1% local win: single pass dataflow

Author: lqd

compiler/rustc_borrowck/src/dataflow.rs

@@ -39,9 +39,10 @@ impl<'a, 'tcx> Analysis<'tcx> for Borrowck<'a, 'tcx> {
         }
     }
 
-    fn initialize_start_block(&self, _body: &mir::Body<'tcx>, _state: &mut Self::Domain) {
-        // This is only reachable from `iterate_to_fixpoint`, which this analysis doesn't use.
-        unreachable!();
+    fn initialize_start_block(&self, body: &mir::Body<'tcx>, state: &mut Self::Domain) {
+        self.borrows.initialize_start_block(body, &mut state.borrows);
+        self.uninits.initialize_start_block(body, &mut state.uninits);
+        self.ever_inits.initialize_start_block(body, &mut state.ever_inits);
     }
 
     fn apply_early_statement_effect(
@@ -83,30 +84,36 @@ impl<'a, 'tcx> Analysis<'tcx> for Borrowck<'a, 'tcx> {
         term: &'mir mir::Terminator<'tcx>,
         loc: Location,
     ) -> TerminatorEdges<'mir, 'tcx> {
-        self.borrows.apply_primary_terminator_effect(&mut state.borrows, term, loc);
-        self.uninits.apply_primary_terminator_effect(&mut state.uninits, term, loc);
-        self.ever_inits.apply_primary_terminator_effect(&mut state.ever_inits, term, loc);
+        let _edges1 = self.borrows.apply_primary_terminator_effect(&mut state.borrows, term, loc);
+        let _edges2 = self.uninits.apply_primary_terminator_effect(&mut state.uninits, term, loc);
+        let edges3 =
+            self.ever_inits.apply_primary_terminator_effect(&mut state.ever_inits, term, loc);
 
-        // This return value doesn't matter. It's only used by `iterate_to_fixpoint`, which this
-        // analysis doesn't use.
-        TerminatorEdges::None
+        // assert_eq!(_edges1, _edges2);
+        // assert_eq!(_edges2, edges3);
+
+        edges3
     }
 
     fn apply_call_return_effect(
         &mut self,
-        _state: &mut Self::Domain,
-        _block: BasicBlock,
-        _return_places: CallReturnPlaces<'_, 'tcx>,
+        state: &mut Self::Domain,
+        block: BasicBlock,
+        return_places: CallReturnPlaces<'_, 'tcx>,
     ) {
-        // This is only reachable from `iterate_to_fixpoint`, which this analysis doesn't use.
-        unreachable!();
+        self.borrows.apply_call_return_effect(&mut state.borrows, block, return_places);
+        self.uninits.apply_call_return_effect(&mut state.uninits, block, return_places);
+        self.ever_inits.apply_call_return_effect(&mut state.ever_inits, block, return_places);
     }
 }
 
 impl JoinSemiLattice for BorrowckDomain {
-    fn join(&mut self, _other: &Self) -> bool {
-        // This is only reachable from `iterate_to_fixpoint`, which this analysis doesn't use.
-        unreachable!();
+    fn join(&mut self, other: &Self) -> bool {
+        let mut changed = false;
+        changed |= self.borrows.join(&other.borrows);
+        changed |= self.uninits.join(&other.uninits);
+        changed |= self.ever_inits.join(&other.ever_inits);
+        changed
     }
 }
 

compiler/rustc_borrowck/src/lib.rs

@@ -436,15 +436,19 @@ fn do_mir_borrowck<'tcx>(
     // Compute and report region errors, if any.
     mbcx.report_region_errors(nll_errors);
 
-    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_analysis,
-        &flow_entry_states,
-        &mut mbcx,
-    );
+    if body.basic_blocks.is_cfg_cyclic() {
+        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_analysis,
+            &flow_entry_states,
+            &mut mbcx,
+        );
+    } else {
+        compute_dataflow(tcx, body, &move_data, &borrow_set, &regioncx, &mut mbcx);
+    }
 
     mbcx.report_move_errors();
 
@@ -497,6 +501,186 @@ fn do_mir_borrowck<'tcx>(
     result
 }
 
+fn compute_dataflow<'a, 'tcx>(
+    tcx: TyCtxt<'tcx>,
+    body: &'a Body<'tcx>,
+
+    move_data: &'a MoveData<'tcx>,
+    borrow_set: &'a BorrowSet<'tcx>,
+    regioncx: &RegionInferenceContext<'tcx>,
+
+    vis: &mut MirBorrowckCtxt<'a, '_, 'tcx>,
+) {
+    let borrows = Borrows::new(tcx, body, regioncx, borrow_set);
+    let uninits = MaybeUninitializedPlaces::new(tcx, body, move_data);
+    let ever_inits = EverInitializedPlaces::new(body, move_data);
+
+    let mut analysis = Borrowck { borrows, uninits, ever_inits };
+
+    // Set up lazy state for the CFG
+    use rustc_middle::mir;
+    use rustc_mir_dataflow::JoinSemiLattice;
+
+    let mut results: IndexVec<BasicBlock, Option<BorrowckDomain>> =
+        IndexVec::from_elem_n(None, body.basic_blocks.len());
+
+    // Ensure the start block has some state in it;
+    results[mir::START_BLOCK] = Some(analysis.bottom_value(body));
+    analysis.initialize_start_block(body, results[mir::START_BLOCK].as_mut().unwrap());
+
+    for (_idx, (block, block_data)) in traversal::reverse_postorder(body).enumerate() {
+        // Apply effects in block
+        let mut block_state = results[block].take().unwrap_or_else(|| analysis.bottom_value(body));
+
+        vis.visit_block_start(&mut block_state);
+
+        for (statement_index, statement) in block_data.statements.iter().enumerate() {
+            let location = Location { block, statement_index };
+            analysis.apply_early_statement_effect(&mut block_state, statement, location);
+            vis.visit_after_early_statement_effect(
+                &mut analysis,
+                &block_state,
+                statement,
+                location,
+            );
+
+            analysis.apply_primary_statement_effect(&mut block_state, statement, location);
+            vis.visit_after_primary_statement_effect(
+                &mut analysis,
+                &block_state,
+                statement,
+                location,
+            );
+        }
+        let terminator = block_data.terminator();
+        let location = Location { block, statement_index: block_data.statements.len() };
+        analysis.apply_early_terminator_effect(&mut block_state, terminator, location);
+        vis.visit_after_early_terminator_effect(&mut analysis, &block_state, terminator, location);
+
+        let edges =
+            analysis.apply_primary_terminator_effect(&mut block_state, terminator, location);
+        vis.visit_after_primary_terminator_effect(
+            &mut analysis,
+            &block_state,
+            terminator,
+            location,
+        );
+
+        // notify visitor the block is ready
+        vis.visit_block_end(&mut block_state);
+
+        match edges {
+            TerminatorEdges::None => {}
+            TerminatorEdges::Single(target) => match results[target].as_mut() {
+                None => {
+                    results[target] = Some(block_state);
+                }
+                Some(existing_state) => {
+                    existing_state.join(&block_state);
+                }
+            },
+            TerminatorEdges::Double(target, unwind) if target == unwind => {
+                // wtf
+                match results[target].as_mut() {
+                    None => {
+                        results[target] = Some(block_state);
+                    }
+                    Some(existing_state) => {
+                        existing_state.join(&block_state);
+                    }
+                }
+            }
+            TerminatorEdges::Double(target, unwind) => match results.pick2_mut(target, unwind) {
+                (None, None) => {
+                    results[target] = Some(block_state.clone());
+                    results[unwind] = Some(block_state);
+                }
+                (None, Some(unwind_state)) => {
+                    unwind_state.join(&block_state);
+                    results[target] = Some(block_state);
+                }
+                (Some(target_state), None) => {
+                    target_state.join(&block_state);
+                    results[unwind] = Some(block_state);
+                }
+                (Some(target_state), Some(unwind_state)) => {
+                    target_state.join(&block_state);
+                    unwind_state.join(&block_state);
+                }
+            },
+            TerminatorEdges::AssignOnReturn { return_, cleanup, place } => {
+                // This must be done *first*, otherwise the unwind path will see the assignments.
+                if let Some(cleanup) = cleanup {
+                    match results[cleanup].as_mut() {
+                        None => {
+                            results[cleanup] = Some(block_state.clone());
+                        }
+                        Some(existing_state) => {
+                            existing_state.join(&block_state);
+                        }
+                    }
+                }
+
+                if !return_.is_empty() {
+                    analysis.apply_call_return_effect(&mut block_state, block, place);
+
+                    // fixme: optimize, if we've merged the previous target states instead
+                    // of moving, we don't need to clone it.
+
+                    let target_count = return_.len();
+                    for &target in return_.iter().take(target_count - 1) {
+                        match results[target].as_mut() {
+                            None => {
+                                results[target] = Some(block_state.clone());
+                            }
+                            Some(existing_state) => {
+                                existing_state.join(&block_state);
+                            }
+                        }
+                    }
+
+                    let target = *return_.last().unwrap();
+                    match results[target].as_mut() {
+                        None => {
+                            results[target] = Some(block_state.clone());
+                        }
+                        Some(existing_state) => {
+                            existing_state.join(&block_state);
+                        }
+                    }
+                }
+            }
+            TerminatorEdges::SwitchInt { targets, discr } => {
+                if let Some(_data) = analysis.get_switch_int_data(block, discr) {
+                    todo!("wat. this is unused in tests");
+                } else {
+                    let target_count = targets.all_targets().len();
+                    for &target in targets.all_targets().iter().take(target_count - 1) {
+                        match results[target].as_mut() {
+                            None => {
+                                results[target] = Some(block_state.clone());
+                            }
+                            Some(existing_state) => {
+                                existing_state.join(&block_state);
+                            }
+                        }
+                    }
+
+                    let target = *targets.all_targets().last().unwrap();
+                    match results[target].as_mut() {
+                        None => {
+                            results[target] = Some(block_state.clone());
+                        }
+                        Some(existing_state) => {
+                            existing_state.join(&block_state);
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
 fn get_flow_results<'a, 'tcx>(
     tcx: TyCtxt<'tcx>,
     body: &'a Body<'tcx>,