Merge indexed_set.rs into bitvec.rs, and rename it bit_set.rs.

Currently we have two files implementing bitsets (and 2D bit matrices).
This commit combines them into one, taking the best features from each.

This involves renaming a lot of things. The high level changes are as
follows.
- bitvec.rs              --> bit_set.rs
- indexed_set.rs         --> (removed)
- BitArray + IdxSet      --> BitSet (merged, see below)
- BitVector              --> GrowableBitSet
- {,Sparse,Hybrid}IdxSet --> {,Sparse,Hybrid}BitSet
- BitMatrix              --> BitMatrix
- SparseBitMatrix        --> SparseBitMatrix

The changes within the bitset types themselves are as follows.

```
OLD             OLD             NEW
BitArray<C>     IdxSet<T>       BitSet<T>
--------        ------          ------
grow            -               grow
new             -               (remove)
new_empty       new_empty       new_empty
new_filled      new_filled      new_filled
-               to_hybrid       to_hybrid
clear           clear           clear
set_up_to       set_up_to       set_up_to
clear_above     -               clear_above
count           -               count
contains(T)     contains(&T)    contains(T)
contains_all    -               superset
is_empty        -               is_empty
insert(T)       add(&T)         insert(T)
insert_all      -               insert_all()
remove(T)       remove(&T)      remove(T)
words           words           words
words_mut       words_mut       words_mut
-               overwrite       overwrite
merge           union           union
-               subtract        subtract
-               intersect       intersect
iter            iter            iter
```

In general, when choosing names I went with:
- names that are more obvious (e.g. `BitSet` over `IdxSet`).
- names that are more like the Rust libraries (e.g. `T` over `C`,
  `insert` over `add`);
- names that are more set-like (e.g. `union` over `merge`, `superset`
  over `contains_all`, `domain_size` over `num_bits`).

Also, using `T` for index arguments seems more sensible than `&T` --
even though the latter is standard in Rust collection types -- because
indices are always copyable. It also results in fewer `&` and `*`
sigils in practice.

src/librustc/mir/traversal.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use rustc_data_structures::bitvec::BitArray;
+use rustc_data_structures::bit_set::BitSet;
 
 use super::*;
 
@@ -32,7 +32,7 @@ use super::*;
 #[derive(Clone)]
 pub struct Preorder<'a, 'tcx: 'a> {
     mir: &'a Mir<'tcx>,
-    visited: BitArray<BasicBlock>,
+    visited: BitSet<BasicBlock>,
     worklist: Vec<BasicBlock>,
 }
 
@@ -42,7 +42,7 @@ impl<'a, 'tcx> Preorder<'a, 'tcx> {
 
         Preorder {
             mir,
-            visited: BitArray::new(mir.basic_blocks().len()),
+            visited: BitSet::new_empty(mir.basic_blocks().len()),
             worklist,
         }
     }
@@ -104,15 +104,15 @@ impl<'a, 'tcx> ExactSizeIterator for Preorder<'a, 'tcx> {}
 /// A Postorder traversal of this graph is `D B C A` or `D C B A`
 pub struct Postorder<'a, 'tcx: 'a> {
     mir: &'a Mir<'tcx>,
-    visited: BitArray<BasicBlock>,
+    visited: BitSet<BasicBlock>,
     visit_stack: Vec<(BasicBlock, Successors<'a>)>
 }
 
 impl<'a, 'tcx> Postorder<'a, 'tcx> {
     pub fn new(mir: &'a Mir<'tcx>, root: BasicBlock) -> Postorder<'a, 'tcx> {
         let mut po = Postorder {
             mir,
-            visited: BitArray::new(mir.basic_blocks().len()),
+            visited: BitSet::new_empty(mir.basic_blocks().len()),
             visit_stack: Vec::new()
         };
 

src/librustc/traits/select.rs

@@ -44,8 +44,8 @@ use ty::relate::TypeRelation;
 use middle::lang_items;
 use mir::interpret::{GlobalId};
 
+use rustc_data_structures::bit_set::BitSet;
 use rustc_data_structures::sync::Lock;
-use rustc_data_structures::bitvec::BitArray;
 use std::iter;
 use std::cmp;
 use std::fmt;
@@ -3069,7 +3069,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                 } else {
                     return Err(Unimplemented);
                 };
-                let mut ty_params = BitArray::new(substs_a.types().count());
+                let mut ty_params = BitSet::new_empty(substs_a.types().count());
                 let mut found = false;
                 for ty in field.walk() {
                     if let ty::Param(p) = ty.sty {

src/librustc/ty/query/mod.rs

@@ -49,14 +49,14 @@ use util::nodemap::{DefIdSet, DefIdMap, ItemLocalSet};
 use util::common::{ErrorReported};
 use util::profiling::ProfileCategory::*;
 
-use rustc_data_structures::indexed_set::IdxSet;
-use rustc_target::spec::PanicStrategy;
+use rustc_data_structures::bit_set::BitSet;
 use rustc_data_structures::indexed_vec::IndexVec;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::stable_hasher::StableVec;
+use rustc_data_structures::sync::Lrc;
+use rustc_target::spec::PanicStrategy;
 
 use std::ops::Deref;
-use rustc_data_structures::sync::Lrc;
 use std::sync::Arc;
 use syntax_pos::{Span, DUMMY_SP};
 use syntax_pos::symbol::InternedString;
@@ -208,7 +208,7 @@ define_queries! { <'tcx>
         /// Maps DefId's that have an associated Mir to the result
         /// of the MIR qualify_consts pass. The actual meaning of
         /// the value isn't known except to the pass itself.
-        [] fn mir_const_qualif: MirConstQualif(DefId) -> (u8, Lrc<IdxSet<mir::Local>>),
+        [] fn mir_const_qualif: MirConstQualif(DefId) -> (u8, Lrc<BitSet<mir::Local>>),
 
         /// Fetch the MIR for a given def-id right after it's built - this includes
         /// unreachable code.

src/librustc_codegen_llvm/debuginfo/create_scope_map.rs

@@ -21,7 +21,7 @@ use libc::c_uint;
 
 use syntax_pos::Pos;
 
-use rustc_data_structures::bitvec::BitArray;
+use rustc_data_structures::bit_set::BitSet;
 use rustc_data_structures::indexed_vec::{Idx, IndexVec};
 
 use syntax_pos::BytePos;
@@ -64,7 +64,7 @@ pub fn create_mir_scopes(
     };
 
     // Find all the scopes with variables defined in them.
-    let mut has_variables = BitArray::new(mir.source_scopes.len());
+    let mut has_variables = BitSet::new_empty(mir.source_scopes.len());
     for var in mir.vars_iter() {
         let decl = &mir.local_decls[var];
         has_variables.insert(decl.visibility_scope);
@@ -81,7 +81,7 @@ pub fn create_mir_scopes(
 
 fn make_mir_scope(cx: &CodegenCx<'ll, '_>,
                   mir: &Mir,
-                  has_variables: &BitArray<SourceScope>,
+                  has_variables: &BitSet<SourceScope>,
                   debug_context: &FunctionDebugContextData<'ll>,
                   scope: SourceScope,
                   scopes: &mut IndexVec<SourceScope, MirDebugScope<'ll>>) {

src/librustc_codegen_llvm/mir/analyze.rs

@@ -11,7 +11,7 @@
 //! An analysis to determine which locals require allocas and
 //! which do not.
 
-use rustc_data_structures::bitvec::BitArray;
+use rustc_data_structures::bit_set::BitSet;
 use rustc_data_structures::graph::dominators::Dominators;
 use rustc_data_structures::indexed_vec::{Idx, IndexVec};
 use rustc::mir::{self, Location, TerminatorKind};
@@ -22,7 +22,7 @@ use rustc::ty::layout::LayoutOf;
 use type_of::LayoutLlvmExt;
 use super::FunctionCx;
 
-pub fn non_ssa_locals(fx: &FunctionCx<'a, 'll, 'tcx>) -> BitArray<mir::Local> {
+pub fn non_ssa_locals(fx: &FunctionCx<'a, 'll, 'tcx>) -> BitSet<mir::Local> {
     let mir = fx.mir;
     let mut analyzer = LocalAnalyzer::new(fx);
 
@@ -54,7 +54,7 @@ pub fn non_ssa_locals(fx: &FunctionCx<'a, 'll, 'tcx>) -> BitArray<mir::Local> {
 struct LocalAnalyzer<'mir, 'a: 'mir, 'll: 'a, 'tcx: 'll> {
     fx: &'mir FunctionCx<'a, 'll, 'tcx>,
     dominators: Dominators<mir::BasicBlock>,
-    non_ssa_locals: BitArray<mir::Local>,
+    non_ssa_locals: BitSet<mir::Local>,
     // The location of the first visited direct assignment to each
     // local, or an invalid location (out of bounds `block` index).
     first_assignment: IndexVec<mir::Local, Location>
@@ -67,7 +67,7 @@ impl LocalAnalyzer<'mir, 'a, 'll, 'tcx> {
         let mut analyzer = LocalAnalyzer {
             fx,
             dominators: fx.mir.dominators(),
-            non_ssa_locals: BitArray::new(fx.mir.local_decls.len()),
+            non_ssa_locals: BitSet::new_empty(fx.mir.local_decls.len()),
             first_assignment: IndexVec::from_elem(invalid_location, &fx.mir.local_decls)
         };
 

src/librustc_codegen_llvm/mir/mod.rs

@@ -31,7 +31,7 @@ use syntax::symbol::keywords;
 
 use std::iter;
 
-use rustc_data_structures::bitvec::BitArray;
+use rustc_data_structures::bit_set::BitSet;
 use rustc_data_structures::indexed_vec::IndexVec;
 
 pub use self::constant::codegen_static_initializer;
@@ -341,7 +341,7 @@ pub fn codegen_mir(
     debuginfo::start_emitting_source_locations(&fx.debug_context);
 
     let rpo = traversal::reverse_postorder(&mir);
-    let mut visited = BitArray::new(mir.basic_blocks().len());
+    let mut visited = BitSet::new_empty(mir.basic_blocks().len());
 
     // Codegen the body of each block using reverse postorder
     for (bb, _) in rpo {
@@ -435,7 +435,7 @@ fn arg_local_refs(
     bx: &Builder<'a, 'll, 'tcx>,
     fx: &FunctionCx<'a, 'll, 'tcx>,
     scopes: &IndexVec<mir::SourceScope, debuginfo::MirDebugScope<'ll>>,
-    memory_locals: &BitArray<mir::Local>,
+    memory_locals: &BitSet<mir::Local>,
 ) -> Vec<LocalRef<'ll, 'tcx>> {
     let mir = fx.mir;
     let tcx = bx.tcx();