2 files changed, 15 insertions, 5 deletions
diff --git a/src/ir/effects.h b/src/ir/effects.h
index 4f3af012f..55c78f05a 100644
--- a/src/ir/effects.h
+++ b/src/ir/effects.h
@@ -446,8 +446,16 @@ struct EffectAnalyzer
     if (tryDepth == 0) {
       throws = true;
     }
+    if (!ignoreImplicitTraps) { // rethrow traps when the arg is null
+      implicitTrap = true;
+    }
+  }
+  void visitBrOnExn(BrOnExn* curr) {
+    breakNames.insert(curr->name);
+    if (!ignoreImplicitTraps) { // br_on_exn traps when the arg is null
+      implicitTrap = true;
+    }
   }
-  void visitBrOnExn(BrOnExn* curr) { breakNames.insert(curr->name); }
   void visitNop(Nop* curr) {}
   void visitUnreachable(Unreachable* curr) { branches = true; }
   void visitPush(Push* curr) { calls = true; }
diff --git a/src/passes/SimplifyLocals.cpp b/src/passes/SimplifyLocals.cpp
index 23ab1bc92..2f269a00d 100644
--- a/src/passes/SimplifyLocals.cpp
+++ b/src/passes/SimplifyLocals.cpp
@@ -126,8 +126,7 @@ struct SimplifyLocals
                   Expression** currp) {
     // Main processing.
     auto* curr = *currp;
-    if (curr->is<Break>()) {
-      auto* br = curr->cast<Break>();
+    if (auto* br = curr->dynCast<Break>()) {
       if (br->value) {
         // value means the block already has a return value
         self->unoptimizableBlocks.insert(br->name);
@@ -147,6 +146,10 @@ struct SimplifyLocals
         self->unoptimizableBlocks.insert(target);
       }
       // TODO: we could use this info to stop gathering data on these blocks
+    } else if (auto* br = curr->dynCast<BrOnExn>()) {
+      // We cannot optimize the block this targets to have a return value, as
+      // the br_on_exn doesn't support a change to the block's type
+      self->unoptimizableBlocks.insert(br->name);
     }
     self->sinkables.clear();
   }
@@ -162,10 +165,9 @@ struct SimplifyLocals
   static void
   doNoteIfTrue(SimplifyLocals<allowTee, allowStructure, allowNesting>* self,
                Expression** currp) {
-    auto* iff = (*currp)->dynCast<If>();
+    auto* iff = (*currp)->cast<If>();
     if (iff->ifFalse) {
       // We processed the ifTrue side of this if-else, save it on the stack.
-      assert((*currp)->cast<If>()->ifFalse);
       self->ifStack.push_back(std::move(self->sinkables));
     } else {
       // This is an if without an else.