Add asyncify-export-globals argument

In the past emscripten would build the main module as relocatable, but
these days we build it statically and in that case it makes sense for
the main module to define and export these globals, rather than defining
them in JS.

Author: sbc100

src/passes/Asyncify.cpp

@@ -1759,7 +1759,8 @@ struct Asyncify : public Pass {
       String::Split::NewLineOr(","));
     auto asserts = hasArgument("asyncify-asserts");
     auto verbose = hasArgument("asyncify-verbose");
-    auto relocatable = hasArgument("asyncify-relocatable");
+    auto importGlobals = hasArgument("asyncify-relocatable");
+    auto exportGlobals = hasArgument("asyncify-export-globals");
     auto secondaryMemory = hasArgument("asyncify-in-secondary-memory");
     auto propagateAddList = hasArgument("asyncify-propagate-addlist");
 
@@ -1826,7 +1827,7 @@ struct Asyncify : public Pass {
                             verbose);
 
     // Add necessary globals before we emit code to use them.
-    addGlobals(module, relocatable);
+    addGlobals(module, importGlobals, exportGlobals);
 
     // Compute the set of functions we will instrument. All of the passes we run
     // below only need to run there.
@@ -1904,8 +1905,11 @@ struct Asyncify : public Pass {
   }
 
 private:
-  void addGlobals(Module* module, bool imported) {
+  void addGlobals(Module* module, bool imported, bool exported) {
     Builder builder(*module);
+    // It doesn't make sense to both import and export these globals at the
+    // same time.
+    assert(!(imported && exported));
 
     auto asyncifyState = builder.makeGlobal(ASYNCIFY_STATE,
                                             Type::i32,
@@ -1926,6 +1930,11 @@ struct Asyncify : public Pass {
       asyncifyData->base = ASYNCIFY_DATA;
     }
     module->addGlobal(std::move(asyncifyData));
+
+    if (exported) {
+      module->addExport(builder.makeExport(ASYNCIFY_STATE, ASYNCIFY_STATE, ExternalKind::Global));
+      module->addExport(builder.makeExport(ASYNCIFY_DATA, ASYNCIFY_DATA, ExternalKind::Global));
+    }
   }
 
   void addFunctions(Module* module) {

test/lit/passes/asyncify_pass-arg=asyncify-export-globals.wast

@@ -0,0 +1,11 @@
+;; RUN: wasm-opt --enable-mutable-globals --asyncify --pass-arg=asyncify-export-globals -S -o - | filecheck %s
+
+(module
+)
+;; CHECK:      (global $__asyncify_state (mut i32) (i32.const 0))
+
+;; CHECK:      (global $__asyncify_data (mut i32) (i32.const 0))
+
+;; CHECK:      (export "__asyncify_state" (global $__asyncify_state))
+
+;; CHECK:      (export "__asyncify_data" (global $__asyncify_data))