Don't process cycles when stalled

This improves the `inflate-0.1.0` benchmark by about 10% for me.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/librustc_data_structures/obligation_forest/mod.rs b/src/librustc_data_structures/obligation_forest/mod.rs
index c079146edbf..fb2d3291a60 100644
--- a/src/librustc_data_structures/obligation_forest/mod.rs
+++ b/src/librustc_data_structures/obligation_forest/mod.rs
@@ -342,6 +342,16 @@ impl<O: ForestObligation> ObligationForest<O> {
             }
         }
 
+        if stalled {
+            // There's no need to perform marking, cycle processing and compression when nothing
+            // changed.
+            return Outcome {
+                completed: vec![],
+                errors: errors,
+                stalled: stalled,
+            };
+        }
+
         self.mark_as_waiting();
         self.process_cycles(processor);