[wasm][anyref] Allow export of mutable anyref globals

R=titzer@chromium.org

Bug: v8:7581
Change-Id: I4725eada889cc8cf6a3ca537f05b1da2f5e83f2b
Reviewed-on: https://chromium-review.googlesource.com/c/1400413
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58632}

src/wasm/module-compiler.cc

@@ -2077,6 +2077,7 @@ void InstanceBuilder::ProcessExports(Handle<WasmInstanceObject> instance) {
         const WasmGlobal& global = module_->globals[exp.index];
         if (enabled_.mut_global) {
           Handle<JSArrayBuffer> untagged_buffer;
+          Handle<FixedArray> tagged_buffer;
           uint32_t offset;
 
           if (global.mutability && global.imported) {
@@ -2094,17 +2095,21 @@ void InstanceBuilder::ProcessExports(Handle<WasmInstanceObject> instance) {
                   global_addr < backing_store + buffer_size);
             offset = static_cast<uint32_t>(global_addr - backing_store);
           } else {
-            untagged_buffer =
-                handle(instance->untagged_globals_buffer(), isolate_);
+            if (global.type == kWasmAnyRef) {
+              tagged_buffer =
+                  handle(instance->tagged_globals_buffer(), isolate_);
+            } else {
+              untagged_buffer =
+                  handle(instance->untagged_globals_buffer(), isolate_);
+            }
             offset = global.offset;
           }
 
           // Since the global's array untagged_buffer is always provided,
           // allocation should never fail.
           Handle<WasmGlobalObject> global_obj =
-              WasmGlobalObject::New(isolate_, untagged_buffer,
-                                    MaybeHandle<FixedArray>(), global.type,
-                                    offset, global.mutability)
+              WasmGlobalObject::New(isolate_, untagged_buffer, tagged_buffer,
+                                    global.type, offset, global.mutability)
                   .ToHandleChecked();
           desc.set_value(global_obj);
         } else {

src/wasm/wasm-objects.cc

@@ -1106,6 +1106,7 @@ MaybeHandle<WasmGlobalObject> WasmGlobalObject::New(
       isolate->factory()->NewJSObject(global_ctor));
 
   if (type == wasm::kWasmAnyRef) {
+    DCHECK(maybe_untagged_buffer.is_null());
     Handle<FixedArray> tagged_buffer;
     if (!maybe_tagged_buffer.ToHandle(&tagged_buffer)) {
       // If no buffer was provided, create one.
@@ -1114,6 +1115,7 @@ MaybeHandle<WasmGlobalObject> WasmGlobalObject::New(
     }
     global_obj->set_tagged_buffer(*tagged_buffer);
   } else {
+    DCHECK(maybe_tagged_buffer.is_null());
     Handle<JSArrayBuffer> untagged_buffer;
     uint32_t type_size = wasm::ValueTypes::ElementSizeInBytes(type);
     if (!maybe_untagged_buffer.ToHandle(&untagged_buffer)) {

test/mjsunit/wasm/anyref-globals.js

@@ -170,3 +170,27 @@ load("test/mjsunit/wasm/wasm-module-builder.js");
   TestGlobal({a: 11});
   TestGlobal(print);
 })();
+
+(function TestExportImmutableAnyRefGlobal() {
+  print(arguments.callee.name);
+  let builder = new WasmModuleBuilder();
+  const g1 = builder.addGlobal(kWasmAnyRef, true).exportAs("global1");
+  builder.addGlobal(kWasmI32, true); // Dummy.
+  builder.addGlobal(kWasmAnyRef, true); // Dummy.
+  const g2 = builder.addGlobal(kWasmAnyRef, true).exportAs("global2");
+  builder.addFunction("main", kSig_v_rr)
+    .addBody([
+        kExprGetLocal, 0,
+        kExprSetGlobal, g1.index,
+        kExprGetLocal, 1,
+        kExprSetGlobal, g2.index
+    ])
+    .exportAs("main");
+
+  const instance = builder.instantiate();
+  const obj1 = {x: 221};
+  const obj2 = print;
+  instance.exports.main(obj1, obj2);
+  assertSame(obj1, instance.exports.global1.value);
+  assertSame(obj2, instance.exports.global2.value);
+})();

test/mjsunit/wasm/wasm-constants.js

@@ -146,6 +146,7 @@ let kSig_d_d = makeSig([kWasmF64], [kWasmF64]);
 let kSig_r_r = makeSig([kWasmAnyRef], [kWasmAnyRef]);
 let kSig_i_r = makeSig([kWasmAnyRef], [kWasmI32]);
 let kSig_v_r = makeSig([kWasmAnyRef], []);
+let kSig_v_rr = makeSig([kWasmAnyRef, kWasmAnyRef], []);
 let kSig_r_v = makeSig([], [kWasmAnyRef]);
 
 function makeSig(params, results) {