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/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 {