Don't remove events used in instructions (#2412)

Previously RemoveUnusedModuleElements pass only preserved exported
events and did not preserve events used in `throw` and `br_on_exn`
instructions. This fixes it.

1 files changed, 12 insertions, 0 deletions

diff --git a/src/passes/RemoveUnusedModuleElements.cpp b/src/passes/RemoveUnusedModuleElements.cpp
index d4c6d5a5d..806545adf 100644
--- a/src/passes/RemoveUnusedModuleElements.cpp
+++ b/src/passes/RemoveUnusedModuleElements.cpp
@@ -116,6 +116,18 @@ struct ReachabilityAnalyzer : public PostWalker<ReachabilityAnalyzer> {
       usesMemory = true;
     }
   }
+  void visitThrow(Throw* curr) {
+    if (reachable.count(ModuleElement(ModuleElementKind::Event, curr->event)) ==
+        0) {
+      queue.emplace_back(ModuleElementKind::Event, curr->event);
+    }
+  }
+  void visitBrOnExn(BrOnExn* curr) {
+    if (reachable.count(ModuleElement(ModuleElementKind::Event, curr->event)) ==
+        0) {
+      queue.emplace_back(ModuleElementKind::Event, curr->event);
+    }
+  }
 };
 
 // Finds function type usage