diff --git a/src/librustc/session/filesearch.rs b/src/librustc/session/filesearch.rs
index a3eea324fd8..82c2425aead 100644
--- a/src/librustc/session/filesearch.rs
+++ b/src/librustc/session/filesearch.rs
@@ -12,6 +12,7 @@
 
 pub use self::FileMatch::*;
 
+use std::borrow::Cow;
 use std::collections::HashSet;
 use std::env;
 use std::fs;
@@ -67,33 +68,32 @@ impl<'a> FileSearch<'a> {
     {
         self.for_each_lib_search_path(|lib_search_path, kind| {
             debug!("searching {}", lib_search_path.display());
-            match fs::read_dir(lib_search_path) {
-                Ok(files) => {
-                    let files = files.filter_map(|p| p.ok().map(|s| s.path()))
-                                     .collect::<Vec<_>>();
-                    fn is_rlib(p: &Path) -> bool {
-                        p.extension().and_then(|s| s.to_str()) == Some("rlib")
+            let files = match fs::read_dir(lib_search_path) {
+                Ok(files) => files,
+                Err(..) => return,
+            };
+            let files = files.filter_map(|p| p.ok().map(|s| s.path()))
+                             .collect::<Vec<_>>();
+            fn is_rlib(p: &Path) -> bool {
+                p.extension() == Some("rlib".as_ref())
+            }
+            // Reading metadata out of rlibs is faster, and if we find both
+            // an rlib and a dylib we only read one of the files of
+            // metadata, so in the name of speed, bring all rlib files to
+            // the front of the search list.
+            let files1 = files.iter().filter(|p| is_rlib(p));
+            let files2 = files.iter().filter(|p| !is_rlib(p));
+            for path in files1.chain(files2) {
+                debug!("testing {}", path.display());
+                let maybe_picked = pick(path, kind);
+                match maybe_picked {
+                    FileMatches => {
+                        debug!("picked {}", path.display());
                     }
-                    // Reading metadata out of rlibs is faster, and if we find both
-                    // an rlib and a dylib we only read one of the files of
-                    // metadata, so in the name of speed, bring all rlib files to
-                    // the front of the search list.
-                    let files1 = files.iter().filter(|p| is_rlib(p));
-                    let files2 = files.iter().filter(|p| !is_rlib(p));
-                    for path in files1.chain(files2) {
-                        debug!("testing {}", path.display());
-                        let maybe_picked = pick(path, kind);
-                        match maybe_picked {
-                            FileMatches => {
-                                debug!("picked {}", path.display());
-                            }
-                            FileDoesntMatch => {
-                                debug!("rejected {}", path.display());
-                            }
-                        }
+                    FileDoesntMatch => {
+                        debug!("rejected {}", path.display());
                     }
                 }
-                Err(..) => (),
             }
         });
     }
@@ -123,8 +123,8 @@ impl<'a> FileSearch<'a> {
     // Returns a list of directories where target-specific tool binaries are located.
     pub fn get_tools_search_paths(&self) -> Vec<PathBuf> {
         let mut p = PathBuf::from(self.sysroot);
-        p.push(&find_libdir(self.sysroot));
-        p.push(&rustlibdir());
+        p.push(find_libdir(self.sysroot).as_ref());
+        p.push(RUST_LIB_DIR);
         p.push(&self.triple);
         p.push("bin");
         vec![p]
@@ -132,9 +132,9 @@ impl<'a> FileSearch<'a> {
 }
 
 pub fn relative_target_lib_path(sysroot: &Path, target_triple: &str) -> PathBuf {
-    let mut p = PathBuf::from(&find_libdir(sysroot));
+    let mut p = PathBuf::from(find_libdir(sysroot).as_ref());
     assert!(p.is_relative());
-    p.push(&rustlibdir());
+    p.push(RUST_LIB_DIR);
     p.push(target_triple);
     p.push("lib");
     p
@@ -166,7 +166,7 @@ pub fn get_or_default_sysroot() -> PathBuf {
 }
 
 // The name of the directory rustc expects libraries to be located.
-fn find_libdir(sysroot: &Path) -> String {
+fn find_libdir(sysroot: &Path) -> Cow<'static, str> {
     // FIXME: This is a quick hack to make the rustc binary able to locate
     // Rust libraries in Linux environments where libraries might be installed
     // to lib64/lib32. This would be more foolproof by basing the sysroot off
@@ -176,31 +176,23 @@ fn find_libdir(sysroot: &Path) -> String {
     // "lib" (i.e. non-default), this value is used (see issue #16552).
 
     match option_env!("CFG_LIBDIR_RELATIVE") {
-        Some(libdir) if libdir != "lib" => return libdir.to_string(),
-        _ => if sysroot.join(&primary_libdir_name()).join(&rustlibdir()).exists() {
-            return primary_libdir_name();
+        Some(libdir) if libdir != "lib" => return libdir.into(),
+        _ => if sysroot.join(PRIMARY_LIB_DIR).join(RUST_LIB_DIR).exists() {
+            return PRIMARY_LIB_DIR.into();
         } else {
-            return secondary_libdir_name();
+            return SECONDARY_LIB_DIR.into();
         }
     }
 
     #[cfg(target_pointer_width = "64")]
-    fn primary_libdir_name() -> String {
-        "lib64".to_string()
-    }
+    const PRIMARY_LIB_DIR: &'static str = "lib64";
 
     #[cfg(target_pointer_width = "32")]
-    fn primary_libdir_name() -> String {
-        "lib32".to_string()
-    }
+    const PRIMARY_LIB_DIR: &'static str = "lib32";
 
-    fn secondary_libdir_name() -> String {
-        "lib".to_string()
-    }
+    const SECONDARY_LIB_DIR: &'static str = "lib";
 }
 
 // The name of rustc's own place to organize libraries.
 // Used to be "rustc", now the default is "rustlib"
-pub fn rustlibdir() -> String {
-    "rustlib".to_string()
-}
+const RUST_LIB_DIR: &'static str = "rustlib";