Build rustc and codegen backends with -Zno-embed-metadata

While this won't change much for rustc and rustc-dev, it should make
codegen backends a bit smaller by omitting their crate metadata. In
addition it should reduce disk usage while compiling.

Author: bjorn3

src/bootstrap/src/core/build_steps/compile.rs

@@ -1185,13 +1185,15 @@ impl Step for Rustc {
                 {
                     // jemalloc_sys and rustc_public_bridge are not linked into librustc_driver.so,
                     // so we need to distribute them as rlib to be able to use them.
-                    filename.ends_with(".rlib")
-                } else {
-                    // Distribute the rest of the rustc crates as rmeta files only to reduce
-                    // the tarball sizes by about 50%. The object files are linked into
-                    // librustc_driver.so, so it is still possible to link against them.
-                    filename.ends_with(".rmeta")
+                    if filename.ends_with(".rlib") {
+                        return true;
+                    }
                 }
+
+                // Distribute the rest of the rustc crates as rmeta files only to reduce
+                // the tarball sizes by about 50%. The object files are linked into
+                // librustc_driver.so, so it is still possible to link against them.
+                filename.ends_with(".rmeta")
             })),
         );
 
@@ -1732,7 +1734,7 @@ impl Step for GccCodegenBackend {
 
         let _guard =
             builder.msg(Kind::Build, "codegen backend gcc", Mode::Codegen, build_compiler, host);
-        let files = run_cargo(builder, cargo, vec![], &stamp, vec![], ArtifactKeepMode::OnlyRlib);
+        let files = run_cargo(builder, cargo, vec![], &stamp, vec![], ArtifactKeepMode::OnlyDylib);
 
         GccCodegenBackendOutput {
             stamp: write_codegen_backend_stamp(stamp, files, builder.config.dry_run()),
@@ -1808,7 +1810,7 @@ impl Step for CraneliftCodegenBackend {
             build_compiler,
             target,
         );
-        let files = run_cargo(builder, cargo, vec![], &stamp, vec![], ArtifactKeepMode::OnlyRlib);
+        let files = run_cargo(builder, cargo, vec![], &stamp, vec![], ArtifactKeepMode::OnlyDylib);
         write_codegen_backend_stamp(stamp, files, builder.config.dry_run())
     }
 
@@ -2642,6 +2644,8 @@ pub fn add_to_sysroot(
 /// build stamp, and thus be included in dist archives and copied into sysroots by default.
 /// Note that some kinds of artifacts are copied automatically (e.g. native libraries).
 pub enum ArtifactKeepMode {
+    /// Only keep .so files, ignore .rlib and .rmeta files
+    OnlyDylib,
     /// Only keep .rlib files, ignore .rmeta files
     OnlyRlib,
     /// Only keep .rmeta files, ignore .rlib files
@@ -2704,6 +2708,7 @@ pub fn run_cargo(
                 true
             } else {
                 match &artifact_keep_mode {
+                    ArtifactKeepMode::OnlyDylib => false,
                     ArtifactKeepMode::OnlyRlib => filename.ends_with(".rlib"),
                     ArtifactKeepMode::OnlyRmeta => filename.ends_with(".rmeta"),
                     ArtifactKeepMode::BothRlibAndRmeta => {

src/bootstrap/src/core/builder/cargo.rs

@@ -1095,7 +1095,7 @@ impl Builder<'_> {
         // Enable usage of unstable features
         cargo.env("RUSTC_BOOTSTRAP", "1");
 
-        if matches!(mode, Mode::Std) {
+        if matches!(mode, Mode::Std | Mode::Rustc | Mode::Codegen) {
             cargo.arg("-Zno-embed-metadata");
         }