Change the if condition to assertion in fixpoint iterator in run function

Summary: Just found that when checking the component index is not entry, we used if check in the Rust version, while an assertion should be better as that condition should never be true (outer predecessor is impossible to be entry node). And this is what the C++ version does.

Reviewed By: yuxuanchen1997

Differential Revision: D40204333

fbshipit-source-id: 00c8b461ebcf63565fd8dc0e5c47001d048378cf

Author: @

rust/src/fixpoint_iter.rs

@@ -177,12 +177,11 @@ where
                 Self::extrapolate(&context, head, current_state, new_state);
                 context.increase_iteration_count_for(head);
                 for (&component_idx, &num) in self.wpo.get_num_outer_preds(wpo_idx) {
-                    if component_idx != entry_idx {
-                        let old_counter =
-                            wpo_counter[component_idx as usize].fetch_add(num, Ordering::Relaxed);
-                        if old_counter + num == self.wpo.get_num_preds(component_idx) {
-                            worklist.push_back(component_idx);
-                        }
+                    assert!(component_idx != entry_idx);
+                    let old_counter =
+                        wpo_counter[component_idx as usize].fetch_add(num, Ordering::Relaxed);
+                    if old_counter + num == self.wpo.get_num_preds(component_idx) {
+                        worklist.push_back(component_idx);
                     }
                 }