Reduce work to report errors.

Author: cjgillot

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -414,8 +414,6 @@ fn report_eval_error<'tcx>(
     let (error, backtrace) = error.into_parts();
     backtrace.print_backtrace();
 
-    let instance = with_no_trimmed_paths!(cid.instance.to_string());
-
     super::report(
         ecx,
         error,
@@ -430,7 +428,7 @@ fn report_eval_error<'tcx>(
                 diag.subdiagnostic(frame);
             }
             // Add after the frame rendering above, as it adds its own `instance` args.
-            diag.arg("instance", instance);
+            diag.arg("instance", with_no_trimmed_paths!(cid.instance.to_string()));
             diag.arg("num_frames", num_frames);
         },
     )