1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! A classic liveness analysis based on dataflow over the AST. Computes,
12 //! for each local variable in a function, whether that variable is live
13 //! at a given point. Program execution points are identified by their
18 //! The basic model is that each local variable is assigned an index. We
19 //! represent sets of local variables using a vector indexed by this
20 //! index. The value in the vector is either 0, indicating the variable
21 //! is dead, or the id of an expression that uses the variable.
23 //! We conceptually walk over the AST in reverse execution order. If we
24 //! find a use of a variable, we add it to the set of live variables. If
25 //! we find an assignment to a variable, we remove it from the set of live
26 //! variables. When we have to merge two flows, we take the union of
27 //! those two flows---if the variable is live on both paths, we simply
28 //! pick one id. In the event of loops, we continue doing this until a
29 //! fixed point is reached.
31 //! ## Checking initialization
33 //! At the function entry point, all variables must be dead. If this is
34 //! not the case, we can report an error using the id found in the set of
35 //! live variables, which identifies a use of the variable which is not
36 //! dominated by an assignment.
40 //! After each explicit move, the variable must be dead.
42 //! ## Computing last uses
44 //! Any use of the variable where the variable is dead afterwards is a
47 //! # Implementation details
49 //! The actual implementation contains two (nested) walks over the AST.
50 //! The outer walk has the job of building up the ir_maps instance for the
51 //! enclosing function. On the way down the tree, it identifies those AST
52 //! nodes and variable IDs that will be needed for the liveness analysis
53 //! and assigns them contiguous IDs. The liveness id for an AST node is
54 //! called a `live_node` (it's a newtype'd usize) and the id for a variable
55 //! is called a `variable` (another newtype'd usize).
57 //! On the way back up the tree, as we are about to exit from a function
58 //! declaration we allocate a `liveness` instance. Now that we know
59 //! precisely how many nodes and variables we need, we can allocate all
60 //! the various arrays that we will need to precisely the right size. We then
61 //! perform the actual propagation on the `liveness` instance.
63 //! This propagation is encoded in the various `propagate_through_*()`
64 //! methods. It effectively does a reverse walk of the AST; whenever we
65 //! reach a loop node, we iterate until a fixed point is reached.
67 //! ## The `Users` struct
69 //! At each live node `N`, we track three pieces of information for each
70 //! variable `V` (these are encapsulated in the `Users` struct):
72 //! - `reader`: the `LiveNode` ID of some node which will read the value
73 //! that `V` holds on entry to `N`. Formally: a node `M` such
74 //! that there exists a path `P` from `N` to `M` where `P` does not
75 //! write `V`. If the `reader` is `invalid_node()`, then the current
76 //! value will never be read (the variable is dead, essentially).
78 //! - `writer`: the `LiveNode` ID of some node which will write the
79 //! variable `V` and which is reachable from `N`. Formally: a node `M`
80 //! such that there exists a path `P` from `N` to `M` and `M` writes
81 //! `V`. If the `writer` is `invalid_node()`, then there is no writer
82 //! of `V` that follows `N`.
84 //! - `used`: a boolean value indicating whether `V` is *used*. We
85 //! distinguish a *read* from a *use* in that a *use* is some read that
86 //! is not just used to generate a new value. For example, `x += 1` is
87 //! a read but not a use. This is used to generate better warnings.
89 //! ## Special Variables
91 //! We generate various special variables for various, well, special purposes.
92 //! These are described in the `specials` struct:
94 //! - `exit_ln`: a live node that is generated to represent every 'exit' from
95 //! the function, whether it be by explicit return, panic, or other means.
97 //! - `fallthrough_ln`: a live node that represents a fallthrough
99 //! - `no_ret_var`: a synthetic variable that is only 'read' from, the
100 //! fallthrough node. This allows us to detect functions where we fail
101 //! to return explicitly.
102 //! - `clean_exit_var`: a synthetic variable that is only 'read' from the
103 //! fallthrough node. It is only live if the function could converge
104 //! via means other than an explicit `return` expression. That is, it is
105 //! only dead if the end of the function's block can never be reached.
106 //! It is the responsibility of typeck to ensure that there are no
107 //! `return` expressions in a function declared as diverging.
108 use self::LoopKind::*;
109 use self::LiveNodeKind::*;
110 use self::VarKind::*;
113 use middle::mem_categorization::Typer;
114 use middle::pat_util;
117 use middle::ty::ClosureTyper;
119 use util::nodemap::NodeMap;
121 use std::{fmt, usize};
122 use std::io::prelude::*;
124 use std::iter::repeat;
126 use syntax::ast::{self, NodeId, Expr};
127 use syntax::codemap::{BytePos, original_sp, Span};
128 use syntax::parse::token::{self, special_idents};
129 use syntax::print::pprust::{expr_to_string, block_to_string};
131 use syntax::ast_util;
132 use syntax::visit::{self, Visitor, FnKind};
134 /// For use with `propagate_through_loop`.
136 /// An endless `loop` loop.
138 /// A `while` loop, with the given expression as condition.
142 #[derive(Copy, PartialEq)]
143 struct Variable(usize);
145 #[derive(Copy, PartialEq)]
146 struct LiveNode(usize);
149 fn get(&self) -> usize { let Variable(v) = *self; v }
153 fn get(&self) -> usize { let LiveNode(v) = *self; v }
156 impl Clone for LiveNode {
157 fn clone(&self) -> LiveNode {
162 #[derive(Copy, PartialEq, Debug)]
170 fn live_node_kind_to_string(lnk: LiveNodeKind, cx: &ty::ctxt) -> String {
171 let cm = cx.sess.codemap();
174 format!("Free var node [{}]", cm.span_to_string(s))
177 format!("Expr node [{}]", cm.span_to_string(s))
180 format!("Var def node [{}]", cm.span_to_string(s))
182 ExitNode => "Exit node".to_string(),
186 impl<'a, 'tcx, 'v> Visitor<'v> for IrMaps<'a, 'tcx> {
187 fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v ast::FnDecl,
188 b: &'v ast::Block, s: Span, id: NodeId) {
189 visit_fn(self, fk, fd, b, s, id);
191 fn visit_local(&mut self, l: &ast::Local) { visit_local(self, l); }
192 fn visit_expr(&mut self, ex: &Expr) { visit_expr(self, ex); }
193 fn visit_arm(&mut self, a: &ast::Arm) { visit_arm(self, a); }
196 pub fn check_crate(tcx: &ty::ctxt) {
197 visit::walk_crate(&mut IrMaps::new(tcx), tcx.map.krate());
198 tcx.sess.abort_if_errors();
201 impl fmt::Debug for LiveNode {
202 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
203 write!(f, "ln({})", self.get())
207 impl fmt::Debug for Variable {
208 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
209 write!(f, "v({})", self.get())
213 // ______________________________________________________________________
216 // This is the first pass and the one that drives the main
217 // computation. It walks up and down the IR once. On the way down,
218 // we count for each function the number of variables as well as
219 // liveness nodes. A liveness node is basically an expression or
220 // capture clause that does something of interest: either it has
221 // interesting control flow or it uses/defines a local variable.
223 // On the way back up, at each function node we create liveness sets
224 // (we now know precisely how big to make our various vectors and so
225 // forth) and then do the data-flow propagation to compute the set
226 // of live variables at each program point.
228 // Finally, we run back over the IR one last time and, using the
229 // computed liveness, check various safety conditions. For example,
230 // there must be no live nodes at the definition site for a variable
231 // unless it has an initializer. Similarly, each non-mutable local
232 // variable must not be assigned if there is some successor
233 // assignment. And so forth.
236 fn is_valid(&self) -> bool {
237 self.get() != usize::MAX
241 fn invalid_node() -> LiveNode { LiveNode(usize::MAX) }
248 #[derive(Copy, Debug)]
254 #[derive(Copy, Debug)]
256 Arg(NodeId, ast::Ident),
262 struct IrMaps<'a, 'tcx: 'a> {
263 tcx: &'a ty::ctxt<'tcx>,
265 num_live_nodes: usize,
267 live_node_map: NodeMap<LiveNode>,
268 variable_map: NodeMap<Variable>,
269 capture_info_map: NodeMap<Rc<Vec<CaptureInfo>>>,
270 var_kinds: Vec<VarKind>,
271 lnks: Vec<LiveNodeKind>,
274 impl<'a, 'tcx> IrMaps<'a, 'tcx> {
275 fn new(tcx: &'a ty::ctxt<'tcx>) -> IrMaps<'a, 'tcx> {
280 live_node_map: NodeMap(),
281 variable_map: NodeMap(),
282 capture_info_map: NodeMap(),
283 var_kinds: Vec::new(),
288 fn add_live_node(&mut self, lnk: LiveNodeKind) -> LiveNode {
289 let ln = LiveNode(self.num_live_nodes);
291 self.num_live_nodes += 1;
293 debug!("{:?} is of kind {}", ln,
294 live_node_kind_to_string(lnk, self.tcx));
299 fn add_live_node_for_node(&mut self, node_id: NodeId, lnk: LiveNodeKind) {
300 let ln = self.add_live_node(lnk);
301 self.live_node_map.insert(node_id, ln);
303 debug!("{:?} is node {}", ln, node_id);
306 fn add_variable(&mut self, vk: VarKind) -> Variable {
307 let v = Variable(self.num_vars);
308 self.var_kinds.push(vk);
312 Local(LocalInfo { id: node_id, .. }) | Arg(node_id, _) => {
313 self.variable_map.insert(node_id, v);
315 ImplicitRet | CleanExit => {}
318 debug!("{:?} is {:?}", v, vk);
323 fn variable(&self, node_id: NodeId, span: Span) -> Variable {
324 match self.variable_map.get(&node_id) {
329 .span_bug(span, &format!("no variable registered for id {}",
335 fn variable_name(&self, var: Variable) -> String {
336 match self.var_kinds[var.get()] {
337 Local(LocalInfo { ident: nm, .. }) | Arg(_, nm) => {
338 token::get_ident(nm).to_string()
340 ImplicitRet => "<implicit-ret>".to_string(),
341 CleanExit => "<clean-exit>".to_string()
345 fn set_captures(&mut self, node_id: NodeId, cs: Vec<CaptureInfo>) {
346 self.capture_info_map.insert(node_id, Rc::new(cs));
349 fn lnk(&self, ln: LiveNode) -> LiveNodeKind {
354 impl<'a, 'tcx, 'v> Visitor<'v> for Liveness<'a, 'tcx> {
355 fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v ast::FnDecl,
356 b: &'v ast::Block, s: Span, n: NodeId) {
357 check_fn(self, fk, fd, b, s, n);
359 fn visit_local(&mut self, l: &ast::Local) {
360 check_local(self, l);
362 fn visit_expr(&mut self, ex: &Expr) {
363 check_expr(self, ex);
365 fn visit_arm(&mut self, a: &ast::Arm) {
370 fn visit_fn(ir: &mut IrMaps,
378 // swap in a new set of IR maps for this function body:
379 let mut fn_maps = IrMaps::new(ir.tcx);
381 debug!("creating fn_maps: {:?}", &fn_maps as *const IrMaps);
383 for arg in &decl.inputs {
384 pat_util::pat_bindings(&ir.tcx.def_map,
386 |_bm, arg_id, _x, path1| {
387 debug!("adding argument {}", arg_id);
388 let ident = path1.node;
389 fn_maps.add_variable(Arg(arg_id, ident));
393 // gather up the various local variables, significant expressions,
395 visit::walk_fn(&mut fn_maps, fk, decl, body, sp);
397 // Special nodes and variables:
398 // - exit_ln represents the end of the fn, either by return or panic
399 // - implicit_ret_var is a pseudo-variable that represents
400 // an implicit return
401 let specials = Specials {
402 exit_ln: fn_maps.add_live_node(ExitNode),
403 fallthrough_ln: fn_maps.add_live_node(ExitNode),
404 no_ret_var: fn_maps.add_variable(ImplicitRet),
405 clean_exit_var: fn_maps.add_variable(CleanExit)
409 let mut lsets = Liveness::new(&mut fn_maps, specials);
410 let entry_ln = lsets.compute(decl, body);
412 // check for various error conditions
413 lsets.visit_block(body);
414 lsets.check_ret(id, sp, fk, entry_ln, body);
415 lsets.warn_about_unused_args(decl, entry_ln);
418 fn visit_local(ir: &mut IrMaps, local: &ast::Local) {
419 pat_util::pat_bindings(&ir.tcx.def_map, &*local.pat, |_, p_id, sp, path1| {
420 debug!("adding local variable {}", p_id);
421 let name = path1.node;
422 ir.add_live_node_for_node(p_id, VarDefNode(sp));
423 ir.add_variable(Local(LocalInfo {
428 visit::walk_local(ir, local);
431 fn visit_arm(ir: &mut IrMaps, arm: &ast::Arm) {
432 for pat in &arm.pats {
433 pat_util::pat_bindings(&ir.tcx.def_map, &**pat, |bm, p_id, sp, path1| {
434 debug!("adding local variable {} from match with bm {:?}",
436 let name = path1.node;
437 ir.add_live_node_for_node(p_id, VarDefNode(sp));
438 ir.add_variable(Local(LocalInfo {
444 visit::walk_arm(ir, arm);
447 fn visit_expr(ir: &mut IrMaps, expr: &Expr) {
449 // live nodes required for uses or definitions of variables:
450 ast::ExprPath(..) => {
451 let def = ir.tcx.def_map.borrow()[expr.id].full_def();
452 debug!("expr {}: path that leads to {:?}", expr.id, def);
453 if let DefLocal(..) = def {
454 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
456 visit::walk_expr(ir, expr);
458 ast::ExprClosure(..) => {
459 // Interesting control flow (for loops can contain labeled
460 // breaks or continues)
461 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
463 // Make a live_node for each captured variable, with the span
464 // being the location that the variable is used. This results
465 // in better error messages than just pointing at the closure
466 // construction site.
467 let mut call_caps = Vec::new();
468 ty::with_freevars(ir.tcx, expr.id, |freevars| {
470 if let DefLocal(rv) = fv.def {
471 let fv_ln = ir.add_live_node(FreeVarNode(fv.span));
472 call_caps.push(CaptureInfo {ln: fv_ln,
477 ir.set_captures(expr.id, call_caps);
479 visit::walk_expr(ir, expr);
482 // live nodes required for interesting control flow:
483 ast::ExprIf(..) | ast::ExprMatch(..) | ast::ExprWhile(..) | ast::ExprLoop(..) => {
484 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
485 visit::walk_expr(ir, expr);
487 ast::ExprIfLet(..) => {
488 ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
490 ast::ExprWhileLet(..) => {
491 ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet");
493 ast::ExprForLoop(..) => {
494 ir.tcx.sess.span_bug(expr.span, "non-desugared ExprForLoop");
496 ast::ExprBinary(op, _, _) if ast_util::lazy_binop(op.node) => {
497 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
498 visit::walk_expr(ir, expr);
501 // otherwise, live nodes are not required:
502 ast::ExprIndex(..) | ast::ExprField(..) | ast::ExprTupField(..) |
503 ast::ExprVec(..) | ast::ExprCall(..) | ast::ExprMethodCall(..) |
504 ast::ExprTup(..) | ast::ExprBinary(..) | ast::ExprAddrOf(..) |
505 ast::ExprCast(..) | ast::ExprUnary(..) | ast::ExprBreak(_) |
506 ast::ExprAgain(_) | ast::ExprLit(_) | ast::ExprRet(..) |
507 ast::ExprBlock(..) | ast::ExprAssign(..) | ast::ExprAssignOp(..) |
508 ast::ExprMac(..) | ast::ExprStruct(..) | ast::ExprRepeat(..) |
509 ast::ExprParen(..) | ast::ExprInlineAsm(..) | ast::ExprBox(..) |
510 ast::ExprRange(..) => {
511 visit::walk_expr(ir, expr);
516 // ______________________________________________________________________
517 // Computing liveness sets
519 // Actually we compute just a bit more than just liveness, but we use
520 // the same basic propagation framework in all cases.
522 #[derive(Clone, Copy)]
529 fn invalid_users() -> Users {
531 reader: invalid_node(),
532 writer: invalid_node(),
540 fallthrough_ln: LiveNode,
541 no_ret_var: Variable,
542 clean_exit_var: Variable
545 const ACC_READ: u32 = 1;
546 const ACC_WRITE: u32 = 2;
547 const ACC_USE: u32 = 4;
549 struct Liveness<'a, 'tcx: 'a> {
550 ir: &'a mut IrMaps<'a, 'tcx>,
552 successors: Vec<LiveNode>,
554 // The list of node IDs for the nested loop scopes
556 loop_scope: Vec<NodeId>,
557 // mappings from loop node ID to LiveNode
558 // ("break" label should map to loop node ID,
559 // it probably doesn't now)
560 break_ln: NodeMap<LiveNode>,
561 cont_ln: NodeMap<LiveNode>
564 impl<'a, 'tcx> Liveness<'a, 'tcx> {
565 fn new(ir: &'a mut IrMaps<'a, 'tcx>, specials: Specials) -> Liveness<'a, 'tcx> {
566 let num_live_nodes = ir.num_live_nodes;
567 let num_vars = ir.num_vars;
571 successors: repeat(invalid_node()).take(num_live_nodes).collect(),
572 users: repeat(invalid_users()).take(num_live_nodes * num_vars).collect(),
573 loop_scope: Vec::new(),
579 fn live_node(&self, node_id: NodeId, span: Span) -> LiveNode {
580 match self.ir.live_node_map.get(&node_id) {
583 // This must be a mismatch between the ir_map construction
584 // above and the propagation code below; the two sets of
585 // code have to agree about which AST nodes are worth
586 // creating liveness nodes for.
587 self.ir.tcx.sess.span_bug(
589 &format!("no live node registered for node {}",
595 fn variable(&self, node_id: NodeId, span: Span) -> Variable {
596 self.ir.variable(node_id, span)
599 fn pat_bindings<F>(&mut self, pat: &ast::Pat, mut f: F) where
600 F: FnMut(&mut Liveness<'a, 'tcx>, LiveNode, Variable, Span, NodeId),
602 pat_util::pat_bindings(&self.ir.tcx.def_map, pat, |_bm, p_id, sp, _n| {
603 let ln = self.live_node(p_id, sp);
604 let var = self.variable(p_id, sp);
605 f(self, ln, var, sp, p_id);
609 fn arm_pats_bindings<F>(&mut self, pat: Option<&ast::Pat>, f: F) where
610 F: FnMut(&mut Liveness<'a, 'tcx>, LiveNode, Variable, Span, NodeId),
614 self.pat_bindings(pat, f);
620 fn define_bindings_in_pat(&mut self, pat: &ast::Pat, succ: LiveNode)
622 self.define_bindings_in_arm_pats(Some(pat), succ)
625 fn define_bindings_in_arm_pats(&mut self, pat: Option<&ast::Pat>, succ: LiveNode)
628 self.arm_pats_bindings(pat, |this, ln, var, _sp, _id| {
629 this.init_from_succ(ln, succ);
630 this.define(ln, var);
636 fn idx(&self, ln: LiveNode, var: Variable) -> usize {
637 ln.get() * self.ir.num_vars + var.get()
640 fn live_on_entry(&self, ln: LiveNode, var: Variable)
641 -> Option<LiveNodeKind> {
642 assert!(ln.is_valid());
643 let reader = self.users[self.idx(ln, var)].reader;
644 if reader.is_valid() {Some(self.ir.lnk(reader))} else {None}
648 Is this variable live on entry to any of its successor nodes?
650 fn live_on_exit(&self, ln: LiveNode, var: Variable)
651 -> Option<LiveNodeKind> {
652 let successor = self.successors[ln.get()];
653 self.live_on_entry(successor, var)
656 fn used_on_entry(&self, ln: LiveNode, var: Variable) -> bool {
657 assert!(ln.is_valid());
658 self.users[self.idx(ln, var)].used
661 fn assigned_on_entry(&self, ln: LiveNode, var: Variable)
662 -> Option<LiveNodeKind> {
663 assert!(ln.is_valid());
664 let writer = self.users[self.idx(ln, var)].writer;
665 if writer.is_valid() {Some(self.ir.lnk(writer))} else {None}
668 fn assigned_on_exit(&self, ln: LiveNode, var: Variable)
669 -> Option<LiveNodeKind> {
670 let successor = self.successors[ln.get()];
671 self.assigned_on_entry(successor, var)
674 fn indices2<F>(&mut self, ln: LiveNode, succ_ln: LiveNode, mut op: F) where
675 F: FnMut(&mut Liveness<'a, 'tcx>, usize, usize),
677 let node_base_idx = self.idx(ln, Variable(0));
678 let succ_base_idx = self.idx(succ_ln, Variable(0));
679 for var_idx in 0..self.ir.num_vars {
680 op(self, node_base_idx + var_idx, succ_base_idx + var_idx);
684 fn write_vars<F>(&self,
688 -> io::Result<()> where
689 F: FnMut(usize) -> LiveNode,
691 let node_base_idx = self.idx(ln, Variable(0));
692 for var_idx in 0..self.ir.num_vars {
693 let idx = node_base_idx + var_idx;
694 if test(idx).is_valid() {
695 try!(write!(wr, " {:?}", Variable(var_idx)));
701 fn find_loop_scope(&self,
702 opt_label: Option<ast::Ident>,
708 // Refers to a labeled loop. Use the results of resolve
710 match self.ir.tcx.def_map.borrow().get(&id).map(|d| d.full_def()) {
711 Some(DefLabel(loop_id)) => loop_id,
712 _ => self.ir.tcx.sess.span_bug(sp, "label on break/loop \
713 doesn't refer to a loop")
717 // Vanilla 'break' or 'loop', so use the enclosing
719 if self.loop_scope.len() == 0 {
720 self.ir.tcx.sess.span_bug(sp, "break outside loop");
722 *self.loop_scope.last().unwrap()
728 #[allow(unused_must_use)]
729 fn ln_str(&self, ln: LiveNode) -> String {
730 let mut wr = Vec::new();
732 let wr = &mut wr as &mut Write;
733 write!(wr, "[ln({:?}) of kind {:?} reads", ln.get(), self.ir.lnk(ln));
734 self.write_vars(wr, ln, |idx| self.users[idx].reader);
735 write!(wr, " writes");
736 self.write_vars(wr, ln, |idx| self.users[idx].writer);
737 write!(wr, " precedes {:?}]", self.successors[ln.get()]);
739 String::from_utf8(wr).unwrap()
742 fn init_empty(&mut self, ln: LiveNode, succ_ln: LiveNode) {
743 self.successors[ln.get()] = succ_ln;
745 // It is not necessary to initialize the
746 // values to empty because this is the value
747 // they have when they are created, and the sets
748 // only grow during iterations.
750 // self.indices(ln) { |idx|
751 // self.users[idx] = invalid_users();
755 fn init_from_succ(&mut self, ln: LiveNode, succ_ln: LiveNode) {
756 // more efficient version of init_empty() / merge_from_succ()
757 self.successors[ln.get()] = succ_ln;
759 self.indices2(ln, succ_ln, |this, idx, succ_idx| {
760 this.users[idx] = this.users[succ_idx]
762 debug!("init_from_succ(ln={}, succ={})",
763 self.ln_str(ln), self.ln_str(succ_ln));
766 fn merge_from_succ(&mut self,
771 if ln == succ_ln { return false; }
773 let mut changed = false;
774 self.indices2(ln, succ_ln, |this, idx, succ_idx| {
775 changed |= copy_if_invalid(this.users[succ_idx].reader,
776 &mut this.users[idx].reader);
777 changed |= copy_if_invalid(this.users[succ_idx].writer,
778 &mut this.users[idx].writer);
779 if this.users[succ_idx].used && !this.users[idx].used {
780 this.users[idx].used = true;
785 debug!("merge_from_succ(ln={:?}, succ={}, first_merge={}, changed={})",
786 ln, self.ln_str(succ_ln), first_merge, changed);
789 fn copy_if_invalid(src: LiveNode, dst: &mut LiveNode) -> bool {
790 if src.is_valid() && !dst.is_valid() {
799 // Indicates that a local variable was *defined*; we know that no
800 // uses of the variable can precede the definition (resolve checks
801 // this) so we just clear out all the data.
802 fn define(&mut self, writer: LiveNode, var: Variable) {
803 let idx = self.idx(writer, var);
804 self.users[idx].reader = invalid_node();
805 self.users[idx].writer = invalid_node();
807 debug!("{:?} defines {:?} (idx={}): {}", writer, var,
808 idx, self.ln_str(writer));
811 // Either read, write, or both depending on the acc bitset
812 fn acc(&mut self, ln: LiveNode, var: Variable, acc: u32) {
813 debug!("{:?} accesses[{:x}] {:?}: {}",
814 ln, acc, var, self.ln_str(ln));
816 let idx = self.idx(ln, var);
817 let user = &mut self.users[idx];
819 if (acc & ACC_WRITE) != 0 {
820 user.reader = invalid_node();
824 // Important: if we both read/write, must do read second
825 // or else the write will override.
826 if (acc & ACC_READ) != 0 {
830 if (acc & ACC_USE) != 0 {
835 // _______________________________________________________________________
837 fn compute(&mut self, decl: &ast::FnDecl, body: &ast::Block) -> LiveNode {
838 // if there is a `break` or `again` at the top level, then it's
839 // effectively a return---this only occurs in `for` loops,
840 // where the body is really a closure.
842 debug!("compute: using id for block, {}", block_to_string(body));
844 let exit_ln = self.s.exit_ln;
845 let entry_ln: LiveNode =
846 self.with_loop_nodes(body.id, exit_ln, exit_ln,
847 |this| this.propagate_through_fn_block(decl, body));
849 // hack to skip the loop unless debug! is enabled:
850 debug!("^^ liveness computation results for body {} (entry={:?})",
852 for ln_idx in 0..self.ir.num_live_nodes {
853 debug!("{:?}", self.ln_str(LiveNode(ln_idx)));
862 fn propagate_through_fn_block(&mut self, _: &ast::FnDecl, blk: &ast::Block)
864 // the fallthrough exit is only for those cases where we do not
865 // explicitly return:
867 self.init_from_succ(s.fallthrough_ln, s.exit_ln);
868 if blk.expr.is_none() {
869 self.acc(s.fallthrough_ln, s.no_ret_var, ACC_READ)
871 self.acc(s.fallthrough_ln, s.clean_exit_var, ACC_READ);
873 self.propagate_through_block(blk, s.fallthrough_ln)
876 fn propagate_through_block(&mut self, blk: &ast::Block, succ: LiveNode)
878 let succ = self.propagate_through_opt_expr(blk.expr.as_ref().map(|e| &**e), succ);
879 blk.stmts.iter().rev().fold(succ, |succ, stmt| {
880 self.propagate_through_stmt(&**stmt, succ)
884 fn propagate_through_stmt(&mut self, stmt: &ast::Stmt, succ: LiveNode)
887 ast::StmtDecl(ref decl, _) => {
888 self.propagate_through_decl(&**decl, succ)
891 ast::StmtExpr(ref expr, _) | ast::StmtSemi(ref expr, _) => {
892 self.propagate_through_expr(&**expr, succ)
895 ast::StmtMac(..) => {
896 self.ir.tcx.sess.span_bug(stmt.span, "unexpanded macro");
901 fn propagate_through_decl(&mut self, decl: &ast::Decl, succ: LiveNode)
904 ast::DeclLocal(ref local) => {
905 self.propagate_through_local(&**local, succ)
907 ast::DeclItem(_) => succ,
911 fn propagate_through_local(&mut self, local: &ast::Local, succ: LiveNode)
913 // Note: we mark the variable as defined regardless of whether
914 // there is an initializer. Initially I had thought to only mark
915 // the live variable as defined if it was initialized, and then we
916 // could check for uninit variables just by scanning what is live
917 // at the start of the function. But that doesn't work so well for
918 // immutable variables defined in a loop:
919 // loop { let x; x = 5; }
920 // because the "assignment" loops back around and generates an error.
922 // So now we just check that variables defined w/o an
923 // initializer are not live at the point of their
924 // initialization, which is mildly more complex than checking
925 // once at the func header but otherwise equivalent.
927 let succ = self.propagate_through_opt_expr(local.init.as_ref().map(|e| &**e), succ);
928 self.define_bindings_in_pat(&*local.pat, succ)
931 fn propagate_through_exprs(&mut self, exprs: &[P<Expr>], succ: LiveNode)
933 exprs.iter().rev().fold(succ, |succ, expr| {
934 self.propagate_through_expr(&**expr, succ)
938 fn propagate_through_opt_expr(&mut self,
939 opt_expr: Option<&Expr>,
942 opt_expr.map_or(succ, |expr| self.propagate_through_expr(expr, succ))
945 fn propagate_through_expr(&mut self, expr: &Expr, succ: LiveNode)
947 debug!("propagate_through_expr: {}", expr_to_string(expr));
950 // Interesting cases with control flow or which gen/kill
952 ast::ExprPath(..) => {
953 self.access_path(expr, succ, ACC_READ | ACC_USE)
956 ast::ExprField(ref e, _) => {
957 self.propagate_through_expr(&**e, succ)
960 ast::ExprTupField(ref e, _) => {
961 self.propagate_through_expr(&**e, succ)
964 ast::ExprClosure(_, _, ref blk) => {
965 debug!("{} is an ExprClosure",
966 expr_to_string(expr));
969 The next-node for a break is the successor of the entire
970 loop. The next-node for a continue is the top of this loop.
972 let node = self.live_node(expr.id, expr.span);
973 self.with_loop_nodes(blk.id, succ, node, |this| {
975 // the construction of a closure itself is not important,
976 // but we have to consider the closed over variables.
977 let caps = match this.ir.capture_info_map.get(&expr.id) {
978 Some(caps) => caps.clone(),
980 this.ir.tcx.sess.span_bug(expr.span, "no registered caps");
983 caps.iter().rev().fold(succ, |succ, cap| {
984 this.init_from_succ(cap.ln, succ);
985 let var = this.variable(cap.var_nid, expr.span);
986 this.acc(cap.ln, var, ACC_READ | ACC_USE);
992 ast::ExprIf(ref cond, ref then, ref els) => {
1006 let else_ln = self.propagate_through_opt_expr(els.as_ref().map(|e| &**e), succ);
1007 let then_ln = self.propagate_through_block(&**then, succ);
1008 let ln = self.live_node(expr.id, expr.span);
1009 self.init_from_succ(ln, else_ln);
1010 self.merge_from_succ(ln, then_ln, false);
1011 self.propagate_through_expr(&**cond, ln)
1014 ast::ExprIfLet(..) => {
1015 self.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
1018 ast::ExprWhile(ref cond, ref blk, _) => {
1019 self.propagate_through_loop(expr, WhileLoop(&**cond), &**blk, succ)
1022 ast::ExprWhileLet(..) => {
1023 self.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet");
1026 ast::ExprForLoop(..) => {
1027 self.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprForLoop");
1030 // Note that labels have been resolved, so we don't need to look
1031 // at the label ident
1032 ast::ExprLoop(ref blk, _) => {
1033 self.propagate_through_loop(expr, LoopLoop, &**blk, succ)
1036 ast::ExprMatch(ref e, ref arms, _) => {
1051 let ln = self.live_node(expr.id, expr.span);
1052 self.init_empty(ln, succ);
1053 let mut first_merge = true;
1056 self.propagate_through_expr(&*arm.body, succ);
1058 self.propagate_through_opt_expr(arm.guard.as_ref().map(|e| &**e), body_succ);
1059 // only consider the first pattern; any later patterns must have
1060 // the same bindings, and we also consider the first pattern to be
1061 // the "authoritative" set of ids
1063 self.define_bindings_in_arm_pats(arm.pats.first().map(|p| &**p),
1065 self.merge_from_succ(ln, arm_succ, first_merge);
1066 first_merge = false;
1068 self.propagate_through_expr(&**e, ln)
1071 ast::ExprRet(ref o_e) => {
1072 // ignore succ and subst exit_ln:
1073 let exit_ln = self.s.exit_ln;
1074 self.propagate_through_opt_expr(o_e.as_ref().map(|e| &**e), exit_ln)
1077 ast::ExprBreak(opt_label) => {
1078 // Find which label this break jumps to
1079 let sc = self.find_loop_scope(opt_label, expr.id, expr.span);
1081 // Now that we know the label we're going to,
1082 // look it up in the break loop nodes table
1084 match self.break_ln.get(&sc) {
1086 None => self.ir.tcx.sess.span_bug(expr.span,
1087 "break to unknown label")
1091 ast::ExprAgain(opt_label) => {
1092 // Find which label this expr continues to
1093 let sc = self.find_loop_scope(opt_label, expr.id, expr.span);
1095 // Now that we know the label we're going to,
1096 // look it up in the continue loop nodes table
1098 match self.cont_ln.get(&sc) {
1100 None => self.ir.tcx.sess.span_bug(expr.span,
1101 "loop to unknown label")
1105 ast::ExprAssign(ref l, ref r) => {
1106 // see comment on lvalues in
1107 // propagate_through_lvalue_components()
1108 let succ = self.write_lvalue(&**l, succ, ACC_WRITE);
1109 let succ = self.propagate_through_lvalue_components(&**l, succ);
1110 self.propagate_through_expr(&**r, succ)
1113 ast::ExprAssignOp(_, ref l, ref r) => {
1114 // see comment on lvalues in
1115 // propagate_through_lvalue_components()
1116 let succ = self.write_lvalue(&**l, succ, ACC_WRITE|ACC_READ);
1117 let succ = self.propagate_through_expr(&**r, succ);
1118 self.propagate_through_lvalue_components(&**l, succ)
1121 // Uninteresting cases: just propagate in rev exec order
1123 ast::ExprVec(ref exprs) => {
1124 self.propagate_through_exprs(&exprs[..], succ)
1127 ast::ExprRepeat(ref element, ref count) => {
1128 let succ = self.propagate_through_expr(&**count, succ);
1129 self.propagate_through_expr(&**element, succ)
1132 ast::ExprStruct(_, ref fields, ref with_expr) => {
1133 let succ = self.propagate_through_opt_expr(with_expr.as_ref().map(|e| &**e), succ);
1134 fields.iter().rev().fold(succ, |succ, field| {
1135 self.propagate_through_expr(&*field.expr, succ)
1139 ast::ExprCall(ref f, ref args) => {
1140 let diverges = !self.ir.tcx.is_method_call(expr.id) && {
1141 ty::ty_fn_ret(ty::expr_ty_adjusted(self.ir.tcx, &**f)).diverges()
1143 let succ = if diverges {
1148 let succ = self.propagate_through_exprs(&args[..], succ);
1149 self.propagate_through_expr(&**f, succ)
1152 ast::ExprMethodCall(_, _, ref args) => {
1153 let method_call = ty::MethodCall::expr(expr.id);
1154 let method_ty = self.ir.tcx.method_map.borrow().get(&method_call).unwrap().ty;
1155 let diverges = ty::ty_fn_ret(method_ty).diverges();
1156 let succ = if diverges {
1161 self.propagate_through_exprs(&args[..], succ)
1164 ast::ExprTup(ref exprs) => {
1165 self.propagate_through_exprs(&exprs[..], succ)
1168 ast::ExprBinary(op, ref l, ref r) if ast_util::lazy_binop(op.node) => {
1169 let r_succ = self.propagate_through_expr(&**r, succ);
1171 let ln = self.live_node(expr.id, expr.span);
1172 self.init_from_succ(ln, succ);
1173 self.merge_from_succ(ln, r_succ, false);
1175 self.propagate_through_expr(&**l, ln)
1178 ast::ExprIndex(ref l, ref r) |
1179 ast::ExprBinary(_, ref l, ref r) |
1180 ast::ExprBox(Some(ref l), ref r) => {
1181 let r_succ = self.propagate_through_expr(&**r, succ);
1182 self.propagate_through_expr(&**l, r_succ)
1185 ast::ExprRange(ref e1, ref e2) => {
1186 let succ = e2.as_ref().map_or(succ, |e| self.propagate_through_expr(&**e, succ));
1187 e1.as_ref().map_or(succ, |e| self.propagate_through_expr(&**e, succ))
1190 ast::ExprBox(None, ref e) |
1191 ast::ExprAddrOf(_, ref e) |
1192 ast::ExprCast(ref e, _) |
1193 ast::ExprUnary(_, ref e) |
1194 ast::ExprParen(ref e) => {
1195 self.propagate_through_expr(&**e, succ)
1198 ast::ExprInlineAsm(ref ia) => {
1200 let succ = ia.outputs.iter().rev().fold(succ, |succ, &(_, ref expr, _)| {
1201 // see comment on lvalues
1202 // in propagate_through_lvalue_components()
1203 let succ = self.write_lvalue(&**expr, succ, ACC_WRITE);
1204 self.propagate_through_lvalue_components(&**expr, succ)
1206 // Inputs are executed first. Propagate last because of rev order
1207 ia.inputs.iter().rev().fold(succ, |succ, &(_, ref expr)| {
1208 self.propagate_through_expr(&**expr, succ)
1212 ast::ExprLit(..) => {
1216 ast::ExprBlock(ref blk) => {
1217 self.propagate_through_block(&**blk, succ)
1220 ast::ExprMac(..) => {
1221 self.ir.tcx.sess.span_bug(expr.span, "unexpanded macro");
1226 fn propagate_through_lvalue_components(&mut self,
1232 // In general, the full flow graph structure for an
1233 // assignment/move/etc can be handled in one of two ways,
1234 // depending on whether what is being assigned is a "tracked
1235 // value" or not. A tracked value is basically a local
1236 // variable or argument.
1238 // The two kinds of graphs are:
1240 // Tracked lvalue Untracked lvalue
1241 // ----------------------++-----------------------
1245 // (rvalue) || (rvalue)
1248 // (write of lvalue) || (lvalue components)
1253 // ----------------------++-----------------------
1255 // I will cover the two cases in turn:
1257 // # Tracked lvalues
1259 // A tracked lvalue is a local variable/argument `x`. In
1260 // these cases, the link_node where the write occurs is linked
1261 // to node id of `x`. The `write_lvalue()` routine generates
1262 // the contents of this node. There are no subcomponents to
1265 // # Non-tracked lvalues
1267 // These are lvalues like `x[5]` or `x.f`. In that case, we
1268 // basically ignore the value which is written to but generate
1269 // reads for the components---`x` in these two examples. The
1270 // components reads are generated by
1271 // `propagate_through_lvalue_components()` (this fn).
1273 // # Illegal lvalues
1275 // It is still possible to observe assignments to non-lvalues;
1276 // these errors are detected in the later pass borrowck. We
1277 // just ignore such cases and treat them as reads.
1280 ast::ExprPath(..) => succ,
1281 ast::ExprField(ref e, _) => self.propagate_through_expr(&**e, succ),
1282 ast::ExprTupField(ref e, _) => self.propagate_through_expr(&**e, succ),
1283 _ => self.propagate_through_expr(expr, succ)
1287 // see comment on propagate_through_lvalue()
1288 fn write_lvalue(&mut self, expr: &Expr, succ: LiveNode, acc: u32)
1291 ast::ExprPath(..) => {
1292 self.access_path(expr, succ, acc)
1295 // We do not track other lvalues, so just propagate through
1296 // to their subcomponents. Also, it may happen that
1297 // non-lvalues occur here, because those are detected in the
1298 // later pass borrowck.
1303 fn access_path(&mut self, expr: &Expr, succ: LiveNode, acc: u32)
1305 match self.ir.tcx.def_map.borrow()[expr.id].full_def() {
1307 let ln = self.live_node(expr.id, expr.span);
1309 self.init_from_succ(ln, succ);
1310 let var = self.variable(nid, expr.span);
1311 self.acc(ln, var, acc);
1319 fn propagate_through_loop(&mut self,
1328 We model control flow like this:
1346 let mut first_merge = true;
1347 let ln = self.live_node(expr.id, expr.span);
1348 self.init_empty(ln, succ);
1352 // If this is not a `loop` loop, then it's possible we bypass
1353 // the body altogether. Otherwise, the only way is via a `break`
1354 // in the loop body.
1355 self.merge_from_succ(ln, succ, first_merge);
1356 first_merge = false;
1359 debug!("propagate_through_loop: using id for loop body {} {}",
1360 expr.id, block_to_string(body));
1362 let cond_ln = match kind {
1364 WhileLoop(ref cond) => self.propagate_through_expr(&**cond, ln),
1366 let body_ln = self.with_loop_nodes(expr.id, succ, ln, |this| {
1367 this.propagate_through_block(body, cond_ln)
1370 // repeat until fixed point is reached:
1371 while self.merge_from_succ(ln, body_ln, first_merge) {
1372 first_merge = false;
1374 let new_cond_ln = match kind {
1376 WhileLoop(ref cond) => {
1377 self.propagate_through_expr(&**cond, ln)
1380 assert!(cond_ln == new_cond_ln);
1381 assert!(body_ln == self.with_loop_nodes(expr.id, succ, ln,
1382 |this| this.propagate_through_block(body, cond_ln)));
1388 fn with_loop_nodes<R, F>(&mut self,
1389 loop_node_id: NodeId,
1394 F: FnOnce(&mut Liveness<'a, 'tcx>) -> R,
1396 debug!("with_loop_nodes: {} {}", loop_node_id, break_ln.get());
1397 self.loop_scope.push(loop_node_id);
1398 self.break_ln.insert(loop_node_id, break_ln);
1399 self.cont_ln.insert(loop_node_id, cont_ln);
1401 self.loop_scope.pop();
1406 // _______________________________________________________________________
1407 // Checking for error conditions
1409 fn check_local(this: &mut Liveness, local: &ast::Local) {
1412 this.warn_about_unused_or_dead_vars_in_pat(&*local.pat);
1415 this.pat_bindings(&*local.pat, |this, ln, var, sp, id| {
1416 this.warn_about_unused(sp, id, ln, var);
1421 visit::walk_local(this, local);
1424 fn check_arm(this: &mut Liveness, arm: &ast::Arm) {
1425 // only consider the first pattern; any later patterns must have
1426 // the same bindings, and we also consider the first pattern to be
1427 // the "authoritative" set of ids
1428 this.arm_pats_bindings(arm.pats.first().map(|p| &**p), |this, ln, var, sp, id| {
1429 this.warn_about_unused(sp, id, ln, var);
1431 visit::walk_arm(this, arm);
1434 fn check_expr(this: &mut Liveness, expr: &Expr) {
1436 ast::ExprAssign(ref l, ref r) => {
1437 this.check_lvalue(&**l);
1438 this.visit_expr(&**r);
1440 visit::walk_expr(this, expr);
1443 ast::ExprAssignOp(_, ref l, _) => {
1444 this.check_lvalue(&**l);
1446 visit::walk_expr(this, expr);
1449 ast::ExprInlineAsm(ref ia) => {
1450 for &(_, ref input) in &ia.inputs {
1451 this.visit_expr(&**input);
1454 // Output operands must be lvalues
1455 for &(_, ref out, _) in &ia.outputs {
1456 this.check_lvalue(&**out);
1457 this.visit_expr(&**out);
1460 visit::walk_expr(this, expr);
1463 // no correctness conditions related to liveness
1464 ast::ExprCall(..) | ast::ExprMethodCall(..) | ast::ExprIf(..) |
1465 ast::ExprMatch(..) | ast::ExprWhile(..) | ast::ExprLoop(..) |
1466 ast::ExprIndex(..) | ast::ExprField(..) | ast::ExprTupField(..) |
1467 ast::ExprVec(..) | ast::ExprTup(..) | ast::ExprBinary(..) |
1468 ast::ExprCast(..) | ast::ExprUnary(..) | ast::ExprRet(..) |
1469 ast::ExprBreak(..) | ast::ExprAgain(..) | ast::ExprLit(_) |
1470 ast::ExprBlock(..) | ast::ExprMac(..) | ast::ExprAddrOf(..) |
1471 ast::ExprStruct(..) | ast::ExprRepeat(..) | ast::ExprParen(..) |
1472 ast::ExprClosure(..) | ast::ExprPath(..) | ast::ExprBox(..) |
1473 ast::ExprRange(..) => {
1474 visit::walk_expr(this, expr);
1476 ast::ExprIfLet(..) => {
1477 this.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
1479 ast::ExprWhileLet(..) => {
1480 this.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet");
1482 ast::ExprForLoop(..) => {
1483 this.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprForLoop");
1488 fn check_fn(_v: &Liveness,
1490 _decl: &ast::FnDecl,
1494 // do not check contents of nested fns
1497 impl<'a, 'tcx> Liveness<'a, 'tcx> {
1498 fn fn_ret(&self, id: NodeId) -> ty::PolyFnOutput<'tcx> {
1499 let fn_ty = ty::node_id_to_type(self.ir.tcx, id);
1501 ty::ty_closure(closure_def_id, substs) =>
1502 self.ir.tcx.closure_type(closure_def_id, substs).sig.output(),
1504 ty::ty_fn_ret(fn_ty),
1515 // within the fn body, late-bound regions are liberated:
1517 ty::liberate_late_bound_regions(
1519 region::DestructionScopeData::new(body.id),
1523 ty::FnConverging(t_ret)
1524 if self.live_on_entry(entry_ln, self.s.no_ret_var).is_some() => {
1526 if ty::type_is_nil(t_ret) {
1527 // for nil return types, it is ok to not return a value expl.
1529 let ends_with_stmt = match body.expr {
1530 None if body.stmts.len() > 0 =>
1531 match body.stmts.first().unwrap().node {
1532 ast::StmtSemi(ref e, _) => {
1533 ty::expr_ty(self.ir.tcx, &**e) == t_ret
1539 span_err!(self.ir.tcx.sess, sp, E0269, "not all control paths return a value");
1541 let last_stmt = body.stmts.first().unwrap();
1542 let original_span = original_sp(self.ir.tcx.sess.codemap(),
1543 last_stmt.span, sp);
1544 let span_semicolon = Span {
1545 lo: original_span.hi - BytePos(1),
1546 hi: original_span.hi,
1547 expn_id: original_span.expn_id
1549 self.ir.tcx.sess.span_help(
1550 span_semicolon, "consider removing this semicolon:");
1555 if self.live_on_entry(entry_ln, self.s.clean_exit_var).is_some() => {
1556 span_err!(self.ir.tcx.sess, sp, E0270,
1557 "computation may converge in a function marked as diverging");
1564 fn check_lvalue(&mut self, expr: &Expr) {
1566 ast::ExprPath(..) => {
1567 if let DefLocal(nid) = self.ir.tcx.def_map.borrow()[expr.id].full_def() {
1568 // Assignment to an immutable variable or argument: only legal
1569 // if there is no later assignment. If this local is actually
1570 // mutable, then check for a reassignment to flag the mutability
1572 let ln = self.live_node(expr.id, expr.span);
1573 let var = self.variable(nid, expr.span);
1574 self.warn_about_dead_assign(expr.span, expr.id, ln, var);
1578 // For other kinds of lvalues, no checks are required,
1579 // and any embedded expressions are actually rvalues
1580 visit::walk_expr(self, expr);
1585 fn should_warn(&self, var: Variable) -> Option<String> {
1586 let name = self.ir.variable_name(var);
1587 if name.len() == 0 || name.as_bytes()[0] == ('_' as u8) {
1594 fn warn_about_unused_args(&self, decl: &ast::FnDecl, entry_ln: LiveNode) {
1595 for arg in &decl.inputs {
1596 pat_util::pat_bindings(&self.ir.tcx.def_map,
1598 |_bm, p_id, sp, path1| {
1599 let var = self.variable(p_id, sp);
1600 // Ignore unused self.
1601 let ident = path1.node;
1602 if ident.name != special_idents::self_.name {
1603 self.warn_about_unused(sp, p_id, entry_ln, var);
1609 fn warn_about_unused_or_dead_vars_in_pat(&mut self, pat: &ast::Pat) {
1610 self.pat_bindings(pat, |this, ln, var, sp, id| {
1611 if !this.warn_about_unused(sp, id, ln, var) {
1612 this.warn_about_dead_assign(sp, id, ln, var);
1617 fn warn_about_unused(&self,
1623 if !self.used_on_entry(ln, var) {
1624 let r = self.should_warn(var);
1625 if let Some(name) = r {
1627 // annoying: for parameters in funcs like `fn(x: int)
1628 // {ret}`, there is only one node, so asking about
1629 // assigned_on_exit() is not meaningful.
1630 let is_assigned = if ln == self.s.exit_ln {
1633 self.assigned_on_exit(ln, var).is_some()
1637 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_VARIABLES, id, sp,
1638 format!("variable `{}` is assigned to, but never used",
1641 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_VARIABLES, id, sp,
1642 format!("unused variable: `{}`", name));
1651 fn warn_about_dead_assign(&self,
1656 if self.live_on_exit(ln, var).is_none() {
1657 let r = self.should_warn(var);
1658 if let Some(name) = r {
1659 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_ASSIGNMENTS, id, sp,
1660 format!("value assigned to `{}` is never read", name));