diff --git a/RELEASES.md b/RELEASES.md
index 13042ab07e217..e969b91b2b643 100644
--- a/RELEASES.md
+++ b/RELEASES.md
@@ -216,7 +216,7 @@ Language
 
 Compiler
 --------
-- [Added the `armv5te-unknown-linux-musl` target.][50423]
+- [Added the `armv5te-unknown-linux-musleabi` target.][50423]
 
 Libraries
 ---------
diff --git a/src/liballoc/vec.rs b/src/liballoc/vec.rs
index 5efe1e23309a7..cc913dfbb4b01 100644
--- a/src/liballoc/vec.rs
+++ b/src/liballoc/vec.rs
@@ -690,14 +690,20 @@ impl<T> Vec<T> {
     /// [`drain`]: #method.drain
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn truncate(&mut self, len: usize) {
+        let current_len = self.len;
         unsafe {
+            let mut ptr = self.as_mut_ptr().offset(self.len as isize);
+            // Set the final length at the end, keeping in mind that
+            // dropping an element might panic. Works around a missed
+            // optimization, as seen in the following issue:
+            // https://github.com/rust-lang/rust/issues/51802
+            let mut local_len = SetLenOnDrop::new(&mut self.len);
+
             // drop any extra elements
-            while len < self.len {
-                // decrement len before the drop_in_place(), so a panic on Drop
-                // doesn't re-drop the just-failed value.
-                self.len -= 1;
-                let len = self.len;
-                ptr::drop_in_place(self.get_unchecked_mut(len));
+            for _ in len..current_len {
+                local_len.decrement_len(1);
+                ptr = ptr.offset(-1);
+                ptr::drop_in_place(ptr);
             }
         }
     }
@@ -1512,6 +1518,11 @@ impl<'a> SetLenOnDrop<'a> {
     fn increment_len(&mut self, increment: usize) {
         self.local_len += increment;
     }
+
+    #[inline]
+    fn decrement_len(&mut self, decrement: usize) {
+        self.local_len -= decrement;
+    }
 }
 
 impl<'a> Drop for SetLenOnDrop<'a> {
diff --git a/src/libcore/slice/memchr.rs b/src/libcore/slice/memchr.rs
index 72e7b57a6cb3c..c9d3c7fea9839 100644
--- a/src/libcore/slice/memchr.rs
+++ b/src/libcore/slice/memchr.rs
@@ -100,24 +100,30 @@ pub fn memrchr(x: u8, text: &[u8]) -> Option<usize> {
     // - the first remaining bytes, < 2 word size
     let len = text.len();
     let ptr = text.as_ptr();
-    let usize_bytes = mem::size_of::<usize>();
+    type Chunk = usize;
 
-    let mut offset = {
-        // We call this just to obtain the length of the suffix
-        let (_, _, suffix) = unsafe { text.align_to::<usize>() };
-        len - suffix.len()
+    let (min_aligned_offset, max_aligned_offset) = {
+        // We call this just to obtain the length of the prefix and suffix.
+        // In the middle we always process two chunks at once.
+        let (prefix, _, suffix) = unsafe { text.align_to::<(Chunk, Chunk)>() };
+        (prefix.len(), len - suffix.len())
     };
+
+    let mut offset = max_aligned_offset;
     if let Some(index) = text[offset..].iter().rposition(|elt| *elt == x) {
         return Some(offset + index);
     }
 
-    // search the body of the text
+    // search the body of the text, make sure we don't cross min_aligned_offset.
+    // offset is always aligned, so just testing `>` is sufficient and avoids possible
+    // overflow.
     let repeated_x = repeat_byte(x);
+    let chunk_bytes = mem::size_of::<Chunk>();
 
-    while offset >= 2 * usize_bytes {
+    while offset > min_aligned_offset {
         unsafe {
-            let u = *(ptr.offset(offset as isize - 2 * usize_bytes as isize) as *const usize);
-            let v = *(ptr.offset(offset as isize - usize_bytes as isize) as *const usize);
+            let u = *(ptr.offset(offset as isize - 2 * chunk_bytes as isize) as *const Chunk);
+            let v = *(ptr.offset(offset as isize - chunk_bytes as isize) as *const Chunk);
 
             // break if there is a matching byte
             let zu = contains_zero_byte(u ^ repeated_x);
@@ -126,7 +132,7 @@ pub fn memrchr(x: u8, text: &[u8]) -> Option<usize> {
                 break;
             }
         }
-        offset -= 2 * usize_bytes;
+        offset -= 2 * chunk_bytes;
     }
 
     // find the byte before the point the body loop stopped
diff --git a/src/librustc/mir/traversal.rs b/src/librustc/mir/traversal.rs
index 86fd825850fc5..c178a9063c9ac 100644
--- a/src/librustc/mir/traversal.rs
+++ b/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::BitVector;
+use rustc_data_structures::bitvec::BitArray;
 
 use super::*;
 
@@ -32,7 +32,7 @@ use super::*;
 #[derive(Clone)]
 pub struct Preorder<'a, 'tcx: 'a> {
     mir: &'a Mir<'tcx>,
-    visited: BitVector<BasicBlock>,
+    visited: BitArray<BasicBlock>,
     worklist: Vec<BasicBlock>,
 }
 
@@ -42,7 +42,7 @@ impl<'a, 'tcx> Preorder<'a, 'tcx> {
 
         Preorder {
             mir,
-            visited: BitVector::new(mir.basic_blocks().len()),
+            visited: BitArray::new(mir.basic_blocks().len()),
             worklist,
         }
     }
@@ -104,7 +104,7 @@ 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: BitVector<BasicBlock>,
+    visited: BitArray<BasicBlock>,
     visit_stack: Vec<(BasicBlock, Successors<'a>)>
 }
 
@@ -112,7 +112,7 @@ impl<'a, 'tcx> Postorder<'a, 'tcx> {
     pub fn new(mir: &'a Mir<'tcx>, root: BasicBlock) -> Postorder<'a, 'tcx> {
         let mut po = Postorder {
             mir,
-            visited: BitVector::new(mir.basic_blocks().len()),
+            visited: BitArray::new(mir.basic_blocks().len()),
             visit_stack: Vec::new()
         };
 
diff --git a/src/librustc/traits/select.rs b/src/librustc/traits/select.rs
index 40171345f558b..35184ca6a2559 100644
--- a/src/librustc/traits/select.rs
+++ b/src/librustc/traits/select.rs
@@ -45,7 +45,7 @@ use middle::lang_items;
 use mir::interpret::{GlobalId};
 
 use rustc_data_structures::sync::Lock;
-use rustc_data_structures::bitvec::BitVector;
+use rustc_data_structures::bitvec::BitArray;
 use std::iter;
 use std::cmp;
 use std::fmt;
@@ -3056,7 +3056,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                 } else {
                     return Err(Unimplemented);
                 };
-                let mut ty_params = BitVector::new(substs_a.types().count());
+                let mut ty_params = BitArray::new(substs_a.types().count());
                 let mut found = false;
                 for ty in field.walk() {
                     if let ty::TyParam(p) = ty.sty {
diff --git a/src/librustc_codegen_llvm/debuginfo/create_scope_map.rs b/src/librustc_codegen_llvm/debuginfo/create_scope_map.rs
index 5273032f2d7f5..a76f1d50fa7bf 100644
--- a/src/librustc_codegen_llvm/debuginfo/create_scope_map.rs
+++ b/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::BitVector;
+use rustc_data_structures::bitvec::BitArray;
 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 = BitVector::new(mir.source_scopes.len());
+    let mut has_variables = BitArray::new(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: &BitVector<SourceScope>,
+                  has_variables: &BitArray<SourceScope>,
                   debug_context: &FunctionDebugContextData<'ll>,
                   scope: SourceScope,
                   scopes: &mut IndexVec<SourceScope, MirDebugScope<'ll>>) {
diff --git a/src/librustc_codegen_llvm/mir/analyze.rs b/src/librustc_codegen_llvm/mir/analyze.rs
index 2c2058035241f..993138aee1cec 100644
--- a/src/librustc_codegen_llvm/mir/analyze.rs
+++ b/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::BitVector;
+use rustc_data_structures::bitvec::BitArray;
 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>) -> BitVector<mir::Local> {
+pub fn non_ssa_locals(fx: &FunctionCx<'a, 'll, 'tcx>) -> BitArray<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>) -> BitVector<mir::Local> {
 struct LocalAnalyzer<'mir, 'a: 'mir, 'll: 'a, 'tcx: 'll> {
     fx: &'mir FunctionCx<'a, 'll, 'tcx>,
     dominators: Dominators<mir::BasicBlock>,
-    non_ssa_locals: BitVector<mir::Local>,
+    non_ssa_locals: BitArray<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: BitVector::new(fx.mir.local_decls.len()),
+            non_ssa_locals: BitArray::new(fx.mir.local_decls.len()),
             first_assignment: IndexVec::from_elem(invalid_location, &fx.mir.local_decls)
         };
 
diff --git a/src/librustc_codegen_llvm/mir/mod.rs b/src/librustc_codegen_llvm/mir/mod.rs
index 8cdd0398eff96..a099cb5c64b21 100644
--- a/src/librustc_codegen_llvm/mir/mod.rs
+++ b/src/librustc_codegen_llvm/mir/mod.rs
@@ -31,7 +31,7 @@ use syntax::symbol::keywords;
 
 use std::iter;
 
-use rustc_data_structures::bitvec::BitVector;
+use rustc_data_structures::bitvec::BitArray;
 use rustc_data_structures::indexed_vec::{IndexVec, Idx};
 
 pub use self::constant::codegen_static_initializer;
@@ -323,7 +323,7 @@ pub fn codegen_mir(
     debuginfo::start_emitting_source_locations(&fx.debug_context);
 
     let rpo = traversal::reverse_postorder(&mir);
-    let mut visited = BitVector::new(mir.basic_blocks().len());
+    let mut visited = BitArray::new(mir.basic_blocks().len());
 
     // Codegen the body of each block using reverse postorder
     for (bb, _) in rpo {
@@ -417,7 +417,7 @@ fn arg_local_refs(
     bx: &Builder<'a, 'll, 'tcx>,
     fx: &FunctionCx<'a, 'll, 'tcx>,
     scopes: &IndexVec<mir::SourceScope, debuginfo::MirDebugScope<'ll>>,
-    memory_locals: &BitVector<mir::Local>,
+    memory_locals: &BitArray<mir::Local>,
 ) -> Vec<LocalRef<'ll, 'tcx>> {
     let mir = fx.mir;
     let tcx = bx.tcx();
diff --git a/src/librustc_data_structures/bitvec.rs b/src/librustc_data_structures/bitvec.rs
index 04d6cb5e2a6d2..6e8a45d034250 100644
--- a/src/librustc_data_structures/bitvec.rs
+++ b/src/librustc_data_structures/bitvec.rs
@@ -9,24 +9,74 @@
 // except according to those terms.
 
 use indexed_vec::{Idx, IndexVec};
-use std::iter::FromIterator;
 use std::marker::PhantomData;
 
 type Word = u128;
 const WORD_BITS: usize = 128;
 
-/// A very simple BitVector type.
+/// A very simple BitArray type.
+///
+/// It does not support resizing after creation; use `BitVector` for that.
 #[derive(Clone, Debug, PartialEq)]
-pub struct BitVector<C: Idx> {
+pub struct BitArray<C: Idx> {
     data: Vec<Word>,
     marker: PhantomData<C>,
 }
 
+#[derive(Clone, Debug, PartialEq)]
+pub struct BitVector<C: Idx> {
+    data: BitArray<C>,
+}
+
 impl<C: Idx> BitVector<C> {
+    pub fn grow(&mut self, num_bits: C) {
+        self.data.grow(num_bits)
+    }
+
+    pub fn new() -> BitVector<C> {
+        BitVector {
+            data: BitArray::new(0),
+        }
+    }
+
+    pub fn with_capacity(bits: usize) -> BitVector<C> {
+        BitVector {
+            data: BitArray::new(bits),
+        }
+    }
+
+    /// Returns true if the bit has changed.
+    #[inline]
+    pub fn insert(&mut self, bit: C) -> bool {
+        self.grow(bit);
+        self.data.insert(bit)
+    }
+
     #[inline]
-    pub fn new(num_bits: usize) -> BitVector<C> {
+    pub fn contains(&self, bit: C) -> bool {
+        let (word, mask) = word_mask(bit);
+        if let Some(word) = self.data.data.get(word) {
+            (word & mask) != 0
+        } else {
+            false
+        }
+    }
+}
+
+impl<C: Idx> BitArray<C> {
+    // Do not make this method public, instead switch your use case to BitVector.
+    #[inline]
+    fn grow(&mut self, num_bits: C) {
         let num_words = words(num_bits);
-        BitVector {
+        if self.data.len() <= num_words {
+            self.data.resize(num_words + 1, 0)
+        }
+    }
+
+    #[inline]
+    pub fn new(num_bits: usize) -> BitArray<C> {
+        let num_words = words(num_bits);
+        BitArray {
             data: vec![0; num_words],
             marker: PhantomData,
         }
@@ -54,7 +104,7 @@ impl<C: Idx> BitVector<C> {
     ///
     /// The two vectors must have the same length.
     #[inline]
-    pub fn contains_all(&self, other: &BitVector<C>) -> bool {
+    pub fn contains_all(&self, other: &BitArray<C>) -> bool {
         assert_eq!(self.data.len(), other.data.len());
         self.data.iter().zip(&other.data).all(|(a, b)| (a & b) == *b)
     }
@@ -94,7 +144,7 @@ impl<C: Idx> BitVector<C> {
     }
 
     #[inline]
-    pub fn merge(&mut self, all: &BitVector<C>) -> bool {
+    pub fn merge(&mut self, all: &BitArray<C>) -> bool {
         assert!(self.data.len() == all.data.len());
         let mut changed = false;
         for (i, j) in self.data.iter_mut().zip(&all.data) {
@@ -107,18 +157,10 @@ impl<C: Idx> BitVector<C> {
         changed
     }
 
-    #[inline]
-    pub fn grow(&mut self, num_bits: C) {
-        let num_words = words(num_bits);
-        if self.data.len() < num_words {
-            self.data.resize(num_words, 0)
-        }
-    }
-
     /// Iterates over indexes of set bits in a sorted order
     #[inline]
-    pub fn iter<'a>(&'a self) -> BitVectorIter<'a, C> {
-        BitVectorIter {
+    pub fn iter<'a>(&'a self) -> BitIter<'a, C> {
+        BitIter {
             iter: self.data.iter(),
             current: 0,
             idx: 0,
@@ -127,14 +169,14 @@ impl<C: Idx> BitVector<C> {
     }
 }
 
-pub struct BitVectorIter<'a, C: Idx> {
+pub struct BitIter<'a, C: Idx> {
     iter: ::std::slice::Iter<'a, Word>,
     current: Word,
     idx: usize,
     marker: PhantomData<C>
 }
 
-impl<'a, C: Idx> Iterator for BitVectorIter<'a, C> {
+impl<'a, C: Idx> Iterator for BitIter<'a, C> {
     type Item = C;
     fn next(&mut self) -> Option<C> {
         while self.current == 0 {
@@ -163,30 +205,6 @@ impl<'a, C: Idx> Iterator for BitVectorIter<'a, C> {
     }
 }
 
-impl<C: Idx> FromIterator<bool> for BitVector<C> {
-    fn from_iter<I>(iter: I) -> BitVector<C>
-    where
-        I: IntoIterator<Item = bool>,
-    {
-        let iter = iter.into_iter();
-        let (len, _) = iter.size_hint();
-        // Make the minimum length for the bitvector WORD_BITS bits since that's
-        // the smallest non-zero size anyway.
-        let len = if len < WORD_BITS { WORD_BITS } else { len };
-        let mut bv = BitVector::new(len);
-        for (idx, val) in iter.enumerate() {
-            if idx > len {
-                bv.grow(C::new(idx));
-            }
-            if val {
-                bv.insert(C::new(idx));
-            }
-        }
-
-        bv
-    }
-}
-
 /// A "bit matrix" is basically a matrix of booleans represented as
 /// one gigantic bitvector. In other words, it is as if you have
 /// `rows` bitvectors, each of length `columns`.
@@ -288,9 +306,9 @@ impl<R: Idx, C: Idx> BitMatrix<R, C> {
 
     /// Iterates through all the columns set to true in a given row of
     /// the matrix.
-    pub fn iter<'a>(&'a self, row: R) -> BitVectorIter<'a, C> {
+    pub fn iter<'a>(&'a self, row: R) -> BitIter<'a, C> {
         let (start, end) = self.range(row);
-        BitVectorIter {
+        BitIter {
             iter: self.vector[start..end].iter(),
             current: 0,
             idx: 0,
@@ -308,7 +326,7 @@ where
     C: Idx,
 {
     columns: usize,
-    vector: IndexVec<R, BitVector<C>>,
+    vector: IndexVec<R, BitArray<C>>,
 }
 
 impl<R: Idx, C: Idx> SparseBitMatrix<R, C> {
@@ -323,7 +341,7 @@ impl<R: Idx, C: Idx> SparseBitMatrix<R, C> {
     fn ensure_row(&mut self, row: R) {
         let columns = self.columns;
         self.vector
-            .ensure_contains_elem(row, || BitVector::new(columns));
+            .ensure_contains_elem(row, || BitArray::new(columns));
     }
 
     /// Sets the cell at `(row, column)` to true. Put another way, insert
@@ -361,7 +379,7 @@ impl<R: Idx, C: Idx> SparseBitMatrix<R, C> {
     }
 
     /// Merge a row, `from`, into the `into` row.
-    pub fn merge_into(&mut self, into: R, from: &BitVector<C>) -> bool {
+    pub fn merge_into(&mut self, into: R, from: &BitArray<C>) -> bool {
         self.ensure_row(into);
         self.vector[into].merge(from)
     }
@@ -388,11 +406,11 @@ impl<R: Idx, C: Idx> SparseBitMatrix<R, C> {
     }
 
     /// Iterates through each row and the accompanying bit set.
-    pub fn iter_enumerated<'a>(&'a self) -> impl Iterator<Item = (R, &'a BitVector<C>)> + 'a {
+    pub fn iter_enumerated<'a>(&'a self) -> impl Iterator<Item = (R, &'a BitArray<C>)> + 'a {
         self.vector.iter_enumerated()
     }
 
-    pub fn row(&self, row: R) -> Option<&BitVector<C>> {
+    pub fn row(&self, row: R) -> Option<&BitArray<C>> {
         self.vector.get(row)
     }
 }
@@ -412,7 +430,7 @@ fn word_mask<C: Idx>(index: C) -> (usize, Word) {
 
 #[test]
 fn bitvec_iter_works() {
-    let mut bitvec: BitVector<usize> = BitVector::new(100);
+    let mut bitvec: BitArray<usize> = BitArray::new(100);
     bitvec.insert(1);
     bitvec.insert(10);
     bitvec.insert(19);
@@ -430,7 +448,7 @@ fn bitvec_iter_works() {
 
 #[test]
 fn bitvec_iter_works_2() {
-    let mut bitvec: BitVector<usize> = BitVector::new(319);
+    let mut bitvec: BitArray<usize> = BitArray::new(319);
     bitvec.insert(0);
     bitvec.insert(127);
     bitvec.insert(191);
@@ -441,8 +459,8 @@ fn bitvec_iter_works_2() {
 
 #[test]
 fn union_two_vecs() {
-    let mut vec1: BitVector<usize> = BitVector::new(65);
-    let mut vec2: BitVector<usize> = BitVector::new(65);
+    let mut vec1: BitArray<usize> = BitArray::new(65);
+    let mut vec2: BitArray<usize> = BitArray::new(65);
     assert!(vec1.insert(3));
     assert!(!vec1.insert(3));
     assert!(vec2.insert(5));
@@ -458,7 +476,7 @@ fn union_two_vecs() {
 
 #[test]
 fn grow() {
-    let mut vec1: BitVector<usize> = BitVector::new(65);
+    let mut vec1: BitVector<usize> = BitVector::with_capacity(65);
     for index in 0..65 {
         assert!(vec1.insert(index));
         assert!(!vec1.insert(index));
diff --git a/src/librustc_data_structures/graph/implementation/mod.rs b/src/librustc_data_structures/graph/implementation/mod.rs
index dbfc09116bbaa..cf9403db658f4 100644
--- a/src/librustc_data_structures/graph/implementation/mod.rs
+++ b/src/librustc_data_structures/graph/implementation/mod.rs
@@ -30,7 +30,7 @@
 //! the field `next_edge`). Each of those fields is an array that should
 //! be indexed by the direction (see the type `Direction`).
 
-use bitvec::BitVector;
+use bitvec::BitArray;
 use std::fmt::Debug;
 use std::usize;
 use snapshot_vec::{SnapshotVec, SnapshotVecDelegate};
@@ -266,7 +266,7 @@ impl<N: Debug, E: Debug> Graph<N, E> {
         direction: Direction,
         entry_node: NodeIndex,
     ) -> Vec<NodeIndex> {
-        let mut visited = BitVector::new(self.len_nodes());
+        let mut visited = BitArray::new(self.len_nodes());
         let mut stack = vec![];
         let mut result = Vec::with_capacity(self.len_nodes());
         let mut push_node = |stack: &mut Vec<_>, node: NodeIndex| {
@@ -348,7 +348,7 @@ where
 {
     graph: &'g Graph<N, E>,
     stack: Vec<NodeIndex>,
-    visited: BitVector<usize>,
+    visited: BitArray<usize>,
     direction: Direction,
 }
 
@@ -358,7 +358,7 @@ impl<'g, N: Debug, E: Debug> DepthFirstTraversal<'g, N, E> {
         start_node: NodeIndex,
         direction: Direction,
     ) -> Self {
-        let mut visited = BitVector::new(graph.len_nodes());
+        let mut visited = BitArray::new(graph.len_nodes());
         visited.insert(start_node.node_id());
         DepthFirstTraversal {
             graph,
diff --git a/src/librustc_data_structures/small_vec.rs b/src/librustc_data_structures/small_vec.rs
index b5f52d54ae471..76b01beb4bad3 100644
--- a/src/librustc_data_structures/small_vec.rs
+++ b/src/librustc_data_structures/small_vec.rs
@@ -169,18 +169,11 @@ impl<A: Array> FromIterator<A::Element> for SmallVec<A> {
 
 impl<A: Array> Extend<A::Element> for SmallVec<A> {
     fn extend<I: IntoIterator<Item=A::Element>>(&mut self, iter: I) {
-        if self.is_array() {
-            let iter = iter.into_iter();
-            self.reserve(iter.size_hint().0);
-
-            for el in iter {
-                self.push(el);
-            }
-        } else {
-            match self.0 {
-                AccumulateVec::Heap(ref mut vec) => vec.extend(iter),
-                _ => unreachable!()
-            }
+        let iter = iter.into_iter();
+        self.reserve(iter.size_hint().0);
+        match self.0 {
+            AccumulateVec::Heap(ref mut vec) => vec.extend(iter),
+            _ => iter.for_each(|el| self.push(el))
         }
     }
 }
diff --git a/src/librustc_lint/lib.rs b/src/librustc_lint/lib.rs
index 78a8c494f48c5..b92ac0ff57bd8 100644
--- a/src/librustc_lint/lib.rs
+++ b/src/librustc_lint/lib.rs
@@ -45,7 +45,6 @@ use rustc::lint::{LateContext, LateLintPass, LintPass, LintArray};
 use rustc::lint::builtin::{
     BARE_TRAIT_OBJECTS,
     ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE,
-    MACRO_USE_EXTERN_CRATE,
     ELIDED_LIFETIMES_IN_PATHS,
     parser::QUESTION_MARK_MACRO_SEP
 };
@@ -195,11 +194,18 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
     add_lint_group!(sess,
                     "rust_2018_idioms",
                     BARE_TRAIT_OBJECTS,
-                    UNREACHABLE_PUB,
                     UNUSED_EXTERN_CRATES,
-                    MACRO_USE_EXTERN_CRATE,
-                    ELIDED_LIFETIMES_IN_PATHS,
-                    ELLIPSIS_INCLUSIVE_RANGE_PATTERNS);
+                    ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
+                    ELIDED_LIFETIMES_IN_PATHS
+
+                    // FIXME(#52665, #47816) not always applicable and not all
+                    // macros are ready for this yet.
+                    // UNREACHABLE_PUB,
+
+                    // FIXME macro crates are not up for this yet, too much
+                    // breakage is seen if we try to encourage this lint.
+                    // MACRO_USE_EXTERN_CRATE,
+                    );
 
     // Guidelines for creating a future incompatibility lint:
     //
diff --git a/src/librustc_mir/borrow_check/places_conflict.rs b/src/librustc_mir/borrow_check/places_conflict.rs
index c44af00365479..640ae31d45b34 100644
--- a/src/librustc_mir/borrow_check/places_conflict.rs
+++ b/src/librustc_mir/borrow_check/places_conflict.rs
@@ -329,6 +329,13 @@ fn place_element_conflict<'a, 'gcx: 'tcx, 'tcx>(
         }
         (Place::Promoted(p1), Place::Promoted(p2)) => {
             if p1.0 == p2.0 {
+                if let ty::TyArray(_, size) = p1.1.sty {
+                    if size.unwrap_usize(tcx) == 0 {
+                        // Ignore conflicts with promoted [T; 0].
+                        debug!("place_element_conflict: IGNORE-LEN-0-PROMOTED");
+                        return Overlap::Disjoint;
+                    }
+                }
                 // the same promoted - base case, equal
                 debug!("place_element_conflict: DISJOINT-OR-EQ-PROMOTED");
                 Overlap::EqualOrDisjoint
diff --git a/src/librustc_mir/build/matches/mod.rs b/src/librustc_mir/build/matches/mod.rs
index 6a447d81dc3cb..6b6ec749bcbe6 100644
--- a/src/librustc_mir/build/matches/mod.rs
+++ b/src/librustc_mir/build/matches/mod.rs
@@ -18,7 +18,7 @@ use build::{GuardFrame, GuardFrameLocal, LocalsForNode};
 use build::ForGuard::{self, OutsideGuard, RefWithinGuard, ValWithinGuard};
 use build::scope::{CachedBlock, DropKind};
 use rustc_data_structures::fx::FxHashMap;
-use rustc_data_structures::bitvec::BitVector;
+use rustc_data_structures::bitvec::BitArray;
 use rustc::ty::{self, Ty};
 use rustc::mir::*;
 use rustc::hir;
@@ -496,7 +496,7 @@ enum TestKind<'tcx> {
     // test the branches of enum
     Switch {
         adt_def: &'tcx ty::AdtDef,
-        variants: BitVector<usize>,
+        variants: BitArray<usize>,
     },
 
     // test the branches of enum
diff --git a/src/librustc_mir/build/matches/test.rs b/src/librustc_mir/build/matches/test.rs
index f8bfb5b48ba99..7106e02284da3 100644
--- a/src/librustc_mir/build/matches/test.rs
+++ b/src/librustc_mir/build/matches/test.rs
@@ -19,7 +19,7 @@ use build::Builder;
 use build::matches::{Candidate, MatchPair, Test, TestKind};
 use hair::*;
 use rustc_data_structures::fx::FxHashMap;
-use rustc_data_structures::bitvec::BitVector;
+use rustc_data_structures::bitvec::BitArray;
 use rustc::ty::{self, Ty};
 use rustc::ty::util::IntTypeExt;
 use rustc::mir::*;
@@ -38,7 +38,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                     span: match_pair.pattern.span,
                     kind: TestKind::Switch {
                         adt_def: adt_def.clone(),
-                        variants: BitVector::new(adt_def.variants.len()),
+                        variants: BitArray::new(adt_def.variants.len()),
                     },
                 }
             }
@@ -149,7 +149,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
     pub fn add_variants_to_switch<'pat>(&mut self,
                                         test_place: &Place<'tcx>,
                                         candidate: &Candidate<'pat, 'tcx>,
-                                        variants: &mut BitVector<usize>)
+                                        variants: &mut BitArray<usize>)
                                         -> bool
     {
         let match_pair = match candidate.match_pairs.iter().find(|mp| mp.place == *test_place) {
diff --git a/src/librustc_mir/dataflow/impls/borrowed_locals.rs b/src/librustc_mir/dataflow/impls/borrowed_locals.rs
index 96f4c6b60f511..c8c41c13b0fbb 100644
--- a/src/librustc_mir/dataflow/impls/borrowed_locals.rs
+++ b/src/librustc_mir/dataflow/impls/borrowed_locals.rs
@@ -15,9 +15,9 @@ use rustc::mir::visit::Visitor;
 use dataflow::BitDenotation;
 
 /// This calculates if any part of a MIR local could have previously been borrowed.
-/// This means that once a local has been borrowed, its bit will always be set
-/// from that point and onwards, even if the borrow ends. You could also think of this
-/// as computing the lifetimes of infinite borrows.
+/// This means that once a local has been borrowed, its bit will be set
+/// from that point and onwards, until we see a StorageDead statement for the local,
+/// at which points there is no memory associated with the local, so it cannot be borrowed.
 /// This is used to compute which locals are live during a yield expression for
 /// immovable generators.
 #[derive(Copy, Clone)]
@@ -50,9 +50,17 @@ impl<'a, 'tcx> BitDenotation for HaveBeenBorrowedLocals<'a, 'tcx> {
     fn statement_effect(&self,
                         sets: &mut BlockSets<Local>,
                         loc: Location) {
+        let stmt = &self.mir[loc.block].statements[loc.statement_index];
+
         BorrowedLocalsVisitor {
             sets,
-        }.visit_statement(loc.block, &self.mir[loc.block].statements[loc.statement_index], loc);
+        }.visit_statement(loc.block, stmt, loc);
+
+        // StorageDead invalidates all borrows and raw pointers to a local
+        match stmt.kind {
+            StatementKind::StorageDead(l) => sets.kill(&l),
+            _ => (),
+        }
     }
 
     fn terminator_effect(&self,
diff --git a/src/librustc_mir/monomorphize/collector.rs b/src/librustc_mir/monomorphize/collector.rs
index 5f05783b15cce..6283ee9cfe648 100644
--- a/src/librustc_mir/monomorphize/collector.rs
+++ b/src/librustc_mir/monomorphize/collector.rs
@@ -240,7 +240,7 @@ impl<'tcx> InliningMap<'tcx> {
         InliningMap {
             index: FxHashMap(),
             targets: Vec::new(),
-            inlines: BitVector::new(1024),
+            inlines: BitVector::with_capacity(1024),
         }
     }
 
diff --git a/src/librustc_mir/transform/generator.rs b/src/librustc_mir/transform/generator.rs
index 6a9258fe2c918..a3647edd155d3 100644
--- a/src/librustc_mir/transform/generator.rs
+++ b/src/librustc_mir/transform/generator.rs
@@ -433,7 +433,8 @@ fn locals_live_across_suspend_points<'a, 'tcx,>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                 // The `liveness` variable contains the liveness of MIR locals ignoring borrows.
                 // This is correct for movable generators since borrows cannot live across
                 // suspension points. However for immovable generators we need to account for
-                // borrows, so we conseratively assume that all borrowed locals live forever.
+                // borrows, so we conseratively assume that all borrowed locals are live until
+                // we find a StorageDead statement referencing the locals.
                 // To do this we just union our `liveness` result with `borrowed_locals`, which
                 // contains all the locals which has been borrowed before this suspension point.
                 // If a borrow is converted to a raw reference, we must also assume that it lives
diff --git a/src/librustc_mir/transform/inline.rs b/src/librustc_mir/transform/inline.rs
index 46fab544aafe9..85115427edae9 100644
--- a/src/librustc_mir/transform/inline.rs
+++ b/src/librustc_mir/transform/inline.rs
@@ -14,7 +14,7 @@ use rustc::hir;
 use rustc::hir::CodegenFnAttrFlags;
 use rustc::hir::def_id::DefId;
 
-use rustc_data_structures::bitvec::BitVector;
+use rustc_data_structures::bitvec::BitArray;
 use rustc_data_structures::indexed_vec::{Idx, IndexVec};
 
 use rustc::mir::*;
@@ -271,7 +271,7 @@ impl<'a, 'tcx> Inliner<'a, 'tcx> {
         // Traverse the MIR manually so we can account for the effects of
         // inlining on the CFG.
         let mut work_list = vec![START_BLOCK];
-        let mut visited = BitVector::new(callee_mir.basic_blocks().len());
+        let mut visited = BitArray::new(callee_mir.basic_blocks().len());
         while let Some(bb) = work_list.pop() {
             if !visited.insert(bb.index()) { continue; }
             let blk = &callee_mir.basic_blocks()[bb];
diff --git a/src/librustc_mir/transform/qualify_consts.rs b/src/librustc_mir/transform/qualify_consts.rs
index 8a12a604ef202..208679d2aa08a 100644
--- a/src/librustc_mir/transform/qualify_consts.rs
+++ b/src/librustc_mir/transform/qualify_consts.rs
@@ -14,7 +14,7 @@
 //! The Qualif flags below can be used to also provide better
 //! diagnostics as to why a constant rvalue wasn't promoted.
 
-use rustc_data_structures::bitvec::BitVector;
+use rustc_data_structures::bitvec::BitArray;
 use rustc_data_structures::indexed_set::IdxSetBuf;
 use rustc_data_structures::indexed_vec::{IndexVec, Idx};
 use rustc_data_structures::fx::FxHashSet;
@@ -116,7 +116,7 @@ struct Qualifier<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     param_env: ty::ParamEnv<'tcx>,
     local_qualif: IndexVec<Local, Option<Qualif>>,
     qualif: Qualif,
-    const_fn_arg_vars: BitVector<Local>,
+    const_fn_arg_vars: BitArray<Local>,
     temp_promotion_state: IndexVec<Local, TempState>,
     promotion_candidates: Vec<Candidate>
 }
@@ -150,7 +150,7 @@ impl<'a, 'tcx> Qualifier<'a, 'tcx, 'tcx> {
             param_env,
             local_qualif,
             qualif: Qualif::empty(),
-            const_fn_arg_vars: BitVector::new(mir.local_decls.len()),
+            const_fn_arg_vars: BitArray::new(mir.local_decls.len()),
             temp_promotion_state: temps,
             promotion_candidates: vec![]
         }
@@ -284,7 +284,7 @@ impl<'a, 'tcx> Qualifier<'a, 'tcx, 'tcx> {
 
         let mir = self.mir;
 
-        let mut seen_blocks = BitVector::new(mir.basic_blocks().len());
+        let mut seen_blocks = BitArray::new(mir.basic_blocks().len());
         let mut bb = START_BLOCK;
         loop {
             seen_blocks.insert(bb.index());
diff --git a/src/librustc_mir/transform/remove_noop_landing_pads.rs b/src/librustc_mir/transform/remove_noop_landing_pads.rs
index a7ef93eaec6b9..04a7a81eb126f 100644
--- a/src/librustc_mir/transform/remove_noop_landing_pads.rs
+++ b/src/librustc_mir/transform/remove_noop_landing_pads.rs
@@ -10,7 +10,7 @@
 
 use rustc::ty::TyCtxt;
 use rustc::mir::*;
-use rustc_data_structures::bitvec::BitVector;
+use rustc_data_structures::bitvec::BitArray;
 use transform::{MirPass, MirSource};
 use util::patch::MirPatch;
 
@@ -45,7 +45,7 @@ impl RemoveNoopLandingPads {
         &self,
         bb: BasicBlock,
         mir: &Mir,
-        nop_landing_pads: &BitVector<BasicBlock>,
+        nop_landing_pads: &BitArray<BasicBlock>,
     ) -> bool {
         for stmt in &mir[bb].statements {
             match stmt.kind {
@@ -111,7 +111,7 @@ impl RemoveNoopLandingPads {
 
         let mut jumps_folded = 0;
         let mut landing_pads_removed = 0;
-        let mut nop_landing_pads = BitVector::new(mir.basic_blocks().len());
+        let mut nop_landing_pads = BitArray::new(mir.basic_blocks().len());
 
         // This is a post-order traversal, so that if A post-dominates B
         // then A will be visited before B.
diff --git a/src/librustc_mir/transform/simplify.rs b/src/librustc_mir/transform/simplify.rs
index 6b8d5a1489388..6e8471c672934 100644
--- a/src/librustc_mir/transform/simplify.rs
+++ b/src/librustc_mir/transform/simplify.rs
@@ -37,7 +37,7 @@
 //! naively generate still contains the `_a = ()` write in the unreachable block "after" the
 //! return.
 
-use rustc_data_structures::bitvec::BitVector;
+use rustc_data_structures::bitvec::BitArray;
 use rustc_data_structures::indexed_vec::{Idx, IndexVec};
 use rustc::ty::TyCtxt;
 use rustc::mir::*;
@@ -249,7 +249,7 @@ impl<'a, 'tcx: 'a> CfgSimplifier<'a, 'tcx> {
 }
 
 pub fn remove_dead_blocks(mir: &mut Mir) {
-    let mut seen = BitVector::new(mir.basic_blocks().len());
+    let mut seen = BitArray::new(mir.basic_blocks().len());
     for (bb, _) in traversal::preorder(mir) {
         seen.insert(bb.index());
     }
@@ -285,7 +285,7 @@ impl MirPass for SimplifyLocals {
                           tcx: TyCtxt<'a, 'tcx, 'tcx>,
                           _: MirSource,
                           mir: &mut Mir<'tcx>) {
-        let mut marker = DeclMarker { locals: BitVector::new(mir.local_decls.len()) };
+        let mut marker = DeclMarker { locals: BitArray::new(mir.local_decls.len()) };
         marker.visit_mir(mir);
         // Return pointer and arguments are always live
         marker.locals.insert(RETURN_PLACE);
@@ -310,7 +310,7 @@ impl MirPass for SimplifyLocals {
 /// Construct the mapping while swapping out unused stuff out from the `vec`.
 fn make_local_map<'tcx, V>(
     vec: &mut IndexVec<Local, V>,
-    mask: BitVector<Local>,
+    mask: BitArray<Local>,
 ) -> IndexVec<Local, Option<Local>> {
     let mut map: IndexVec<Local, Option<Local>> = IndexVec::from_elem(None, &*vec);
     let mut used = Local::new(0);
@@ -326,7 +326,7 @@ fn make_local_map<'tcx, V>(
 }
 
 struct DeclMarker {
-    pub locals: BitVector<Local>,
+    pub locals: BitArray<Local>,
 }
 
 impl<'tcx> Visitor<'tcx> for DeclMarker {
diff --git a/src/librustc_resolve/resolve_imports.rs b/src/librustc_resolve/resolve_imports.rs
index 260179de99b80..b6ad2f316a0a2 100644
--- a/src/librustc_resolve/resolve_imports.rs
+++ b/src/librustc_resolve/resolve_imports.rs
@@ -691,6 +691,8 @@ impl<'a, 'b:'a> ImportResolver<'a, 'b> {
                             expansion: directive.expansion,
                         });
                         let _ = self.try_define(directive.parent, target, TypeNS, binding);
+                        let import = self.import_map.entry(directive.id).or_default();
+                        import[TypeNS] = Some(PathResolution::new(binding.def()));
                         return None;
                     }
                 }
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 7454f79ed6bbb..45566230fdaae 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -1194,7 +1194,8 @@ fn resolve(cx: &DocContext, path_str: &str, is_val: bool) -> Result<(Def, Option
         })?;
         match ty.def {
             Def::Struct(did) | Def::Union(did) | Def::Enum(did) | Def::TyAlias(did) => {
-                let item = cx.tcx.inherent_impls(did).iter()
+                let item = cx.tcx.inherent_impls(did)
+                                 .iter()
                                  .flat_map(|imp| cx.tcx.associated_items(*imp))
                                  .find(|item| item.ident.name == item_name);
                 if let Some(item) = item {
@@ -1205,26 +1206,29 @@ fn resolve(cx: &DocContext, path_str: &str, is_val: bool) -> Result<(Def, Option
                     };
                     Ok((ty.def, Some(format!("{}.{}", out, item_name))))
                 } else {
-                    let is_enum = match ty.def {
-                        Def::Enum(_) => true,
-                        _ => false,
-                    };
-                    let elem = if is_enum {
-                        cx.tcx.adt_def(did).all_fields().find(|item| item.ident.name == item_name)
-                    } else {
-                        cx.tcx.adt_def(did)
-                              .non_enum_variant()
-                              .fields
-                              .iter()
-                              .find(|item| item.ident.name == item_name)
-                    };
-                    if let Some(item) = elem {
-                        Ok((ty.def,
-                            Some(format!("{}.{}",
-                                         if is_enum { "variant" } else { "structfield" },
-                                         item.ident))))
-                    } else {
-                        Err(())
+                    match cx.tcx.type_of(did).sty {
+                        ty::TyAdt(def, _) => {
+                            if let Some(item) = if def.is_enum() {
+                                def.all_fields().find(|item| item.ident.name == item_name)
+                            } else {
+                                def.non_enum_variant()
+                                   .fields
+                                   .iter()
+                                   .find(|item| item.ident.name == item_name)
+                            } {
+                                Ok((ty.def,
+                                    Some(format!("{}.{}",
+                                                 if def.is_enum() {
+                                                     "variant"
+                                                 } else {
+                                                     "structfield"
+                                                 },
+                                                 item.ident))))
+                            } else {
+                                Err(())
+                            }
+                        }
+                        _ => Err(()),
                     }
                 }
             }
diff --git a/src/librustdoc/visit_ast.rs b/src/librustdoc/visit_ast.rs
index 09d304b71a2c1..287913d2cc9b8 100644
--- a/src/librustdoc/visit_ast.rs
+++ b/src/librustdoc/visit_ast.rs
@@ -105,8 +105,8 @@ impl<'a, 'tcx, 'rcx> RustdocVisitor<'a, 'tcx, 'rcx> {
     }
 
     pub fn visit_variant_data(&mut self, item: &hir::Item,
-                            name: ast::Name, sd: &hir::VariantData,
-                            generics: &hir::Generics) -> Struct {
+                              name: ast::Name, sd: &hir::VariantData,
+                              generics: &hir::Generics) -> Struct {
         debug!("Visiting struct");
         let struct_type = struct_type_from_def(&*sd);
         Struct {
diff --git a/src/libstd/io/mod.rs b/src/libstd/io/mod.rs
index 5e89ad45f81d2..b83f3fbe7a59c 100644
--- a/src/libstd/io/mod.rs
+++ b/src/libstd/io/mod.rs
@@ -354,19 +354,26 @@ fn append_to_string<F>(buf: &mut String, f: F) -> Result<usize>
 // avoid paying to allocate and zero a huge chunk of memory if the reader only
 // has 4 bytes while still making large reads if the reader does have a ton
 // of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
-// time is 4,500 times (!) slower than this if the reader has a very small
-// amount of data to return.
+// time is 4,500 times (!) slower than a default reservation size of 32 if the
+// reader has a very small amount of data to return.
 //
 // Because we're extending the buffer with uninitialized data for trusted
 // readers, we need to make sure to truncate that if any of this panics.
 fn read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize> {
+    read_to_end_with_reservation(r, buf, 32)
+}
+
+fn read_to_end_with_reservation<R: Read + ?Sized>(r: &mut R,
+                                                  buf: &mut Vec<u8>,
+                                                  reservation_size: usize) -> Result<usize>
+{
     let start_len = buf.len();
     let mut g = Guard { len: buf.len(), buf: buf };
     let ret;
     loop {
         if g.len == g.buf.len() {
             unsafe {
-                g.buf.reserve(32);
+                g.buf.reserve(reservation_size);
                 let capacity = g.buf.capacity();
                 g.buf.set_len(capacity);
                 r.initializer().initialize(&mut g.buf[g.len..]);
@@ -1899,6 +1906,12 @@ impl<T: Read> Read for Take<T> {
     unsafe fn initializer(&self) -> Initializer {
         self.inner.initializer()
     }
+
+    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
+        let reservation_size = cmp::min(self.limit, 32) as usize;
+
+        read_to_end_with_reservation(self, buf, reservation_size)
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index d59c9dd6b53e8..28c1e4324de7a 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -23,6 +23,7 @@ use ext::hygiene::{Mark, SyntaxContext};
 use print::pprust;
 use ptr::P;
 use rustc_data_structures::indexed_vec;
+use rustc_data_structures::indexed_vec::Idx;
 use symbol::{Symbol, keywords};
 use tokenstream::{ThinTokenStream, TokenStream};
 
@@ -1910,9 +1911,18 @@ pub enum AttrStyle {
     Inner,
 }
 
-#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
+#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, PartialOrd, Ord, Copy)]
 pub struct AttrId(pub usize);
 
+impl Idx for AttrId {
+    fn new(idx: usize) -> Self {
+        AttrId(idx)
+    }
+    fn index(self) -> usize {
+        self.0
+    }
+}
+
 /// Meta-data associated with an item
 /// Doc-comments are promoted to attributes that have is_sugared_doc = true
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
diff --git a/src/libsyntax/attr/mod.rs b/src/libsyntax/attr/mod.rs
index 137b94230a3cd..7fbc5d4c41a50 100644
--- a/src/libsyntax/attr/mod.rs
+++ b/src/libsyntax/attr/mod.rs
@@ -41,51 +41,27 @@ use std::iter;
 
 pub fn mark_used(attr: &Attribute) {
     debug!("Marking {:?} as used.", attr);
-    let AttrId(id) = attr.id;
     GLOBALS.with(|globals| {
-        let mut slot = globals.used_attrs.lock();
-        let idx = (id / 64) as usize;
-        let shift = id % 64;
-        if slot.len() <= idx {
-            slot.resize(idx + 1, 0);
-        }
-        slot[idx] |= 1 << shift;
+        globals.used_attrs.lock().insert(attr.id);
     });
 }
 
 pub fn is_used(attr: &Attribute) -> bool {
-    let AttrId(id) = attr.id;
     GLOBALS.with(|globals| {
-        let slot = globals.used_attrs.lock();
-        let idx = (id / 64) as usize;
-        let shift = id % 64;
-        slot.get(idx).map(|bits| bits & (1 << shift) != 0)
-            .unwrap_or(false)
+        globals.used_attrs.lock().contains(attr.id)
     })
 }
 
 pub fn mark_known(attr: &Attribute) {
     debug!("Marking {:?} as known.", attr);
-    let AttrId(id) = attr.id;
     GLOBALS.with(|globals| {
-        let mut slot = globals.known_attrs.lock();
-        let idx = (id / 64) as usize;
-        let shift = id % 64;
-        if slot.len() <= idx {
-            slot.resize(idx + 1, 0);
-        }
-        slot[idx] |= 1 << shift;
+        globals.known_attrs.lock().insert(attr.id);
     });
 }
 
 pub fn is_known(attr: &Attribute) -> bool {
-    let AttrId(id) = attr.id;
     GLOBALS.with(|globals| {
-        let slot = globals.known_attrs.lock();
-        let idx = (id / 64) as usize;
-        let shift = id % 64;
-        slot.get(idx).map(|bits| bits & (1 << shift) != 0)
-            .unwrap_or(false)
+        globals.known_attrs.lock().contains(attr.id)
     })
 }
 
diff --git a/src/libsyntax/lib.rs b/src/libsyntax/lib.rs
index 60de94821bba0..0c105865e0c2e 100644
--- a/src/libsyntax/lib.rs
+++ b/src/libsyntax/lib.rs
@@ -43,6 +43,8 @@ extern crate rustc_target;
 extern crate serialize as rustc_serialize; // used by deriving
 
 use rustc_data_structures::sync::Lock;
+use rustc_data_structures::bitvec::BitVector;
+use ast::AttrId;
 
 // A variant of 'try!' that panics on an Err. This is used as a crutch on the
 // way towards a non-panic!-prone parser. It should be used for fatal parsing
@@ -75,16 +77,18 @@ macro_rules! unwrap_or {
 }
 
 pub struct Globals {
-    used_attrs: Lock<Vec<u64>>,
-    known_attrs: Lock<Vec<u64>>,
+    used_attrs: Lock<BitVector<AttrId>>,
+    known_attrs: Lock<BitVector<AttrId>>,
     syntax_pos_globals: syntax_pos::Globals,
 }
 
 impl Globals {
     fn new() -> Globals {
         Globals {
-            used_attrs: Lock::new(Vec::new()),
-            known_attrs: Lock::new(Vec::new()),
+            // We have no idea how many attributes their will be, so just
+            // initiate the vectors with 0 bits. We'll grow them as necessary.
+            used_attrs: Lock::new(BitVector::new()),
+            known_attrs: Lock::new(BitVector::new()),
             syntax_pos_globals: syntax_pos::Globals::new(),
         }
     }
diff --git a/src/libsyntax/parse/token.rs b/src/libsyntax/parse/token.rs
index fd8f394a600f0..c449cc0a6525a 100644
--- a/src/libsyntax/parse/token.rs
+++ b/src/libsyntax/parse/token.rs
@@ -104,6 +104,7 @@ pub(crate) fn ident_can_begin_expr(ident: ast::Ident, is_raw: bool) -> bool {
     !ident_token.is_reserved_ident() ||
     ident_token.is_path_segment_keyword() ||
     [
+        keywords::Async.name(),
         keywords::Do.name(),
         keywords::Box.name(),
         keywords::Break.name(),
diff --git a/src/test/codegen/vec-clear.rs b/src/test/codegen/vec-clear.rs
new file mode 100644
index 0000000000000..a73dd077cea11
--- /dev/null
+++ b/src/test/codegen/vec-clear.rs
@@ -0,0 +1,21 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -O
+
+#![crate_type = "lib"]
+
+// CHECK-LABEL: @vec_clear
+#[no_mangle]
+pub fn vec_clear(x: &mut Vec<u32>) {
+    // CHECK-NOT: load
+    // CHECK-NOT: icmp
+    x.clear()
+}
diff --git a/src/test/compile-fail/auxiliary/issue-52489.rs b/src/test/compile-fail/auxiliary/issue-52489.rs
new file mode 100644
index 0000000000000..68d1ef8d776aa
--- /dev/null
+++ b/src/test/compile-fail/auxiliary/issue-52489.rs
@@ -0,0 +1,13 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![crate_type = "lib"]
+#![unstable(feature = "issue_52489_unstable", issue = "0")]
+#![feature(staged_api)]
diff --git a/src/test/compile-fail/issue-52489.rs b/src/test/compile-fail/issue-52489.rs
new file mode 100644
index 0000000000000..c43cc12ca0229
--- /dev/null
+++ b/src/test/compile-fail/issue-52489.rs
@@ -0,0 +1,17 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// edition:2018
+// aux-build:issue-52489.rs
+
+use issue_52489;
+//~^ ERROR use of unstable library feature 'issue_52489_unstable'
+
+fn main() {}
diff --git a/src/test/run-pass/generator/yield-in-initializer.rs b/src/test/run-pass/generator/yield-in-initializer.rs
new file mode 100644
index 0000000000000..3042061226b39
--- /dev/null
+++ b/src/test/run-pass/generator/yield-in-initializer.rs
@@ -0,0 +1,25 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(generators)]
+
+fn main() {
+    static || {
+        loop {
+            // Test that `opt` is not live across the yield, even when borrowed in a loop
+            // See https://github.com/rust-lang/rust/issues/52792
+            let opt = {
+                yield;
+                true
+            };
+            &opt;
+        }
+    };
+}
diff --git a/src/test/rustdoc-ui/intra-doc-alias-ice.rs b/src/test/rustdoc-ui/intra-doc-alias-ice.rs
new file mode 100644
index 0000000000000..a459ab5dd2bea
--- /dev/null
+++ b/src/test/rustdoc-ui/intra-doc-alias-ice.rs
@@ -0,0 +1,16 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![deny(intra_doc_link_resolution_failure)]
+
+pub type TypeAlias = usize;
+
+/// [broken cross-reference](TypeAlias::hoge) //~ ERROR
+pub fn some_public_item() {}
diff --git a/src/test/rustdoc-ui/intra-doc-alias-ice.stderr b/src/test/rustdoc-ui/intra-doc-alias-ice.stderr
new file mode 100644
index 0000000000000..231963976ea75
--- /dev/null
+++ b/src/test/rustdoc-ui/intra-doc-alias-ice.stderr
@@ -0,0 +1,13 @@
+error: `[TypeAlias::hoge]` cannot be resolved, ignoring it...
+  --> $DIR/intra-doc-alias-ice.rs:15:30
+   |
+15 | /// [broken cross-reference](TypeAlias::hoge) //~ ERROR
+   |                              ^^^^^^^^^^^^^^^ cannot be resolved, ignoring
+   |
+note: lint level defined here
+  --> $DIR/intra-doc-alias-ice.rs:11:9
+   |
+11 | #![deny(intra_doc_link_resolution_failure)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = help: to escape `[` and `]` characters, just add '/' before them like `/[` or `/]`
+
diff --git a/src/test/ui/asm-out-assign-imm.nll.stderr b/src/test/ui/asm-out-assign-imm.nll.stderr
index fbd58cd4c2260..45b0c84275be4 100644
--- a/src/test/ui/asm-out-assign-imm.nll.stderr
+++ b/src/test/ui/asm-out-assign-imm.nll.stderr
@@ -1,5 +1,5 @@
 error[E0384]: cannot assign twice to immutable variable `x`
-  --> $DIR/asm-out-assign-imm.rs:33:9
+  --> $DIR/asm-out-assign-imm.rs:34:9
    |
 LL |     let x: isize;
    |         - consider changing this to `mut x`
diff --git a/src/test/ui/asm-out-assign-imm.rs b/src/test/ui/asm-out-assign-imm.rs
index f5bb07a9b35aa..73143f1154631 100644
--- a/src/test/ui/asm-out-assign-imm.rs
+++ b/src/test/ui/asm-out-assign-imm.rs
@@ -16,6 +16,7 @@
 // ignore-sparc
 // ignore-sparc64
 // ignore-mips
+// ignore-mips64
 
 #![feature(asm)]
 
diff --git a/src/test/ui/asm-out-assign-imm.stderr b/src/test/ui/asm-out-assign-imm.stderr
index 7075914fa04bd..83cb8092e16a2 100644
--- a/src/test/ui/asm-out-assign-imm.stderr
+++ b/src/test/ui/asm-out-assign-imm.stderr
@@ -1,5 +1,5 @@
 error[E0384]: cannot assign twice to immutable variable `x`
-  --> $DIR/asm-out-assign-imm.rs:33:9
+  --> $DIR/asm-out-assign-imm.rs:34:9
    |
 LL |     x = 1;
    |     ----- first assignment to `x`
diff --git a/src/test/ui/async-matches-expr.rs b/src/test/ui/async-matches-expr.rs
new file mode 100644
index 0000000000000..d6959f9ddd805
--- /dev/null
+++ b/src/test/ui/async-matches-expr.rs
@@ -0,0 +1,23 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-pass
+// edition:2018
+
+#![feature(async_await, await_macro)]
+
+macro_rules! match_expr {
+    ($x:expr) => {}
+}
+
+fn main() {
+    match_expr!(async {});
+    match_expr!(async || {});
+}
diff --git a/src/test/ui/issue-49579.rs b/src/test/ui/issue-49579.rs
new file mode 100644
index 0000000000000..e4e97c58d8aa3
--- /dev/null
+++ b/src/test/ui/issue-49579.rs
@@ -0,0 +1,27 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+
+// compile-pass
+
+#![feature(nll)]
+
+fn fibs(n: u32) -> impl Iterator<Item=u128> {
+    (0 .. n)
+    .scan((0, 1), |st, _| {
+        *st = (st.1, st.0 + st.1);
+        Some(*st)
+    })
+    .map(&|(f, _)| f)
+}
+
+fn main() {
+    println!("{:?}", fibs(10).collect::<Vec<_>>());
+}
diff --git a/src/test/ui/issue-49824.nll.stderr b/src/test/ui/issue-49824.nll.stderr
new file mode 100644
index 0000000000000..59345754e9f59
--- /dev/null
+++ b/src/test/ui/issue-49824.nll.stderr
@@ -0,0 +1,20 @@
+error: unsatisfied lifetime constraints
+  --> $DIR/issue-49824.rs:22:9
+   |
+LL |         || {
+   |    _____-
+   |   |_____|
+   |  ||
+LL |  ||         || {
+   |  ||_________^
+LL | |||             let _y = &mut x;
+LL | |||         }
+   | |||_________^ requires that `'1` must outlive `'2`
+LL |  ||     };
+   |  ||     -
+   |  ||_____|
+   |  |______lifetime `'1` represents the closure body
+   |         lifetime `'2` appears in return type
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/issue-49824.rs b/src/test/ui/issue-49824.rs
new file mode 100644
index 0000000000000..1f3e575288427
--- /dev/null
+++ b/src/test/ui/issue-49824.rs
@@ -0,0 +1,26 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(rustc_attrs)]
+
+// This test checks that a failure occurs with NLL but does not fail with the
+// legacy AST output. Check issue-49824.nll.stderr for expected compilation error
+// output under NLL and #49824 for more information.
+
+#[rustc_error]
+fn main() {
+    //~^ compilation successful
+    let mut x = 0;
+    || {
+        || {
+            let _y = &mut x;
+        }
+    };
+}
diff --git a/src/test/ui/issue-49824.stderr b/src/test/ui/issue-49824.stderr
new file mode 100644
index 0000000000000..b6cafe5e9e994
--- /dev/null
+++ b/src/test/ui/issue-49824.stderr
@@ -0,0 +1,14 @@
+error: compilation successful
+  --> $DIR/issue-49824.rs:18:1
+   |
+LL | / fn main() {
+LL | |     //~^ compilation successful
+LL | |     let mut x = 0;
+LL | |     || {
+...  |
+LL | |     };
+LL | | }
+   | |_^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/nll/promotable-mutable-zst-doesnt-conflict.rs b/src/test/ui/nll/promotable-mutable-zst-doesnt-conflict.rs
new file mode 100644
index 0000000000000..be38556961271
--- /dev/null
+++ b/src/test/ui/nll/promotable-mutable-zst-doesnt-conflict.rs
@@ -0,0 +1,23 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Check that mutable promoted length zero arrays don't check for conflicting
+// access
+
+// run-pass
+
+#![feature(nll)]
+
+pub fn main() {
+    let mut x: Vec<&[i32; 0]> = Vec::new();
+    for i in 0..10 {
+        x.push(&[]);
+    }
+}
diff --git a/src/test/ui/rust-2018/macro-use-warned-against.rs b/src/test/ui/rust-2018/macro-use-warned-against.rs
index f7a6b56028080..f50419434ae1d 100644
--- a/src/test/ui/rust-2018/macro-use-warned-against.rs
+++ b/src/test/ui/rust-2018/macro-use-warned-against.rs
@@ -12,7 +12,7 @@
 // aux-build:macro-use-warned-against2.rs
 // compile-pass
 
-#![warn(rust_2018_idioms, unused)]
+#![warn(macro_use_extern_crate, unused)]
 #![feature(use_extern_macros)]
 
 #[macro_use] //~ WARN should be replaced at use sites with a `use` statement
diff --git a/src/test/ui/rust-2018/macro-use-warned-against.stderr b/src/test/ui/rust-2018/macro-use-warned-against.stderr
index bebad31510f56..7af404fab790e 100644
--- a/src/test/ui/rust-2018/macro-use-warned-against.stderr
+++ b/src/test/ui/rust-2018/macro-use-warned-against.stderr
@@ -7,9 +7,8 @@ LL | #[macro_use] //~ WARN should be replaced at use sites with a `use` statemen
 note: lint level defined here
   --> $DIR/macro-use-warned-against.rs:15:9
    |
-LL | #![warn(rust_2018_idioms, unused)]
-   |         ^^^^^^^^^^^^^^^^
-   = note: #[warn(macro_use_extern_crate)] implied by #[warn(rust_2018_idioms)]
+LL | #![warn(macro_use_extern_crate, unused)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused `#[macro_use]` import
   --> $DIR/macro-use-warned-against.rs:20:1
@@ -18,9 +17,9 @@ LL | #[macro_use] //~ WARN unused `#[macro_use]`
    | ^^^^^^^^^^^^
    |
 note: lint level defined here
-  --> $DIR/macro-use-warned-against.rs:15:27
+  --> $DIR/macro-use-warned-against.rs:15:33
    |
-LL | #![warn(rust_2018_idioms, unused)]
-   |                           ^^^^^^
+LL | #![warn(macro_use_extern_crate, unused)]
+   |                                 ^^^^^^
    = note: #[warn(unused_imports)] implied by #[warn(unused)]
 
diff --git a/src/test/ui/target-feature-gate.rs b/src/test/ui/target-feature-gate.rs
index 69208f151360b..c2dc927c4b524 100644
--- a/src/test/ui/target-feature-gate.rs
+++ b/src/test/ui/target-feature-gate.rs
@@ -12,6 +12,8 @@
 // ignore-aarch64
 // ignore-wasm
 // ignore-emscripten
+// ignore-mips
+// ignore-mips64
 // gate-test-sse4a_target_feature
 // gate-test-powerpc_target_feature
 // gate-test-avx512_target_feature
diff --git a/src/test/ui/target-feature-gate.stderr b/src/test/ui/target-feature-gate.stderr
index a6f794a1a1ab2..24141d0064fb0 100644
--- a/src/test/ui/target-feature-gate.stderr
+++ b/src/test/ui/target-feature-gate.stderr
@@ -1,5 +1,5 @@
 error[E0658]: the target feature `avx512bw` is currently unstable (see issue #44839)
-  --> $DIR/target-feature-gate.rs:26:18
+  --> $DIR/target-feature-gate.rs:28:18
    |
 LL | #[target_feature(enable = "avx512bw")]
    |                  ^^^^^^^^^^^^^^^^^^^
diff --git a/src/test/ui/target-feature-wrong.rs b/src/test/ui/target-feature-wrong.rs
index 8983c0ea79bd9..fe611141379c4 100644
--- a/src/test/ui/target-feature-wrong.rs
+++ b/src/test/ui/target-feature-wrong.rs
@@ -13,6 +13,7 @@
 // ignore-wasm
 // ignore-emscripten
 // ignore-mips
+// ignore-mips64
 // ignore-powerpc
 // ignore-powerpc64
 // ignore-powerpc64le
diff --git a/src/test/ui/target-feature-wrong.stderr b/src/test/ui/target-feature-wrong.stderr
index d4e1c978104b6..21c73b7ddbff0 100644
--- a/src/test/ui/target-feature-wrong.stderr
+++ b/src/test/ui/target-feature-wrong.stderr
@@ -1,35 +1,35 @@
 error: #[target_feature] attribute must be of the form #[target_feature(..)]
-  --> $DIR/target-feature-wrong.rs:25:1
+  --> $DIR/target-feature-wrong.rs:26:1
    |
 LL | #[target_feature = "+sse2"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: the feature named `foo` is not valid for this target
-  --> $DIR/target-feature-wrong.rs:27:18
+  --> $DIR/target-feature-wrong.rs:28:18
    |
 LL | #[target_feature(enable = "foo")]
    |                  ^^^^^^^^^^^^^^
 
 error: #[target_feature(..)] only accepts sub-keys of `enable` currently
-  --> $DIR/target-feature-wrong.rs:29:18
+  --> $DIR/target-feature-wrong.rs:30:18
    |
 LL | #[target_feature(bar)]
    |                  ^^^
 
 error: #[target_feature(..)] only accepts sub-keys of `enable` currently
-  --> $DIR/target-feature-wrong.rs:31:18
+  --> $DIR/target-feature-wrong.rs:32:18
    |
 LL | #[target_feature(disable = "baz")]
    |                  ^^^^^^^^^^^^^^^
 
 error: #[target_feature(..)] can only be applied to `unsafe` function
-  --> $DIR/target-feature-wrong.rs:35:1
+  --> $DIR/target-feature-wrong.rs:36:1
    |
 LL | #[target_feature(enable = "sse2")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: attribute should be applied to a function
-  --> $DIR/target-feature-wrong.rs:39:1
+  --> $DIR/target-feature-wrong.rs:40:1
    |
 LL | #[target_feature(enable = "sse2")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -38,7 +38,7 @@ LL | mod another {}
    | -------------- not a function
 
 error: cannot use #[inline(always)] with #[target_feature]
-  --> $DIR/target-feature-wrong.rs:43:1
+  --> $DIR/target-feature-wrong.rs:44:1
    |
 LL | #[inline(always)]
    | ^^^^^^^^^^^^^^^^^