1505 _decl: &ast::FnDecl,
1509 // do not check contents of nested fns
1512 impl<'a, 'tcx> Liveness<'a, 'tcx> {
1513 fn fn_ret(&self, id: NodeId) -> ty::FnOutput<'tcx> {
1514 let fn_ty = ty::node_id_to_type(self.ir.tcx, id);
1516 ty::ty_unboxed_closure(closure_def_id, _, _) =>
1517 self.ir.tcx.unboxed_closures()
1519 .get(&closure_def_id)
1524 _ => ty::ty_fn_ret(fn_ty)
1533 body: &ast::Block) {
1534 match self.fn_ret(id) {
1535 ty::FnConverging(t_ret)
1536 if self.live_on_entry(entry_ln, self.s.no_ret_var).is_some() => {
1538 if ty::type_is_nil(t_ret) {
1539 // for nil return types, it is ok to not return a value expl.
1541 let ends_with_stmt = match body.expr {
1542 None if body.stmts.len() > 0 =>
1543 match body.stmts.last().unwrap().node {
1544 ast::StmtSemi(ref e, _) => {
1545 ty::expr_ty(self.ir.tcx, &**e) == t_ret
1551 self.ir.tcx.sess.span_err(
1552 sp, "not all control paths return a value");
1554 let last_stmt = body.stmts.last().unwrap();
1555 let original_span = original_sp(self.ir.tcx.sess.codemap(),
1556 last_stmt.span, sp);
1557 let span_semicolon = Span {
1558 lo: original_span.hi - BytePos(1),
1559 hi: original_span.hi,
1560 expn_id: original_span.expn_id
1562 self.ir.tcx.sess.span_help(
1563 span_semicolon, "consider removing this semicolon:");
1568 if self.live_on_entry(entry_ln, self.s.clean_exit_var).is_some() => {
1569 self.ir.tcx.sess.span_err(sp,
1570 "computation may converge in a function marked as diverging");
1577 fn check_lvalue(&mut self, expr: &Expr) {
1579 ast::ExprPath(_) => {
1580 match self.ir.tcx.def_map.borrow()[expr.id].clone() {
1582 // Assignment to an immutable variable or argument: only legal
1583 // if there is no later assignment. If this local is actually
1584 // mutable, then check for a reassignment to flag the mutability
1586 let ln = self.live_node(expr.id, expr.span);
1587 let var = self.variable(nid, expr.span);
1588 self.warn_about_dead_assign(expr.span, expr.id, ln, var);
1595 // For other kinds of lvalues, no checks are required,
1596 // and any embedded expressions are actually rvalues
1597 visit::walk_expr(self, expr);
1602 fn should_warn(&self, var: Variable) -> Option<String> {
1603 let name = self.ir.variable_name(var);
1604 if name.len() == 0 || name.as_bytes()[0] == ('_' as u8) {
1611 fn warn_about_unused_args(&self, decl: &ast::FnDecl, entry_ln: LiveNode) {
1612 for arg in decl.inputs.iter() {
1613 pat_util::pat_bindings(&self.ir.tcx.def_map,
1615 |_bm, p_id, sp, path1| {
1616 let var = self.variable(p_id, sp);
1617 // Ignore unused self.
1618 let ident = path1.node;
1619 if ident.name != special_idents::self_.name {
1620 self.warn_about_unused(sp, p_id, entry_ln, var);
1626 fn warn_about_unused_or_dead_vars_in_pat(&mut self, pat: &ast::Pat) {
1627 self.pat_bindings(pat, |this, ln, var, sp, id| {
1628 if !this.warn_about_unused(sp, id, ln, var) {
1629 this.warn_about_dead_assign(sp, id, ln, var);
1634 fn warn_about_unused(&self,
1640 if !self.used_on_entry(ln, var) {
1641 let r = self.should_warn(var);
1642 for name in r.iter() {
1644 // annoying: for parameters in funcs like `fn(x: int)
1645 // {ret}`, there is only one node, so asking about
1646 // assigned_on_exit() is not meaningful.
1647 let is_assigned = if ln == self.s.exit_ln {
1650 self.assigned_on_exit(ln, var).is_some()
1654 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_VARIABLES, id, sp,
1655 format!("variable `{}` is assigned to, but never used",
1658 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_VARIABLES, id, sp,
1659 format!("unused variable: `{}`", *name));
1668 fn warn_about_dead_assign(&self,
1673 if self.live_on_exit(ln, var).is_none() {
1674 let r = self.should_warn(var);
1675 for name in r.iter() {
1676 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_ASSIGNMENTS, id, sp,
1677 format!("value assigned to `{}` is never read", *name));