Auto merge of #52335 - nnethercote:BitSlice-fixes, r=nikomatsakis

`BitSlice` fixes

`propagate_bits_into_entry_set_for` and `BitSlice::bitwise` are hot for some benchmarks under NLL. I tried and failed to speed them up. (Increasing the size of `bit_slice::Word` from `usize` to `u128` caused a slowdown, even though decreasing the size of `bitvec::Word` from `u128` to `u64` also caused a slowdown. Weird.)

Anyway, along the way I fixed up several problems in and around the `BitSlice` code.

r? @nikomatsakis

Author: bors

Diff for: src/librustc_data_structures/bitslice.rs

@@ -28,9 +28,9 @@ impl BitSlice for [Word] {
     fn clear_bit(&mut self, idx: usize) -> bool {
         let words = self;
         debug!("clear_bit: words={} idx={}",
-               bits_to_string(words, words.len() * mem::size_of::<Word>()), bit_str(idx));
+               bits_to_string(words, words.len() * mem::size_of::<Word>() * 8), idx);
         let BitLookup { word, bit_in_word, bit_mask } = bit_lookup(idx);
-        debug!("word={} bit_in_word={} bit_mask={}", word, bit_in_word, bit_mask);
+        debug!("word={} bit_in_word={} bit_mask=0x{:x}", word, bit_in_word, bit_mask);
         let oldv = words[word];
         let newv = oldv & !bit_mask;
         words[word] = newv;
@@ -42,7 +42,7 @@ impl BitSlice for [Word] {
     fn set_bit(&mut self, idx: usize) -> bool {
         let words = self;
         debug!("set_bit: words={} idx={}",
-               bits_to_string(words, words.len() * mem::size_of::<Word>()), bit_str(idx));
+               bits_to_string(words, words.len() * mem::size_of::<Word>() * 8), idx);
         let BitLookup { word, bit_in_word, bit_mask } = bit_lookup(idx);
         debug!("word={} bit_in_word={} bit_mask={}", word, bit_in_word, bit_mask);
         let oldv = words[word];
@@ -78,13 +78,6 @@ fn bit_lookup(bit: usize) -> BitLookup {
     BitLookup { word: word, bit_in_word: bit_in_word, bit_mask: bit_mask }
 }
 
-
-fn bit_str(bit: Word) -> String {
-    let byte = bit >> 3;
-    let lobits = 1 << (bit & 0b111);
-    format!("[{}:{}-{:02x}]", bit, byte, lobits)
-}
-
 pub fn bits_to_string(words: &[Word], bits: usize) -> String {
     let mut result = String::new();
     let mut sep = '[';
@@ -95,7 +88,7 @@ pub fn bits_to_string(words: &[Word], bits: usize) -> String {
     let mut i = 0;
     for &word in words.iter() {
         let mut v = word;
-        loop { // for each byte in `v`:
+        for _ in 0..mem::size_of::<Word>() { // for each byte in `v`:
             let remain = bits - i;
             // If less than a byte remains, then mask just that many bits.
             let mask = if remain <= 8 { (1 << remain) - 1 } else { 0xFF };
@@ -110,14 +103,15 @@ pub fn bits_to_string(words: &[Word], bits: usize) -> String {
             i += 8;
             sep = '-';
         }
+        sep = '|';
     }
     result.push(']');
     return result
 }
 
 #[inline]
-pub fn bitwise<Op:BitwiseOperator>(out_vec: &mut [usize],
-                                   in_vec: &[usize],
+pub fn bitwise<Op:BitwiseOperator>(out_vec: &mut [Word],
+                                   in_vec: &[Word],
                                    op: &Op) -> bool {
     assert_eq!(out_vec.len(), in_vec.len());
     let mut changed = false;
@@ -132,21 +126,21 @@ pub fn bitwise<Op:BitwiseOperator>(out_vec: &mut [usize],
 
 pub trait BitwiseOperator {
     /// Applies some bit-operation pointwise to each of the bits in the two inputs.
-    fn join(&self, pred1: usize, pred2: usize) -> usize;
+    fn join(&self, pred1: Word, pred2: Word) -> Word;
 }
 
 pub struct Intersect;
 impl BitwiseOperator for Intersect {
     #[inline]
-    fn join(&self, a: usize, b: usize) -> usize { a & b }
+    fn join(&self, a: Word, b: Word) -> Word { a & b }
 }
 pub struct Union;
 impl BitwiseOperator for Union {
     #[inline]
-    fn join(&self, a: usize, b: usize) -> usize { a | b }
+    fn join(&self, a: Word, b: Word) -> Word { a | b }
 }
 pub struct Subtract;
 impl BitwiseOperator for Subtract {
     #[inline]
-    fn join(&self, a: usize, b: usize) -> usize { a & !b }
+    fn join(&self, a: Word, b: Word) -> Word { a & !b }
 }

Diff for: src/librustc_mir/dataflow/impls/borrowed_locals.rs

@@ -74,7 +74,7 @@ impl<'a, 'tcx> BitDenotation for HaveBeenBorrowedLocals<'a, 'tcx> {
 
 impl<'a, 'tcx> BitwiseOperator for HaveBeenBorrowedLocals<'a, 'tcx> {
     #[inline]
-    fn join(&self, pred1: usize, pred2: usize) -> usize {
+    fn join(&self, pred1: Word, pred2: Word) -> Word {
         pred1 | pred2 // "maybe" means we union effects of both preds
     }
 }

Diff for: src/librustc_mir/dataflow/impls/borrows.rs

@@ -20,7 +20,7 @@ use rustc::ty::TyCtxt;
 use rustc::ty::{RegionKind, RegionVid};
 use rustc::ty::RegionKind::ReScope;
 
-use rustc_data_structures::bitslice::BitwiseOperator;
+use rustc_data_structures::bitslice::{BitwiseOperator, Word};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::indexed_set::IdxSet;
 use rustc_data_structures::indexed_vec::IndexVec;
@@ -370,7 +370,7 @@ impl<'a, 'gcx, 'tcx> BitDenotation for Borrows<'a, 'gcx, 'tcx> {
 
 impl<'a, 'gcx, 'tcx> BitwiseOperator for Borrows<'a, 'gcx, 'tcx> {
     #[inline]
-    fn join(&self, pred1: usize, pred2: usize) -> usize {
+    fn join(&self, pred1: Word, pred2: Word) -> Word {
         pred1 | pred2 // union effects of preds when computing reservations
     }
 }

Diff for: 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::bitslice::{BitwiseOperator};
+use rustc_data_structures::bitslice::{BitwiseOperator, Word};
 use rustc_data_structures::indexed_set::{IdxSet};
 use rustc_data_structures::indexed_vec::Idx;
 
@@ -663,35 +663,35 @@ impl<'a, 'gcx, 'tcx> BitDenotation for EverInitializedPlaces<'a, 'gcx, 'tcx> {
 
 impl<'a, 'gcx, 'tcx> BitwiseOperator for MaybeInitializedPlaces<'a, 'gcx, 'tcx> {
     #[inline]
-    fn join(&self, pred1: usize, pred2: usize) -> usize {
+    fn join(&self, pred1: Word, pred2: Word) -> Word {
         pred1 | pred2 // "maybe" means we union effects of both preds
     }
 }
 
 impl<'a, 'gcx, 'tcx> BitwiseOperator for MaybeUninitializedPlaces<'a, 'gcx, 'tcx> {
     #[inline]
-    fn join(&self, pred1: usize, pred2: usize) -> usize {
+    fn join(&self, pred1: Word, pred2: Word) -> Word {
         pred1 | pred2 // "maybe" means we union effects of both preds
     }
 }
 
 impl<'a, 'gcx, 'tcx> BitwiseOperator for DefinitelyInitializedPlaces<'a, 'gcx, 'tcx> {
     #[inline]
-    fn join(&self, pred1: usize, pred2: usize) -> usize {
+    fn join(&self, pred1: Word, pred2: Word) -> Word {
         pred1 & pred2 // "definitely" means we intersect effects of both preds
     }
 }
 
 impl<'a, 'gcx, 'tcx> BitwiseOperator for MovingOutStatements<'a, 'gcx, 'tcx> {
     #[inline]
-    fn join(&self, pred1: usize, pred2: usize) -> usize {
+    fn join(&self, pred1: Word, pred2: Word) -> Word {
         pred1 | pred2 // moves from both preds are in scope
     }
 }
 
 impl<'a, 'gcx, 'tcx> BitwiseOperator for EverInitializedPlaces<'a, 'gcx, 'tcx> {
     #[inline]
-    fn join(&self, pred1: usize, pred2: usize) -> usize {
+    fn join(&self, pred1: Word, pred2: Word) -> Word {
         pred1 | pred2 // inits from both preds are in scope
     }
 }

Diff for: src/librustc_mir/dataflow/impls/storage_liveness.rs

@@ -69,7 +69,7 @@ impl<'a, 'tcx> BitDenotation for MaybeStorageLive<'a, 'tcx> {
 
 impl<'a, 'tcx> BitwiseOperator for MaybeStorageLive<'a, 'tcx> {
     #[inline]
-    fn join(&self, pred1: usize, pred2: usize) -> usize {
+    fn join(&self, pred1: Word, pred2: Word) -> Word {
         pred1 | pred2 // "maybe" means we union effects of both preds
     }
 }

Diff for: src/librustc_mir/dataflow/mod.rs

@@ -12,7 +12,7 @@ use syntax::ast::{self, MetaItem};
 
 use rustc_data_structures::indexed_set::{IdxSet, IdxSetBuf};
 use rustc_data_structures::indexed_vec::Idx;
-use rustc_data_structures::bitslice::{bitwise, BitwiseOperator};
+use rustc_data_structures::bitslice::{bitwise, BitwiseOperator, Word};
 use rustc_data_structures::work_queue::WorkQueue;
 
 use rustc::ty::{self, TyCtxt};
@@ -467,7 +467,7 @@ pub struct AllSets<E: Idx> {
     bits_per_block: usize,
 
     /// Number of words associated with each block entry
-    /// equal to bits_per_block / usize::BITS, rounded up.
+    /// equal to bits_per_block / (mem::size_of::<Word> * 8), rounded up.
     words_per_block: usize,
 
     /// For each block, bits generated by executing the statements in
@@ -734,9 +734,11 @@ impl<'a, 'tcx, D> DataflowAnalysis<'a, 'tcx, D> where D: BitDenotation
                dead_unwinds: &'a IdxSet<mir::BasicBlock>,
                denotation: D) -> Self where D: InitialFlow {
         let bits_per_block = denotation.bits_per_block();
-        let usize_bits = mem::size_of::<usize>() * 8;
-        let words_per_block = (bits_per_block + usize_bits - 1) / usize_bits;
-        let num_overall = Self::num_bits_overall(mir, bits_per_block);
+        let bits_per_word = mem::size_of::<Word>() * 8;
+        let words_per_block = (bits_per_block + bits_per_word - 1) / bits_per_word;
+        let bits_per_block_rounded_up = words_per_block * bits_per_word; // a multiple of word size
+        let num_blocks = mir.basic_blocks().len();
+        let num_overall = num_blocks * bits_per_block_rounded_up;
 
         let zeroes = Bits::new(IdxSetBuf::new_empty(num_overall));
         let on_entry = Bits::new(if D::bottom_value() {
@@ -774,18 +776,6 @@ impl<'a, 'tcx, D> DataflowAnalysis<'a, 'tcx, D> where D: BitDenotation
             }
         }
     }
-
-    fn num_bits_overall(mir: &Mir, bits_per_block: usize) -> usize {
-        let usize_bits = mem::size_of::<usize>() * 8;
-        let words_per_block = (bits_per_block + usize_bits - 1) / usize_bits;
-
-        // (now rounded up to multiple of word size)
-        let bits_per_block = words_per_block * usize_bits;
-
-        let num_blocks = mir.basic_blocks().len();
-        let num_overall = num_blocks * bits_per_block;
-        num_overall
-    }
 }
 
 impl<'a, 'tcx: 'a, D> DataflowAnalysis<'a, 'tcx, D> where D: BitDenotation