Rollup merge of #132338 - nnethercote:rm-Engine, r=nnethercote

Remove `Engine`

It's just unnecessary plumbing. Removing it results in less code, and simpler code.

r? ``@cjgillot``

Author: matthiaskrgr

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

compiler/rustc_const_eval/src/check_consts/check.rs

@@ -64,8 +64,7 @@ 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)
         });
 
@@ -94,8 +93,7 @@ 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)
         });
 
@@ -124,8 +122,7 @@ 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)
         });
 
@@ -240,8 +237,7 @@ 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_mir_dataflow/src/framework/mod.rs

@@ -7,18 +7,17 @@
 //!
 //! The `impls` module contains several examples of dataflow analyses.
 //!
-//! Create an `Engine` for your analysis using the `into_engine` method on the `Analysis` trait,
-//! then call `iterate_to_fixpoint`. From there, you can use a `ResultsCursor` to inspect the
-//! fixpoint solution to your dataflow problem, or implement the `ResultsVisitor` interface and use
-//! `visit_results`. The following example uses the `ResultsCursor` approach.
+//! Then call `iterate_to_fixpoint` on your type that impls `Analysis` to get a `Results`. From
+//! there, you can use a `ResultsCursor` to inspect the fixpoint solution to your dataflow problem,
+//! or implement the `ResultsVisitor` interface and use `visit_results`. The following example uses
+//! the `ResultsCursor` approach.
 //!
 //! ```ignore (cross-crate-imports)
-//! use rustc_const_eval::dataflow::Analysis; // Makes `into_engine` available.
+//! use rustc_const_eval::dataflow::Analysis; // Makes `iterate_to_fixpoint` available.
 //!
 //! fn do_my_analysis(tcx: TyCtxt<'tcx>, body: &mir::Body<'tcx>) {
 //!     let analysis = MyAnalysis::new()
-//!         .into_engine(tcx, body)
-//!         .iterate_to_fixpoint()
+//!         .iterate_to_fixpoint(tcx, body, None)
 //!         .into_results_cursor(body);
 //!
 //!     // Print the dataflow state *after* each statement in the start block.
@@ -34,23 +33,29 @@
 
 use std::cmp::Ordering;
 
-use rustc_index::Idx;
+use rustc_data_structures::work_queue::WorkQueue;
 use rustc_index::bit_set::{BitSet, ChunkedBitSet, HybridBitSet};
-use rustc_middle::mir::{self, BasicBlock, CallReturnPlaces, Location, TerminatorEdges};
+use rustc_index::{Idx, IndexVec};
+use rustc_middle::bug;
+use rustc_middle::mir::{self, BasicBlock, CallReturnPlaces, Location, TerminatorEdges, traversal};
 use rustc_middle::ty::TyCtxt;
+use tracing::error;
+
+use self::results::write_graphviz_results;
+use super::fmt::DebugWithContext;
 
 mod cursor;
 mod direction;
-mod engine;
 pub mod fmt;
 pub mod graphviz;
 pub mod lattice;
+mod results;
 mod visitor;
 
 pub use self::cursor::ResultsCursor;
 pub use self::direction::{Backward, Direction, Forward};
-pub use self::engine::{Engine, Results};
 pub use self::lattice::{JoinSemiLattice, MaybeReachable};
+pub use self::results::Results;
 pub use self::visitor::{ResultsVisitable, ResultsVisitor, visit_results};
 
 /// Analysis domains are all bitsets of various kinds. This trait holds
@@ -223,26 +228,92 @@ pub trait Analysis<'tcx> {
 
     /* Extension methods */
 
-    /// Creates an `Engine` to find the fixpoint for this dataflow problem.
+    /// Finds the fixpoint for this dataflow problem.
     ///
     /// You shouldn't need to override this. Its purpose is to enable method chaining like so:
     ///
     /// ```ignore (cross-crate-imports)
     /// let results = MyAnalysis::new(tcx, body)
-    ///     .into_engine(tcx, body, def_id)
-    ///     .iterate_to_fixpoint()
+    ///     .iterate_to_fixpoint(tcx, body, None)
     ///     .into_results_cursor(body);
     /// ```
-    #[inline]
-    fn into_engine<'mir>(
-        self,
+    /// You can optionally add a `pass_name` to the graphviz output for this particular run of a
+    /// dataflow analysis. Some analyses are run multiple times in the compilation pipeline.
+    /// Without a `pass_name` to differentiates them, only the results for the latest run will be
+    /// saved.
+    fn iterate_to_fixpoint<'mir>(
+        mut self,
         tcx: TyCtxt<'tcx>,
         body: &'mir mir::Body<'tcx>,
-    ) -> Engine<'mir, 'tcx, Self>
+        pass_name: Option<&'static str>,
+    ) -> Results<'tcx, Self>
     where
         Self: Sized,
+        Self::Domain: DebugWithContext<Self>,
     {
-        Engine::new(tcx, body, self)
+        let mut entry_sets =
+            IndexVec::from_fn_n(|_| self.bottom_value(body), body.basic_blocks.len());
+        self.initialize_start_block(body, &mut entry_sets[mir::START_BLOCK]);
+
+        if Self::Direction::IS_BACKWARD && entry_sets[mir::START_BLOCK] != self.bottom_value(body) {
+            bug!("`initialize_start_block` is not yet supported for backward dataflow analyses");
+        }
+
+        let mut dirty_queue: WorkQueue<BasicBlock> = WorkQueue::with_none(body.basic_blocks.len());
+
+        if Self::Direction::IS_FORWARD {
+            for (bb, _) in traversal::reverse_postorder(body) {
+                dirty_queue.insert(bb);
+            }
+        } else {
+            // Reverse post-order on the reverse CFG may generate a better iteration order for
+            // backward dataflow analyses, but probably not enough to matter.
+            for (bb, _) in traversal::postorder(body) {
+                dirty_queue.insert(bb);
+            }
+        }
+
+        // `state` is not actually used between iterations;
+        // this is just an optimization to avoid reallocating
+        // every iteration.
+        let mut state = self.bottom_value(body);
+        while let Some(bb) = dirty_queue.pop() {
+            let bb_data = &body[bb];
+
+            // Set the state to the entry state of the block.
+            // This is equivalent to `state = entry_sets[bb].clone()`,
+            // but it saves an allocation, thus improving compile times.
+            state.clone_from(&entry_sets[bb]);
+
+            // Apply the block transfer function, using the cached one if it exists.
+            let edges = Self::Direction::apply_effects_in_block(&mut self, &mut state, bb, bb_data);
+
+            Self::Direction::join_state_into_successors_of(
+                &mut self,
+                body,
+                &mut state,
+                bb,
+                edges,
+                |target: BasicBlock, state: &Self::Domain| {
+                    let set_changed = entry_sets[target].join(state);
+                    if set_changed {
+                        dirty_queue.insert(target);
+                    }
+                },
+            );
+        }
+
+        let results = Results { analysis: self, entry_sets };
+
+        if tcx.sess.opts.unstable_opts.dump_mir_dataflow {
+            let (res, results) = write_graphviz_results(tcx, body, results, pass_name);
+            if let Err(e) = res {
+                error!("Failed to write graphviz dataflow results: {}", e);
+            }
+            results
+        } else {
+            results
+        }
     }
 }
 

compiler/rustc_mir_dataflow/src/framework/engine.rs renamed to compiler/rustc_mir_dataflow/src/framework/results.rs

@@ -1,23 +1,19 @@
-//! A solver for dataflow problems.
+//! Dataflow analysis results.
 
 use std::ffi::OsString;
 use std::path::PathBuf;
 
-use rustc_data_structures::work_queue::WorkQueue;
 use rustc_hir::def_id::DefId;
 use rustc_index::IndexVec;
-use rustc_middle::bug;
 use rustc_middle::mir::{self, BasicBlock, create_dump_file, dump_enabled, traversal};
 use rustc_middle::ty::TyCtxt;
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_span::symbol::{Symbol, sym};
-use tracing::{debug, error};
+use tracing::debug;
 use {rustc_ast as ast, rustc_graphviz as dot};
 
 use super::fmt::DebugWithContext;
-use super::{
-    Analysis, Direction, JoinSemiLattice, ResultsCursor, ResultsVisitor, graphviz, visit_results,
-};
+use super::{Analysis, ResultsCursor, ResultsVisitor, graphviz, visit_results};
 use crate::errors::{
     DuplicateValuesFor, PathMustEndInFilename, RequiresAnArgument, UnknownFormatter,
 };
@@ -65,124 +61,17 @@ where
         body: &'mir mir::Body<'tcx>,
         vis: &mut impl ResultsVisitor<'mir, 'tcx, Self, Domain = A::Domain>,
     ) {
-        let blocks = mir::traversal::reachable(body);
+        let blocks = traversal::reachable(body);
         visit_results(body, blocks.map(|(bb, _)| bb), self, vis)
     }
 }
 
-/// A solver for dataflow problems.
-pub struct Engine<'mir, 'tcx, A>
-where
-    A: Analysis<'tcx>,
-{
-    tcx: TyCtxt<'tcx>,
-    body: &'mir mir::Body<'tcx>,
-    entry_sets: IndexVec<BasicBlock, A::Domain>,
-    pass_name: Option<&'static str>,
-    analysis: A,
-}
-
-impl<'mir, 'tcx, A, D> Engine<'mir, 'tcx, A>
-where
-    A: Analysis<'tcx, Domain = D>,
-    D: Clone + JoinSemiLattice,
-{
-    /// Creates a new `Engine` to solve a dataflow problem with an arbitrary transfer
-    /// function.
-    pub(crate) fn new(tcx: TyCtxt<'tcx>, body: &'mir mir::Body<'tcx>, analysis: A) -> Self {
-        let mut entry_sets =
-            IndexVec::from_fn_n(|_| analysis.bottom_value(body), body.basic_blocks.len());
-        analysis.initialize_start_block(body, &mut entry_sets[mir::START_BLOCK]);
-
-        if A::Direction::IS_BACKWARD && entry_sets[mir::START_BLOCK] != analysis.bottom_value(body)
-        {
-            bug!("`initialize_start_block` is not yet supported for backward dataflow analyses");
-        }
-
-        Engine { analysis, tcx, body, pass_name: None, entry_sets }
-    }
-
-    /// Adds an identifier to the graphviz output for this particular run of a dataflow analysis.
-    ///
-    /// Some analyses are run multiple times in the compilation pipeline. Give them a `pass_name`
-    /// to differentiate them. Otherwise, only the results for the latest run will be saved.
-    pub fn pass_name(mut self, name: &'static str) -> Self {
-        self.pass_name = Some(name);
-        self
-    }
-
-    /// Computes the fixpoint for this dataflow problem and returns it.
-    pub fn iterate_to_fixpoint(self) -> Results<'tcx, A>
-    where
-        A::Domain: DebugWithContext<A>,
-    {
-        let Engine { mut analysis, body, mut entry_sets, tcx, pass_name } = self;
-
-        let mut dirty_queue: WorkQueue<BasicBlock> = WorkQueue::with_none(body.basic_blocks.len());
-
-        if A::Direction::IS_FORWARD {
-            for (bb, _) in traversal::reverse_postorder(body) {
-                dirty_queue.insert(bb);
-            }
-        } else {
-            // Reverse post-order on the reverse CFG may generate a better iteration order for
-            // backward dataflow analyses, but probably not enough to matter.
-            for (bb, _) in traversal::postorder(body) {
-                dirty_queue.insert(bb);
-            }
-        }
-
-        // `state` is not actually used between iterations;
-        // this is just an optimization to avoid reallocating
-        // every iteration.
-        let mut state = analysis.bottom_value(body);
-        while let Some(bb) = dirty_queue.pop() {
-            let bb_data = &body[bb];
-
-            // Set the state to the entry state of the block.
-            // This is equivalent to `state = entry_sets[bb].clone()`,
-            // but it saves an allocation, thus improving compile times.
-            state.clone_from(&entry_sets[bb]);
-
-            // Apply the block transfer function, using the cached one if it exists.
-            let edges =
-                A::Direction::apply_effects_in_block(&mut analysis, &mut state, bb, bb_data);
-
-            A::Direction::join_state_into_successors_of(
-                &mut analysis,
-                body,
-                &mut state,
-                bb,
-                edges,
-                |target: BasicBlock, state: &A::Domain| {
-                    let set_changed = entry_sets[target].join(state);
-                    if set_changed {
-                        dirty_queue.insert(target);
-                    }
-                },
-            );
-        }
-
-        let results = Results { analysis, entry_sets };
-
-        if tcx.sess.opts.unstable_opts.dump_mir_dataflow {
-            let (res, results) = write_graphviz_results(tcx, body, results, pass_name);
-            if let Err(e) = res {
-                error!("Failed to write graphviz dataflow results: {}", e);
-            }
-            results
-        } else {
-            results
-        }
-    }
-}
-
 // Graphviz
 
 /// Writes a DOT file containing the results of a dataflow analysis if the user requested it via
 /// `rustc_mir` attributes and `-Z dump-mir-dataflow`. The `Result` in and the `Results` out are
 /// the same.
-fn write_graphviz_results<'tcx, A>(
+pub(super) fn write_graphviz_results<'tcx, A>(
     tcx: TyCtxt<'tcx>,
     body: &mir::Body<'tcx>,
     results: Results<'tcx, A>,