Move some calls to before calling codegen_crate

`--emit mir`, `#[rustc_symbol_name]` and `#[rustc_def_path]` now run
before codegen and thus work even if codegen fails. This can help with
debugging.

compiler/rustc_driver_impl/messages.ftl

@@ -1,3 +1,5 @@
+driver_impl_cant_emit_mir = could not emit MIR: {$error}
+
 driver_impl_ice = the compiler unexpectedly panicked. this is a bug.
 driver_impl_ice_bug_report = we would appreciate a bug report: {$bug_report_url}
 driver_impl_ice_bug_report_internal_feature = using internal features is not supported and expected to cause internal compiler errors when used incorrectly

compiler/rustc_driver_impl/src/lib.rs

@@ -108,7 +108,7 @@ mod signal_handler {
 }
 
 use crate::session_diagnostics::{
-    RLinkEmptyVersionNumber, RLinkEncodingVersionMismatch, RLinkRustcVersionMismatch,
+    CantEmitMIR, RLinkEmptyVersionNumber, RLinkEncodingVersionMismatch, RLinkRustcVersionMismatch,
     RLinkWrongFileType, RlinkCorruptFile, RlinkNotAFile, RlinkUnableToRead, UnstableFeatureUsage,
 };
 
@@ -374,6 +374,12 @@ pub fn run_compiler(at_args: &[String], callbacks: &mut (dyn Callbacks + Send))
                 return early_exit();
             }
 
+            if tcx.sess.opts.output_types.contains_key(&OutputType::Mir) {
+                if let Err(error) = rustc_mir_transform::dump_mir::emit_mir(tcx) {
+                    tcx.dcx().emit_fatal(CantEmitMIR { error });
+                }
+            }
+
             Some(Linker::codegen_and_build_linker(tcx, &*compiler.codegen_backend))
         });
 

compiler/rustc_driver_impl/src/session_diagnostics.rs

@@ -2,6 +2,12 @@ use std::error::Error;
 
 use rustc_macros::{Diagnostic, Subdiagnostic};
 
+#[derive(Diagnostic)]
+#[diag(driver_impl_cant_emit_mir)]
+pub struct CantEmitMIR {
+    pub error: std::io::Error,
+}
+
 #[derive(Diagnostic)]
 #[diag(driver_impl_rlink_unable_to_read)]
 pub(crate) struct RlinkUnableToRead {

compiler/rustc_interface/messages.ftl

@@ -3,9 +3,6 @@ interface_abi_required_feature =
     .note = this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 interface_abi_required_feature_issue = for more information, see issue #116344 <https://github.com/rust-lang/rust/issues/116344>
 
-interface_cant_emit_mir =
-    could not emit MIR: {$error}
-
 interface_crate_name_does_not_match = `--crate-name` and `#[crate_name]` are required to match, but `{$crate_name}` != `{$attr_crate_name}`
 
 interface_crate_name_invalid = crate names cannot start with a `-`, but `{$crate_name}` has a leading hyphen

compiler/rustc_interface/src/errors.rs

@@ -73,12 +73,6 @@ pub struct TempsDirError;
 #[diag(interface_out_dir_error)]
 pub struct OutDirError;
 
-#[derive(Diagnostic)]
-#[diag(interface_cant_emit_mir)]
-pub struct CantEmitMIR {
-    pub error: io::Error,
-}
-
 #[derive(Diagnostic)]
 #[diag(interface_rustc_error_fatal)]
 pub struct RustcErrorFatal {

compiler/rustc_interface/src/passes.rs

@@ -1078,6 +1078,15 @@ pub(crate) fn start_codegen<'tcx>(
     codegen_backend: &dyn CodegenBackend,
     tcx: TyCtxt<'tcx>,
 ) -> Box<dyn Any> {
+    // Hook for UI tests.
+    check_for_rustc_errors_attr(tcx);
+
+    // Don't run this test assertions when not doing codegen. Compiletest tries to build
+    // build-fail tests in check mode first and expects it to not give an error in that case.
+    if tcx.sess.opts.output_types.should_codegen() {
+        rustc_symbol_mangling::test::report_symbol_names(tcx);
+    }
+
     // Don't do code generation if there were any errors. Likewise if
     // there were any delayed bugs, because codegen will likely cause
     // more ICEs, obscuring the original problem.
@@ -1085,9 +1094,6 @@ pub(crate) fn start_codegen<'tcx>(
         guar.raise_fatal();
     }
 
-    // Hook for UI tests.
-    check_for_rustc_errors_attr(tcx);
-
     info!("Pre-codegen\n{:?}", tcx.debug_stats());
 
     let (metadata, need_metadata_module) = rustc_metadata::fs::encode_and_write_metadata(tcx);
@@ -1096,20 +1102,8 @@ pub(crate) fn start_codegen<'tcx>(
         codegen_backend.codegen_crate(tcx, metadata, need_metadata_module)
     });
 
-    // Don't run this test assertions when not doing codegen. Compiletest tries to build
-    // build-fail tests in check mode first and expects it to not give an error in that case.
-    if tcx.sess.opts.output_types.should_codegen() {
-        rustc_symbol_mangling::test::report_symbol_names(tcx);
-    }
-
     info!("Post-codegen\n{:?}", tcx.debug_stats());
 
-    if tcx.sess.opts.output_types.contains_key(&OutputType::Mir) {
-        if let Err(error) = rustc_mir_transform::dump_mir::emit_mir(tcx) {
-            tcx.dcx().emit_fatal(errors::CantEmitMIR { error });
-        }
-    }
-
     // This must run after monomorphization so that all generic types
     // have been instantiated.
     if tcx.sess.opts.unstable_opts.print_type_sizes {