Add tracing to various miscellaneous functions

Also use tracing macro syntax instead of format()

Author: Stypox

src/machine.rs

@@ -1111,6 +1111,7 @@ impl<'tcx> Machine<'tcx> for MiriMachine<'tcx> {
     ) -> InterpResult<'tcx, Option<(&'tcx mir::Body<'tcx>, ty::Instance<'tcx>)>> {
         // For foreign items, try to see if we can emulate them.
         if ecx.tcx.is_foreign_item(instance.def_id()) {
+            let _trace = enter_trace_span!("emulate_foreign_item");
             // An external function call that does not have a MIR body. We either find MIR elsewhere
             // or emulate its effect.
             // This will be Ok(None) if we're emulating the intrinsic entirely within Miri (no need
@@ -1123,6 +1124,7 @@ impl<'tcx> Machine<'tcx> for MiriMachine<'tcx> {
         }
 
         // Otherwise, load the MIR.
+        let _trace = enter_trace_span!("load_mir");
         interp_ok(Some((ecx.load_mir(instance.def, None)?, instance)))
     }