rustbuild: Compile rustc with ThinLTO

src/bootstrap/bin/rustc.rs

@@ -175,6 +175,9 @@ fn main() {
         if let Ok(s) = env::var("RUSTC_CODEGEN_UNITS") {
             cmd.arg("-C").arg(format!("codegen-units={}", s));
         }
+        if stage != "0" && env::var("RUSTC_THINLTO").is_ok() {
+            cmd.arg("-Ccodegen-units=16").arg("-Zthinlto");
+        }
 
         // Emit save-analysis info.
         if env::var("RUSTC_SAVE_ANALYSIS") == Ok("api".to_string()) {

src/bootstrap/builder.rs

@@ -471,8 +471,6 @@ impl<'a> Builder<'a> {
              .env("RUSTC", self.out.join("bootstrap/debug/rustc"))
              .env("RUSTC_REAL", self.rustc(compiler))
              .env("RUSTC_STAGE", stage.to_string())
-             .env("RUSTC_CODEGEN_UNITS",
-                  self.config.rust_codegen_units.to_string())
              .env("RUSTC_DEBUG_ASSERTIONS",
                   self.config.rust_debug_assertions.to_string())
              .env("RUSTC_SYSROOT", self.sysroot(compiler))
@@ -486,6 +484,10 @@ impl<'a> Builder<'a> {
              })
              .env("TEST_MIRI", self.config.test_miri.to_string());
 
+        if let Some(n) = self.config.rust_codegen_units {
+            cargo.env("RUSTC_CODEGEN_UNITS", n.to_string());
+        }
+
         if let Some(host_linker) = self.build.linker(compiler.host) {
             cargo.env("RUSTC_HOST_LINKER", host_linker);
         }
@@ -618,6 +620,14 @@ impl<'a> Builder<'a> {
         // FIXME: cargo bench does not accept `--release`
         if self.config.rust_optimize && cmd != "bench" {
             cargo.arg("--release");
+
+            if mode != Mode::Libstd &&
+               self.config.rust_codegen_units.is_none() &&
+               self.build.is_rust_llvm(compiler.host)
+
+            {
+                cargo.env("RUSTC_THINLTO", "1");
+            }
         }
         if self.config.locked_deps {
             cargo.arg("--locked");

src/bootstrap/config.rs

@@ -81,7 +81,7 @@ pub struct Config {
 
     // rust codegen options
     pub rust_optimize: bool,
-    pub rust_codegen_units: u32,
+    pub rust_codegen_units: Option<u32>,
     pub rust_debug_assertions: bool,
     pub rust_debuginfo: bool,
     pub rust_debuginfo_lines: bool,
@@ -307,7 +307,6 @@ impl Config {
         config.submodules = true;
         config.docs = true;
         config.rust_rpath = true;
-        config.rust_codegen_units = 1;
         config.channel = "dev".to_string();
         config.codegen_tests = true;
         config.ignore_git = false;
@@ -470,8 +469,8 @@ impl Config {
             config.musl_root = rust.musl_root.clone().map(PathBuf::from);
 
             match rust.codegen_units {
-                Some(0) => config.rust_codegen_units = num_cpus::get() as u32,
-                Some(n) => config.rust_codegen_units = n,
+                Some(0) => config.rust_codegen_units = Some(num_cpus::get() as u32),
+                Some(n) => config.rust_codegen_units = Some(n),
                 None => {}
             }
         }

src/libstd/collections/hash/map.rs

@@ -1113,6 +1113,7 @@ impl<K, V, S> HashMap<K, V, S>
     /// assert_eq!(map.get(&2), None);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
     pub fn get<Q: ?Sized>(&self, k: &Q) -> Option<&V>
         where K: Borrow<Q>,
               Q: Hash + Eq
@@ -2554,6 +2555,7 @@ impl<K, S, Q: ?Sized> super::Recover<Q> for HashMap<K, (), S>
 {
     type Key = K;
 
+    #[inline]
     fn get(&self, key: &Q) -> Option<&K> {
         self.search(key).into_occupied_bucket().map(|bucket| bucket.into_refs().0)
     }
@@ -2566,6 +2568,7 @@ impl<K, S, Q: ?Sized> super::Recover<Q> for HashMap<K, (), S>
         self.search_mut(key).into_occupied_bucket().map(|bucket| pop_internal(bucket).0)
     }
 
+    #[inline]
     fn replace(&mut self, key: K) -> Option<K> {
         self.reserve(1);