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

Author: bjorn3

build_system/build_sysroot.rs

@@ -197,7 +197,8 @@ 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());
     }
@@ -224,8 +225,6 @@ fn build_clif_sysroot_for_triple(
             prefix.to_str().unwrap()
         ));
     }
-    rustflags.push("-Clto=thin".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);
@@ -237,7 +236,6 @@ fn build_clif_sysroot_for_triple(
     if compiler.triple.contains("apple") {
         build_cmd.env("CARGO_PROFILE_RELEASE_SPLIT_DEBUGINFO", "packed");
     }
-    build_cmd.env("CARGO_PROFILE_RELEASE_LTO", "thin");
     spawn_and_wait(build_cmd);
 
     for entry in fs::read_dir(build_dir.join("deps")).unwrap() {

src/lib.rs

@@ -211,13 +211,17 @@ 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 => driver::aot::run_aot(tcx),
                 Lto::Thin | Lto::Fat => {
-                    if tcx.crate_name(LOCAL_CRATE) == sym::compiler_builtins {
-                        return driver::aot::run_aot(tcx);
-                    }
-
                     #[cfg(feature = "lto")]
                     return driver::lto::run_lto(tcx);