WIP

Author: Kobzol

src/bootstrap/src/core/build_steps/tool.rs

@@ -645,7 +645,7 @@ impl Step for Rustdoc {
         }
 
         // NOTE: Never modify the rustflags here, it breaks the build cache for other tools!
-        let cargo = prepare_tool_cargo(
+        let mut cargo = prepare_tool_cargo(
             builder,
             build_compiler,
             Mode::ToolRustc,
@@ -655,6 +655,8 @@ impl Step for Rustdoc {
             SourceType::InTree,
             features.as_slice(),
         );
+        cargo.env("CARGO_PROFILE_RELEASE_LTO", "thin");
+        cargo.env("CARGO_PROFILE_RELEASE_CODEGEN_UNITS", "1");
 
         let _guard = builder.msg_tool(
             Kind::Build,