Remove `CodegenBackend::target_override`.

Backend and target selection is a mess: the target can override the
backend (via `Target::default_codegen_backend`), *and* the backend can
override the target (via `CodegenBackend::target_override`).

The code that handles this is ugly. It calls `build_target_config`
twice, once before getting the backend and once again afterward. It also
must check that both overrides aren't triggering at the same time.

This commit removes the latter override. It's used in rust-gpu but
@eddyb said via Zulip that removing it would be ok. This simplifies the
code greatly, and will allow some nice follow-up refactorings.

1 files changed, 13 insertions, 42 deletions

diff --git a/compiler/rustc_interface/src/interface.rs b/compiler/rustc_interface/src/interface.rs
index 1a82e6c6910..8ba14d37982 100644
--- a/compiler/rustc_interface/src/interface.rs
+++ b/compiler/rustc_interface/src/interface.rs
@@ -341,51 +341,22 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
 
             let sysroot = filesearch::materialize_sysroot(config.opts.maybe_sysroot.clone());
 
-            let (codegen_backend, target_override) = match config.make_codegen_backend {
-                None => {
-                    // Build a target without override, so that it can override the backend if needed
-                    let target =
-                        config::build_target_config(&early_dcx, &config.opts, None, &sysroot);
-
-                    let backend = util::get_codegen_backend(
-                        &early_dcx,
-                        &sysroot,
-                        config.opts.unstable_opts.codegen_backend.as_deref(),
-                        &target,
-                    );
-
-                    // target_override is documented to be called before init(), so this is okay
-                    let target_override = backend.target_override(&config.opts);
-
-                    // Assert that we don't use target's override of the backend and
-                    // backend's override of the target at the same time
-                    if config.opts.unstable_opts.codegen_backend.is_none()
-                        && target.default_codegen_backend.is_some()
-                        && target_override.is_some()
-                    {
-                        rustc_middle::bug!(
-                            "Codegen backend requested target override even though the target requested the backend"
-                        );
-                    }
-
-                    (backend, target_override)
-                }
+            let target = config::build_target_config(&early_dcx, &config.opts, &sysroot);
+
+            let codegen_backend = match config.make_codegen_backend {
+                None => util::get_codegen_backend(
+                    &early_dcx,
+                    &sysroot,
+                    config.opts.unstable_opts.codegen_backend.as_deref(),
+                    &target,
+                ),
                 Some(make_codegen_backend) => {
-                    // N.B. `make_codegen_backend` takes precedence over `target.default_codegen_backend`,
-                    //      which is ignored in this case.
-                    let backend = make_codegen_backend(&config.opts);
-
-                    // target_override is documented to be called before init(), so this is okay
-                    let target_override = backend.target_override(&config.opts);
-
-                    (backend, target_override)
+                    // N.B. `make_codegen_backend` takes precedence over
+                    // `target.default_codegen_backend`, which is ignored in this case.
+                    make_codegen_backend(&config.opts)
                 }
             };
 
-            // Re-build target with the (potential) override
-            let target_cfg =
-                config::build_target_config(&early_dcx, &config.opts, target_override, &sysroot);
-
             let temps_dir = config.opts.unstable_opts.temps_dir.as_deref().map(PathBuf::from);
 
             let bundle = match rustc_errors::fluent_bundle(
@@ -418,7 +389,7 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
                 locale_resources,
                 config.lint_caps,
                 config.file_loader,
-                target_cfg,
+                target,
                 sysroot,
                 util::rustc_version_str().unwrap_or("unknown"),
                 config.ice_file,