Eliminate BitwiseOperator.

`BitwiseOperator` is an unnecessarily low-level thing. This commit
replaces it with `BitSetOperator`, which works on `BitSet`s instead of
words. Within `bit_set.rs`, the commit eliminates `Intersect`, `Union`,
and `Subtract` by instead passing a function to `bitwise()`.

Author: nnethercote

src/librustc_data_structures/bit_set.rs

@@ -160,7 +160,7 @@ impl<T: Idx> BitSet<T> {
     /// Set `self = self & other` and return true if `self` changed.
     /// (i.e., if any bits were removed).
     pub fn intersect(&mut self, other: &BitSet<T>) -> bool {
-        bitwise(self.words_mut(), other.words(), &Intersect)
+        bitwise(self.words_mut(), other.words(), |a, b| { a & b })
     }
 
     /// Get a slice of the underlying words.
@@ -241,13 +241,13 @@ pub trait SubtractFromBitSet<T: Idx> {
 
 impl<T: Idx> UnionIntoBitSet<T> for BitSet<T> {
     fn union_into(&self, other: &mut BitSet<T>) -> bool {
-        bitwise(other.words_mut(), self.words(), &Union)
+        bitwise(other.words_mut(), self.words(), |a, b| { a | b })
     }
 }
 
 impl<T: Idx> SubtractFromBitSet<T> for BitSet<T> {
     fn subtract_from(&self, other: &mut BitSet<T>) -> bool {
-        bitwise(other.words_mut(), self.words(), &Subtract)
+        bitwise(other.words_mut(), self.words(), |a, b| { a & !b })
     }
 }
 
@@ -300,43 +300,26 @@ impl<'a, T: Idx> Iterator for BitIter<'a, T> {
     }
 }
 
-pub trait BitwiseOperator {
-    /// Applies some bit-operation pointwise to each of the bits in the two inputs.
-    fn join(&self, pred1: Word, pred2: Word) -> Word;
+pub trait BitSetOperator {
+    /// Combine one bitset into another.
+    fn join<T: Idx>(&self, inout_set: &mut BitSet<T>, in_set: &BitSet<T>) -> bool;
 }
 
 #[inline]
-pub fn bitwise<Op: BitwiseOperator>(out_vec: &mut [Word], in_vec: &[Word], op: &Op) -> bool
+fn bitwise<Op>(out_vec: &mut [Word], in_vec: &[Word], op: Op) -> bool
+    where Op: Fn(Word, Word) -> Word
 {
     assert_eq!(out_vec.len(), in_vec.len());
     let mut changed = false;
     for (out_elem, in_elem) in out_vec.iter_mut().zip(in_vec.iter()) {
         let old_val = *out_elem;
-        let new_val = op.join(old_val, *in_elem);
+        let new_val = op(old_val, *in_elem);
         *out_elem = new_val;
         changed |= old_val != new_val;
     }
     changed
 }
 
-pub struct Intersect;
-impl BitwiseOperator for Intersect {
-    #[inline]
-    fn join(&self, a: Word, b: Word) -> Word { a & b }
-}
-
-pub struct Union;
-impl BitwiseOperator for Union {
-    #[inline]
-    fn join(&self, a: Word, b: Word) -> Word { a | b }
-}
-
-pub struct Subtract;
-impl BitwiseOperator for Subtract {
-    #[inline]
-    fn join(&self, a: Word, b: Word) -> Word { a & !b }
-}
-
 const SPARSE_MAX: usize = 8;
 
 /// A fixed-size bitset type with a sparse representation and a maximum of

src/librustc_mir/dataflow/impls/borrowed_locals.rs

@@ -80,10 +80,10 @@ impl<'a, 'tcx> BitDenotation for HaveBeenBorrowedLocals<'a, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> BitwiseOperator for HaveBeenBorrowedLocals<'a, 'tcx> {
+impl<'a, 'tcx> BitSetOperator for HaveBeenBorrowedLocals<'a, 'tcx> {
     #[inline]
-    fn join(&self, pred1: Word, pred2: Word) -> Word {
-        pred1 | pred2 // "maybe" means we union effects of both preds
+    fn join<T: Idx>(&self, inout_set: &mut BitSet<T>, in_set: &BitSet<T>) -> bool {
+        inout_set.union(in_set) // "maybe" means we union effects of both preds
     }
 }
 

src/librustc_mir/dataflow/impls/borrows.rs

@@ -20,9 +20,9 @@ use rustc::ty::TyCtxt;
 use rustc::ty::{RegionKind, RegionVid};
 use rustc::ty::RegionKind::ReScope;
 
-use rustc_data_structures::bit_set::{BitSet, BitwiseOperator, Word};
+use rustc_data_structures::bit_set::{BitSet, BitSetOperator};
 use rustc_data_structures::fx::FxHashMap;
-use rustc_data_structures::indexed_vec::IndexVec;
+use rustc_data_structures::indexed_vec::{Idx, IndexVec};
 use rustc_data_structures::sync::Lrc;
 
 use dataflow::{BitDenotation, BlockSets, InitialFlow};
@@ -410,10 +410,10 @@ impl<'a, 'gcx, 'tcx> BitDenotation for Borrows<'a, 'gcx, 'tcx> {
     }
 }
 
-impl<'a, 'gcx, 'tcx> BitwiseOperator for Borrows<'a, 'gcx, 'tcx> {
+impl<'a, 'gcx, 'tcx> BitSetOperator for Borrows<'a, 'gcx, 'tcx> {
     #[inline]
-    fn join(&self, pred1: Word, pred2: Word) -> Word {
-        pred1 | pred2 // union effects of preds when computing reservations
+    fn join<T: Idx>(&self, inout_set: &mut BitSet<T>, in_set: &BitSet<T>) -> bool {
+        inout_set.union(in_set) // "maybe" means we union effects of both preds
     }
 }
 

src/librustc_mir/dataflow/impls/mod.rs

@@ -14,7 +14,7 @@
 
 use rustc::ty::TyCtxt;
 use rustc::mir::{self, Mir, Location};
-use rustc_data_structures::bit_set::{BitSet, BitwiseOperator, Word};
+use rustc_data_structures::bit_set::{BitSet, BitSetOperator};
 use rustc_data_structures::indexed_vec::Idx;
 
 use super::MoveDataParamEnv;
@@ -549,31 +549,31 @@ impl<'a, 'gcx, 'tcx> BitDenotation for EverInitializedPlaces<'a, 'gcx, 'tcx> {
     }
 }
 
-impl<'a, 'gcx, 'tcx> BitwiseOperator for MaybeInitializedPlaces<'a, 'gcx, 'tcx> {
+impl<'a, 'gcx, 'tcx> BitSetOperator for MaybeInitializedPlaces<'a, 'gcx, 'tcx> {
     #[inline]
-    fn join(&self, pred1: Word, pred2: Word) -> Word {
-        pred1 | pred2 // "maybe" means we union effects of both preds
+    fn join<T: Idx>(&self, inout_set: &mut BitSet<T>, in_set: &BitSet<T>) -> bool {
+        inout_set.union(in_set) // "maybe" means we union effects of both preds
     }
 }
 
-impl<'a, 'gcx, 'tcx> BitwiseOperator for MaybeUninitializedPlaces<'a, 'gcx, 'tcx> {
+impl<'a, 'gcx, 'tcx> BitSetOperator for MaybeUninitializedPlaces<'a, 'gcx, 'tcx> {
     #[inline]
-    fn join(&self, pred1: Word, pred2: Word) -> Word {
-        pred1 | pred2 // "maybe" means we union effects of both preds
+    fn join<T: Idx>(&self, inout_set: &mut BitSet<T>, in_set: &BitSet<T>) -> bool {
+        inout_set.union(in_set) // "maybe" means we union effects of both preds
     }
 }
 
-impl<'a, 'gcx, 'tcx> BitwiseOperator for DefinitelyInitializedPlaces<'a, 'gcx, 'tcx> {
+impl<'a, 'gcx, 'tcx> BitSetOperator for DefinitelyInitializedPlaces<'a, 'gcx, 'tcx> {
     #[inline]
-    fn join(&self, pred1: Word, pred2: Word) -> Word {
-        pred1 & pred2 // "definitely" means we intersect effects of both preds
+    fn join<T: Idx>(&self, inout_set: &mut BitSet<T>, in_set: &BitSet<T>) -> bool {
+        inout_set.intersect(in_set) // "definitely" means we intersect effects of both preds
     }
 }
 
-impl<'a, 'gcx, 'tcx> BitwiseOperator for EverInitializedPlaces<'a, 'gcx, 'tcx> {
+impl<'a, 'gcx, 'tcx> BitSetOperator for EverInitializedPlaces<'a, 'gcx, 'tcx> {
     #[inline]
-    fn join(&self, pred1: Word, pred2: Word) -> Word {
-        pred1 | pred2 // inits from both preds are in scope
+    fn join<T: Idx>(&self, inout_set: &mut BitSet<T>, in_set: &BitSet<T>) -> bool {
+        inout_set.union(in_set) // inits from both preds are in scope
     }
 }
 

src/librustc_mir/dataflow/impls/storage_liveness.rs

@@ -67,10 +67,10 @@ impl<'a, 'tcx> BitDenotation for MaybeStorageLive<'a, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> BitwiseOperator for MaybeStorageLive<'a, 'tcx> {
+impl<'a, 'tcx> BitSetOperator for MaybeStorageLive<'a, 'tcx> {
     #[inline]
-    fn join(&self, pred1: Word, pred2: Word) -> Word {
-        pred1 | pred2 // "maybe" means we union effects of both preds
+    fn join<T: Idx>(&self, inout_set: &mut BitSet<T>, in_set: &BitSet<T>) -> bool {
+        inout_set.union(in_set) // "maybe" means we union effects of both preds
     }
 }
 

src/librustc_mir/dataflow/mod.rs

@@ -10,7 +10,7 @@
 
 use syntax::ast::{self, MetaItem};
 
-use rustc_data_structures::bit_set::{bitwise, BitwiseOperator, BitSet, HybridBitSet};
+use rustc_data_structures::bit_set::{BitSet, BitSetOperator, HybridBitSet};
 use rustc_data_structures::indexed_vec::Idx;
 use rustc_data_structures::work_queue::WorkQueue;
 
@@ -561,7 +561,7 @@ pub trait InitialFlow {
     fn bottom_value() -> bool;
 }
 
-pub trait BitDenotation: BitwiseOperator {
+pub trait BitDenotation: BitSetOperator {
     /// Specifies what index type is used to access the bitvector.
     type Idx: Idx;
 
@@ -830,10 +830,8 @@ impl<'a, 'tcx: 'a, D> DataflowAnalysis<'a, 'tcx, D> where D: BitDenotation
                                          in_out: &BitSet<D::Idx>,
                                          bb: mir::BasicBlock,
                                          dirty_queue: &mut WorkQueue<mir::BasicBlock>) {
-        let entry_set = self.flow_state.sets.for_block(bb.index()).on_entry;
-        let set_changed = bitwise(entry_set.words_mut(),
-                                  in_out.words(),
-                                  &self.flow_state.operator);
+        let entry_set = &mut self.flow_state.sets.for_block(bb.index()).on_entry;
+        let set_changed = self.flow_state.operator.join(entry_set, &in_out);
         if set_changed {
             dirty_queue.insert(bb);
         }