Finish dep graph encoding before calling save_dep_graph and fix free_global_ctxt timing

Author: Zoxc

compiler/rustc_interface/src/queries.rs

@@ -347,6 +347,11 @@ impl Compiler {
         let queries = Queries::new(self);
         let ret = f(&queries);
 
+        // Finish the dep graph encoding before we call `save_dep_graph`.
+        if let Err((path, error)) = queries.finish() {
+            self.sess.dcx().emit_fatal(errors::FailedWritingFile { path: &path, error });
+        }
+
         // NOTE: intentionally does not compute the global context if it hasn't been built yet,
         // since that likely means there was a parse error.
         if let Some(Ok(gcx)) = &mut *queries.gcx.result.borrow_mut() {
@@ -360,16 +365,13 @@ impl Compiler {
             }
 
             self.sess.time("serialize_dep_graph", || gcx.enter(rustc_incremental::save_dep_graph));
-            queries.dep_graph_serialized_tx.send(()).ok();
         }
 
+        queries.dep_graph_serialized_tx.send(()).ok();
+
         // The timer's lifetime spans the dropping of `queries`, which contains
         // the global context.
         _timer = Some(self.sess.timer("free_global_ctxt"));
-        if let Err((path, error)) = queries.finish() {
-            self.sess.dcx().emit_fatal(errors::FailedWritingFile { path: &path, error });
-        }
-
         ret
     }
 }