Separate Analysis and Results.

`Results` contains and `Analysis` and an `EntryStates`. The unfortunate
thing about this is that the analysis needs to be mutable everywhere
(`&mut Analysis`) which forces the `Results` to be mutable everywhere,
even though `EntryStates` is immutable everywhere.

To fix this, this commit renames `Results` as `AnalysisAndResults`,
renames `EntryStates` as `Results`, and separates the analysis and
results as much as possible. (`AnalysisAndResults` doesn't get much use,
it's mostly there to facilitate method chaining of
`iterate_to_fixpoint`.)

`Results` is immutable everywhere, which:
- is a bit clearer on how the data is used,
- avoids an unnecessary clone of entry states in
  `locals_live_across_suspend_points`, and
- moves the results outside the `RefCell` in Formatter.

The commit also reformulates `ResultsHandle` as the generic `CowMut`,
which is simpler than `ResultsHandle` because it doesn't need the
`'tcx` lifetime and the trait bounds. It also which sits nicely
alongside the new use of `Cow` in `ResultsCursor`.

Author: nnethercote

compiler/rustc_borrowck/src/lib.rs

@@ -47,7 +47,7 @@ use rustc_mir_dataflow::impls::{
 use rustc_mir_dataflow::move_paths::{
     InitIndex, InitLocation, LookupResult, MoveData, MovePathIndex,
 };
-use rustc_mir_dataflow::{Analysis, EntryStates, Results, ResultsVisitor, visit_results};
+use rustc_mir_dataflow::{Analysis, Results, ResultsVisitor, visit_results};
 use rustc_session::lint::builtin::{TAIL_EXPR_DROP_ORDER, UNUSED_MUT};
 use rustc_span::{ErrorGuaranteed, Span, Symbol};
 use smallvec::SmallVec;
@@ -461,11 +461,13 @@ fn do_mir_borrowck<'tcx>(
     // Compute and report region errors, if any.
     mbcx.report_region_errors(nll_errors);
 
-    let mut flow_results = get_flow_results(tcx, body, &move_data, &borrow_set, &regioncx);
+    let (mut flow_analysis, flow_entry_states) =
+        get_flow_results(tcx, body, &move_data, &borrow_set, &regioncx);
     visit_results(
         body,
         traversal::reverse_postorder(body).map(|(bb, _)| bb),
-        &mut flow_results,
+        &mut flow_analysis,
+        &flow_entry_states,
         &mut mbcx,
     );
 
@@ -525,7 +527,7 @@ fn get_flow_results<'a, 'tcx>(
     move_data: &'a MoveData<'tcx>,
     borrow_set: &'a BorrowSet<'tcx>,
     regioncx: &RegionInferenceContext<'tcx>,
-) -> Results<'tcx, Borrowck<'a, 'tcx>> {
+) -> (Borrowck<'a, 'tcx>, Results<BorrowckDomain>) {
     // We compute these three analyses individually, but them combine them into
     // a single results so that `mbcx` can visit them all together.
     let borrows = Borrows::new(tcx, body, regioncx, borrow_set).iterate_to_fixpoint(
@@ -550,14 +552,14 @@ fn get_flow_results<'a, 'tcx>(
         ever_inits: ever_inits.analysis,
     };
 
-    assert_eq!(borrows.entry_states.len(), uninits.entry_states.len());
-    assert_eq!(borrows.entry_states.len(), ever_inits.entry_states.len());
-    let entry_states: EntryStates<'_, Borrowck<'_, '_>> =
-        itertools::izip!(borrows.entry_states, uninits.entry_states, ever_inits.entry_states)
+    assert_eq!(borrows.results.len(), uninits.results.len());
+    assert_eq!(borrows.results.len(), ever_inits.results.len());
+    let results: Results<_> =
+        itertools::izip!(borrows.results, uninits.results, ever_inits.results)
             .map(|(borrows, uninits, ever_inits)| BorrowckDomain { borrows, uninits, ever_inits })
             .collect();
 
-    Results { analysis, entry_states }
+    (analysis, results)
 }
 
 pub(crate) struct BorrowckInferCtxt<'tcx> {

compiler/rustc_mir_dataflow/src/framework/cursor.rs

@@ -1,5 +1,6 @@
 //! Random access inspection of the results of a dataflow analysis.
 
+use std::borrow::Cow;
 use std::cmp::Ordering;
 use std::ops::{Deref, DerefMut};
 
@@ -9,38 +10,30 @@ use rustc_middle::mir::{self, BasicBlock, Location};
 
 use super::{Analysis, Direction, Effect, EffectIndex, Results};
 
-/// Some `ResultsCursor`s want to own a `Results`, and some want to borrow a `Results`, either
-/// mutable or immutably. This type allows all of the above. It's similar to `Cow`.
-pub enum ResultsHandle<'a, 'tcx, A>
-where
-    A: Analysis<'tcx>,
-{
-    BorrowedMut(&'a mut Results<'tcx, A>),
-    Owned(Results<'tcx, A>),
+/// Some `ResultsCursor`s want to own an `Analysis`, and some want to borrow an `Analysis`, either
+/// mutable or immutably. This type allows all of the above. It's similar to `Cow`, but `Cow`
+/// doesn't allow mutable borrowing.
+enum CowMut<'a, T> {
+    BorrowedMut(&'a mut T),
+    Owned(T),
 }
 
-impl<'tcx, A> Deref for ResultsHandle<'_, 'tcx, A>
-where
-    A: Analysis<'tcx>,
-{
-    type Target = Results<'tcx, A>;
+impl<T> Deref for CowMut<'_, T> {
+    type Target = T;
 
-    fn deref(&self) -> &Results<'tcx, A> {
+    fn deref(&self) -> &T {
         match self {
-            ResultsHandle::BorrowedMut(borrowed) => borrowed,
-            ResultsHandle::Owned(owned) => owned,
+            CowMut::BorrowedMut(borrowed) => borrowed,
+            CowMut::Owned(owned) => owned,
         }
     }
 }
 
-impl<'tcx, A> DerefMut for ResultsHandle<'_, 'tcx, A>
-where
-    A: Analysis<'tcx>,
-{
-    fn deref_mut(&mut self) -> &mut Results<'tcx, A> {
+impl<T> DerefMut for CowMut<'_, T> {
+    fn deref_mut(&mut self) -> &mut T {
         match self {
-            ResultsHandle::BorrowedMut(borrowed) => borrowed,
-            ResultsHandle::Owned(owned) => owned,
+            CowMut::BorrowedMut(borrowed) => borrowed,
+            CowMut::Owned(owned) => owned,
         }
     }
 }
@@ -60,7 +53,8 @@ where
     A: Analysis<'tcx>,
 {
     body: &'mir mir::Body<'tcx>,
-    results: ResultsHandle<'mir, 'tcx, A>,
+    analysis: CowMut<'mir, A>,
+    results: Cow<'mir, Results<A::Domain>>,
     state: A::Domain,
 
     pos: CursorPosition,
@@ -88,11 +82,15 @@ where
         self.body
     }
 
-    /// Returns a new cursor that can inspect `results`.
-    pub fn new(body: &'mir mir::Body<'tcx>, results: ResultsHandle<'mir, 'tcx, A>) -> Self {
-        let bottom_value = results.analysis.bottom_value(body);
+    fn new(
+        body: &'mir mir::Body<'tcx>,
+        analysis: CowMut<'mir, A>,
+        results: Cow<'mir, Results<A::Domain>>,
+    ) -> Self {
+        let bottom_value = analysis.bottom_value(body);
         ResultsCursor {
             body,
+            analysis,
             results,
 
             // Initialize to the `bottom_value` and set `state_needs_reset` to tell the cursor that
@@ -107,6 +105,24 @@ where
         }
     }
 
+    /// Returns a new cursor that takes ownership of and inspects analysis results.
+    pub fn new_owning(
+        body: &'mir mir::Body<'tcx>,
+        analysis: A,
+        results: Results<A::Domain>,
+    ) -> Self {
+        Self::new(body, CowMut::Owned(analysis), Cow::Owned(results))
+    }
+
+    /// Returns a new cursor that borrows and inspects analysis results.
+    pub fn new_borrowing(
+        body: &'mir mir::Body<'tcx>,
+        analysis: &'mir mut A,
+        results: &'mir Results<A::Domain>,
+    ) -> Self {
+        Self::new(body, CowMut::BorrowedMut(analysis), Cow::Borrowed(results))
+    }
+
     /// Allows inspection of unreachable basic blocks even with `debug_assertions` enabled.
     #[cfg(test)]
     pub(crate) fn allow_unreachable(&mut self) {
@@ -116,7 +132,7 @@ where
 
     /// Returns the `Analysis` used to generate the underlying `Results`.
     pub fn analysis(&self) -> &A {
-        &self.results.analysis
+        &self.analysis
     }
 
     /// Resets the cursor to hold the entry set for the given basic block.
@@ -128,7 +144,7 @@ where
         #[cfg(debug_assertions)]
         assert!(self.reachable_blocks.contains(block));
 
-        self.state.clone_from(self.results.entry_set_for_block(block));
+        self.state.clone_from(&self.results[block]);
         self.pos = CursorPosition::block_entry(block);
         self.state_needs_reset = false;
     }
@@ -220,7 +236,7 @@ where
         let target_effect_index = effect.at_index(target.statement_index);
 
         A::Direction::apply_effects_in_range(
-            &mut self.results.analysis,
+            &mut *self.analysis,
             &mut self.state,
             target.block,
             block_data,
@@ -236,7 +252,7 @@ where
     /// 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.analysis, &mut self.state);
+        f(&mut self.analysis, &mut self.state);
         self.state_needs_reset = true;
     }
 }

compiler/rustc_mir_dataflow/src/framework/direction.rs

@@ -5,7 +5,7 @@ use rustc_middle::mir::{
 };
 
 use super::visitor::ResultsVisitor;
-use super::{Analysis, Effect, EffectIndex, Results};
+use super::{Analysis, Effect, EffectIndex};
 
 pub trait Direction {
     const IS_FORWARD: bool;
@@ -36,13 +36,13 @@ pub trait Direction {
         A: Analysis<'tcx>;
 
     /// Called by `ResultsVisitor` to recompute the analysis domain values for
-    /// all locations in a basic block (starting from the entry value stored
-    /// in `Results`) and to visit them with `vis`.
+    /// all locations in a basic block (starting from `entry_state` and to
+    /// visit them with `vis`.
     fn visit_results_in_block<'mir, 'tcx, A>(
         state: &mut A::Domain,
         block: BasicBlock,
         block_data: &'mir mir::BasicBlockData<'tcx>,
-        results: &mut Results<'tcx, A>,
+        analysis: &mut A,
         vis: &mut impl ResultsVisitor<'tcx, A>,
     ) where
         A: Analysis<'tcx>;
@@ -211,18 +211,15 @@ impl Direction for Backward {
         state: &mut A::Domain,
         block: BasicBlock,
         block_data: &'mir mir::BasicBlockData<'tcx>,
-        results: &mut Results<'tcx, A>,
+        analysis: &mut A,
         vis: &mut impl ResultsVisitor<'tcx, A>,
     ) where
         A: Analysis<'tcx>,
     {
-        state.clone_from(results.entry_set_for_block(block));
-
         vis.visit_block_end(state);
 
         let loc = Location { block, statement_index: block_data.statements.len() };
         let term = block_data.terminator();
-        let analysis = &mut results.analysis;
         analysis.apply_early_terminator_effect(state, term, loc);
         vis.visit_after_early_terminator_effect(analysis, state, term, loc);
         analysis.apply_primary_terminator_effect(state, term, loc);
@@ -394,16 +391,13 @@ impl Direction for Forward {
         state: &mut A::Domain,
         block: BasicBlock,
         block_data: &'mir mir::BasicBlockData<'tcx>,
-        results: &mut Results<'tcx, A>,
+        analysis: &mut A,
         vis: &mut impl ResultsVisitor<'tcx, A>,
     ) where
         A: Analysis<'tcx>,
     {
-        state.clone_from(results.entry_set_for_block(block));
-
         vis.visit_block_start(state);
 
-        let analysis = &mut results.analysis;
         for (statement_index, stmt) in block_data.statements.iter().enumerate() {
             let loc = Location { block, statement_index };
             analysis.apply_early_statement_effect(state, stmt, loc);

compiler/rustc_mir_dataflow/src/framework/graphviz.rs

@@ -21,7 +21,9 @@ use tracing::debug;
 use {rustc_ast as ast, rustc_graphviz as dot};
 
 use super::fmt::{DebugDiffWithAdapter, DebugWithAdapter, DebugWithContext};
-use super::{Analysis, CallReturnPlaces, Direction, Results, ResultsCursor, ResultsVisitor};
+use super::{
+    Analysis, CallReturnPlaces, Direction, Results, ResultsCursor, ResultsVisitor, visit_results,
+};
 use crate::errors::{
     DuplicateValuesFor, PathMustEndInFilename, RequiresAnArgument, UnknownFormatter,
 };
@@ -32,7 +34,8 @@ use crate::errors::{
 pub(super) fn write_graphviz_results<'tcx, A>(
     tcx: TyCtxt<'tcx>,
     body: &Body<'tcx>,
-    results: &mut Results<'tcx, A>,
+    analysis: &mut A,
+    results: &Results<A::Domain>,
     pass_name: Option<&'static str>,
 ) -> std::io::Result<()>
 where
@@ -77,7 +80,7 @@ where
 
     let mut buf = Vec::new();
 
-    let graphviz = Formatter::new(body, results, style);
+    let graphviz = Formatter::new(body, analysis, results, style);
     let mut render_opts =
         vec![dot::RenderOption::Fontname(tcx.sess.opts.unstable_opts.graphviz_font.clone())];
     if tcx.sess.opts.unstable_opts.graphviz_dark_mode {
@@ -203,10 +206,11 @@ where
 {
     body: &'mir Body<'tcx>,
     // The `RefCell` is used because `<Formatter as Labeller>::node_label`
-    // takes `&self`, but it needs to modify the results. This is also the
+    // takes `&self`, but it needs to modify the analysis. This is also the
     // reason for the `Formatter`/`BlockFormatter` split; `BlockFormatter` has
     // the operations that involve the mutation, i.e. within the `borrow_mut`.
-    results: RefCell<&'mir mut Results<'tcx, A>>,
+    analysis: RefCell<&'mir mut A>,
+    results: &'mir Results<A::Domain>,
     style: OutputStyle,
     reachable: DenseBitSet<BasicBlock>,
 }
@@ -217,11 +221,12 @@ where
 {
     fn new(
         body: &'mir Body<'tcx>,
-        results: &'mir mut Results<'tcx, A>,
+        analysis: &'mir mut A,
+        results: &'mir Results<A::Domain>,
         style: OutputStyle,
     ) -> Self {
         let reachable = traversal::reachable_as_bitset(body);
-        Formatter { body, results: results.into(), style, reachable }
+        Formatter { body, analysis: analysis.into(), results, style, reachable }
     }
 }
 
@@ -259,12 +264,12 @@ where
     }
 
     fn node_label(&self, block: &Self::Node) -> dot::LabelText<'_> {
-        let mut results = self.results.borrow_mut();
+        let analysis = &mut **self.analysis.borrow_mut();
 
-        let diffs = StateDiffCollector::run(self.body, *block, *results, self.style);
+        let diffs = StateDiffCollector::run(self.body, *block, analysis, self.results, self.style);
 
         let mut fmt = BlockFormatter {
-            cursor: results.as_results_cursor(self.body),
+            cursor: ResultsCursor::new_borrowing(self.body, analysis, self.results),
             style: self.style,
             bg: Background::Light,
         };
@@ -692,20 +697,21 @@ impl<D> StateDiffCollector<D> {
     fn run<'tcx, A>(
         body: &Body<'tcx>,
         block: BasicBlock,
-        results: &mut Results<'tcx, A>,
+        analysis: &mut A,
+        results: &Results<A::Domain>,
         style: OutputStyle,
     ) -> Self
     where
         A: Analysis<'tcx, Domain = D>,
         D: DebugWithContext<A>,
     {
         let mut collector = StateDiffCollector {
-            prev_state: results.analysis.bottom_value(body),
+            prev_state: analysis.bottom_value(body),
             after: vec![],
             before: (style == OutputStyle::BeforeAndAfter).then_some(vec![]),
         };
 
-        results.visit_with(body, std::iter::once(block), &mut collector);
+        visit_results(body, std::iter::once(block), analysis, results, &mut collector);
         collector
     }
 }