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RFC-2229: Implement Precise Capture Analysis #78801

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4 changes: 4 additions & 0 deletions compiler/rustc_feature/src/active.rs
Original file line number Diff line number Diff line change
Expand Up @@ -616,6 +616,9 @@ declare_features! (
/// Enables `#[cfg(panic = "...")]` config key.
(active, cfg_panic, "1.49.0", Some(77443), None),

/// Allows capturing disjoint fields in a closure/generator (RFC 2229).
(active, capture_disjoint_fields, "1.49.0", Some(53488), None),

// -------------------------------------------------------------------------
// feature-group-end: actual feature gates
// -------------------------------------------------------------------------
Expand All @@ -639,6 +642,7 @@ pub const INCOMPLETE_FEATURES: &[Symbol] = &[
sym::inline_const,
sym::repr128,
sym::unsized_locals,
sym::capture_disjoint_fields,
];

/// Some features are not allowed to be used together at the same time, if
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_feature/src/builtin_attrs.rs
Original file line number Diff line number Diff line change
Expand Up @@ -547,6 +547,7 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
// ==========================================================================

rustc_attr!(TEST, rustc_outlives, Normal, template!(Word)),
rustc_attr!(TEST, rustc_capture_analysis, Normal, template!(Word)),
rustc_attr!(TEST, rustc_variance, Normal, template!(Word)),
rustc_attr!(TEST, rustc_layout, Normal, template!(List: "field1, field2, ...")),
rustc_attr!(TEST, rustc_regions, Normal, template!(Word)),
Expand Down
7 changes: 7 additions & 0 deletions compiler/rustc_middle/src/ty/context.rs
Original file line number Diff line number Diff line change
Expand Up @@ -415,6 +415,10 @@ pub struct TypeckResults<'tcx> {
/// entire variable.
pub closure_captures: ty::UpvarListMap,

/// Tracks the minimum captures required for a closure;
/// see `MinCaptureInformationMap` for more details.
pub closure_min_captures: ty::MinCaptureInformationMap<'tcx>,

/// Stores the type, expression, span and optional scope span of all types
/// that are live across the yield of this generator (if a generator).
pub generator_interior_types: Vec<GeneratorInteriorTypeCause<'tcx>>,
Expand Down Expand Up @@ -442,6 +446,7 @@ impl<'tcx> TypeckResults<'tcx> {
tainted_by_errors: None,
concrete_opaque_types: Default::default(),
closure_captures: Default::default(),
closure_min_captures: Default::default(),
generator_interior_types: Default::default(),
}
}
Expand Down Expand Up @@ -676,6 +681,7 @@ impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for TypeckResults<'tcx> {
tainted_by_errors,
ref concrete_opaque_types,
ref closure_captures,
ref closure_min_captures,
ref generator_interior_types,
} = *self;

Expand Down Expand Up @@ -709,6 +715,7 @@ impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for TypeckResults<'tcx> {
tainted_by_errors.hash_stable(hcx, hasher);
concrete_opaque_types.hash_stable(hcx, hasher);
closure_captures.hash_stable(hcx, hasher);
closure_min_captures.hash_stable(hcx, hasher);
generator_interior_types.hash_stable(hcx, hasher);
})
}
Expand Down
57 changes: 57 additions & 0 deletions compiler/rustc_middle/src/ty/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@ pub use self::IntVarValue::*;
pub use self::Variance::*;

use crate::hir::exports::ExportMap;
use crate::hir::place::Place as HirPlace;
use crate::ich::StableHashingContext;
use crate::middle::cstore::CrateStoreDyn;
use crate::middle::resolve_lifetime::ObjectLifetimeDefault;
Expand Down Expand Up @@ -674,6 +675,12 @@ pub struct UpvarId {
pub closure_expr_id: LocalDefId,
}

impl UpvarId {
pub fn new(var_hir_id: hir::HirId, closure_def_id: LocalDefId) -> UpvarId {
UpvarId { var_path: UpvarPath { hir_id: var_hir_id }, closure_expr_id: closure_def_id }
}
}

#[derive(Clone, PartialEq, Debug, TyEncodable, TyDecodable, Copy, HashStable)]
pub enum BorrowKind {
/// Data must be immutable and is aliasable.
Expand Down Expand Up @@ -756,6 +763,56 @@ pub struct UpvarBorrow<'tcx> {
pub region: ty::Region<'tcx>,
}

/// Given the closure DefId this map provides a map of root variables to minimum
/// set of `CapturedPlace`s that need to be tracked to support all captures of that closure.
pub type MinCaptureInformationMap<'tcx> = FxHashMap<DefId, RootVariableMinCaptureList<'tcx>>;

/// Part of `MinCaptureInformationMap`; Maps a root variable to the list of `CapturedPlace`.
/// Used to track the minimum set of `Place`s that need to be captured to support all
/// Places captured by the closure starting at a given root variable.
///
/// This provides a convenient and quick way of checking if a variable being used within
/// a closure is a capture of a local variable.
pub type RootVariableMinCaptureList<'tcx> = FxIndexMap<hir::HirId, MinCaptureList<'tcx>>;

/// Part of `MinCaptureInformationMap`; List of `CapturePlace`s.
pub type MinCaptureList<'tcx> = Vec<CapturedPlace<'tcx>>;

/// A `Place` and the corresponding `CaptureInfo`.
#[derive(PartialEq, Clone, Debug, TyEncodable, TyDecodable, HashStable)]
pub struct CapturedPlace<'tcx> {
pub place: HirPlace<'tcx>,
pub info: CaptureInfo<'tcx>,
}

/// Part of `MinCaptureInformationMap`; describes the capture kind (&, &mut, move)
/// for a particular capture as well as identifying the part of the source code
/// that triggered this capture to occur.
#[derive(PartialEq, Clone, Debug, Copy, TyEncodable, TyDecodable, HashStable)]
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pub struct CaptureInfo<'tcx> {
/// Expr Id pointing to use that resulted in selecting the current capture kind
///
/// If the user doesn't enable feature `capture_disjoint_fields` (RFC 2229) then, it is
/// possible that we don't see the use of a particular place resulting in expr_id being
/// None. In such case we fallback on uvpars_mentioned for span.
///
/// Eg:
/// ```rust
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/// let x = ...;
///
/// let c = || {
/// let _ = x
/// }
/// ```
///
/// In this example, if `capture_disjoint_fields` is **not** set, then x will be captured,
/// but we won't see it being used during capture analysis, since it's essentially a discard.
pub expr_id: Option<hir::HirId>,

/// Capture mode that was selected
pub capture_kind: UpvarCapture<'tcx>,
}

pub type UpvarListMap = FxHashMap<DefId, FxIndexMap<hir::HirId, UpvarId>>;
pub type UpvarCaptureMap<'tcx> = FxHashMap<UpvarId, UpvarCapture<'tcx>>;

Expand Down
27 changes: 14 additions & 13 deletions compiler/rustc_mir/src/borrow_check/diagnostics/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -383,16 +383,14 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
self.describe_field_from_ty(&ty, field, variant_index)
}
ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
// `tcx.upvars_mentioned(def_id)` returns an `Option`, which is `None` in case
// the closure comes from another crate. But in that case we wouldn't
// be borrowck'ing it, so we can just unwrap:
let (&var_id, _) = self
.infcx
.tcx
.upvars_mentioned(def_id)
.unwrap()
.get_index(field.index())
.unwrap();
// We won't be borrowck'ing here if the closure came from another crate,
// so it's safe to call `expect_local`.
//
// We know the field exists so it's safe to call operator[] and `unwrap` here.
let (&var_id, _) =
self.infcx.tcx.typeck(def_id.expect_local()).closure_captures[&def_id]
.get_index(field.index())
.unwrap();

self.infcx.tcx.hir().name(var_id).to_string()
}
Expand Down Expand Up @@ -967,9 +965,12 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
let expr = &self.infcx.tcx.hir().expect_expr(hir_id).kind;
debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
if let hir::ExprKind::Closure(.., body_id, args_span, _) = expr {
for ((upvar_hir_id, upvar), place) in
self.infcx.tcx.upvars_mentioned(def_id)?.iter().zip(places)
for (upvar_hir_id, place) in
self.infcx.tcx.typeck(def_id.expect_local()).closure_captures[&def_id]
.keys()
.zip(places)
{
let span = self.infcx.tcx.upvars_mentioned(local_did)?[upvar_hir_id].span;
match place {
Operand::Copy(place) | Operand::Move(place)
if target_place == place.as_ref() =>
Expand All @@ -991,7 +992,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
let usage_span =
match self.infcx.tcx.typeck(local_did).upvar_capture(upvar_id) {
ty::UpvarCapture::ByValue(Some(span)) => span,
_ => upvar.span,
_ => span,
};
return Some((*args_span, generator_kind, usage_span));
}
Expand Down
5 changes: 3 additions & 2 deletions compiler/rustc_mir_build/src/thir/cx/expr.rs
Original file line number Diff line number Diff line change
Expand Up @@ -387,8 +387,9 @@ fn make_mirror_unadjusted<'a, 'tcx>(
}
};
let upvars = cx
.tcx
.upvars_mentioned(def_id)
.typeck_results()
.closure_captures
.get(&def_id)
.iter()
.flat_map(|upvars| upvars.iter())
.zip(substs.upvar_tys())
Expand Down
69 changes: 49 additions & 20 deletions compiler/rustc_passes/src/liveness.rs
Original file line number Diff line number Diff line change
Expand Up @@ -317,19 +317,20 @@ impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
// 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 def_id = maps.tcx.hir().local_def_id(hir_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.to_def_id()) {
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(upvars) = maps.tcx.upvars_mentioned(def_id) {
for (&var_hir_id, _upvar) in upvars {
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));
}
Expand All @@ -340,7 +341,7 @@ impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
intravisit::walk_body(&mut maps, body);

// compute liveness
let mut lsets = Liveness::new(&mut maps, def_id);
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);

Expand Down Expand Up @@ -397,10 +398,18 @@ impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
// 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.iter().map(|(&var_id, upvar)| {
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 }
CaptureInfo { ln: upvar_ln, var_hid: *var_id }
}));
}
self.set_captures(expr.hir_id, call_caps);
Expand Down Expand Up @@ -564,6 +573,7 @@ struct Liveness<'a, 'tcx> {
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: RWUTable,

Expand All @@ -587,6 +597,7 @@ impl<'a, 'tcx> 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);
Expand All @@ -600,6 +611,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
typeck_results,
param_env,
upvars,
closure_captures,
successors: IndexVec::from_elem_n(None, num_live_nodes),
rwu_table: RWUTable::new(num_live_nodes * num_vars),
closure_ln,
Expand Down Expand Up @@ -850,14 +862,13 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
// if they are live on the entry to the closure, since only the closure
// itself can access them on subsequent calls.

if let Some(upvars) = self.upvars {
if let Some(closure_captures) = self.closure_captures {
// Mark upvars captured by reference as used after closure exits.
for (&var_hir_id, upvar) in upvars.iter().rev() {
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) {
// 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);
Expand All @@ -869,7 +880,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {

let succ = self.propagate_through_expr(&body.value, self.exit_ln);

if self.upvars.is_none() {
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.
Expand Down Expand Up @@ -1341,7 +1352,21 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
acc: u32,
) -> LiveNode {
match path.res {
Res::Local(hid) => self.access_var(hir_id, hid, succ, acc, path.span),
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,
}
}
Expand Down Expand Up @@ -1531,11 +1556,15 @@ impl<'tcx> Liveness<'_, 'tcx> {
}

fn warn_about_unused_upvars(&self, entry_ln: LiveNode) {
let upvars = match self.upvars {
let closure_captures = match self.closure_captures {
None => return,
Some(upvars) => upvars,
Some(closure_captures) => closure_captures,
};
for (&var_hir_id, upvar) in upvars.iter() {

// 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 },
Expand Down
2 changes: 2 additions & 0 deletions compiler/rustc_span/src/symbol.rs
Original file line number Diff line number Diff line change
Expand Up @@ -318,6 +318,7 @@ symbols! {
call_mut,
call_once,
caller_location,
capture_disjoint_fields,
cdylib,
ceilf32,
ceilf64,
Expand Down Expand Up @@ -909,6 +910,7 @@ symbols! {
rustc_args_required_const,
rustc_attrs,
rustc_builtin_macro,
rustc_capture_analysis,
rustc_clean,
rustc_const_stable,
rustc_const_unstable,
Expand Down
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