pub mod intrinsicck;
pub mod lib_features;
pub mod lang_items;
- pub mod liveness;
pub mod mem_categorization;
pub mod privacy;
pub mod reachable;
+++ /dev/null
-//! 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
-//! IDs.
-//!
-//! # 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 `u32`) and the ID for a variable
-//! is called a `variable` (another newtype'd `u32`).
-//!
-//! 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 `RWU` struct
-//!
-//! At each live node `N`, we track three pieces of information for each
-//! variable `V` (these are encapsulated in the `RWU` 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, panic, or other means.
-//!
-//! - `fallthrough_ln`: a live node that represents a fallthrough
-//!
-//! - `clean_exit_var`: a synthetic variable that is only 'read' from the
-//! fallthrough node. It is only live if the function could converge
-//! via means other than an explicit `return` expression. That is, it is
-//! only dead if the end of the function's block can never be reached.
-//! It is the responsibility of typeck to ensure that there are no
-//! `return` expressions in a function declared as diverging.
-
-use self::LiveNodeKind::*;
-use self::VarKind::*;
-
-use crate::hir;
-use crate::hir::{Expr, HirId};
-use crate::hir::def::*;
-use crate::hir::def_id::DefId;
-use crate::hir::intravisit::{self, Visitor, FnKind, NestedVisitorMap};
-use crate::hir::Node;
-use crate::hir::ptr::P;
-use crate::ty::{self, TyCtxt};
-use crate::ty::query::Providers;
-use crate::lint;
-use crate::util::nodemap::{HirIdMap, HirIdSet};
-
-use errors::Applicability;
-use rustc_data_structures::fx::FxIndexMap;
-use std::collections::VecDeque;
-use std::{fmt, u32};
-use std::io::prelude::*;
-use std::io;
-use std::rc::Rc;
-use syntax::ast;
-use syntax::symbol::sym;
-use syntax_pos::Span;
-
-#[derive(Copy, Clone, PartialEq)]
-struct Variable(u32);
-
-#[derive(Copy, Clone, PartialEq)]
-struct LiveNode(u32);
-
-impl Variable {
- fn get(&self) -> usize { self.0 as usize }
-}
-
-impl LiveNode {
- fn get(&self) -> usize { self.0 as usize }
-}
-
-#[derive(Copy, Clone, PartialEq, Debug)]
-enum LiveNodeKind {
- UpvarNode(Span),
- ExprNode(Span),
- VarDefNode(Span),
- ExitNode
-}
-
-fn live_node_kind_to_string(lnk: LiveNodeKind, tcx: TyCtxt<'_>) -> String {
- let cm = tcx.sess.source_map();
- match lnk {
- UpvarNode(s) => {
- format!("Upvar node [{}]", cm.span_to_string(s))
- }
- ExprNode(s) => {
- format!("Expr node [{}]", cm.span_to_string(s))
- }
- VarDefNode(s) => {
- format!("Var def node [{}]", cm.span_to_string(s))
- }
- ExitNode => "Exit node".to_owned(),
- }
-}
-
-impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
- fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
- NestedVisitorMap::OnlyBodies(&self.tcx.hir())
- }
-
- fn visit_fn(&mut self, fk: FnKind<'tcx>, fd: &'tcx hir::FnDecl,
- b: hir::BodyId, s: Span, id: HirId) {
- visit_fn(self, fk, fd, b, s, id);
- }
-
- fn visit_local(&mut self, l: &'tcx hir::Local) { visit_local(self, l); }
- fn visit_expr(&mut self, ex: &'tcx Expr) { visit_expr(self, ex); }
- fn visit_arm(&mut self, a: &'tcx hir::Arm) { visit_arm(self, a); }
-}
-
-fn check_mod_liveness(tcx: TyCtxt<'_>, module_def_id: DefId) {
- tcx.hir().visit_item_likes_in_module(
- module_def_id,
- &mut IrMaps::new(tcx, module_def_id).as_deep_visitor(),
- );
-}
-
-pub fn provide(providers: &mut Providers<'_>) {
- *providers = Providers {
- check_mod_liveness,
- ..*providers
- };
-}
-
-impl fmt::Debug for LiveNode {
- fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
- write!(f, "ln({})", self.get())
- }
-}
-
-impl fmt::Debug for Variable {
- fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
- write!(f, "v({})", self.get())
- }
-}
-
-// ______________________________________________________________________
-// 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.
-
-impl LiveNode {
- fn is_valid(&self) -> bool {
- self.0 != u32::MAX
- }
-}
-
-fn invalid_node() -> LiveNode { LiveNode(u32::MAX) }
-
-struct CaptureInfo {
- ln: LiveNode,
- var_hid: HirId
-}
-
-#[derive(Copy, Clone, Debug)]
-struct LocalInfo {
- id: HirId,
- name: ast::Name,
- is_shorthand: bool,
-}
-
-#[derive(Copy, Clone, Debug)]
-enum VarKind {
- Param(HirId, ast::Name),
- Local(LocalInfo),
- CleanExit
-}
-
-struct IrMaps<'tcx> {
- tcx: TyCtxt<'tcx>,
- body_owner: DefId,
- num_live_nodes: usize,
- num_vars: usize,
- live_node_map: HirIdMap<LiveNode>,
- variable_map: HirIdMap<Variable>,
- capture_info_map: HirIdMap<Rc<Vec<CaptureInfo>>>,
- var_kinds: Vec<VarKind>,
- lnks: Vec<LiveNodeKind>,
-}
-
-impl IrMaps<'tcx> {
- fn new(tcx: TyCtxt<'tcx>, body_owner: DefId) -> IrMaps<'tcx> {
- IrMaps {
- tcx,
- body_owner,
- num_live_nodes: 0,
- num_vars: 0,
- live_node_map: HirIdMap::default(),
- variable_map: HirIdMap::default(),
- capture_info_map: Default::default(),
- var_kinds: Vec::new(),
- lnks: Vec::new(),
- }
- }
-
- fn add_live_node(&mut self, lnk: LiveNodeKind) -> LiveNode {
- let ln = LiveNode(self.num_live_nodes as u32);
- self.lnks.push(lnk);
- self.num_live_nodes += 1;
-
- debug!("{:?} is of kind {}", ln,
- live_node_kind_to_string(lnk, self.tcx));
-
- ln
- }
-
- fn add_live_node_for_node(&mut self, hir_id: HirId, lnk: LiveNodeKind) {
- let ln = self.add_live_node(lnk);
- self.live_node_map.insert(hir_id, ln);
-
- debug!("{:?} is node {:?}", ln, hir_id);
- }
-
- fn add_variable(&mut self, vk: VarKind) -> Variable {
- let v = Variable(self.num_vars as u32);
- self.var_kinds.push(vk);
- self.num_vars += 1;
-
- match vk {
- Local(LocalInfo { id: node_id, .. }) | Param(node_id, _) => {
- self.variable_map.insert(node_id, v);
- },
- CleanExit => {}
- }
-
- debug!("{:?} is {:?}", v, vk);
-
- v
- }
-
- fn variable(&self, hir_id: HirId, span: Span) -> Variable {
- match self.variable_map.get(&hir_id) {
- Some(&var) => var,
- None => {
- span_bug!(span, "no variable registered for id {:?}", hir_id);
- }
- }
- }
-
- fn variable_name(&self, var: Variable) -> String {
- match self.var_kinds[var.get()] {
- Local(LocalInfo { name, .. }) | Param(_, name) => {
- name.to_string()
- },
- CleanExit => "<clean-exit>".to_owned()
- }
- }
-
- fn variable_is_shorthand(&self, var: Variable) -> bool {
- match self.var_kinds[var.get()] {
- Local(LocalInfo { is_shorthand, .. }) => is_shorthand,
- Param(..) | CleanExit => false
- }
- }
-
- fn set_captures(&mut self, hir_id: HirId, cs: Vec<CaptureInfo>) {
- self.capture_info_map.insert(hir_id, Rc::new(cs));
- }
-
- fn lnk(&self, ln: LiveNode) -> LiveNodeKind {
- self.lnks[ln.get()]
- }
-}
-
-fn visit_fn<'tcx>(
- ir: &mut IrMaps<'tcx>,
- fk: FnKind<'tcx>,
- decl: &'tcx hir::FnDecl,
- body_id: hir::BodyId,
- sp: Span,
- id: hir::HirId,
-) {
- debug!("visit_fn");
-
- // swap in a new set of IR maps for this function body:
- let def_id = ir.tcx.hir().local_def_id(id);
- let mut fn_maps = IrMaps::new(ir.tcx, def_id);
-
- // Don't run unused pass for #[derive()]
- if let FnKind::Method(..) = fk {
- let parent = ir.tcx.hir().get_parent_item(id);
- if let Some(Node::Item(i)) = ir.tcx.hir().find(parent) {
- if i.attrs.iter().any(|a| a.check_name(sym::automatically_derived)) {
- return;
- }
- }
- }
-
- debug!("creating fn_maps: {:p}", &fn_maps);
-
- let body = ir.tcx.hir().body(body_id);
-
- for param in &body.params {
- let is_shorthand = match param.pat.kind {
- crate::hir::PatKind::Struct(..) => true,
- _ => false,
- };
- param.pat.each_binding(|_bm, hir_id, _x, ident| {
- debug!("adding parameters {:?}", hir_id);
- let var = if is_shorthand {
- Local(LocalInfo {
- id: hir_id,
- name: ident.name,
- is_shorthand: true,
- })
- } else {
- Param(hir_id, ident.name)
- };
- fn_maps.add_variable(var);
- })
- };
-
- // gather up the various local variables, significant expressions,
- // and so forth:
- intravisit::walk_fn(&mut fn_maps, fk, decl, body_id, sp, id);
-
- // compute liveness
- let mut lsets = Liveness::new(&mut fn_maps, body_id);
- let entry_ln = lsets.compute(&body.value);
-
- // check for various error conditions
- lsets.visit_body(body);
- lsets.warn_about_unused_args(body, entry_ln);
-}
-
-fn add_from_pat(ir: &mut IrMaps<'_>, pat: &P<hir::Pat>) {
- // For struct patterns, take note of which fields used shorthand
- // (`x` rather than `x: x`).
- let mut shorthand_field_ids = HirIdSet::default();
- let mut pats = VecDeque::new();
- pats.push_back(pat);
- while let Some(pat) = pats.pop_front() {
- use crate::hir::PatKind::*;
- match &pat.kind {
- Binding(.., inner_pat) => {
- pats.extend(inner_pat.iter());
- }
- Struct(_, fields, _) => {
- let ids = fields.iter().filter(|f| f.is_shorthand).map(|f| f.pat.hir_id);
- shorthand_field_ids.extend(ids);
- }
- Ref(inner_pat, _) | Box(inner_pat) => {
- pats.push_back(inner_pat);
- }
- TupleStruct(_, inner_pats, _) | Tuple(inner_pats, _) | Or(inner_pats) => {
- pats.extend(inner_pats.iter());
- }
- Slice(pre_pats, inner_pat, post_pats) => {
- pats.extend(pre_pats.iter());
- pats.extend(inner_pat.iter());
- pats.extend(post_pats.iter());
- }
- _ => {}
- }
- }
-
- pat.each_binding(|_, hir_id, _, ident| {
- ir.add_live_node_for_node(hir_id, VarDefNode(ident.span));
- ir.add_variable(Local(LocalInfo {
- id: hir_id,
- name: ident.name,
- is_shorthand: shorthand_field_ids.contains(&hir_id)
- }));
- });
-}
-
-fn visit_local<'tcx>(ir: &mut IrMaps<'tcx>, local: &'tcx hir::Local) {
- add_from_pat(ir, &local.pat);
- intravisit::walk_local(ir, local);
-}
-
-fn visit_arm<'tcx>(ir: &mut IrMaps<'tcx>, arm: &'tcx hir::Arm) {
- add_from_pat(ir, &arm.pat);
- intravisit::walk_arm(ir, arm);
-}
-
-fn visit_expr<'tcx>(ir: &mut IrMaps<'tcx>, expr: &'tcx Expr) {
- match expr.kind {
- // live nodes required for uses or definitions of variables:
- hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => {
- debug!("expr {}: path that leads to {:?}", expr.hir_id, path.res);
- if let Res::Local(var_hir_id) = path.res {
- let upvars = ir.tcx.upvars(ir.body_owner);
- if !upvars.map_or(false, |upvars| upvars.contains_key(&var_hir_id)) {
- ir.add_live_node_for_node(expr.hir_id, ExprNode(expr.span));
- }
- }
- intravisit::walk_expr(ir, expr);
- }
- hir::ExprKind::Closure(..) => {
- // Interesting control flow (for loops can contain labeled
- // breaks or continues)
- ir.add_live_node_for_node(expr.hir_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 mut call_caps = Vec::new();
- let closure_def_id = ir.tcx.hir().local_def_id(expr.hir_id);
- if let Some(upvars) = ir.tcx.upvars(closure_def_id) {
- let parent_upvars = ir.tcx.upvars(ir.body_owner);
- call_caps.extend(upvars.iter().filter_map(|(&var_id, upvar)| {
- let has_parent = parent_upvars
- .map_or(false, |upvars| upvars.contains_key(&var_id));
- if !has_parent {
- let upvar_ln = ir.add_live_node(UpvarNode(upvar.span));
- Some(CaptureInfo { ln: upvar_ln, var_hid: var_id })
- } else {
- None
- }
- }));
- }
- ir.set_captures(expr.hir_id, call_caps);
- let old_body_owner = ir.body_owner;
- ir.body_owner = closure_def_id;
- intravisit::walk_expr(ir, expr);
- ir.body_owner = old_body_owner;
- }
-
- // live nodes required for interesting control flow:
- hir::ExprKind::Match(..) |
- hir::ExprKind::Loop(..) => {
- ir.add_live_node_for_node(expr.hir_id, ExprNode(expr.span));
- intravisit::walk_expr(ir, expr);
- }
- hir::ExprKind::Binary(op, ..) if op.node.is_lazy() => {
- ir.add_live_node_for_node(expr.hir_id, ExprNode(expr.span));
- intravisit::walk_expr(ir, expr);
- }
-
- // otherwise, live nodes are not required:
- hir::ExprKind::Index(..) |
- hir::ExprKind::Field(..) |
- hir::ExprKind::Array(..) |
- hir::ExprKind::Call(..) |
- hir::ExprKind::MethodCall(..) |
- hir::ExprKind::Tup(..) |
- hir::ExprKind::Binary(..) |
- hir::ExprKind::AddrOf(..) |
- hir::ExprKind::Cast(..) |
- hir::ExprKind::DropTemps(..) |
- hir::ExprKind::Unary(..) |
- hir::ExprKind::Break(..) |
- hir::ExprKind::Continue(_) |
- hir::ExprKind::Lit(_) |
- hir::ExprKind::Ret(..) |
- hir::ExprKind::Block(..) |
- hir::ExprKind::Assign(..) |
- hir::ExprKind::AssignOp(..) |
- hir::ExprKind::Struct(..) |
- hir::ExprKind::Repeat(..) |
- hir::ExprKind::InlineAsm(..) |
- hir::ExprKind::Box(..) |
- hir::ExprKind::Yield(..) |
- hir::ExprKind::Type(..) |
- hir::ExprKind::Err |
- hir::ExprKind::Path(hir::QPath::TypeRelative(..)) => {
- 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 RWU {
- reader: LiveNode,
- writer: LiveNode,
- used: bool
-}
-
-/// Conceptually, this is like a `Vec<RWU>`. But the number of `RWU`s can get
-/// very large, so it uses a more compact representation that takes advantage
-/// of the fact that when the number of `RWU`s is large, most of them have an
-/// invalid reader and an invalid writer.
-struct RWUTable {
- /// Each entry in `packed_rwus` is either INV_INV_FALSE, INV_INV_TRUE, or
- /// an index into `unpacked_rwus`. In the common cases, this compacts the
- /// 65 bits of data into 32; in the uncommon cases, it expands the 65 bits
- /// in 96.
- ///
- /// More compact representations are possible -- e.g., use only 2 bits per
- /// packed `RWU` and make the secondary table a HashMap that maps from
- /// indices to `RWU`s -- but this one strikes a good balance between size
- /// and speed.
- packed_rwus: Vec<u32>,
- unpacked_rwus: Vec<RWU>,
-}
-
-// A constant representing `RWU { reader: invalid_node(); writer: invalid_node(); used: false }`.
-const INV_INV_FALSE: u32 = u32::MAX;
-
-// A constant representing `RWU { reader: invalid_node(); writer: invalid_node(); used: true }`.
-const INV_INV_TRUE: u32 = u32::MAX - 1;
-
-impl RWUTable {
- fn new(num_rwus: usize) -> RWUTable {
- Self {
- packed_rwus: vec![INV_INV_FALSE; num_rwus],
- unpacked_rwus: vec![],
- }
- }
-
- fn get(&self, idx: usize) -> RWU {
- let packed_rwu = self.packed_rwus[idx];
- match packed_rwu {
- INV_INV_FALSE => RWU { reader: invalid_node(), writer: invalid_node(), used: false },
- INV_INV_TRUE => RWU { reader: invalid_node(), writer: invalid_node(), used: true },
- _ => self.unpacked_rwus[packed_rwu as usize],
- }
- }
-
- fn get_reader(&self, idx: usize) -> LiveNode {
- let packed_rwu = self.packed_rwus[idx];
- match packed_rwu {
- INV_INV_FALSE | INV_INV_TRUE => invalid_node(),
- _ => self.unpacked_rwus[packed_rwu as usize].reader,
- }
- }
-
- fn get_writer(&self, idx: usize) -> LiveNode {
- let packed_rwu = self.packed_rwus[idx];
- match packed_rwu {
- INV_INV_FALSE | INV_INV_TRUE => invalid_node(),
- _ => self.unpacked_rwus[packed_rwu as usize].writer,
- }
- }
-
- fn get_used(&self, idx: usize) -> bool {
- let packed_rwu = self.packed_rwus[idx];
- match packed_rwu {
- INV_INV_FALSE => false,
- INV_INV_TRUE => true,
- _ => self.unpacked_rwus[packed_rwu as usize].used,
- }
- }
-
- #[inline]
- fn copy_packed(&mut self, dst_idx: usize, src_idx: usize) {
- self.packed_rwus[dst_idx] = self.packed_rwus[src_idx];
- }
-
- fn assign_unpacked(&mut self, idx: usize, rwu: RWU) {
- if rwu.reader == invalid_node() && rwu.writer == invalid_node() {
- // When we overwrite an indexing entry in `self.packed_rwus` with
- // `INV_INV_{TRUE,FALSE}` we don't remove the corresponding entry
- // from `self.unpacked_rwus`; it's not worth the effort, and we
- // can't have entries shifting around anyway.
- self.packed_rwus[idx] = if rwu.used {
- INV_INV_TRUE
- } else {
- INV_INV_FALSE
- }
- } else {
- // Add a new RWU to `unpacked_rwus` and make `packed_rwus[idx]`
- // point to it.
- self.packed_rwus[idx] = self.unpacked_rwus.len() as u32;
- self.unpacked_rwus.push(rwu);
- }
- }
-
- fn assign_inv_inv(&mut self, idx: usize) {
- self.packed_rwus[idx] = if self.get_used(idx) {
- INV_INV_TRUE
- } else {
- INV_INV_FALSE
- };
- }
-}
-
-#[derive(Copy, Clone)]
-struct Specials {
- exit_ln: LiveNode,
- fallthrough_ln: LiveNode,
- clean_exit_var: Variable
-}
-
-const ACC_READ: u32 = 1;
-const ACC_WRITE: u32 = 2;
-const ACC_USE: u32 = 4;
-
-struct Liveness<'a, 'tcx> {
- ir: &'a mut IrMaps<'tcx>,
- tables: &'a ty::TypeckTables<'tcx>,
- s: Specials,
- successors: Vec<LiveNode>,
- rwu_table: RWUTable,
-
- // mappings from loop node ID to LiveNode
- // ("break" label should map to loop node ID,
- // it probably doesn't now)
- break_ln: HirIdMap<LiveNode>,
- cont_ln: HirIdMap<LiveNode>,
-}
-
-impl<'a, 'tcx> Liveness<'a, 'tcx> {
- fn new(ir: &'a mut IrMaps<'tcx>, body: hir::BodyId) -> Liveness<'a, 'tcx> {
- // Special nodes and variables:
- // - exit_ln represents the end of the fn, either by return or panic
- // - implicit_ret_var is a pseudo-variable that represents
- // an implicit return
- let specials = Specials {
- exit_ln: ir.add_live_node(ExitNode),
- fallthrough_ln: ir.add_live_node(ExitNode),
- clean_exit_var: ir.add_variable(CleanExit)
- };
-
- let tables = ir.tcx.body_tables(body);
-
- let num_live_nodes = ir.num_live_nodes;
- let num_vars = ir.num_vars;
-
- Liveness {
- ir,
- tables,
- s: specials,
- successors: vec![invalid_node(); num_live_nodes],
- rwu_table: RWUTable::new(num_live_nodes * num_vars),
- break_ln: Default::default(),
- cont_ln: Default::default(),
- }
- }
-
- fn live_node(&self, hir_id: HirId, span: Span) -> LiveNode {
- match self.ir.live_node_map.get(&hir_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 {:?}",
- hir_id);
- }
- }
- }
-
- fn variable(&self, hir_id: HirId, span: Span) -> Variable {
- self.ir.variable(hir_id, span)
- }
-
- fn define_bindings_in_pat(&mut self, pat: &hir::Pat, mut succ: LiveNode) -> LiveNode {
- // In an or-pattern, 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.
- pat.each_binding_or_first(&mut |_, hir_id, pat_sp, ident| {
- let ln = self.live_node(hir_id, pat_sp);
- let var = self.variable(hir_id, ident.span);
- self.init_from_succ(ln, succ);
- self.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.rwu_table.get_reader(self.idx(ln, var));
- 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.rwu_table.get_used(self.idx(ln, var))
- }
-
- fn assigned_on_entry(&self, ln: LiveNode, var: Variable)
- -> Option<LiveNodeKind> {
- assert!(ln.is_valid());
- let writer = self.rwu_table.get_writer(self.idx(ln, var));
- 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 dyn 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 as u32))?;
- }
- }
- Ok(())
- }
-
-
- #[allow(unused_must_use)]
- fn ln_str(&self, ln: LiveNode) -> String {
- let mut wr = Vec::new();
- {
- let wr = &mut wr as &mut dyn Write;
- write!(wr, "[ln({:?}) of kind {:?} reads", ln.get(), self.ir.lnk(ln));
- self.write_vars(wr, ln, |idx| self.rwu_table.get_reader(idx));
- write!(wr, " writes");
- self.write_vars(wr, ln, |idx| self.rwu_table.get_writer(idx));
- 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 RWUs here because they are all
- // set to INV_INV_FALSE when they are created, and the sets only grow
- // during iterations.
- }
-
- 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.rwu_table.copy_packed(idx, 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| {
- let mut rwu = this.rwu_table.get(idx);
- let succ_rwu = this.rwu_table.get(succ_idx);
- if succ_rwu.reader.is_valid() && !rwu.reader.is_valid() {
- rwu.reader = succ_rwu.reader;
- changed = true
- }
-
- if succ_rwu.writer.is_valid() && !rwu.writer.is_valid() {
- rwu.writer = succ_rwu.writer;
- changed = true
- }
-
- if succ_rwu.used && !rwu.used {
- rwu.used = true;
- changed = true;
- }
-
- if changed {
- this.rwu_table.assign_unpacked(idx, rwu);
- }
- });
-
- debug!("merge_from_succ(ln={:?}, succ={}, first_merge={}, changed={})",
- ln, self.ln_str(succ_ln), first_merge, changed);
- return changed;
- }
-
- // 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.rwu_table.assign_inv_inv(idx);
-
- 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 mut rwu = self.rwu_table.get(idx);
-
- if (acc & ACC_WRITE) != 0 {
- rwu.reader = invalid_node();
- rwu.writer = ln;
- }
-
- // Important: if we both read/write, must do read second
- // or else the write will override.
- if (acc & ACC_READ) != 0 {
- rwu.reader = ln;
- }
-
- if (acc & ACC_USE) != 0 {
- rwu.used = true;
- }
-
- self.rwu_table.assign_unpacked(idx, rwu);
- }
-
- fn compute(&mut self, body: &hir::Expr) -> LiveNode {
- debug!("compute: using id for body, {}",
- self.ir.tcx.hir().hir_to_pretty_string(body.hir_id));
-
- // 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);
- self.acc(s.fallthrough_ln, s.clean_exit_var, ACC_READ);
-
- let entry_ln = self.propagate_through_expr(body, s.fallthrough_ln);
-
- // 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 as u32)));
- }
- body.hir_id
- },
- entry_ln);
-
- entry_ln
- }
-
- fn propagate_through_block(&mut self, blk: &hir::Block, succ: LiveNode)
- -> LiveNode {
- if blk.targeted_by_break {
- self.break_ln.insert(blk.hir_id, succ);
- }
- 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.kind {
- hir::StmtKind::Local(ref local) => {
- // 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)
- }
- hir::StmtKind::Item(..) => succ,
- hir::StmtKind::Expr(ref expr) | hir::StmtKind::Semi(ref expr) => {
- self.propagate_through_expr(&expr, succ)
- }
- }
- }
-
- fn propagate_through_exprs(&mut self, exprs: &[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: {}", self.ir.tcx.hir().hir_to_pretty_string(expr.hir_id));
-
- match expr.kind {
- // Interesting cases with control flow or which gen/kill
- hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => {
- self.access_path(expr.hir_id, path, succ, ACC_READ | ACC_USE)
- }
-
- hir::ExprKind::Field(ref e, _) => {
- self.propagate_through_expr(&e, succ)
- }
-
- hir::ExprKind::Closure(..) => {
- debug!("{} is an ExprKind::Closure",
- self.ir.tcx.hir().hir_to_pretty_string(expr.hir_id));
-
- // the construction of a closure itself is not important,
- // but we have to consider the closed over variables.
- let caps = self.ir.capture_info_map.get(&expr.hir_id).cloned().unwrap_or_else(||
- span_bug!(expr.span, "no registered caps"));
-
- caps.iter().rev().fold(succ, |succ, cap| {
- self.init_from_succ(cap.ln, succ);
- let var = self.variable(cap.var_hid, expr.span);
- self.acc(cap.ln, var, ACC_READ | ACC_USE);
- cap.ln
- })
- }
-
- // Note that labels have been resolved, so we don't need to look
- // at the label ident
- hir::ExprKind::Loop(ref blk, _, _) => {
- self.propagate_through_loop(expr, &blk, succ)
- }
-
- hir::ExprKind::Match(ref e, ref arms, _) => {
- //
- // (e)
- // |
- // v
- // (expr)
- // / | \
- // | | |
- // v v v
- // (..arms..)
- // | | |
- // v v v
- // ( succ )
- //
- //
- let ln = self.live_node(expr.hir_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(|hir::Guard::If(e)| &**e),
- body_succ
- );
- let arm_succ = self.define_bindings_in_pat(&arm.pat, guard_succ);
- self.merge_from_succ(ln, arm_succ, first_merge);
- first_merge = false;
- };
- self.propagate_through_expr(&e, ln)
- }
-
- hir::ExprKind::Ret(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::ExprKind::Break(label, ref opt_expr) => {
- // Find which label this break jumps to
- let target = match label.target_id {
- Ok(hir_id) => self.break_ln.get(&hir_id),
- Err(err) => span_bug!(expr.span, "loop scope error: {}", err),
- }.cloned();
-
- // Now that we know the label we're going to,
- // look it up in the break loop nodes table
-
- match target {
- Some(b) => self.propagate_through_opt_expr(opt_expr.as_ref().map(|e| &**e), b),
- None => span_bug!(expr.span, "break to unknown label")
- }
- }
-
- hir::ExprKind::Continue(label) => {
- // Find which label this expr continues to
- let sc = label.target_id.unwrap_or_else(|err|
- span_bug!(expr.span, "loop scope error: {}", err));
-
- // Now that we know the label we're going to,
- // look it up in the continue loop nodes table
- self.cont_ln.get(&sc).cloned().unwrap_or_else(||
- span_bug!(expr.span, "continue to unknown label"))
- }
-
- hir::ExprKind::Assign(ref l, ref r) => {
- // see comment on places in
- // propagate_through_place_components()
- let succ = self.write_place(&l, succ, ACC_WRITE);
- let succ = self.propagate_through_place_components(&l, succ);
- self.propagate_through_expr(&r, succ)
- }
-
- hir::ExprKind::AssignOp(_, ref l, ref r) => {
- // an overloaded assign op is like a method call
- if self.tables.is_method_call(expr) {
- let succ = self.propagate_through_expr(&l, succ);
- self.propagate_through_expr(&r, succ)
- } else {
- // see comment on places in
- // propagate_through_place_components()
- let succ = self.write_place(&l, succ, ACC_WRITE|ACC_READ);
- let succ = self.propagate_through_expr(&r, succ);
- self.propagate_through_place_components(&l, succ)
- }
- }
-
- // Uninteresting cases: just propagate in rev exec order
-
- hir::ExprKind::Array(ref exprs) => {
- self.propagate_through_exprs(exprs, succ)
- }
-
- hir::ExprKind::Struct(_, 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::ExprKind::Call(ref f, ref args) => {
- let m = self.ir.tcx.hir().get_module_parent(expr.hir_id);
- let succ = if self.ir.tcx.is_ty_uninhabited_from(m, self.tables.expr_ty(expr)) {
- self.s.exit_ln
- } else {
- succ
- };
- let succ = self.propagate_through_exprs(args, succ);
- self.propagate_through_expr(&f, succ)
- }
-
- hir::ExprKind::MethodCall(.., ref args) => {
- let m = self.ir.tcx.hir().get_module_parent(expr.hir_id);
- let succ = if self.ir.tcx.is_ty_uninhabited_from(m, self.tables.expr_ty(expr)) {
- self.s.exit_ln
- } else {
- succ
- };
-
- self.propagate_through_exprs(args, succ)
- }
-
- hir::ExprKind::Tup(ref exprs) => {
- self.propagate_through_exprs(exprs, succ)
- }
-
- hir::ExprKind::Binary(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.hir_id, expr.span);
- self.init_from_succ(ln, succ);
- self.merge_from_succ(ln, r_succ, false);
-
- self.propagate_through_expr(&l, ln)
- }
-
- hir::ExprKind::Index(ref l, ref r) |
- hir::ExprKind::Binary(_, ref l, ref r) => {
- let r_succ = self.propagate_through_expr(&r, succ);
- self.propagate_through_expr(&l, r_succ)
- }
-
- hir::ExprKind::Box(ref e) |
- hir::ExprKind::AddrOf(_, ref e) |
- hir::ExprKind::Cast(ref e, _) |
- hir::ExprKind::Type(ref e, _) |
- hir::ExprKind::DropTemps(ref e) |
- hir::ExprKind::Unary(_, ref e) |
- hir::ExprKind::Yield(ref e, _) |
- hir::ExprKind::Repeat(ref e, _) => {
- self.propagate_through_expr(&e, succ)
- }
-
- hir::ExprKind::InlineAsm(ref ia, ref outputs, ref inputs) => {
- let succ = ia.outputs.iter().zip(outputs).rev().fold(succ, |succ, (o, output)| {
- // see comment on places
- // in propagate_through_place_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_place(output, succ, acc);
- self.propagate_through_place_components(output, succ)
- }});
-
- // Inputs are executed first. Propagate last because of rev order
- self.propagate_through_exprs(inputs, succ)
- }
-
- hir::ExprKind::Lit(..) | hir::ExprKind::Err |
- hir::ExprKind::Path(hir::QPath::TypeRelative(..)) => {
- succ
- }
-
- // Note that labels have been resolved, so we don't need to look
- // at the label ident
- hir::ExprKind::Block(ref blk, _) => {
- self.propagate_through_block(&blk, succ)
- }
- }
- }
-
- fn propagate_through_place_components(&mut self,
- expr: &Expr,
- succ: LiveNode)
- -> LiveNode {
- // # Places
- //
- // 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 place Untracked place
- // ----------------------++-----------------------
- // ||
- // | || |
- // v || v
- // (rvalue) || (rvalue)
- // | || |
- // v || v
- // (write of place) || (place components)
- // | || |
- // v || v
- // (succ) || (succ)
- // ||
- // ----------------------++-----------------------
- //
- // I will cover the two cases in turn:
- //
- // # Tracked places
- //
- // A tracked place 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_place()` routine generates
- // the contents of this node. There are no subcomponents to
- // consider.
- //
- // # Non-tracked places
- //
- // These are places 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_place_components()` (this fn).
- //
- // # Illegal places
- //
- // It is still possible to observe assignments to non-places;
- // these errors are detected in the later pass borrowck. We
- // just ignore such cases and treat them as reads.
-
- match expr.kind {
- hir::ExprKind::Path(_) => succ,
- hir::ExprKind::Field(ref e, _) => self.propagate_through_expr(&e, succ),
- _ => self.propagate_through_expr(expr, succ)
- }
- }
-
- // see comment on propagate_through_place()
- fn write_place(&mut self, expr: &Expr, succ: LiveNode, acc: u32) -> LiveNode {
- match expr.kind {
- hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => {
- self.access_path(expr.hir_id, path, succ, acc)
- }
-
- // We do not track other places, so just propagate through
- // to their subcomponents. Also, it may happen that
- // non-places occur here, because those are detected in the
- // later pass borrowck.
- _ => succ
- }
- }
-
- fn access_var(&mut self, hir_id: HirId, var_hid: HirId, succ: LiveNode, acc: u32, span: Span)
- -> LiveNode {
- let ln = self.live_node(hir_id, span);
- if acc != 0 {
- self.init_from_succ(ln, succ);
- let var = self.variable(var_hid, span);
- self.acc(ln, var, acc);
- }
- ln
- }
-
- fn access_path(&mut self, hir_id: HirId, path: &hir::Path, succ: LiveNode, acc: u32)
- -> LiveNode {
- match path.res {
- Res::Local(hid) => {
- let upvars = self.ir.tcx.upvars(self.ir.body_owner);
- if !upvars.map_or(false, |upvars| upvars.contains_key(&hid)) {
- self.access_var(hir_id, hid, succ, acc, path.span)
- } else {
- succ
- }
- }
- _ => succ
- }
- }
-
- fn propagate_through_loop(
- &mut self,
- expr: &Expr,
- body: &hir::Block,
- succ: LiveNode
- ) -> LiveNode {
- /*
- We model control flow like this:
-
- (expr) <-+
- | |
- v |
- (body) --+
-
- Note that a `continue` expression targeting the `loop` will have a successor of `expr`.
- Meanwhile, a `break` expression will have a successor of `succ`.
- */
-
- // first iteration:
- let mut first_merge = true;
- let ln = self.live_node(expr.hir_id, expr.span);
- self.init_empty(ln, succ);
- debug!("propagate_through_loop: using id for loop body {} {}",
- expr.hir_id, self.ir.tcx.hir().hir_to_pretty_string(body.hir_id));
-
- self.break_ln.insert(expr.hir_id, succ);
-
- self.cont_ln.insert(expr.hir_id, ln);
-
- let body_ln = self.propagate_through_block(body, ln);
-
- // repeat until fixed point is reached:
- while self.merge_from_succ(ln, body_ln, first_merge) {
- first_merge = false;
- assert_eq!(body_ln, self.propagate_through_block(body, ln));
- }
-
- ln
- }
-}
-
-// _______________________________________________________________________
-// Checking for error conditions
-
-impl<'a, 'tcx> Visitor<'tcx> for Liveness<'a, 'tcx> {
- fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
- NestedVisitorMap::None
- }
-
- fn visit_local(&mut self, local: &'tcx hir::Local) {
- self.check_unused_vars_in_pat(&local.pat, None, |spans, hir_id, ln, var| {
- if local.init.is_some() {
- self.warn_about_dead_assign(spans, hir_id, ln, var);
- }
- });
-
- intravisit::walk_local(self, local);
- }
-
- fn visit_expr(&mut self, ex: &'tcx Expr) {
- check_expr(self, ex);
- }
-
- fn visit_arm(&mut self, arm: &'tcx hir::Arm) {
- self.check_unused_vars_in_pat(&arm.pat, None, |_, _, _, _| {});
- intravisit::walk_arm(self, arm);
- }
-}
-
-fn check_expr<'tcx>(this: &mut Liveness<'_, 'tcx>, expr: &'tcx Expr) {
- match expr.kind {
- hir::ExprKind::Assign(ref l, _) => {
- this.check_place(&l);
- }
-
- hir::ExprKind::AssignOp(_, ref l, _) => {
- if !this.tables.is_method_call(expr) {
- this.check_place(&l);
- }
- }
-
- hir::ExprKind::InlineAsm(ref ia, ref outputs, ref inputs) => {
- for input in inputs {
- this.visit_expr(input);
- }
-
- // Output operands must be places
- for (o, output) in ia.outputs.iter().zip(outputs) {
- if !o.is_indirect {
- this.check_place(output);
- }
- this.visit_expr(output);
- }
- }
-
- // no correctness conditions related to liveness
- hir::ExprKind::Call(..) | hir::ExprKind::MethodCall(..) |
- hir::ExprKind::Match(..) | hir::ExprKind::Loop(..) |
- hir::ExprKind::Index(..) | hir::ExprKind::Field(..) |
- hir::ExprKind::Array(..) | hir::ExprKind::Tup(..) | hir::ExprKind::Binary(..) |
- hir::ExprKind::Cast(..) | hir::ExprKind::DropTemps(..) | hir::ExprKind::Unary(..) |
- hir::ExprKind::Ret(..) | hir::ExprKind::Break(..) | hir::ExprKind::Continue(..) |
- hir::ExprKind::Lit(_) | hir::ExprKind::Block(..) | hir::ExprKind::AddrOf(..) |
- hir::ExprKind::Struct(..) | hir::ExprKind::Repeat(..) |
- hir::ExprKind::Closure(..) | hir::ExprKind::Path(_) | hir::ExprKind::Yield(..) |
- hir::ExprKind::Box(..) | hir::ExprKind::Type(..) | hir::ExprKind::Err => {}
- }
-
- intravisit::walk_expr(this, expr);
-}
-
-impl<'tcx> Liveness<'_, 'tcx> {
- fn check_place(&mut self, expr: &'tcx Expr) {
- match expr.kind {
- hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => {
- if let Res::Local(var_hid) = path.res {
- let upvars = self.ir.tcx.upvars(self.ir.body_owner);
- if !upvars.map_or(false, |upvars| upvars.contains_key(&var_hid)) {
- // 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.hir_id, expr.span);
- let var = self.variable(var_hid, expr.span);
- self.warn_about_dead_assign(vec![expr.span], expr.hir_id, ln, var);
- }
- }
- }
- _ => {
- // For other kinds of places, 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] == b'_' {
- None
- } else {
- Some(name)
- }
- }
-
- fn warn_about_unused_args(&self, body: &hir::Body, entry_ln: LiveNode) {
- for p in &body.params {
- self.check_unused_vars_in_pat(&p.pat, Some(entry_ln), |spans, hir_id, ln, var| {
- if self.live_on_entry(ln, var).is_none() {
- self.report_dead_assign(hir_id, spans, var, true);
- }
- });
- }
- }
-
- fn check_unused_vars_in_pat(
- &self,
- pat: &hir::Pat,
- entry_ln: Option<LiveNode>,
- on_used_on_entry: impl Fn(Vec<Span>, HirId, LiveNode, Variable),
- ) {
- // In an or-pattern, only consider the variable; any later patterns must have the same
- // bindings, and we also consider the first pattern to be the "authoritative" set of ids.
- // However, we should take the spans of variables with the same name from the later
- // patterns so the suggestions to prefix with underscores will apply to those too.
- let mut vars: FxIndexMap<String, (LiveNode, Variable, HirId, Vec<Span>)> = <_>::default();
-
- pat.each_binding(|_, hir_id, pat_sp, ident| {
- let ln = entry_ln.unwrap_or_else(|| self.live_node(hir_id, pat_sp));
- let var = self.variable(hir_id, ident.span);
- vars.entry(self.ir.variable_name(var))
- .and_modify(|(.., spans)| spans.push(ident.span))
- .or_insert_with(|| (ln, var, hir_id, vec![ident.span]));
- });
-
- for (_, (ln, var, id, spans)) in vars {
- if self.used_on_entry(ln, var) {
- on_used_on_entry(spans, id, ln, var);
- } else {
- self.report_unused(spans, id, ln, var);
- }
- }
- }
-
- fn report_unused(&self, spans: Vec<Span>, hir_id: HirId, ln: LiveNode, var: Variable) {
- if let Some(name) = self.should_warn(var).filter(|name| name != "self") {
- // 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.lint_hir_note(
- lint::builtin::UNUSED_VARIABLES,
- hir_id,
- spans,
- &format!("variable `{}` is assigned to, but never used", name),
- &format!("consider using `_{}` instead", name),
- );
- } else {
- let mut err = self.ir.tcx.struct_span_lint_hir(
- lint::builtin::UNUSED_VARIABLES,
- hir_id,
- spans.clone(),
- &format!("unused variable: `{}`", name),
- );
-
- if self.ir.variable_is_shorthand(var) {
- if let Node::Binding(pat) = self.ir.tcx.hir().get(hir_id) {
- // Handle `ref` and `ref mut`.
- let spans = spans.iter()
- .map(|_span| (pat.span, format!("{}: _", name)))
- .collect();
-
- err.multipart_suggestion(
- "try ignoring the field",
- spans,
- Applicability::MachineApplicable,
- );
- }
- } else {
- err.multipart_suggestion(
- "consider prefixing with an underscore",
- spans.iter().map(|span| (*span, format!("_{}", name))).collect(),
- Applicability::MachineApplicable,
- );
- }
-
- err.emit()
- }
- }
- }
-
- fn warn_about_dead_assign(&self, spans: Vec<Span>, hir_id: HirId, ln: LiveNode, var: Variable) {
- if self.live_on_exit(ln, var).is_none() {
- self.report_dead_assign(hir_id, spans, var, false);
- }
- }
-
- fn report_dead_assign(&self, hir_id: HirId, spans: Vec<Span>, var: Variable, is_param: bool) {
- if let Some(name) = self.should_warn(var) {
- if is_param {
- self.ir.tcx.struct_span_lint_hir(lint::builtin::UNUSED_ASSIGNMENTS, hir_id, spans,
- &format!("value passed to `{}` is never read", name))
- .help("maybe it is overwritten before being read?")
- .emit();
- } else {
- self.ir.tcx.struct_span_lint_hir(lint::builtin::UNUSED_ASSIGNMENTS, hir_id, spans,
- &format!("value assigned to `{}` is never read", name))
- .help("maybe it is overwritten before being read?")
- .emit();
- }
- }
- }
-}
traits::provide(providers);
stability::provide(providers);
middle::intrinsicck::provide(providers);
- middle::liveness::provide(providers);
reachable::provide(providers);
rustc_passes::provide(providers);
rustc_traits::provide(providers);
pub mod hir_stats;
pub mod layout_test;
pub mod loops;
+mod liveness;
pub fn provide(providers: &mut Providers<'_>) {
loops::provide(providers);
+ liveness::provide(providers);
}
--- /dev/null
+//! 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
+//! IDs.
+//!
+//! # 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 `u32`) and the ID for a variable
+//! is called a `variable` (another newtype'd `u32`).
+//!
+//! 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 `RWU` struct
+//!
+//! At each live node `N`, we track three pieces of information for each
+//! variable `V` (these are encapsulated in the `RWU` 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, panic, or other means.
+//!
+//! - `fallthrough_ln`: a live node that represents a fallthrough
+//!
+//! - `clean_exit_var`: a synthetic variable that is only 'read' from the
+//! fallthrough node. It is only live if the function could converge
+//! via means other than an explicit `return` expression. That is, it is
+//! only dead if the end of the function's block can never be reached.
+//! It is the responsibility of typeck to ensure that there are no
+//! `return` expressions in a function declared as diverging.
+
+use self::LiveNodeKind::*;
+use self::VarKind::*;
+
+use rustc::hir;
+use rustc::hir::{Expr, HirId};
+use rustc::hir::def::*;
+use rustc::hir::def_id::DefId;
+use rustc::hir::intravisit::{self, Visitor, FnKind, NestedVisitorMap};
+use rustc::hir::Node;
+use rustc::hir::ptr::P;
+use rustc::ty::{self, TyCtxt};
+use rustc::ty::query::Providers;
+use rustc::lint;
+use rustc::util::nodemap::{HirIdMap, HirIdSet};
+
+use errors::Applicability;
+use rustc_data_structures::fx::FxIndexMap;
+use std::collections::VecDeque;
+use std::{fmt, u32};
+use std::io::prelude::*;
+use std::io;
+use std::rc::Rc;
+use syntax::ast;
+use syntax::symbol::sym;
+use syntax_pos::Span;
+
+#[derive(Copy, Clone, PartialEq)]
+struct Variable(u32);
+
+#[derive(Copy, Clone, PartialEq)]
+struct LiveNode(u32);
+
+impl Variable {
+ fn get(&self) -> usize { self.0 as usize }
+}
+
+impl LiveNode {
+ fn get(&self) -> usize { self.0 as usize }
+}
+
+#[derive(Copy, Clone, PartialEq, Debug)]
+enum LiveNodeKind {
+ UpvarNode(Span),
+ ExprNode(Span),
+ VarDefNode(Span),
+ ExitNode
+}
+
+fn live_node_kind_to_string(lnk: LiveNodeKind, tcx: TyCtxt<'_>) -> String {
+ let cm = tcx.sess.source_map();
+ match lnk {
+ UpvarNode(s) => {
+ format!("Upvar node [{}]", cm.span_to_string(s))
+ }
+ ExprNode(s) => {
+ format!("Expr node [{}]", cm.span_to_string(s))
+ }
+ VarDefNode(s) => {
+ format!("Var def node [{}]", cm.span_to_string(s))
+ }
+ ExitNode => "Exit node".to_owned(),
+ }
+}
+
+impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
+ fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
+ NestedVisitorMap::OnlyBodies(&self.tcx.hir())
+ }
+
+ fn visit_fn(&mut self, fk: FnKind<'tcx>, fd: &'tcx hir::FnDecl,
+ b: hir::BodyId, s: Span, id: HirId) {
+ visit_fn(self, fk, fd, b, s, id);
+ }
+
+ fn visit_local(&mut self, l: &'tcx hir::Local) { visit_local(self, l); }
+ fn visit_expr(&mut self, ex: &'tcx Expr) { visit_expr(self, ex); }
+ fn visit_arm(&mut self, a: &'tcx hir::Arm) { visit_arm(self, a); }
+}
+
+fn check_mod_liveness(tcx: TyCtxt<'_>, module_def_id: DefId) {
+ tcx.hir().visit_item_likes_in_module(
+ module_def_id,
+ &mut IrMaps::new(tcx, module_def_id).as_deep_visitor(),
+ );
+}
+
+pub fn provide(providers: &mut Providers<'_>) {
+ *providers = Providers {
+ check_mod_liveness,
+ ..*providers
+ };
+}
+
+impl fmt::Debug for LiveNode {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ write!(f, "ln({})", self.get())
+ }
+}
+
+impl fmt::Debug for Variable {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ write!(f, "v({})", self.get())
+ }
+}
+
+// ______________________________________________________________________
+// 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.
+
+impl LiveNode {
+ fn is_valid(&self) -> bool {
+ self.0 != u32::MAX
+ }
+}
+
+fn invalid_node() -> LiveNode { LiveNode(u32::MAX) }
+
+struct CaptureInfo {
+ ln: LiveNode,
+ var_hid: HirId
+}
+
+#[derive(Copy, Clone, Debug)]
+struct LocalInfo {
+ id: HirId,
+ name: ast::Name,
+ is_shorthand: bool,
+}
+
+#[derive(Copy, Clone, Debug)]
+enum VarKind {
+ Param(HirId, ast::Name),
+ Local(LocalInfo),
+ CleanExit
+}
+
+struct IrMaps<'tcx> {
+ tcx: TyCtxt<'tcx>,
+ body_owner: DefId,
+ num_live_nodes: usize,
+ num_vars: usize,
+ live_node_map: HirIdMap<LiveNode>,
+ variable_map: HirIdMap<Variable>,
+ capture_info_map: HirIdMap<Rc<Vec<CaptureInfo>>>,
+ var_kinds: Vec<VarKind>,
+ lnks: Vec<LiveNodeKind>,
+}
+
+impl IrMaps<'tcx> {
+ fn new(tcx: TyCtxt<'tcx>, body_owner: DefId) -> IrMaps<'tcx> {
+ IrMaps {
+ tcx,
+ body_owner,
+ num_live_nodes: 0,
+ num_vars: 0,
+ live_node_map: HirIdMap::default(),
+ variable_map: HirIdMap::default(),
+ capture_info_map: Default::default(),
+ var_kinds: Vec::new(),
+ lnks: Vec::new(),
+ }
+ }
+
+ fn add_live_node(&mut self, lnk: LiveNodeKind) -> LiveNode {
+ let ln = LiveNode(self.num_live_nodes as u32);
+ self.lnks.push(lnk);
+ self.num_live_nodes += 1;
+
+ debug!("{:?} is of kind {}", ln,
+ live_node_kind_to_string(lnk, self.tcx));
+
+ ln
+ }
+
+ fn add_live_node_for_node(&mut self, hir_id: HirId, lnk: LiveNodeKind) {
+ let ln = self.add_live_node(lnk);
+ self.live_node_map.insert(hir_id, ln);
+
+ debug!("{:?} is node {:?}", ln, hir_id);
+ }
+
+ fn add_variable(&mut self, vk: VarKind) -> Variable {
+ let v = Variable(self.num_vars as u32);
+ self.var_kinds.push(vk);
+ self.num_vars += 1;
+
+ match vk {
+ Local(LocalInfo { id: node_id, .. }) | Param(node_id, _) => {
+ self.variable_map.insert(node_id, v);
+ },
+ CleanExit => {}
+ }
+
+ debug!("{:?} is {:?}", v, vk);
+
+ v
+ }
+
+ fn variable(&self, hir_id: HirId, span: Span) -> Variable {
+ match self.variable_map.get(&hir_id) {
+ Some(&var) => var,
+ None => {
+ span_bug!(span, "no variable registered for id {:?}", hir_id);
+ }
+ }
+ }
+
+ fn variable_name(&self, var: Variable) -> String {
+ match self.var_kinds[var.get()] {
+ Local(LocalInfo { name, .. }) | Param(_, name) => {
+ name.to_string()
+ },
+ CleanExit => "<clean-exit>".to_owned()
+ }
+ }
+
+ fn variable_is_shorthand(&self, var: Variable) -> bool {
+ match self.var_kinds[var.get()] {
+ Local(LocalInfo { is_shorthand, .. }) => is_shorthand,
+ Param(..) | CleanExit => false
+ }
+ }
+
+ fn set_captures(&mut self, hir_id: HirId, cs: Vec<CaptureInfo>) {
+ self.capture_info_map.insert(hir_id, Rc::new(cs));
+ }
+
+ fn lnk(&self, ln: LiveNode) -> LiveNodeKind {
+ self.lnks[ln.get()]
+ }
+}
+
+fn visit_fn<'tcx>(
+ ir: &mut IrMaps<'tcx>,
+ fk: FnKind<'tcx>,
+ decl: &'tcx hir::FnDecl,
+ body_id: hir::BodyId,
+ sp: Span,
+ id: hir::HirId,
+) {
+ debug!("visit_fn");
+
+ // swap in a new set of IR maps for this function body:
+ let def_id = ir.tcx.hir().local_def_id(id);
+ let mut fn_maps = IrMaps::new(ir.tcx, def_id);
+
+ // Don't run unused pass for #[derive()]
+ if let FnKind::Method(..) = fk {
+ let parent = ir.tcx.hir().get_parent_item(id);
+ if let Some(Node::Item(i)) = ir.tcx.hir().find(parent) {
+ if i.attrs.iter().any(|a| a.check_name(sym::automatically_derived)) {
+ return;
+ }
+ }
+ }
+
+ debug!("creating fn_maps: {:p}", &fn_maps);
+
+ let body = ir.tcx.hir().body(body_id);
+
+ for param in &body.params {
+ let is_shorthand = match param.pat.kind {
+ rustc::hir::PatKind::Struct(..) => true,
+ _ => false,
+ };
+ param.pat.each_binding(|_bm, hir_id, _x, ident| {
+ debug!("adding parameters {:?}", hir_id);
+ let var = if is_shorthand {
+ Local(LocalInfo {
+ id: hir_id,
+ name: ident.name,
+ is_shorthand: true,
+ })
+ } else {
+ Param(hir_id, ident.name)
+ };
+ fn_maps.add_variable(var);
+ })
+ };
+
+ // gather up the various local variables, significant expressions,
+ // and so forth:
+ intravisit::walk_fn(&mut fn_maps, fk, decl, body_id, sp, id);
+
+ // compute liveness
+ let mut lsets = Liveness::new(&mut fn_maps, body_id);
+ let entry_ln = lsets.compute(&body.value);
+
+ // check for various error conditions
+ lsets.visit_body(body);
+ lsets.warn_about_unused_args(body, entry_ln);
+}
+
+fn add_from_pat(ir: &mut IrMaps<'_>, pat: &P<hir::Pat>) {
+ // For struct patterns, take note of which fields used shorthand
+ // (`x` rather than `x: x`).
+ let mut shorthand_field_ids = HirIdSet::default();
+ let mut pats = VecDeque::new();
+ pats.push_back(pat);
+ while let Some(pat) = pats.pop_front() {
+ use rustc::hir::PatKind::*;
+ match &pat.kind {
+ Binding(.., inner_pat) => {
+ pats.extend(inner_pat.iter());
+ }
+ Struct(_, fields, _) => {
+ let ids = fields.iter().filter(|f| f.is_shorthand).map(|f| f.pat.hir_id);
+ shorthand_field_ids.extend(ids);
+ }
+ Ref(inner_pat, _) | Box(inner_pat) => {
+ pats.push_back(inner_pat);
+ }
+ TupleStruct(_, inner_pats, _) | Tuple(inner_pats, _) | Or(inner_pats) => {
+ pats.extend(inner_pats.iter());
+ }
+ Slice(pre_pats, inner_pat, post_pats) => {
+ pats.extend(pre_pats.iter());
+ pats.extend(inner_pat.iter());
+ pats.extend(post_pats.iter());
+ }
+ _ => {}
+ }
+ }
+
+ pat.each_binding(|_, hir_id, _, ident| {
+ ir.add_live_node_for_node(hir_id, VarDefNode(ident.span));
+ ir.add_variable(Local(LocalInfo {
+ id: hir_id,
+ name: ident.name,
+ is_shorthand: shorthand_field_ids.contains(&hir_id)
+ }));
+ });
+}
+
+fn visit_local<'tcx>(ir: &mut IrMaps<'tcx>, local: &'tcx hir::Local) {
+ add_from_pat(ir, &local.pat);
+ intravisit::walk_local(ir, local);
+}
+
+fn visit_arm<'tcx>(ir: &mut IrMaps<'tcx>, arm: &'tcx hir::Arm) {
+ add_from_pat(ir, &arm.pat);
+ intravisit::walk_arm(ir, arm);
+}
+
+fn visit_expr<'tcx>(ir: &mut IrMaps<'tcx>, expr: &'tcx Expr) {
+ match expr.kind {
+ // live nodes required for uses or definitions of variables:
+ hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => {
+ debug!("expr {}: path that leads to {:?}", expr.hir_id, path.res);
+ if let Res::Local(var_hir_id) = path.res {
+ let upvars = ir.tcx.upvars(ir.body_owner);
+ if !upvars.map_or(false, |upvars| upvars.contains_key(&var_hir_id)) {
+ ir.add_live_node_for_node(expr.hir_id, ExprNode(expr.span));
+ }
+ }
+ intravisit::walk_expr(ir, expr);
+ }
+ hir::ExprKind::Closure(..) => {
+ // Interesting control flow (for loops can contain labeled
+ // breaks or continues)
+ ir.add_live_node_for_node(expr.hir_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 mut call_caps = Vec::new();
+ let closure_def_id = ir.tcx.hir().local_def_id(expr.hir_id);
+ if let Some(upvars) = ir.tcx.upvars(closure_def_id) {
+ let parent_upvars = ir.tcx.upvars(ir.body_owner);
+ call_caps.extend(upvars.iter().filter_map(|(&var_id, upvar)| {
+ let has_parent = parent_upvars
+ .map_or(false, |upvars| upvars.contains_key(&var_id));
+ if !has_parent {
+ let upvar_ln = ir.add_live_node(UpvarNode(upvar.span));
+ Some(CaptureInfo { ln: upvar_ln, var_hid: var_id })
+ } else {
+ None
+ }
+ }));
+ }
+ ir.set_captures(expr.hir_id, call_caps);
+ let old_body_owner = ir.body_owner;
+ ir.body_owner = closure_def_id;
+ intravisit::walk_expr(ir, expr);
+ ir.body_owner = old_body_owner;
+ }
+
+ // live nodes required for interesting control flow:
+ hir::ExprKind::Match(..) |
+ hir::ExprKind::Loop(..) => {
+ ir.add_live_node_for_node(expr.hir_id, ExprNode(expr.span));
+ intravisit::walk_expr(ir, expr);
+ }
+ hir::ExprKind::Binary(op, ..) if op.node.is_lazy() => {
+ ir.add_live_node_for_node(expr.hir_id, ExprNode(expr.span));
+ intravisit::walk_expr(ir, expr);
+ }
+
+ // otherwise, live nodes are not required:
+ hir::ExprKind::Index(..) |
+ hir::ExprKind::Field(..) |
+ hir::ExprKind::Array(..) |
+ hir::ExprKind::Call(..) |
+ hir::ExprKind::MethodCall(..) |
+ hir::ExprKind::Tup(..) |
+ hir::ExprKind::Binary(..) |
+ hir::ExprKind::AddrOf(..) |
+ hir::ExprKind::Cast(..) |
+ hir::ExprKind::DropTemps(..) |
+ hir::ExprKind::Unary(..) |
+ hir::ExprKind::Break(..) |
+ hir::ExprKind::Continue(_) |
+ hir::ExprKind::Lit(_) |
+ hir::ExprKind::Ret(..) |
+ hir::ExprKind::Block(..) |
+ hir::ExprKind::Assign(..) |
+ hir::ExprKind::AssignOp(..) |
+ hir::ExprKind::Struct(..) |
+ hir::ExprKind::Repeat(..) |
+ hir::ExprKind::InlineAsm(..) |
+ hir::ExprKind::Box(..) |
+ hir::ExprKind::Yield(..) |
+ hir::ExprKind::Type(..) |
+ hir::ExprKind::Err |
+ hir::ExprKind::Path(hir::QPath::TypeRelative(..)) => {
+ 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 RWU {
+ reader: LiveNode,
+ writer: LiveNode,
+ used: bool
+}
+
+/// Conceptually, this is like a `Vec<RWU>`. But the number of `RWU`s can get
+/// very large, so it uses a more compact representation that takes advantage
+/// of the fact that when the number of `RWU`s is large, most of them have an
+/// invalid reader and an invalid writer.
+struct RWUTable {
+ /// Each entry in `packed_rwus` is either INV_INV_FALSE, INV_INV_TRUE, or
+ /// an index into `unpacked_rwus`. In the common cases, this compacts the
+ /// 65 bits of data into 32; in the uncommon cases, it expands the 65 bits
+ /// in 96.
+ ///
+ /// More compact representations are possible -- e.g., use only 2 bits per
+ /// packed `RWU` and make the secondary table a HashMap that maps from
+ /// indices to `RWU`s -- but this one strikes a good balance between size
+ /// and speed.
+ packed_rwus: Vec<u32>,
+ unpacked_rwus: Vec<RWU>,
+}
+
+// A constant representing `RWU { reader: invalid_node(); writer: invalid_node(); used: false }`.
+const INV_INV_FALSE: u32 = u32::MAX;
+
+// A constant representing `RWU { reader: invalid_node(); writer: invalid_node(); used: true }`.
+const INV_INV_TRUE: u32 = u32::MAX - 1;
+
+impl RWUTable {
+ fn new(num_rwus: usize) -> RWUTable {
+ Self {
+ packed_rwus: vec![INV_INV_FALSE; num_rwus],
+ unpacked_rwus: vec![],
+ }
+ }
+
+ fn get(&self, idx: usize) -> RWU {
+ let packed_rwu = self.packed_rwus[idx];
+ match packed_rwu {
+ INV_INV_FALSE => RWU { reader: invalid_node(), writer: invalid_node(), used: false },
+ INV_INV_TRUE => RWU { reader: invalid_node(), writer: invalid_node(), used: true },
+ _ => self.unpacked_rwus[packed_rwu as usize],
+ }
+ }
+
+ fn get_reader(&self, idx: usize) -> LiveNode {
+ let packed_rwu = self.packed_rwus[idx];
+ match packed_rwu {
+ INV_INV_FALSE | INV_INV_TRUE => invalid_node(),
+ _ => self.unpacked_rwus[packed_rwu as usize].reader,
+ }
+ }
+
+ fn get_writer(&self, idx: usize) -> LiveNode {
+ let packed_rwu = self.packed_rwus[idx];
+ match packed_rwu {
+ INV_INV_FALSE | INV_INV_TRUE => invalid_node(),
+ _ => self.unpacked_rwus[packed_rwu as usize].writer,
+ }
+ }
+
+ fn get_used(&self, idx: usize) -> bool {
+ let packed_rwu = self.packed_rwus[idx];
+ match packed_rwu {
+ INV_INV_FALSE => false,
+ INV_INV_TRUE => true,
+ _ => self.unpacked_rwus[packed_rwu as usize].used,
+ }
+ }
+
+ #[inline]
+ fn copy_packed(&mut self, dst_idx: usize, src_idx: usize) {
+ self.packed_rwus[dst_idx] = self.packed_rwus[src_idx];
+ }
+
+ fn assign_unpacked(&mut self, idx: usize, rwu: RWU) {
+ if rwu.reader == invalid_node() && rwu.writer == invalid_node() {
+ // When we overwrite an indexing entry in `self.packed_rwus` with
+ // `INV_INV_{TRUE,FALSE}` we don't remove the corresponding entry
+ // from `self.unpacked_rwus`; it's not worth the effort, and we
+ // can't have entries shifting around anyway.
+ self.packed_rwus[idx] = if rwu.used {
+ INV_INV_TRUE
+ } else {
+ INV_INV_FALSE
+ }
+ } else {
+ // Add a new RWU to `unpacked_rwus` and make `packed_rwus[idx]`
+ // point to it.
+ self.packed_rwus[idx] = self.unpacked_rwus.len() as u32;
+ self.unpacked_rwus.push(rwu);
+ }
+ }
+
+ fn assign_inv_inv(&mut self, idx: usize) {
+ self.packed_rwus[idx] = if self.get_used(idx) {
+ INV_INV_TRUE
+ } else {
+ INV_INV_FALSE
+ };
+ }
+}
+
+#[derive(Copy, Clone)]
+struct Specials {
+ exit_ln: LiveNode,
+ fallthrough_ln: LiveNode,
+ clean_exit_var: Variable
+}
+
+const ACC_READ: u32 = 1;
+const ACC_WRITE: u32 = 2;
+const ACC_USE: u32 = 4;
+
+struct Liveness<'a, 'tcx> {
+ ir: &'a mut IrMaps<'tcx>,
+ tables: &'a ty::TypeckTables<'tcx>,
+ s: Specials,
+ successors: Vec<LiveNode>,
+ rwu_table: RWUTable,
+
+ // mappings from loop node ID to LiveNode
+ // ("break" label should map to loop node ID,
+ // it probably doesn't now)
+ break_ln: HirIdMap<LiveNode>,
+ cont_ln: HirIdMap<LiveNode>,
+}
+
+impl<'a, 'tcx> Liveness<'a, 'tcx> {
+ fn new(ir: &'a mut IrMaps<'tcx>, body: hir::BodyId) -> Liveness<'a, 'tcx> {
+ // Special nodes and variables:
+ // - exit_ln represents the end of the fn, either by return or panic
+ // - implicit_ret_var is a pseudo-variable that represents
+ // an implicit return
+ let specials = Specials {
+ exit_ln: ir.add_live_node(ExitNode),
+ fallthrough_ln: ir.add_live_node(ExitNode),
+ clean_exit_var: ir.add_variable(CleanExit)
+ };
+
+ let tables = ir.tcx.body_tables(body);
+
+ let num_live_nodes = ir.num_live_nodes;
+ let num_vars = ir.num_vars;
+
+ Liveness {
+ ir,
+ tables,
+ s: specials,
+ successors: vec![invalid_node(); num_live_nodes],
+ rwu_table: RWUTable::new(num_live_nodes * num_vars),
+ break_ln: Default::default(),
+ cont_ln: Default::default(),
+ }
+ }
+
+ fn live_node(&self, hir_id: HirId, span: Span) -> LiveNode {
+ match self.ir.live_node_map.get(&hir_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 {:?}",
+ hir_id);
+ }
+ }
+ }
+
+ fn variable(&self, hir_id: HirId, span: Span) -> Variable {
+ self.ir.variable(hir_id, span)
+ }
+
+ fn define_bindings_in_pat(&mut self, pat: &hir::Pat, mut succ: LiveNode) -> LiveNode {
+ // In an or-pattern, 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.
+ pat.each_binding_or_first(&mut |_, hir_id, pat_sp, ident| {
+ let ln = self.live_node(hir_id, pat_sp);
+ let var = self.variable(hir_id, ident.span);
+ self.init_from_succ(ln, succ);
+ self.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.rwu_table.get_reader(self.idx(ln, var));
+ 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.rwu_table.get_used(self.idx(ln, var))
+ }
+
+ fn assigned_on_entry(&self, ln: LiveNode, var: Variable)
+ -> Option<LiveNodeKind> {
+ assert!(ln.is_valid());
+ let writer = self.rwu_table.get_writer(self.idx(ln, var));
+ 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 dyn 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 as u32))?;
+ }
+ }
+ Ok(())
+ }
+
+
+ #[allow(unused_must_use)]
+ fn ln_str(&self, ln: LiveNode) -> String {
+ let mut wr = Vec::new();
+ {
+ let wr = &mut wr as &mut dyn Write;
+ write!(wr, "[ln({:?}) of kind {:?} reads", ln.get(), self.ir.lnk(ln));
+ self.write_vars(wr, ln, |idx| self.rwu_table.get_reader(idx));
+ write!(wr, " writes");
+ self.write_vars(wr, ln, |idx| self.rwu_table.get_writer(idx));
+ 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 RWUs here because they are all
+ // set to INV_INV_FALSE when they are created, and the sets only grow
+ // during iterations.
+ }
+
+ 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.rwu_table.copy_packed(idx, 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| {
+ let mut rwu = this.rwu_table.get(idx);
+ let succ_rwu = this.rwu_table.get(succ_idx);
+ if succ_rwu.reader.is_valid() && !rwu.reader.is_valid() {
+ rwu.reader = succ_rwu.reader;
+ changed = true
+ }
+
+ if succ_rwu.writer.is_valid() && !rwu.writer.is_valid() {
+ rwu.writer = succ_rwu.writer;
+ changed = true
+ }
+
+ if succ_rwu.used && !rwu.used {
+ rwu.used = true;
+ changed = true;
+ }
+
+ if changed {
+ this.rwu_table.assign_unpacked(idx, rwu);
+ }
+ });
+
+ debug!("merge_from_succ(ln={:?}, succ={}, first_merge={}, changed={})",
+ ln, self.ln_str(succ_ln), first_merge, changed);
+ return changed;
+ }
+
+ // 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.rwu_table.assign_inv_inv(idx);
+
+ 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 mut rwu = self.rwu_table.get(idx);
+
+ if (acc & ACC_WRITE) != 0 {
+ rwu.reader = invalid_node();
+ rwu.writer = ln;
+ }
+
+ // Important: if we both read/write, must do read second
+ // or else the write will override.
+ if (acc & ACC_READ) != 0 {
+ rwu.reader = ln;
+ }
+
+ if (acc & ACC_USE) != 0 {
+ rwu.used = true;
+ }
+
+ self.rwu_table.assign_unpacked(idx, rwu);
+ }
+
+ fn compute(&mut self, body: &hir::Expr) -> LiveNode {
+ debug!("compute: using id for body, {}",
+ self.ir.tcx.hir().hir_to_pretty_string(body.hir_id));
+
+ // 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);
+ self.acc(s.fallthrough_ln, s.clean_exit_var, ACC_READ);
+
+ let entry_ln = self.propagate_through_expr(body, s.fallthrough_ln);
+
+ // 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 as u32)));
+ }
+ body.hir_id
+ },
+ entry_ln);
+
+ entry_ln
+ }
+
+ fn propagate_through_block(&mut self, blk: &hir::Block, succ: LiveNode)
+ -> LiveNode {
+ if blk.targeted_by_break {
+ self.break_ln.insert(blk.hir_id, succ);
+ }
+ 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.kind {
+ hir::StmtKind::Local(ref local) => {
+ // 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)
+ }
+ hir::StmtKind::Item(..) => succ,
+ hir::StmtKind::Expr(ref expr) | hir::StmtKind::Semi(ref expr) => {
+ self.propagate_through_expr(&expr, succ)
+ }
+ }
+ }
+
+ fn propagate_through_exprs(&mut self, exprs: &[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: {}", self.ir.tcx.hir().hir_to_pretty_string(expr.hir_id));
+
+ match expr.kind {
+ // Interesting cases with control flow or which gen/kill
+ hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => {
+ self.access_path(expr.hir_id, path, succ, ACC_READ | ACC_USE)
+ }
+
+ hir::ExprKind::Field(ref e, _) => {
+ self.propagate_through_expr(&e, succ)
+ }
+
+ hir::ExprKind::Closure(..) => {
+ debug!("{} is an ExprKind::Closure",
+ self.ir.tcx.hir().hir_to_pretty_string(expr.hir_id));
+
+ // the construction of a closure itself is not important,
+ // but we have to consider the closed over variables.
+ let caps = self.ir.capture_info_map.get(&expr.hir_id).cloned().unwrap_or_else(||
+ span_bug!(expr.span, "no registered caps"));
+
+ caps.iter().rev().fold(succ, |succ, cap| {
+ self.init_from_succ(cap.ln, succ);
+ let var = self.variable(cap.var_hid, expr.span);
+ self.acc(cap.ln, var, ACC_READ | ACC_USE);
+ cap.ln
+ })
+ }
+
+ // Note that labels have been resolved, so we don't need to look
+ // at the label ident
+ hir::ExprKind::Loop(ref blk, _, _) => {
+ self.propagate_through_loop(expr, &blk, succ)
+ }
+
+ hir::ExprKind::Match(ref e, ref arms, _) => {
+ //
+ // (e)
+ // |
+ // v
+ // (expr)
+ // / | \
+ // | | |
+ // v v v
+ // (..arms..)
+ // | | |
+ // v v v
+ // ( succ )
+ //
+ //
+ let ln = self.live_node(expr.hir_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(|hir::Guard::If(e)| &**e),
+ body_succ
+ );
+ let arm_succ = self.define_bindings_in_pat(&arm.pat, guard_succ);
+ self.merge_from_succ(ln, arm_succ, first_merge);
+ first_merge = false;
+ };
+ self.propagate_through_expr(&e, ln)
+ }
+
+ hir::ExprKind::Ret(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::ExprKind::Break(label, ref opt_expr) => {
+ // Find which label this break jumps to
+ let target = match label.target_id {
+ Ok(hir_id) => self.break_ln.get(&hir_id),
+ Err(err) => span_bug!(expr.span, "loop scope error: {}", err),
+ }.cloned();
+
+ // Now that we know the label we're going to,
+ // look it up in the break loop nodes table
+
+ match target {
+ Some(b) => self.propagate_through_opt_expr(opt_expr.as_ref().map(|e| &**e), b),
+ None => span_bug!(expr.span, "break to unknown label")
+ }
+ }
+
+ hir::ExprKind::Continue(label) => {
+ // Find which label this expr continues to
+ let sc = label.target_id.unwrap_or_else(|err|
+ span_bug!(expr.span, "loop scope error: {}", err));
+
+ // Now that we know the label we're going to,
+ // look it up in the continue loop nodes table
+ self.cont_ln.get(&sc).cloned().unwrap_or_else(||
+ span_bug!(expr.span, "continue to unknown label"))
+ }
+
+ hir::ExprKind::Assign(ref l, ref r) => {
+ // see comment on places in
+ // propagate_through_place_components()
+ let succ = self.write_place(&l, succ, ACC_WRITE);
+ let succ = self.propagate_through_place_components(&l, succ);
+ self.propagate_through_expr(&r, succ)
+ }
+
+ hir::ExprKind::AssignOp(_, ref l, ref r) => {
+ // an overloaded assign op is like a method call
+ if self.tables.is_method_call(expr) {
+ let succ = self.propagate_through_expr(&l, succ);
+ self.propagate_through_expr(&r, succ)
+ } else {
+ // see comment on places in
+ // propagate_through_place_components()
+ let succ = self.write_place(&l, succ, ACC_WRITE|ACC_READ);
+ let succ = self.propagate_through_expr(&r, succ);
+ self.propagate_through_place_components(&l, succ)
+ }
+ }
+
+ // Uninteresting cases: just propagate in rev exec order
+
+ hir::ExprKind::Array(ref exprs) => {
+ self.propagate_through_exprs(exprs, succ)
+ }
+
+ hir::ExprKind::Struct(_, 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::ExprKind::Call(ref f, ref args) => {
+ let m = self.ir.tcx.hir().get_module_parent(expr.hir_id);
+ let succ = if self.ir.tcx.is_ty_uninhabited_from(m, self.tables.expr_ty(expr)) {
+ self.s.exit_ln
+ } else {
+ succ
+ };
+ let succ = self.propagate_through_exprs(args, succ);
+ self.propagate_through_expr(&f, succ)
+ }
+
+ hir::ExprKind::MethodCall(.., ref args) => {
+ let m = self.ir.tcx.hir().get_module_parent(expr.hir_id);
+ let succ = if self.ir.tcx.is_ty_uninhabited_from(m, self.tables.expr_ty(expr)) {
+ self.s.exit_ln
+ } else {
+ succ
+ };
+
+ self.propagate_through_exprs(args, succ)
+ }
+
+ hir::ExprKind::Tup(ref exprs) => {
+ self.propagate_through_exprs(exprs, succ)
+ }
+
+ hir::ExprKind::Binary(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.hir_id, expr.span);
+ self.init_from_succ(ln, succ);
+ self.merge_from_succ(ln, r_succ, false);
+
+ self.propagate_through_expr(&l, ln)
+ }
+
+ hir::ExprKind::Index(ref l, ref r) |
+ hir::ExprKind::Binary(_, ref l, ref r) => {
+ let r_succ = self.propagate_through_expr(&r, succ);
+ self.propagate_through_expr(&l, r_succ)
+ }
+
+ hir::ExprKind::Box(ref e) |
+ hir::ExprKind::AddrOf(_, ref e) |
+ hir::ExprKind::Cast(ref e, _) |
+ hir::ExprKind::Type(ref e, _) |
+ hir::ExprKind::DropTemps(ref e) |
+ hir::ExprKind::Unary(_, ref e) |
+ hir::ExprKind::Yield(ref e, _) |
+ hir::ExprKind::Repeat(ref e, _) => {
+ self.propagate_through_expr(&e, succ)
+ }
+
+ hir::ExprKind::InlineAsm(ref ia, ref outputs, ref inputs) => {
+ let succ = ia.outputs.iter().zip(outputs).rev().fold(succ, |succ, (o, output)| {
+ // see comment on places
+ // in propagate_through_place_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_place(output, succ, acc);
+ self.propagate_through_place_components(output, succ)
+ }});
+
+ // Inputs are executed first. Propagate last because of rev order
+ self.propagate_through_exprs(inputs, succ)
+ }
+
+ hir::ExprKind::Lit(..) | hir::ExprKind::Err |
+ hir::ExprKind::Path(hir::QPath::TypeRelative(..)) => {
+ succ
+ }
+
+ // Note that labels have been resolved, so we don't need to look
+ // at the label ident
+ hir::ExprKind::Block(ref blk, _) => {
+ self.propagate_through_block(&blk, succ)
+ }
+ }
+ }
+
+ fn propagate_through_place_components(&mut self,
+ expr: &Expr,
+ succ: LiveNode)
+ -> LiveNode {
+ // # Places
+ //
+ // 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 place Untracked place
+ // ----------------------++-----------------------
+ // ||
+ // | || |
+ // v || v
+ // (rvalue) || (rvalue)
+ // | || |
+ // v || v
+ // (write of place) || (place components)
+ // | || |
+ // v || v
+ // (succ) || (succ)
+ // ||
+ // ----------------------++-----------------------
+ //
+ // I will cover the two cases in turn:
+ //
+ // # Tracked places
+ //
+ // A tracked place 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_place()` routine generates
+ // the contents of this node. There are no subcomponents to
+ // consider.
+ //
+ // # Non-tracked places
+ //
+ // These are places 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_place_components()` (this fn).
+ //
+ // # Illegal places
+ //
+ // It is still possible to observe assignments to non-places;
+ // these errors are detected in the later pass borrowck. We
+ // just ignore such cases and treat them as reads.
+
+ match expr.kind {
+ hir::ExprKind::Path(_) => succ,
+ hir::ExprKind::Field(ref e, _) => self.propagate_through_expr(&e, succ),
+ _ => self.propagate_through_expr(expr, succ)
+ }
+ }
+
+ // see comment on propagate_through_place()
+ fn write_place(&mut self, expr: &Expr, succ: LiveNode, acc: u32) -> LiveNode {
+ match expr.kind {
+ hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => {
+ self.access_path(expr.hir_id, path, succ, acc)
+ }
+
+ // We do not track other places, so just propagate through
+ // to their subcomponents. Also, it may happen that
+ // non-places occur here, because those are detected in the
+ // later pass borrowck.
+ _ => succ
+ }
+ }
+
+ fn access_var(&mut self, hir_id: HirId, var_hid: HirId, succ: LiveNode, acc: u32, span: Span)
+ -> LiveNode {
+ let ln = self.live_node(hir_id, span);
+ if acc != 0 {
+ self.init_from_succ(ln, succ);
+ let var = self.variable(var_hid, span);
+ self.acc(ln, var, acc);
+ }
+ ln
+ }
+
+ fn access_path(&mut self, hir_id: HirId, path: &hir::Path, succ: LiveNode, acc: u32)
+ -> LiveNode {
+ match path.res {
+ Res::Local(hid) => {
+ let upvars = self.ir.tcx.upvars(self.ir.body_owner);
+ if !upvars.map_or(false, |upvars| upvars.contains_key(&hid)) {
+ self.access_var(hir_id, hid, succ, acc, path.span)
+ } else {
+ succ
+ }
+ }
+ _ => succ
+ }
+ }
+
+ fn propagate_through_loop(
+ &mut self,
+ expr: &Expr,
+ body: &hir::Block,
+ succ: LiveNode
+ ) -> LiveNode {
+ /*
+ We model control flow like this:
+
+ (expr) <-+
+ | |
+ v |
+ (body) --+
+
+ Note that a `continue` expression targeting the `loop` will have a successor of `expr`.
+ Meanwhile, a `break` expression will have a successor of `succ`.
+ */
+
+ // first iteration:
+ let mut first_merge = true;
+ let ln = self.live_node(expr.hir_id, expr.span);
+ self.init_empty(ln, succ);
+ debug!("propagate_through_loop: using id for loop body {} {}",
+ expr.hir_id, self.ir.tcx.hir().hir_to_pretty_string(body.hir_id));
+
+ self.break_ln.insert(expr.hir_id, succ);
+
+ self.cont_ln.insert(expr.hir_id, ln);
+
+ let body_ln = self.propagate_through_block(body, ln);
+
+ // repeat until fixed point is reached:
+ while self.merge_from_succ(ln, body_ln, first_merge) {
+ first_merge = false;
+ assert_eq!(body_ln, self.propagate_through_block(body, ln));
+ }
+
+ ln
+ }
+}
+
+// _______________________________________________________________________
+// Checking for error conditions
+
+impl<'a, 'tcx> Visitor<'tcx> for Liveness<'a, 'tcx> {
+ fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
+ NestedVisitorMap::None
+ }
+
+ fn visit_local(&mut self, local: &'tcx hir::Local) {
+ self.check_unused_vars_in_pat(&local.pat, None, |spans, hir_id, ln, var| {
+ if local.init.is_some() {
+ self.warn_about_dead_assign(spans, hir_id, ln, var);
+ }
+ });
+
+ intravisit::walk_local(self, local);
+ }
+
+ fn visit_expr(&mut self, ex: &'tcx Expr) {
+ check_expr(self, ex);
+ }
+
+ fn visit_arm(&mut self, arm: &'tcx hir::Arm) {
+ self.check_unused_vars_in_pat(&arm.pat, None, |_, _, _, _| {});
+ intravisit::walk_arm(self, arm);
+ }
+}
+
+fn check_expr<'tcx>(this: &mut Liveness<'_, 'tcx>, expr: &'tcx Expr) {
+ match expr.kind {
+ hir::ExprKind::Assign(ref l, _) => {
+ this.check_place(&l);
+ }
+
+ hir::ExprKind::AssignOp(_, ref l, _) => {
+ if !this.tables.is_method_call(expr) {
+ this.check_place(&l);
+ }
+ }
+
+ hir::ExprKind::InlineAsm(ref ia, ref outputs, ref inputs) => {
+ for input in inputs {
+ this.visit_expr(input);
+ }
+
+ // Output operands must be places
+ for (o, output) in ia.outputs.iter().zip(outputs) {
+ if !o.is_indirect {
+ this.check_place(output);
+ }
+ this.visit_expr(output);
+ }
+ }
+
+ // no correctness conditions related to liveness
+ hir::ExprKind::Call(..) | hir::ExprKind::MethodCall(..) |
+ hir::ExprKind::Match(..) | hir::ExprKind::Loop(..) |
+ hir::ExprKind::Index(..) | hir::ExprKind::Field(..) |
+ hir::ExprKind::Array(..) | hir::ExprKind::Tup(..) | hir::ExprKind::Binary(..) |
+ hir::ExprKind::Cast(..) | hir::ExprKind::DropTemps(..) | hir::ExprKind::Unary(..) |
+ hir::ExprKind::Ret(..) | hir::ExprKind::Break(..) | hir::ExprKind::Continue(..) |
+ hir::ExprKind::Lit(_) | hir::ExprKind::Block(..) | hir::ExprKind::AddrOf(..) |
+ hir::ExprKind::Struct(..) | hir::ExprKind::Repeat(..) |
+ hir::ExprKind::Closure(..) | hir::ExprKind::Path(_) | hir::ExprKind::Yield(..) |
+ hir::ExprKind::Box(..) | hir::ExprKind::Type(..) | hir::ExprKind::Err => {}
+ }
+
+ intravisit::walk_expr(this, expr);
+}
+
+impl<'tcx> Liveness<'_, 'tcx> {
+ fn check_place(&mut self, expr: &'tcx Expr) {
+ match expr.kind {
+ hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => {
+ if let Res::Local(var_hid) = path.res {
+ let upvars = self.ir.tcx.upvars(self.ir.body_owner);
+ if !upvars.map_or(false, |upvars| upvars.contains_key(&var_hid)) {
+ // 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.hir_id, expr.span);
+ let var = self.variable(var_hid, expr.span);
+ self.warn_about_dead_assign(vec![expr.span], expr.hir_id, ln, var);
+ }
+ }
+ }
+ _ => {
+ // For other kinds of places, 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] == b'_' {
+ None
+ } else {
+ Some(name)
+ }
+ }
+
+ fn warn_about_unused_args(&self, body: &hir::Body, entry_ln: LiveNode) {
+ for p in &body.params {
+ self.check_unused_vars_in_pat(&p.pat, Some(entry_ln), |spans, hir_id, ln, var| {
+ if self.live_on_entry(ln, var).is_none() {
+ self.report_dead_assign(hir_id, spans, var, true);
+ }
+ });
+ }
+ }
+
+ fn check_unused_vars_in_pat(
+ &self,
+ pat: &hir::Pat,
+ entry_ln: Option<LiveNode>,
+ on_used_on_entry: impl Fn(Vec<Span>, HirId, LiveNode, Variable),
+ ) {
+ // In an or-pattern, only consider the variable; any later patterns must have the same
+ // bindings, and we also consider the first pattern to be the "authoritative" set of ids.
+ // However, we should take the spans of variables with the same name from the later
+ // patterns so the suggestions to prefix with underscores will apply to those too.
+ let mut vars: FxIndexMap<String, (LiveNode, Variable, HirId, Vec<Span>)> = <_>::default();
+
+ pat.each_binding(|_, hir_id, pat_sp, ident| {
+ let ln = entry_ln.unwrap_or_else(|| self.live_node(hir_id, pat_sp));
+ let var = self.variable(hir_id, ident.span);
+ vars.entry(self.ir.variable_name(var))
+ .and_modify(|(.., spans)| spans.push(ident.span))
+ .or_insert_with(|| (ln, var, hir_id, vec![ident.span]));
+ });
+
+ for (_, (ln, var, id, spans)) in vars {
+ if self.used_on_entry(ln, var) {
+ on_used_on_entry(spans, id, ln, var);
+ } else {
+ self.report_unused(spans, id, ln, var);
+ }
+ }
+ }
+
+ fn report_unused(&self, spans: Vec<Span>, hir_id: HirId, ln: LiveNode, var: Variable) {
+ if let Some(name) = self.should_warn(var).filter(|name| name != "self") {
+ // 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.lint_hir_note(
+ lint::builtin::UNUSED_VARIABLES,
+ hir_id,
+ spans,
+ &format!("variable `{}` is assigned to, but never used", name),
+ &format!("consider using `_{}` instead", name),
+ );
+ } else {
+ let mut err = self.ir.tcx.struct_span_lint_hir(
+ lint::builtin::UNUSED_VARIABLES,
+ hir_id,
+ spans.clone(),
+ &format!("unused variable: `{}`", name),
+ );
+
+ if self.ir.variable_is_shorthand(var) {
+ if let Node::Binding(pat) = self.ir.tcx.hir().get(hir_id) {
+ // Handle `ref` and `ref mut`.
+ let spans = spans.iter()
+ .map(|_span| (pat.span, format!("{}: _", name)))
+ .collect();
+
+ err.multipart_suggestion(
+ "try ignoring the field",
+ spans,
+ Applicability::MachineApplicable,
+ );
+ }
+ } else {
+ err.multipart_suggestion(
+ "consider prefixing with an underscore",
+ spans.iter().map(|span| (*span, format!("_{}", name))).collect(),
+ Applicability::MachineApplicable,
+ );
+ }
+
+ err.emit()
+ }
+ }
+ }
+
+ fn warn_about_dead_assign(&self, spans: Vec<Span>, hir_id: HirId, ln: LiveNode, var: Variable) {
+ if self.live_on_exit(ln, var).is_none() {
+ self.report_dead_assign(hir_id, spans, var, false);
+ }
+ }
+
+ fn report_dead_assign(&self, hir_id: HirId, spans: Vec<Span>, var: Variable, is_param: bool) {
+ if let Some(name) = self.should_warn(var) {
+ if is_param {
+ self.ir.tcx.struct_span_lint_hir(lint::builtin::UNUSED_ASSIGNMENTS, hir_id, spans,
+ &format!("value passed to `{}` is never read", name))
+ .help("maybe it is overwritten before being read?")
+ .emit();
+ } else {
+ self.ir.tcx.struct_span_lint_hir(lint::builtin::UNUSED_ASSIGNMENTS, hir_id, spans,
+ &format!("value assigned to `{}` is never read", name))
+ .help("maybe it is overwritten before being read?")
+ .emit();
+ }
+ }
+ }
+}
projects / rust.git / commitdiff