Add a `Visitor` for dataflow results

2 files changed, 275 insertions, 0 deletions

diff --git a/src/librustc_mir/dataflow/generic/mod.rs b/src/librustc_mir/dataflow/generic/mod.rs
index ed742143150..d961ba7fffa 100644
--- a/src/librustc_mir/dataflow/generic/mod.rs
+++ b/src/librustc_mir/dataflow/generic/mod.rs
@@ -45,9 +45,12 @@ use crate::dataflow::BottomValue;
 mod cursor;
 mod engine;
 mod graphviz;
+mod visitor;
 
 pub use self::cursor::{ResultsCursor, ResultsRefCursor};
 pub use self::engine::Engine;
+pub use self::visitor::{visit_results, ResultsVisitor};
+pub use self::visitor::{BorrowckFlowState, BorrowckResults};
 
 /// A dataflow analysis that has converged to fixpoint.
 pub struct Results<'tcx, A>
diff --git a/src/librustc_mir/dataflow/generic/visitor.rs b/src/librustc_mir/dataflow/generic/visitor.rs
new file mode 100644
index 00000000000..5bad8c61a0c
--- /dev/null
+++ b/src/librustc_mir/dataflow/generic/visitor.rs
@@ -0,0 +1,272 @@
+use rustc::mir::{self, BasicBlock, Location};
+use rustc_index::bit_set::BitSet;
+
+use super::{Analysis, Results};
+use crate::dataflow::impls::{borrows::Borrows, EverInitializedPlaces, MaybeUninitializedPlaces};
+
+/// Calls the corresponding method in `ResultsVisitor` for every location in a `mir::Body` with the
+/// dataflow state at that location.
+pub fn visit_results<F>(
+    body: &'mir mir::Body<'tcx>,
+    blocks: impl IntoIterator<Item = BasicBlock>,
+    results: &impl ResultsVisitable<'tcx, FlowState = F>,
+    vis: &mut impl ResultsVisitor<'mir, 'tcx, FlowState = F>,
+) {
+    let mut state = results.new_flow_state(body);
+
+    for block in blocks {
+        let block_data = &body[block];
+        results.reset_to_block_start(&mut state, block);
+
+        for (statement_index, stmt) in block_data.statements.iter().enumerate() {
+            let loc = Location { block, statement_index };
+
+            results.reconstruct_before_statement_effect(&mut state, stmt, loc);
+            vis.visit_statement(&mut state, stmt, loc);
+
+            results.reconstruct_statement_effect(&mut state, stmt, loc);
+            vis.visit_statement_exit(&mut state, stmt, loc);
+        }
+
+        let loc = body.terminator_loc(block);
+        let term = block_data.terminator();
+
+        results.reconstruct_before_terminator_effect(&mut state, term, loc);
+        vis.visit_terminator(&mut state, term, loc);
+
+        results.reconstruct_terminator_effect(&mut state, term, loc);
+        vis.visit_terminator_exit(&mut state, term, loc);
+    }
+}
+
+pub trait ResultsVisitor<'mir, 'tcx> {
+    type FlowState;
+
+    /// Called with the `before_statement_effect` of the given statement applied to `state` but not
+    /// its `statement_effect`.
+    fn visit_statement(
+        &mut self,
+        _state: &Self::FlowState,
+        _statement: &'mir mir::Statement<'tcx>,
+        _location: Location,
+    ) {
+    }
+
+    /// Called with both the `before_statement_effect` and the `statement_effect` of the given
+    /// statement applied to `state`.
+    fn visit_statement_exit(
+        &mut self,
+        _state: &Self::FlowState,
+        _statement: &'mir mir::Statement<'tcx>,
+        _location: Location,
+    ) {
+    }
+
+    /// Called with the `before_terminator_effect` of the given terminator applied to `state` but not
+    /// its `terminator_effect`.
+    fn visit_terminator(
+        &mut self,
+        _state: &Self::FlowState,
+        _terminator: &'mir mir::Terminator<'tcx>,
+        _location: Location,
+    ) {
+    }
+
+    /// Called with both the `before_terminator_effect` and the `terminator_effect` of the given
+    /// terminator applied to `state`.
+    ///
+    /// The `call_return_effect` (if one exists) will *not* be applied to `state`.
+    fn visit_terminator_exit(
+        &mut self,
+        _state: &Self::FlowState,
+        _terminator: &'mir mir::Terminator<'tcx>,
+        _location: Location,
+    ) {
+    }
+}
+
+/// Things that can be visited by a `ResultsVisitor`.
+///
+/// This trait exists so that we can visit the results of multiple dataflow analyses simultaneously.
+/// DO NOT IMPLEMENT MANUALLY. Instead, use the `impl_visitable` macro below.
+pub trait ResultsVisitable<'tcx> {
+    type FlowState;
+
+    /// Creates an empty `FlowState` to hold the transient state for these dataflow results.
+    ///
+    /// The value of the newly created `FlowState` will be overwritten by `reset_to_block_start`
+    /// before it can be observed by a `ResultsVisitor`.
+    fn new_flow_state(&self, body: &mir::Body<'tcx>) -> Self::FlowState;
+
+    fn reset_to_block_start(&self, state: &mut Self::FlowState, block: BasicBlock);
+
+    fn reconstruct_before_statement_effect(
+        &self,
+        state: &mut Self::FlowState,
+        statement: &mir::Statement<'tcx>,
+        location: Location,
+    );
+
+    fn reconstruct_statement_effect(
+        &self,
+        state: &mut Self::FlowState,
+        statement: &mir::Statement<'tcx>,
+        location: Location,
+    );
+
+    fn reconstruct_before_terminator_effect(
+        &self,
+        state: &mut Self::FlowState,
+        terminator: &mir::Terminator<'tcx>,
+        location: Location,
+    );
+
+    fn reconstruct_terminator_effect(
+        &self,
+        state: &mut Self::FlowState,
+        terminator: &mir::Terminator<'tcx>,
+        location: Location,
+    );
+}
+
+impl<'tcx, A> ResultsVisitable<'tcx> for Results<'tcx, A>
+where
+    A: Analysis<'tcx>,
+{
+    type FlowState = BitSet<A::Idx>;
+
+    fn new_flow_state(&self, body: &mir::Body<'tcx>) -> Self::FlowState {
+        BitSet::new_empty(self.analysis.bits_per_block(body))
+    }
+
+    fn reset_to_block_start(&self, state: &mut Self::FlowState, block: BasicBlock) {
+        state.overwrite(&self.entry_set_for_block(block));
+    }
+
+    fn reconstruct_before_statement_effect(
+        &self,
+        state: &mut Self::FlowState,
+        stmt: &mir::Statement<'tcx>,
+        loc: Location,
+    ) {
+        self.analysis.apply_before_statement_effect(state, stmt, loc);
+    }
+
+    fn reconstruct_statement_effect(
+        &self,
+        state: &mut Self::FlowState,
+        stmt: &mir::Statement<'tcx>,
+        loc: Location,
+    ) {
+        self.analysis.apply_statement_effect(state, stmt, loc);
+    }
+
+    fn reconstruct_before_terminator_effect(
+        &self,
+        state: &mut Self::FlowState,
+        term: &mir::Terminator<'tcx>,
+        loc: Location,
+    ) {
+        self.analysis.apply_before_terminator_effect(state, term, loc);
+    }
+
+    fn reconstruct_terminator_effect(
+        &self,
+        state: &mut Self::FlowState,
+        term: &mir::Terminator<'tcx>,
+        loc: Location,
+    ) {
+        self.analysis.apply_terminator_effect(state, term, loc);
+    }
+}
+
+/// A tuple with named fields that can hold either the results or the transient state of the
+/// dataflow analyses used by the borrow checker.
+#[derive(Debug)]
+pub struct BorrowckAnalyses<B, U, E> {
+    pub borrows: B,
+    pub uninits: U,
+    pub ever_inits: E,
+}
+
+/// The results of the dataflow analyses used by the borrow checker.
+pub type BorrowckResults<'mir, 'tcx> = BorrowckAnalyses<
+    Results<'tcx, Borrows<'mir, 'tcx>>,
+    Results<'tcx, MaybeUninitializedPlaces<'mir, 'tcx>>,
+    Results<'tcx, EverInitializedPlaces<'mir, 'tcx>>,
+>;
+
+/// The transient state of the dataflow analyses used by the borrow checker.
+pub type BorrowckFlowState<'mir, 'tcx> =
+    <BorrowckResults<'mir, 'tcx> as ResultsVisitable<'tcx>>::FlowState;
+
+macro_rules! impl_visitable {
+    ( $(
+        $T:ident { $( $field:ident : $A:ident ),* $(,)? }
+    )* ) => { $(
+        impl<'tcx, $($A),*> ResultsVisitable<'tcx> for $T<$( Results<'tcx, $A> ),*>
+        where
+            $( $A: Analysis<'tcx>, )*
+        {
+            type FlowState = $T<$( BitSet<$A::Idx> ),*>;
+
+            fn new_flow_state(&self, body: &mir::Body<'tcx>) -> Self::FlowState {
+                $T {
+                    $( $field: BitSet::new_empty(self.$field.analysis.bits_per_block(body)) ),*
+                }
+            }
+
+            fn reset_to_block_start(
+                &self,
+                state: &mut Self::FlowState,
+                block: BasicBlock,
+            ) {
+                $( state.$field.overwrite(&self.$field.entry_sets[block]); )*
+            }
+
+            fn reconstruct_before_statement_effect(
+                &self,
+                state: &mut Self::FlowState,
+                stmt: &mir::Statement<'tcx>,
+                loc: Location,
+            ) {
+                $( self.$field.analysis
+                    .apply_before_statement_effect(&mut state.$field, stmt, loc); )*
+            }
+
+            fn reconstruct_statement_effect(
+                &self,
+                state: &mut Self::FlowState,
+                stmt: &mir::Statement<'tcx>,
+                loc: Location,
+            ) {
+                $( self.$field.analysis
+                    .apply_statement_effect(&mut state.$field, stmt, loc); )*
+            }
+
+            fn reconstruct_before_terminator_effect(
+                &self,
+                state: &mut Self::FlowState,
+                term: &mir::Terminator<'tcx>,
+                loc: Location,
+            ) {
+                $( self.$field.analysis
+                    .apply_before_terminator_effect(&mut state.$field, term, loc); )*
+            }
+
+            fn reconstruct_terminator_effect(
+                &self,
+                state: &mut Self::FlowState,
+                term: &mir::Terminator<'tcx>,
+                loc: Location,
+            ) {
+                $( self.$field.analysis
+                    .apply_terminator_effect(&mut state.$field, term, loc); )*
+            }
+        }
+    )* }
+}
+
+impl_visitable! {
+    BorrowckAnalyses { borrows: B, uninits: U, ever_inits: E }
+}