bootstrap: Link LLVM tools dynamically in order to save time in ThinLTO builds.

Author: michaelwoerister

src/bootstrap/dist.rs

@@ -1924,16 +1924,27 @@ impl Step for LlvmTools {
         drop(fs::remove_dir_all(&image));
 
         // Prepare the image directory
-        let bindir = builder
+        let src_bindir = builder
             .llvm_out(target)
             .join("bin");
-        let dst = image.join("lib/rustlib")
+        let dst_bindir = image.join("lib/rustlib")
             .join(target)
             .join("bin");
-        t!(fs::create_dir_all(&dst));
+        t!(fs::create_dir_all(&dst_bindir));
         for tool in LLVM_TOOLS {
-            let exe = bindir.join(exe(tool, &target));
-            builder.install(&exe, &dst, 0o755);
+            let exe = src_bindir.join(exe(tool, &target));
+            builder.install(&exe, &dst_bindir, 0o755);
+        }
+
+        if builder.llvm_link_tools_dynamically(target) {
+            let src_libdir = builder
+                .llvm_out(target)
+                .join("lib");
+            let dst_libdir = image.join("lib/rustlib")
+                .join(target)
+                .join("lib");
+            t!(fs::create_dir_all(&dst_libdir));
+            builder.install(&src_libdir.join("libLLVM.so"), &dst_libdir, 0o644);
         }
 
         // Prepare the overlay

src/bootstrap/lib.rs

@@ -1012,6 +1012,10 @@ impl Build {
         self.rust_version()
     }
 
+    fn llvm_link_tools_dynamically(&self, target: Interned<String>) -> bool {
+        target.contains("linux-gnu") || target.contains("apple-darwin")
+    }
+
     /// Returns the `version` string associated with this compiler for Rust
     /// itself.
     ///

src/bootstrap/native.rs

@@ -170,13 +170,10 @@ impl Step for Llvm {
 
         // This setting makes the LLVM tools link to the dynamic LLVM library,
         // which saves both memory during parallel links and overall disk space
-        // for the tools.  We don't distribute any of those tools, so this is
-        // just a local concern.  However, it doesn't work well everywhere.
-        //
-        // If we are shipping llvm tools then we statically link them LLVM
-        if (target.contains("linux-gnu") || target.contains("apple-darwin")) &&
-            !builder.config.llvm_tools_enabled {
-                cfg.define("LLVM_LINK_LLVM_DYLIB", "ON");
+        // for the tools. We don't do this on every platform as it doesn't work
+        // equally well everywhere.
+        if builder.llvm_link_tools_dynamically(target) {
+            cfg.define("LLVM_LINK_LLVM_DYLIB", "ON");
         }
 
         // For distribution we want the LLVM tools to be *statically* linked to libstdc++