Auto merge of #132062 - nnethercote:still-more-rustc_mir_dataflow-cleanups, r=<try>

Still more `rustc_mir_dataflow` cleanups

A sequel to #118203, #118230, #118638, and #131481.

I'm pleased with this PR. It cleans up a few things that have been bugging me for a while. It took quite some effort to find these improvements.

r? `@cjgillot`

Author: bors

compiler/rustc_borrowck/src/dataflow.rs

@@ -44,7 +44,7 @@ impl<'a, 'tcx> ResultsVisitable<'tcx> for BorrowckResults<'a, 'tcx> {
     }
 
     fn reconstruct_before_statement_effect(
-        &mut self,
+        &self,
         state: &mut Self::Domain,
         stmt: &mir::Statement<'tcx>,
         loc: Location,
@@ -55,7 +55,7 @@ impl<'a, 'tcx> ResultsVisitable<'tcx> for BorrowckResults<'a, 'tcx> {
     }
 
     fn reconstruct_statement_effect(
-        &mut self,
+        &self,
         state: &mut Self::Domain,
         stmt: &mir::Statement<'tcx>,
         loc: Location,
@@ -66,7 +66,7 @@ impl<'a, 'tcx> ResultsVisitable<'tcx> for BorrowckResults<'a, 'tcx> {
     }
 
     fn reconstruct_before_terminator_effect(
-        &mut self,
+        &self,
         state: &mut Self::Domain,
         term: &mir::Terminator<'tcx>,
         loc: Location,
@@ -77,7 +77,7 @@ impl<'a, 'tcx> ResultsVisitable<'tcx> for BorrowckResults<'a, 'tcx> {
     }
 
     fn reconstruct_terminator_effect(
-        &mut self,
+        &self,
         state: &mut Self::Domain,
         term: &mir::Terminator<'tcx>,
         loc: Location,
@@ -511,7 +511,7 @@ impl<'tcx> rustc_mir_dataflow::Analysis<'tcx> for Borrows<'_, 'tcx> {
     }
 
     fn apply_before_statement_effect(
-        &mut self,
+        &self,
         trans: &mut Self::Domain,
         _statement: &mir::Statement<'tcx>,
         location: Location,
@@ -520,7 +520,7 @@ impl<'tcx> rustc_mir_dataflow::Analysis<'tcx> for Borrows<'_, 'tcx> {
     }
 
     fn apply_statement_effect(
-        &mut self,
+        &self,
         trans: &mut Self::Domain,
         stmt: &mir::Statement<'tcx>,
         location: Location,
@@ -568,7 +568,7 @@ impl<'tcx> rustc_mir_dataflow::Analysis<'tcx> for Borrows<'_, 'tcx> {
     }
 
     fn apply_before_terminator_effect(
-        &mut self,
+        &self,
         trans: &mut Self::Domain,
         _terminator: &mir::Terminator<'tcx>,
         location: Location,
@@ -577,7 +577,7 @@ impl<'tcx> rustc_mir_dataflow::Analysis<'tcx> for Borrows<'_, 'tcx> {
     }
 
     fn apply_terminator_effect<'mir>(
-        &mut self,
+        &self,
         trans: &mut Self::Domain,
         terminator: &'mir mir::Terminator<'tcx>,
         _location: Location,

compiler/rustc_borrowck/src/lib.rs

@@ -193,9 +193,7 @@ fn do_mir_borrowck<'tcx>(
         .map(|(idx, body)| (idx, MoveData::gather_moves(body, tcx, |_| true)));
 
     let mut flow_inits = MaybeInitializedPlaces::new(tcx, body, &move_data)
-        .into_engine(tcx, body)
-        .pass_name("borrowck")
-        .iterate_to_fixpoint()
+        .iterate_to_fixpoint(tcx, body, Some("borrowck"))
         .into_results_cursor(body);
 
     let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(def).is_fn_or_closure();
@@ -243,18 +241,21 @@ fn do_mir_borrowck<'tcx>(
     // usage significantly on some benchmarks.
     drop(flow_inits);
 
-    let flow_borrows = Borrows::new(tcx, body, &regioncx, &borrow_set)
-        .into_engine(tcx, body)
-        .pass_name("borrowck")
-        .iterate_to_fixpoint();
-    let flow_uninits = MaybeUninitializedPlaces::new(tcx, body, &move_data)
-        .into_engine(tcx, body)
-        .pass_name("borrowck")
-        .iterate_to_fixpoint();
-    let flow_ever_inits = EverInitializedPlaces::new(body, &move_data)
-        .into_engine(tcx, body)
-        .pass_name("borrowck")
-        .iterate_to_fixpoint();
+    let flow_borrows = Borrows::new(tcx, body, &regioncx, &borrow_set).iterate_to_fixpoint(
+        tcx,
+        body,
+        Some("borrowck"),
+    );
+    let flow_uninits = MaybeUninitializedPlaces::new(tcx, body, &move_data).iterate_to_fixpoint(
+        tcx,
+        body,
+        Some("borrowck"),
+    );
+    let flow_ever_inits = EverInitializedPlaces::new(body, &move_data).iterate_to_fixpoint(
+        tcx,
+        body,
+        Some("borrowck"),
+    );
 
     let movable_coroutine =
         // The first argument is the coroutine type passed by value
@@ -602,7 +603,7 @@ impl<'a, 'tcx, R> rustc_mir_dataflow::ResultsVisitor<'a, 'tcx, R>
 
     fn visit_statement_before_primary_effect(
         &mut self,
-        _results: &mut R,
+        _results: &R,
         state: &BorrowckDomain<'a, 'tcx>,
         stmt: &'a Statement<'tcx>,
         location: Location,
@@ -672,7 +673,7 @@ impl<'a, 'tcx, R> rustc_mir_dataflow::ResultsVisitor<'a, 'tcx, R>
 
     fn visit_terminator_before_primary_effect(
         &mut self,
-        _results: &mut R,
+        _results: &R,
         state: &BorrowckDomain<'a, 'tcx>,
         term: &'a Terminator<'tcx>,
         loc: Location,
@@ -785,7 +786,7 @@ impl<'a, 'tcx, R> rustc_mir_dataflow::ResultsVisitor<'a, 'tcx, R>
 
     fn visit_terminator_after_primary_effect(
         &mut self,
-        _results: &mut R,
+        _results: &R,
         state: &BorrowckDomain<'a, 'tcx>,
         term: &'a Terminator<'tcx>,
         loc: Location,

compiler/rustc_const_eval/src/check_consts/check.rs

@@ -63,8 +63,7 @@ impl<'mir, 'tcx> Qualifs<'mir, 'tcx> {
             let ConstCx { tcx, body, .. } = *ccx;
 
             FlowSensitiveAnalysis::new(NeedsDrop, ccx)
-                .into_engine(tcx, body)
-                .iterate_to_fixpoint()
+                .iterate_to_fixpoint(tcx, body, None)
                 .into_results_cursor(body)
         });
 
@@ -93,8 +92,7 @@ impl<'mir, 'tcx> Qualifs<'mir, 'tcx> {
             let ConstCx { tcx, body, .. } = *ccx;
 
             FlowSensitiveAnalysis::new(NeedsNonConstDrop, ccx)
-                .into_engine(tcx, body)
-                .iterate_to_fixpoint()
+                .iterate_to_fixpoint(tcx, body, None)
                 .into_results_cursor(body)
         });
 
@@ -123,8 +121,7 @@ impl<'mir, 'tcx> Qualifs<'mir, 'tcx> {
             let ConstCx { tcx, body, .. } = *ccx;
 
             FlowSensitiveAnalysis::new(HasMutInterior, ccx)
-                .into_engine(tcx, body)
-                .iterate_to_fixpoint()
+                .iterate_to_fixpoint(tcx, body, None)
                 .into_results_cursor(body)
         });
 
@@ -239,8 +236,7 @@ impl<'mir, 'tcx> Checker<'mir, 'tcx> {
                 let always_live_locals = &always_storage_live_locals(&ccx.body);
                 let mut maybe_storage_live =
                     MaybeStorageLive::new(Cow::Borrowed(always_live_locals))
-                        .into_engine(ccx.tcx, &ccx.body)
-                        .iterate_to_fixpoint()
+                        .iterate_to_fixpoint(ccx.tcx, &ccx.body, None)
                         .into_results_cursor(&ccx.body);
 
                 // And then check all `Return` in the MIR, and if a local is "maybe live" at a

compiler/rustc_const_eval/src/check_consts/resolver.rs

@@ -330,7 +330,7 @@ where
     }
 
     fn apply_statement_effect(
-        &mut self,
+        &self,
         state: &mut Self::Domain,
         statement: &mir::Statement<'tcx>,
         location: Location,
@@ -339,7 +339,7 @@ where
     }
 
     fn apply_terminator_effect<'mir>(
-        &mut self,
+        &self,
         state: &mut Self::Domain,
         terminator: &'mir mir::Terminator<'tcx>,
         location: Location,
@@ -349,7 +349,7 @@ where
     }
 
     fn apply_call_return_effect(
-        &mut self,
+        &self,
         state: &mut Self::Domain,
         block: BasicBlock,
         return_places: CallReturnPlaces<'_, 'tcx>,

compiler/rustc_mir_dataflow/src/framework/cursor.rs

@@ -1,13 +1,39 @@
 //! Random access inspection of the results of a dataflow analysis.
 
 use std::cmp::Ordering;
+use std::ops::Deref;
 
 #[cfg(debug_assertions)]
 use rustc_index::bit_set::BitSet;
 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`. This type
+/// allows either. We could use `Cow` but that would require `Results` and `A` to impl `Clone`. So
+/// this is a greatly cut-down alternative to `Cow`.
+pub enum ResultsHandle<'a, 'tcx, A>
+where
+    A: Analysis<'tcx>,
+{
+    Borrowed(&'a Results<'tcx, A>),
+    Owned(Results<'tcx, A>),
+}
+
+impl<'tcx, A> Deref for ResultsHandle<'_, 'tcx, A>
+where
+    A: Analysis<'tcx>,
+{
+    type Target = Results<'tcx, A>;
+
+    fn deref(&self) -> &Results<'tcx, A> {
+        match self {
+            ResultsHandle::Borrowed(borrowed) => borrowed,
+            ResultsHandle::Owned(owned) => owned,
+        }
+    }
+}
+
 /// 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
@@ -19,7 +45,7 @@ where
     A: Analysis<'tcx>,
 {
     body: &'mir mir::Body<'tcx>,
-    results: Results<'tcx, A>,
+    results: ResultsHandle<'mir, 'tcx, A>,
     state: A::Domain,
 
     pos: CursorPosition,
@@ -47,13 +73,8 @@ where
         self.body
     }
 
-    /// Unwraps this cursor, returning the underlying `Results`.
-    pub fn into_results(self) -> Results<'tcx, A> {
-        self.results
-    }
-
     /// Returns a new cursor that can inspect `results`.
-    pub fn new(body: &'mir mir::Body<'tcx>, results: Results<'tcx, A>) -> Self {
+    pub fn new(body: &'mir mir::Body<'tcx>, results: ResultsHandle<'mir, 'tcx, A>) -> Self {
         let bottom_value = results.analysis.bottom_value(body);
         ResultsCursor {
             body,
@@ -83,21 +104,11 @@ where
         &self.results
     }
 
-    /// Returns the underlying `Results`.
-    pub fn mut_results(&mut self) -> &mut Results<'tcx, A> {
-        &mut self.results
-    }
-
     /// Returns the `Analysis` used to generate the underlying `Results`.
     pub fn analysis(&self) -> &A {
         &self.results.analysis
     }
 
-    /// Returns the `Analysis` used to generate the underlying `Results`.
-    pub fn mut_analysis(&mut self) -> &mut A {
-        &mut self.results.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.
@@ -199,7 +210,7 @@ where
         let target_effect_index = effect.at_index(target.statement_index);
 
         A::Direction::apply_effects_in_range(
-            &mut self.results.analysis,
+            &self.results.analysis,
             &mut self.state,
             target.block,
             block_data,
@@ -214,8 +225,8 @@ 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);
+    pub fn apply_custom_effect(&mut self, f: impl FnOnce(&A, &mut A::Domain)) {
+        f(&self.results.analysis, &mut self.state);
         self.state_needs_reset = true;
     }
 }