[wasm][asm.js] Ignore duplicate exports in asm.js.

src/wasm/wasm-module.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <memory>
 
+#include "src/base/adapters.h"
 #include "src/base/atomic-utils.h"
 #include "src/code-stubs.h"
 #include "src/compiler/wasm-compiler.h"
 #include "src/debug/interface-types.h"
 #include "src/macro-assembler.h"
 #include "src/objects.h"
 #include "src/property-descriptor.h"
 #include "src/simulator.h"
 #include "src/snapshot/snapshot.h"
 #include "src/v8.h"
@@ skipping 1726 matching lines @@
       exports_object =
           isolate_->factory()->NewJSObject(object_function, TENURED);
       Handle<String> exports_name =
           isolate_->factory()->InternalizeUtf8String("exports");
       JSObject::AddProperty(instance, exports_name, exports_object, READ_ONLY);
     }
 
     PropertyDescriptor desc;
     desc.set_writable(false);
 
-    // Process each export in the export table.
+    // Count up export indexes.
     int export_index = 0;
     for (auto exp : module_->export_table) {
+      if (exp.kind == kExternalFunction) {
+        ++export_index;
+      }
+    }
+    // Process each export in the export table (go in reverse so asm.js
+    // can skip duplicates).
+    for (auto exp : base::Reversed(module_->export_table)) {
       Handle<String> name =
           ExtractStringFromModuleBytes(isolate_, compiled_module_,
                                        exp.name_offset, exp.name_length)
               .ToHandleChecked();
       switch (exp.kind) {
         case kExternalFunction: {
           // Wrap and export the code as a JSFunction.
           WasmFunction& function = module_->functions[exp.index];
           int func_index =
-              static_cast<int>(module_->functions.size() + export_index);
+              static_cast<int>(module_->functions.size() + --export_index);
           Handle<JSFunction> js_function = js_wrappers_[exp.index];
           if (js_function.is_null()) {
             // Wrap the exported code as a JSFunction.
             Handle<Code> export_code =
                 code_table->GetValueChecked<Code>(isolate_, func_index);
             MaybeHandle<String> func_name;
             if (module_->origin == kAsmJsOrigin) {
               // For modules arising from asm.js, honor the names section.
               func_name = ExtractStringFromModuleBytes(
                               isolate_, compiled_module_, function.name_offset,
                               function.name_length)
                               .ToHandleChecked();
             }
             js_function = WasmExportedFunction::New(
                 isolate_, instance, func_name, function.func_index,
                 static_cast<int>(function.sig->parameter_count()), export_code);
             js_wrappers_[exp.index] = js_function;
           }
           desc.set_value(js_function);
-          export_index++;
           break;
         }
         case kExternalTable: {
           // Export a table as a WebAssembly.Table object.
           TableInstance& table_instance = table_instances_[exp.index];
           WasmIndirectFunctionTable& table =
               module_->function_tables[exp.index];
           if (table_instance.table_object.is_null()) {
             uint32_t maximum =
                 table.has_max ? table.max_size : kV8MaxWasmTableSize;
@@ skipping 42 matching lines @@
               UNREACHABLE();
           }
           desc.set_value(isolate_->factory()->NewNumber(num));
           break;
         }
         default:
           UNREACHABLE();
           break;
       }
 
+      // Skip duplicates for asm.js.
+      if (module_->origin == kAsmJsOrigin) {
+        v8::Maybe<bool> status =
+            JSReceiver::HasOwnProperty(exports_object, name);
+        if (status.FromMaybe(false)) {
+          continue;
+        }
+      }
       v8::Maybe<bool> status = JSReceiver::DefineOwnProperty(
           isolate_, exports_object, name, &desc, Object::THROW_ON_ERROR);
       if (!status.IsJust()) {
         thrower_->TypeError("export of %.*s failed.", name->length(),
                             name->ToCString().get());
         return;
       }
     }
   }
 
@@ skipping 521 matching lines @@
 MaybeHandle<String> WasmCompiledModule::GetFunctionName(
     Handle<WasmCompiledModule> compiled_module, uint32_t func_index) {
   DCHECK_LT(func_index, compiled_module->module()->functions.size());
   WasmFunction& function = compiled_module->module()->functions[func_index];
   Isolate* isolate = compiled_module->GetIsolate();
   MaybeHandle<String> string = ExtractStringFromModuleBytes(
       isolate, compiled_module, function.name_offset, function.name_length);
   if (!string.is_null()) return string.ToHandleChecked();
   return {};
 }