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1d56943f34
The words "before" and "after" have an obvious temporal meaning, e.g.
`seek_before_primary_effect`,
`visit_statement_{before,after}_primary_effect`. But "before" is also
used to name the effect that occurs before the primary effect of a
statement/terminator; this is `Effect::Before`. This leads to the
confusing possibility of talking about things happening "before/after
the before event".
This commit removes this awkward overloading of "before" by renaming
`Effect::Before` as `Effect::Early`. It also renames some of the
`Analysis` and `ResultsVisitor` methods to be more consistent.
Here are the before and after names:
- `Effect::{Before,Primary}` -> `Effect::{Early,Primary}`
- `apply_before_statement_effect` -> `apply_early_statement_effect`
- `apply_statement_effect` -> `apply_primary_statement_effect`
- `visit_statement_before_primary_effect` -> `visit_after_early_statement_effect`
- `visit_statement_after_primary_effect` -> `visit_after_primary_statement_effect`
(And s/statement/terminator/ for all the terminator events.)
623 lines
22 KiB
Rust
623 lines
22 KiB
Rust
use std::assert_matches::assert_matches;
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use rustc_index::Idx;
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use rustc_index::bit_set::{BitSet, MixedBitSet};
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use rustc_middle::bug;
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use rustc_middle::mir::{self, Body, CallReturnPlaces, Location, TerminatorEdges};
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use rustc_middle::ty::{self, TyCtxt};
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use tracing::{debug, instrument};
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use crate::elaborate_drops::DropFlagState;
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use crate::framework::SwitchIntEdgeEffects;
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use crate::move_paths::{HasMoveData, InitIndex, InitKind, LookupResult, MoveData, MovePathIndex};
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use crate::{
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Analysis, GenKill, MaybeReachable, drop_flag_effects, drop_flag_effects_for_function_entry,
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drop_flag_effects_for_location, on_all_children_bits, on_lookup_result_bits,
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};
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/// `MaybeInitializedPlaces` tracks all places that might be
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/// initialized upon reaching a particular point in the control flow
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/// for a function.
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///
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/// For example, in code like the following, we have corresponding
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/// dataflow information shown in the right-hand comments.
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///
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/// ```rust
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/// struct S;
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/// fn foo(pred: bool) { // maybe-init:
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/// // {}
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/// let a = S; let mut b = S; let c; let d; // {a, b}
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///
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/// if pred {
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/// drop(a); // { b}
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/// b = S; // { b}
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///
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/// } else {
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/// drop(b); // {a}
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/// d = S; // {a, d}
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///
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/// } // {a, b, d}
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///
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/// c = S; // {a, b, c, d}
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/// }
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/// ```
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///
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/// To determine whether a place is *definitely* initialized at a
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/// particular control-flow point, one can take the set-complement
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/// of the data from `MaybeUninitializedPlaces` at the corresponding
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/// control-flow point.
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///
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/// Similarly, at a given `drop` statement, the set-intersection
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/// between this data and `MaybeUninitializedPlaces` yields the set of
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/// places that would require a dynamic drop-flag at that statement.
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pub struct MaybeInitializedPlaces<'a, 'tcx> {
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tcx: TyCtxt<'tcx>,
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body: &'a Body<'tcx>,
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move_data: &'a MoveData<'tcx>,
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skip_unreachable_unwind: bool,
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}
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impl<'a, 'tcx> MaybeInitializedPlaces<'a, 'tcx> {
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pub fn new(tcx: TyCtxt<'tcx>, body: &'a Body<'tcx>, move_data: &'a MoveData<'tcx>) -> Self {
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MaybeInitializedPlaces { tcx, body, move_data, skip_unreachable_unwind: false }
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}
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pub fn skipping_unreachable_unwind(mut self) -> Self {
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self.skip_unreachable_unwind = true;
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self
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}
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pub fn is_unwind_dead(
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&self,
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place: mir::Place<'tcx>,
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state: &<Self as Analysis<'tcx>>::Domain,
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) -> bool {
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if let LookupResult::Exact(path) = self.move_data().rev_lookup.find(place.as_ref()) {
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let mut maybe_live = false;
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on_all_children_bits(self.move_data(), path, |child| {
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maybe_live |= state.contains(child);
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});
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!maybe_live
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} else {
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false
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}
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}
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}
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impl<'a, 'tcx> HasMoveData<'tcx> for MaybeInitializedPlaces<'a, 'tcx> {
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fn move_data(&self) -> &MoveData<'tcx> {
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self.move_data
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}
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}
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/// `MaybeUninitializedPlaces` tracks all places that might be
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/// uninitialized upon reaching a particular point in the control flow
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/// for a function.
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///
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/// For example, in code like the following, we have corresponding
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/// dataflow information shown in the right-hand comments.
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///
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/// ```rust
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/// struct S;
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/// fn foo(pred: bool) { // maybe-uninit:
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/// // {a, b, c, d}
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/// let a = S; let mut b = S; let c; let d; // { c, d}
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///
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/// if pred {
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/// drop(a); // {a, c, d}
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/// b = S; // {a, c, d}
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///
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/// } else {
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/// drop(b); // { b, c, d}
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/// d = S; // { b, c }
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///
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/// } // {a, b, c, d}
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///
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/// c = S; // {a, b, d}
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/// }
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/// ```
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///
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/// To determine whether a place is *definitely* uninitialized at a
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/// particular control-flow point, one can take the set-complement
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/// of the data from `MaybeInitializedPlaces` at the corresponding
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/// control-flow point.
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///
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/// Similarly, at a given `drop` statement, the set-intersection
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/// between this data and `MaybeInitializedPlaces` yields the set of
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/// places that would require a dynamic drop-flag at that statement.
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pub struct MaybeUninitializedPlaces<'a, 'tcx> {
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tcx: TyCtxt<'tcx>,
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body: &'a Body<'tcx>,
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move_data: &'a MoveData<'tcx>,
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mark_inactive_variants_as_uninit: bool,
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skip_unreachable_unwind: BitSet<mir::BasicBlock>,
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}
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impl<'a, 'tcx> MaybeUninitializedPlaces<'a, 'tcx> {
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pub fn new(tcx: TyCtxt<'tcx>, body: &'a Body<'tcx>, move_data: &'a MoveData<'tcx>) -> Self {
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MaybeUninitializedPlaces {
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tcx,
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body,
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move_data,
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mark_inactive_variants_as_uninit: false,
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skip_unreachable_unwind: BitSet::new_empty(body.basic_blocks.len()),
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}
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}
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/// Causes inactive enum variants to be marked as "maybe uninitialized" after a switch on an
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/// enum discriminant.
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///
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/// This is correct in a vacuum but is not the default because it causes problems in the borrow
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/// checker, where this information gets propagated along `FakeEdge`s.
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pub fn mark_inactive_variants_as_uninit(mut self) -> Self {
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self.mark_inactive_variants_as_uninit = true;
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self
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}
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pub fn skipping_unreachable_unwind(
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mut self,
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unreachable_unwind: BitSet<mir::BasicBlock>,
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) -> Self {
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self.skip_unreachable_unwind = unreachable_unwind;
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self
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}
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}
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impl<'tcx> HasMoveData<'tcx> for MaybeUninitializedPlaces<'_, 'tcx> {
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fn move_data(&self) -> &MoveData<'tcx> {
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self.move_data
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}
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}
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/// `EverInitializedPlaces` tracks all places that might have ever been
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/// initialized upon reaching a particular point in the control flow
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/// for a function, without an intervening `StorageDead`.
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///
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/// This dataflow is used to determine if an immutable local variable may
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/// be assigned to.
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///
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/// For example, in code like the following, we have corresponding
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/// dataflow information shown in the right-hand comments.
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///
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/// ```rust
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/// struct S;
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/// fn foo(pred: bool) { // ever-init:
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/// // { }
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/// let a = S; let mut b = S; let c; let d; // {a, b }
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///
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/// if pred {
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/// drop(a); // {a, b, }
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/// b = S; // {a, b, }
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///
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/// } else {
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/// drop(b); // {a, b, }
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/// d = S; // {a, b, d }
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///
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/// } // {a, b, d }
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///
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/// c = S; // {a, b, c, d }
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/// }
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/// ```
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pub struct EverInitializedPlaces<'a, 'tcx> {
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body: &'a Body<'tcx>,
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move_data: &'a MoveData<'tcx>,
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}
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impl<'a, 'tcx> EverInitializedPlaces<'a, 'tcx> {
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pub fn new(body: &'a Body<'tcx>, move_data: &'a MoveData<'tcx>) -> Self {
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EverInitializedPlaces { body, move_data }
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}
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}
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impl<'tcx> HasMoveData<'tcx> for EverInitializedPlaces<'_, 'tcx> {
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fn move_data(&self) -> &MoveData<'tcx> {
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self.move_data
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}
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}
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impl<'a, 'tcx> MaybeInitializedPlaces<'a, 'tcx> {
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fn update_bits(
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state: &mut <Self as Analysis<'tcx>>::Domain,
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path: MovePathIndex,
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dfstate: DropFlagState,
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) {
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match dfstate {
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DropFlagState::Absent => state.kill(path),
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DropFlagState::Present => state.gen_(path),
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}
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}
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}
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impl<'tcx> MaybeUninitializedPlaces<'_, 'tcx> {
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fn update_bits(
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state: &mut <Self as Analysis<'tcx>>::Domain,
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path: MovePathIndex,
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dfstate: DropFlagState,
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) {
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match dfstate {
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DropFlagState::Absent => state.gen_(path),
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DropFlagState::Present => state.kill(path),
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}
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}
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}
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impl<'tcx> Analysis<'tcx> for MaybeInitializedPlaces<'_, 'tcx> {
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/// There can be many more `MovePathIndex` than there are locals in a MIR body.
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/// We use a mixed bitset to avoid paying too high a memory footprint.
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type Domain = MaybeReachable<MixedBitSet<MovePathIndex>>;
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const NAME: &'static str = "maybe_init";
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fn bottom_value(&self, _: &mir::Body<'tcx>) -> Self::Domain {
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// bottom = uninitialized
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MaybeReachable::Unreachable
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}
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fn initialize_start_block(&self, _: &mir::Body<'tcx>, state: &mut Self::Domain) {
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*state =
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MaybeReachable::Reachable(MixedBitSet::new_empty(self.move_data().move_paths.len()));
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drop_flag_effects_for_function_entry(self.body, self.move_data, |path, s| {
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assert!(s == DropFlagState::Present);
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state.gen_(path);
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});
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}
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fn apply_primary_statement_effect(
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&mut self,
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state: &mut Self::Domain,
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statement: &mir::Statement<'tcx>,
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location: Location,
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) {
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drop_flag_effects_for_location(self.body, self.move_data, location, |path, s| {
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Self::update_bits(state, path, s)
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});
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// Mark all places as "maybe init" if they are mutably borrowed. See #90752.
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if self.tcx.sess.opts.unstable_opts.precise_enum_drop_elaboration
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&& let Some((_, rvalue)) = statement.kind.as_assign()
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&& let mir::Rvalue::Ref(_, mir::BorrowKind::Mut { .. }, place)
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// FIXME: Does `&raw const foo` allow mutation? See #90413.
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| mir::Rvalue::RawPtr(_, place) = rvalue
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&& let LookupResult::Exact(mpi) = self.move_data().rev_lookup.find(place.as_ref())
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{
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on_all_children_bits(self.move_data(), mpi, |child| {
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state.gen_(child);
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})
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}
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}
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fn apply_primary_terminator_effect<'mir>(
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&mut self,
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state: &mut Self::Domain,
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terminator: &'mir mir::Terminator<'tcx>,
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location: Location,
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) -> TerminatorEdges<'mir, 'tcx> {
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let mut edges = terminator.edges();
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if self.skip_unreachable_unwind
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&& let mir::TerminatorKind::Drop { target, unwind, place, replace: _ } = terminator.kind
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&& matches!(unwind, mir::UnwindAction::Cleanup(_))
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&& self.is_unwind_dead(place, state)
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{
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edges = TerminatorEdges::Single(target);
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}
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drop_flag_effects_for_location(self.body, self.move_data, location, |path, s| {
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Self::update_bits(state, path, s)
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});
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edges
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}
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fn apply_call_return_effect(
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&mut self,
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state: &mut Self::Domain,
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_block: mir::BasicBlock,
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return_places: CallReturnPlaces<'_, 'tcx>,
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) {
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return_places.for_each(|place| {
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// when a call returns successfully, that means we need to set
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// the bits for that dest_place to 1 (initialized).
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on_lookup_result_bits(
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self.move_data(),
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self.move_data().rev_lookup.find(place.as_ref()),
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|mpi| {
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state.gen_(mpi);
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},
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);
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});
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}
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fn apply_switch_int_edge_effects(
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&mut self,
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block: mir::BasicBlock,
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discr: &mir::Operand<'tcx>,
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edge_effects: &mut impl SwitchIntEdgeEffects<Self::Domain>,
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) {
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if !self.tcx.sess.opts.unstable_opts.precise_enum_drop_elaboration {
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return;
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}
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let enum_ = discr.place().and_then(|discr| {
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switch_on_enum_discriminant(self.tcx, self.body, &self.body[block], discr)
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});
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let Some((enum_place, enum_def)) = enum_ else {
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return;
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};
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let mut discriminants = enum_def.discriminants(self.tcx);
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edge_effects.apply(|state, edge| {
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let Some(value) = edge.value else {
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return;
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};
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// MIR building adds discriminants to the `values` array in the same order as they
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// are yielded by `AdtDef::discriminants`. We rely on this to match each
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// discriminant in `values` to its corresponding variant in linear time.
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let (variant, _) = discriminants
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.find(|&(_, discr)| discr.val == value)
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.expect("Order of `AdtDef::discriminants` differed from `SwitchInt::values`");
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// Kill all move paths that correspond to variants we know to be inactive along this
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// particular outgoing edge of a `SwitchInt`.
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drop_flag_effects::on_all_inactive_variants(
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self.move_data(),
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enum_place,
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variant,
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|mpi| state.kill(mpi),
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);
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});
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}
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}
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/// There can be many more `MovePathIndex` than there are locals in a MIR body.
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/// We use a mixed bitset to avoid paying too high a memory footprint.
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pub type MaybeUninitializedPlacesDomain = MixedBitSet<MovePathIndex>;
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impl<'tcx> Analysis<'tcx> for MaybeUninitializedPlaces<'_, 'tcx> {
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type Domain = MaybeUninitializedPlacesDomain;
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const NAME: &'static str = "maybe_uninit";
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fn bottom_value(&self, _: &mir::Body<'tcx>) -> Self::Domain {
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// bottom = initialized (`initialize_start_block` overwrites this on first entry)
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MixedBitSet::new_empty(self.move_data().move_paths.len())
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}
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// sets state bits for Arg places
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fn initialize_start_block(&self, _: &mir::Body<'tcx>, state: &mut Self::Domain) {
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// set all bits to 1 (uninit) before gathering counter-evidence
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state.insert_all();
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drop_flag_effects_for_function_entry(self.body, self.move_data, |path, s| {
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assert!(s == DropFlagState::Present);
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state.remove(path);
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});
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}
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fn apply_primary_statement_effect(
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&mut self,
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state: &mut Self::Domain,
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_statement: &mir::Statement<'tcx>,
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location: Location,
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) {
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drop_flag_effects_for_location(self.body, self.move_data, location, |path, s| {
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Self::update_bits(state, path, s)
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});
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|
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// Unlike in `MaybeInitializedPlaces` above, we don't need to change the state when a
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// mutable borrow occurs. Places cannot become uninitialized through a mutable reference.
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}
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fn apply_primary_terminator_effect<'mir>(
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&mut self,
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state: &mut Self::Domain,
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terminator: &'mir mir::Terminator<'tcx>,
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location: Location,
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) -> TerminatorEdges<'mir, 'tcx> {
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drop_flag_effects_for_location(self.body, self.move_data, location, |path, s| {
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Self::update_bits(state, path, s)
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});
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if self.skip_unreachable_unwind.contains(location.block) {
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let mir::TerminatorKind::Drop { target, unwind, .. } = terminator.kind else { bug!() };
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assert_matches!(unwind, mir::UnwindAction::Cleanup(_));
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TerminatorEdges::Single(target)
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} else {
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terminator.edges()
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}
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}
|
|
|
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fn apply_call_return_effect(
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&mut self,
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state: &mut Self::Domain,
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_block: mir::BasicBlock,
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return_places: CallReturnPlaces<'_, 'tcx>,
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) {
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return_places.for_each(|place| {
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// when a call returns successfully, that means we need to set
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|
// the bits for that dest_place to 0 (initialized).
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on_lookup_result_bits(
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self.move_data(),
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self.move_data().rev_lookup.find(place.as_ref()),
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|mpi| {
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state.kill(mpi);
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},
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);
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});
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}
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|
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fn apply_switch_int_edge_effects(
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&mut self,
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|
block: mir::BasicBlock,
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|
discr: &mir::Operand<'tcx>,
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|
edge_effects: &mut impl SwitchIntEdgeEffects<Self::Domain>,
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|
) {
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if !self.tcx.sess.opts.unstable_opts.precise_enum_drop_elaboration {
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return;
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}
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|
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if !self.mark_inactive_variants_as_uninit {
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return;
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}
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let enum_ = discr.place().and_then(|discr| {
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switch_on_enum_discriminant(self.tcx, self.body, &self.body[block], discr)
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|
});
|
|
|
|
let Some((enum_place, enum_def)) = enum_ else {
|
|
return;
|
|
};
|
|
|
|
let mut discriminants = enum_def.discriminants(self.tcx);
|
|
edge_effects.apply(|state, edge| {
|
|
let Some(value) = edge.value else {
|
|
return;
|
|
};
|
|
|
|
// MIR building adds discriminants to the `values` array in the same order as they
|
|
// are yielded by `AdtDef::discriminants`. We rely on this to match each
|
|
// discriminant in `values` to its corresponding variant in linear time.
|
|
let (variant, _) = discriminants
|
|
.find(|&(_, discr)| discr.val == value)
|
|
.expect("Order of `AdtDef::discriminants` differed from `SwitchInt::values`");
|
|
|
|
// Mark all move paths that correspond to variants other than this one as maybe
|
|
// uninitialized (in reality, they are *definitely* uninitialized).
|
|
drop_flag_effects::on_all_inactive_variants(
|
|
self.move_data(),
|
|
enum_place,
|
|
variant,
|
|
|mpi| state.gen_(mpi),
|
|
);
|
|
});
|
|
}
|
|
}
|
|
|
|
/// There can be many more `InitIndex` than there are locals in a MIR body.
|
|
/// We use a mixed bitset to avoid paying too high a memory footprint.
|
|
pub type EverInitializedPlacesDomain = MixedBitSet<InitIndex>;
|
|
|
|
impl<'tcx> Analysis<'tcx> for EverInitializedPlaces<'_, 'tcx> {
|
|
type Domain = EverInitializedPlacesDomain;
|
|
|
|
const NAME: &'static str = "ever_init";
|
|
|
|
fn bottom_value(&self, _: &mir::Body<'tcx>) -> Self::Domain {
|
|
// bottom = no initialized variables by default
|
|
MixedBitSet::new_empty(self.move_data().inits.len())
|
|
}
|
|
|
|
fn initialize_start_block(&self, body: &mir::Body<'tcx>, state: &mut Self::Domain) {
|
|
for arg_init in 0..body.arg_count {
|
|
state.insert(InitIndex::new(arg_init));
|
|
}
|
|
}
|
|
|
|
#[instrument(skip(self, state), level = "debug")]
|
|
fn apply_primary_statement_effect(
|
|
&mut self,
|
|
state: &mut Self::Domain,
|
|
stmt: &mir::Statement<'tcx>,
|
|
location: Location,
|
|
) {
|
|
let move_data = self.move_data();
|
|
let init_path_map = &move_data.init_path_map;
|
|
let init_loc_map = &move_data.init_loc_map;
|
|
let rev_lookup = &move_data.rev_lookup;
|
|
|
|
debug!("initializes move_indexes {:?}", init_loc_map[location]);
|
|
state.gen_all(init_loc_map[location].iter().copied());
|
|
|
|
if let mir::StatementKind::StorageDead(local) = stmt.kind {
|
|
// End inits for StorageDead, so that an immutable variable can
|
|
// be reinitialized on the next iteration of the loop.
|
|
if let Some(move_path_index) = rev_lookup.find_local(local) {
|
|
debug!(
|
|
"clears the ever initialized status of {:?}",
|
|
init_path_map[move_path_index]
|
|
);
|
|
state.kill_all(init_path_map[move_path_index].iter().copied());
|
|
}
|
|
}
|
|
}
|
|
|
|
#[instrument(skip(self, state, terminator), level = "debug")]
|
|
fn apply_primary_terminator_effect<'mir>(
|
|
&mut self,
|
|
state: &mut Self::Domain,
|
|
terminator: &'mir mir::Terminator<'tcx>,
|
|
location: Location,
|
|
) -> TerminatorEdges<'mir, 'tcx> {
|
|
let (body, move_data) = (self.body, self.move_data());
|
|
let term = body[location.block].terminator();
|
|
let init_loc_map = &move_data.init_loc_map;
|
|
debug!(?term);
|
|
debug!("initializes move_indexes {:?}", init_loc_map[location]);
|
|
state.gen_all(
|
|
init_loc_map[location]
|
|
.iter()
|
|
.filter(|init_index| {
|
|
move_data.inits[**init_index].kind != InitKind::NonPanicPathOnly
|
|
})
|
|
.copied(),
|
|
);
|
|
terminator.edges()
|
|
}
|
|
|
|
fn apply_call_return_effect(
|
|
&mut self,
|
|
state: &mut Self::Domain,
|
|
block: mir::BasicBlock,
|
|
_return_places: CallReturnPlaces<'_, 'tcx>,
|
|
) {
|
|
let move_data = self.move_data();
|
|
let init_loc_map = &move_data.init_loc_map;
|
|
|
|
let call_loc = self.body.terminator_loc(block);
|
|
for init_index in &init_loc_map[call_loc] {
|
|
state.gen_(*init_index);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Inspect a `SwitchInt`-terminated basic block to see if the condition of that `SwitchInt` is
|
|
/// an enum discriminant.
|
|
///
|
|
/// We expect such blocks to have a call to `discriminant` as their last statement like so:
|
|
///
|
|
/// ```text
|
|
/// ...
|
|
/// _42 = discriminant(_1)
|
|
/// SwitchInt(_42, ..)
|
|
/// ```
|
|
///
|
|
/// If the basic block matches this pattern, this function returns the place corresponding to the
|
|
/// enum (`_1` in the example above) as well as the `AdtDef` of that enum.
|
|
fn switch_on_enum_discriminant<'mir, 'tcx>(
|
|
tcx: TyCtxt<'tcx>,
|
|
body: &'mir mir::Body<'tcx>,
|
|
block: &'mir mir::BasicBlockData<'tcx>,
|
|
switch_on: mir::Place<'tcx>,
|
|
) -> Option<(mir::Place<'tcx>, ty::AdtDef<'tcx>)> {
|
|
for statement in block.statements.iter().rev() {
|
|
match &statement.kind {
|
|
mir::StatementKind::Assign(box (lhs, mir::Rvalue::Discriminant(discriminated)))
|
|
if *lhs == switch_on =>
|
|
{
|
|
match discriminated.ty(body, tcx).ty.kind() {
|
|
ty::Adt(def, _) => return Some((*discriminated, *def)),
|
|
|
|
// `Rvalue::Discriminant` is also used to get the active yield point for a
|
|
// coroutine, but we do not need edge-specific effects in that case. This may
|
|
// change in the future.
|
|
ty::Coroutine(..) => return None,
|
|
|
|
t => bug!("`discriminant` called on unexpected type {:?}", t),
|
|
}
|
|
}
|
|
mir::StatementKind::Coverage(_) => continue,
|
|
_ => return None,
|
|
}
|
|
}
|
|
None
|
|
}
|