Put the codegen backend dylib in the codegen-backends dir of the sysroot

This will make it possible in the future to switch between the Cranelift
and LLVM backends in Cargo.toml or .cargo/config.toml even when using a
local build of cg_clif.

Author: bjorn3

build_system/build_sysroot.rs

@@ -31,14 +31,33 @@ pub(crate) fn build_sysroot(
 
     let is_native = bootstrap_host_compiler.triple == target_triple;
 
-    let cg_clif_dylib_path = match cg_clif_dylib_src {
+    let cg_clif_backend_name = match cg_clif_dylib_src {
         CodegenBackend::Local(src_path) => {
-            // Copy the backend
-            let cg_clif_dylib_path = dist_dir.join("lib").join(src_path.file_name().unwrap());
+            // Create the codegen-backends dir in the sysroot
+            let dylib_dir = dist_dir
+                .join("lib")
+                .join("rustlib")
+                .join(&bootstrap_host_compiler.triple)
+                .join("codegen-backends");
+            fs::create_dir_all(&dylib_dir).unwrap();
+
+            // Copy the backend into the sysroot
+            let target_dylib_name = get_file_name(
+                &bootstrap_host_compiler.rustc,
+                "rustc_codegen_cranelift_local",
+                "dylib",
+            )
+            .replace("cranelift_local", "cranelift-local");
+            let cg_clif_dylib_path = dylib_dir.join(target_dylib_name);
             try_hard_link(src_path, &cg_clif_dylib_path);
-            CodegenBackend::Local(cg_clif_dylib_path)
+
+            // This is using a different name from rustup distributed versions of cg_clif to allow
+            // switching between a locally built and rustup distributed version and to ensure that
+            // the rustup distributed version doesn't accidentally gets picked when trying to use
+            // the locally built version.
+            "cranelift-local".to_owned()
         }
-        CodegenBackend::Builtin(name) => CodegenBackend::Builtin(name.clone()),
+        CodegenBackend::Builtin(name) => name.clone(),
     };
 
     // Build and copy rustc and cargo wrappers
@@ -69,17 +88,16 @@ pub(crate) fn build_sysroot(
                 .env("RUSTC", &bootstrap_host_compiler.rustc)
                 .env("RUSTDOC", &bootstrap_host_compiler.rustdoc);
         }
-        if let CodegenBackend::Builtin(name) = cg_clif_dylib_src {
-            build_cargo_wrapper_cmd.env("BUILTIN_BACKEND", name);
-        }
+        build_cargo_wrapper_cmd.env("HOST_TUPLE", &bootstrap_host_compiler.triple);
+        build_cargo_wrapper_cmd.env("BUILTIN_BACKEND", &cg_clif_backend_name);
         spawn_and_wait(build_cargo_wrapper_cmd);
         try_hard_link(wrapper_path, dist_dir.join("bin").join(wrapper_name));
     }
 
     let host = build_sysroot_for_triple(
         dirs,
         bootstrap_host_compiler.clone(),
-        &cg_clif_dylib_path,
+        &cg_clif_dylib_src,
         sysroot_kind,
         panic_unwind_support,
     );
@@ -94,7 +112,7 @@ pub(crate) fn build_sysroot(
                 bootstrap_target_compiler.set_cross_linker_and_runner();
                 bootstrap_target_compiler
             },
-            &cg_clif_dylib_path,
+            &cg_clif_dylib_src,
             sysroot_kind,
             panic_unwind_support,
         )

build_system/tests.rs

@@ -156,6 +156,8 @@ const EXTENDED_SYSROOT_SUITE: &[TestCase] = &[
         RAND.clean(&runner.dirs);
 
         if runner.is_native {
+            // FIXME all cargo tests are using both cargo-clif and rustc-clif, making usage of plain
+            // cargo-clif untested.
             let mut test_cmd = RAND.test(&runner.target_compiler, &runner.dirs);
             test_cmd.arg("--workspace").arg("--").arg("-q");
             spawn_and_wait(test_cmd);

scripts/cargo-clif.rs

@@ -17,16 +17,7 @@ fn main() {
         rustflags.push("-Cpanic=abort".to_owned());
         rustflags.push("-Zpanic-abort-tests".to_owned());
     }
-    if let Some(name) = option_env!("BUILTIN_BACKEND") {
-        rustflags.push(format!("-Zcodegen-backend={name}"));
-    } else {
-        let dylib = sysroot.join("lib").join(
-            env::consts::DLL_PREFIX.to_string()
-                + "rustc_codegen_cranelift"
-                + env::consts::DLL_SUFFIX,
-        );
-        rustflags.push(format!("-Zcodegen-backend={}", dylib.to_str().unwrap()));
-    }
+    rustflags.push(concat!("-Zcodegen-backend=", env!("BUILTIN_BACKEND")).to_owned());
     rustflags.push("--sysroot".to_owned());
     rustflags.push(sysroot.to_str().unwrap().to_owned());
 

scripts/rustc-clif.rs

@@ -11,23 +11,13 @@ fn main() {
         sysroot = sysroot.parent().unwrap();
     }
 
-    let cg_clif_dylib_path = sysroot.join("lib").join(
-        env::consts::DLL_PREFIX.to_string() + "rustc_codegen_cranelift" + env::consts::DLL_SUFFIX,
-    );
-
     let passed_args = std::env::args_os().skip(1).collect::<Vec<_>>();
     let mut args = vec![];
     if !cfg!(support_panic_unwind) {
         args.push(OsString::from("-Cpanic=abort"));
         args.push(OsString::from("-Zpanic-abort-tests"));
     }
-    if let Some(name) = option_env!("BUILTIN_BACKEND") {
-        args.push(OsString::from(format!("-Zcodegen-backend={name}")))
-    } else {
-        let mut codegen_backend_arg = OsString::from("-Zcodegen-backend=");
-        codegen_backend_arg.push(cg_clif_dylib_path);
-        args.push(codegen_backend_arg);
-    }
+    args.push(OsString::from(concat!("-Zcodegen-backend=", env!("BUILTIN_BACKEND"))));
     if !passed_args
         .iter()
         .any(|arg| arg == "--sysroot" || arg.to_str().is_some_and(|s| s.starts_with("--sysroot=")))