2 files changed, 18 insertions, 1 deletions
diff --git a/src/ast/type-updating.h b/src/ast/type-updating.h
index 8063b3e59..c5f1d5344 100644
--- a/src/ast/type-updating.h
+++ b/src/ast/type-updating.h
@@ -266,6 +266,19 @@ struct TypeUpdater : public ExpressionStackWalker<TypeUpdater, UnifiedExpression
       }
     }
   }
+
+  // efficiently update the type of an if, given the data we know. this
+  // can remove a concrete type and turn the if unreachable when it is
+  // unreachable
+  void maybeUpdateTypeToUnreachable(If* curr) {
+    if (!isConcreteWasmType(curr->type)) {
+      return; // nothing concrete to change to unreachable
+    }
+    curr->finalize();
+    if (curr->type == unreachable) {
+      propagateTypesUp(curr);
+    }
+  }
 };
 
 } // namespace wasm
diff --git a/src/passes/DeadCodeElimination.cpp b/src/passes/DeadCodeElimination.cpp
index e5673a0cc..48fc4a91c 100644
--- a/src/passes/DeadCodeElimination.cpp
+++ b/src/passes/DeadCodeElimination.cpp
@@ -216,7 +216,7 @@ struct DeadCodeElimination : public WalkerPass<PostWalker<DeadCodeElimination>>
       replaceCurrent(curr->condition);
     }
     // the if may have had a type, but can now be unreachable, which allows more reduction outside
-    curr->finalize();
+    typeUpdater.maybeUpdateTypeToUnreachable(curr);
   }
 
   static void scan(DeadCodeElimination* self, Expression** currp) {
@@ -351,6 +351,10 @@ struct DeadCodeElimination : public WalkerPass<PostWalker<DeadCodeElimination>>
     blockifyReachableOperands({ curr->value }, curr->type);
   }
 
+  void visitSetGlobal(SetGlobal* curr) {
+    blockifyReachableOperands({ curr->value }, curr->type);
+  }
+
   void visitLoad(Load* curr) {
     blockifyReachableOperands({ curr->ptr }, curr->type);
   }