[WIP] Support hybrid LTO/non-LTO rlibs.

Author: bjorn3

build_system/build_sysroot.rs

@@ -212,7 +212,8 @@ fn build_clif_sysroot_for_triple(
     }
 
     // Build sysroot
-    let mut rustflags = vec!["-Zforce-unstable-if-unmarked".to_owned()];
+    let mut rustflags =
+        vec!["-Zforce-unstable-if-unmarked".to_owned(), "-Cembed-bitcode=yes".to_owned()];
     if !panic_unwind_support {
         rustflags.push("-Cpanic=abort".to_owned());
     }
@@ -237,8 +238,6 @@ fn build_clif_sysroot_for_triple(
         rustflags.push("--remap-path-prefix".to_owned());
         rustflags.push(format!("library/={}/library", prefix.to_str().unwrap()));
     }
-    rustflags.push("-Clto=fat".to_owned());
-    rustflags.push("-Zdylib-lto".to_owned());
     rustflags.push("-Cembed-bitcode=yes".to_owned());
     compiler.rustflags.extend(rustflags);
     let mut build_cmd = STANDARD_LIBRARY.build(&compiler, dirs);
@@ -256,7 +255,6 @@ fn build_clif_sysroot_for_triple(
     if env::var_os("CARGO_BUILD_INCREMENTAL").is_none() {
         build_cmd.env("CARGO_BUILD_INCREMENTAL", "true");
     }
-    build_cmd.env("CARGO_PROFILE_RELEASE_LTO", "thin");
     spawn_and_wait(build_cmd);
 
     for entry in fs::read_dir(build_dir.join("build"))

src/lib.rs

@@ -222,18 +222,19 @@ impl CodegenBackend for CraneliftCodegenBackend {
             #[cfg(not(feature = "jit"))]
             tcx.dcx().fatal("jit support was disabled when compiling rustc_codegen_cranelift");
         } else {
+            if tcx.sess.opts.cg.linker_plugin_lto.enabled() {
+                #[cfg(feature = "lto")]
+                return driver::lto::run_lto(tcx);
+
+                #[cfg(not(feature = "lto"))]
+                tcx.dcx().fatal("LTO support was disabled when compiling rustc_codegen_cranelift");
+            }
+
             match tcx.sess.lto() {
                 Lto::No | Lto::ThinLocal => {
                     Box::new(rustc_codegen_ssa::base::codegen_crate(driver::aot::AotDriver, tcx))
                 }
                 Lto::Thin | Lto::Fat => {
-                    if tcx.is_compiler_builtins(LOCAL_CRATE) {
-                        return Box::new(rustc_codegen_ssa::base::codegen_crate(
-                            driver::aot::AotDriver,
-                            tcx,
-                        ));
-                    }
-
                     // #[cfg(feature = "lto")]
                     // return Box::new(rustc_codegen_ssa::base::codegen_crate(
                     //     driver::lto::LtoDriver,