Allocate numerical values of DefIndexes from two seperate ranges.

This way we can have all item-likes occupy a dense range of
DefIndexes, which is good for making fast, array-based
dictionaries.

Author: michaelwoerister

src/librustc/hir/def_id.rs

@@ -78,33 +78,86 @@ impl serialize::UseSpecializedDecodable for CrateNum {
 /// A DefIndex is an index into the hir-map for a crate, identifying a
 /// particular definition. It should really be considered an interned
 /// shorthand for a particular DefPath.
+///
+/// At the moment we are allocating the numerical values of DefIndexes into two
+/// ranges: the "low" range (starting at zero) and the "high" range (starting at
+/// DEF_INDEX_HI_START). This allows us to allocate the DefIndexes of all
+/// item-likes (Items, TraitItems, and ImplItems) into one of these ranges and
+/// consequently use a simple array for lookup tables keyed by DefIndex and
+/// known to be densely populated. This is especially important for the HIR map.
+///
+/// Since the DefIndex is mostly treated as an opaque ID, you probably
+/// don't have to care about these ranges.
 #[derive(Clone, Debug, Eq, Ord, PartialOrd, PartialEq, RustcEncodable,
            RustcDecodable, Hash, Copy)]
 pub struct DefIndex(u32);
 
 impl DefIndex {
+    #[inline]
     pub fn new(x: usize) -> DefIndex {
         assert!(x < (u32::MAX as usize));
         DefIndex(x as u32)
     }
 
+    #[inline]
     pub fn from_u32(x: u32) -> DefIndex {
         DefIndex(x)
     }
 
+    #[inline]
     pub fn as_usize(&self) -> usize {
         self.0 as usize
     }
 
+    #[inline]
     pub fn as_u32(&self) -> u32 {
         self.0
     }
+
+    #[inline]
+    pub fn address_space(&self) -> DefIndexAddressSpace {
+        if self.0 < DEF_INDEX_HI_START.0 {
+            DefIndexAddressSpace::Low
+        } else {
+            DefIndexAddressSpace::High
+        }
+    }
+
+    /// Converts this DefIndex into a zero-based array index.
+    /// This index is the offset within the given "range" of the DefIndex,
+    /// that is, if the DefIndex is part of the "high" range, the resulting
+    /// index will be (DefIndex - DEF_INDEX_HI_START).
+    #[inline]
+    pub fn as_array_index(&self) -> usize {
+        (self.0 & !DEF_INDEX_HI_START.0) as usize
+    }
 }
 
+/// The start of the "high" range of DefIndexes.
+const DEF_INDEX_HI_START: DefIndex = DefIndex(1 << 31);
+
 /// The crate root is always assigned index 0 by the AST Map code,
 /// thanks to `NodeCollector::new`.
 pub const CRATE_DEF_INDEX: DefIndex = DefIndex(0);
 
+#[derive(Copy, Clone, Eq, PartialEq, Hash)]
+pub enum DefIndexAddressSpace {
+    Low = 0,
+    High = 1,
+}
+
+impl DefIndexAddressSpace {
+    #[inline]
+    pub fn index(&self) -> usize {
+        *self as usize
+    }
+
+    #[inline]
+    pub fn start(&self) -> usize {
+        self.index() * DEF_INDEX_HI_START.as_usize()
+    }
+}
+
 /// A DefId identifies a particular *definition*, by combining a crate
 /// index and a def index.
 #[derive(Clone, Eq, Ord, PartialOrd, PartialEq, RustcEncodable, RustcDecodable, Hash, Copy)]

src/librustc/hir/lowering.rs

@@ -41,7 +41,7 @@
 // in the HIR, especially for multiple identifiers.
 
 use hir;
-use hir::map::{Definitions, DefKey};
+use hir::map::{Definitions, DefKey, REGULAR_SPACE};
 use hir::map::definitions::DefPathData;
 use hir::def_id::{DefIndex, DefId, CRATE_DEF_INDEX};
 use hir::def::{Def, PathResolution};
@@ -2711,7 +2711,10 @@ impl<'a> LoweringContext<'a> {
         let def_id = {
             let defs = self.resolver.definitions();
             let def_path_data = DefPathData::Binding(name.as_str());
-            let def_index = defs.create_def_with_parent(parent_def, id, def_path_data);
+            let def_index = defs.create_def_with_parent(parent_def,
+                                                        id,
+                                                        def_path_data,
+                                                        REGULAR_SPACE);
             DefId::local(def_index)
         };
 

src/librustc/hir/map/def_collector.rs

@@ -9,13 +9,15 @@
 // except according to those terms.
 
 use hir::map::definitions::*;
-use hir::def_id::{CRATE_DEF_INDEX, DefIndex};
+use hir::def_id::{CRATE_DEF_INDEX, DefIndex, DefIndexAddressSpace};
 
 use syntax::ast::*;
 use syntax::ext::hygiene::Mark;
 use syntax::visit;
 use syntax::symbol::{Symbol, keywords};
 
+use hir::map::{ITEM_LIKE_SPACE, REGULAR_SPACE};
+
 /// Creates def ids for nodes in the AST.
 pub struct DefCollector<'a> {
     definitions: &'a mut Definitions,
@@ -39,23 +41,31 @@ impl<'a> DefCollector<'a> {
     }
 
     pub fn collect_root(&mut self) {
-        let root = self.create_def_with_parent(None, CRATE_NODE_ID, DefPathData::CrateRoot);
+        let root = self.create_def_with_parent(None,
+                                               CRATE_NODE_ID,
+                                               DefPathData::CrateRoot,
+                                               ITEM_LIKE_SPACE);
         assert_eq!(root, CRATE_DEF_INDEX);
         self.parent_def = Some(root);
     }
 
-    fn create_def(&mut self, node_id: NodeId, data: DefPathData) -> DefIndex {
+    fn create_def(&mut self,
+                  node_id: NodeId,
+                  data: DefPathData,
+                  address_space: DefIndexAddressSpace)
+                  -> DefIndex {
         let parent_def = self.parent_def;
         debug!("create_def(node_id={:?}, data={:?}, parent_def={:?})", node_id, data, parent_def);
-        self.definitions.create_def_with_parent(parent_def, node_id, data)
+        self.definitions.create_def_with_parent(parent_def, node_id, data, address_space)
     }
 
     fn create_def_with_parent(&mut self,
                               parent: Option<DefIndex>,
                               node_id: NodeId,
-                              data: DefPathData)
+                              data: DefPathData,
+                              address_space: DefIndexAddressSpace)
                               -> DefIndex {
-        self.definitions.create_def_with_parent(parent, node_id, data)
+        self.definitions.create_def_with_parent(parent, node_id, data, address_space)
     }
 
     pub fn with_parent<F: FnOnce(&mut Self)>(&mut self, parent_def: DefIndex, f: F) {
@@ -76,7 +86,7 @@ impl<'a> DefCollector<'a> {
             _ => {}
         }
 
-        self.create_def(expr.id, DefPathData::Initializer);
+        self.create_def(expr.id, DefPathData::Initializer, REGULAR_SPACE);
     }
 
     fn visit_macro_invoc(&mut self, id: NodeId, const_expr: bool) {
@@ -118,27 +128,32 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
                     ViewPathSimple(..) => {}
                     ViewPathList(_, ref imports) => {
                         for import in imports {
-                            self.create_def(import.node.id, DefPathData::Misc);
+                            self.create_def(import.node.id,
+                                            DefPathData::Misc,
+                                            ITEM_LIKE_SPACE);
                         }
                     }
                 }
                 DefPathData::Misc
             }
         };
-        let def = self.create_def(i.id, def_data);
+        let def = self.create_def(i.id, def_data, ITEM_LIKE_SPACE);
 
         self.with_parent(def, |this| {
             match i.node {
                 ItemKind::Enum(ref enum_definition, _) => {
                     for v in &enum_definition.variants {
                         let variant_def_index =
                             this.create_def(v.node.data.id(),
-                                            DefPathData::EnumVariant(v.node.name.name.as_str()));
+                                            DefPathData::EnumVariant(v.node.name.name.as_str()),
+                                            REGULAR_SPACE);
                         this.with_parent(variant_def_index, |this| {
                             for (index, field) in v.node.data.fields().iter().enumerate() {
                                 let name = field.ident.map(|ident| ident.name)
                                     .unwrap_or_else(|| Symbol::intern(&index.to_string()));
-                                this.create_def(field.id, DefPathData::Field(name.as_str()));
+                                this.create_def(field.id,
+                                                DefPathData::Field(name.as_str()),
+                                                REGULAR_SPACE);
                             }
 
                             if let Some(ref expr) = v.node.disr_expr {
@@ -151,13 +166,14 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
                     // If this is a tuple-like struct, register the constructor.
                     if !struct_def.is_struct() {
                         this.create_def(struct_def.id(),
-                                        DefPathData::StructCtor);
+                                        DefPathData::StructCtor,
+                                        REGULAR_SPACE);
                     }
 
                     for (index, field) in struct_def.fields().iter().enumerate() {
                         let name = field.ident.map(|ident| ident.name.as_str())
                             .unwrap_or(Symbol::intern(&index.to_string()).as_str());
-                        this.create_def(field.id, DefPathData::Field(name));
+                        this.create_def(field.id, DefPathData::Field(name), REGULAR_SPACE);
                     }
                 }
                 _ => {}
@@ -168,7 +184,8 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
 
     fn visit_foreign_item(&mut self, foreign_item: &'a ForeignItem) {
         let def = self.create_def(foreign_item.id,
-                                  DefPathData::ValueNs(foreign_item.ident.name.as_str()));
+                                  DefPathData::ValueNs(foreign_item.ident.name.as_str()),
+                                  REGULAR_SPACE);
 
         self.with_parent(def, |this| {
             visit::walk_foreign_item(this, foreign_item);
@@ -177,7 +194,9 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
 
     fn visit_generics(&mut self, generics: &'a Generics) {
         for ty_param in generics.ty_params.iter() {
-            self.create_def(ty_param.id, DefPathData::TypeParam(ty_param.ident.name.as_str()));
+            self.create_def(ty_param.id,
+                            DefPathData::TypeParam(ty_param.ident.name.as_str()),
+                            REGULAR_SPACE);
         }
 
         visit::walk_generics(self, generics);
@@ -191,7 +210,7 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
             TraitItemKind::Macro(..) => return self.visit_macro_invoc(ti.id, false),
         };
 
-        let def = self.create_def(ti.id, def_data);
+        let def = self.create_def(ti.id, def_data, ITEM_LIKE_SPACE);
         self.with_parent(def, |this| {
             if let TraitItemKind::Const(_, Some(ref expr)) = ti.node {
                 this.visit_const_expr(expr);
@@ -209,7 +228,7 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
             ImplItemKind::Macro(..) => return self.visit_macro_invoc(ii.id, false),
         };
 
-        let def = self.create_def(ii.id, def_data);
+        let def = self.create_def(ii.id, def_data, ITEM_LIKE_SPACE);
         self.with_parent(def, |this| {
             if let ImplItemKind::Const(_, ref expr) = ii.node {
                 this.visit_const_expr(expr);
@@ -225,7 +244,9 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
         match pat.node {
             PatKind::Mac(..) => return self.visit_macro_invoc(pat.id, false),
             PatKind::Ident(_, id, _) => {
-                let def = self.create_def(pat.id, DefPathData::Binding(id.node.name.as_str()));
+                let def = self.create_def(pat.id,
+                                          DefPathData::Binding(id.node.name.as_str()),
+                                          REGULAR_SPACE);
                 self.parent_def = Some(def);
             }
             _ => {}
@@ -242,7 +263,9 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
             ExprKind::Mac(..) => return self.visit_macro_invoc(expr.id, false),
             ExprKind::Repeat(_, ref count) => self.visit_const_expr(count),
             ExprKind::Closure(..) => {
-                let def = self.create_def(expr.id, DefPathData::ClosureExpr);
+                let def = self.create_def(expr.id,
+                                          DefPathData::ClosureExpr,
+                                          REGULAR_SPACE);
                 self.parent_def = Some(def);
             }
             _ => {}
@@ -257,7 +280,7 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
             TyKind::Mac(..) => return self.visit_macro_invoc(ty.id, false),
             TyKind::Array(_, ref length) => self.visit_const_expr(length),
             TyKind::ImplTrait(..) => {
-                self.create_def(ty.id, DefPathData::ImplTrait);
+                self.create_def(ty.id, DefPathData::ImplTrait, REGULAR_SPACE);
             }
             TyKind::Typeof(ref expr) => self.visit_const_expr(expr),
             _ => {}
@@ -266,7 +289,9 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
     }
 
     fn visit_lifetime_def(&mut self, def: &'a LifetimeDef) {
-        self.create_def(def.lifetime.id, DefPathData::LifetimeDef(def.lifetime.name.as_str()));
+        self.create_def(def.lifetime.id,
+                        DefPathData::LifetimeDef(def.lifetime.name.as_str()),
+                        REGULAR_SPACE);
     }
 
     fn visit_stmt(&mut self, stmt: &'a Stmt) {