Use LTO for librustdoc

Author: Kobzol

compiler/rustc_codegen_llvm/src/back/lto.rs

@@ -132,7 +132,10 @@ fn prepare_lto(
                         let module = SerializedModule::FromRlib(data.to_vec());
                         upstream_modules.push((module, CString::new(name).unwrap()));
                     }
-                    Err(msg) => return Err(diag_handler.fatal(&msg)),
+                    Err(msg) => {
+                        eprintln!("Couldn't add bitcode from {name}");
+                        return Err(diag_handler.fatal(&msg));
+                    }
                 }
             }
         }

src/bootstrap/tool.rs

@@ -540,7 +540,7 @@ impl Step for Rustdoc {
             features.push("jemalloc".to_string());
         }
 
-        let cargo = prepare_tool_cargo(
+        let mut cargo = prepare_tool_cargo(
             builder,
             build_compiler,
             Mode::ToolRustc,
@@ -551,6 +551,11 @@ impl Step for Rustdoc {
             features.as_slice(),
         );
 
+        if build_compiler.stage == 1 {
+            cargo.rustflag("-Cembed-bitcode=yes");
+            cargo.rustflag("-Clto=thin");
+        }
+
         builder.info(&format!(
             "Building rustdoc for stage{} ({})",
             target_compiler.stage, target_compiler.host

src/librustdoc/clean/blanket_impl.rs

@@ -55,7 +55,7 @@ impl<'a, 'tcx> BlanketImplFinder<'a, 'tcx> {
                 // FIXME(eddyb) ignoring `obligations` might cause false positives.
                 drop(obligations);
 
-                trace!(
+                tracing::trace!(
                     "invoking predicate_may_hold: param_env={:?}, impl_trait_ref={:?}, impl_ty={:?}",
                     param_env,
                     impl_trait_ref,
@@ -87,9 +87,10 @@ impl<'a, 'tcx> BlanketImplFinder<'a, 'tcx> {
                         _ => continue 'blanket_impls,
                     }
                 }
-                debug!(
+                tracing::debug!(
                     "get_blanket_impls: found applicable impl for trait_ref={:?}, ty={:?}",
-                    trait_ref, ty
+                    trait_ref,
+                    ty
                 );
 
                 cx.generated_synthetics.insert((ty.0, trait_def_id));