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+//! 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, Visitor};
+use rustc_hir::{Expr, HirId, HirIdMap, HirIdSet};
+use rustc_index::vec::IndexVec;
+use rustc_middle::hir::nested_filter;
+use rustc_middle::ty::query::Providers;
+use rustc_middle::ty::{self, DefIdTree, RootVariableMinCaptureList, Ty, 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, HirId),
+ VarDefNode(Span, HirId),
+ 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_diagnostic_string(s)),
+ ExprNode(s, _) => format!("Expr node [{}]", sm.span_to_diagnostic_string(s)),
+ VarDefNode(s, _) => format!("Var def node [{}]", sm.span_to_diagnostic_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));
+}
+
+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<'tcx> 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 collect_shorthand_field_ids(&self, pat: &hir::Pat<'tcx>) -> HirIdSet {
+ // 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 (short, not_short): (Vec<_>, _) =
+ fields.iter().partition(|f| f.is_shorthand);
+ shorthand_field_ids.extend(short.iter().map(|f| f.pat.hir_id));
+ pats.extend(not_short.iter().map(|f| f.pat));
+ }
+ 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());
+ }
+ _ => {}
+ }
+ }
+
+ shorthand_field_ids
+ }
+
+ fn add_from_pat(&mut self, pat: &hir::Pat<'tcx>) {
+ let shorthand_field_ids = self.collect_shorthand_field_ids(pat);
+
+ pat.each_binding(|_, hir_id, _, ident| {
+ self.add_live_node_for_node(hir_id, VarDefNode(ident.span, hir_id));
+ 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 NestedFilter = nested_filter::OnlyBodies;
+
+ fn nested_visit_map(&mut self) -> Self::Map {
+ 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()]
+ let parent = self.tcx.local_parent(local_def_id);
+ if let DefKind::Impl = self.tcx.def_kind(parent)
+ && self.tcx.has_attr(parent.to_def_id(), sym::automatically_derived)
+ {
+ return;
+ }
+
+ // Don't run unused pass for #[naked]
+ if self.tcx.has_attr(def_id, sym::naked) {
+ return;
+ }
+
+ if let Some(upvars) = maps.tcx.upvars_mentioned(def_id) {
+ for &var_hir_id in upvars.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);
+ if local.els.is_some() {
+ self.add_live_node_for_node(local.hir_id, ExprNode(local.span, local.hir_id));
+ }
+ 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 let_expr)) = arm.guard {
+ self.add_from_pat(let_expr.pat);
+ }
+ intravisit::walk_arm(self, arm);
+ }
+
+ fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
+ let shorthand_field_ids = self.collect_shorthand_field_ids(param.pat);
+ param.pat.each_binding(|_bm, hir_id, _x, ident| {
+ let var = match param.pat.kind {
+ rustc_hir::PatKind::Struct(..) => Local(LocalInfo {
+ id: hir_id,
+ name: ident.name,
+ is_shorthand: shorthand_field_ids.contains(&hir_id),
+ }),
+ _ => 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, expr.hir_id));
+ }
+ 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, expr.hir_id));
+
+ // Make a live_node for each mentioned 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(upvars) = self.tcx.upvars_mentioned(closure_def_id) {
+ call_caps.extend(upvars.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);
+ }
+
+ hir::ExprKind::Let(let_expr) => {
+ self.add_from_pat(let_expr.pat);
+ intravisit::walk_expr(self, expr);
+ }
+
+ // live nodes required for interesting control flow:
+ hir::ExprKind::If(..)
+ | hir::ExprKind::Match(..)
+ | hir::ExprKind::Loop(..)
+ | hir::ExprKind::Yield(..) => {
+ self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span, expr.hir_id));
+ 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, expr.hir_id));
+ 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::Box(..)
+ | 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>,
+ typeck_results: &'a ty::TypeckResults<'tcx>,
+ param_env: ty::ParamEnv<'tcx>,
+ closure_min_captures: Option<&'tcx RootVariableMinCaptureList<'tcx>>,
+ 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 closure_min_captures = typeck_results.closure_min_captures.get(&body_owner);
+ 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,
+ typeck_results,
+ param_env,
+ closure_min_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_min_captures) = self.closure_min_captures {
+ // Mark upvars captured by reference as used after closure exits.
+ for (&var_hir_id, min_capture_list) in closure_min_captures {
+ for captured_place in min_capture_list {
+ match captured_place.info.capture_kind {
+ ty::UpvarCapture::ByRef(_) => {
+ let var = self.variable(
+ var_hir_id,
+ captured_place.get_capture_kind_span(self.ir.tcx),
+ );
+ 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_min_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, 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.
+
+ if let Some(els) = local.els {
+ // Eventually, `let pat: ty = init else { els };` is mostly equivalent to
+ // `let (bindings, ...) = match init { pat => (bindings, ...), _ => els };`
+ // except that extended lifetime applies at the `init` location.
+ //
+ // (e)
+ // |
+ // v
+ // (expr)
+ // / \
+ // | |
+ // v v
+ // bindings els
+ // |
+ // v
+ // ( succ )
+ //
+ if let Some(init) = local.init {
+ let else_ln = self.propagate_through_block(els, succ);
+ let ln = self.live_node(local.hir_id, local.span);
+ self.init_from_succ(ln, succ);
+ self.merge_from_succ(ln, else_ln);
+ let succ = self.propagate_through_expr(init, ln);
+ self.define_bindings_in_pat(&local.pat, succ)
+ } else {
+ span_bug!(
+ stmt.span,
+ "variable is uninitialized but an unexpected else branch is found"
+ )
+ }
+ } else {
+ let succ = self.propagate_through_opt_expr(local.init, 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
+ })
+ }
+
+ hir::ExprKind::Let(let_expr) => {
+ let succ = self.propagate_through_expr(let_expr.init, succ);
+ self.define_bindings_in_pat(let_expr.pat, succ)
+ }
+
+ // 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::Yield(ref e, ..) => {
+ let yield_ln = self.live_node(expr.hir_id, expr.span);
+ self.init_from_succ(yield_ln, succ);
+ self.merge_from_succ(yield_ln, self.exit_ln);
+ self.propagate_through_expr(e, yield_ln)
+ }
+
+ 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(let_expr) => {
+ let let_bind = self.define_bindings_in_pat(let_expr.pat, body_succ);
+ self.propagate_through_expr(let_expr.init, 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 succ = self.check_is_ty_uninhabited(expr, succ);
+ let succ = self.propagate_through_exprs(args, succ);
+ self.propagate_through_expr(&f, succ)
+ }
+
+ hir::ExprKind::MethodCall(.., ref args, _) => {
+ let succ = self.check_is_ty_uninhabited(expr, 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::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::SymFn { .. }
+ | hir::InlineAsmOperand::SymStatic { .. } => {}
+ 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, .. } => {
+ 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);
+ }
+ hir::InlineAsmOperand::Const { .. }
+ | hir::InlineAsmOperand::SymFn { .. }
+ | hir::InlineAsmOperand::SymStatic { .. } => {}
+ }
+ }
+ 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) => self.access_var(hir_id, hid, succ, acc, path.span),
+ _ => 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
+ }
+
+ fn check_is_ty_uninhabited(&mut self, expr: &Expr<'_>, succ: LiveNode) -> LiveNode {
+ let ty = self.typeck_results.expr_ty(expr);
+ let m = self.ir.tcx.parent_module(expr.hir_id).to_def_id();
+ if self.ir.tcx.is_ty_uninhabited_from(m, ty, self.param_env) {
+ match self.ir.lnks[succ] {
+ LiveNodeKind::ExprNode(succ_span, succ_id) => {
+ self.warn_about_unreachable(expr.span, ty, succ_span, succ_id, "expression");
+ }
+ LiveNodeKind::VarDefNode(succ_span, succ_id) => {
+ self.warn_about_unreachable(expr.span, ty, succ_span, succ_id, "definition");
+ }
+ _ => {}
+ };
+ self.exit_ln
+ } else {
+ succ
+ }
+ }
+
+ fn warn_about_unreachable(
+ &mut self,
+ orig_span: Span,
+ orig_ty: Ty<'tcx>,
+ expr_span: Span,
+ expr_id: HirId,
+ descr: &str,
+ ) {
+ if !orig_ty.is_never() {
+ // Unreachable code warnings are already emitted during type checking.
+ // However, during type checking, full type information is being
+ // calculated but not yet available, so the check for diverging
+ // expressions due to uninhabited result types is pretty crude and
+ // only checks whether ty.is_never(). Here, we have full type
+ // information available and can issue warnings for less obviously
+ // uninhabited types (e.g. empty enums). The check above is used so
+ // that we do not emit the same warning twice if the uninhabited type
+ // is indeed `!`.
+
+ self.ir.tcx.struct_span_lint_hir(
+ lint::builtin::UNREACHABLE_CODE,
+ expr_id,
+ expr_span,
+ |lint| {
+ let msg = format!("unreachable {}", descr);
+ lint.build(&msg)
+ .span_label(expr_span, &msg)
+ .span_label(orig_span, "any code following this expression is unreachable")
+ .span_note(
+ orig_span,
+ &format!(
+ "this expression has type `{}`, which is uninhabited",
+ orig_ty
+ ),
+ )
+ .emit();
+ },
+ );
+ }
+ }
+}
+
+// _______________________________________________________________________
+// Checking for error conditions
+
+impl<'a, 'tcx> Visitor<'tcx> for Liveness<'a, 'tcx> {
+ 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);
+ intravisit::walk_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::Let(let_expr) => {
+ this.check_unused_vars_in_pat(let_expr.pat, None, |_, _, _, _| {});
+ }
+
+ // 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 => {}
+ }
+}
+
+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 = 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 Some(closure_min_captures) = self.closure_min_captures else {
+ return;
+ };
+
+ // If closure_min_captures is Some(), upvars must be Some() too.
+ for (&var_hir_id, min_capture_list) in closure_min_captures {
+ for captured_place in min_capture_list {
+ match captured_place.info.capture_kind {
+ ty::UpvarCapture::ByValue => {}
+ ty::UpvarCapture::ByRef(..) => continue,
+ };
+ let span = captured_place.get_capture_kind_span(self.ir.tcx);
+ let var = self.variable(var_hir_id, span);
+ 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![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![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_unused_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, 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, ident.span);
+ 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(|(_, _, ident_span)| ident_span).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, 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(|(_, _, ident_span)| ident_span)
+ .collect::<Vec<_>>(),
+ |lint| {
+ lint.build(&format!("variable `{}` is assigned to, but never used", name))
+ .note(&format!("consider using `_{}` instead", name))
+ .emit();
+ },
+ )
+ } else {
+ let (shorthands, non_shorthands): (Vec<_>, Vec<_>) =
+ hir_ids_and_spans.iter().copied().partition(|(hir_id, _, ident_span)| {
+ let var = self.variable(*hir_id, *ident_span);
+ self.ir.variable_is_shorthand(var)
+ });
+
+ // 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() {
+ let shorthands = shorthands
+ .into_iter()
+ .map(|(_, pat_span, _)| (pat_span, format!("{}: _", name)))
+ .chain(
+ non_shorthands
+ .into_iter()
+ .map(|(_, pat_span, _)| (pat_span, "_".to_string())),
+ )
+ .collect::<Vec<_>>();
+
+ self.ir.tcx.struct_span_lint_hir(
+ lint::builtin::UNUSED_VARIABLES,
+ first_hir_id,
+ hir_ids_and_spans
+ .iter()
+ .map(|(_, pat_span, _)| *pat_span)
+ .collect::<Vec<_>>(),
+ |lint| {
+ let mut err = lint.build(&format!("unused variable: `{}`", name));
+ err.multipart_suggestion(
+ "try ignoring the field",
+ shorthands,
+ Applicability::MachineApplicable,
+ );
+ err.emit();
+ },
+ );
+ } else {
+ let non_shorthands = non_shorthands
+ .into_iter()
+ .map(|(_, _, ident_span)| (ident_span, format!("_{}", name)))
+ .collect::<Vec<_>>();
+
+ self.ir.tcx.struct_span_lint_hir(
+ lint::builtin::UNUSED_VARIABLES,
+ first_hir_id,
+ hir_ids_and_spans
+ .iter()
+ .map(|(_, _, ident_span)| *ident_span)
+ .collect::<Vec<_>>(),
+ |lint| {
+ let mut err = lint.build(&format!("unused variable: `{}`", name));
+ err.multipart_suggestion(
+ "if this is intentional, prefix it with an underscore",
+ non_shorthands,
+ 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_unused_assign(hir_id, spans, var, |name| {
+ format!("value assigned to `{}` is never read", name)
+ });
+ }
+ }
+
+ fn report_unused_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();
+ },
+ )
+ }
+ }
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-06-12 13:45:44 +0000