Link with ld.gold by default

To disable, pass `-C disable-gold`

Author: brson

src/librustc/session/config.rs

@@ -515,6 +515,8 @@ options! {CodegenOptions, CodegenSetter, basic_codegen_options,
         "explicitly enable the cfg(debug_assertions) directive"),
     inline_threshold: Option<usize> = (None, parse_opt_uint,
         "set the inlining threshold for"),
+    disable_gold: bool = (false, parse_bool,
+        "disable use of the ld.gold linker"),
 }
 
 

src/librustc_trans/back/link.rs

@@ -1060,6 +1060,10 @@ fn link_args(cmd: &mut Linker,
         cmd.args(&rpath::get_rpath_flags(&mut rpath_config));
     }
 
+    // Use the gold linker if possible instead of ld. It is much
+    // faster.
+    cmd.try_gold_linker();
+
     // Finally add all the linker arguments provided on the command line along
     // with any #[link_args] attributes found inside the crate
     if let Some(ref args) = sess.opts.cg.link_args {

src/librustc_trans/back/linker.rs

@@ -56,6 +56,7 @@ pub trait Linker {
     fn no_whole_archives(&mut self);
     fn export_symbols(&mut self, sess: &Session, trans: &CrateTranslation,
                       tmpdir: &Path);
+    fn try_gold_linker(&mut self);
 }
 
 pub struct GnuLinker<'a> {
@@ -199,6 +200,24 @@ impl<'a> Linker for GnuLinker<'a> {
     fn export_symbols(&mut self, _: &Session, _: &CrateTranslation, _: &Path) {
         // noop, visibility in object files takes care of this
     }
+
+    fn try_gold_linker(&mut self) {
+        let gold_exists = Path::new("/usr/bin/ld.gold").exists();
+        let opt_out = self.sess.opts.cg.disable_gold;
+
+        match (gold_exists, opt_out) {
+            (true, false) => {
+                info!("linking with ld.gold");
+                self.cmd.arg("-fuse-ld=gold");
+            }
+            (false, _) => {
+                info!("ld.gold not found. linking with ld");
+            }
+            (_, true) => {
+                info!("opting out of ld.gold");
+            }
+        }
+    }
 }
 
 pub struct MsvcLinker<'a> {
@@ -358,4 +377,6 @@ impl<'a> Linker for MsvcLinker<'a> {
         arg.push(path);
         self.cmd.arg(&arg);
     }
+
+    fn try_gold_linker(&mut self) {}
 }