Let backends define custom targets

Add a target_override hook that takes priority over builtin targets.

2 files changed, 10 insertions, 6 deletions

diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
index dc4fa807f78..72e10bc4304 100644
--- a/compiler/rustc_interface/src/tests.rs
+++ b/compiler/rustc_interface/src/tests.rs
@@ -40,6 +40,7 @@ fn mk_session(matches: getopts::Matches) -> (Session, CfgSpecs) {
         DiagnosticOutput::Default,
         Default::default(),
         None,
+        None,
     );
     (sess, cfg)
 }
diff --git a/compiler/rustc_interface/src/util.rs b/compiler/rustc_interface/src/util.rs
index f15eb413833..c4d89850dad 100644
--- a/compiler/rustc_interface/src/util.rs
+++ b/compiler/rustc_interface/src/util.rs
@@ -65,6 +65,10 @@ pub fn create_session(
     lint_caps: FxHashMap<lint::LintId, lint::Level>,
     descriptions: Registry,
 ) -> (Lrc<Session>, Lrc<Box<dyn CodegenBackend>>) {
+    let codegen_backend = get_codegen_backend(sopts.debugging_opts.codegen_backend.as_deref());
+    // target_override is documented to be called before init(), so this is okay
+    let target_override = codegen_backend.target_override(&sopts);
+
     let mut sess = session::build_session(
         sopts,
         input_path,
@@ -72,9 +76,10 @@ pub fn create_session(
         diagnostic_output,
         lint_caps,
         file_loader,
+        target_override,
     );
 
-    let codegen_backend = get_codegen_backend(&sess);
+    codegen_backend.init(&sess);
 
     let mut cfg = config::build_configuration(&sess, config::to_crate_config(cfg));
     add_configuration(&mut cfg, &mut sess, &*codegen_backend);
@@ -219,13 +224,13 @@ fn load_backend_from_dylib(path: &Path) -> fn() -> Box<dyn CodegenBackend> {
     }
 }
 
-pub fn get_codegen_backend(sess: &Session) -> Box<dyn CodegenBackend> {
+pub fn get_codegen_backend(codegen_name: Option<&str>) -> Box<dyn CodegenBackend> {
     static INIT: Once = Once::new();
 
     static mut LOAD: fn() -> Box<dyn CodegenBackend> = || unreachable!();
 
     INIT.call_once(|| {
-        let codegen_name = sess.opts.debugging_opts.codegen_backend.as_deref().unwrap_or("llvm");
+        let codegen_name = codegen_name.unwrap_or("llvm");
         let backend = match codegen_name {
             filename if filename.contains('.') => load_backend_from_dylib(filename.as_ref()),
             codegen_name => get_builtin_codegen_backend(codegen_name),
@@ -235,9 +240,7 @@ pub fn get_codegen_backend(sess: &Session) -> Box<dyn CodegenBackend> {
             LOAD = backend;
         }
     });
-    let backend = unsafe { LOAD() };
-    backend.init(sess);
-    backend
+    unsafe { LOAD() }
 }
 
 // This is used for rustdoc, but it uses similar machinery to codegen backend