[WIP] Refactor dep graph representation both in memory and on disk

Cargo.lock

@@ -2780,6 +2780,7 @@ name = "rustc_data_structures"
 version = "0.0.0"
 dependencies = [
  "cfg-if 0.1.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "crossbeam-utils 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "ena 0.13.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "graphviz 0.0.0",
  "indexmap 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",

src/bootstrap/config.rs

@@ -567,7 +567,7 @@ impl Config {
             set(&mut config.lld_enabled, rust.lld);
             set(&mut config.lldb_enabled, rust.lldb);
             set(&mut config.llvm_tools_enabled, rust.llvm_tools);
-            config.rustc_parallel = rust.parallel_compiler.unwrap_or(false);
+            config.rustc_parallel = rust.parallel_compiler.unwrap_or(true);
             config.rustc_default_linker = rust.default_linker.clone();
             config.musl_root = rust.musl_root.clone().map(PathBuf::from);
             config.save_toolstates = rust.save_toolstates.clone().map(PathBuf::from);

src/librustc/dep_graph/dep_node.rs

@@ -106,10 +106,23 @@ macro_rules! define_dep_nodes {
                        $({ $($struct_arg_name:ident : $struct_arg_ty:ty),* })*
       ,)*
     ) => (
+        // Used to get an unique integer per dep kind
+        enum DepKindCounter {
+            $($variant),*
+        }
+
+        /// Encodes `eval_always` in the lowest bit of the discriminant
+        const fn dep_kind_discriminant(kind: DepKindCounter, eval_always: bool) -> isize {
+            (((kind as u16) << 1) | (eval_always as u16)) as isize
+        }
+
         #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash,
                  RustcEncodable, RustcDecodable)]
         pub enum DepKind {
-            $($variant),*
+            $($variant = dep_kind_discriminant(
+                DepKindCounter::$variant,
+                contains_eval_always_attr!($($attr),*),
+            )),*
         }
 
         impl DepKind {
@@ -155,11 +168,8 @@ macro_rules! define_dep_nodes {
 
             #[inline(always)]
             pub fn is_eval_always(&self) -> bool {
-                match *self {
-                    $(
-                        DepKind :: $variant => { contains_eval_always_attr!($($attr), *) }
-                    )*
-                }
+                // `eval_always` is encoded in the lowest bit of DepNodeKind
+                *self as u16 & 1 == 1
             }
 
             #[allow(unreachable_code)]