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;
117 use middle::ty::ClosureTyper;
119 use util::nodemap::NodeMap;
121 use std::{fmt, old_io, uint};
123 use std::iter::repeat;
124 use syntax::ast::{self, NodeId, Expr};
125 use syntax::codemap::{BytePos, original_sp, Span};
126 use syntax::parse::token::{self, special_idents};
127 use syntax::print::pprust::{expr_to_string, block_to_string};
129 use syntax::ast_util;
130 use syntax::visit::{self, Visitor, FnKind};
132 /// For use with `propagate_through_loop`.
134 /// An endless `loop` loop.
136 /// A `while` loop, with the given expression as condition.
140 #[derive(Copy, PartialEq)]
141 struct Variable(uint);
143 #[derive(Copy, PartialEq)]
144 struct LiveNode(uint);
147 fn get(&self) -> uint { let Variable(v) = *self; v }
151 fn get(&self) -> uint { let LiveNode(v) = *self; v }
154 impl Clone for LiveNode {
155 fn clone(&self) -> LiveNode {
160 #[derive(Copy, PartialEq, Debug)]
168 fn live_node_kind_to_string(lnk: LiveNodeKind, cx: &ty::ctxt) -> String {
169 let cm = cx.sess.codemap();
172 format!("Free var node [{}]", cm.span_to_string(s))
175 format!("Expr node [{}]", cm.span_to_string(s))
178 format!("Var def node [{}]", cm.span_to_string(s))
180 ExitNode => "Exit node".to_string(),
184 impl<'a, 'tcx, 'v> Visitor<'v> for IrMaps<'a, 'tcx> {
185 fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v ast::FnDecl,
186 b: &'v ast::Block, s: Span, id: NodeId) {
187 visit_fn(self, fk, fd, b, s, id);
189 fn visit_local(&mut self, l: &ast::Local) { visit_local(self, l); }
190 fn visit_expr(&mut self, ex: &Expr) { visit_expr(self, ex); }
191 fn visit_arm(&mut self, a: &ast::Arm) { visit_arm(self, a); }
194 pub fn check_crate(tcx: &ty::ctxt) {
195 visit::walk_crate(&mut IrMaps::new(tcx), tcx.map.krate());
196 tcx.sess.abort_if_errors();
199 impl fmt::Debug for LiveNode {
200 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
201 write!(f, "ln({})", self.get())
205 impl fmt::Debug for Variable {
206 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
207 write!(f, "v({})", self.get())
211 // ______________________________________________________________________
214 // This is the first pass and the one that drives the main
215 // computation. It walks up and down the IR once. On the way down,
216 // we count for each function the number of variables as well as
217 // liveness nodes. A liveness node is basically an expression or
218 // capture clause that does something of interest: either it has
219 // interesting control flow or it uses/defines a local variable.
221 // On the way back up, at each function node we create liveness sets
222 // (we now know precisely how big to make our various vectors and so
223 // forth) and then do the data-flow propagation to compute the set
224 // of live variables at each program point.
226 // Finally, we run back over the IR one last time and, using the
227 // computed liveness, check various safety conditions. For example,
228 // there must be no live nodes at the definition site for a variable
229 // unless it has an initializer. Similarly, each non-mutable local
230 // variable must not be assigned if there is some successor
231 // assignment. And so forth.
234 fn is_valid(&self) -> bool {
235 self.get() != uint::MAX
239 fn invalid_node() -> LiveNode { LiveNode(uint::MAX) }
246 #[derive(Copy, Debug)]
252 #[derive(Copy, Debug)]
254 Arg(NodeId, ast::Ident),
260 struct IrMaps<'a, 'tcx: 'a> {
261 tcx: &'a ty::ctxt<'tcx>,
263 num_live_nodes: uint,
265 live_node_map: NodeMap<LiveNode>,
266 variable_map: NodeMap<Variable>,
267 capture_info_map: NodeMap<Rc<Vec<CaptureInfo>>>,
268 var_kinds: Vec<VarKind>,
269 lnks: Vec<LiveNodeKind>,
272 impl<'a, 'tcx> IrMaps<'a, 'tcx> {
273 fn new(tcx: &'a ty::ctxt<'tcx>) -> IrMaps<'a, 'tcx> {
278 live_node_map: NodeMap(),
279 variable_map: NodeMap(),
280 capture_info_map: NodeMap(),
281 var_kinds: Vec::new(),
286 fn add_live_node(&mut self, lnk: LiveNodeKind) -> LiveNode {
287 let ln = LiveNode(self.num_live_nodes);
289 self.num_live_nodes += 1;
291 debug!("{:?} is of kind {}", ln,
292 live_node_kind_to_string(lnk, self.tcx));
297 fn add_live_node_for_node(&mut self, node_id: NodeId, lnk: LiveNodeKind) {
298 let ln = self.add_live_node(lnk);
299 self.live_node_map.insert(node_id, ln);
301 debug!("{:?} is node {}", ln, node_id);
304 fn add_variable(&mut self, vk: VarKind) -> Variable {
305 let v = Variable(self.num_vars);
306 self.var_kinds.push(vk);
310 Local(LocalInfo { id: node_id, .. }) | Arg(node_id, _) => {
311 self.variable_map.insert(node_id, v);
313 ImplicitRet | CleanExit => {}
316 debug!("{:?} is {:?}", v, vk);
321 fn variable(&self, node_id: NodeId, span: Span) -> Variable {
322 match self.variable_map.get(&node_id) {
327 .span_bug(span, &format!("no variable registered for id {}",
333 fn variable_name(&self, var: Variable) -> String {
334 match self.var_kinds[var.get()] {
335 Local(LocalInfo { ident: nm, .. }) | Arg(_, nm) => {
336 token::get_ident(nm).to_string()
338 ImplicitRet => "<implicit-ret>".to_string(),
339 CleanExit => "<clean-exit>".to_string()
343 fn set_captures(&mut self, node_id: NodeId, cs: Vec<CaptureInfo>) {
344 self.capture_info_map.insert(node_id, Rc::new(cs));
347 fn lnk(&self, ln: LiveNode) -> LiveNodeKind {
352 impl<'a, 'tcx, 'v> Visitor<'v> for Liveness<'a, 'tcx> {
353 fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v ast::FnDecl,
354 b: &'v ast::Block, s: Span, n: NodeId) {
355 check_fn(self, fk, fd, b, s, n);
357 fn visit_local(&mut self, l: &ast::Local) {
358 check_local(self, l);
360 fn visit_expr(&mut self, ex: &Expr) {
361 check_expr(self, ex);
363 fn visit_arm(&mut self, a: &ast::Arm) {
368 fn visit_fn(ir: &mut IrMaps,
376 // swap in a new set of IR maps for this function body:
377 let mut fn_maps = IrMaps::new(ir.tcx);
379 debug!("creating fn_maps: {:?}", &fn_maps as *const IrMaps);
381 for arg in &decl.inputs {
382 pat_util::pat_bindings(&ir.tcx.def_map,
384 |_bm, arg_id, _x, path1| {
385 debug!("adding argument {}", arg_id);
386 let ident = path1.node;
387 fn_maps.add_variable(Arg(arg_id, ident));
391 // gather up the various local variables, significant expressions,
393 visit::walk_fn(&mut fn_maps, fk, decl, body, sp);
395 // Special nodes and variables:
396 // - exit_ln represents the end of the fn, either by return or panic
397 // - implicit_ret_var is a pseudo-variable that represents
398 // an implicit return
399 let specials = Specials {
400 exit_ln: fn_maps.add_live_node(ExitNode),
401 fallthrough_ln: fn_maps.add_live_node(ExitNode),
402 no_ret_var: fn_maps.add_variable(ImplicitRet),
403 clean_exit_var: fn_maps.add_variable(CleanExit)
407 let mut lsets = Liveness::new(&mut fn_maps, specials);
408 let entry_ln = lsets.compute(decl, body);
410 // check for various error conditions
411 lsets.visit_block(body);
412 lsets.check_ret(id, sp, fk, entry_ln, body);
413 lsets.warn_about_unused_args(decl, entry_ln);
416 fn visit_local(ir: &mut IrMaps, local: &ast::Local) {
417 pat_util::pat_bindings(&ir.tcx.def_map, &*local.pat, |_, p_id, sp, path1| {
418 debug!("adding local variable {}", p_id);
419 let name = path1.node;
420 ir.add_live_node_for_node(p_id, VarDefNode(sp));
421 ir.add_variable(Local(LocalInfo {
426 visit::walk_local(ir, local);
429 fn visit_arm(ir: &mut IrMaps, arm: &ast::Arm) {
430 for pat in &arm.pats {
431 pat_util::pat_bindings(&ir.tcx.def_map, &**pat, |bm, p_id, sp, path1| {
432 debug!("adding local variable {} from match with bm {:?}",
434 let name = path1.node;
435 ir.add_live_node_for_node(p_id, VarDefNode(sp));
436 ir.add_variable(Local(LocalInfo {
442 visit::walk_arm(ir, arm);
445 fn visit_expr(ir: &mut IrMaps, expr: &Expr) {
447 // live nodes required for uses or definitions of variables:
448 ast::ExprPath(_) | ast::ExprQPath(_) => {
449 let def = ir.tcx.def_map.borrow()[expr.id].clone();
450 debug!("expr {}: path that leads to {:?}", expr.id, def);
451 if let DefLocal(..) = def {
452 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
454 visit::walk_expr(ir, expr);
456 ast::ExprClosure(..) => {
457 // Interesting control flow (for loops can contain labeled
458 // breaks or continues)
459 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
461 // Make a live_node for each captured variable, with the span
462 // being the location that the variable is used. This results
463 // in better error messages than just pointing at the closure
464 // construction site.
465 let mut call_caps = Vec::new();
466 ty::with_freevars(ir.tcx, expr.id, |freevars| {
468 if let DefLocal(rv) = fv.def {
469 let fv_ln = ir.add_live_node(FreeVarNode(fv.span));
470 call_caps.push(CaptureInfo {ln: fv_ln,
475 ir.set_captures(expr.id, call_caps);
477 visit::walk_expr(ir, expr);
480 // live nodes required for interesting control flow:
481 ast::ExprIf(..) | ast::ExprMatch(..) | ast::ExprWhile(..) | ast::ExprLoop(..) => {
482 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
483 visit::walk_expr(ir, expr);
485 ast::ExprIfLet(..) => {
486 ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
488 ast::ExprWhileLet(..) => {
489 ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet");
491 ast::ExprForLoop(..) => {
492 ir.tcx.sess.span_bug(expr.span, "non-desugared ExprForLoop");
494 ast::ExprBinary(op, _, _) if ast_util::lazy_binop(op.node) => {
495 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
496 visit::walk_expr(ir, expr);
499 // otherwise, live nodes are not required:
500 ast::ExprIndex(..) | ast::ExprField(..) | ast::ExprTupField(..) |
501 ast::ExprVec(..) | ast::ExprCall(..) | ast::ExprMethodCall(..) |
502 ast::ExprTup(..) | ast::ExprBinary(..) | ast::ExprAddrOf(..) |
503 ast::ExprCast(..) | ast::ExprUnary(..) | ast::ExprBreak(_) |
504 ast::ExprAgain(_) | ast::ExprLit(_) | ast::ExprRet(..) |
505 ast::ExprBlock(..) | ast::ExprAssign(..) | ast::ExprAssignOp(..) |
506 ast::ExprMac(..) | ast::ExprStruct(..) | ast::ExprRepeat(..) |
507 ast::ExprParen(..) | ast::ExprInlineAsm(..) | ast::ExprBox(..) |
508 ast::ExprRange(..) => {
509 visit::walk_expr(ir, expr);
514 // ______________________________________________________________________
515 // Computing liveness sets
517 // Actually we compute just a bit more than just liveness, but we use
518 // the same basic propagation framework in all cases.
520 #[derive(Clone, Copy)]
527 fn invalid_users() -> Users {
529 reader: invalid_node(),
530 writer: invalid_node(),
538 fallthrough_ln: LiveNode,
539 no_ret_var: Variable,
540 clean_exit_var: Variable
543 static ACC_READ: uint = 1;
544 static ACC_WRITE: uint = 2;
545 static ACC_USE: uint = 4;
547 struct Liveness<'a, 'tcx: 'a> {
548 ir: &'a mut IrMaps<'a, 'tcx>,
550 successors: Vec<LiveNode>,
552 // The list of node IDs for the nested loop scopes
554 loop_scope: Vec<NodeId>,
555 // mappings from loop node ID to LiveNode
556 // ("break" label should map to loop node ID,
557 // it probably doesn't now)
558 break_ln: NodeMap<LiveNode>,
559 cont_ln: NodeMap<LiveNode>
562 impl<'a, 'tcx> Liveness<'a, 'tcx> {
563 fn new(ir: &'a mut IrMaps<'a, 'tcx>, specials: Specials) -> Liveness<'a, 'tcx> {
564 let num_live_nodes = ir.num_live_nodes;
565 let num_vars = ir.num_vars;
569 successors: repeat(invalid_node()).take(num_live_nodes).collect(),
570 users: repeat(invalid_users()).take(num_live_nodes * num_vars).collect(),
571 loop_scope: Vec::new(),
577 fn live_node(&self, node_id: NodeId, span: Span) -> LiveNode {
578 match self.ir.live_node_map.get(&node_id) {
581 // This must be a mismatch between the ir_map construction
582 // above and the propagation code below; the two sets of
583 // code have to agree about which AST nodes are worth
584 // creating liveness nodes for.
585 self.ir.tcx.sess.span_bug(
587 &format!("no live node registered for node {}",
593 fn variable(&self, node_id: NodeId, span: Span) -> Variable {
594 self.ir.variable(node_id, span)
597 fn pat_bindings<F>(&mut self, pat: &ast::Pat, mut f: F) where
598 F: FnMut(&mut Liveness<'a, 'tcx>, LiveNode, Variable, Span, NodeId),
600 pat_util::pat_bindings(&self.ir.tcx.def_map, pat, |_bm, p_id, sp, _n| {
601 let ln = self.live_node(p_id, sp);
602 let var = self.variable(p_id, sp);
603 f(self, ln, var, sp, p_id);
607 fn arm_pats_bindings<F>(&mut self, pat: Option<&ast::Pat>, f: F) where
608 F: FnMut(&mut Liveness<'a, 'tcx>, LiveNode, Variable, Span, NodeId),
612 self.pat_bindings(pat, f);
618 fn define_bindings_in_pat(&mut self, pat: &ast::Pat, succ: LiveNode)
620 self.define_bindings_in_arm_pats(Some(pat), succ)
623 fn define_bindings_in_arm_pats(&mut self, pat: Option<&ast::Pat>, succ: LiveNode)
626 self.arm_pats_bindings(pat, |this, ln, var, _sp, _id| {
627 this.init_from_succ(ln, succ);
628 this.define(ln, var);
634 fn idx(&self, ln: LiveNode, var: Variable) -> uint {
635 ln.get() * self.ir.num_vars + var.get()
638 fn live_on_entry(&self, ln: LiveNode, var: Variable)
639 -> Option<LiveNodeKind> {
640 assert!(ln.is_valid());
641 let reader = self.users[self.idx(ln, var)].reader;
642 if reader.is_valid() {Some(self.ir.lnk(reader))} else {None}
646 Is this variable live on entry to any of its successor nodes?
648 fn live_on_exit(&self, ln: LiveNode, var: Variable)
649 -> Option<LiveNodeKind> {
650 let successor = self.successors[ln.get()];
651 self.live_on_entry(successor, var)
654 fn used_on_entry(&self, ln: LiveNode, var: Variable) -> bool {
655 assert!(ln.is_valid());
656 self.users[self.idx(ln, var)].used
659 fn assigned_on_entry(&self, ln: LiveNode, var: Variable)
660 -> Option<LiveNodeKind> {
661 assert!(ln.is_valid());
662 let writer = self.users[self.idx(ln, var)].writer;
663 if writer.is_valid() {Some(self.ir.lnk(writer))} else {None}
666 fn assigned_on_exit(&self, ln: LiveNode, var: Variable)
667 -> Option<LiveNodeKind> {
668 let successor = self.successors[ln.get()];
669 self.assigned_on_entry(successor, var)
672 fn indices2<F>(&mut self, ln: LiveNode, succ_ln: LiveNode, mut op: F) where
673 F: FnMut(&mut Liveness<'a, 'tcx>, uint, uint),
675 let node_base_idx = self.idx(ln, Variable(0));
676 let succ_base_idx = self.idx(succ_ln, Variable(0));
677 for var_idx in 0..self.ir.num_vars {
678 op(self, node_base_idx + var_idx, succ_base_idx + var_idx);
682 fn write_vars<F>(&self,
683 wr: &mut old_io::Writer,
686 -> old_io::IoResult<()> where
687 F: FnMut(uint) -> LiveNode,
689 let node_base_idx = self.idx(ln, Variable(0));
690 for var_idx in 0..self.ir.num_vars {
691 let idx = node_base_idx + var_idx;
692 if test(idx).is_valid() {
693 try!(write!(wr, " {:?}", Variable(var_idx)));
699 fn find_loop_scope(&self,
700 opt_label: Option<ast::Ident>,
706 // Refers to a labeled loop. Use the results of resolve
708 match self.ir.tcx.def_map.borrow().get(&id) {
709 Some(&DefLabel(loop_id)) => loop_id,
710 _ => self.ir.tcx.sess.span_bug(sp, "label on break/loop \
711 doesn't refer to a loop")
715 // Vanilla 'break' or 'loop', so use the enclosing
717 if self.loop_scope.len() == 0 {
718 self.ir.tcx.sess.span_bug(sp, "break outside loop");
720 *self.loop_scope.last().unwrap()
726 #[allow(unused_must_use)]
727 fn ln_str(&self, ln: LiveNode) -> String {
728 let mut wr = Vec::new();
730 let wr = &mut wr as &mut old_io::Writer;
731 write!(wr, "[ln({:?}) of kind {:?} reads", ln.get(), self.ir.lnk(ln));
732 self.write_vars(wr, ln, |idx| self.users[idx].reader);
733 write!(wr, " writes");
734 self.write_vars(wr, ln, |idx| self.users[idx].writer);
735 write!(wr, " precedes {:?}]", self.successors[ln.get()]);
737 String::from_utf8(wr).unwrap()
740 fn init_empty(&mut self, ln: LiveNode, succ_ln: LiveNode) {
741 self.successors[ln.get()] = succ_ln;
743 // It is not necessary to initialize the
744 // values to empty because this is the value
745 // they have when they are created, and the sets
746 // only grow during iterations.
748 // self.indices(ln) { |idx|
749 // self.users[idx] = invalid_users();
753 fn init_from_succ(&mut self, ln: LiveNode, succ_ln: LiveNode) {
754 // more efficient version of init_empty() / merge_from_succ()
755 self.successors[ln.get()] = succ_ln;
757 self.indices2(ln, succ_ln, |this, idx, succ_idx| {
758 this.users[idx] = this.users[succ_idx]
760 debug!("init_from_succ(ln={}, succ={})",
761 self.ln_str(ln), self.ln_str(succ_ln));
764 fn merge_from_succ(&mut self,
769 if ln == succ_ln { return false; }
771 let mut changed = false;
772 self.indices2(ln, succ_ln, |this, idx, succ_idx| {
773 changed |= copy_if_invalid(this.users[succ_idx].reader,
774 &mut this.users[idx].reader);
775 changed |= copy_if_invalid(this.users[succ_idx].writer,
776 &mut this.users[idx].writer);
777 if this.users[succ_idx].used && !this.users[idx].used {
778 this.users[idx].used = true;
783 debug!("merge_from_succ(ln={:?}, succ={}, first_merge={}, changed={})",
784 ln, self.ln_str(succ_ln), first_merge, changed);
787 fn copy_if_invalid(src: LiveNode, dst: &mut LiveNode) -> bool {
788 if src.is_valid() && !dst.is_valid() {
797 // Indicates that a local variable was *defined*; we know that no
798 // uses of the variable can precede the definition (resolve checks
799 // this) so we just clear out all the data.
800 fn define(&mut self, writer: LiveNode, var: Variable) {
801 let idx = self.idx(writer, var);
802 self.users[idx].reader = invalid_node();
803 self.users[idx].writer = invalid_node();
805 debug!("{:?} defines {:?} (idx={}): {}", writer, var,
806 idx, self.ln_str(writer));
809 // Either read, write, or both depending on the acc bitset
810 fn acc(&mut self, ln: LiveNode, var: Variable, acc: uint) {
811 debug!("{:?} accesses[{:x}] {:?}: {}",
812 ln, acc, var, self.ln_str(ln));
814 let idx = self.idx(ln, var);
815 let user = &mut self.users[idx];
817 if (acc & ACC_WRITE) != 0 {
818 user.reader = invalid_node();
822 // Important: if we both read/write, must do read second
823 // or else the write will override.
824 if (acc & ACC_READ) != 0 {
828 if (acc & ACC_USE) != 0 {
833 // _______________________________________________________________________
835 fn compute(&mut self, decl: &ast::FnDecl, body: &ast::Block) -> LiveNode {
836 // if there is a `break` or `again` at the top level, then it's
837 // effectively a return---this only occurs in `for` loops,
838 // where the body is really a closure.
840 debug!("compute: using id for block, {}", block_to_string(body));
842 let exit_ln = self.s.exit_ln;
843 let entry_ln: LiveNode =
844 self.with_loop_nodes(body.id, exit_ln, exit_ln,
845 |this| this.propagate_through_fn_block(decl, body));
847 // hack to skip the loop unless debug! is enabled:
848 debug!("^^ liveness computation results for body {} (entry={:?})",
850 for ln_idx in 0..self.ir.num_live_nodes {
851 debug!("{:?}", self.ln_str(LiveNode(ln_idx)));
860 fn propagate_through_fn_block(&mut self, _: &ast::FnDecl, blk: &ast::Block)
862 // the fallthrough exit is only for those cases where we do not
863 // explicitly return:
865 self.init_from_succ(s.fallthrough_ln, s.exit_ln);
866 if blk.expr.is_none() {
867 self.acc(s.fallthrough_ln, s.no_ret_var, ACC_READ)
869 self.acc(s.fallthrough_ln, s.clean_exit_var, ACC_READ);
871 self.propagate_through_block(blk, s.fallthrough_ln)
874 fn propagate_through_block(&mut self, blk: &ast::Block, succ: LiveNode)
876 let succ = self.propagate_through_opt_expr(blk.expr.as_ref().map(|e| &**e), succ);
877 blk.stmts.iter().rev().fold(succ, |succ, stmt| {
878 self.propagate_through_stmt(&**stmt, succ)
882 fn propagate_through_stmt(&mut self, stmt: &ast::Stmt, succ: LiveNode)
885 ast::StmtDecl(ref decl, _) => {
886 self.propagate_through_decl(&**decl, succ)
889 ast::StmtExpr(ref expr, _) | ast::StmtSemi(ref expr, _) => {
890 self.propagate_through_expr(&**expr, succ)
893 ast::StmtMac(..) => {
894 self.ir.tcx.sess.span_bug(stmt.span, "unexpanded macro");
899 fn propagate_through_decl(&mut self, decl: &ast::Decl, succ: LiveNode)
902 ast::DeclLocal(ref local) => {
903 self.propagate_through_local(&**local, succ)
905 ast::DeclItem(_) => succ,
909 fn propagate_through_local(&mut self, local: &ast::Local, succ: LiveNode)
911 // Note: we mark the variable as defined regardless of whether
912 // there is an initializer. Initially I had thought to only mark
913 // the live variable as defined if it was initialized, and then we
914 // could check for uninit variables just by scanning what is live
915 // at the start of the function. But that doesn't work so well for
916 // immutable variables defined in a loop:
917 // loop { let x; x = 5; }
918 // because the "assignment" loops back around and generates an error.
920 // So now we just check that variables defined w/o an
921 // initializer are not live at the point of their
922 // initialization, which is mildly more complex than checking
923 // once at the func header but otherwise equivalent.
925 let succ = self.propagate_through_opt_expr(local.init.as_ref().map(|e| &**e), succ);
926 self.define_bindings_in_pat(&*local.pat, succ)
929 fn propagate_through_exprs(&mut self, exprs: &[P<Expr>], succ: LiveNode)
931 exprs.iter().rev().fold(succ, |succ, expr| {
932 self.propagate_through_expr(&**expr, succ)
936 fn propagate_through_opt_expr(&mut self,
937 opt_expr: Option<&Expr>,
940 opt_expr.map_or(succ, |expr| self.propagate_through_expr(expr, succ))
943 fn propagate_through_expr(&mut self, expr: &Expr, succ: LiveNode)
945 debug!("propagate_through_expr: {}", expr_to_string(expr));
948 // Interesting cases with control flow or which gen/kill
950 ast::ExprPath(_) | ast::ExprQPath(_) => {
951 self.access_path(expr, succ, ACC_READ | ACC_USE)
954 ast::ExprField(ref e, _) => {
955 self.propagate_through_expr(&**e, succ)
958 ast::ExprTupField(ref e, _) => {
959 self.propagate_through_expr(&**e, succ)
962 ast::ExprClosure(_, _, ref blk) => {
963 debug!("{} is an ExprClosure",
964 expr_to_string(expr));
967 The next-node for a break is the successor of the entire
968 loop. The next-node for a continue is the top of this loop.
970 let node = self.live_node(expr.id, expr.span);
971 self.with_loop_nodes(blk.id, succ, node, |this| {
973 // the construction of a closure itself is not important,
974 // but we have to consider the closed over variables.
975 let caps = match this.ir.capture_info_map.get(&expr.id) {
976 Some(caps) => caps.clone(),
978 this.ir.tcx.sess.span_bug(expr.span, "no registered caps");
981 caps.iter().rev().fold(succ, |succ, cap| {
982 this.init_from_succ(cap.ln, succ);
983 let var = this.variable(cap.var_nid, expr.span);
984 this.acc(cap.ln, var, ACC_READ | ACC_USE);
990 ast::ExprIf(ref cond, ref then, ref els) => {
1004 let else_ln = self.propagate_through_opt_expr(els.as_ref().map(|e| &**e), succ);
1005 let then_ln = self.propagate_through_block(&**then, succ);
1006 let ln = self.live_node(expr.id, expr.span);
1007 self.init_from_succ(ln, else_ln);
1008 self.merge_from_succ(ln, then_ln, false);
1009 self.propagate_through_expr(&**cond, ln)
1012 ast::ExprIfLet(..) => {
1013 self.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
1016 ast::ExprWhile(ref cond, ref blk, _) => {
1017 self.propagate_through_loop(expr, WhileLoop(&**cond), &**blk, succ)
1020 ast::ExprWhileLet(..) => {
1021 self.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet");
1024 ast::ExprForLoop(..) => {
1025 self.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprForLoop");
1028 // Note that labels have been resolved, so we don't need to look
1029 // at the label ident
1030 ast::ExprLoop(ref blk, _) => {
1031 self.propagate_through_loop(expr, LoopLoop, &**blk, succ)
1034 ast::ExprMatch(ref e, ref arms, _) => {
1049 let ln = self.live_node(expr.id, expr.span);
1050 self.init_empty(ln, succ);
1051 let mut first_merge = true;
1054 self.propagate_through_expr(&*arm.body, succ);
1056 self.propagate_through_opt_expr(arm.guard.as_ref().map(|e| &**e), body_succ);
1057 // only consider the first pattern; any later patterns must have
1058 // the same bindings, and we also consider the first pattern to be
1059 // the "authoritative" set of ids
1061 self.define_bindings_in_arm_pats(arm.pats.first().map(|p| &**p),
1063 self.merge_from_succ(ln, arm_succ, first_merge);
1064 first_merge = false;
1066 self.propagate_through_expr(&**e, ln)
1069 ast::ExprRet(ref o_e) => {
1070 // ignore succ and subst exit_ln:
1071 let exit_ln = self.s.exit_ln;
1072 self.propagate_through_opt_expr(o_e.as_ref().map(|e| &**e), exit_ln)
1075 ast::ExprBreak(opt_label) => {
1076 // Find which label this break jumps to
1077 let sc = self.find_loop_scope(opt_label, expr.id, expr.span);
1079 // Now that we know the label we're going to,
1080 // look it up in the break loop nodes table
1082 match self.break_ln.get(&sc) {
1084 None => self.ir.tcx.sess.span_bug(expr.span,
1085 "break to unknown label")
1089 ast::ExprAgain(opt_label) => {
1090 // Find which label this expr continues to
1091 let sc = self.find_loop_scope(opt_label, expr.id, expr.span);
1093 // Now that we know the label we're going to,
1094 // look it up in the continue loop nodes table
1096 match self.cont_ln.get(&sc) {
1098 None => self.ir.tcx.sess.span_bug(expr.span,
1099 "loop to unknown label")
1103 ast::ExprAssign(ref l, ref r) => {
1104 // see comment on lvalues in
1105 // propagate_through_lvalue_components()
1106 let succ = self.write_lvalue(&**l, succ, ACC_WRITE);
1107 let succ = self.propagate_through_lvalue_components(&**l, succ);
1108 self.propagate_through_expr(&**r, succ)
1111 ast::ExprAssignOp(_, ref l, ref r) => {
1112 // see comment on lvalues in
1113 // propagate_through_lvalue_components()
1114 let succ = self.write_lvalue(&**l, succ, ACC_WRITE|ACC_READ);
1115 let succ = self.propagate_through_expr(&**r, succ);
1116 self.propagate_through_lvalue_components(&**l, succ)
1119 // Uninteresting cases: just propagate in rev exec order
1121 ast::ExprVec(ref exprs) => {
1122 self.propagate_through_exprs(&exprs[..], succ)
1125 ast::ExprRepeat(ref element, ref count) => {
1126 let succ = self.propagate_through_expr(&**count, succ);
1127 self.propagate_through_expr(&**element, succ)
1130 ast::ExprStruct(_, ref fields, ref with_expr) => {
1131 let succ = self.propagate_through_opt_expr(with_expr.as_ref().map(|e| &**e), succ);
1132 fields.iter().rev().fold(succ, |succ, field| {
1133 self.propagate_through_expr(&*field.expr, succ)
1137 ast::ExprCall(ref f, ref args) => {
1138 let diverges = !self.ir.tcx.is_method_call(expr.id) && {
1139 ty::ty_fn_ret(ty::expr_ty_adjusted(self.ir.tcx, &**f)).diverges()
1141 let succ = if diverges {
1146 let succ = self.propagate_through_exprs(&args[..], succ);
1147 self.propagate_through_expr(&**f, succ)
1150 ast::ExprMethodCall(_, _, ref args) => {
1151 let method_call = ty::MethodCall::expr(expr.id);
1152 let method_ty = self.ir.tcx.method_map.borrow().get(&method_call).unwrap().ty;
1153 let diverges = ty::ty_fn_ret(method_ty).diverges();
1154 let succ = if diverges {
1159 self.propagate_through_exprs(&args[..], succ)
1162 ast::ExprTup(ref exprs) => {
1163 self.propagate_through_exprs(&exprs[..], succ)
1166 ast::ExprBinary(op, ref l, ref r) if ast_util::lazy_binop(op.node) => {
1167 let r_succ = self.propagate_through_expr(&**r, succ);
1169 let ln = self.live_node(expr.id, expr.span);
1170 self.init_from_succ(ln, succ);
1171 self.merge_from_succ(ln, r_succ, false);
1173 self.propagate_through_expr(&**l, ln)
1176 ast::ExprIndex(ref l, ref r) |
1177 ast::ExprBinary(_, ref l, ref r) |
1178 ast::ExprBox(Some(ref l), ref r) => {
1179 let r_succ = self.propagate_through_expr(&**r, succ);
1180 self.propagate_through_expr(&**l, r_succ)
1183 ast::ExprRange(ref e1, ref e2) => {
1184 let succ = e2.as_ref().map_or(succ, |e| self.propagate_through_expr(&**e, succ));
1185 e1.as_ref().map_or(succ, |e| self.propagate_through_expr(&**e, succ))
1188 ast::ExprBox(None, ref e) |
1189 ast::ExprAddrOf(_, ref e) |
1190 ast::ExprCast(ref e, _) |
1191 ast::ExprUnary(_, ref e) |
1192 ast::ExprParen(ref e) => {
1193 self.propagate_through_expr(&**e, succ)
1196 ast::ExprInlineAsm(ref ia) => {
1198 let succ = ia.outputs.iter().rev().fold(succ, |succ, &(_, ref expr, _)| {
1199 // see comment on lvalues
1200 // in propagate_through_lvalue_components()
1201 let succ = self.write_lvalue(&**expr, succ, ACC_WRITE);
1202 self.propagate_through_lvalue_components(&**expr, succ)
1204 // Inputs are executed first. Propagate last because of rev order
1205 ia.inputs.iter().rev().fold(succ, |succ, &(_, ref expr)| {
1206 self.propagate_through_expr(&**expr, succ)
1210 ast::ExprLit(..) => {
1214 ast::ExprBlock(ref blk) => {
1215 self.propagate_through_block(&**blk, succ)
1218 ast::ExprMac(..) => {
1219 self.ir.tcx.sess.span_bug(expr.span, "unexpanded macro");
1224 fn propagate_through_lvalue_components(&mut self,
1230 // In general, the full flow graph structure for an
1231 // assignment/move/etc can be handled in one of two ways,
1232 // depending on whether what is being assigned is a "tracked
1233 // value" or not. A tracked value is basically a local
1234 // variable or argument.
1236 // The two kinds of graphs are:
1238 // Tracked lvalue Untracked lvalue
1239 // ----------------------++-----------------------
1243 // (rvalue) || (rvalue)
1246 // (write of lvalue) || (lvalue components)
1251 // ----------------------++-----------------------
1253 // I will cover the two cases in turn:
1255 // # Tracked lvalues
1257 // A tracked lvalue is a local variable/argument `x`. In
1258 // these cases, the link_node where the write occurs is linked
1259 // to node id of `x`. The `write_lvalue()` routine generates
1260 // the contents of this node. There are no subcomponents to
1263 // # Non-tracked lvalues
1265 // These are lvalues like `x[5]` or `x.f`. In that case, we
1266 // basically ignore the value which is written to but generate
1267 // reads for the components---`x` in these two examples. The
1268 // components reads are generated by
1269 // `propagate_through_lvalue_components()` (this fn).
1271 // # Illegal lvalues
1273 // It is still possible to observe assignments to non-lvalues;
1274 // these errors are detected in the later pass borrowck. We
1275 // just ignore such cases and treat them as reads.
1278 ast::ExprPath(_) | ast::ExprQPath(_) => succ,
1279 ast::ExprField(ref e, _) => self.propagate_through_expr(&**e, succ),
1280 ast::ExprTupField(ref e, _) => self.propagate_through_expr(&**e, succ),
1281 _ => self.propagate_through_expr(expr, succ)
1285 // see comment on propagate_through_lvalue()
1286 fn write_lvalue(&mut self, expr: &Expr, succ: LiveNode, acc: uint)
1289 ast::ExprPath(_) | ast::ExprQPath(_) => {
1290 self.access_path(expr, succ, acc)
1293 // We do not track other lvalues, so just propagate through
1294 // to their subcomponents. Also, it may happen that
1295 // non-lvalues occur here, because those are detected in the
1296 // later pass borrowck.
1301 fn access_path(&mut self, expr: &Expr, succ: LiveNode, acc: uint)
1303 match self.ir.tcx.def_map.borrow()[expr.id].clone() {
1305 let ln = self.live_node(expr.id, expr.span);
1307 self.init_from_succ(ln, succ);
1308 let var = self.variable(nid, expr.span);
1309 self.acc(ln, var, acc);
1317 fn propagate_through_loop(&mut self,
1326 We model control flow like this:
1344 let mut first_merge = true;
1345 let ln = self.live_node(expr.id, expr.span);
1346 self.init_empty(ln, succ);
1350 // If this is not a `loop` loop, then it's possible we bypass
1351 // the body altogether. Otherwise, the only way is via a `break`
1352 // in the loop body.
1353 self.merge_from_succ(ln, succ, first_merge);
1354 first_merge = false;
1357 debug!("propagate_through_loop: using id for loop body {} {}",
1358 expr.id, block_to_string(body));
1360 let cond_ln = match kind {
1362 WhileLoop(ref cond) => self.propagate_through_expr(&**cond, ln),
1364 let body_ln = self.with_loop_nodes(expr.id, succ, ln, |this| {
1365 this.propagate_through_block(body, cond_ln)
1368 // repeat until fixed point is reached:
1369 while self.merge_from_succ(ln, body_ln, first_merge) {
1370 first_merge = false;
1372 let new_cond_ln = match kind {
1374 WhileLoop(ref cond) => {
1375 self.propagate_through_expr(&**cond, ln)
1378 assert!(cond_ln == new_cond_ln);
1379 assert!(body_ln == self.with_loop_nodes(expr.id, succ, ln,
1380 |this| this.propagate_through_block(body, cond_ln)));
1386 fn with_loop_nodes<R, F>(&mut self,
1387 loop_node_id: NodeId,
1392 F: FnOnce(&mut Liveness<'a, 'tcx>) -> R,
1394 debug!("with_loop_nodes: {} {}", loop_node_id, break_ln.get());
1395 self.loop_scope.push(loop_node_id);
1396 self.break_ln.insert(loop_node_id, break_ln);
1397 self.cont_ln.insert(loop_node_id, cont_ln);
1399 self.loop_scope.pop();
1404 // _______________________________________________________________________
1405 // Checking for error conditions
1407 fn check_local(this: &mut Liveness, local: &ast::Local) {
1410 this.warn_about_unused_or_dead_vars_in_pat(&*local.pat);
1413 this.pat_bindings(&*local.pat, |this, ln, var, sp, id| {
1414 this.warn_about_unused(sp, id, ln, var);
1419 visit::walk_local(this, local);
1422 fn check_arm(this: &mut Liveness, arm: &ast::Arm) {
1423 // only consider the first pattern; any later patterns must have
1424 // the same bindings, and we also consider the first pattern to be
1425 // the "authoritative" set of ids
1426 this.arm_pats_bindings(arm.pats.first().map(|p| &**p), |this, ln, var, sp, id| {
1427 this.warn_about_unused(sp, id, ln, var);
1429 visit::walk_arm(this, arm);
1432 fn check_expr(this: &mut Liveness, expr: &Expr) {
1434 ast::ExprAssign(ref l, ref r) => {
1435 this.check_lvalue(&**l);
1436 this.visit_expr(&**r);
1438 visit::walk_expr(this, expr);
1441 ast::ExprAssignOp(_, ref l, _) => {
1442 this.check_lvalue(&**l);
1444 visit::walk_expr(this, expr);
1447 ast::ExprInlineAsm(ref ia) => {
1448 for &(_, ref input) in &ia.inputs {
1449 this.visit_expr(&**input);
1452 // Output operands must be lvalues
1453 for &(_, ref out, _) in &ia.outputs {
1454 this.check_lvalue(&**out);
1455 this.visit_expr(&**out);
1458 visit::walk_expr(this, expr);
1461 // no correctness conditions related to liveness
1462 ast::ExprCall(..) | ast::ExprMethodCall(..) | ast::ExprIf(..) |
1463 ast::ExprMatch(..) | ast::ExprWhile(..) | ast::ExprLoop(..) |
1464 ast::ExprIndex(..) | ast::ExprField(..) | ast::ExprTupField(..) |
1465 ast::ExprVec(..) | ast::ExprTup(..) | ast::ExprBinary(..) |
1466 ast::ExprCast(..) | ast::ExprUnary(..) | ast::ExprRet(..) |
1467 ast::ExprBreak(..) | ast::ExprAgain(..) | ast::ExprLit(_) |
1468 ast::ExprBlock(..) | ast::ExprMac(..) | ast::ExprAddrOf(..) |
1469 ast::ExprStruct(..) | ast::ExprRepeat(..) | ast::ExprParen(..) |
1470 ast::ExprClosure(..) | ast::ExprPath(..) | ast::ExprBox(..) |
1471 ast::ExprRange(..) | ast::ExprQPath(..) => {
1472 visit::walk_expr(this, expr);
1474 ast::ExprIfLet(..) => {
1475 this.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
1477 ast::ExprWhileLet(..) => {
1478 this.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet");
1480 ast::ExprForLoop(..) => {
1481 this.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprForLoop");
1486 fn check_fn(_v: &Liveness,
1488 _decl: &ast::FnDecl,
1492 // do not check contents of nested fns
1495 impl<'a, 'tcx> Liveness<'a, 'tcx> {
1496 fn fn_ret(&self, id: NodeId) -> ty::PolyFnOutput<'tcx> {
1497 let fn_ty = ty::node_id_to_type(self.ir.tcx, id);
1499 ty::ty_closure(closure_def_id, _, substs) =>
1500 self.ir.tcx.closure_type(closure_def_id, substs).sig.output(),
1502 ty::ty_fn_ret(fn_ty),
1513 // within the fn body, late-bound regions are liberated:
1515 ty::liberate_late_bound_regions(
1517 region::DestructionScopeData::new(body.id),
1521 ty::FnConverging(t_ret)
1522 if self.live_on_entry(entry_ln, self.s.no_ret_var).is_some() => {
1524 if ty::type_is_nil(t_ret) {
1525 // for nil return types, it is ok to not return a value expl.
1527 let ends_with_stmt = match body.expr {
1528 None if body.stmts.len() > 0 =>
1529 match body.stmts.first().unwrap().node {
1530 ast::StmtSemi(ref e, _) => {
1531 ty::expr_ty(self.ir.tcx, &**e) == t_ret
1537 span_err!(self.ir.tcx.sess, sp, E0269, "not all control paths return a value");
1539 let last_stmt = body.stmts.first().unwrap();
1540 let original_span = original_sp(self.ir.tcx.sess.codemap(),
1541 last_stmt.span, sp);
1542 let span_semicolon = Span {
1543 lo: original_span.hi - BytePos(1),
1544 hi: original_span.hi,
1545 expn_id: original_span.expn_id
1547 self.ir.tcx.sess.span_help(
1548 span_semicolon, "consider removing this semicolon:");
1553 if self.live_on_entry(entry_ln, self.s.clean_exit_var).is_some() => {
1554 span_err!(self.ir.tcx.sess, sp, E0270,
1555 "computation may converge in a function marked as diverging");
1562 fn check_lvalue(&mut self, expr: &Expr) {
1564 ast::ExprPath(_) | ast::ExprQPath(_) => {
1565 if let DefLocal(nid) = self.ir.tcx.def_map.borrow()[expr.id].clone() {
1566 // Assignment to an immutable variable or argument: only legal
1567 // if there is no later assignment. If this local is actually
1568 // mutable, then check for a reassignment to flag the mutability
1570 let ln = self.live_node(expr.id, expr.span);
1571 let var = self.variable(nid, expr.span);
1572 self.warn_about_dead_assign(expr.span, expr.id, ln, var);
1576 // For other kinds of lvalues, no checks are required,
1577 // and any embedded expressions are actually rvalues
1578 visit::walk_expr(self, expr);
1583 fn should_warn(&self, var: Variable) -> Option<String> {
1584 let name = self.ir.variable_name(var);
1585 if name.len() == 0 || name.as_bytes()[0] == ('_' as u8) {
1592 fn warn_about_unused_args(&self, decl: &ast::FnDecl, entry_ln: LiveNode) {
1593 for arg in &decl.inputs {
1594 pat_util::pat_bindings(&self.ir.tcx.def_map,
1596 |_bm, p_id, sp, path1| {
1597 let var = self.variable(p_id, sp);
1598 // Ignore unused self.
1599 let ident = path1.node;
1600 if ident.name != special_idents::self_.name {
1601 self.warn_about_unused(sp, p_id, entry_ln, var);
1607 fn warn_about_unused_or_dead_vars_in_pat(&mut self, pat: &ast::Pat) {
1608 self.pat_bindings(pat, |this, ln, var, sp, id| {
1609 if !this.warn_about_unused(sp, id, ln, var) {
1610 this.warn_about_dead_assign(sp, id, ln, var);
1615 fn warn_about_unused(&self,
1621 if !self.used_on_entry(ln, var) {
1622 let r = self.should_warn(var);
1623 if let Some(name) = r {
1625 // annoying: for parameters in funcs like `fn(x: int)
1626 // {ret}`, there is only one node, so asking about
1627 // assigned_on_exit() is not meaningful.
1628 let is_assigned = if ln == self.s.exit_ln {
1631 self.assigned_on_exit(ln, var).is_some()
1635 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_VARIABLES, id, sp,
1636 format!("variable `{}` is assigned to, but never used",
1639 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_VARIABLES, id, sp,
1640 format!("unused variable: `{}`", name));
1649 fn warn_about_dead_assign(&self,
1654 if self.live_on_exit(ln, var).is_none() {
1655 let r = self.should_warn(var);
1656 if let Some(name) = r {
1657 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_ASSIGNMENTS, id, sp,
1658 format!("value assigned to `{}` is never read", name));