PostEmscripten: Preserve __em_js__ exports in side modules (#5780)

Author: sbc100

src/passes/PostEmscripten.cpp

@@ -186,10 +186,13 @@ IString EM_JS_PREFIX("__em_js__");
 IString EM_JS_DEPS_PREFIX("__em_lib_deps_");
 
 struct EmJsWalker : public PostWalker<EmJsWalker> {
+  bool sideModule;
   std::vector<Export> toRemove;
 
+  EmJsWalker(bool sideModule) : sideModule(sideModule) {}
+
   void visitExport(Export* curr) {
-    if (curr->name.startsWith(EM_JS_PREFIX)) {
+    if (!sideModule && curr->name.startsWith(EM_JS_PREFIX)) {
       toRemove.push_back(*curr);
     }
     if (curr->name.startsWith(EM_JS_DEPS_PREFIX)) {
@@ -215,14 +218,15 @@ struct PostEmscripten : public Pass {
     auto& options = getPassOptions();
     auto sideModule = options.hasArgument("post-emscripten-side-module");
     if (!sideModule) {
+      removeData(module, segmentOffsets, "__start_em_asm", "__stop_em_asm");
+      removeData(module, segmentOffsets, "__start_em_js", "__stop_em_js");
+
       // 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_js");
@@ -232,7 +236,9 @@ struct PostEmscripten : public Pass {
   }
 
   void removeEmJsExports(Module& module) {
-    EmJsWalker walker;
+    auto& options = getPassOptions();
+    auto sideModule = options.hasArgument("post-emscripten-side-module");
+    EmJsWalker walker(sideModule);
     walker.walkModule(&module);
     for (const Export& exp : walker.toRemove) {
       if (exp.kind == ExternalKind::Function) {

test/lit/passes/post-emscripten-side-module.wast

@@ -0,0 +1,49 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py --all-items and should not be edited.
+;; RUN: wasm-opt %s --post-emscripten --pass-arg=post-emscripten-side-module -S -o - | filecheck %s
+
+;; Checks that the __start_em_asm/__stop_em_asm are preserverd, along with
+;; all __em_js__ exports.
+
+(module
+ ;; CHECK:      (global $em_asm_start i32 (i32.const 1000))
+ (global $em_asm_start i32 (i32.const 1000))
+ ;; CHECK:      (global $em_asm_stop i32 (i32.const 1011))
+ (global $em_asm_stop i32 (i32.const 1011))
+ ;; CHECK:      (global $em_js_start i32 (i32.const 2006))
+ (global $em_js_start i32 (i32.const 2006))
+ ;; CHECK:      (global $em_js_stop i32 (i32.const 2015))
+ (global $em_js_stop i32 (i32.const 2015))
+ ;; CHECK:      (global $__em_js__foo i32 (i32.const 2015))
+ (global $__em_js__foo i32 (i32.const 2015))
+ ;; CHECK:      (global $em_lib_deps_start i32 (i32.const 3000))
+ (global $em_lib_deps_start i32 (i32.const 3000))
+ ;; CHECK:      (global $em_lib_deps_stop i32 (i32.const 3009))
+ (global $em_lib_deps_stop i32 (i32.const 3009))
+ ;; CHECK:      (global $foo_start i32 (i32.const 4000))
+ (global $foo_start i32 (i32.const 4000))
+ ;; CHECK:      (global $foo_stop i32 (i32.const 4015))
+ (global $foo_stop i32 (i32.const 4015))
+ (memory 10 10)
+ ;; CHECK:      (memory $0 10 10)
+
+ ;; CHECK:      (data $data1 (i32.const 1000) "hello world")
+ (data $data1 (i32.const 1000) "hello world")
+ ;; CHECK:      (data $data2 (i32.const 2000) "hello DELETE ME world")
+ (data $data2 (i32.const 2000) "hello DELETE ME world")
+ ;; CHECK:      (data $data3 (i32.const 3000) "")
+ (data $data3 (i32.const 3000) "some deps")
+ ;; CHECK:      (export "__start_em_asm" (global $em_asm_start))
+ (export "__start_em_asm" (global $em_asm_start))
+ ;; CHECK:      (export "__stop_em_asm" (global $em_asm_stop))
+ (export "__stop_em_asm" (global $em_asm_stop))
+ (export "__start_em_js" (global $em_js_start))
+ (export "__stop_em_js" (global $em_js_stop))
+ ;; CHECK:      (export "__em_js__foo" (global $__em_js__foo))
+ (export "__em_js__foo" (global $__em_js__foo))
+ (export "__start_em_lib_deps" (global $em_lib_deps_start))
+ (export "__stop_em_lib_deps" (global $em_lib_deps_stop))
+ ;; CHECK:      (export "__start_foo" (global $foo_start))
+ (export "__start_foo" (global $foo_start))
+ ;; CHECK:      (export "__stop_foo" (global $foo_stop))
+ (export "__stop_foo" (global $foo_stop))
+)

test/lit/passes/post-emscripten.wast

@@ -41,4 +41,3 @@
  ;; CHECK:      (export "__stop_foo" (global $foo_stop))
  (export "__stop_foo" (global $foo_stop))
 )
-