[asm.js] Maintain insertion order of exports.

This makes sure that the observable property order of the module export
maintains insertion order. Now that properties are configurable, we no
longer need to reverse the export processing.

R=clemensh@chromium.org
TEST=mjsunit/asm/asm-validation
BUG=chromium:715420

Change-Id: Ib2024254c07bdad7fee1cf2fa0bd3e847721f5b5
Reviewed-on: https://chromium-review.googlesource.com/488022Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44891}

src/wasm/wasm-module.cc

@@ -5,7 +5,6 @@
 #include <memory>
 
 #include "src/assembler-inl.h"
-#include "src/base/adapters.h"
 #include "src/base/atomic-utils.h"
 #include "src/code-stubs.h"
 #include "src/compiler/wasm-compiler.h"
@@ -1867,28 +1866,23 @@ class InstantiationHelper {
     desc.set_enumerable(true);
     desc.set_configurable(module_->is_asm_js());
 
-    // Count up export indexes.
-    int export_index = 0;
-    for (auto exp : module_->export_table) {
-      if (exp.kind == kExternalFunction) {
-        ++export_index;
-      }
-    }
-
     // Store weak references to all exported functions.
     Handle<FixedArray> weak_exported_functions;
     if (compiled_module->has_weak_exported_functions()) {
       weak_exported_functions = compiled_module->weak_exported_functions();
     } else {
+      int export_count = 0;
+      for (WasmExport& exp : module_->export_table) {
+        if (exp.kind == kExternalFunction) ++export_count;
+      }
       weak_exported_functions =
-          isolate_->factory()->NewFixedArray(export_index);
+          isolate_->factory()->NewFixedArray(export_count);
       compiled_module->set_weak_exported_functions(weak_exported_functions);
     }
-    DCHECK_EQ(export_index, weak_exported_functions->length());
 
-    // Process each export in the export table (go in reverse so asm.js
-    // can skip duplicates).
-    for (auto exp : base::Reversed(module_->export_table)) {
+    // Process each export in the export table.
+    int export_index = 0;  // Index into {weak_exported_functions}.
+    for (WasmExport& exp : module_->export_table) {
       Handle<String> name =
           WasmCompiledModule::ExtractUtf8StringFromModuleBytes(
               isolate_, compiled_module_, exp.name_offset, exp.name_length)
@@ -1907,7 +1901,7 @@ class InstantiationHelper {
           // 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.
@@ -1931,6 +1925,7 @@ class InstantiationHelper {
               isolate_->factory()->NewWeakCell(js_function);
           DCHECK_GT(weak_exported_functions->length(), export_index);
           weak_exported_functions->set(export_index, *weak_export);
+          export_index++;
           break;
         }
         case kExternalTable: {
@@ -1998,13 +1993,6 @@ class InstantiationHelper {
           break;
       }
 
-      // Skip duplicates for asm.js.
-      if (module_->is_asm_js()) {
-        v8::Maybe<bool> status = JSReceiver::HasOwnProperty(export_to, name);
-        if (status.FromMaybe(false)) {
-          continue;
-        }
-      }
       v8::Maybe<bool> status = JSReceiver::DefineOwnProperty(
           isolate_, export_to, name, &desc, Object::THROW_ON_ERROR);
       if (!status.IsJust()) {
@@ -2013,6 +2001,7 @@ class InstantiationHelper {
         return;
       }
     }
+    DCHECK_EQ(export_index, weak_exported_functions->length());
 
     if (module_->is_wasm()) {
       v8::Maybe<bool> success = JSReceiver::SetIntegrityLevel(

test/mjsunit/asm/asm-validation.js

@@ -484,3 +484,15 @@ function assertValidAsm(func) {
   assertTrue(o.__single_function__ === undefined);
   assertTrue(o.__foreign_init__ === undefined);
 })();
+
+(function TestAsmExportOrderPreserved() {
+  function Module() {
+    "use asm";
+    function f() {}
+    return { a:f, b:f, x:f, c:f, d:f };
+  }
+  var m = Module();
+  assertValidAsm(Module);
+  var props = Object.getOwnPropertyNames(m);
+  assertEquals(["a","b","x","c","d"], props);
+})();