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;
116 use middle::ty::UnboxedClosureTyper;
118 use util::nodemap::NodeMap;
120 use std::{fmt, io, uint};
122 use std::iter::repeat;
123 use syntax::ast::{self, NodeId, Expr};
124 use syntax::codemap::{BytePos, original_sp, Span};
125 use syntax::parse::token::{self, special_idents};
126 use syntax::print::pprust::{expr_to_string, block_to_string};
128 use syntax::ast_util;
129 use syntax::visit::{self, Visitor, FnKind};
131 /// For use with `propagate_through_loop`.
133 /// An endless `loop` loop.
135 /// A `while` loop, with the given expression as condition.
137 /// A `for` loop, with the given pattern to bind.
138 ForLoop(&'a ast::Pat),
141 #[derive(Copy, PartialEq)]
142 struct Variable(uint);
144 #[derive(Copy, PartialEq)]
145 struct LiveNode(uint);
148 fn get(&self) -> uint { let Variable(v) = *self; v }
152 fn get(&self) -> uint { let LiveNode(v) = *self; v }
155 impl Clone for LiveNode {
156 fn clone(&self) -> LiveNode {
161 #[derive(Copy, PartialEq, Show)]
169 fn live_node_kind_to_string(lnk: LiveNodeKind, cx: &ty::ctxt) -> String {
170 let cm = cx.sess.codemap();
173 format!("Free var node [{}]", cm.span_to_string(s))
176 format!("Expr node [{}]", cm.span_to_string(s))
179 format!("Var def node [{}]", cm.span_to_string(s))
181 ExitNode => "Exit node".to_string(),
185 impl<'a, 'tcx, 'v> Visitor<'v> for IrMaps<'a, 'tcx> {
186 fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v ast::FnDecl,
187 b: &'v ast::Block, s: Span, id: NodeId) {
188 visit_fn(self, fk, fd, b, s, id);
190 fn visit_local(&mut self, l: &ast::Local) { visit_local(self, l); }
191 fn visit_expr(&mut self, ex: &Expr) { visit_expr(self, ex); }
192 fn visit_arm(&mut self, a: &ast::Arm) { visit_arm(self, a); }
195 pub fn check_crate(tcx: &ty::ctxt) {
196 visit::walk_crate(&mut IrMaps::new(tcx), tcx.map.krate());
197 tcx.sess.abort_if_errors();
200 impl fmt::Show for LiveNode {
201 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
202 write!(f, "ln({})", self.get())
206 impl fmt::Show for Variable {
207 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
208 write!(f, "v({})", self.get())
212 // ______________________________________________________________________
215 // This is the first pass and the one that drives the main
216 // computation. It walks up and down the IR once. On the way down,
217 // we count for each function the number of variables as well as
218 // liveness nodes. A liveness node is basically an expression or
219 // capture clause that does something of interest: either it has
220 // interesting control flow or it uses/defines a local variable.
222 // On the way back up, at each function node we create liveness sets
223 // (we now know precisely how big to make our various vectors and so
224 // forth) and then do the data-flow propagation to compute the set
225 // of live variables at each program point.
227 // Finally, we run back over the IR one last time and, using the
228 // computed liveness, check various safety conditions. For example,
229 // there must be no live nodes at the definition site for a variable
230 // unless it has an initializer. Similarly, each non-mutable local
231 // variable must not be assigned if there is some successor
232 // assignment. And so forth.
235 fn is_valid(&self) -> bool {
236 self.get() != uint::MAX
240 fn invalid_node() -> LiveNode { LiveNode(uint::MAX) }
247 #[derive(Copy, Show)]
253 #[derive(Copy, Show)]
255 Arg(NodeId, ast::Ident),
261 struct IrMaps<'a, 'tcx: 'a> {
262 tcx: &'a ty::ctxt<'tcx>,
264 num_live_nodes: uint,
266 live_node_map: NodeMap<LiveNode>,
267 variable_map: NodeMap<Variable>,
268 capture_info_map: NodeMap<Rc<Vec<CaptureInfo>>>,
269 var_kinds: Vec<VarKind>,
270 lnks: Vec<LiveNodeKind>,
273 impl<'a, 'tcx> IrMaps<'a, 'tcx> {
274 fn new(tcx: &'a ty::ctxt<'tcx>) -> IrMaps<'a, 'tcx> {
279 live_node_map: NodeMap::new(),
280 variable_map: NodeMap::new(),
281 capture_info_map: NodeMap::new(),
282 var_kinds: Vec::new(),
287 fn add_live_node(&mut self, lnk: LiveNodeKind) -> LiveNode {
288 let ln = LiveNode(self.num_live_nodes);
290 self.num_live_nodes += 1;
292 debug!("{} is of kind {}", ln.to_string(),
293 live_node_kind_to_string(lnk, self.tcx));
298 fn add_live_node_for_node(&mut self, node_id: NodeId, lnk: LiveNodeKind) {
299 let ln = self.add_live_node(lnk);
300 self.live_node_map.insert(node_id, ln);
302 debug!("{} is node {}", ln.to_string(), node_id);
305 fn add_variable(&mut self, vk: VarKind) -> Variable {
306 let v = Variable(self.num_vars);
307 self.var_kinds.push(vk);
311 Local(LocalInfo { id: node_id, .. }) | Arg(node_id, _) => {
312 self.variable_map.insert(node_id, v);
314 ImplicitRet | CleanExit => {}
317 debug!("{} is {}", v.to_string(), vk);
322 fn variable(&self, node_id: NodeId, span: Span) -> Variable {
323 match self.variable_map.get(&node_id) {
328 .span_bug(span, format!("no variable registered for id {}",
334 fn variable_name(&self, var: Variable) -> String {
335 match self.var_kinds[var.get()] {
336 Local(LocalInfo { ident: nm, .. }) | Arg(_, nm) => {
337 token::get_ident(nm).get().to_string()
339 ImplicitRet => "<implicit-ret>".to_string(),
340 CleanExit => "<clean-exit>".to_string()
344 fn set_captures(&mut self, node_id: NodeId, cs: Vec<CaptureInfo>) {
345 self.capture_info_map.insert(node_id, Rc::new(cs));
348 fn lnk(&self, ln: LiveNode) -> LiveNodeKind {
353 impl<'a, 'tcx, 'v> Visitor<'v> for Liveness<'a, 'tcx> {
354 fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v ast::FnDecl,
355 b: &'v ast::Block, s: Span, n: NodeId) {
356 check_fn(self, fk, fd, b, s, n);
358 fn visit_local(&mut self, l: &ast::Local) {
359 check_local(self, l);
361 fn visit_expr(&mut self, ex: &Expr) {
362 check_expr(self, ex);
364 fn visit_arm(&mut self, a: &ast::Arm) {
369 fn visit_fn(ir: &mut IrMaps,
377 // swap in a new set of IR maps for this function body:
378 let mut fn_maps = IrMaps::new(ir.tcx);
380 debug!("creating fn_maps: {}", &fn_maps as *const IrMaps);
382 for arg in decl.inputs.iter() {
383 pat_util::pat_bindings(&ir.tcx.def_map,
385 |_bm, arg_id, _x, path1| {
386 debug!("adding argument {}", arg_id);
387 let ident = path1.node;
388 fn_maps.add_variable(Arg(arg_id, ident));
392 // gather up the various local variables, significant expressions,
394 visit::walk_fn(&mut fn_maps, fk, decl, body, sp);
396 // Special nodes and variables:
397 // - exit_ln represents the end of the fn, either by return or panic
398 // - implicit_ret_var is a pseudo-variable that represents
399 // an implicit return
400 let specials = Specials {
401 exit_ln: fn_maps.add_live_node(ExitNode),
402 fallthrough_ln: fn_maps.add_live_node(ExitNode),
403 no_ret_var: fn_maps.add_variable(ImplicitRet),
404 clean_exit_var: fn_maps.add_variable(CleanExit)
408 let mut lsets = Liveness::new(&mut fn_maps, specials);
409 let entry_ln = lsets.compute(decl, body);
411 // check for various error conditions
412 lsets.visit_block(body);
413 lsets.check_ret(id, sp, fk, entry_ln, body);
414 lsets.warn_about_unused_args(decl, entry_ln);
417 fn visit_local(ir: &mut IrMaps, local: &ast::Local) {
418 pat_util::pat_bindings(&ir.tcx.def_map, &*local.pat, |_, p_id, sp, path1| {
419 debug!("adding local variable {}", p_id);
420 let name = path1.node;
421 ir.add_live_node_for_node(p_id, VarDefNode(sp));
422 ir.add_variable(Local(LocalInfo {
427 visit::walk_local(ir, local);
430 fn visit_arm(ir: &mut IrMaps, arm: &ast::Arm) {
431 for pat in arm.pats.iter() {
432 pat_util::pat_bindings(&ir.tcx.def_map, &**pat, |bm, p_id, sp, path1| {
433 debug!("adding local variable {} from match with bm {}",
435 let name = path1.node;
436 ir.add_live_node_for_node(p_id, VarDefNode(sp));
437 ir.add_variable(Local(LocalInfo {
443 visit::walk_arm(ir, arm);
446 fn visit_expr(ir: &mut IrMaps, expr: &Expr) {
448 // live nodes required for uses or definitions of variables:
449 ast::ExprPath(_) => {
450 let def = ir.tcx.def_map.borrow()[expr.id].clone();
451 debug!("expr {}: path that leads to {}", expr.id, def);
452 if let DefLocal(..) = def {
453 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
455 visit::walk_expr(ir, expr);
457 ast::ExprClosure(..) => {
458 // Interesting control flow (for loops can contain labeled
459 // breaks or continues)
460 ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
462 // Make a live_node for each captured variable, with the span
463 // being the location that the variable is used. This results
464 // in better error messages than just pointing at the closure
465 // construction site.
466 let mut call_caps = Vec::new();
467 ty::with_freevars(ir.tcx, expr.id, |freevars| {
468 for fv in freevars.iter() {
469 if let DefLocal(rv) = fv.def {
470 let fv_ln = ir.add_live_node(FreeVarNode(fv.span));
471 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::ExprRange(..) => {
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.
532 #[derive(Clone, Copy)]
539 fn invalid_users() -> Users {
541 reader: invalid_node(),
542 writer: invalid_node(),
550 fallthrough_ln: LiveNode,
551 no_ret_var: Variable,
552 clean_exit_var: Variable
555 static ACC_READ: uint = 1u;
556 static ACC_WRITE: uint = 2u;
557 static ACC_USE: uint = 4u;
559 struct Liveness<'a, 'tcx: 'a> {
560 ir: &'a mut IrMaps<'a, 'tcx>,
562 successors: Vec<LiveNode>,
564 // The list of node IDs for the nested loop scopes
566 loop_scope: Vec<NodeId>,
567 // mappings from loop node ID to LiveNode
568 // ("break" label should map to loop node ID,
569 // it probably doesn't now)
570 break_ln: NodeMap<LiveNode>,
571 cont_ln: NodeMap<LiveNode>
574 impl<'a, 'tcx> Liveness<'a, 'tcx> {
575 fn new(ir: &'a mut IrMaps<'a, 'tcx>, specials: Specials) -> Liveness<'a, 'tcx> {
576 let num_live_nodes = ir.num_live_nodes;
577 let num_vars = ir.num_vars;
581 successors: repeat(invalid_node()).take(num_live_nodes).collect(),
582 users: repeat(invalid_users()).take(num_live_nodes * num_vars).collect(),
583 loop_scope: Vec::new(),
584 break_ln: NodeMap::new(),
585 cont_ln: NodeMap::new(),
589 fn live_node(&self, node_id: NodeId, span: Span) -> LiveNode {
590 match self.ir.live_node_map.get(&node_id) {
593 // This must be a mismatch between the ir_map construction
594 // above and the propagation code below; the two sets of
595 // code have to agree about which AST nodes are worth
596 // creating liveness nodes for.
597 self.ir.tcx.sess.span_bug(
599 format!("no live node registered for node {}",
605 fn variable(&self, node_id: NodeId, span: Span) -> Variable {
606 self.ir.variable(node_id, span)
609 fn pat_bindings<F>(&mut self, pat: &ast::Pat, mut f: F) where
610 F: FnMut(&mut Liveness<'a, 'tcx>, LiveNode, Variable, Span, NodeId),
612 pat_util::pat_bindings(&self.ir.tcx.def_map, pat, |_bm, p_id, sp, _n| {
613 let ln = self.live_node(p_id, sp);
614 let var = self.variable(p_id, sp);
615 f(self, ln, var, sp, p_id);
619 fn arm_pats_bindings<F>(&mut self, pat: Option<&ast::Pat>, f: F) where
620 F: FnMut(&mut Liveness<'a, 'tcx>, LiveNode, Variable, Span, NodeId),
624 self.pat_bindings(pat, f);
630 fn define_bindings_in_pat(&mut self, pat: &ast::Pat, succ: LiveNode)
632 self.define_bindings_in_arm_pats(Some(pat), succ)
635 fn define_bindings_in_arm_pats(&mut self, pat: Option<&ast::Pat>, succ: LiveNode)
638 self.arm_pats_bindings(pat, |this, ln, var, _sp, _id| {
639 this.init_from_succ(ln, succ);
640 this.define(ln, var);
646 fn idx(&self, ln: LiveNode, var: Variable) -> uint {
647 ln.get() * self.ir.num_vars + var.get()
650 fn live_on_entry(&self, ln: LiveNode, var: Variable)
651 -> Option<LiveNodeKind> {
652 assert!(ln.is_valid());
653 let reader = self.users[self.idx(ln, var)].reader;
654 if reader.is_valid() {Some(self.ir.lnk(reader))} else {None}
658 Is this variable live on entry to any of its successor nodes?
660 fn live_on_exit(&self, ln: LiveNode, var: Variable)
661 -> Option<LiveNodeKind> {
662 let successor = self.successors[ln.get()];
663 self.live_on_entry(successor, var)
666 fn used_on_entry(&self, ln: LiveNode, var: Variable) -> bool {
667 assert!(ln.is_valid());
668 self.users[self.idx(ln, var)].used
671 fn assigned_on_entry(&self, ln: LiveNode, var: Variable)
672 -> Option<LiveNodeKind> {
673 assert!(ln.is_valid());
674 let writer = self.users[self.idx(ln, var)].writer;
675 if writer.is_valid() {Some(self.ir.lnk(writer))} else {None}
678 fn assigned_on_exit(&self, ln: LiveNode, var: Variable)
679 -> Option<LiveNodeKind> {
680 let successor = self.successors[ln.get()];
681 self.assigned_on_entry(successor, var)
684 fn indices2<F>(&mut self, ln: LiveNode, succ_ln: LiveNode, mut op: F) where
685 F: FnMut(&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);
694 fn write_vars<F>(&self,
698 -> io::IoResult<()> where
699 F: FnMut(uint) -> LiveNode,
701 let node_base_idx = self.idx(ln, Variable(0));
702 for var_idx in range(0u, self.ir.num_vars) {
703 let idx = node_base_idx + var_idx;
704 if test(idx).is_valid() {
705 try!(write!(wr, " {}", Variable(var_idx).to_string()));
711 fn find_loop_scope(&self,
712 opt_label: Option<ast::Ident>,
718 // Refers to a labeled loop. Use the results of resolve
720 match self.ir.tcx.def_map.borrow().get(&id) {
721 Some(&DefLabel(loop_id)) => loop_id,
722 _ => self.ir.tcx.sess.span_bug(sp, "label on break/loop \
723 doesn't refer to a loop")
727 // Vanilla 'break' or 'loop', so use the enclosing
729 if self.loop_scope.len() == 0 {
730 self.ir.tcx.sess.span_bug(sp, "break outside loop");
732 *self.loop_scope.last().unwrap()
738 #[allow(unused_must_use)]
739 fn ln_str(&self, ln: LiveNode) -> String {
740 let mut wr = Vec::new();
742 let wr = &mut wr as &mut io::Writer;
743 write!(wr, "[ln({}) of kind {} reads", ln.get(), self.ir.lnk(ln));
744 self.write_vars(wr, ln, |idx| self.users[idx].reader);
745 write!(wr, " writes");
746 self.write_vars(wr, ln, |idx| self.users[idx].writer);
747 write!(wr, " precedes {}]", self.successors[ln.get()].to_string());
749 String::from_utf8(wr).unwrap()
752 fn init_empty(&mut self, ln: LiveNode, succ_ln: LiveNode) {
753 self.successors[ln.get()] = succ_ln;
755 // It is not necessary to initialize the
756 // values to empty because this is the value
757 // they have when they are created, and the sets
758 // only grow during iterations.
760 // self.indices(ln) { |idx|
761 // self.users[idx] = invalid_users();
765 fn init_from_succ(&mut self, ln: LiveNode, succ_ln: LiveNode) {
766 // more efficient version of init_empty() / merge_from_succ()
767 self.successors[ln.get()] = succ_ln;
769 self.indices2(ln, succ_ln, |this, idx, succ_idx| {
770 this.users[idx] = this.users[succ_idx]
772 debug!("init_from_succ(ln={}, succ={})",
773 self.ln_str(ln), self.ln_str(succ_ln));
776 fn merge_from_succ(&mut self,
781 if ln == succ_ln { return false; }
783 let mut changed = false;
784 self.indices2(ln, succ_ln, |this, idx, succ_idx| {
785 changed |= copy_if_invalid(this.users[succ_idx].reader,
786 &mut this.users[idx].reader);
787 changed |= copy_if_invalid(this.users[succ_idx].writer,
788 &mut this.users[idx].writer);
789 if this.users[succ_idx].used && !this.users[idx].used {
790 this.users[idx].used = true;
795 debug!("merge_from_succ(ln={}, succ={}, first_merge={}, changed={})",
796 ln.to_string(), self.ln_str(succ_ln), first_merge, changed);
799 fn copy_if_invalid(src: LiveNode, dst: &mut LiveNode) -> bool {
800 if src.is_valid() && !dst.is_valid() {
809 // Indicates that a local variable was *defined*; we know that no
810 // uses of the variable can precede the definition (resolve checks
811 // this) so we just clear out all the data.
812 fn define(&mut self, writer: LiveNode, var: Variable) {
813 let idx = self.idx(writer, var);
814 self.users[idx].reader = invalid_node();
815 self.users[idx].writer = invalid_node();
817 debug!("{} defines {} (idx={}): {}", writer.to_string(), var.to_string(),
818 idx, self.ln_str(writer));
821 // Either read, write, or both depending on the acc bitset
822 fn acc(&mut self, ln: LiveNode, var: Variable, acc: uint) {
823 debug!("{} accesses[{:x}] {}: {}",
824 ln.to_string(), acc, var.to_string(), self.ln_str(ln));
826 let idx = self.idx(ln, var);
827 let user = &mut self.users[idx];
829 if (acc & ACC_WRITE) != 0 {
830 user.reader = invalid_node();
834 // Important: if we both read/write, must do read second
835 // or else the write will override.
836 if (acc & ACC_READ) != 0 {
840 if (acc & ACC_USE) != 0 {
845 // _______________________________________________________________________
847 fn compute(&mut self, decl: &ast::FnDecl, body: &ast::Block) -> LiveNode {
848 // if there is a `break` or `again` at the top level, then it's
849 // effectively a return---this only occurs in `for` loops,
850 // where the body is really a closure.
852 debug!("compute: using id for block, {}", block_to_string(body));
854 let exit_ln = self.s.exit_ln;
855 let entry_ln: LiveNode =
856 self.with_loop_nodes(body.id, exit_ln, exit_ln,
857 |this| this.propagate_through_fn_block(decl, body));
859 // hack to skip the loop unless debug! is enabled:
860 debug!("^^ liveness computation results for body {} (entry={})",
862 for ln_idx in range(0u, self.ir.num_live_nodes) {
863 debug!("{}", self.ln_str(LiveNode(ln_idx)));
867 entry_ln.to_string());
872 fn propagate_through_fn_block(&mut self, _: &ast::FnDecl, blk: &ast::Block)
874 // the fallthrough exit is only for those cases where we do not
875 // explicitly return:
877 self.init_from_succ(s.fallthrough_ln, s.exit_ln);
878 if blk.expr.is_none() {
879 self.acc(s.fallthrough_ln, s.no_ret_var, ACC_READ)
881 self.acc(s.fallthrough_ln, s.clean_exit_var, ACC_READ);
883 self.propagate_through_block(blk, s.fallthrough_ln)
886 fn propagate_through_block(&mut self, blk: &ast::Block, succ: LiveNode)
888 let succ = self.propagate_through_opt_expr(blk.expr.as_ref().map(|e| &**e), succ);
889 blk.stmts.iter().rev().fold(succ, |succ, stmt| {
890 self.propagate_through_stmt(&**stmt, succ)
894 fn propagate_through_stmt(&mut self, stmt: &ast::Stmt, succ: LiveNode)
897 ast::StmtDecl(ref decl, _) => {
898 self.propagate_through_decl(&**decl, succ)
901 ast::StmtExpr(ref expr, _) | ast::StmtSemi(ref expr, _) => {
902 self.propagate_through_expr(&**expr, succ)
905 ast::StmtMac(..) => {
906 self.ir.tcx.sess.span_bug(stmt.span, "unexpanded macro");
911 fn propagate_through_decl(&mut self, decl: &ast::Decl, succ: LiveNode)
914 ast::DeclLocal(ref local) => {
915 self.propagate_through_local(&**local, succ)
917 ast::DeclItem(_) => succ,
921 fn propagate_through_local(&mut self, local: &ast::Local, succ: LiveNode)
923 // Note: we mark the variable as defined regardless of whether
924 // there is an initializer. Initially I had thought to only mark
925 // the live variable as defined if it was initialized, and then we
926 // could check for uninit variables just by scanning what is live
927 // at the start of the function. But that doesn't work so well for
928 // immutable variables defined in a loop:
929 // loop { let x; x = 5; }
930 // because the "assignment" loops back around and generates an error.
932 // So now we just check that variables defined w/o an
933 // initializer are not live at the point of their
934 // initialization, which is mildly more complex than checking
935 // once at the func header but otherwise equivalent.
937 let succ = self.propagate_through_opt_expr(local.init.as_ref().map(|e| &**e), succ);
938 self.define_bindings_in_pat(&*local.pat, succ)
941 fn propagate_through_exprs(&mut self, exprs: &[P<Expr>], succ: LiveNode)
943 exprs.iter().rev().fold(succ, |succ, expr| {
944 self.propagate_through_expr(&**expr, succ)
948 fn propagate_through_opt_expr(&mut self,
949 opt_expr: Option<&Expr>,
952 opt_expr.map_or(succ, |expr| self.propagate_through_expr(expr, succ))
955 fn propagate_through_expr(&mut self, expr: &Expr, succ: LiveNode)
957 debug!("propagate_through_expr: {}", expr_to_string(expr));
960 // Interesting cases with control flow or which gen/kill
962 ast::ExprPath(_) => {
963 self.access_path(expr, succ, ACC_READ | ACC_USE)
966 ast::ExprField(ref e, _) => {
967 self.propagate_through_expr(&**e, succ)
970 ast::ExprTupField(ref e, _) => {
971 self.propagate_through_expr(&**e, succ)
974 ast::ExprClosure(_, _, _, ref blk) => {
975 debug!("{} is an ExprClosure",
976 expr_to_string(expr));
979 The next-node for a break is the successor of the entire
980 loop. The next-node for a continue is the top of this loop.
982 let node = self.live_node(expr.id, expr.span);
983 self.with_loop_nodes(blk.id, succ, node, |this| {
985 // the construction of a closure itself is not important,
986 // but we have to consider the closed over variables.
987 let caps = match this.ir.capture_info_map.get(&expr.id) {
988 Some(caps) => caps.clone(),
990 this.ir.tcx.sess.span_bug(expr.span, "no registered caps");
993 caps.iter().rev().fold(succ, |succ, cap| {
994 this.init_from_succ(cap.ln, succ);
995 let var = this.variable(cap.var_nid, expr.span);
996 this.acc(cap.ln, var, ACC_READ | ACC_USE);
1002 ast::ExprIf(ref cond, ref then, ref els) => {
1016 let else_ln = self.propagate_through_opt_expr(els.as_ref().map(|e| &**e), succ);
1017 let then_ln = self.propagate_through_block(&**then, succ);
1018 let ln = self.live_node(expr.id, expr.span);
1019 self.init_from_succ(ln, else_ln);
1020 self.merge_from_succ(ln, then_ln, false);
1021 self.propagate_through_expr(&**cond, ln)
1024 ast::ExprIfLet(..) => {
1025 self.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
1028 ast::ExprWhile(ref cond, ref blk, _) => {
1029 self.propagate_through_loop(expr, WhileLoop(&**cond), &**blk, succ)
1032 ast::ExprWhileLet(..) => {
1033 self.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet");
1036 ast::ExprForLoop(ref pat, ref head, ref blk, _) => {
1037 let ln = self.propagate_through_loop(expr, ForLoop(&**pat), &**blk, succ);
1038 self.propagate_through_expr(&**head, ln)
1041 // Note that labels have been resolved, so we don't need to look
1042 // at the label ident
1043 ast::ExprLoop(ref blk, _) => {
1044 self.propagate_through_loop(expr, LoopLoop, &**blk, succ)
1047 ast::ExprMatch(ref e, ref arms, _) => {
1062 let ln = self.live_node(expr.id, expr.span);
1063 self.init_empty(ln, succ);
1064 let mut first_merge = true;
1065 for arm in arms.iter() {
1067 self.propagate_through_expr(&*arm.body, succ);
1069 self.propagate_through_opt_expr(arm.guard.as_ref().map(|e| &**e), body_succ);
1070 // only consider the first pattern; any later patterns must have
1071 // the same bindings, and we also consider the first pattern to be
1072 // the "authoritative" set of ids
1074 self.define_bindings_in_arm_pats(arm.pats.first().map(|p| &**p),
1076 self.merge_from_succ(ln, arm_succ, first_merge);
1077 first_merge = false;
1079 self.propagate_through_expr(&**e, ln)
1082 ast::ExprRet(ref o_e) => {
1083 // ignore succ and subst exit_ln:
1084 let exit_ln = self.s.exit_ln;
1085 self.propagate_through_opt_expr(o_e.as_ref().map(|e| &**e), exit_ln)
1088 ast::ExprBreak(opt_label) => {
1089 // Find which label this break jumps to
1090 let sc = self.find_loop_scope(opt_label, expr.id, expr.span);
1092 // Now that we know the label we're going to,
1093 // look it up in the break loop nodes table
1095 match self.break_ln.get(&sc) {
1097 None => self.ir.tcx.sess.span_bug(expr.span,
1098 "break to unknown label")
1102 ast::ExprAgain(opt_label) => {
1103 // Find which label this expr continues to
1104 let sc = self.find_loop_scope(opt_label, expr.id, expr.span);
1106 // Now that we know the label we're going to,
1107 // look it up in the continue loop nodes table
1109 match self.cont_ln.get(&sc) {
1111 None => self.ir.tcx.sess.span_bug(expr.span,
1112 "loop to unknown label")
1116 ast::ExprAssign(ref l, ref r) => {
1117 // see comment on lvalues in
1118 // propagate_through_lvalue_components()
1119 let succ = self.write_lvalue(&**l, succ, ACC_WRITE);
1120 let succ = self.propagate_through_lvalue_components(&**l, succ);
1121 self.propagate_through_expr(&**r, succ)
1124 ast::ExprAssignOp(_, ref l, ref r) => {
1125 // see comment on lvalues in
1126 // propagate_through_lvalue_components()
1127 let succ = self.write_lvalue(&**l, succ, ACC_WRITE|ACC_READ);
1128 let succ = self.propagate_through_expr(&**r, succ);
1129 self.propagate_through_lvalue_components(&**l, succ)
1132 // Uninteresting cases: just propagate in rev exec order
1134 ast::ExprVec(ref exprs) => {
1135 self.propagate_through_exprs(exprs[], succ)
1138 ast::ExprRepeat(ref element, ref count) => {
1139 let succ = self.propagate_through_expr(&**count, succ);
1140 self.propagate_through_expr(&**element, succ)
1143 ast::ExprStruct(_, ref fields, ref with_expr) => {
1144 let succ = self.propagate_through_opt_expr(with_expr.as_ref().map(|e| &**e), succ);
1145 fields.iter().rev().fold(succ, |succ, field| {
1146 self.propagate_through_expr(&*field.expr, succ)
1150 ast::ExprCall(ref f, ref args) => {
1151 let diverges = !self.ir.tcx.is_method_call(expr.id) && {
1152 let t_ret = ty::ty_fn_ret(ty::expr_ty_adjusted(self.ir.tcx, &**f));
1153 t_ret == ty::FnDiverging
1155 let succ = if diverges {
1160 let succ = self.propagate_through_exprs(args[], succ);
1161 self.propagate_through_expr(&**f, succ)
1164 ast::ExprMethodCall(_, _, ref args) => {
1165 let method_call = ty::MethodCall::expr(expr.id);
1166 let method_ty = self.ir.tcx.method_map.borrow().get(&method_call).unwrap().ty;
1167 let diverges = ty::ty_fn_ret(method_ty) == ty::FnDiverging;
1168 let succ = if diverges {
1173 self.propagate_through_exprs(args[], succ)
1176 ast::ExprTup(ref exprs) => {
1177 self.propagate_through_exprs(exprs[], succ)
1180 ast::ExprBinary(op, ref l, ref r) if ast_util::lazy_binop(op) => {
1181 let r_succ = self.propagate_through_expr(&**r, succ);
1183 let ln = self.live_node(expr.id, expr.span);
1184 self.init_from_succ(ln, succ);
1185 self.merge_from_succ(ln, r_succ, false);
1187 self.propagate_through_expr(&**l, ln)
1190 ast::ExprIndex(ref l, ref r) |
1191 ast::ExprBinary(_, ref l, ref r) |
1192 ast::ExprBox(Some(ref l), ref r) => {
1193 let r_succ = self.propagate_through_expr(&**r, succ);
1194 self.propagate_through_expr(&**l, r_succ)
1197 ast::ExprRange(ref e1, ref e2) => {
1198 let succ = e2.as_ref().map_or(succ, |e| self.propagate_through_expr(&**e, succ));
1199 e1.as_ref().map_or(succ, |e| self.propagate_through_expr(&**e, succ))
1202 ast::ExprBox(None, ref e) |
1203 ast::ExprAddrOf(_, ref e) |
1204 ast::ExprCast(ref e, _) |
1205 ast::ExprUnary(_, ref e) |
1206 ast::ExprParen(ref e) => {
1207 self.propagate_through_expr(&**e, succ)
1210 ast::ExprInlineAsm(ref ia) => {
1212 let succ = ia.outputs.iter().rev().fold(succ, |succ, &(_, ref expr, _)| {
1213 // see comment on lvalues
1214 // in propagate_through_lvalue_components()
1215 let succ = self.write_lvalue(&**expr, succ, ACC_WRITE);
1216 self.propagate_through_lvalue_components(&**expr, succ)
1218 // Inputs are executed first. Propagate last because of rev order
1219 ia.inputs.iter().rev().fold(succ, |succ, &(_, ref expr)| {
1220 self.propagate_through_expr(&**expr, succ)
1224 ast::ExprLit(..) => {
1228 ast::ExprBlock(ref blk) => {
1229 self.propagate_through_block(&**blk, succ)
1232 ast::ExprMac(..) => {
1233 self.ir.tcx.sess.span_bug(expr.span, "unexpanded macro");
1238 fn propagate_through_lvalue_components(&mut self,
1244 // In general, the full flow graph structure for an
1245 // assignment/move/etc can be handled in one of two ways,
1246 // depending on whether what is being assigned is a "tracked
1247 // value" or not. A tracked value is basically a local
1248 // variable or argument.
1250 // The two kinds of graphs are:
1252 // Tracked lvalue Untracked lvalue
1253 // ----------------------++-----------------------
1257 // (rvalue) || (rvalue)
1260 // (write of lvalue) || (lvalue components)
1265 // ----------------------++-----------------------
1267 // I will cover the two cases in turn:
1269 // # Tracked lvalues
1271 // A tracked lvalue is a local variable/argument `x`. In
1272 // these cases, the link_node where the write occurs is linked
1273 // to node id of `x`. The `write_lvalue()` routine generates
1274 // the contents of this node. There are no subcomponents to
1277 // # Non-tracked lvalues
1279 // These are lvalues like `x[5]` or `x.f`. In that case, we
1280 // basically ignore the value which is written to but generate
1281 // reads for the components---`x` in these two examples. The
1282 // components reads are generated by
1283 // `propagate_through_lvalue_components()` (this fn).
1285 // # Illegal lvalues
1287 // It is still possible to observe assignments to non-lvalues;
1288 // these errors are detected in the later pass borrowck. We
1289 // just ignore such cases and treat them as reads.
1292 ast::ExprPath(_) => succ,
1293 ast::ExprField(ref e, _) => self.propagate_through_expr(&**e, succ),
1294 ast::ExprTupField(ref e, _) => self.propagate_through_expr(&**e, succ),
1295 _ => self.propagate_through_expr(expr, succ)
1299 // see comment on propagate_through_lvalue()
1300 fn write_lvalue(&mut self, expr: &Expr, succ: LiveNode, acc: uint)
1303 ast::ExprPath(_) => self.access_path(expr, succ, acc),
1305 // We do not track other lvalues, so just propagate through
1306 // to their subcomponents. Also, it may happen that
1307 // non-lvalues occur here, because those are detected in the
1308 // later pass borrowck.
1313 fn access_path(&mut self, expr: &Expr, succ: LiveNode, acc: uint)
1315 match self.ir.tcx.def_map.borrow()[expr.id].clone() {
1317 let ln = self.live_node(expr.id, expr.span);
1319 self.init_from_succ(ln, succ);
1320 let var = self.variable(nid, expr.span);
1321 self.acc(ln, var, acc);
1329 fn propagate_through_loop(&mut self,
1338 We model control flow like this:
1356 let mut first_merge = true;
1357 let ln = self.live_node(expr.id, expr.span);
1358 self.init_empty(ln, succ);
1362 // If this is not a `loop` loop, then it's possible we bypass
1363 // the body altogether. Otherwise, the only way is via a `break`
1364 // in the loop body.
1365 self.merge_from_succ(ln, succ, first_merge);
1366 first_merge = false;
1369 debug!("propagate_through_loop: using id for loop body {} {}",
1370 expr.id, block_to_string(body));
1372 let cond_ln = match kind {
1374 ForLoop(ref pat) => self.define_bindings_in_pat(*pat, ln),
1375 WhileLoop(ref cond) => self.propagate_through_expr(&**cond, ln),
1377 let body_ln = self.with_loop_nodes(expr.id, succ, ln, |this| {
1378 this.propagate_through_block(body, cond_ln)
1381 // repeat until fixed point is reached:
1382 while self.merge_from_succ(ln, body_ln, first_merge) {
1383 first_merge = false;
1385 let new_cond_ln = match kind {
1387 ForLoop(ref pat) => {
1388 self.define_bindings_in_pat(*pat, ln)
1390 WhileLoop(ref cond) => {
1391 self.propagate_through_expr(&**cond, ln)
1394 assert!(cond_ln == new_cond_ln);
1395 assert!(body_ln == self.with_loop_nodes(expr.id, succ, ln,
1396 |this| this.propagate_through_block(body, cond_ln)));
1402 fn with_loop_nodes<R, F>(&mut self,
1403 loop_node_id: NodeId,
1408 F: FnOnce(&mut Liveness<'a, 'tcx>) -> R,
1410 debug!("with_loop_nodes: {} {}", loop_node_id, break_ln.get());
1411 self.loop_scope.push(loop_node_id);
1412 self.break_ln.insert(loop_node_id, break_ln);
1413 self.cont_ln.insert(loop_node_id, cont_ln);
1415 self.loop_scope.pop();
1420 // _______________________________________________________________________
1421 // Checking for error conditions
1423 fn check_local(this: &mut Liveness, local: &ast::Local) {
1426 this.warn_about_unused_or_dead_vars_in_pat(&*local.pat);
1429 this.pat_bindings(&*local.pat, |this, ln, var, sp, id| {
1430 this.warn_about_unused(sp, id, ln, var);
1435 visit::walk_local(this, local);
1438 fn check_arm(this: &mut Liveness, arm: &ast::Arm) {
1439 // only consider the first pattern; any later patterns must have
1440 // the same bindings, and we also consider the first pattern to be
1441 // the "authoritative" set of ids
1442 this.arm_pats_bindings(arm.pats.first().map(|p| &**p), |this, ln, var, sp, id| {
1443 this.warn_about_unused(sp, id, ln, var);
1445 visit::walk_arm(this, arm);
1448 fn check_expr(this: &mut Liveness, expr: &Expr) {
1450 ast::ExprAssign(ref l, ref r) => {
1451 this.check_lvalue(&**l);
1452 this.visit_expr(&**r);
1454 visit::walk_expr(this, expr);
1457 ast::ExprAssignOp(_, ref l, _) => {
1458 this.check_lvalue(&**l);
1460 visit::walk_expr(this, expr);
1463 ast::ExprInlineAsm(ref ia) => {
1464 for &(_, ref input) in ia.inputs.iter() {
1465 this.visit_expr(&**input);
1468 // Output operands must be lvalues
1469 for &(_, ref out, _) in ia.outputs.iter() {
1470 this.check_lvalue(&**out);
1471 this.visit_expr(&**out);
1474 visit::walk_expr(this, expr);
1477 ast::ExprForLoop(ref pat, _, _, _) => {
1478 this.pat_bindings(&**pat, |this, ln, var, sp, id| {
1479 this.warn_about_unused(sp, id, ln, var);
1482 visit::walk_expr(this, expr);
1485 // no correctness conditions related to liveness
1486 ast::ExprCall(..) | ast::ExprMethodCall(..) | ast::ExprIf(..) |
1487 ast::ExprMatch(..) | ast::ExprWhile(..) | ast::ExprLoop(..) |
1488 ast::ExprIndex(..) | ast::ExprField(..) | ast::ExprTupField(..) |
1489 ast::ExprVec(..) | ast::ExprTup(..) | ast::ExprBinary(..) |
1490 ast::ExprCast(..) | ast::ExprUnary(..) | ast::ExprRet(..) |
1491 ast::ExprBreak(..) | ast::ExprAgain(..) | ast::ExprLit(_) |
1492 ast::ExprBlock(..) | ast::ExprMac(..) | ast::ExprAddrOf(..) |
1493 ast::ExprStruct(..) | ast::ExprRepeat(..) | ast::ExprParen(..) |
1494 ast::ExprClosure(..) | ast::ExprPath(..) | ast::ExprBox(..) |
1495 ast::ExprRange(..) => {
1496 visit::walk_expr(this, expr);
1498 ast::ExprIfLet(..) => {
1499 this.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
1501 ast::ExprWhileLet(..) => {
1502 this.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet");
1507 fn check_fn(_v: &Liveness,
1509 _decl: &ast::FnDecl,
1513 // do not check contents of nested fns
1516 impl<'a, 'tcx> Liveness<'a, 'tcx> {
1517 fn fn_ret(&self, id: NodeId) -> ty::FnOutput<'tcx> {
1518 let fn_ty = ty::node_id_to_type(self.ir.tcx, id);
1520 ty::ty_unboxed_closure(closure_def_id, _, substs) =>
1521 self.ir.tcx.unboxed_closure_type(closure_def_id, substs).sig.0.output,
1523 ty::ty_fn_ret(fn_ty),
1532 body: &ast::Block) {
1533 match self.fn_ret(id) {
1534 ty::FnConverging(t_ret)
1535 if self.live_on_entry(entry_ln, self.s.no_ret_var).is_some() => {
1537 if ty::type_is_nil(t_ret) {
1538 // for nil return types, it is ok to not return a value expl.
1540 let ends_with_stmt = match body.expr {
1541 None if body.stmts.len() > 0 =>
1542 match body.stmts.first().unwrap().node {
1543 ast::StmtSemi(ref e, _) => {
1544 ty::expr_ty(self.ir.tcx, &**e) == t_ret
1550 self.ir.tcx.sess.span_err(
1551 sp, "not all control paths return a value");
1553 let last_stmt = body.stmts.first().unwrap();
1554 let original_span = original_sp(self.ir.tcx.sess.codemap(),
1555 last_stmt.span, sp);
1556 let span_semicolon = Span {
1557 lo: original_span.hi - BytePos(1),
1558 hi: original_span.hi,
1559 expn_id: original_span.expn_id
1561 self.ir.tcx.sess.span_help(
1562 span_semicolon, "consider removing this semicolon:");
1567 if self.live_on_entry(entry_ln, self.s.clean_exit_var).is_some() => {
1568 self.ir.tcx.sess.span_err(sp,
1569 "computation may converge in a function marked as diverging");
1576 fn check_lvalue(&mut self, expr: &Expr) {
1578 ast::ExprPath(_) => {
1579 if let DefLocal(nid) = self.ir.tcx.def_map.borrow()[expr.id].clone() {
1580 // Assignment to an immutable variable or argument: only legal
1581 // if there is no later assignment. If this local is actually
1582 // mutable, then check for a reassignment to flag the mutability
1584 let ln = self.live_node(expr.id, expr.span);
1585 let var = self.variable(nid, expr.span);
1586 self.warn_about_dead_assign(expr.span, expr.id, ln, var);
1590 // For other kinds of lvalues, no checks are required,
1591 // and any embedded expressions are actually rvalues
1592 visit::walk_expr(self, expr);
1597 fn should_warn(&self, var: Variable) -> Option<String> {
1598 let name = self.ir.variable_name(var);
1599 if name.len() == 0 || name.as_bytes()[0] == ('_' as u8) {
1606 fn warn_about_unused_args(&self, decl: &ast::FnDecl, entry_ln: LiveNode) {
1607 for arg in decl.inputs.iter() {
1608 pat_util::pat_bindings(&self.ir.tcx.def_map,
1610 |_bm, p_id, sp, path1| {
1611 let var = self.variable(p_id, sp);
1612 // Ignore unused self.
1613 let ident = path1.node;
1614 if ident.name != special_idents::self_.name {
1615 self.warn_about_unused(sp, p_id, entry_ln, var);
1621 fn warn_about_unused_or_dead_vars_in_pat(&mut self, pat: &ast::Pat) {
1622 self.pat_bindings(pat, |this, ln, var, sp, id| {
1623 if !this.warn_about_unused(sp, id, ln, var) {
1624 this.warn_about_dead_assign(sp, id, ln, var);
1629 fn warn_about_unused(&self,
1635 if !self.used_on_entry(ln, var) {
1636 let r = self.should_warn(var);
1637 for name in r.iter() {
1639 // annoying: for parameters in funcs like `fn(x: int)
1640 // {ret}`, there is only one node, so asking about
1641 // assigned_on_exit() is not meaningful.
1642 let is_assigned = if ln == self.s.exit_ln {
1645 self.assigned_on_exit(ln, var).is_some()
1649 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_VARIABLES, id, sp,
1650 format!("variable `{}` is assigned to, but never used",
1653 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_VARIABLES, id, sp,
1654 format!("unused variable: `{}`", *name));
1663 fn warn_about_dead_assign(&self,
1668 if self.live_on_exit(ln, var).is_none() {
1669 let r = self.should_warn(var);
1670 for name in r.iter() {
1671 self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_ASSIGNMENTS, id, sp,
1672 format!("value assigned to `{}` is never read", *name));