analysis: fix use counts (again ...)

src/ir/analysis.rs

@@ -24,29 +24,36 @@ pub fn count_expr_uses(ctx: &Context, sys: &TransitionSystem) -> Vec<u32> {
             .iter()
             .map(|(e, _)| *e),
     );
+    // ensure that all roots start with count 1
+    for expr in todo.iter() {
+        *use_count.get_mut(*expr) = 1;
+    }
 
     while let Some(expr) = todo.pop() {
-        // when we process an item for the first time, we set the count to 1
-        *use_count.get_mut(expr) = 1;
         if let Some(state) = states.get(&expr) {
             // for states, we also want to mark the initial and the next expression as used
             if let Some(init) = state.init {
-                *use_count.get_mut(init) = 1;
-                todo.push(init);
+                let count = use_count.get_mut(init);
+                if *count == 0 {
+                    *count = 1;
+                    todo.push(init);
+                }
             }
             if let Some(next) = state.next {
-                *use_count.get_mut(next) = 1;
-                todo.push(next);
+                let count = use_count.get_mut(next);
+                if *count == 0 {
+                    *count = 1;
+                    todo.push(next);
+                }
             }
         }
 
         ctx.get(expr).for_each_child(|child| {
             let count = use_count.get_mut(*child);
             let is_first_use = *count == 0;
+            *count += 1;
             if is_first_use {
                 todo.push(*child);
-            } else {
-                *count += 1;
             }
         });
     }