// Copyright 2012 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 or the MIT license // , at your // option. This file may not be copied, modified, or distributed // except according to those terms. /*! * A classic liveness analysis based on dataflow over the AST. Computes, * for each local variable in a function, whether that variable is live * at a given point. Program execution points are identified by their * id. * * # Basic idea * * The basic model is that each local variable is assigned an index. We * represent sets of local variables using a vector indexed by this * index. The value in the vector is either 0, indicating the variable * is dead, or the id of an expression that uses the variable. * * We conceptually walk over the AST in reverse execution order. If we * find a use of a variable, we add it to the set of live variables. If * we find an assignment to a variable, we remove it from the set of live * variables. When we have to merge two flows, we take the union of * those two flows---if the variable is live on both paths, we simply * pick one id. In the event of loops, we continue doing this until a * fixed point is reached. * * ## Checking initialization * * At the function entry point, all variables must be dead. If this is * not the case, we can report an error using the id found in the set of * live variables, which identifies a use of the variable which is not * dominated by an assignment. * * ## Checking moves * * After each explicit move, the variable must be dead. * * ## Computing last uses * * Any use of the variable where the variable is dead afterwards is a * last use. * * # Implementation details * * The actual implementation contains two (nested) walks over the AST. * The outer walk has the job of building up the ir_maps instance for the * enclosing function. On the way down the tree, it identifies those AST * nodes and variable IDs that will be needed for the liveness analysis * and assigns them contiguous IDs. The liveness id for an AST node is * called a `live_node` (it's a newtype'd uint) and the id for a variable * is called a `variable` (another newtype'd uint). * * On the way back up the tree, as we are about to exit from a function * declaration we allocate a `liveness` instance. Now that we know * precisely how many nodes and variables we need, we can allocate all * the various arrays that we will need to precisely the right size. We then * perform the actual propagation on the `liveness` instance. * * This propagation is encoded in the various `propagate_through_*()` * methods. It effectively does a reverse walk of the AST; whenever we * reach a loop node, we iterate until a fixed point is reached. * * ## The `Users` struct * * At each live node `N`, we track three pieces of information for each * variable `V` (these are encapsulated in the `Users` struct): * * - `reader`: the `LiveNode` ID of some node which will read the value * that `V` holds on entry to `N`. Formally: a node `M` such * that there exists a path `P` from `N` to `M` where `P` does not * write `V`. If the `reader` is `invalid_node()`, then the current * value will never be read (the variable is dead, essentially). * * - `writer`: the `LiveNode` ID of some node which will write the * variable `V` and which is reachable from `N`. Formally: a node `M` * such that there exists a path `P` from `N` to `M` and `M` writes * `V`. If the `writer` is `invalid_node()`, then there is no writer * of `V` that follows `N`. * * - `used`: a boolean value indicating whether `V` is *used*. We * distinguish a *read* from a *use* in that a *use* is some read that * is not just used to generate a new value. For example, `x += 1` is * a read but not a use. This is used to generate better warnings. * * ## Special Variables * * We generate various special variables for various, well, special purposes. * These are described in the `specials` struct: * * - `exit_ln`: a live node that is generated to represent every 'exit' from * the function, whether it be by explicit return, fail, or other means. * * - `fallthrough_ln`: a live node that represents a fallthrough * * - `no_ret_var`: a synthetic variable that is only 'read' from, the * fallthrough node. This allows us to detect functions where we fail * to return explicitly. */ use core::prelude::*; use middle::lint::{unused_variable, dead_assignment}; use middle::pat_util; use middle::ty; use middle::typeck; use middle::moves; use util::ppaux::ty_to_str; use core::hashmap::HashMap; use core::io::WriterUtil; use core::io; use core::ptr; use core::to_str; use core::uint; use core::vec; use core::util::with; use syntax::ast::*; use syntax::codemap::span; use syntax::parse::token::special_idents; use syntax::print::pprust::{expr_to_str, block_to_str}; use syntax::visit::{fk_anon, fk_dtor, fk_fn_block, fk_item_fn, fk_method}; use syntax::visit::{vt}; use syntax::{visit, ast_util}; // Maps from an expr id to a list of variable ids for which this expr // is the last use. Typically, the expr is a path and the node id is // the local/argument/etc that the path refers to. However, it also // possible for the expr to be a closure, in which case the list is a // list of closed over variables that can be moved into the closure. // // Very subtle (#2633): borrowck will remove entries from this table // if it detects an outstanding loan (that is, the addr is taken). pub type last_use_map = @mut HashMap; #[deriving(Eq)] struct Variable(uint); #[deriving(Eq)] struct LiveNode(uint); #[deriving(Eq)] enum LiveNodeKind { FreeVarNode(span), ExprNode(span), VarDefNode(span), ExitNode } fn live_node_kind_to_str(lnk: LiveNodeKind, cx: ty::ctxt) -> ~str { let cm = cx.sess.codemap; match lnk { FreeVarNode(s) => fmt!("Free var node [%s]", cm.span_to_str(s)), ExprNode(s) => fmt!("Expr node [%s]", cm.span_to_str(s)), VarDefNode(s) => fmt!("Var def node [%s]", cm.span_to_str(s)), ExitNode => ~"Exit node" } } pub fn check_crate(tcx: ty::ctxt, method_map: typeck::method_map, variable_moves_map: moves::VariableMovesMap, capture_map: moves::CaptureMap, crate: @crate) -> last_use_map { let visitor = visit::mk_vt(@visit::Visitor { visit_fn: visit_fn, visit_local: visit_local, visit_expr: visit_expr, visit_arm: visit_arm, visit_item: visit_item, .. *visit::default_visitor() }); let last_use_map = @mut HashMap::new(); let initial_maps = @mut IrMaps(tcx, method_map, variable_moves_map, capture_map, last_use_map, 0); visit::visit_crate(crate, initial_maps, visitor); tcx.sess.abort_if_errors(); return last_use_map; } impl to_str::ToStr for LiveNode { fn to_str(&self) -> ~str { fmt!("ln(%u)", **self) } } impl to_str::ToStr for Variable { fn to_str(&self) -> ~str { fmt!("v(%u)", **self) } } // ______________________________________________________________________ // Creating ir_maps // // This is the first pass and the one that drives the main // computation. It walks up and down the IR once. On the way down, // we count for each function the number of variables as well as // liveness nodes. A liveness node is basically an expression or // capture clause that does something of interest: either it has // interesting control flow or it uses/defines a local variable. // // On the way back up, at each function node we create liveness sets // (we now know precisely how big to make our various vectors and so // forth) and then do the data-flow propagation to compute the set // of live variables at each program point. // // Finally, we run back over the IR one last time and, using the // computed liveness, check various safety conditions. For example, // there must be no live nodes at the definition site for a variable // unless it has an initializer. Similarly, each non-mutable local // variable must not be assigned if there is some successor // assignment. And so forth. pub impl LiveNode { fn is_valid(&self) -> bool { **self != uint::max_value } } fn invalid_node() -> LiveNode { LiveNode(uint::max_value) } struct CaptureInfo { ln: LiveNode, is_move: bool, var_nid: node_id } enum LocalKind { FromMatch(binding_mode), FromLetWithInitializer, FromLetNoInitializer } struct LocalInfo { id: node_id, ident: ident, is_mutbl: bool, kind: LocalKind, } enum VarKind { Arg(node_id, ident, rmode), Local(LocalInfo), ImplicitRet } fn relevant_def(def: def) -> Option { match def { def_binding(nid, _) | def_arg(nid, _, _) | def_local(nid, _) | def_self(nid, _) => Some(nid), _ => None } } struct IrMaps { tcx: ty::ctxt, method_map: typeck::method_map, variable_moves_map: moves::VariableMovesMap, capture_map: moves::CaptureMap, last_use_map: last_use_map, num_live_nodes: uint, num_vars: uint, live_node_map: HashMap, variable_map: HashMap, capture_info_map: HashMap, var_kinds: ~[VarKind], lnks: ~[LiveNodeKind], cur_item: node_id, } fn IrMaps(tcx: ty::ctxt, method_map: typeck::method_map, variable_moves_map: moves::VariableMovesMap, capture_map: moves::CaptureMap, last_use_map: last_use_map, cur_item: node_id) -> IrMaps { IrMaps { tcx: tcx, method_map: method_map, variable_moves_map: variable_moves_map, capture_map: capture_map, last_use_map: last_use_map, num_live_nodes: 0, num_vars: 0, live_node_map: HashMap::new(), variable_map: HashMap::new(), capture_info_map: HashMap::new(), var_kinds: ~[], lnks: ~[], cur_item: cur_item, } } pub impl IrMaps { fn add_live_node(&mut self, lnk: LiveNodeKind) -> LiveNode { let ln = LiveNode(self.num_live_nodes); self.lnks.push(lnk); self.num_live_nodes += 1; debug!("%s is of kind %s", ln.to_str(), live_node_kind_to_str(lnk, self.tcx)); ln } fn add_live_node_for_node(&mut self, node_id: node_id, lnk: LiveNodeKind) { let ln = self.add_live_node(lnk); self.live_node_map.insert(node_id, ln); debug!("%s is node %d", ln.to_str(), node_id); } fn add_variable(&mut self, vk: VarKind) -> Variable { let v = Variable(self.num_vars); self.var_kinds.push(vk); self.num_vars += 1; match vk { Local(LocalInfo {id:node_id, _}) | Arg(node_id, _, _) => { self.variable_map.insert(node_id, v); } ImplicitRet => {} } debug!("%s is %?", v.to_str(), vk); v } fn variable(&mut self, node_id: node_id, span: span) -> Variable { match self.variable_map.find(&node_id) { Some(&var) => var, None => { self.tcx.sess.span_bug( span, fmt!("No variable registered for id %d", node_id)); } } } fn variable_name(&mut self, var: Variable) -> @~str { match self.var_kinds[*var] { Local(LocalInfo {ident: nm, _}) | Arg(_, nm, _) => self.tcx.sess.str_of(nm), ImplicitRet => @~"" } } fn set_captures(&mut self, node_id: node_id, cs: ~[CaptureInfo]) { self.capture_info_map.insert(node_id, @cs); } fn captures(&mut self, expr: @expr) -> @~[CaptureInfo] { match self.capture_info_map.find(&expr.id) { Some(&caps) => caps, None => { self.tcx.sess.span_bug(expr.span, ~"no registered caps"); } } } fn lnk(&mut self, ln: LiveNode) -> LiveNodeKind { self.lnks[*ln] } fn add_last_use(&mut self, expr_id: node_id, var: Variable) { let vk = self.var_kinds[*var]; debug!("Node %d is a last use of variable %?", expr_id, vk); match vk { Arg(id, _, by_copy) | Local(LocalInfo {id: id, kind: FromLetNoInitializer, _}) | Local(LocalInfo {id: id, kind: FromLetWithInitializer, _}) | Local(LocalInfo {id: id, kind: FromMatch(_), _}) => { let v = match self.last_use_map.find(&expr_id) { Some(&v) => v, None => { let v = @mut ~[]; self.last_use_map.insert(expr_id, v); v } }; v.push(id); } Arg(_, _, by_ref) | ImplicitRet => { debug!("--but it is not owned"); } } } } fn visit_item(item: @item, self: @mut IrMaps, v: vt<@mut IrMaps>) { do with(&mut self.cur_item, item.id) { visit::visit_item(item, self, v) } } fn visit_fn(fk: &visit::fn_kind, decl: &fn_decl, body: &blk, sp: span, id: node_id, self: @mut IrMaps, v: vt<@mut IrMaps>) { debug!("visit_fn: id=%d", id); let _i = ::util::common::indenter(); // swap in a new set of IR maps for this function body: let fn_maps = @mut IrMaps(self.tcx, self.method_map, self.variable_moves_map, self.capture_map, self.last_use_map, self.cur_item); debug!("creating fn_maps: %x", ptr::addr_of(&(*fn_maps)) as uint); for decl.inputs.each |arg| { let mode = ty::resolved_mode(self.tcx, arg.mode); do pat_util::pat_bindings(self.tcx.def_map, arg.pat) |_bm, arg_id, _x, path| { debug!("adding argument %d", arg_id); let ident = ast_util::path_to_ident(path); fn_maps.add_variable(Arg(arg_id, ident, mode)); } }; // Add `self`, whether explicit or implicit. match *fk { fk_method(_, _, method) => { match method.self_ty.node { sty_value | sty_region(*) | sty_box(_) | sty_uniq(_) => { fn_maps.add_variable(Arg(method.self_id, special_idents::self_, by_copy)); } sty_static => {} } } fk_dtor(_, _, self_id, _) => { fn_maps.add_variable(Arg(self_id, special_idents::self_, by_copy)); } fk_item_fn(*) | fk_anon(*) | fk_fn_block(*) => {} } // gather up the various local variables, significant expressions, // and so forth: visit::visit_fn(fk, decl, body, sp, id, fn_maps, v); // Special nodes and variables: // - exit_ln represents the end of the fn, either by return or fail // - implicit_ret_var is a pseudo-variable that represents // an implicit return let specials = Specials { exit_ln: fn_maps.add_live_node(ExitNode), fallthrough_ln: fn_maps.add_live_node(ExitNode), no_ret_var: fn_maps.add_variable(ImplicitRet) }; // compute liveness let lsets = @Liveness(fn_maps, specials); let entry_ln = (*lsets).compute(decl, body); // check for various error conditions let check_vt = visit::mk_vt(@visit::Visitor { visit_fn: check_fn, visit_local: check_local, visit_expr: check_expr, visit_arm: check_arm, .. *visit::default_visitor() }); (check_vt.visit_block)(body, lsets, check_vt); lsets.check_ret(id, sp, fk, entry_ln); lsets.warn_about_unused_args(decl, entry_ln); } fn visit_local(local: @local, self: @mut IrMaps, vt: vt<@mut IrMaps>) { let def_map = self.tcx.def_map; do pat_util::pat_bindings(def_map, local.node.pat) |_bm, p_id, sp, path| { debug!("adding local variable %d", p_id); let name = ast_util::path_to_ident(path); self.add_live_node_for_node(p_id, VarDefNode(sp)); let kind = match local.node.init { Some(_) => FromLetWithInitializer, None => FromLetNoInitializer }; self.add_variable(Local(LocalInfo { id: p_id, ident: name, is_mutbl: local.node.is_mutbl, kind: kind })); } visit::visit_local(local, self, vt); } fn visit_arm(arm: &arm, self: @mut IrMaps, vt: vt<@mut IrMaps>) { let def_map = self.tcx.def_map; for arm.pats.each |pat| { do pat_util::pat_bindings(def_map, *pat) |bm, p_id, sp, path| { debug!("adding local variable %d from match with bm %?", p_id, bm); let name = ast_util::path_to_ident(path); self.add_live_node_for_node(p_id, VarDefNode(sp)); self.add_variable(Local(LocalInfo { id: p_id, ident: name, is_mutbl: false, kind: FromMatch(bm) })); } } visit::visit_arm(arm, self, vt); } fn visit_expr(expr: @expr, self: @mut IrMaps, vt: vt<@mut IrMaps>) { match expr.node { // live nodes required for uses or definitions of variables: expr_path(_) => { let def = *self.tcx.def_map.get(&expr.id); debug!("expr %d: path that leads to %?", expr.id, def); if relevant_def(def).is_some() { self.add_live_node_for_node(expr.id, ExprNode(expr.span)); } visit::visit_expr(expr, self, vt); } expr_fn_block(*) => { // Interesting control flow (for loops can contain labeled // breaks or continues) self.add_live_node_for_node(expr.id, ExprNode(expr.span)); // Make a live_node for each captured variable, with the span // being the location that the variable is used. This results // in better error messages than just pointing at the closure // construction site. let cvs = self.capture_map.get(&expr.id); let mut call_caps = ~[]; for cvs.each |cv| { match relevant_def(cv.def) { Some(rv) => { let cv_ln = self.add_live_node(FreeVarNode(cv.span)); let is_move = match cv.mode { // var must be dead afterwards moves::CapMove => true, // var can stil be used moves::CapCopy | moves::CapRef => false }; call_caps.push(CaptureInfo {ln: cv_ln, is_move: is_move, var_nid: rv}); } None => {} } } self.set_captures(expr.id, call_caps); visit::visit_expr(expr, self, vt); } // live nodes required for interesting control flow: expr_if(*) | expr_match(*) | expr_while(*) | expr_loop(*) => { self.add_live_node_for_node(expr.id, ExprNode(expr.span)); visit::visit_expr(expr, self, vt); } expr_binary(op, _, _) if ast_util::lazy_binop(op) => { self.add_live_node_for_node(expr.id, ExprNode(expr.span)); visit::visit_expr(expr, self, vt); } // otherwise, live nodes are not required: expr_index(*) | expr_field(*) | expr_vstore(*) | expr_vec(*) | expr_call(*) | expr_method_call(*) | expr_tup(*) | expr_log(*) | expr_binary(*) | expr_addr_of(*) | expr_copy(*) | expr_loop_body(*) | expr_do_body(*) | expr_cast(*) | expr_unary(*) | expr_break(_) | expr_again(_) | expr_lit(_) | expr_ret(*) | expr_block(*) | expr_assign(*) | expr_swap(*) | expr_assign_op(*) | expr_mac(*) | expr_struct(*) | expr_repeat(*) | expr_paren(*) | expr_inline_asm(*) => { visit::visit_expr(expr, self, vt); } } } // ______________________________________________________________________ // Computing liveness sets // // Actually we compute just a bit more than just liveness, but we use // the same basic propagation framework in all cases. struct Users { reader: LiveNode, writer: LiveNode, used: bool } fn invalid_users() -> Users { Users { reader: invalid_node(), writer: invalid_node(), used: false } } struct Specials { exit_ln: LiveNode, fallthrough_ln: LiveNode, no_ret_var: Variable } static ACC_READ: uint = 1u; static ACC_WRITE: uint = 2u; static ACC_USE: uint = 4u; type LiveNodeMap = @mut HashMap; struct Liveness { tcx: ty::ctxt, ir: @mut IrMaps, s: Specials, successors: @mut ~[LiveNode], users: @mut ~[Users], // The list of node IDs for the nested loop scopes // we're in. loop_scope: @mut ~[node_id], // mappings from loop node ID to LiveNode // ("break" label should map to loop node ID, // it probably doesn't now) break_ln: LiveNodeMap, cont_ln: LiveNodeMap } fn Liveness(ir: @mut IrMaps, specials: Specials) -> Liveness { Liveness { ir: ir, tcx: ir.tcx, s: specials, successors: @mut vec::from_elem(ir.num_live_nodes, invalid_node()), users: @mut vec::from_elem(ir.num_live_nodes * ir.num_vars, invalid_users()), loop_scope: @mut ~[], break_ln: @mut HashMap::new(), cont_ln: @mut HashMap::new() } } pub impl Liveness { fn live_node(&self, node_id: node_id, span: span) -> LiveNode { let ir: &mut IrMaps = self.ir; match ir.live_node_map.find(&node_id) { Some(&ln) => ln, None => { // This must be a mismatch between the ir_map construction // above and the propagation code below; the two sets of // code have to agree about which AST nodes are worth // creating liveness nodes for. self.tcx.sess.span_bug( span, fmt!("No live node registered for node %d", node_id)); } } } fn variable_from_path(&self, expr: @expr) -> Option { match expr.node { expr_path(_) => { let def = *self.tcx.def_map.get(&expr.id); relevant_def(def).map( |rdef| self.variable(*rdef, expr.span) ) } _ => None } } fn variable(&self, node_id: node_id, span: span) -> Variable { self.ir.variable(node_id, span) } fn variable_from_def_map(&self, node_id: node_id, span: span) -> Option { match self.tcx.def_map.find(&node_id) { Some(&def) => { relevant_def(def).map( |rdef| self.variable(*rdef, span) ) } None => { self.tcx.sess.span_bug( span, ~"Not present in def map") } } } fn pat_bindings(&self, pat: @pat, f: &fn(LiveNode, Variable, span, node_id)) { let def_map = self.tcx.def_map; do pat_util::pat_bindings(def_map, pat) |_bm, p_id, sp, _n| { let ln = self.live_node(p_id, sp); let var = self.variable(p_id, sp); f(ln, var, sp, p_id); } } fn arm_pats_bindings(&self, pats: &[@pat], f: &fn(LiveNode, Variable, span, node_id)) { // only consider the first pattern; any later patterns must have // the same bindings, and we also consider the first pattern to be // the "authoratative" set of ids if !pats.is_empty() { self.pat_bindings(pats[0], f) } } fn define_bindings_in_pat(&self, pat: @pat, succ: LiveNode) -> LiveNode { self.define_bindings_in_arm_pats([pat], succ) } fn define_bindings_in_arm_pats(&self, pats: &[@pat], succ: LiveNode) -> LiveNode { let mut succ = succ; do self.arm_pats_bindings(pats) |ln, var, _sp, _id| { self.init_from_succ(ln, succ); self.define(ln, var); succ = ln; } succ } fn idx(&self, ln: LiveNode, var: Variable) -> uint { *ln * self.ir.num_vars + *var } fn live_on_entry(&self, ln: LiveNode, var: Variable) -> Option { assert!(ln.is_valid()); let reader = self.users[self.idx(ln, var)].reader; if reader.is_valid() {Some(self.ir.lnk(reader))} else {None} } /* Is this variable live on entry to any of its successor nodes? */ fn live_on_exit(&self, ln: LiveNode, var: Variable) -> Option { self.live_on_entry(copy self.successors[*ln], var) } fn used_on_entry(&self, ln: LiveNode, var: Variable) -> bool { assert!(ln.is_valid()); self.users[self.idx(ln, var)].used } fn assigned_on_entry(&self, ln: LiveNode, var: Variable) -> Option { assert!(ln.is_valid()); let writer = self.users[self.idx(ln, var)].writer; if writer.is_valid() {Some(self.ir.lnk(writer))} else {None} } fn assigned_on_exit(&self, ln: LiveNode, var: Variable) -> Option { self.assigned_on_entry(copy self.successors[*ln], var) } fn indices(&self, ln: LiveNode, op: &fn(uint)) { let node_base_idx = self.idx(ln, Variable(0)); for uint::range(0, self.ir.num_vars) |var_idx| { op(node_base_idx + var_idx) } } fn indices2(&self, ln: LiveNode, succ_ln: LiveNode, op: &fn(uint, uint)) { let node_base_idx = self.idx(ln, Variable(0u)); let succ_base_idx = self.idx(succ_ln, Variable(0u)); for uint::range(0u, self.ir.num_vars) |var_idx| { op(node_base_idx + var_idx, succ_base_idx + var_idx); } } fn write_vars(&self, wr: @io::Writer, ln: LiveNode, test: &fn(uint) -> LiveNode) { let node_base_idx = self.idx(ln, Variable(0)); for uint::range(0, self.ir.num_vars) |var_idx| { let idx = node_base_idx + var_idx; if test(idx).is_valid() { wr.write_str(~" "); wr.write_str(Variable(var_idx).to_str()); } } } fn find_loop_scope(&self, opt_label: Option, id: node_id, sp: span) -> node_id { match opt_label { Some(_) => // Refers to a labeled loop. Use the results of resolve // to find with one match self.tcx.def_map.find(&id) { Some(&def_label(loop_id)) => loop_id, _ => self.tcx.sess.span_bug(sp, ~"Label on break/loop \ doesn't refer to a loop") }, None => { // Vanilla 'break' or 'loop', so use the enclosing // loop scope let loop_scope = &mut *self.loop_scope; if loop_scope.len() == 0 { self.tcx.sess.span_bug(sp, ~"break outside loop"); } else { // FIXME(#5275): this shouldn't have to be a method... self.last_loop_scope() } } } } fn last_loop_scope(&self) -> node_id { let loop_scope = &mut *self.loop_scope; *loop_scope.last() } fn ln_str(&self, ln: LiveNode) -> ~str { do io::with_str_writer |wr| { wr.write_str(~"[ln("); wr.write_uint(*ln); wr.write_str(~") of kind "); wr.write_str(fmt!("%?", copy self.ir.lnks[*ln])); wr.write_str(~" reads"); self.write_vars(wr, ln, |idx| self.users[idx].reader ); wr.write_str(~" writes"); self.write_vars(wr, ln, |idx| self.users[idx].writer ); wr.write_str(~" "); wr.write_str(~" precedes "); wr.write_str((copy self.successors[*ln]).to_str()); wr.write_str(~"]"); } } fn init_empty(&self, ln: LiveNode, succ_ln: LiveNode) { self.successors[*ln] = succ_ln; // It is not necessary to initialize the // values to empty because this is the value // they have when they are created, and the sets // only grow during iterations. // // self.indices(ln) { |idx| // self.users[idx] = invalid_users(); // } } fn init_from_succ(&self, ln: LiveNode, succ_ln: LiveNode) { // more efficient version of init_empty() / merge_from_succ() self.successors[*ln] = succ_ln; self.indices2(ln, succ_ln, |idx, succ_idx| { self.users[idx] = self.users[succ_idx] }); debug!("init_from_succ(ln=%s, succ=%s)", self.ln_str(ln), self.ln_str(succ_ln)); } fn merge_from_succ(&self, ln: LiveNode, succ_ln: LiveNode, first_merge: bool) -> bool { if ln == succ_ln { return false; } let mut changed = false; do self.indices2(ln, succ_ln) |idx, succ_idx| { let users = &mut *self.users; changed |= copy_if_invalid(copy users[succ_idx].reader, &mut users[idx].reader); changed |= copy_if_invalid(copy users[succ_idx].writer, &mut users[idx].writer); if users[succ_idx].used && !users[idx].used { users[idx].used = true; changed = true; } } debug!("merge_from_succ(ln=%s, succ=%s, first_merge=%b, changed=%b)", ln.to_str(), self.ln_str(succ_ln), first_merge, changed); return changed; fn copy_if_invalid(src: LiveNode, dst: &mut LiveNode) -> bool { if src.is_valid() { if !dst.is_valid() { *dst = src; return true; } } return false; } } // Indicates that a local variable was *defined*; we know that no // uses of the variable can precede the definition (resolve checks // this) so we just clear out all the data. fn define(&self, writer: LiveNode, var: Variable) { let idx = self.idx(writer, var); self.users[idx].reader = invalid_node(); self.users[idx].writer = invalid_node(); debug!("%s defines %s (idx=%u): %s", writer.to_str(), var.to_str(), idx, self.ln_str(writer)); } // Either read, write, or both depending on the acc bitset fn acc(&self, ln: LiveNode, var: Variable, acc: uint) { let idx = self.idx(ln, var); let users = &mut *self.users; let user = &mut users[idx]; if (acc & ACC_WRITE) != 0 { user.reader = invalid_node(); user.writer = ln; } // Important: if we both read/write, must do read second // or else the write will override. if (acc & ACC_READ) != 0 { user.reader = ln; } if (acc & ACC_USE) != 0 { user.used = true; } debug!("%s accesses[%x] %s: %s", ln.to_str(), acc, var.to_str(), self.ln_str(ln)); } // _______________________________________________________________________ fn compute(&self, decl: &fn_decl, body: &blk) -> LiveNode { // if there is a `break` or `again` at the top level, then it's // effectively a return---this only occurs in `for` loops, // where the body is really a closure. debug!("compute: using id for block, %s", block_to_str(body, self.tcx.sess.intr())); let entry_ln: LiveNode = self.with_loop_nodes(body.node.id, self.s.exit_ln, self.s.exit_ln, || { self.propagate_through_fn_block(decl, body) }); // hack to skip the loop unless debug! is enabled: debug!("^^ liveness computation results for body %d (entry=%s)", { for uint::range(0u, self.ir.num_live_nodes) |ln_idx| { debug!("%s", self.ln_str(LiveNode(ln_idx))); } body.node.id }, entry_ln.to_str()); entry_ln } fn propagate_through_fn_block(&self, decl: &fn_decl, blk: &blk) -> LiveNode { // inputs passed by & mode should be considered live on exit: for decl.inputs.each |arg| { match ty::resolved_mode(self.tcx, arg.mode) { by_ref => { // By val and by ref do not own, so register a // read at the end. This will prevent us from // moving out of such variables but also prevent // us from registering last uses and so forth. do pat_util::pat_bindings(self.tcx.def_map, arg.pat) |_bm, arg_id, _sp, _path| { let var = self.variable(arg_id, blk.span); self.acc(self.s.exit_ln, var, ACC_READ); } } by_copy => { // By copy is an owned mode. If we don't use the // variable, nobody will. } } } // the fallthrough exit is only for those cases where we do not // explicitly return: self.init_from_succ(self.s.fallthrough_ln, self.s.exit_ln); if blk.node.expr.is_none() { self.acc(self.s.fallthrough_ln, self.s.no_ret_var, ACC_READ) } self.propagate_through_block(blk, self.s.fallthrough_ln) } fn propagate_through_block(&self, blk: &blk, succ: LiveNode) -> LiveNode { let succ = self.propagate_through_opt_expr(blk.node.expr, succ); do blk.node.stmts.foldr(succ) |stmt, succ| { self.propagate_through_stmt(*stmt, succ) } } fn propagate_through_stmt(&self, stmt: @stmt, succ: LiveNode) -> LiveNode { match stmt.node { stmt_decl(decl, _) => { return self.propagate_through_decl(decl, succ); } stmt_expr(expr, _) | stmt_semi(expr, _) => { return self.propagate_through_expr(expr, succ); } stmt_mac(*) => { self.tcx.sess.span_bug(stmt.span, ~"unexpanded macro"); } } } fn propagate_through_decl(&self, decl: @decl, succ: LiveNode) -> LiveNode { match decl.node { decl_local(ref locals) => { do locals.foldr(succ) |local, succ| { self.propagate_through_local(*local, succ) } } decl_item(_) => { succ } } } fn propagate_through_local(&self, local: @local, succ: LiveNode) -> LiveNode { // Note: we mark the variable as defined regardless of whether // there is an initializer. Initially I had thought to only mark // the live variable as defined if it was initialized, and then we // could check for uninit variables just by scanning what is live // at the start of the function. But that doesn't work so well for // immutable variables defined in a loop: // loop { let x; x = 5; } // because the "assignment" loops back around and generates an error. // // So now we just check that variables defined w/o an // initializer are not live at the point of their // initialization, which is mildly more complex than checking // once at the func header but otherwise equivalent. let succ = self.propagate_through_opt_expr(local.node.init, succ); self.define_bindings_in_pat(local.node.pat, succ) } fn propagate_through_exprs(&self, exprs: &[@expr], succ: LiveNode) -> LiveNode { do exprs.foldr(succ) |expr, succ| { self.propagate_through_expr(*expr, succ) } } fn propagate_through_opt_expr(&self, opt_expr: Option<@expr>, succ: LiveNode) -> LiveNode { do iter::foldl(&opt_expr, succ) |succ, expr| { self.propagate_through_expr(*expr, *succ) } } fn propagate_through_expr(&self, expr: @expr, succ: LiveNode) -> LiveNode { debug!("propagate_through_expr: %s", expr_to_str(expr, self.tcx.sess.intr())); match expr.node { // Interesting cases with control flow or which gen/kill expr_path(_) => { self.access_path(expr, succ, ACC_READ | ACC_USE) } expr_field(e, _, _) => { self.propagate_through_expr(e, succ) } expr_fn_block(_, ref blk) => { debug!("%s is an expr_fn_block", expr_to_str(expr, self.tcx.sess.intr())); /* The next-node for a break is the successor of the entire loop. The next-node for a continue is the top of this loop. */ self.with_loop_nodes(blk.node.id, succ, self.live_node(expr.id, expr.span), || { // the construction of a closure itself is not important, // but we have to consider the closed over variables. let caps = self.ir.captures(expr); do caps.foldr(succ) |cap, succ| { self.init_from_succ(cap.ln, succ); let var = self.variable(cap.var_nid, expr.span); self.acc(cap.ln, var, ACC_READ | ACC_USE); cap.ln } }) } expr_if(cond, ref then, els) => { // // (cond) // | // v // (expr) // / \ // | | // v v // (then)(els) // | | // v v // ( succ ) // let else_ln = self.propagate_through_opt_expr(els, succ); let then_ln = self.propagate_through_block(then, succ); let ln = self.live_node(expr.id, expr.span); self.init_from_succ(ln, else_ln); self.merge_from_succ(ln, then_ln, false); self.propagate_through_expr(cond, ln) } expr_while(cond, ref blk) => { self.propagate_through_loop(expr, Some(cond), blk, succ) } // Note that labels have been resolved, so we don't need to look // at the label ident expr_loop(ref blk, _) => { self.propagate_through_loop(expr, None, blk, succ) } expr_match(e, ref arms) => { // // (e) // | // v // (expr) // / | \ // | | | // v v v // (..arms..) // | | | // v v v // ( succ ) // // let ln = self.live_node(expr.id, expr.span); self.init_empty(ln, succ); let mut first_merge = true; for arms.each |arm| { let body_succ = self.propagate_through_block(&arm.body, succ); let guard_succ = self.propagate_through_opt_expr(arm.guard, body_succ); let arm_succ = self.define_bindings_in_arm_pats(arm.pats, guard_succ); self.merge_from_succ(ln, arm_succ, first_merge); first_merge = false; }; self.propagate_through_expr(e, ln) } expr_ret(o_e) => { // ignore succ and subst exit_ln: self.propagate_through_opt_expr(o_e, self.s.exit_ln) } expr_break(opt_label) => { // Find which label this break jumps to let sc = self.find_loop_scope(opt_label, expr.id, expr.span); // Now that we know the label we're going to, // look it up in the break loop nodes table match self.break_ln.find(&sc) { Some(&b) => b, None => self.tcx.sess.span_bug(expr.span, ~"Break to unknown label") } } expr_again(opt_label) => { // Find which label this expr continues to to let sc = self.find_loop_scope(opt_label, expr.id, expr.span); // Now that we know the label we're going to, // look it up in the continue loop nodes table match self.cont_ln.find(&sc) { Some(&b) => b, None => self.tcx.sess.span_bug(expr.span, ~"Loop to unknown label") } } expr_assign(l, r) => { // see comment on lvalues in // propagate_through_lvalue_components() let succ = self.write_lvalue(l, succ, ACC_WRITE); let succ = self.propagate_through_lvalue_components(l, succ); self.propagate_through_expr(r, succ) } expr_swap(l, r) => { // see comment on lvalues in // propagate_through_lvalue_components() // I count swaps as `used` cause it might be something like: // foo.bar <-> x // and I am too lazy to distinguish this case from // y <-> x // (where both x, y are unused) just for a warning. let succ = self.write_lvalue(r, succ, ACC_WRITE|ACC_READ|ACC_USE); let succ = self.write_lvalue(l, succ, ACC_WRITE|ACC_READ|ACC_USE); let succ = self.propagate_through_lvalue_components(r, succ); self.propagate_through_lvalue_components(l, succ) } expr_assign_op(_, l, r) => { // see comment on lvalues in // propagate_through_lvalue_components() let succ = self.write_lvalue(l, succ, ACC_WRITE|ACC_READ); let succ = self.propagate_through_expr(r, succ); self.propagate_through_lvalue_components(l, succ) } // Uninteresting cases: just propagate in rev exec order expr_vstore(expr, _) => { self.propagate_through_expr(expr, succ) } expr_vec(ref exprs, _) => { self.propagate_through_exprs(*exprs, succ) } expr_repeat(element, count, _) => { let succ = self.propagate_through_expr(count, succ); self.propagate_through_expr(element, succ) } expr_struct(_, ref fields, with_expr) => { let succ = self.propagate_through_opt_expr(with_expr, succ); do (*fields).foldr(succ) |field, succ| { self.propagate_through_expr(field.node.expr, succ) } } expr_call(f, ref args, _) => { // calling a fn with bot return type means that the fn // will fail, and hence the successors can be ignored let t_ret = ty::ty_fn_ret(ty::expr_ty(self.tcx, f)); let succ = if ty::type_is_bot(t_ret) {self.s.exit_ln} else {succ}; let succ = self.propagate_through_exprs(*args, succ); self.propagate_through_expr(f, succ) } expr_method_call(rcvr, _, _, ref args, _) => { // calling a method with bot return type means that the method // will fail, and hence the successors can be ignored let t_ret = ty::ty_fn_ret(ty::node_id_to_type(self.tcx, expr.callee_id)); let succ = if ty::type_is_bot(t_ret) {self.s.exit_ln} else {succ}; let succ = self.propagate_through_exprs(*args, succ); self.propagate_through_expr(rcvr, succ) } expr_tup(ref exprs) => { self.propagate_through_exprs(*exprs, succ) } expr_binary(op, l, r) if ast_util::lazy_binop(op) => { let r_succ = self.propagate_through_expr(r, succ); let ln = self.live_node(expr.id, expr.span); self.init_from_succ(ln, succ); self.merge_from_succ(ln, r_succ, false); self.propagate_through_expr(l, ln) } expr_log(l, r) | expr_index(l, r) | expr_binary(_, l, r) => { self.propagate_through_exprs(~[l, r], succ) } expr_addr_of(_, e) | expr_copy(e) | expr_loop_body(e) | expr_do_body(e) | expr_cast(e, _) | expr_unary(_, e) | expr_paren(e) => { self.propagate_through_expr(e, succ) } expr_inline_asm(ref ia) =>{ let succ = do ia.inputs.foldr(succ) |&(_, expr), succ| { self.propagate_through_expr(expr, succ) }; do ia.outputs.foldr(succ) |&(_, expr), succ| { self.propagate_through_expr(expr, succ) } } expr_lit(*) => { succ } expr_block(ref blk) => { self.propagate_through_block(blk, succ) } expr_mac(*) => { self.tcx.sess.span_bug(expr.span, ~"unexpanded macro"); } } } fn propagate_through_lvalue_components(&self, expr: @expr, succ: LiveNode) -> LiveNode { // # Lvalues // // In general, the full flow graph structure for an // assignment/move/etc can be handled in one of two ways, // depending on whether what is being assigned is a "tracked // value" or not. A tracked value is basically a local // variable or argument. // // The two kinds of graphs are: // // Tracked lvalue Untracked lvalue // ----------------------++----------------------- // || // | || | // v || v // (rvalue) || (rvalue) // | || | // v || v // (write of lvalue) || (lvalue components) // | || | // v || v // (succ) || (succ) // || // ----------------------++----------------------- // // I will cover the two cases in turn: // // # Tracked lvalues // // A tracked lvalue is a local variable/argument `x`. In // these cases, the link_node where the write occurs is linked // to node id of `x`. The `write_lvalue()` routine generates // the contents of this node. There are no subcomponents to // consider. // // # Non-tracked lvalues // // These are lvalues like `x[5]` or `x.f`. In that case, we // basically ignore the value which is written to but generate // reads for the components---`x` in these two examples. The // components reads are generated by // `propagate_through_lvalue_components()` (this fn). // // # Illegal lvalues // // It is still possible to observe assignments to non-lvalues; // these errors are detected in the later pass borrowck. We // just ignore such cases and treat them as reads. match expr.node { expr_path(_) => succ, expr_field(e, _, _) => self.propagate_through_expr(e, succ), _ => self.propagate_through_expr(expr, succ) } } // see comment on propagate_through_lvalue() fn write_lvalue(&self, expr: @expr, succ: LiveNode, acc: uint) -> LiveNode { match expr.node { expr_path(_) => self.access_path(expr, succ, acc), // We do not track other lvalues, so just propagate through // to their subcomponents. Also, it may happen that // non-lvalues occur here, because those are detected in the // later pass borrowck. _ => succ } } fn access_path(&self, expr: @expr, succ: LiveNode, acc: uint) -> LiveNode { let def = *self.tcx.def_map.get(&expr.id); match relevant_def(def) { Some(nid) => { let ln = self.live_node(expr.id, expr.span); if acc != 0u { self.init_from_succ(ln, succ); let var = self.variable(nid, expr.span); self.acc(ln, var, acc); } ln } None => succ } } fn propagate_through_loop(&self, expr: @expr, cond: Option<@expr>, body: &blk, succ: LiveNode) -> LiveNode { /* We model control flow like this: (cond) <--+ | | v | +-- (expr) | | | | | v | | (body) ---+ | | v (succ) */ // first iteration: let mut first_merge = true; let ln = self.live_node(expr.id, expr.span); self.init_empty(ln, succ); if cond.is_some() { // if there is a condition, then it's possible we bypass // the body altogether. otherwise, the only way is via a // break in the loop body. self.merge_from_succ(ln, succ, first_merge); first_merge = false; } debug!("propagate_through_loop: using id for loop body %d %s", expr.id, block_to_str(body, self.tcx.sess.intr())); let cond_ln = self.propagate_through_opt_expr(cond, ln); let body_ln = self.with_loop_nodes(expr.id, succ, ln, || { self.propagate_through_block(body, cond_ln) }); // repeat until fixed point is reached: while self.merge_from_succ(ln, body_ln, first_merge) { first_merge = false; assert!(cond_ln == self.propagate_through_opt_expr(cond, ln)); assert!(body_ln == self.with_loop_nodes(expr.id, succ, ln, || { self.propagate_through_block(body, cond_ln) })); } cond_ln } fn with_loop_nodes(&self, loop_node_id: node_id, break_ln: LiveNode, cont_ln: LiveNode, f: &fn() -> R) -> R { debug!("with_loop_nodes: %d %u", loop_node_id, *break_ln); self.loop_scope.push(loop_node_id); self.break_ln.insert(loop_node_id, break_ln); self.cont_ln.insert(loop_node_id, cont_ln); let r = f(); self.loop_scope.pop(); r } } // _______________________________________________________________________ // Checking for error conditions fn check_local(local: @local, self: @Liveness, vt: vt<@Liveness>) { match local.node.init { Some(_) => { // Initializer: self.warn_about_unused_or_dead_vars_in_pat(local.node.pat); if !local.node.is_mutbl { self.check_for_reassignments_in_pat(local.node.pat); } } None => { // No initializer: the variable might be unused; if not, it // should not be live at this point. debug!("check_local() with no initializer"); do self.pat_bindings(local.node.pat) |ln, var, sp, id| { if !self.warn_about_unused(sp, id, ln, var) { match self.live_on_exit(ln, var) { None => { /* not live: good */ } Some(lnk) => { self.report_illegal_read( local.span, lnk, var, PossiblyUninitializedVariable); } } } } } } visit::visit_local(local, self, vt); } fn check_arm(arm: &arm, self: @Liveness, vt: vt<@Liveness>) { do self.arm_pats_bindings(arm.pats) |ln, var, sp, id| { self.warn_about_unused(sp, id, ln, var); } visit::visit_arm(arm, self, vt); } fn check_expr(expr: @expr, self: @Liveness, vt: vt<@Liveness>) { match expr.node { expr_path(_) => { for self.variable_from_def_map(expr.id, expr.span).each |var| { let ln = self.live_node(expr.id, expr.span); self.consider_last_use(expr, ln, *var); match self.ir.variable_moves_map.find(&expr.id) { None => {} Some(&entire_expr) => { debug!("(checking expr) is a move: `%s`", expr_to_str(expr, self.tcx.sess.intr())); self.check_move_from_var(ln, *var, entire_expr); } } } visit::visit_expr(expr, self, vt); } expr_fn_block(*) => { let caps = self.ir.captures(expr); for caps.each |cap| { let var = self.variable(cap.var_nid, expr.span); self.consider_last_use(expr, cap.ln, var); if cap.is_move { self.check_move_from_var(cap.ln, var, expr); } } visit::visit_expr(expr, self, vt); } expr_assign(l, r) => { self.check_lvalue(l, vt); (vt.visit_expr)(r, self, vt); visit::visit_expr(expr, self, vt); } expr_assign_op(_, l, _) => { self.check_lvalue(l, vt); visit::visit_expr(expr, self, vt); } expr_inline_asm(ref ia) => { for ia.inputs.each |&(_, in)| { (vt.visit_expr)(in, self, vt); } // Output operands must be lvalues for ia.outputs.each |&(_, out)| { match out.node { expr_addr_of(_, inner) => { self.check_lvalue(inner, vt); } _ => {} } (vt.visit_expr)(out, self, vt); } visit::visit_expr(expr, self, vt); } // no correctness conditions related to liveness expr_call(*) | expr_method_call(*) | expr_if(*) | expr_match(*) | expr_while(*) | expr_loop(*) | expr_index(*) | expr_field(*) | expr_vstore(*) | expr_vec(*) | expr_tup(*) | expr_log(*) | expr_binary(*) | expr_copy(*) | expr_loop_body(*) | expr_do_body(*) | expr_cast(*) | expr_unary(*) | expr_ret(*) | expr_break(*) | expr_again(*) | expr_lit(_) | expr_block(*) | expr_swap(*) | expr_mac(*) | expr_addr_of(*) | expr_struct(*) | expr_repeat(*) | expr_paren(*) => { visit::visit_expr(expr, self, vt); } } } fn check_fn(_fk: &visit::fn_kind, _decl: &fn_decl, _body: &blk, _sp: span, _id: node_id, _self: @Liveness, _v: vt<@Liveness>) { // do not check contents of nested fns } enum ReadKind { PossiblyUninitializedVariable, PossiblyUninitializedField, MovedValue, PartiallyMovedValue } pub impl Liveness { fn check_ret(@self, id: node_id, sp: span, _fk: &visit::fn_kind, entry_ln: LiveNode) { if self.live_on_entry(entry_ln, self.s.no_ret_var).is_some() { // if no_ret_var is live, then we fall off the end of the // function without any kind of return expression: let t_ret = ty::ty_fn_ret(ty::node_id_to_type(self.tcx, id)); if ty::type_is_nil(t_ret) { // for nil return types, it is ok to not return a value expl. } else if ty::type_is_bot(t_ret) { // for bot return types, not ok. Function should fail. self.tcx.sess.span_err( sp, ~"some control paths may return"); } else { self.tcx.sess.span_err( sp, ~"not all control paths return a value"); } } } fn check_move_from_var(@self, ln: LiveNode, var: Variable, move_expr: @expr) { /*! * * Checks whether `var` is live on entry to any of the * successors of `ln`. If it is, report an error. * `move_expr` is the expression which caused the variable * to be moved. * * Note that `move_expr` is not necessarily a reference to the * variable. It might be an expression like `x.f` which could * cause a move of the variable `x`, or a closure creation. */ debug!("check_move_from_var(%s, %s)", ln.to_str(), var.to_str()); match self.live_on_exit(ln, var) { None => {} Some(lnk) => self.report_illegal_move(lnk, var, move_expr) } } fn consider_last_use(@self, expr: @expr, ln: LiveNode, var: Variable) { debug!("consider_last_use(expr.id=%?, ln=%s, var=%s)", expr.id, ln.to_str(), var.to_str()); match self.live_on_exit(ln, var) { Some(_) => {} None => self.ir.add_last_use(expr.id, var) } } fn check_lvalue(@self, expr: @expr, vt: vt<@Liveness>) { match expr.node { expr_path(_) => { match *self.tcx.def_map.get(&expr.id) { def_local(nid, false) => { // Assignment to an immutable variable or argument: // only legal if there is no later assignment. let ln = self.live_node(expr.id, expr.span); let var = self.variable(nid, expr.span); self.check_for_reassignment(ln, var, expr.span); self.warn_about_dead_assign(expr.span, expr.id, ln, var); } def => { match relevant_def(def) { Some(nid) => { let ln = self.live_node(expr.id, expr.span); let var = self.variable(nid, expr.span); self.warn_about_dead_assign(expr.span, expr.id, ln, var); } None => {} } } } } _ => { // For other kinds of lvalues, no checks are required, // and any embedded expressions are actually rvalues visit::visit_expr(expr, self, vt); } } } fn check_for_reassignments_in_pat(@self, pat: @pat) { do self.pat_bindings(pat) |ln, var, sp, _id| { self.check_for_reassignment(ln, var, sp); } } fn check_for_reassignment(@self, ln: LiveNode, var: Variable, orig_span: span) { match self.assigned_on_exit(ln, var) { Some(ExprNode(span)) => { self.tcx.sess.span_err( span, ~"re-assignment of immutable variable"); self.tcx.sess.span_note( orig_span, ~"prior assignment occurs here"); } Some(lnk) => { self.tcx.sess.span_bug( orig_span, fmt!("illegal writer: %?", lnk)); } None => {} } } fn report_illegal_move(@self, lnk: LiveNodeKind, var: Variable, move_expr: @expr) { // the only time that it is possible to have a moved variable // used by ExitNode would be arguments or fields in a ctor. // we give a slightly different error message in those cases. if lnk == ExitNode { // FIXME #4715: this seems like it should be reported in the // borrow checker let vk = self.ir.var_kinds[*var]; match vk { Arg(_, name, _) => { self.tcx.sess.span_err( move_expr.span, fmt!("illegal move from argument `%s`, which is not \ copy or move mode", *self.tcx.sess.str_of(name))); return; } Local(*) | ImplicitRet => { self.tcx.sess.span_bug( move_expr.span, fmt!("illegal reader (%?) for `%?`", lnk, vk)); } } } match move_expr.node { expr_fn_block(*) => { self.report_illegal_read( move_expr.span, lnk, var, MovedValue); let name = self.ir.variable_name(var); self.tcx.sess.span_note( move_expr.span, fmt!("`%s` moved into closure environment here \ because its type is moved by default", *name)); } expr_path(*) => { self.report_illegal_read( move_expr.span, lnk, var, MovedValue); self.report_move_location( move_expr, var, "", "it"); } expr_field(*) => { self.report_illegal_read( move_expr.span, lnk, var, PartiallyMovedValue); self.report_move_location( move_expr, var, "field of ", "the field"); } expr_index(*) => { self.report_illegal_read( move_expr.span, lnk, var, PartiallyMovedValue); self.report_move_location( move_expr, var, "element of ", "the element"); } _ => { self.report_illegal_read( move_expr.span, lnk, var, PartiallyMovedValue); self.report_move_location( move_expr, var, "subcomponent of ", "the subcomponent"); } }; } fn report_move_location(@self, move_expr: @expr, var: Variable, expr_descr: &str, pronoun: &str) { let move_expr_ty = ty::expr_ty(self.tcx, move_expr); let name = self.ir.variable_name(var); self.tcx.sess.span_note( move_expr.span, fmt!("%s`%s` moved here because %s has type %s, \ which is moved by default (use `copy` to override)", expr_descr, *name, pronoun, ty_to_str(self.tcx, move_expr_ty))); } fn report_illegal_read(@self, chk_span: span, lnk: LiveNodeKind, var: Variable, rk: ReadKind) { let msg = match rk { PossiblyUninitializedVariable => "possibly uninitialized \ variable", PossiblyUninitializedField => "possibly uninitialized field", MovedValue => "moved value", PartiallyMovedValue => "partially moved value" }; let name = self.ir.variable_name(var); match lnk { FreeVarNode(span) => { self.tcx.sess.span_err( span, fmt!("capture of %s: `%s`", msg, *name)); } ExprNode(span) => { self.tcx.sess.span_err( span, fmt!("use of %s: `%s`", msg, *name)); } ExitNode | VarDefNode(_) => { self.tcx.sess.span_bug( chk_span, fmt!("illegal reader: %?", lnk)); } } } fn should_warn(@self, var: Variable) -> Option<@~str> { let name = self.ir.variable_name(var); if name[0] == ('_' as u8) { None } else { Some(name) } } fn warn_about_unused_args(@self, decl: &fn_decl, entry_ln: LiveNode) { for decl.inputs.each |arg| { do pat_util::pat_bindings(self.tcx.def_map, arg.pat) |_bm, p_id, sp, _n| { let var = self.variable(p_id, sp); self.warn_about_unused(sp, p_id, entry_ln, var); } } } fn warn_about_unused_or_dead_vars_in_pat(@self, pat: @pat) { do self.pat_bindings(pat) |ln, var, sp, id| { if !self.warn_about_unused(sp, id, ln, var) { self.warn_about_dead_assign(sp, id, ln, var); } } } fn warn_about_unused(@self, sp: span, id: node_id, ln: LiveNode, var: Variable) -> bool { if !self.used_on_entry(ln, var) { for self.should_warn(var).each |name| { // annoying: for parameters in funcs like `fn(x: int) // {ret}`, there is only one node, so asking about // assigned_on_exit() is not meaningful. let is_assigned = if ln == self.s.exit_ln { false } else { self.assigned_on_exit(ln, var).is_some() }; if is_assigned { self.tcx.sess.span_lint(unused_variable, id, self.ir.cur_item, sp, fmt!("variable `%s` is assigned to, \ but never used", **name)); } else { self.tcx.sess.span_lint(unused_variable, id, self.ir.cur_item, sp, fmt!("unused variable: `%s`", **name)); } } return true; } return false; } fn warn_about_dead_assign(@self, sp: span, id: node_id, ln: LiveNode, var: Variable) { if self.live_on_exit(ln, var).is_none() { for self.should_warn(var).each |name| { self.tcx.sess.span_lint(dead_assignment, id, self.ir.cur_item, sp, fmt!("value assigned to `%s` is never read", **name)); } } } }