Remove Engine.

It's no longer needed. `Engine::iterate_to_fixpoint` can be inlined into
`Analysis::iterate_to_fixpoint` and removed. The commit also renames
`engine.rs` as `results.rs`.

Author: nnethercote

Diff for: compiler/rustc_mir_dataflow/src/framework/mod.rs

@@ -33,25 +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
@@ -238,7 +242,7 @@ pub trait Analysis<'tcx> {
     /// Without a `pass_name` to differentiates them, only the results for the latest run will be
     /// saved.
     fn iterate_to_fixpoint<'mir>(
-        self,
+        mut self,
         tcx: TyCtxt<'tcx>,
         body: &'mir mir::Body<'tcx>,
         pass_name: Option<&'static str>,
@@ -247,7 +251,69 @@ pub trait Analysis<'tcx> {
         Self: Sized,
         Self::Domain: DebugWithContext<Self>,
     {
-        Engine::iterate_to_fixpoint(tcx, body, self, pass_name)
+        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
+        }
     }
 }
 

Diff for: 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,
 };
@@ -65,101 +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;
-
-impl Engine {
-    /// Creates a new `Engine` to solve a dataflow problem with an arbitrary transfer
-    /// function.
-    pub(crate) fn iterate_to_fixpoint<'mir, 'tcx, A>(
-        tcx: TyCtxt<'tcx>,
-        body: &'mir mir::Body<'tcx>,
-        mut analysis: A,
-        pass_name: Option<&'static str>,
-    ) -> Results<'tcx, A>
-    where
-        A: Analysis<'tcx>,
-        A::Domain: DebugWithContext<A> + Clone + JoinSemiLattice,
-    {
-        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");
-        }
-
-        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>,

Diff for: compiler/rustc_mir_dataflow/src/lib.rs

@@ -18,9 +18,9 @@ pub use self::drop_flag_effects::{
     move_path_children_matching, on_all_children_bits, on_lookup_result_bits,
 };
 pub use self::framework::{
-    Analysis, Backward, Direction, Engine, Forward, GenKill, JoinSemiLattice, MaybeReachable,
-    Results, ResultsCursor, ResultsVisitable, ResultsVisitor, SwitchIntEdgeEffects, fmt, graphviz,
-    lattice, visit_results,
+    Analysis, Backward, Direction, Forward, GenKill, JoinSemiLattice, MaybeReachable, Results,
+    ResultsCursor, ResultsVisitable, ResultsVisitor, SwitchIntEdgeEffects, fmt, graphviz, lattice,
+    visit_results,
 };
 use self::move_paths::MoveData;