Make NodeId a newtype_index to enable niche optimizations

src/librustc/hir/intravisit.rs

@@ -49,7 +49,6 @@ use hir::map::{self, Map};
 use super::itemlikevisit::DeepVisitor;
 
 use std::cmp;
-use std::u32;
 
 #[derive(Copy, Clone)]
 pub enum FnKind<'a> {
@@ -1152,8 +1151,8 @@ pub struct IdRange {
 impl IdRange {
     pub fn max() -> IdRange {
         IdRange {
-            min: NodeId::from_u32(u32::MAX),
-            max: NodeId::from_u32(u32::MIN),
+            min: NodeId::MAX,
+            max: NodeId::from_u32(0),
         }
     }
 

src/librustc/hir/map/hir_id_validator.rs

@@ -124,7 +124,7 @@ impl<'a, 'hir: 'a> HirIdValidator<'a, 'hir> {
                                        .enumerate()
                                        .find(|&(_, &entry)| hir_id == entry)
                                        .expect("no node_to_hir_id entry");
-                let node_id = NodeId::new(node_id);
+                let node_id = NodeId::from_usize(node_id);
                 missing_items.push(format!("[local_id: {}, node:{}]",
                                            local_id,
                                            self.hir_map.node_to_string(node_id)));

src/librustc/session/mod.rs

@@ -393,7 +393,7 @@ impl Session {
 
         match id.as_usize().checked_add(count) {
             Some(next) => {
-                self.next_node_id.set(ast::NodeId::new(next));
+                self.next_node_id.set(ast::NodeId::from_usize(next));
             }
             None => bug!("Input too large, ran out of node ids!"),
         }
@@ -1160,7 +1160,7 @@ pub fn build_session_(
         recursion_limit: Once::new(),
         type_length_limit: Once::new(),
         const_eval_stack_frame_limit: 100,
-        next_node_id: OneThread::new(Cell::new(NodeId::new(1))),
+        next_node_id: OneThread::new(Cell::new(NodeId::from_u32(1))),
         allocator_kind: Once::new(),
         injected_panic_runtime: Once::new(),
         imported_macro_spans: OneThread::new(RefCell::new(FxHashMap::default())),

src/librustc_driver/pretty.rs

@@ -566,7 +566,7 @@ impl FromStr for UserIdentifiedItem {
     type Err = ();
     fn from_str(s: &str) -> Result<UserIdentifiedItem, ()> {
         Ok(s.parse()
-            .map(ast::NodeId::new)
+            .map(ast::NodeId::from_u32)
             .map(ItemViaNode)
             .unwrap_or_else(|_| ItemViaPath(s.split("::").map(|s| s.to_string()).collect())))
     }

src/librustc_resolve/resolve_imports.rs

@@ -663,7 +663,7 @@ impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
         let mut errors = false;
         let mut seen_spans = FxHashSet::default();
         let mut error_vec = Vec::new();
-        let mut prev_root_id: NodeId = NodeId::new(0);
+        let mut prev_root_id: NodeId = NodeId::from_u32(0);
         for i in 0 .. self.determined_imports.len() {
             let import = self.determined_imports[i];
             let error = self.finalize_import(import);

src/libsyntax/ast.rs

@@ -18,7 +18,6 @@ pub use util::parser::ExprPrecedence;
 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 rustc_target::spec::abi::Abi;
 use source_map::{dummy_spanned, respan, Spanned};
@@ -31,7 +30,6 @@ use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::sync::Lrc;
 use serialize::{self, Decoder, Encoder};
 use std::fmt;
-use std::u32;
 
 pub use rustc_target::abi::FloatTy;
 
@@ -213,71 +211,53 @@ pub struct ParenthesisedArgs {
     pub output: Option<P<Ty>>,
 }
 
-#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
-pub struct NodeId(u32);
+// hack to ensure that we don't try to access the private parts of `NodeId` in this module
+mod node_id_inner {
+    use rustc_data_structures::indexed_vec::Idx;
+    newtype_index! {
+        pub struct NodeId {
+            ENCODABLE = custom
+        }
+    }
+}
+
+pub use self::node_id_inner::NodeId;
 
 impl NodeId {
-    pub fn new(x: usize) -> NodeId {
-        assert!(x < (u32::MAX as usize));
-        NodeId(x as u32)
-    }
-
-    pub fn from_u32(x: u32) -> NodeId {
-        NodeId(x)
-    }
-
-    pub fn as_usize(&self) -> usize {
-        self.0 as usize
-    }
-
-    pub fn as_u32(&self) -> u32 {
-        self.0
-    }
-
     pub fn placeholder_from_mark(mark: Mark) -> Self {
-        NodeId(mark.as_u32())
+        NodeId::from_u32(mark.as_u32())
     }
 
     pub fn placeholder_to_mark(self) -> Mark {
-        Mark::from_u32(self.0)
+        Mark::from_u32(self.as_u32())
     }
 }
 
 impl fmt::Display for NodeId {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        fmt::Display::fmt(&self.0, f)
+        fmt::Display::fmt(&self.as_u32(), f)
     }
 }
 
 impl serialize::UseSpecializedEncodable for NodeId {
     fn default_encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
-        s.emit_u32(self.0)
+        s.emit_u32(self.as_u32())
     }
 }
 
 impl serialize::UseSpecializedDecodable for NodeId {
     fn default_decode<D: Decoder>(d: &mut D) -> Result<NodeId, D::Error> {
-        d.read_u32().map(NodeId)
-    }
-}
-
-impl indexed_vec::Idx for NodeId {
-    fn new(idx: usize) -> Self {
-        NodeId::new(idx)
-    }
-
-    fn index(self) -> usize {
-        self.as_usize()
+        d.read_u32().map(NodeId::from_u32)
     }
 }
 
 /// Node id used to represent the root of the crate.
-pub const CRATE_NODE_ID: NodeId = NodeId(0);
+pub const CRATE_NODE_ID: NodeId = NodeId::from_u32_const(0);
 
 /// When parsing and doing expansions, we initially give all AST nodes this AST
 /// node value. Then later, in the renumber pass, we renumber them to have
 /// small, positive ids.
-pub const DUMMY_NODE_ID: NodeId = NodeId(!0);
+pub const DUMMY_NODE_ID: NodeId = NodeId::MAX;
 
 /// A modifier on a bound, currently this is only used for `?Sized`, where the
 /// modifier is `Maybe`. Negative bounds should also be handled here.

src/libsyntax/lib.rs

@@ -26,6 +26,7 @@
 #![feature(rustc_diagnostic_macros)]
 #![feature(slice_sort_by_cached_key)]
 #![feature(str_escape)]
+#![feature(step_trait)]
 #![feature(try_trait)]
 #![feature(unicode_internals)]
 
@@ -37,7 +38,7 @@ extern crate serialize;
 #[macro_use] extern crate log;
 pub extern crate rustc_errors as errors;
 extern crate syntax_pos;
-extern crate rustc_data_structures;
+#[macro_use] extern crate rustc_data_structures;
 extern crate rustc_target;
 #[macro_use] extern crate scoped_tls;
 #[macro_use]