attempt to fix swift_once; doesn't work

Author: zhuowei

include/swift/Runtime/Once.h

@@ -44,6 +44,10 @@ typedef std::once_flag swift_once_t;
 /// extent of type swift_once_t.
 SWIFT_RUNTIME_EXPORT
 void swift_once(swift_once_t *predicate, void (*fn)(void *), void *context);
+#ifdef __wasm__
+// WebAssembly: hack
+void swift_once_real(swift_once_t *predicate, void (*fn)(void *), void *context);
+#endif
 
 }
 

stdlib/public/runtime/CompatibilityOverride.cpp

@@ -49,7 +49,12 @@ static_assert(std::is_pod<OverrideSection>::value,
 static OverrideSection *getOverrideSectionPtr() {
   static OverrideSection *OverrideSectionPtr;
   static swift_once_t Predicate;
+  // WebAssembly: hack
+#ifdef __wasm__
+  swift_once_real(&Predicate, [](void *) {
+#else
   swift_once(&Predicate, [](void *) {
+#endif
     size_t Size;
     OverrideSectionPtr = static_cast<OverrideSection *>(
                              lookupSection("__DATA", "__swift52_hooks", &Size));

stdlib/public/runtime/HeapObject.cpp

@@ -152,7 +152,13 @@ swift::swift_initStaticObject(HeapMetadata const *metadata,
   // refcount to 1 while another thread already incremented it - and would
   // decrement it to 0 afterwards.
   InitStaticObjectContext Ctx = { object, metadata };
+#ifdef __wasm__
+  // WebAssembly: hack: swift_once has been modified to take a function pointer without a parameter.
+  // so use the _real version that does have a parameter
+  swift_once_real(token, initStaticObjectWithContext, &Ctx);
+#else
   swift_once(token, initStaticObjectWithContext, &Ctx);
+#endif
 
   return object;
 }

stdlib/public/runtime/Once.cpp

@@ -52,7 +52,28 @@ void swift::swift_once(swift_once_t *predicate, void (*fn)(void *),
   dispatch_once_f(predicate, context, fn);
 #elif defined(__CYGWIN__)
   _swift_once_f(predicate, context, fn);
+#elif defined(__wasm__)
+  // WebAssembly: hack: Swift compiler passes in a fn that doesn't take a parameter,
+  // which is invalid in WebAssembly. So swift_once casts the function.
+  // The correct way to fix this is to change 
+  // SILGenModule::emitLazyGlobalInitializer
+  // but this is OK as a proof of concept.
+  // Keep a copy of the unmodified swift_once function below.
+  std::call_once(*predicate, [fn, context]() { ((void (*)())fn)(); });
 #else
   std::call_once(*predicate, [fn, context]() { fn(context); });
 #endif
 }
+
+#ifdef __wasm__
+void swift::swift_once_real(swift_once_t *predicate, void (*fn)(void *),
+                       void *context) {
+#if defined(__APPLE__)
+  dispatch_once_f(predicate, context, fn);
+#elif defined(__CYGWIN__)
+  _swift_once_f(predicate, context, fn);
+#else
+  std::call_once(*predicate, [fn, context]() { fn(context); });
+#endif
+}
+#endif