Couple of changes to FileSearch and SearchPath

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -637,7 +637,7 @@ fn link_dwarf_object<'a>(sess: &'a Session, executable_out_filename: &Path) {
     cmd.arg("-o");
     cmd.arg(&dwp_out_filename);
 
-    let mut new_path = sess.host_filesearch(PathKind::All).get_tools_search_paths(false);
+    let mut new_path = sess.get_tools_search_paths(false);
     if let Some(path) = env::var_os("PATH") {
         new_path.extend(env::split_paths(&path));
     }
@@ -2555,8 +2555,7 @@ fn add_gcc_ld_path(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
             match ld_impl {
                 LdImpl::Lld => {
                     if sess.target.lld_flavor == LldFlavor::Ld64 {
-                        let tools_path =
-                            sess.host_filesearch(PathKind::All).get_tools_search_paths(false);
+                        let tools_path = sess.get_tools_search_paths(false);
                         let ld64_exe = tools_path
                             .into_iter()
                             .map(|p| p.join("gcc-ld"))
@@ -2571,8 +2570,7 @@ fn add_gcc_ld_path(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
                             arg
                         });
                     } else {
-                        let tools_path =
-                            sess.host_filesearch(PathKind::All).get_tools_search_paths(false);
+                        let tools_path = sess.get_tools_search_paths(false);
                         let lld_path = tools_path
                             .into_iter()
                             .map(|p| p.join("gcc-ld"))

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -15,7 +15,6 @@ use rustc_middle::middle::dependency_format::Linkage;
 use rustc_middle::ty::TyCtxt;
 use rustc_serialize::{json, Encoder};
 use rustc_session::config::{self, CrateType, DebugInfo, LinkerPluginLto, Lto, OptLevel, Strip};
-use rustc_session::search_paths::PathKind;
 use rustc_session::Session;
 use rustc_span::symbol::Symbol;
 use rustc_target::spec::{LinkOutputKind, LinkerFlavor, LldFlavor};
@@ -101,7 +100,7 @@ pub fn get_linker<'a>(
 
     // The compiler's sysroot often has some bundled tools, so add it to the
     // PATH for the child.
-    let mut new_path = sess.host_filesearch(PathKind::All).get_tools_search_paths(self_contained);
+    let mut new_path = sess.get_tools_search_paths(self_contained);
     let mut msvc_changed_path = false;
     if sess.target.is_like_msvc {
         if let Some(ref tool) = msvc_tool {

compiler/rustc_driver/src/lib.rs

@@ -677,10 +677,7 @@ impl RustcDefaultCalls {
                     println!("{}", targets.join("\n"));
                 }
                 Sysroot => println!("{}", sess.sysroot.display()),
-                TargetLibdir => println!(
-                    "{}",
-                    sess.target_tlib_path.as_ref().unwrap_or(&sess.host_tlib_path).dir.display()
-                ),
+                TargetLibdir => println!("{}", sess.target_tlib_path.dir.display()),
                 TargetSpec => println!("{}", sess.target.to_json().pretty()),
                 FileNames | CrateName => {
                     let input = input.unwrap_or_else(|| {

compiler/rustc_session/src/filesearch.rs

@@ -1,3 +1,5 @@
+//! A module for searching for libraries
+
 pub use self::FileMatch::*;
 
 use std::env;
@@ -14,8 +16,6 @@ pub enum FileMatch {
     FileDoesntMatch,
 }
 
-// A module for searching for libraries
-
 #[derive(Clone)]
 pub struct FileSearch<'a> {
     sysroot: &'a Path,
@@ -83,22 +83,10 @@ impl<'a> FileSearch<'a> {
         FileSearch { sysroot, triple, search_paths, tlib_path, kind }
     }
 
-    // Returns just the directories within the search paths.
+    /// Returns just the directories within the search paths.
     pub fn search_path_dirs(&self) -> Vec<PathBuf> {
         self.search_paths().map(|sp| sp.dir.to_path_buf()).collect()
     }
-
-    // Returns a list of directories where target-specific tool binaries are located.
-    pub fn get_tools_search_paths(&self, self_contained: bool) -> Vec<PathBuf> {
-        let rustlib_path = rustc_target::target_rustlib_path(self.sysroot, &self.triple);
-        let p = std::array::IntoIter::new([
-            Path::new(&self.sysroot),
-            Path::new(&rustlib_path),
-            Path::new("bin"),
-        ])
-        .collect::<PathBuf>();
-        if self_contained { vec![p.clone(), p.join("self-contained")] } else { vec![p] }
-    }
 }
 
 pub fn make_target_lib_path(sysroot: &Path, target_triple: &str) -> PathBuf {
@@ -107,8 +95,8 @@ pub fn make_target_lib_path(sysroot: &Path, target_triple: &str) -> PathBuf {
         .collect::<PathBuf>()
 }
 
-// This function checks if sysroot is found using env::args().next(), and if it
-// is not found, uses env::current_exe() to imply sysroot.
+/// This function checks if sysroot is found using env::args().next(), and if it
+/// is not found, uses env::current_exe() to imply sysroot.
 pub fn get_or_default_sysroot() -> PathBuf {
     // Follow symlinks.  If the resolved path is relative, make it absolute.
     fn canonicalize(path: PathBuf) -> PathBuf {

compiler/rustc_session/src/search_paths.rs

@@ -9,17 +9,17 @@ pub struct SearchPath {
     pub files: Vec<SearchPathFile>,
 }
 
-// The obvious implementation of `SearchPath::files` is a `Vec<PathBuf>`. But
-// it is searched repeatedly by `find_library_crate`, and the searches involve
-// checking the prefix and suffix of the filename of each `PathBuf`. This is
-// doable, but very slow, because it involves calls to `file_name` and
-// `extension` that are themselves slow.
-//
-// This type augments the `PathBuf` with an `Option<String>` containing the
-// `PathBuf`'s filename. The prefix and suffix checking is much faster on the
-// `Option<String>` than the `PathBuf`. (It's an `Option` because
-// `Path::file_name` can fail; if that happens then all subsequent checking
-// will also fail, which is fine.)
+/// The obvious implementation of `SearchPath::files` is a `Vec<PathBuf>`. But
+/// it is searched repeatedly by `find_library_crate`, and the searches involve
+/// checking the prefix and suffix of the filename of each `PathBuf`. This is
+/// doable, but very slow, because it involves calls to `file_name` and
+/// `extension` that are themselves slow.
+///
+/// This type augments the `PathBuf` with an `Option<String>` containing the
+/// `PathBuf`'s filename. The prefix and suffix checking is much faster on the
+/// `Option<String>` than the `PathBuf`. (It's an `Option` because
+/// `Path::file_name` can fail; if that happens then all subsequent checking
+/// will also fail, which is fine.)
 #[derive(Clone, Debug)]
 pub struct SearchPathFile {
     pub path: PathBuf,

compiler/rustc_session/src/session.rs

@@ -36,7 +36,7 @@ use std::fmt;
 use std::io::Write;
 use std::num::NonZeroU32;
 use std::ops::{Div, Mul};
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 use std::str::FromStr;
 use std::sync::Arc;
 use std::time::Duration;
@@ -131,9 +131,8 @@ pub struct Session {
     pub target: Target,
     pub host: Target,
     pub opts: config::Options,
-    pub host_tlib_path: SearchPath,
-    /// `None` if the host and target are the same.
-    pub target_tlib_path: Option<SearchPath>,
+    pub host_tlib_path: Lrc<SearchPath>,
+    pub target_tlib_path: Lrc<SearchPath>,
     pub parse_sess: ParseSess,
     pub sysroot: PathBuf,
     /// The name of the root source file of the crate, in the local file system.
@@ -784,8 +783,7 @@ impl Session {
             &self.sysroot,
             self.opts.target_triple.triple(),
             &self.opts.search_paths,
-            // `target_tlib_path == None` means it's the same as `host_tlib_path`.
-            self.target_tlib_path.as_ref().unwrap_or(&self.host_tlib_path),
+            &self.target_tlib_path,
             kind,
         )
     }
@@ -799,6 +797,18 @@ impl Session {
         )
     }
 
+    /// Returns a list of directories where target-specific tool binaries are located.
+    pub fn get_tools_search_paths(&self, self_contained: bool) -> Vec<PathBuf> {
+        let rustlib_path = rustc_target::target_rustlib_path(&self.sysroot, &config::host_triple());
+        let p = std::array::IntoIter::new([
+            Path::new(&self.sysroot),
+            Path::new(&rustlib_path),
+            Path::new("bin"),
+        ])
+        .collect::<PathBuf>();
+        if self_contained { vec![p.clone(), p.join("self-contained")] } else { vec![p] }
+    }
+
     pub fn init_incr_comp_session(
         &self,
         session_dir: PathBuf,
@@ -1242,11 +1252,13 @@ pub fn build_session(
 
     let host_triple = config::host_triple();
     let target_triple = sopts.target_triple.triple();
-    let host_tlib_path = SearchPath::from_sysroot_and_triple(&sysroot, host_triple);
+    let host_tlib_path = Lrc::new(SearchPath::from_sysroot_and_triple(&sysroot, host_triple));
     let target_tlib_path = if host_triple == target_triple {
-        None
+        // Use the same `SearchPath` if host and target triple are identical to avoid unnecessary
+        // rescanning of the target lib path and an unnecessary allocation.
+        host_tlib_path.clone()
     } else {
-        Some(SearchPath::from_sysroot_and_triple(&sysroot, target_triple))
+        Lrc::new(SearchPath::from_sysroot_and_triple(&sysroot, target_triple))
     };
 
     let file_path_mapping = sopts.file_path_mapping();