Auto merge of #52958 - pietroalbini:rollup, r=pietroalbini

Rollup of 15 pull requests

Successful merges:

 - #52793 (Add test for NLL: unexpected "free region `` does not outlive" error )
 - #52799 (Use BitVector for global sets of AttrId)
 - #52809 (Add test for unexpected region for local data ReStatic)
 - #52834 ([NLL] Allow conflicting borrows of promoted length zero arrays)
 - #52835 (Fix Alias intra doc ICE)
 - #52854 (fix memrchr in miri)
 - #52899 (tests/ui: Add missing mips{64} ignores)
 - #52908 (Use SetLenOnDrop in Vec::truncate())
 - #52915 (Don't count MIR locals as borrowed after StorageDead when finding locals live across a yield terminator)
 - #52926 (rustc: Trim down the `rust_2018_idioms` lint group)
 - #52930 (rustc_resolve: record single-segment extern crate import resolutions.)
 - #52939 (Make io::Read::read_to_end consider io::Take::limit)
 - #52942 (Another SmallVec.extend optimization)
 - #52947 (1.27 actually added the `armv5te-unknown-linux-musleabi` target)
 - #52954 (async can begin expressions)

Failed merges:

r? @ghost

4 files changed, 24 insertions, 33 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index d59c9dd6b53..28c1e4324de 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 137b94230a3..7fbc5d4c41a 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 60de94821bb..0c105865e0c 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 fd8f394a600..c449cc0a652 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(),