diff --git a/src/pass.h b/src/pass.h
index 47e7a2789fc..c9f239e1d08 100644
--- a/src/pass.h
+++ b/src/pass.h
@@ -188,7 +188,7 @@ struct PassOptions {
   bool debugInfo = false;
   // Arbitrary string arguments from the commandline, which we forward to
   // passes.
-  std::map<std::string, std::string> arguments;
+  std::unordered_map<std::string, std::string> arguments;
 
   // Effect info computed for functions. One pass can generate this and then
   // other passes later can benefit from it. It is up to the sequence of passes
@@ -217,15 +217,19 @@ struct PassOptions {
     return PassOptions(); // defaults are to not optimize
   }
 
+  bool hasArgument(std::string key) {
+    return arguments.count(key) > 0;
+  }
+
   std::string getArgument(std::string key, std::string errorTextIfMissing) {
-    if (arguments.count(key) == 0) {
+    if (!hasArgument(key)) {
       Fatal() << errorTextIfMissing;
     }
     return arguments[key];
   }
 
   std::string getArgumentOrDefault(std::string key, std::string default_) {
-    if (arguments.count(key) == 0) {
+    if (!hasArgument(key)) {
       return default_;
     }
     return arguments[key];
diff --git a/src/passes/Asyncify.cpp b/src/passes/Asyncify.cpp
index 9be731d0604..a97c2019e89 100644
--- a/src/passes/Asyncify.cpp
+++ b/src/passes/Asyncify.cpp
@@ -1536,8 +1536,7 @@ struct Asyncify : public Pass {
     String::Split listedImports(stateChangingImports, ",");
     // TODO: consider renaming asyncify-ignore-indirect to
     //       asyncify-ignore-nondirect, but that could break users.
-    auto ignoreNonDirect =
-      options.getArgumentOrDefault("asyncify-ignore-indirect", "") == "";
+    auto ignoreNonDirect = options.hasArgument("asyncify-ignore-indirect");
     std::string removeListInput =
       options.getArgumentOrDefault("asyncify-removelist", "");
     if (removeListInput.empty()) {
@@ -1558,12 +1557,10 @@ struct Asyncify : public Pass {
     }
     String::Split onlyList(
       String::trim(read_possible_response_file(onlyListInput)), ",");
-    auto asserts = options.getArgumentOrDefault("asyncify-asserts", "") != "";
-    auto verbose = options.getArgumentOrDefault("asyncify-verbose", "") != "";
-    auto relocatable =
-      options.getArgumentOrDefault("asyncify-relocatable", "") != "";
-    auto secondaryMemory =
-      options.getArgumentOrDefault("asyncify-in-secondary-memory", "") != "";
+    auto asserts = options.hasArgument("asyncify-asserts");
+    auto verbose = options.hasArgument("asyncify-verbose");
+    auto relocatable = options.hasArgument("asyncify-relocatable");
+    auto secondaryMemory = options.hasArgument("asyncify-in-secondary-memory");
 
     // Ensure there is a memory, as we need it.
     if (secondaryMemory) {
diff --git a/src/passes/PostEmscripten.cpp b/src/passes/PostEmscripten.cpp
index 86b7b8bc3ad..ea4922e3a1b 100644
--- a/src/passes/PostEmscripten.cpp
+++ b/src/passes/PostEmscripten.cpp
@@ -214,12 +214,19 @@ struct PostEmscripten : public Pass {
     std::vector<Address> segmentOffsets; // segment index => address offset
     calcSegmentOffsets(module, segmentOffsets);
 
-    removeData(module, segmentOffsets, "__start_em_asm", "__stop_em_asm");
+    auto& options = getPassOptions();
+    auto sideModule = options.hasArgument("post-emscripten-side-module");
+    if (!sideModule) {
+      // Side modules read EM_ASM data from the module based on these exports
+      // so we need to keep them around in that case.
+      removeData(module, segmentOffsets, "__start_em_asm", "__stop_em_asm");
+      module.removeExport("__start_em_asm");
+      module.removeExport("__stop_em_asm");
+    }
+
     removeData(module, segmentOffsets, "__start_em_js", "__stop_em_js");
     removeData(
       module, segmentOffsets, "__start_em_lib_deps", "__stop_em_lib_deps");
-    module.removeExport("__start_em_asm");
-    module.removeExport("__stop_em_asm");
     module.removeExport("__start_em_js");
     module.removeExport("__stop_em_js");
     module.removeExport("__start_em_lib_deps");