1640 lines
57 KiB
Rust
1640 lines
57 KiB
Rust
// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! A classic liveness analysis based on dataflow over the AST. Computes,
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//! for each local variable in a function, whether that variable is live
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//! at a given point. Program execution points are identified by their
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//! id.
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//!
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//! # Basic idea
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//!
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//! The basic model is that each local variable is assigned an index. We
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//! represent sets of local variables using a vector indexed by this
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//! index. The value in the vector is either 0, indicating the variable
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//! is dead, or the id of an expression that uses the variable.
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//!
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//! We conceptually walk over the AST in reverse execution order. If we
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//! find a use of a variable, we add it to the set of live variables. If
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//! we find an assignment to a variable, we remove it from the set of live
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//! variables. When we have to merge two flows, we take the union of
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//! those two flows---if the variable is live on both paths, we simply
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//! pick one id. In the event of loops, we continue doing this until a
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//! fixed point is reached.
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//!
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//! ## Checking initialization
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//!
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//! At the function entry point, all variables must be dead. If this is
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//! not the case, we can report an error using the id found in the set of
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//! live variables, which identifies a use of the variable which is not
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//! dominated by an assignment.
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//!
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//! ## Checking moves
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//!
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//! After each explicit move, the variable must be dead.
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//!
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//! ## Computing last uses
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//!
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//! Any use of the variable where the variable is dead afterwards is a
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//! last use.
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//!
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//! # Implementation details
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//!
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//! The actual implementation contains two (nested) walks over the AST.
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//! The outer walk has the job of building up the ir_maps instance for the
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//! enclosing function. On the way down the tree, it identifies those AST
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//! nodes and variable IDs that will be needed for the liveness analysis
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//! and assigns them contiguous IDs. The liveness id for an AST node is
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//! called a `live_node` (it's a newtype'd usize) and the id for a variable
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//! is called a `variable` (another newtype'd usize).
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//!
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//! On the way back up the tree, as we are about to exit from a function
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//! declaration we allocate a `liveness` instance. Now that we know
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//! precisely how many nodes and variables we need, we can allocate all
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//! the various arrays that we will need to precisely the right size. We then
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//! perform the actual propagation on the `liveness` instance.
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//!
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//! This propagation is encoded in the various `propagate_through_*()`
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//! methods. It effectively does a reverse walk of the AST; whenever we
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//! reach a loop node, we iterate until a fixed point is reached.
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//!
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//! ## The `Users` struct
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//!
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//! At each live node `N`, we track three pieces of information for each
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//! variable `V` (these are encapsulated in the `Users` struct):
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//!
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//! - `reader`: the `LiveNode` ID of some node which will read the value
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//! that `V` holds on entry to `N`. Formally: a node `M` such
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//! that there exists a path `P` from `N` to `M` where `P` does not
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//! write `V`. If the `reader` is `invalid_node()`, then the current
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//! value will never be read (the variable is dead, essentially).
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//!
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//! - `writer`: the `LiveNode` ID of some node which will write the
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//! variable `V` and which is reachable from `N`. Formally: a node `M`
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//! such that there exists a path `P` from `N` to `M` and `M` writes
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//! `V`. If the `writer` is `invalid_node()`, then there is no writer
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//! of `V` that follows `N`.
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//!
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//! - `used`: a boolean value indicating whether `V` is *used*. We
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//! distinguish a *read* from a *use* in that a *use* is some read that
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//! is not just used to generate a new value. For example, `x += 1` is
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//! a read but not a use. This is used to generate better warnings.
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//!
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//! ## Special Variables
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//!
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//! We generate various special variables for various, well, special purposes.
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//! These are described in the `specials` struct:
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//!
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//! - `exit_ln`: a live node that is generated to represent every 'exit' from
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//! the function, whether it be by explicit return, panic, or other means.
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//!
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//! - `fallthrough_ln`: a live node that represents a fallthrough
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//!
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//! - `no_ret_var`: a synthetic variable that is only 'read' from, the
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//! fallthrough node. This allows us to detect functions where we fail
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//! to return explicitly.
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//! - `clean_exit_var`: a synthetic variable that is only 'read' from the
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//! fallthrough node. It is only live if the function could converge
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//! via means other than an explicit `return` expression. That is, it is
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//! only dead if the end of the function's block can never be reached.
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//! It is the responsibility of typeck to ensure that there are no
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//! `return` expressions in a function declared as diverging.
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use self::LoopKind::*;
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use self::LiveNodeKind::*;
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use self::VarKind::*;
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use dep_graph::DepNode;
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use hir::def::*;
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use hir::pat_util;
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use ty::{self, Ty, TyCtxt, ParameterEnvironment};
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use traits::{self, Reveal};
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use ty::subst::Subst;
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use lint;
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use util::nodemap::NodeMap;
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use std::{fmt, usize};
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use std::io::prelude::*;
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use std::io;
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use std::rc::Rc;
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use syntax::ast::{self, NodeId};
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use syntax::codemap::original_sp;
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use syntax::parse::token::keywords;
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use syntax::ptr::P;
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use syntax_pos::{BytePos, Span};
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use hir::Expr;
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use hir;
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use hir::print::{expr_to_string, block_to_string};
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use hir::intravisit::{self, Visitor, FnKind};
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/// For use with `propagate_through_loop`.
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enum LoopKind<'a> {
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/// An endless `loop` loop.
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LoopLoop,
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/// A `while` loop, with the given expression as condition.
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WhileLoop(&'a Expr),
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}
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#[derive(Copy, Clone, PartialEq)]
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struct Variable(usize);
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#[derive(Copy, PartialEq)]
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struct LiveNode(usize);
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impl Variable {
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fn get(&self) -> usize { let Variable(v) = *self; v }
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}
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impl LiveNode {
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fn get(&self) -> usize { let LiveNode(v) = *self; v }
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}
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impl Clone for LiveNode {
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fn clone(&self) -> LiveNode {
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LiveNode(self.get())
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}
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}
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#[derive(Copy, Clone, PartialEq, Debug)]
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enum LiveNodeKind {
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FreeVarNode(Span),
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ExprNode(Span),
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VarDefNode(Span),
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ExitNode
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}
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fn live_node_kind_to_string(lnk: LiveNodeKind, tcx: TyCtxt) -> String {
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let cm = tcx.sess.codemap();
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match lnk {
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FreeVarNode(s) => {
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format!("Free var node [{}]", cm.span_to_string(s))
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}
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ExprNode(s) => {
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format!("Expr node [{}]", cm.span_to_string(s))
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}
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VarDefNode(s) => {
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format!("Var def node [{}]", cm.span_to_string(s))
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}
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ExitNode => "Exit node".to_string(),
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}
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}
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impl<'a, 'tcx, 'v> Visitor<'v> for IrMaps<'a, 'tcx> {
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fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v hir::FnDecl,
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b: &'v hir::Block, s: Span, id: NodeId) {
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visit_fn(self, fk, fd, b, s, id);
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}
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fn visit_local(&mut self, l: &hir::Local) { visit_local(self, l); }
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fn visit_expr(&mut self, ex: &Expr) { visit_expr(self, ex); }
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fn visit_arm(&mut self, a: &hir::Arm) { visit_arm(self, a); }
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}
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pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
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let _task = tcx.dep_graph.in_task(DepNode::Liveness);
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tcx.map.krate().visit_all_items(&mut IrMaps::new(tcx));
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tcx.sess.abort_if_errors();
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}
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impl fmt::Debug for LiveNode {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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write!(f, "ln({})", self.get())
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}
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}
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impl fmt::Debug for Variable {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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write!(f, "v({})", self.get())
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}
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}
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// ______________________________________________________________________
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// Creating ir_maps
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//
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// This is the first pass and the one that drives the main
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// computation. It walks up and down the IR once. On the way down,
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// we count for each function the number of variables as well as
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// liveness nodes. A liveness node is basically an expression or
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// capture clause that does something of interest: either it has
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// interesting control flow or it uses/defines a local variable.
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//
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// On the way back up, at each function node we create liveness sets
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// (we now know precisely how big to make our various vectors and so
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// forth) and then do the data-flow propagation to compute the set
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// of live variables at each program point.
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//
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// Finally, we run back over the IR one last time and, using the
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// computed liveness, check various safety conditions. For example,
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// there must be no live nodes at the definition site for a variable
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// unless it has an initializer. Similarly, each non-mutable local
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// variable must not be assigned if there is some successor
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// assignment. And so forth.
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impl LiveNode {
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fn is_valid(&self) -> bool {
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self.get() != usize::MAX
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}
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}
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fn invalid_node() -> LiveNode { LiveNode(usize::MAX) }
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struct CaptureInfo {
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ln: LiveNode,
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var_nid: NodeId
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}
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#[derive(Copy, Clone, Debug)]
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struct LocalInfo {
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id: NodeId,
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name: ast::Name
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}
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#[derive(Copy, Clone, Debug)]
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enum VarKind {
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Arg(NodeId, ast::Name),
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Local(LocalInfo),
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ImplicitRet,
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CleanExit
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}
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struct IrMaps<'a, 'tcx: 'a> {
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tcx: TyCtxt<'a, 'tcx, 'tcx>,
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num_live_nodes: usize,
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num_vars: usize,
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live_node_map: NodeMap<LiveNode>,
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variable_map: NodeMap<Variable>,
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capture_info_map: NodeMap<Rc<Vec<CaptureInfo>>>,
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var_kinds: Vec<VarKind>,
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lnks: Vec<LiveNodeKind>,
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}
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impl<'a, 'tcx> IrMaps<'a, 'tcx> {
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fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> IrMaps<'a, 'tcx> {
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IrMaps {
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tcx: tcx,
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num_live_nodes: 0,
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num_vars: 0,
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live_node_map: NodeMap(),
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variable_map: NodeMap(),
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capture_info_map: NodeMap(),
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var_kinds: Vec::new(),
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lnks: Vec::new(),
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}
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}
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fn add_live_node(&mut self, lnk: LiveNodeKind) -> LiveNode {
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let ln = LiveNode(self.num_live_nodes);
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self.lnks.push(lnk);
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self.num_live_nodes += 1;
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debug!("{:?} is of kind {}", ln,
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live_node_kind_to_string(lnk, self.tcx));
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ln
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}
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fn add_live_node_for_node(&mut self, node_id: NodeId, lnk: LiveNodeKind) {
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let ln = self.add_live_node(lnk);
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self.live_node_map.insert(node_id, ln);
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debug!("{:?} is node {}", ln, node_id);
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}
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fn add_variable(&mut self, vk: VarKind) -> Variable {
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let v = Variable(self.num_vars);
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self.var_kinds.push(vk);
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self.num_vars += 1;
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match vk {
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Local(LocalInfo { id: node_id, .. }) | Arg(node_id, _) => {
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self.variable_map.insert(node_id, v);
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},
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ImplicitRet | CleanExit => {}
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}
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debug!("{:?} is {:?}", v, vk);
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v
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}
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fn variable(&self, node_id: NodeId, span: Span) -> Variable {
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match self.variable_map.get(&node_id) {
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Some(&var) => var,
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None => {
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span_bug!(span, "no variable registered for id {}", node_id);
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}
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}
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}
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fn variable_name(&self, var: Variable) -> String {
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match self.var_kinds[var.get()] {
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Local(LocalInfo { name, .. }) | Arg(_, name) => {
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name.to_string()
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},
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ImplicitRet => "<implicit-ret>".to_string(),
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CleanExit => "<clean-exit>".to_string()
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}
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}
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fn set_captures(&mut self, node_id: NodeId, cs: Vec<CaptureInfo>) {
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self.capture_info_map.insert(node_id, Rc::new(cs));
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}
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fn lnk(&self, ln: LiveNode) -> LiveNodeKind {
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self.lnks[ln.get()]
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}
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}
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impl<'a, 'tcx, 'v> Visitor<'v> for Liveness<'a, 'tcx> {
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fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v hir::FnDecl,
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b: &'v hir::Block, s: Span, n: NodeId) {
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check_fn(self, fk, fd, b, s, n);
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}
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fn visit_local(&mut self, l: &hir::Local) {
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check_local(self, l);
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}
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fn visit_expr(&mut self, ex: &Expr) {
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check_expr(self, ex);
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}
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fn visit_arm(&mut self, a: &hir::Arm) {
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check_arm(self, a);
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}
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}
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fn visit_fn(ir: &mut IrMaps,
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fk: FnKind,
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decl: &hir::FnDecl,
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body: &hir::Block,
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sp: Span,
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id: ast::NodeId) {
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debug!("visit_fn");
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// swap in a new set of IR maps for this function body:
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let mut fn_maps = IrMaps::new(ir.tcx);
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debug!("creating fn_maps: {:?}", &fn_maps as *const IrMaps);
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for arg in &decl.inputs {
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pat_util::pat_bindings(&arg.pat, |_bm, arg_id, _x, path1| {
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debug!("adding argument {}", arg_id);
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let name = path1.node;
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fn_maps.add_variable(Arg(arg_id, name));
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})
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};
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// gather up the various local variables, significant expressions,
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// and so forth:
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intravisit::walk_fn(&mut fn_maps, fk, decl, body, sp, id);
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// Special nodes and variables:
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// - exit_ln represents the end of the fn, either by return or panic
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// - implicit_ret_var is a pseudo-variable that represents
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// an implicit return
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let specials = Specials {
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exit_ln: fn_maps.add_live_node(ExitNode),
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fallthrough_ln: fn_maps.add_live_node(ExitNode),
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no_ret_var: fn_maps.add_variable(ImplicitRet),
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clean_exit_var: fn_maps.add_variable(CleanExit)
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};
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// compute liveness
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let mut lsets = Liveness::new(&mut fn_maps, specials);
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let entry_ln = lsets.compute(decl, body);
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// check for various error conditions
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lsets.visit_block(body);
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lsets.check_ret(id, sp, fk, entry_ln, body);
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lsets.warn_about_unused_args(decl, entry_ln);
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}
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fn visit_local(ir: &mut IrMaps, local: &hir::Local) {
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pat_util::pat_bindings(&local.pat, |_, p_id, sp, path1| {
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debug!("adding local variable {}", p_id);
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let name = path1.node;
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ir.add_live_node_for_node(p_id, VarDefNode(sp));
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ir.add_variable(Local(LocalInfo {
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id: p_id,
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name: name
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}));
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});
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intravisit::walk_local(ir, local);
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}
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fn visit_arm(ir: &mut IrMaps, arm: &hir::Arm) {
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for pat in &arm.pats {
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pat_util::pat_bindings(&pat, |bm, p_id, sp, path1| {
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debug!("adding local variable {} from match with bm {:?}",
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p_id, bm);
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let name = path1.node;
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ir.add_live_node_for_node(p_id, VarDefNode(sp));
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ir.add_variable(Local(LocalInfo {
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id: p_id,
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name: name
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}));
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})
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}
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intravisit::walk_arm(ir, arm);
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}
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fn visit_expr(ir: &mut IrMaps, expr: &Expr) {
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match expr.node {
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// live nodes required for uses or definitions of variables:
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hir::ExprPath(..) => {
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let def = ir.tcx.expect_def(expr.id);
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debug!("expr {}: path that leads to {:?}", expr.id, def);
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if let Def::Local(..) = def {
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ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
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}
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intravisit::walk_expr(ir, expr);
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}
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hir::ExprClosure(..) => {
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// Interesting control flow (for loops can contain labeled
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// breaks or continues)
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ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
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// Make a live_node for each captured variable, with the span
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// being the location that the variable is used. This results
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// in better error messages than just pointing at the closure
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// construction site.
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let mut call_caps = Vec::new();
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ir.tcx.with_freevars(expr.id, |freevars| {
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for fv in freevars {
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if let Def::Local(_, rv) = fv.def {
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let fv_ln = ir.add_live_node(FreeVarNode(fv.span));
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call_caps.push(CaptureInfo {ln: fv_ln,
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var_nid: rv});
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}
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}
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});
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ir.set_captures(expr.id, call_caps);
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intravisit::walk_expr(ir, expr);
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}
|
|
|
|
// live nodes required for interesting control flow:
|
|
hir::ExprIf(..) | hir::ExprMatch(..) | hir::ExprWhile(..) | hir::ExprLoop(..) => {
|
|
ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
|
|
intravisit::walk_expr(ir, expr);
|
|
}
|
|
hir::ExprBinary(op, _, _) if op.node.is_lazy() => {
|
|
ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
|
|
intravisit::walk_expr(ir, expr);
|
|
}
|
|
|
|
// otherwise, live nodes are not required:
|
|
hir::ExprIndex(..) | hir::ExprField(..) | hir::ExprTupField(..) |
|
|
hir::ExprVec(..) | hir::ExprCall(..) | hir::ExprMethodCall(..) |
|
|
hir::ExprTup(..) | hir::ExprBinary(..) | hir::ExprAddrOf(..) |
|
|
hir::ExprCast(..) | hir::ExprUnary(..) | hir::ExprBreak(_) |
|
|
hir::ExprAgain(_) | hir::ExprLit(_) | hir::ExprRet(..) |
|
|
hir::ExprBlock(..) | hir::ExprAssign(..) | hir::ExprAssignOp(..) |
|
|
hir::ExprStruct(..) | hir::ExprRepeat(..) |
|
|
hir::ExprInlineAsm(..) | hir::ExprBox(..) |
|
|
hir::ExprType(..) => {
|
|
intravisit::walk_expr(ir, expr);
|
|
}
|
|
}
|
|
}
|
|
|
|
// ______________________________________________________________________
|
|
// Computing liveness sets
|
|
//
|
|
// Actually we compute just a bit more than just liveness, but we use
|
|
// the same basic propagation framework in all cases.
|
|
|
|
#[derive(Clone, Copy)]
|
|
struct Users {
|
|
reader: LiveNode,
|
|
writer: LiveNode,
|
|
used: bool
|
|
}
|
|
|
|
fn invalid_users() -> Users {
|
|
Users {
|
|
reader: invalid_node(),
|
|
writer: invalid_node(),
|
|
used: false
|
|
}
|
|
}
|
|
|
|
#[derive(Copy, Clone)]
|
|
struct Specials {
|
|
exit_ln: LiveNode,
|
|
fallthrough_ln: LiveNode,
|
|
no_ret_var: Variable,
|
|
clean_exit_var: Variable
|
|
}
|
|
|
|
const ACC_READ: u32 = 1;
|
|
const ACC_WRITE: u32 = 2;
|
|
const ACC_USE: u32 = 4;
|
|
|
|
struct Liveness<'a, 'tcx: 'a> {
|
|
ir: &'a mut IrMaps<'a, 'tcx>,
|
|
s: Specials,
|
|
successors: Vec<LiveNode>,
|
|
users: Vec<Users>,
|
|
// The list of node IDs for the nested loop scopes
|
|
// we're in.
|
|
loop_scope: Vec<NodeId>,
|
|
// mappings from loop node ID to LiveNode
|
|
// ("break" label should map to loop node ID,
|
|
// it probably doesn't now)
|
|
break_ln: NodeMap<LiveNode>,
|
|
cont_ln: NodeMap<LiveNode>
|
|
}
|
|
|
|
impl<'a, 'tcx> Liveness<'a, 'tcx> {
|
|
fn new(ir: &'a mut IrMaps<'a, 'tcx>, specials: Specials) -> Liveness<'a, 'tcx> {
|
|
let num_live_nodes = ir.num_live_nodes;
|
|
let num_vars = ir.num_vars;
|
|
Liveness {
|
|
ir: ir,
|
|
s: specials,
|
|
successors: vec![invalid_node(); num_live_nodes],
|
|
users: vec![invalid_users(); num_live_nodes * num_vars],
|
|
loop_scope: Vec::new(),
|
|
break_ln: NodeMap(),
|
|
cont_ln: NodeMap(),
|
|
}
|
|
}
|
|
|
|
fn live_node(&self, node_id: NodeId, span: Span) -> LiveNode {
|
|
match self.ir.live_node_map.get(&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.
|
|
span_bug!(
|
|
span,
|
|
"no live node registered for node {}",
|
|
node_id);
|
|
}
|
|
}
|
|
}
|
|
|
|
fn variable(&self, node_id: NodeId, span: Span) -> Variable {
|
|
self.ir.variable(node_id, span)
|
|
}
|
|
|
|
fn pat_bindings<F>(&mut self, pat: &hir::Pat, mut f: F) where
|
|
F: FnMut(&mut Liveness<'a, 'tcx>, LiveNode, Variable, Span, NodeId),
|
|
{
|
|
pat_util::pat_bindings(pat, |_bm, p_id, sp, _n| {
|
|
let ln = self.live_node(p_id, sp);
|
|
let var = self.variable(p_id, sp);
|
|
f(self, ln, var, sp, p_id);
|
|
})
|
|
}
|
|
|
|
fn arm_pats_bindings<F>(&mut self, pat: Option<&hir::Pat>, f: F) where
|
|
F: FnMut(&mut Liveness<'a, 'tcx>, LiveNode, Variable, Span, NodeId),
|
|
{
|
|
if let Some(pat) = pat {
|
|
self.pat_bindings(pat, f);
|
|
}
|
|
}
|
|
|
|
fn define_bindings_in_pat(&mut self, pat: &hir::Pat, succ: LiveNode)
|
|
-> LiveNode {
|
|
self.define_bindings_in_arm_pats(Some(pat), succ)
|
|
}
|
|
|
|
fn define_bindings_in_arm_pats(&mut self, pat: Option<&hir::Pat>, succ: LiveNode)
|
|
-> LiveNode {
|
|
let mut succ = succ;
|
|
self.arm_pats_bindings(pat, |this, ln, var, _sp, _id| {
|
|
this.init_from_succ(ln, succ);
|
|
this.define(ln, var);
|
|
succ = ln;
|
|
});
|
|
succ
|
|
}
|
|
|
|
fn idx(&self, ln: LiveNode, var: Variable) -> usize {
|
|
ln.get() * self.ir.num_vars + var.get()
|
|
}
|
|
|
|
fn live_on_entry(&self, ln: LiveNode, var: Variable)
|
|
-> Option<LiveNodeKind> {
|
|
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<LiveNodeKind> {
|
|
let successor = self.successors[ln.get()];
|
|
self.live_on_entry(successor, 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<LiveNodeKind> {
|
|
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<LiveNodeKind> {
|
|
let successor = self.successors[ln.get()];
|
|
self.assigned_on_entry(successor, var)
|
|
}
|
|
|
|
fn indices2<F>(&mut self, ln: LiveNode, succ_ln: LiveNode, mut op: F) where
|
|
F: FnMut(&mut Liveness<'a, 'tcx>, usize, usize),
|
|
{
|
|
let node_base_idx = self.idx(ln, Variable(0));
|
|
let succ_base_idx = self.idx(succ_ln, Variable(0));
|
|
for var_idx in 0..self.ir.num_vars {
|
|
op(self, node_base_idx + var_idx, succ_base_idx + var_idx);
|
|
}
|
|
}
|
|
|
|
fn write_vars<F>(&self,
|
|
wr: &mut Write,
|
|
ln: LiveNode,
|
|
mut test: F)
|
|
-> io::Result<()> where
|
|
F: FnMut(usize) -> LiveNode,
|
|
{
|
|
let node_base_idx = self.idx(ln, Variable(0));
|
|
for var_idx in 0..self.ir.num_vars {
|
|
let idx = node_base_idx + var_idx;
|
|
if test(idx).is_valid() {
|
|
write!(wr, " {:?}", Variable(var_idx))?;
|
|
}
|
|
}
|
|
Ok(())
|
|
}
|
|
|
|
fn find_loop_scope(&self,
|
|
opt_label: Option<ast::Name>,
|
|
id: NodeId,
|
|
sp: Span)
|
|
-> NodeId {
|
|
match opt_label {
|
|
Some(_) => {
|
|
// Refers to a labeled loop. Use the results of resolve
|
|
// to find with one
|
|
match self.ir.tcx.expect_def(id) {
|
|
Def::Label(loop_id) => loop_id,
|
|
_ => span_bug!(sp, "label on break/loop \
|
|
doesn't refer to a loop")
|
|
}
|
|
}
|
|
None => {
|
|
// Vanilla 'break' or 'loop', so use the enclosing
|
|
// loop scope
|
|
if self.loop_scope.is_empty() {
|
|
span_bug!(sp, "break outside loop");
|
|
} else {
|
|
*self.loop_scope.last().unwrap()
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
#[allow(unused_must_use)]
|
|
fn ln_str(&self, ln: LiveNode) -> String {
|
|
let mut wr = Vec::new();
|
|
{
|
|
let wr = &mut wr as &mut Write;
|
|
write!(wr, "[ln({:?}) of kind {:?} reads", ln.get(), self.ir.lnk(ln));
|
|
self.write_vars(wr, ln, |idx| self.users[idx].reader);
|
|
write!(wr, " writes");
|
|
self.write_vars(wr, ln, |idx| self.users[idx].writer);
|
|
write!(wr, " precedes {:?}]", self.successors[ln.get()]);
|
|
}
|
|
String::from_utf8(wr).unwrap()
|
|
}
|
|
|
|
fn init_empty(&mut self, ln: LiveNode, succ_ln: LiveNode) {
|
|
self.successors[ln.get()] = 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(&mut self, ln: LiveNode, succ_ln: LiveNode) {
|
|
// more efficient version of init_empty() / merge_from_succ()
|
|
self.successors[ln.get()] = succ_ln;
|
|
|
|
self.indices2(ln, succ_ln, |this, idx, succ_idx| {
|
|
this.users[idx] = this.users[succ_idx]
|
|
});
|
|
debug!("init_from_succ(ln={}, succ={})",
|
|
self.ln_str(ln), self.ln_str(succ_ln));
|
|
}
|
|
|
|
fn merge_from_succ(&mut self,
|
|
ln: LiveNode,
|
|
succ_ln: LiveNode,
|
|
first_merge: bool)
|
|
-> bool {
|
|
if ln == succ_ln { return false; }
|
|
|
|
let mut changed = false;
|
|
self.indices2(ln, succ_ln, |this, idx, succ_idx| {
|
|
changed |= copy_if_invalid(this.users[succ_idx].reader,
|
|
&mut this.users[idx].reader);
|
|
changed |= copy_if_invalid(this.users[succ_idx].writer,
|
|
&mut this.users[idx].writer);
|
|
if this.users[succ_idx].used && !this.users[idx].used {
|
|
this.users[idx].used = true;
|
|
changed = true;
|
|
}
|
|
});
|
|
|
|
debug!("merge_from_succ(ln={:?}, succ={}, first_merge={}, changed={})",
|
|
ln, self.ln_str(succ_ln), first_merge, changed);
|
|
return changed;
|
|
|
|
fn copy_if_invalid(src: LiveNode, dst: &mut LiveNode) -> bool {
|
|
if src.is_valid() && !dst.is_valid() {
|
|
*dst = src;
|
|
true
|
|
} else {
|
|
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(&mut self, writer: LiveNode, var: Variable) {
|
|
let idx = self.idx(writer, var);
|
|
self.users[idx].reader = invalid_node();
|
|
self.users[idx].writer = invalid_node();
|
|
|
|
debug!("{:?} defines {:?} (idx={}): {}", writer, var,
|
|
idx, self.ln_str(writer));
|
|
}
|
|
|
|
// Either read, write, or both depending on the acc bitset
|
|
fn acc(&mut self, ln: LiveNode, var: Variable, acc: u32) {
|
|
debug!("{:?} accesses[{:x}] {:?}: {}",
|
|
ln, acc, var, self.ln_str(ln));
|
|
|
|
let idx = self.idx(ln, var);
|
|
let user = &mut self.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;
|
|
}
|
|
}
|
|
|
|
// _______________________________________________________________________
|
|
|
|
fn compute(&mut self, decl: &hir::FnDecl, body: &hir::Block) -> 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, {}", block_to_string(body));
|
|
|
|
let exit_ln = self.s.exit_ln;
|
|
let entry_ln: LiveNode =
|
|
self.with_loop_nodes(body.id, exit_ln, exit_ln,
|
|
|this| this.propagate_through_fn_block(decl, body));
|
|
|
|
// hack to skip the loop unless debug! is enabled:
|
|
debug!("^^ liveness computation results for body {} (entry={:?})",
|
|
{
|
|
for ln_idx in 0..self.ir.num_live_nodes {
|
|
debug!("{:?}", self.ln_str(LiveNode(ln_idx)));
|
|
}
|
|
body.id
|
|
},
|
|
entry_ln);
|
|
|
|
entry_ln
|
|
}
|
|
|
|
fn propagate_through_fn_block(&mut self, _: &hir::FnDecl, blk: &hir::Block)
|
|
-> LiveNode {
|
|
// the fallthrough exit is only for those cases where we do not
|
|
// explicitly return:
|
|
let s = self.s;
|
|
self.init_from_succ(s.fallthrough_ln, s.exit_ln);
|
|
if blk.expr.is_none() {
|
|
self.acc(s.fallthrough_ln, s.no_ret_var, ACC_READ)
|
|
}
|
|
self.acc(s.fallthrough_ln, s.clean_exit_var, ACC_READ);
|
|
|
|
self.propagate_through_block(blk, s.fallthrough_ln)
|
|
}
|
|
|
|
fn propagate_through_block(&mut self, blk: &hir::Block, succ: LiveNode)
|
|
-> LiveNode {
|
|
let succ = self.propagate_through_opt_expr(blk.expr.as_ref().map(|e| &**e), succ);
|
|
blk.stmts.iter().rev().fold(succ, |succ, stmt| {
|
|
self.propagate_through_stmt(stmt, succ)
|
|
})
|
|
}
|
|
|
|
fn propagate_through_stmt(&mut self, stmt: &hir::Stmt, succ: LiveNode)
|
|
-> LiveNode {
|
|
match stmt.node {
|
|
hir::StmtDecl(ref decl, _) => {
|
|
self.propagate_through_decl(&decl, succ)
|
|
}
|
|
|
|
hir::StmtExpr(ref expr, _) | hir::StmtSemi(ref expr, _) => {
|
|
self.propagate_through_expr(&expr, succ)
|
|
}
|
|
}
|
|
}
|
|
|
|
fn propagate_through_decl(&mut self, decl: &hir::Decl, succ: LiveNode)
|
|
-> LiveNode {
|
|
match decl.node {
|
|
hir::DeclLocal(ref local) => {
|
|
self.propagate_through_local(&local, succ)
|
|
}
|
|
hir::DeclItem(_) => succ,
|
|
}
|
|
}
|
|
|
|
fn propagate_through_local(&mut self, local: &hir::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.init.as_ref().map(|e| &**e), succ);
|
|
self.define_bindings_in_pat(&local.pat, succ)
|
|
}
|
|
|
|
fn propagate_through_exprs(&mut self, exprs: &[P<Expr>], succ: LiveNode)
|
|
-> LiveNode {
|
|
exprs.iter().rev().fold(succ, |succ, expr| {
|
|
self.propagate_through_expr(&expr, succ)
|
|
})
|
|
}
|
|
|
|
fn propagate_through_opt_expr(&mut self,
|
|
opt_expr: Option<&Expr>,
|
|
succ: LiveNode)
|
|
-> LiveNode {
|
|
opt_expr.map_or(succ, |expr| self.propagate_through_expr(expr, succ))
|
|
}
|
|
|
|
fn propagate_through_expr(&mut self, expr: &Expr, succ: LiveNode)
|
|
-> LiveNode {
|
|
debug!("propagate_through_expr: {}", expr_to_string(expr));
|
|
|
|
match expr.node {
|
|
// Interesting cases with control flow or which gen/kill
|
|
|
|
hir::ExprPath(..) => {
|
|
self.access_path(expr, succ, ACC_READ | ACC_USE)
|
|
}
|
|
|
|
hir::ExprField(ref e, _) => {
|
|
self.propagate_through_expr(&e, succ)
|
|
}
|
|
|
|
hir::ExprTupField(ref e, _) => {
|
|
self.propagate_through_expr(&e, succ)
|
|
}
|
|
|
|
hir::ExprClosure(_, _, ref blk, _) => {
|
|
debug!("{} is an ExprClosure",
|
|
expr_to_string(expr));
|
|
|
|
/*
|
|
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.
|
|
*/
|
|
let node = self.live_node(expr.id, expr.span);
|
|
self.with_loop_nodes(blk.id, succ, node, |this| {
|
|
|
|
// the construction of a closure itself is not important,
|
|
// but we have to consider the closed over variables.
|
|
let caps = match this.ir.capture_info_map.get(&expr.id) {
|
|
Some(caps) => caps.clone(),
|
|
None => {
|
|
span_bug!(expr.span, "no registered caps");
|
|
}
|
|
};
|
|
caps.iter().rev().fold(succ, |succ, cap| {
|
|
this.init_from_succ(cap.ln, succ);
|
|
let var = this.variable(cap.var_nid, expr.span);
|
|
this.acc(cap.ln, var, ACC_READ | ACC_USE);
|
|
cap.ln
|
|
})
|
|
})
|
|
}
|
|
|
|
hir::ExprIf(ref cond, ref then, ref els) => {
|
|
//
|
|
// (cond)
|
|
// |
|
|
// v
|
|
// (expr)
|
|
// / \
|
|
// | |
|
|
// v v
|
|
// (then)(els)
|
|
// | |
|
|
// v v
|
|
// ( succ )
|
|
//
|
|
let else_ln = self.propagate_through_opt_expr(els.as_ref().map(|e| &**e), 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)
|
|
}
|
|
|
|
hir::ExprWhile(ref cond, ref blk, _) => {
|
|
self.propagate_through_loop(expr, WhileLoop(&cond), &blk, succ)
|
|
}
|
|
|
|
// Note that labels have been resolved, so we don't need to look
|
|
// at the label ident
|
|
hir::ExprLoop(ref blk, _) => {
|
|
self.propagate_through_loop(expr, LoopLoop, &blk, succ)
|
|
}
|
|
|
|
hir::ExprMatch(ref 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 arm in arms {
|
|
let body_succ =
|
|
self.propagate_through_expr(&arm.body, succ);
|
|
let guard_succ =
|
|
self.propagate_through_opt_expr(arm.guard.as_ref().map(|e| &**e), body_succ);
|
|
// only consider the first pattern; any later patterns must have
|
|
// the same bindings, and we also consider the first pattern to be
|
|
// the "authoritative" set of ids
|
|
let arm_succ =
|
|
self.define_bindings_in_arm_pats(arm.pats.first().map(|p| &**p),
|
|
guard_succ);
|
|
self.merge_from_succ(ln, arm_succ, first_merge);
|
|
first_merge = false;
|
|
};
|
|
self.propagate_through_expr(&e, ln)
|
|
}
|
|
|
|
hir::ExprRet(ref o_e) => {
|
|
// ignore succ and subst exit_ln:
|
|
let exit_ln = self.s.exit_ln;
|
|
self.propagate_through_opt_expr(o_e.as_ref().map(|e| &**e), exit_ln)
|
|
}
|
|
|
|
hir::ExprBreak(opt_label) => {
|
|
// Find which label this break jumps to
|
|
let sc = self.find_loop_scope(opt_label.map(|l| l.node), 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.get(&sc) {
|
|
Some(&b) => b,
|
|
None => span_bug!(expr.span, "break to unknown label")
|
|
}
|
|
}
|
|
|
|
hir::ExprAgain(opt_label) => {
|
|
// Find which label this expr continues to
|
|
let sc = self.find_loop_scope(opt_label.map(|l| l.node), 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.get(&sc) {
|
|
Some(&b) => b,
|
|
None => span_bug!(expr.span, "loop to unknown label")
|
|
}
|
|
}
|
|
|
|
hir::ExprAssign(ref l, ref 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)
|
|
}
|
|
|
|
hir::ExprAssignOp(_, ref l, ref r) => {
|
|
// an overloaded assign op is like a method call
|
|
if self.ir.tcx.is_method_call(expr.id) {
|
|
let succ = self.propagate_through_expr(&l, succ);
|
|
self.propagate_through_expr(&r, succ)
|
|
} else {
|
|
// 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
|
|
|
|
hir::ExprVec(ref exprs) => {
|
|
self.propagate_through_exprs(&exprs[..], succ)
|
|
}
|
|
|
|
hir::ExprRepeat(ref element, ref count) => {
|
|
let succ = self.propagate_through_expr(&count, succ);
|
|
self.propagate_through_expr(&element, succ)
|
|
}
|
|
|
|
hir::ExprStruct(_, ref fields, ref with_expr) => {
|
|
let succ = self.propagate_through_opt_expr(with_expr.as_ref().map(|e| &**e), succ);
|
|
fields.iter().rev().fold(succ, |succ, field| {
|
|
self.propagate_through_expr(&field.expr, succ)
|
|
})
|
|
}
|
|
|
|
hir::ExprCall(ref f, ref args) => {
|
|
// FIXME(canndrew): This is_never should really be an is_uninhabited
|
|
let diverges = !self.ir.tcx.is_method_call(expr.id) &&
|
|
self.ir.tcx.expr_ty_adjusted(&f).fn_ret().0.is_never();
|
|
let succ = if diverges {
|
|
self.s.exit_ln
|
|
} else {
|
|
succ
|
|
};
|
|
let succ = self.propagate_through_exprs(&args[..], succ);
|
|
self.propagate_through_expr(&f, succ)
|
|
}
|
|
|
|
hir::ExprMethodCall(_, _, ref args) => {
|
|
let method_call = ty::MethodCall::expr(expr.id);
|
|
let method_ty = self.ir.tcx.tables.borrow().method_map[&method_call].ty;
|
|
// FIXME(canndrew): This is_never should really be an is_uninhabited
|
|
let succ = if method_ty.fn_ret().0.is_never() {
|
|
self.s.exit_ln
|
|
} else {
|
|
succ
|
|
};
|
|
self.propagate_through_exprs(&args[..], succ)
|
|
}
|
|
|
|
hir::ExprTup(ref exprs) => {
|
|
self.propagate_through_exprs(&exprs[..], succ)
|
|
}
|
|
|
|
hir::ExprBinary(op, ref l, ref r) if op.node.is_lazy() => {
|
|
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)
|
|
}
|
|
|
|
hir::ExprIndex(ref l, ref r) |
|
|
hir::ExprBinary(_, ref l, ref r) => {
|
|
let r_succ = self.propagate_through_expr(&r, succ);
|
|
self.propagate_through_expr(&l, r_succ)
|
|
}
|
|
|
|
hir::ExprBox(ref e) |
|
|
hir::ExprAddrOf(_, ref e) |
|
|
hir::ExprCast(ref e, _) |
|
|
hir::ExprType(ref e, _) |
|
|
hir::ExprUnary(_, ref e) => {
|
|
self.propagate_through_expr(&e, succ)
|
|
}
|
|
|
|
hir::ExprInlineAsm(ref ia, ref outputs, ref inputs) => {
|
|
let succ = ia.outputs.iter().zip(outputs).rev().fold(succ, |succ, (o, output)| {
|
|
// see comment on lvalues
|
|
// in propagate_through_lvalue_components()
|
|
if o.is_indirect {
|
|
self.propagate_through_expr(output, succ)
|
|
} else {
|
|
let acc = if o.is_rw { ACC_WRITE|ACC_READ } else { ACC_WRITE };
|
|
let succ = self.write_lvalue(output, succ, acc);
|
|
self.propagate_through_lvalue_components(output, succ)
|
|
}
|
|
});
|
|
|
|
// Inputs are executed first. Propagate last because of rev order
|
|
self.propagate_through_exprs(inputs, succ)
|
|
}
|
|
|
|
hir::ExprLit(..) => {
|
|
succ
|
|
}
|
|
|
|
hir::ExprBlock(ref blk) => {
|
|
self.propagate_through_block(&blk, succ)
|
|
}
|
|
}
|
|
}
|
|
|
|
fn propagate_through_lvalue_components(&mut 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 {
|
|
hir::ExprPath(..) => succ,
|
|
hir::ExprField(ref e, _) => self.propagate_through_expr(&e, succ),
|
|
hir::ExprTupField(ref e, _) => self.propagate_through_expr(&e, succ),
|
|
_ => self.propagate_through_expr(expr, succ)
|
|
}
|
|
}
|
|
|
|
// see comment on propagate_through_lvalue()
|
|
fn write_lvalue(&mut self, expr: &Expr, succ: LiveNode, acc: u32)
|
|
-> LiveNode {
|
|
match expr.node {
|
|
hir::ExprPath(..) => {
|
|
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(&mut self, expr: &Expr, succ: LiveNode, acc: u32)
|
|
-> LiveNode {
|
|
match self.ir.tcx.expect_def(expr.id) {
|
|
Def::Local(_, nid) => {
|
|
let ln = self.live_node(expr.id, expr.span);
|
|
if acc != 0 {
|
|
self.init_from_succ(ln, succ);
|
|
let var = self.variable(nid, expr.span);
|
|
self.acc(ln, var, acc);
|
|
}
|
|
ln
|
|
}
|
|
_ => succ
|
|
}
|
|
}
|
|
|
|
fn propagate_through_loop(&mut self,
|
|
expr: &Expr,
|
|
kind: LoopKind,
|
|
body: &hir::Block,
|
|
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);
|
|
match kind {
|
|
LoopLoop => {}
|
|
_ => {
|
|
// If this is not a `loop` loop, 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 {} {}",
|
|
expr.id, block_to_string(body));
|
|
|
|
let cond_ln = match kind {
|
|
LoopLoop => ln,
|
|
WhileLoop(ref cond) => self.propagate_through_expr(&cond, ln),
|
|
};
|
|
let body_ln = self.with_loop_nodes(expr.id, succ, ln, |this| {
|
|
this.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;
|
|
|
|
let new_cond_ln = match kind {
|
|
LoopLoop => ln,
|
|
WhileLoop(ref cond) => {
|
|
self.propagate_through_expr(&cond, ln)
|
|
}
|
|
};
|
|
assert!(cond_ln == new_cond_ln);
|
|
assert!(body_ln == self.with_loop_nodes(expr.id, succ, ln,
|
|
|this| this.propagate_through_block(body, cond_ln)));
|
|
}
|
|
|
|
cond_ln
|
|
}
|
|
|
|
fn with_loop_nodes<R, F>(&mut self,
|
|
loop_node_id: NodeId,
|
|
break_ln: LiveNode,
|
|
cont_ln: LiveNode,
|
|
f: F)
|
|
-> R where
|
|
F: FnOnce(&mut Liveness<'a, 'tcx>) -> R,
|
|
{
|
|
debug!("with_loop_nodes: {} {}", loop_node_id, break_ln.get());
|
|
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);
|
|
self.loop_scope.pop();
|
|
r
|
|
}
|
|
}
|
|
|
|
// _______________________________________________________________________
|
|
// Checking for error conditions
|
|
|
|
fn check_local(this: &mut Liveness, local: &hir::Local) {
|
|
match local.init {
|
|
Some(_) => {
|
|
this.warn_about_unused_or_dead_vars_in_pat(&local.pat);
|
|
},
|
|
None => {
|
|
this.pat_bindings(&local.pat, |this, ln, var, sp, id| {
|
|
this.warn_about_unused(sp, id, ln, var);
|
|
})
|
|
}
|
|
}
|
|
|
|
intravisit::walk_local(this, local);
|
|
}
|
|
|
|
fn check_arm(this: &mut Liveness, arm: &hir::Arm) {
|
|
// only consider the first pattern; any later patterns must have
|
|
// the same bindings, and we also consider the first pattern to be
|
|
// the "authoritative" set of ids
|
|
this.arm_pats_bindings(arm.pats.first().map(|p| &**p), |this, ln, var, sp, id| {
|
|
this.warn_about_unused(sp, id, ln, var);
|
|
});
|
|
intravisit::walk_arm(this, arm);
|
|
}
|
|
|
|
fn check_expr(this: &mut Liveness, expr: &Expr) {
|
|
match expr.node {
|
|
hir::ExprAssign(ref l, _) => {
|
|
this.check_lvalue(&l);
|
|
|
|
intravisit::walk_expr(this, expr);
|
|
}
|
|
|
|
hir::ExprAssignOp(_, ref l, _) => {
|
|
if !this.ir.tcx.is_method_call(expr.id) {
|
|
this.check_lvalue(&l);
|
|
}
|
|
|
|
intravisit::walk_expr(this, expr);
|
|
}
|
|
|
|
hir::ExprInlineAsm(ref ia, ref outputs, ref inputs) => {
|
|
for input in inputs {
|
|
this.visit_expr(input);
|
|
}
|
|
|
|
// Output operands must be lvalues
|
|
for (o, output) in ia.outputs.iter().zip(outputs) {
|
|
if !o.is_indirect {
|
|
this.check_lvalue(output);
|
|
}
|
|
this.visit_expr(output);
|
|
}
|
|
|
|
intravisit::walk_expr(this, expr);
|
|
}
|
|
|
|
// no correctness conditions related to liveness
|
|
hir::ExprCall(..) | hir::ExprMethodCall(..) | hir::ExprIf(..) |
|
|
hir::ExprMatch(..) | hir::ExprWhile(..) | hir::ExprLoop(..) |
|
|
hir::ExprIndex(..) | hir::ExprField(..) | hir::ExprTupField(..) |
|
|
hir::ExprVec(..) | hir::ExprTup(..) | hir::ExprBinary(..) |
|
|
hir::ExprCast(..) | hir::ExprUnary(..) | hir::ExprRet(..) |
|
|
hir::ExprBreak(..) | hir::ExprAgain(..) | hir::ExprLit(_) |
|
|
hir::ExprBlock(..) | hir::ExprAddrOf(..) |
|
|
hir::ExprStruct(..) | hir::ExprRepeat(..) |
|
|
hir::ExprClosure(..) | hir::ExprPath(..) | hir::ExprBox(..) |
|
|
hir::ExprType(..) => {
|
|
intravisit::walk_expr(this, expr);
|
|
}
|
|
}
|
|
}
|
|
|
|
fn check_fn(_v: &Liveness,
|
|
_fk: FnKind,
|
|
_decl: &hir::FnDecl,
|
|
_body: &hir::Block,
|
|
_sp: Span,
|
|
_id: NodeId) {
|
|
// do not check contents of nested fns
|
|
}
|
|
|
|
impl<'a, 'tcx> Liveness<'a, 'tcx> {
|
|
fn fn_ret(&self, id: NodeId) -> ty::Binder<Ty<'tcx>> {
|
|
let fn_ty = self.ir.tcx.node_id_to_type(id);
|
|
match fn_ty.sty {
|
|
ty::TyClosure(closure_def_id, substs) =>
|
|
self.ir.tcx.closure_type(closure_def_id, substs).sig.output(),
|
|
_ => fn_ty.fn_ret()
|
|
}
|
|
}
|
|
|
|
fn check_ret(&self,
|
|
id: NodeId,
|
|
sp: Span,
|
|
_fk: FnKind,
|
|
entry_ln: LiveNode,
|
|
body: &hir::Block)
|
|
{
|
|
// within the fn body, late-bound regions are liberated
|
|
// and must outlive the *call-site* of the function.
|
|
let fn_ret =
|
|
self.ir.tcx.liberate_late_bound_regions(
|
|
self.ir.tcx.region_maps.call_site_extent(id, body.id),
|
|
&self.fn_ret(id));
|
|
|
|
if fn_ret.is_never() {
|
|
// FIXME(durka) this rejects code like `fn foo(x: !) -> ! { x }`
|
|
if self.live_on_entry(entry_ln, self.s.clean_exit_var).is_some() {
|
|
span_err!(self.ir.tcx.sess, sp, E0270,
|
|
"computation may converge in a function marked as diverging");
|
|
}
|
|
} else if self.live_on_entry(entry_ln, self.s.no_ret_var).is_some() {
|
|
let param_env = ParameterEnvironment::for_item(self.ir.tcx, id);
|
|
let t_ret_subst = fn_ret.subst(self.ir.tcx, ¶m_env.free_substs);
|
|
let is_nil = self.ir.tcx.infer_ctxt(None, Some(param_env),
|
|
Reveal::All).enter(|infcx| {
|
|
let cause = traits::ObligationCause::dummy();
|
|
traits::fully_normalize(&infcx, cause, &t_ret_subst).unwrap().is_nil()
|
|
});
|
|
|
|
// for nil return types, it is ok to not return a value expl.
|
|
if !is_nil {
|
|
let ends_with_stmt = match body.expr {
|
|
None if !body.stmts.is_empty() =>
|
|
match body.stmts.last().unwrap().node {
|
|
hir::StmtSemi(ref e, _) => {
|
|
self.ir.tcx.expr_ty(&e) == fn_ret
|
|
},
|
|
_ => false
|
|
},
|
|
_ => false
|
|
};
|
|
let mut err = struct_span_err!(self.ir.tcx.sess,
|
|
sp,
|
|
E0269,
|
|
"not all control paths return a value");
|
|
if ends_with_stmt {
|
|
let last_stmt = body.stmts.last().unwrap();
|
|
let original_span = original_sp(self.ir.tcx.sess.codemap(),
|
|
last_stmt.span, sp);
|
|
let span_semicolon = Span {
|
|
lo: original_span.hi - BytePos(1),
|
|
hi: original_span.hi,
|
|
expn_id: original_span.expn_id
|
|
};
|
|
err.span_help(span_semicolon, "consider removing this semicolon:");
|
|
}
|
|
err.emit();
|
|
}
|
|
}
|
|
}
|
|
|
|
fn check_lvalue(&mut self, expr: &Expr) {
|
|
match expr.node {
|
|
hir::ExprPath(..) => {
|
|
if let Def::Local(_, nid) = self.ir.tcx.expect_def(expr.id) {
|
|
// Assignment to an immutable variable or argument: only legal
|
|
// if there is no later assignment. If this local is actually
|
|
// mutable, then check for a reassignment to flag the mutability
|
|
// as being used.
|
|
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);
|
|
}
|
|
}
|
|
_ => {
|
|
// For other kinds of lvalues, no checks are required,
|
|
// and any embedded expressions are actually rvalues
|
|
intravisit::walk_expr(self, expr);
|
|
}
|
|
}
|
|
}
|
|
|
|
fn should_warn(&self, var: Variable) -> Option<String> {
|
|
let name = self.ir.variable_name(var);
|
|
if name.is_empty() || name.as_bytes()[0] == ('_' as u8) {
|
|
None
|
|
} else {
|
|
Some(name)
|
|
}
|
|
}
|
|
|
|
fn warn_about_unused_args(&self, decl: &hir::FnDecl, entry_ln: LiveNode) {
|
|
for arg in &decl.inputs {
|
|
pat_util::pat_bindings(&arg.pat, |_bm, p_id, sp, path1| {
|
|
let var = self.variable(p_id, sp);
|
|
// Ignore unused self.
|
|
let name = path1.node;
|
|
if name != keywords::SelfValue.name() {
|
|
if !self.warn_about_unused(sp, p_id, entry_ln, var) {
|
|
if self.live_on_entry(entry_ln, var).is_none() {
|
|
self.report_dead_assign(p_id, sp, var, true);
|
|
}
|
|
}
|
|
}
|
|
})
|
|
}
|
|
}
|
|
|
|
fn warn_about_unused_or_dead_vars_in_pat(&mut self, pat: &hir::Pat) {
|
|
self.pat_bindings(pat, |this, ln, var, sp, id| {
|
|
if !this.warn_about_unused(sp, id, ln, var) {
|
|
this.warn_about_dead_assign(sp, id, ln, var);
|
|
}
|
|
})
|
|
}
|
|
|
|
fn warn_about_unused(&self,
|
|
sp: Span,
|
|
id: NodeId,
|
|
ln: LiveNode,
|
|
var: Variable)
|
|
-> bool {
|
|
if !self.used_on_entry(ln, var) {
|
|
let r = self.should_warn(var);
|
|
if let Some(name) = r {
|
|
|
|
// annoying: for parameters in funcs like `fn(x: i32)
|
|
// {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.ir.tcx.sess.add_lint(lint::builtin::UNUSED_VARIABLES, id, sp,
|
|
format!("variable `{}` is assigned to, but never used",
|
|
name));
|
|
} else if name != "self" {
|
|
self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_VARIABLES, id, sp,
|
|
format!("unused variable: `{}`", name));
|
|
}
|
|
}
|
|
true
|
|
} else {
|
|
false
|
|
}
|
|
}
|
|
|
|
fn warn_about_dead_assign(&self,
|
|
sp: Span,
|
|
id: NodeId,
|
|
ln: LiveNode,
|
|
var: Variable) {
|
|
if self.live_on_exit(ln, var).is_none() {
|
|
self.report_dead_assign(id, sp, var, false);
|
|
}
|
|
}
|
|
|
|
fn report_dead_assign(&self, id: NodeId, sp: Span, var: Variable, is_argument: bool) {
|
|
if let Some(name) = self.should_warn(var) {
|
|
if is_argument {
|
|
self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_ASSIGNMENTS, id, sp,
|
|
format!("value passed to `{}` is never read", name));
|
|
} else {
|
|
self.ir.tcx.sess.add_lint(lint::builtin::UNUSED_ASSIGNMENTS, id, sp,
|
|
format!("value assigned to `{}` is never read", name));
|
|
}
|
|
}
|
|
}
|
|
}
|