1617 lines
62 KiB
Rust
1617 lines
62 KiB
Rust
//! 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 `None`, 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 `None`, 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 nodes and variables
|
|
//!
|
|
//! We generate various special nodes for various, well, special purposes.
|
|
//! These are described in the `Liveness` struct.
|
|
|
|
use self::LiveNodeKind::*;
|
|
use self::VarKind::*;
|
|
|
|
use rustc_ast::InlineAsmOptions;
|
|
use rustc_data_structures::fx::FxIndexMap;
|
|
use rustc_errors::Applicability;
|
|
use rustc_hir as hir;
|
|
use rustc_hir::def::*;
|
|
use rustc_hir::def_id::LocalDefId;
|
|
use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
|
|
use rustc_hir::{Expr, HirId, HirIdMap, HirIdSet};
|
|
use rustc_index::vec::IndexVec;
|
|
use rustc_middle::hir::map::Map;
|
|
use rustc_middle::ty::query::Providers;
|
|
use rustc_middle::ty::{self, DefIdTree, TyCtxt};
|
|
use rustc_session::lint;
|
|
use rustc_span::symbol::{kw, sym, Symbol};
|
|
use rustc_span::Span;
|
|
|
|
use std::collections::VecDeque;
|
|
use std::io;
|
|
use std::io::prelude::*;
|
|
use std::rc::Rc;
|
|
|
|
mod rwu_table;
|
|
|
|
rustc_index::newtype_index! {
|
|
pub struct Variable {
|
|
DEBUG_FORMAT = "v({})",
|
|
}
|
|
}
|
|
|
|
rustc_index::newtype_index! {
|
|
pub struct LiveNode {
|
|
DEBUG_FORMAT = "ln({})",
|
|
}
|
|
}
|
|
|
|
#[derive(Copy, Clone, PartialEq, Debug)]
|
|
enum LiveNodeKind {
|
|
UpvarNode(Span),
|
|
ExprNode(Span),
|
|
VarDefNode(Span),
|
|
ClosureNode,
|
|
ExitNode,
|
|
}
|
|
|
|
fn live_node_kind_to_string(lnk: LiveNodeKind, tcx: TyCtxt<'_>) -> String {
|
|
let sm = tcx.sess.source_map();
|
|
match lnk {
|
|
UpvarNode(s) => format!("Upvar node [{}]", sm.span_to_string(s)),
|
|
ExprNode(s) => format!("Expr node [{}]", sm.span_to_string(s)),
|
|
VarDefNode(s) => format!("Var def node [{}]", sm.span_to_string(s)),
|
|
ClosureNode => "Closure node".to_owned(),
|
|
ExitNode => "Exit node".to_owned(),
|
|
}
|
|
}
|
|
|
|
fn check_mod_liveness(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
|
|
tcx.hir().visit_item_likes_in_module(module_def_id, &mut IrMaps::new(tcx).as_deep_visitor());
|
|
}
|
|
|
|
pub fn provide(providers: &mut Providers) {
|
|
*providers = Providers { check_mod_liveness, ..*providers };
|
|
}
|
|
|
|
// ______________________________________________________________________
|
|
// 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.
|
|
|
|
struct CaptureInfo {
|
|
ln: LiveNode,
|
|
var_hid: HirId,
|
|
}
|
|
|
|
#[derive(Copy, Clone, Debug)]
|
|
struct LocalInfo {
|
|
id: HirId,
|
|
name: Symbol,
|
|
is_shorthand: bool,
|
|
}
|
|
|
|
#[derive(Copy, Clone, Debug)]
|
|
enum VarKind {
|
|
Param(HirId, Symbol),
|
|
Local(LocalInfo),
|
|
Upvar(HirId, Symbol),
|
|
}
|
|
|
|
struct IrMaps<'tcx> {
|
|
tcx: TyCtxt<'tcx>,
|
|
live_node_map: HirIdMap<LiveNode>,
|
|
variable_map: HirIdMap<Variable>,
|
|
capture_info_map: HirIdMap<Rc<Vec<CaptureInfo>>>,
|
|
var_kinds: IndexVec<Variable, VarKind>,
|
|
lnks: IndexVec<LiveNode, LiveNodeKind>,
|
|
}
|
|
|
|
impl IrMaps<'tcx> {
|
|
fn new(tcx: TyCtxt<'tcx>) -> IrMaps<'tcx> {
|
|
IrMaps {
|
|
tcx,
|
|
live_node_map: HirIdMap::default(),
|
|
variable_map: HirIdMap::default(),
|
|
capture_info_map: Default::default(),
|
|
var_kinds: IndexVec::new(),
|
|
lnks: IndexVec::new(),
|
|
}
|
|
}
|
|
|
|
fn add_live_node(&mut self, lnk: LiveNodeKind) -> LiveNode {
|
|
let ln = self.lnks.push(lnk);
|
|
|
|
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 = self.var_kinds.push(vk);
|
|
|
|
match vk {
|
|
Local(LocalInfo { id: node_id, .. }) | Param(node_id, _) | Upvar(node_id, _) => {
|
|
self.variable_map.insert(node_id, v);
|
|
}
|
|
}
|
|
|
|
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) -> Symbol {
|
|
match self.var_kinds[var] {
|
|
Local(LocalInfo { name, .. }) | Param(_, name) | Upvar(_, name) => name,
|
|
}
|
|
}
|
|
|
|
fn variable_is_shorthand(&self, var: Variable) -> bool {
|
|
match self.var_kinds[var] {
|
|
Local(LocalInfo { is_shorthand, .. }) => is_shorthand,
|
|
Param(..) | Upvar(..) => false,
|
|
}
|
|
}
|
|
|
|
fn set_captures(&mut self, hir_id: HirId, cs: Vec<CaptureInfo>) {
|
|
self.capture_info_map.insert(hir_id, Rc::new(cs));
|
|
}
|
|
|
|
fn add_from_pat(&mut self, pat: &hir::Pat<'tcx>) {
|
|
// 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| {
|
|
self.add_live_node_for_node(hir_id, VarDefNode(ident.span));
|
|
self.add_variable(Local(LocalInfo {
|
|
id: hir_id,
|
|
name: ident.name,
|
|
is_shorthand: shorthand_field_ids.contains(&hir_id),
|
|
}));
|
|
});
|
|
}
|
|
}
|
|
|
|
impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
|
|
type Map = Map<'tcx>;
|
|
|
|
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
|
|
NestedVisitorMap::OnlyBodies(self.tcx.hir())
|
|
}
|
|
|
|
fn visit_body(&mut self, body: &'tcx hir::Body<'tcx>) {
|
|
debug!("visit_body {:?}", body.id());
|
|
|
|
// swap in a new set of IR maps for this body
|
|
let mut maps = IrMaps::new(self.tcx);
|
|
let hir_id = maps.tcx.hir().body_owner(body.id());
|
|
let local_def_id = maps.tcx.hir().local_def_id(hir_id);
|
|
let def_id = local_def_id.to_def_id();
|
|
|
|
// Don't run unused pass for #[derive()]
|
|
if let Some(parent) = self.tcx.parent(def_id) {
|
|
if let DefKind::Impl = self.tcx.def_kind(parent.expect_local()) {
|
|
if self.tcx.has_attr(parent, sym::automatically_derived) {
|
|
return;
|
|
}
|
|
}
|
|
}
|
|
|
|
if let Some(captures) = maps.tcx.typeck(local_def_id).closure_captures.get(&def_id) {
|
|
for &var_hir_id in captures.keys() {
|
|
let var_name = maps.tcx.hir().name(var_hir_id);
|
|
maps.add_variable(Upvar(var_hir_id, var_name));
|
|
}
|
|
}
|
|
|
|
// gather up the various local variables, significant expressions,
|
|
// and so forth:
|
|
intravisit::walk_body(&mut maps, body);
|
|
|
|
// compute liveness
|
|
let mut lsets = Liveness::new(&mut maps, local_def_id);
|
|
let entry_ln = lsets.compute(&body, hir_id);
|
|
lsets.log_liveness(entry_ln, body.id().hir_id);
|
|
|
|
// check for various error conditions
|
|
lsets.visit_body(body);
|
|
lsets.warn_about_unused_upvars(entry_ln);
|
|
lsets.warn_about_unused_args(body, entry_ln);
|
|
}
|
|
|
|
fn visit_local(&mut self, local: &'tcx hir::Local<'tcx>) {
|
|
self.add_from_pat(&local.pat);
|
|
intravisit::walk_local(self, local);
|
|
}
|
|
|
|
fn visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>) {
|
|
self.add_from_pat(&arm.pat);
|
|
if let Some(hir::Guard::IfLet(ref pat, _)) = arm.guard {
|
|
self.add_from_pat(pat);
|
|
}
|
|
intravisit::walk_arm(self, arm);
|
|
}
|
|
|
|
fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
|
|
let is_shorthand = matches!(param.pat.kind, rustc_hir::PatKind::Struct(..));
|
|
param.pat.each_binding(|_bm, hir_id, _x, ident| {
|
|
let var = if is_shorthand {
|
|
Local(LocalInfo { id: hir_id, name: ident.name, is_shorthand: true })
|
|
} else {
|
|
Param(hir_id, ident.name)
|
|
};
|
|
self.add_variable(var);
|
|
});
|
|
intravisit::walk_param(self, param);
|
|
}
|
|
|
|
fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
|
|
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 {
|
|
self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span));
|
|
}
|
|
intravisit::walk_expr(self, expr);
|
|
}
|
|
hir::ExprKind::Closure(..) => {
|
|
// Interesting control flow (for loops can contain labeled
|
|
// breaks or continues)
|
|
self.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 = self.tcx.hir().local_def_id(expr.hir_id);
|
|
if let Some(captures) = self
|
|
.tcx
|
|
.typeck(closure_def_id)
|
|
.closure_captures
|
|
.get(&closure_def_id.to_def_id())
|
|
{
|
|
// If closure captures is Some, upvars_mentioned must also be Some
|
|
let upvars = self.tcx.upvars_mentioned(closure_def_id).unwrap();
|
|
call_caps.extend(captures.keys().map(|var_id| {
|
|
let upvar = upvars[var_id];
|
|
let upvar_ln = self.add_live_node(UpvarNode(upvar.span));
|
|
CaptureInfo { ln: upvar_ln, var_hid: *var_id }
|
|
}));
|
|
}
|
|
self.set_captures(expr.hir_id, call_caps);
|
|
intravisit::walk_expr(self, expr);
|
|
}
|
|
|
|
// live nodes required for interesting control flow:
|
|
hir::ExprKind::If(..) | hir::ExprKind::Match(..) | hir::ExprKind::Loop(..) => {
|
|
self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span));
|
|
intravisit::walk_expr(self, expr);
|
|
}
|
|
hir::ExprKind::Binary(op, ..) if op.node.is_lazy() => {
|
|
self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span));
|
|
intravisit::walk_expr(self, 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::ConstBlock(..)
|
|
| hir::ExprKind::Ret(..)
|
|
| hir::ExprKind::Block(..)
|
|
| hir::ExprKind::Assign(..)
|
|
| hir::ExprKind::AssignOp(..)
|
|
| hir::ExprKind::Struct(..)
|
|
| hir::ExprKind::Repeat(..)
|
|
| hir::ExprKind::InlineAsm(..)
|
|
| hir::ExprKind::LlvmInlineAsm(..)
|
|
| hir::ExprKind::Box(..)
|
|
| hir::ExprKind::Yield(..)
|
|
| hir::ExprKind::Type(..)
|
|
| hir::ExprKind::Err
|
|
| hir::ExprKind::Path(hir::QPath::TypeRelative(..))
|
|
| hir::ExprKind::Path(hir::QPath::LangItem(..)) => {
|
|
intravisit::walk_expr(self, 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.
|
|
|
|
const ACC_READ: u32 = 1;
|
|
const ACC_WRITE: u32 = 2;
|
|
const ACC_USE: u32 = 4;
|
|
|
|
struct Liveness<'a, 'tcx> {
|
|
ir: &'a mut IrMaps<'tcx>,
|
|
body_owner: LocalDefId,
|
|
typeck_results: &'a ty::TypeckResults<'tcx>,
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
upvars: Option<&'tcx FxIndexMap<hir::HirId, hir::Upvar>>,
|
|
closure_captures: Option<&'tcx FxIndexMap<hir::HirId, ty::UpvarId>>,
|
|
successors: IndexVec<LiveNode, Option<LiveNode>>,
|
|
rwu_table: rwu_table::RWUTable,
|
|
|
|
/// A live node representing a point of execution before closure entry &
|
|
/// after closure exit. Used to calculate liveness of captured variables
|
|
/// through calls to the same closure. Used for Fn & FnMut closures only.
|
|
closure_ln: LiveNode,
|
|
/// A live node representing every 'exit' from the function, whether it be
|
|
/// by explicit return, panic, or other means.
|
|
exit_ln: LiveNode,
|
|
|
|
// 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_owner: LocalDefId) -> Liveness<'a, 'tcx> {
|
|
let typeck_results = ir.tcx.typeck(body_owner);
|
|
let param_env = ir.tcx.param_env(body_owner);
|
|
let upvars = ir.tcx.upvars_mentioned(body_owner);
|
|
let closure_captures = typeck_results.closure_captures.get(&body_owner.to_def_id());
|
|
|
|
let closure_ln = ir.add_live_node(ClosureNode);
|
|
let exit_ln = ir.add_live_node(ExitNode);
|
|
|
|
let num_live_nodes = ir.lnks.len();
|
|
let num_vars = ir.var_kinds.len();
|
|
|
|
Liveness {
|
|
ir,
|
|
body_owner,
|
|
typeck_results,
|
|
param_env,
|
|
upvars,
|
|
closure_captures,
|
|
successors: IndexVec::from_elem_n(None, num_live_nodes),
|
|
rwu_table: rwu_table::RWUTable::new(num_live_nodes, num_vars),
|
|
closure_ln,
|
|
exit_ln,
|
|
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 live_on_entry(&self, ln: LiveNode, var: Variable) -> bool {
|
|
self.rwu_table.get_reader(ln, var)
|
|
}
|
|
|
|
// Is this variable live on entry to any of its successor nodes?
|
|
fn live_on_exit(&self, ln: LiveNode, var: Variable) -> bool {
|
|
let successor = self.successors[ln].unwrap();
|
|
self.live_on_entry(successor, var)
|
|
}
|
|
|
|
fn used_on_entry(&self, ln: LiveNode, var: Variable) -> bool {
|
|
self.rwu_table.get_used(ln, var)
|
|
}
|
|
|
|
fn assigned_on_entry(&self, ln: LiveNode, var: Variable) -> bool {
|
|
self.rwu_table.get_writer(ln, var)
|
|
}
|
|
|
|
fn assigned_on_exit(&self, ln: LiveNode, var: Variable) -> bool {
|
|
let successor = self.successors[ln].unwrap();
|
|
self.assigned_on_entry(successor, var)
|
|
}
|
|
|
|
fn write_vars<F>(&self, wr: &mut dyn Write, mut test: F) -> io::Result<()>
|
|
where
|
|
F: FnMut(Variable) -> bool,
|
|
{
|
|
for var_idx in 0..self.ir.var_kinds.len() {
|
|
let var = Variable::from(var_idx);
|
|
if test(var) {
|
|
write!(wr, " {:?}", var)?;
|
|
}
|
|
}
|
|
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, "[{:?} of kind {:?} reads", ln, self.ir.lnks[ln]);
|
|
self.write_vars(wr, |var| self.rwu_table.get_reader(ln, var));
|
|
write!(wr, " writes");
|
|
self.write_vars(wr, |var| self.rwu_table.get_writer(ln, var));
|
|
write!(wr, " uses");
|
|
self.write_vars(wr, |var| self.rwu_table.get_used(ln, var));
|
|
|
|
write!(wr, " precedes {:?}]", self.successors[ln]);
|
|
}
|
|
String::from_utf8(wr).unwrap()
|
|
}
|
|
|
|
fn log_liveness(&self, entry_ln: LiveNode, hir_id: hir::HirId) {
|
|
// hack to skip the loop unless debug! is enabled:
|
|
debug!(
|
|
"^^ liveness computation results for body {} (entry={:?})",
|
|
{
|
|
for ln_idx in 0..self.ir.lnks.len() {
|
|
debug!("{:?}", self.ln_str(LiveNode::from(ln_idx)));
|
|
}
|
|
hir_id
|
|
},
|
|
entry_ln
|
|
);
|
|
}
|
|
|
|
fn init_empty(&mut self, ln: LiveNode, succ_ln: LiveNode) {
|
|
self.successors[ln] = Some(succ_ln);
|
|
|
|
// It is not necessary to initialize the RWUs here because they are all
|
|
// empty when 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] = Some(succ_ln);
|
|
self.rwu_table.copy(ln, succ_ln);
|
|
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) -> bool {
|
|
if ln == succ_ln {
|
|
return false;
|
|
}
|
|
|
|
let changed = self.rwu_table.union(ln, succ_ln);
|
|
debug!("merge_from_succ(ln={:?}, succ={}, changed={})", ln, self.ln_str(succ_ln), changed);
|
|
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 used = self.rwu_table.get_used(writer, var);
|
|
self.rwu_table.set(writer, var, rwu_table::RWU { reader: false, writer: false, used });
|
|
debug!("{:?} defines {:?}: {}", writer, var, 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 mut rwu = self.rwu_table.get(ln, var);
|
|
|
|
if (acc & ACC_WRITE) != 0 {
|
|
rwu.reader = false;
|
|
rwu.writer = true;
|
|
}
|
|
|
|
// Important: if we both read/write, must do read second
|
|
// or else the write will override.
|
|
if (acc & ACC_READ) != 0 {
|
|
rwu.reader = true;
|
|
}
|
|
|
|
if (acc & ACC_USE) != 0 {
|
|
rwu.used = true;
|
|
}
|
|
|
|
self.rwu_table.set(ln, var, rwu);
|
|
}
|
|
|
|
fn compute(&mut self, body: &hir::Body<'_>, hir_id: HirId) -> LiveNode {
|
|
debug!("compute: for body {:?}", body.id().hir_id);
|
|
|
|
// # Liveness of captured variables
|
|
//
|
|
// When computing the liveness for captured variables we take into
|
|
// account how variable is captured (ByRef vs ByValue) and what is the
|
|
// closure kind (Generator / FnOnce vs Fn / FnMut).
|
|
//
|
|
// Variables captured by reference are assumed to be used on the exit
|
|
// from the closure.
|
|
//
|
|
// In FnOnce closures, variables captured by value are known to be dead
|
|
// on exit since it is impossible to call the closure again.
|
|
//
|
|
// In Fn / FnMut closures, variables captured by value are live on exit
|
|
// if they are live on the entry to the closure, since only the closure
|
|
// itself can access them on subsequent calls.
|
|
|
|
if let Some(closure_captures) = self.closure_captures {
|
|
// Mark upvars captured by reference as used after closure exits.
|
|
// Since closure_captures is Some, upvars must exists too.
|
|
let upvars = self.upvars.unwrap();
|
|
for (&var_hir_id, upvar_id) in closure_captures {
|
|
let upvar = upvars[&var_hir_id];
|
|
match self.typeck_results.upvar_capture(*upvar_id) {
|
|
ty::UpvarCapture::ByRef(_) => {
|
|
let var = self.variable(var_hir_id, upvar.span);
|
|
self.acc(self.exit_ln, var, ACC_READ | ACC_USE);
|
|
}
|
|
ty::UpvarCapture::ByValue(_) => {}
|
|
}
|
|
}
|
|
}
|
|
|
|
let succ = self.propagate_through_expr(&body.value, self.exit_ln);
|
|
|
|
if self.closure_captures.is_none() {
|
|
// Either not a closure, or closure without any captured variables.
|
|
// No need to determine liveness of captured variables, since there
|
|
// are none.
|
|
return succ;
|
|
}
|
|
|
|
let ty = self.typeck_results.node_type(hir_id);
|
|
match ty.kind() {
|
|
ty::Closure(_def_id, substs) => match substs.as_closure().kind() {
|
|
ty::ClosureKind::Fn => {}
|
|
ty::ClosureKind::FnMut => {}
|
|
ty::ClosureKind::FnOnce => return succ,
|
|
},
|
|
ty::Generator(..) => return succ,
|
|
_ => {
|
|
span_bug!(
|
|
body.value.span,
|
|
"{} has upvars so it should have a closure type: {:?}",
|
|
hir_id,
|
|
ty
|
|
);
|
|
}
|
|
};
|
|
|
|
// Propagate through calls to the closure.
|
|
loop {
|
|
self.init_from_succ(self.closure_ln, succ);
|
|
for param in body.params {
|
|
param.pat.each_binding(|_bm, hir_id, _x, ident| {
|
|
let var = self.variable(hir_id, ident.span);
|
|
self.define(self.closure_ln, var);
|
|
})
|
|
}
|
|
|
|
if !self.merge_from_succ(self.exit_ln, self.closure_ln) {
|
|
break;
|
|
}
|
|
assert_eq!(succ, self.propagate_through_expr(&body.value, self.exit_ln));
|
|
}
|
|
|
|
succ
|
|
}
|
|
|
|
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_deref(), 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_deref(), 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: {:?}", expr);
|
|
|
|
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", expr);
|
|
|
|
// 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::If(ref cond, ref then, ref else_opt) => {
|
|
//
|
|
// (cond)
|
|
// |
|
|
// v
|
|
// (expr)
|
|
// / \
|
|
// | |
|
|
// v v
|
|
// (then)(els)
|
|
// | |
|
|
// v v
|
|
// ( succ )
|
|
//
|
|
let else_ln =
|
|
self.propagate_through_opt_expr(else_opt.as_ref().map(|e| &**e), succ);
|
|
let then_ln = self.propagate_through_expr(&then, succ);
|
|
let ln = self.live_node(expr.hir_id, expr.span);
|
|
self.init_from_succ(ln, else_ln);
|
|
self.merge_from_succ(ln, then_ln);
|
|
self.propagate_through_expr(&cond, ln)
|
|
}
|
|
|
|
hir::ExprKind::Match(ref e, 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);
|
|
for arm in arms {
|
|
let body_succ = self.propagate_through_expr(&arm.body, succ);
|
|
|
|
let guard_succ = arm.guard.as_ref().map_or(body_succ, |g| match g {
|
|
hir::Guard::If(e) => self.propagate_through_expr(e, body_succ),
|
|
hir::Guard::IfLet(pat, e) => {
|
|
let let_bind = self.define_bindings_in_pat(pat, body_succ);
|
|
self.propagate_through_expr(e, let_bind)
|
|
}
|
|
});
|
|
let arm_succ = self.define_bindings_in_pat(&arm.pat, guard_succ);
|
|
self.merge_from_succ(ln, arm_succ);
|
|
}
|
|
self.propagate_through_expr(&e, ln)
|
|
}
|
|
|
|
hir::ExprKind::Ret(ref o_e) => {
|
|
// Ignore succ and subst exit_ln.
|
|
self.propagate_through_opt_expr(o_e.as_ref().map(|e| &**e), self.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.typeck_results.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.parent_module(expr.hir_id).to_def_id();
|
|
let succ = if self.ir.tcx.is_ty_uninhabited_from(
|
|
m,
|
|
self.typeck_results.expr_ty(expr),
|
|
self.param_env,
|
|
) {
|
|
self.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.parent_module(expr.hir_id).to_def_id();
|
|
let succ = if self.ir.tcx.is_ty_uninhabited_from(
|
|
m,
|
|
self.typeck_results.expr_ty(expr),
|
|
self.param_env,
|
|
) {
|
|
self.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);
|
|
|
|
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 asm) => {
|
|
// Handle non-returning asm
|
|
let mut succ = if asm.options.contains(InlineAsmOptions::NORETURN) {
|
|
self.exit_ln
|
|
} else {
|
|
succ
|
|
};
|
|
|
|
// Do a first pass for writing outputs only
|
|
for (op, _op_sp) in asm.operands.iter().rev() {
|
|
match op {
|
|
hir::InlineAsmOperand::In { .. }
|
|
| hir::InlineAsmOperand::Const { .. }
|
|
| hir::InlineAsmOperand::Sym { .. } => {}
|
|
hir::InlineAsmOperand::Out { expr, .. } => {
|
|
if let Some(expr) = expr {
|
|
succ = self.write_place(expr, succ, ACC_WRITE);
|
|
}
|
|
}
|
|
hir::InlineAsmOperand::InOut { expr, .. } => {
|
|
succ = self.write_place(expr, succ, ACC_READ | ACC_WRITE | ACC_USE);
|
|
}
|
|
hir::InlineAsmOperand::SplitInOut { out_expr, .. } => {
|
|
if let Some(expr) = out_expr {
|
|
succ = self.write_place(expr, succ, ACC_WRITE);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// Then do a second pass for inputs
|
|
let mut succ = succ;
|
|
for (op, _op_sp) in asm.operands.iter().rev() {
|
|
match op {
|
|
hir::InlineAsmOperand::In { expr, .. }
|
|
| hir::InlineAsmOperand::Const { expr, .. }
|
|
| hir::InlineAsmOperand::Sym { expr, .. } => {
|
|
succ = self.propagate_through_expr(expr, succ)
|
|
}
|
|
hir::InlineAsmOperand::Out { expr, .. } => {
|
|
if let Some(expr) = expr {
|
|
succ = self.propagate_through_place_components(expr, succ);
|
|
}
|
|
}
|
|
hir::InlineAsmOperand::InOut { expr, .. } => {
|
|
succ = self.propagate_through_place_components(expr, succ);
|
|
}
|
|
hir::InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
|
|
if let Some(expr) = out_expr {
|
|
succ = self.propagate_through_place_components(expr, succ);
|
|
}
|
|
succ = self.propagate_through_expr(in_expr, succ);
|
|
}
|
|
}
|
|
}
|
|
succ
|
|
}
|
|
|
|
hir::ExprKind::LlvmInlineAsm(ref asm) => {
|
|
let ia = &asm.inner;
|
|
let outputs = asm.outputs_exprs;
|
|
let inputs = asm.inputs_exprs;
|
|
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::ConstBlock(..)
|
|
| hir::ExprKind::Err
|
|
| hir::ExprKind::Path(hir::QPath::TypeRelative(..))
|
|
| hir::ExprKind::Path(hir::QPath::LangItem(..)) => 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 in_upvars = self.upvars.map_or(false, |u| u.contains_key(&hid));
|
|
let in_captures = self.closure_captures.map_or(false, |c| c.contains_key(&hid));
|
|
|
|
match (in_upvars, in_captures) {
|
|
(false, _) | (true, true) => self.access_var(hir_id, hid, succ, acc, path.span),
|
|
(true, false) => {
|
|
// This case is possible when with RFC-2229, a wild pattern
|
|
// is used within a closure.
|
|
// eg: `let _ = x`. The closure doesn't capture x here,
|
|
// even though it's mentioned in the closure.
|
|
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 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, body);
|
|
|
|
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) {
|
|
assert_eq!(body_ln, self.propagate_through_block(body, ln));
|
|
}
|
|
|
|
ln
|
|
}
|
|
}
|
|
|
|
// _______________________________________________________________________
|
|
// Checking for error conditions
|
|
|
|
impl<'a, 'tcx> Visitor<'tcx> for Liveness<'a, 'tcx> {
|
|
type Map = intravisit::ErasedMap<'tcx>;
|
|
|
|
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
|
|
NestedVisitorMap::None
|
|
}
|
|
|
|
fn visit_local(&mut self, local: &'tcx hir::Local<'tcx>) {
|
|
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<'tcx>) {
|
|
check_expr(self, ex);
|
|
}
|
|
|
|
fn visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>) {
|
|
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<'tcx>) {
|
|
match expr.kind {
|
|
hir::ExprKind::Assign(ref l, ..) => {
|
|
this.check_place(&l);
|
|
}
|
|
|
|
hir::ExprKind::AssignOp(_, ref l, _) => {
|
|
if !this.typeck_results.is_method_call(expr) {
|
|
this.check_place(&l);
|
|
}
|
|
}
|
|
|
|
hir::ExprKind::InlineAsm(ref asm) => {
|
|
for (op, _op_sp) in asm.operands {
|
|
match op {
|
|
hir::InlineAsmOperand::Out { expr, .. } => {
|
|
if let Some(expr) = expr {
|
|
this.check_place(expr);
|
|
}
|
|
}
|
|
hir::InlineAsmOperand::InOut { expr, .. } => {
|
|
this.check_place(expr);
|
|
}
|
|
hir::InlineAsmOperand::SplitInOut { out_expr, .. } => {
|
|
if let Some(out_expr) = out_expr {
|
|
this.check_place(out_expr);
|
|
}
|
|
}
|
|
_ => {}
|
|
}
|
|
}
|
|
}
|
|
|
|
hir::ExprKind::LlvmInlineAsm(ref asm) => {
|
|
for input in asm.inputs_exprs {
|
|
this.visit_expr(input);
|
|
}
|
|
|
|
// Output operands must be places
|
|
for (o, output) in asm.inner.outputs.iter().zip(asm.outputs_exprs) {
|
|
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::If(..)
|
|
| hir::ExprKind::DropTemps(..)
|
|
| hir::ExprKind::Unary(..)
|
|
| hir::ExprKind::Ret(..)
|
|
| hir::ExprKind::Break(..)
|
|
| hir::ExprKind::Continue(..)
|
|
| hir::ExprKind::Lit(_)
|
|
| hir::ExprKind::ConstBlock(..)
|
|
| 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<'tcx>) {
|
|
match expr.kind {
|
|
hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => {
|
|
if let Res::Local(var_hid) = path.res {
|
|
// 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 == kw::Empty {
|
|
return None;
|
|
}
|
|
let name: &str = &name.as_str();
|
|
if name.as_bytes()[0] == b'_' {
|
|
return None;
|
|
}
|
|
Some(name.to_owned())
|
|
}
|
|
|
|
fn warn_about_unused_upvars(&self, entry_ln: LiveNode) {
|
|
let closure_captures = match self.closure_captures {
|
|
None => return,
|
|
Some(closure_captures) => closure_captures,
|
|
};
|
|
|
|
// If closure_captures is Some(), upvars must be Some() too.
|
|
let upvars = self.upvars.unwrap();
|
|
for &var_hir_id in closure_captures.keys() {
|
|
let upvar = upvars[&var_hir_id];
|
|
let var = self.variable(var_hir_id, upvar.span);
|
|
let upvar_id = ty::UpvarId {
|
|
var_path: ty::UpvarPath { hir_id: var_hir_id },
|
|
closure_expr_id: self.body_owner,
|
|
};
|
|
match self.typeck_results.upvar_capture(upvar_id) {
|
|
ty::UpvarCapture::ByValue(_) => {}
|
|
ty::UpvarCapture::ByRef(..) => continue,
|
|
};
|
|
if self.used_on_entry(entry_ln, var) {
|
|
if !self.live_on_entry(entry_ln, var) {
|
|
if let Some(name) = self.should_warn(var) {
|
|
self.ir.tcx.struct_span_lint_hir(
|
|
lint::builtin::UNUSED_ASSIGNMENTS,
|
|
var_hir_id,
|
|
vec![upvar.span],
|
|
|lint| {
|
|
lint.build(&format!("value captured by `{}` is never read", name))
|
|
.help("did you mean to capture by reference instead?")
|
|
.emit();
|
|
},
|
|
);
|
|
}
|
|
}
|
|
} else {
|
|
if let Some(name) = self.should_warn(var) {
|
|
self.ir.tcx.struct_span_lint_hir(
|
|
lint::builtin::UNUSED_VARIABLES,
|
|
var_hir_id,
|
|
vec![upvar.span],
|
|
|lint| {
|
|
lint.build(&format!("unused variable: `{}`", name))
|
|
.help("did you mean to capture by reference instead?")
|
|
.emit();
|
|
},
|
|
);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
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) {
|
|
self.report_unsed_assign(hir_id, spans, var, |name| {
|
|
format!("value passed to `{}` is never read", name)
|
|
});
|
|
}
|
|
});
|
|
}
|
|
}
|
|
|
|
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 ids and 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<Symbol, (LiveNode, Variable, Vec<(HirId, 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);
|
|
let id_and_sp = (hir_id, pat_sp);
|
|
vars.entry(self.ir.variable_name(var))
|
|
.and_modify(|(.., hir_ids_and_spans)| hir_ids_and_spans.push(id_and_sp))
|
|
.or_insert_with(|| (ln, var, vec![id_and_sp]));
|
|
});
|
|
|
|
for (_, (ln, var, hir_ids_and_spans)) in vars {
|
|
if self.used_on_entry(ln, var) {
|
|
let id = hir_ids_and_spans[0].0;
|
|
let spans = hir_ids_and_spans.into_iter().map(|(_, sp)| sp).collect();
|
|
on_used_on_entry(spans, id, ln, var);
|
|
} else {
|
|
self.report_unused(hir_ids_and_spans, ln, var);
|
|
}
|
|
}
|
|
}
|
|
|
|
fn report_unused(&self, hir_ids_and_spans: Vec<(HirId, Span)>, ln: LiveNode, var: Variable) {
|
|
let first_hir_id = hir_ids_and_spans[0].0;
|
|
|
|
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.exit_ln { false } else { self.assigned_on_exit(ln, var) };
|
|
|
|
if is_assigned {
|
|
self.ir.tcx.struct_span_lint_hir(
|
|
lint::builtin::UNUSED_VARIABLES,
|
|
first_hir_id,
|
|
hir_ids_and_spans.into_iter().map(|(_, sp)| sp).collect::<Vec<_>>(),
|
|
|lint| {
|
|
lint.build(&format!("variable `{}` is assigned to, but never used", name))
|
|
.note(&format!("consider using `_{}` instead", name))
|
|
.emit();
|
|
},
|
|
)
|
|
} else {
|
|
self.ir.tcx.struct_span_lint_hir(
|
|
lint::builtin::UNUSED_VARIABLES,
|
|
first_hir_id,
|
|
hir_ids_and_spans.iter().map(|(_, sp)| *sp).collect::<Vec<_>>(),
|
|
|lint| {
|
|
let mut err = lint.build(&format!("unused variable: `{}`", name));
|
|
|
|
let (shorthands, non_shorthands): (Vec<_>, Vec<_>) =
|
|
hir_ids_and_spans.into_iter().partition(|(hir_id, span)| {
|
|
let var = self.variable(*hir_id, *span);
|
|
self.ir.variable_is_shorthand(var)
|
|
});
|
|
|
|
let mut shorthands = shorthands
|
|
.into_iter()
|
|
.map(|(_, span)| (span, format!("{}: _", name)))
|
|
.collect::<Vec<_>>();
|
|
|
|
// If we have both shorthand and non-shorthand, prefer the "try ignoring
|
|
// the field" message, and suggest `_` for the non-shorthands. If we only
|
|
// have non-shorthand, then prefix with an underscore instead.
|
|
if !shorthands.is_empty() {
|
|
shorthands.extend(
|
|
non_shorthands
|
|
.into_iter()
|
|
.map(|(_, span)| (span, "_".to_string()))
|
|
.collect::<Vec<_>>(),
|
|
);
|
|
|
|
err.multipart_suggestion(
|
|
"try ignoring the field",
|
|
shorthands,
|
|
Applicability::MachineApplicable,
|
|
);
|
|
} else {
|
|
err.multipart_suggestion(
|
|
"if this is intentional, prefix it with an underscore",
|
|
non_shorthands
|
|
.into_iter()
|
|
.map(|(_, span)| (span, format!("_{}", name)))
|
|
.collect::<Vec<_>>(),
|
|
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) {
|
|
self.report_unsed_assign(hir_id, spans, var, |name| {
|
|
format!("value assigned to `{}` is never read", name)
|
|
});
|
|
}
|
|
}
|
|
|
|
fn report_unsed_assign(
|
|
&self,
|
|
hir_id: HirId,
|
|
spans: Vec<Span>,
|
|
var: Variable,
|
|
message: impl Fn(&str) -> String,
|
|
) {
|
|
if let Some(name) = self.should_warn(var) {
|
|
self.ir.tcx.struct_span_lint_hir(
|
|
lint::builtin::UNUSED_ASSIGNMENTS,
|
|
hir_id,
|
|
spans,
|
|
|lint| {
|
|
lint.build(&message(&name))
|
|
.help("maybe it is overwritten before being read?")
|
|
.emit();
|
|
},
|
|
)
|
|
}
|
|
}
|
|
}
|