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//! Random access inspection of the results of a dataflow analysis.
use crate::{framework::BitSetExt, CloneAnalysis};
use std::borrow::{Borrow, BorrowMut};
use std::cmp::Ordering;
#[cfg(debug_assertions)]
use rustc_index::bit_set::BitSet;
use rustc_middle::mir::{self, BasicBlock, Location};
use super::{Analysis, Direction, Effect, EffectIndex, EntrySets, Results, ResultsCloned};
// `AnalysisResults` is needed as an impl such as the following has an unconstrained type
// parameter:
// ```
// impl<'tcx, A, E, R> ResultsCursor<'_, 'tcx, A, R>
// where
// A: Analysis<'tcx>,
// E: Borrow<EntrySets<'tcx, A>>,
// R: Results<'tcx, A, E>,
// {}
// ```
/// A type representing the analysis results consumed by a `ResultsCursor`.
pub trait AnalysisResults<'tcx, A>: BorrowMut<Results<'tcx, A, Self::EntrySets>>
where
A: Analysis<'tcx>,
{
/// The type containing the entry sets for this `Results` type.
///
/// Should be either `EntrySets<'tcx, A>` or `&EntrySets<'tcx, A>`.
type EntrySets: Borrow<EntrySets<'tcx, A>>;
}
impl<'tcx, A, E> AnalysisResults<'tcx, A> for Results<'tcx, A, E>
where
A: Analysis<'tcx>,
E: Borrow<EntrySets<'tcx, A>>,
{
type EntrySets = E;
}
impl<'a, 'tcx, A, E> AnalysisResults<'tcx, A> for &'a mut Results<'tcx, A, E>
where
A: Analysis<'tcx>,
E: Borrow<EntrySets<'tcx, A>>,
{
type EntrySets = E;
}
/// A `ResultsCursor` that borrows the underlying `Results`.
pub type ResultsRefCursor<'res, 'mir, 'tcx, A> =
ResultsCursor<'mir, 'tcx, A, &'res mut Results<'tcx, A>>;
/// A `ResultsCursor` which uses a cloned `Analysis` while borrowing the underlying `Results`. This
/// allows multiple cursors over the same `Results`.
pub type ResultsClonedCursor<'res, 'mir, 'tcx, A> =
ResultsCursor<'mir, 'tcx, A, ResultsCloned<'res, 'tcx, A>>;
/// Allows random access inspection of the results of a dataflow analysis.
///
/// This cursor only has linear performance within a basic block when its statements are visited in
/// the same order as the `DIRECTION` of the analysis. In the worst case—when statements are
/// visited in *reverse* order—performance will be quadratic in the number of statements in the
/// block. The order in which basic blocks are inspected has no impact on performance.
///
/// A `ResultsCursor` can either own (the default) or borrow the dataflow results it inspects. The
/// type of ownership is determined by `R` (see `ResultsRefCursor` above).
pub struct ResultsCursor<'mir, 'tcx, A, R = Results<'tcx, A>>
where
A: Analysis<'tcx>,
{
body: &'mir mir::Body<'tcx>,
results: R,
state: A::Domain,
pos: CursorPosition,
/// Indicates that `state` has been modified with a custom effect.
///
/// When this flag is set, we need to reset to an entry set before doing a seek.
state_needs_reset: bool,
#[cfg(debug_assertions)]
reachable_blocks: BitSet<BasicBlock>,
}
impl<'mir, 'tcx, A, R> ResultsCursor<'mir, 'tcx, A, R>
where
A: Analysis<'tcx>,
{
/// Returns the dataflow state at the current location.
pub fn get(&self) -> &A::Domain {
&self.state
}
/// Returns the body this analysis was run on.
pub fn body(&self) -> &'mir mir::Body<'tcx> {
self.body
}
/// Unwraps this cursor, returning the underlying `Results`.
pub fn into_results(self) -> R {
self.results
}
}
impl<'res, 'mir, 'tcx, A> ResultsCursor<'mir, 'tcx, A, ResultsCloned<'res, 'tcx, A>>
where
A: Analysis<'tcx> + CloneAnalysis,
{
/// Creates a new cursor over the same `Results`. Note that the cursor's position is *not*
/// copied.
pub fn new_cursor(&self) -> Self {
Self::new(self.body, self.results.reclone_analysis())
}
}
impl<'mir, 'tcx, A, R> ResultsCursor<'mir, 'tcx, A, R>
where
A: Analysis<'tcx>,
R: AnalysisResults<'tcx, A>,
{
/// Returns a new cursor that can inspect `results`.
pub fn new(body: &'mir mir::Body<'tcx>, results: R) -> Self {
let bottom_value = results.borrow().analysis.bottom_value(body);
ResultsCursor {
body,
results,
// Initialize to the `bottom_value` and set `state_needs_reset` to tell the cursor that
// it needs to reset to block entry before the first seek. The cursor position is
// immaterial.
state_needs_reset: true,
state: bottom_value,
pos: CursorPosition::block_entry(mir::START_BLOCK),
#[cfg(debug_assertions)]
reachable_blocks: mir::traversal::reachable_as_bitset(body),
}
}
/// Allows inspection of unreachable basic blocks even with `debug_assertions` enabled.
#[cfg(test)]
pub(crate) fn allow_unreachable(&mut self) {
#[cfg(debug_assertions)]
self.reachable_blocks.insert_all()
}
/// Returns the underlying `Results`.
pub fn results(&mut self) -> &Results<'tcx, A, R::EntrySets> {
self.results.borrow()
}
/// Returns the underlying `Results`.
pub fn mut_results(&mut self) -> &mut Results<'tcx, A, R::EntrySets> {
self.results.borrow_mut()
}
/// Returns the `Analysis` used to generate the underlying `Results`.
pub fn analysis(&self) -> &A {
&self.results.borrow().analysis
}
/// Returns the `Analysis` used to generate the underlying `Results`.
pub fn mut_analysis(&mut self) -> &mut A {
&mut self.results.borrow_mut().analysis
}
/// Returns both the dataflow state at the current location and the `Analysis`.
pub fn get_with_analysis(&mut self) -> (&A::Domain, &mut A) {
(&self.state, &mut self.results.borrow_mut().analysis)
}
/// Resets the cursor to hold the entry set for the given basic block.
///
/// For forward dataflow analyses, this is the dataflow state prior to the first statement.
///
/// For backward dataflow analyses, this is the dataflow state after the terminator.
pub(super) fn seek_to_block_entry(&mut self, block: BasicBlock) {
#[cfg(debug_assertions)]
assert!(self.reachable_blocks.contains(block));
self.state.clone_from(self.results.borrow().entry_set_for_block(block));
self.pos = CursorPosition::block_entry(block);
self.state_needs_reset = false;
}
/// Resets the cursor to hold the state prior to the first statement in a basic block.
///
/// For forward analyses, this is the entry set for the given block.
///
/// For backward analyses, this is the state that will be propagated to its
/// predecessors (ignoring edge-specific effects).
pub fn seek_to_block_start(&mut self, block: BasicBlock) {
if A::Direction::IS_FORWARD {
self.seek_to_block_entry(block)
} else {
self.seek_after(Location { block, statement_index: 0 }, Effect::Primary)
}
}
/// Resets the cursor to hold the state after the terminator in a basic block.
///
/// For backward analyses, this is the entry set for the given block.
///
/// For forward analyses, this is the state that will be propagated to its
/// successors (ignoring edge-specific effects).
pub fn seek_to_block_end(&mut self, block: BasicBlock) {
if A::Direction::IS_BACKWARD {
self.seek_to_block_entry(block)
} else {
self.seek_after(self.body.terminator_loc(block), Effect::Primary)
}
}
/// Advances the cursor to hold the dataflow state at `target` before its "primary" effect is
/// applied.
///
/// The "before" effect at the target location *will be* applied.
pub fn seek_before_primary_effect(&mut self, target: Location) {
self.seek_after(target, Effect::Before)
}
/// Advances the cursor to hold the dataflow state at `target` after its "primary" effect is
/// applied.
///
/// The "before" effect at the target location will be applied as well.
pub fn seek_after_primary_effect(&mut self, target: Location) {
self.seek_after(target, Effect::Primary)
}
fn seek_after(&mut self, target: Location, effect: Effect) {
assert!(target <= self.body.terminator_loc(target.block));
// Reset to the entry of the target block if any of the following are true:
// - A custom effect has been applied to the cursor state.
// - We are in a different block than the target.
// - We are in the same block but have advanced past the target effect.
if self.state_needs_reset || self.pos.block != target.block {
self.seek_to_block_entry(target.block);
} else if let Some(curr_effect) = self.pos.curr_effect_index {
let mut ord = curr_effect.statement_index.cmp(&target.statement_index);
if A::Direction::IS_BACKWARD {
ord = ord.reverse()
}
match ord.then_with(|| curr_effect.effect.cmp(&effect)) {
Ordering::Equal => return,
Ordering::Greater => self.seek_to_block_entry(target.block),
Ordering::Less => {}
}
}
// At this point, the cursor is in the same block as the target location at an earlier
// statement.
debug_assert_eq!(target.block, self.pos.block);
let block_data = &self.body[target.block];
let next_effect = if A::Direction::IS_FORWARD {
#[rustfmt::skip]
self.pos.curr_effect_index.map_or_else(
|| Effect::Before.at_index(0),
EffectIndex::next_in_forward_order,
)
} else {
self.pos.curr_effect_index.map_or_else(
|| Effect::Before.at_index(block_data.statements.len()),
EffectIndex::next_in_backward_order,
)
};
let analysis = &mut self.results.borrow_mut().analysis;
let target_effect_index = effect.at_index(target.statement_index);
A::Direction::apply_effects_in_range(
analysis,
&mut self.state,
target.block,
block_data,
next_effect..=target_effect_index,
);
self.pos =
CursorPosition { block: target.block, curr_effect_index: Some(target_effect_index) };
}
/// Applies `f` to the cursor's internal state.
///
/// This can be used, e.g., to apply the call return effect directly to the cursor without
/// creating an extra copy of the dataflow state.
pub fn apply_custom_effect(&mut self, f: impl FnOnce(&mut A, &mut A::Domain)) {
f(&mut self.results.borrow_mut().analysis, &mut self.state);
self.state_needs_reset = true;
}
}
impl<'mir, 'tcx, A, R> ResultsCursor<'mir, 'tcx, A, R>
where
A: crate::GenKillAnalysis<'tcx>,
A::Domain: BitSetExt<A::Idx>,
{
pub fn contains(&self, elem: A::Idx) -> bool {
self.get().contains(elem)
}
}
#[derive(Clone, Copy, Debug)]
struct CursorPosition {
block: BasicBlock,
curr_effect_index: Option<EffectIndex>,
}
impl CursorPosition {
fn block_entry(block: BasicBlock) -> CursorPosition {
CursorPosition { block, curr_effect_index: None }
}
}
|