added assert

src/passes/RemoveUnusedModuleElements.cpp

diff --git a/src/passes/RemoveUnusedModuleElements.cpp b/src/passes/RemoveUnusedModuleElements.cpp
index 1b11747..ce5adb2 100644
--- a/src/passes/RemoveUnusedModuleElements.cpp
+++ b/src/passes/RemoveUnusedModuleElements.cpp
@@ -236,6 +236,8 @@
     : rootAllFunctions(rootAllFunctions) {}
 
   void run(PassRunner* runner, Module* module) override {
+    assert(module->memories.size() <= 1);
+
     std::vector<ModuleElement> roots;
     // Module start is a root.
     if (module->start.is()) {