[wasm] Avoid embedding {null} values in WasmCode.

This loads references to {null} values from the instance object instead
of embedding them into the generated code. It is one step towards making
the {WasmCode} objects independent of the Isolate.

Note that this also fixes an issue with the serializer/deserializer that
failed to properly serialize {null} values and accidentally collapsed
them to {undefined} values instead.

R=ahaas@chromium.org
TEST=mjsunit/regress/wasm/regress-7785
BUG=v8:7424,v8:7785

Change-Id: Ie436c2d96890e7c8c89ffe2bd4189a759254775b
Reviewed-on: https://chromium-review.googlesource.com/1070981
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53352}

src/compiler/wasm-compiler.cc

@@ -112,15 +112,13 @@ bool ContainsInt64(wasm::FunctionSig* sig) {
 
 WasmGraphBuilder::WasmGraphBuilder(
     Isolate* isolate, wasm::ModuleEnv* env, Zone* zone, MachineGraph* mcgraph,
-    Handle<Code> centry_stub, Handle<Oddball> anyref_null,
-    wasm::FunctionSig* sig,
+    Handle<Code> centry_stub, wasm::FunctionSig* sig,
     compiler::SourcePositionTable* source_position_table)
     : isolate_(isolate),
       zone_(zone),
       mcgraph_(mcgraph),
       env_(env),
       centry_stub_(centry_stub),
-      anyref_null_(anyref_null),
       cur_buffer_(def_buffer_),
       cur_bufsize_(kDefaultBufferSize),
       has_simd_(ContainsSimd(sig)),
@@ -214,11 +212,9 @@ Node* WasmGraphBuilder::EffectPhi(unsigned count, Node** effects,
 }
 
 Node* WasmGraphBuilder::RefNull() {
-  if (!anyref_null_node_.is_set()) {
-    anyref_null_node_.set(
-        graph()->NewNode(mcgraph()->common()->HeapConstant(anyref_null_)));
-  }
-  return anyref_null_node_.get();
+  Node* null = LOAD_INSTANCE_FIELD(NullValue, MachineType::TaggedPointer());
+  *effect_ = null;
+  return null;
 }
 
 Node* WasmGraphBuilder::CEntryStub() {
@@ -3978,8 +3974,7 @@ class WasmWrapperGraphBuilder : public WasmGraphBuilder {
                           wasm::FunctionSig* sig,
                           compiler::SourcePositionTable* spt)
       : WasmGraphBuilder(jsgraph->isolate(), env, zone, jsgraph,
-                         CodeFactory::CEntry(jsgraph->isolate()),
-                         jsgraph->isolate()->factory()->null_value(), sig, spt),
+                         CodeFactory::CEntry(jsgraph->isolate()), sig, spt),
         jsgraph_(jsgraph) {}
 
   Node* BuildAllocateHeapNumberWithValue(Node* value, Node* control) {
@@ -5007,12 +5002,8 @@ SourcePositionTable* TurbofanWasmCompilationUnit::BuildGraphForWasmFunction(
   // Create a TF graph during decoding.
   SourcePositionTable* source_position_table =
       new (mcgraph_->zone()) SourcePositionTable(mcgraph_->graph());
-  // We get the handle for {null_value()} directly from the isolate although we
-  // are on a background task because the handle is stored in the isolate
-  // anyways, and it is immortal and immovable.
   WasmGraphBuilder builder(wasm_unit_->isolate_, wasm_unit_->env_,
                            mcgraph_->zone(), mcgraph_, wasm_unit_->centry_stub_,
-                           wasm_unit_->isolate_->factory()->null_value(),
                            wasm_unit_->func_body_.sig, source_position_table);
   graph_construction_result_ = wasm::BuildTFGraph(
       wasm_unit_->isolate_->allocator(), &builder, wasm_unit_->func_body_);

src/compiler/wasm-compiler.h

@@ -159,7 +159,7 @@ class WasmGraphBuilder {
 
   WasmGraphBuilder(Isolate* isolate, wasm::ModuleEnv* env, Zone* zone,
                    MachineGraph* mcgraph, Handle<Code> centry_stub,
-                   Handle<Oddball> anyref_null, wasm::FunctionSig* sig,
+                   wasm::FunctionSig* sig,
                    compiler::SourcePositionTable* spt = nullptr);
 
   Node** Buffer(size_t count) {
@@ -344,13 +344,11 @@ class WasmGraphBuilder {
   WasmInstanceCacheNodes* instance_cache_ = nullptr;
 
   Handle<Code> centry_stub_;
-  Handle<Oddball> anyref_null_;
 
   SetOncePointer<Node> instance_node_;
   SetOncePointer<Node> globals_start_;
   SetOncePointer<Node> imported_mutable_globals_;
   SetOncePointer<Node> centry_stub_node_;
-  SetOncePointer<Node> anyref_null_node_;
   SetOncePointer<Node> stack_check_builtin_code_node_;
   const Operator* stack_check_call_operator_ = nullptr;
 

src/wasm/wasm-code-manager.cc

@@ -278,7 +278,7 @@ void WasmCode::Validate() const {
         break;
       case RelocInfo::EMBEDDED_OBJECT: {
         HeapObject* o = it.rinfo()->target_object();
-        DCHECK(o->IsUndefined(o->GetIsolate()) || o->IsNull(o->GetIsolate()));
+        DCHECK(o->IsUndefined(o->GetIsolate()));
         break;
       }
       default:

src/wasm/wasm-objects-inl.h

@@ -155,6 +155,7 @@ OPTIONAL_ACCESSORS(WasmInstanceObject, managed_native_allocations, Foreign,
                    kManagedNativeAllocationsOffset)
 OPTIONAL_ACCESSORS(WasmInstanceObject, managed_indirect_patcher, Foreign,
                    kManagedIndirectPatcherOffset)
+ACCESSORS(WasmInstanceObject, null_value, Oddball, kNullValueOffset)
 
 inline bool WasmInstanceObject::has_indirect_function_table() {
   return indirect_function_table_sig_ids() != nullptr;

src/wasm/wasm-objects.cc

@@ -805,6 +805,7 @@ Handle<WasmInstanceObject> WasmInstanceObject::New(
   instance->set_compiled_module(*compiled_module);
   instance->set_native_context(*isolate->native_context());
   instance->set_module_object(*module_object);
+  instance->set_null_value(isolate->heap()->null_value());
 
   return instance;
 }

src/wasm/wasm-objects.h

@@ -288,6 +288,7 @@ class WasmInstanceObject : public JSObject {
   DECL_OPTIONAL_ACCESSORS(indirect_function_table_instances, FixedArray)
   DECL_OPTIONAL_ACCESSORS(managed_native_allocations, Foreign)
   DECL_OPTIONAL_ACCESSORS(managed_indirect_patcher, Foreign)
+  DECL_ACCESSORS(null_value, Oddball)
   DECL_PRIMITIVE_ACCESSORS(memory_start, byte*)
   DECL_PRIMITIVE_ACCESSORS(memory_size, uint32_t)
   DECL_PRIMITIVE_ACCESSORS(memory_mask, uint32_t)
@@ -318,6 +319,7 @@ class WasmInstanceObject : public JSObject {
   V(kIndirectFunctionTableInstancesOffset, kPointerSize)                \
   V(kManagedNativeAllocationsOffset, kPointerSize)                      \
   V(kManagedIndirectPatcherOffset, kPointerSize)                        \
+  V(kNullValueOffset, kPointerSize)                                     \
   V(kFirstUntaggedOffset, 0)                             /* marker */   \
   V(kMemoryStartOffset, kPointerSize)                    /* untagged */ \
   V(kMemorySizeOffset, kUInt32Size)                      /* untagged */ \

test/cctest/wasm/wasm-run-utils.cc

@@ -268,21 +268,10 @@ void TestBuildingGraph(Zone* zone, compiler::JSGraph* jsgraph,
                        ModuleEnv* module, FunctionSig* sig,
                        compiler::SourcePositionTable* source_position_table,
                        const byte* start, const byte* end) {
-  if (module) {
-    compiler::WasmGraphBuilder builder(
-        jsgraph->isolate(), module, zone, jsgraph,
+  compiler::WasmGraphBuilder builder(jsgraph->isolate(), module, zone, jsgraph,
                                      CodeFactory::CEntry(jsgraph->isolate(), 1),
-        jsgraph->isolate()->factory()->null_value(), sig,
-        source_position_table);
+                                     sig, source_position_table);
   TestBuildingGraphWithBuilder(&builder, zone, sig, start, end);
-  } else {
-    compiler::WasmGraphBuilder builder(
-        jsgraph->isolate(), nullptr, zone, jsgraph,
-        CodeFactory::CEntry(jsgraph->isolate(), 1),
-        jsgraph->isolate()->factory()->null_value(), sig,
-        source_position_table);
-    TestBuildingGraphWithBuilder(&builder, zone, sig, start, end);
-  }
 }
 
 WasmFunctionWrapper::WasmFunctionWrapper(Zone* zone, int num_params)

test/mjsunit/regress/wasm/regress-7785.js

+// Copyright 2018 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.
+
+// Flags: --allow-natives-syntax --experimental-wasm-anyref
+
+load("test/mjsunit/wasm/wasm-constants.js");
+load("test/mjsunit/wasm/wasm-module-builder.js");
+
+(function testAnyRefNull() {
+  const builder = new WasmModuleBuilder();
+  builder.addFunction('main', kSig_r_v)
+      .addBody([kExprRefNull])
+      .exportFunc();
+
+  var wire_bytes = builder.toBuffer();
+  var module = new WebAssembly.Module(wire_bytes);
+  var buffer = %SerializeWasmModule(module);
+  module = %DeserializeWasmModule(buffer, wire_bytes);
+  var instance = new WebAssembly.Instance(module);
+
+  assertEquals(null, instance.exports.main());
+})();
+
+(function testAnyRefIsNull() {
+  const builder = new WasmModuleBuilder();
+  builder.addFunction('main', kSig_i_r)
+      .addBody([kExprGetLocal, 0, kExprRefIsNull])
+      .exportFunc();
+
+  var wire_bytes = builder.toBuffer();
+  var module = new WebAssembly.Module(wire_bytes);
+  var buffer = %SerializeWasmModule(module);
+  module = %DeserializeWasmModule(buffer, wire_bytes);
+  var instance = new WebAssembly.Instance(module);
+
+  assertEquals(0, instance.exports.main({'hello' : 'world'}));
+  assertEquals(0, instance.exports.main(1234));
+  assertEquals(0, instance.exports.main(0));
+  assertEquals(0, instance.exports.main(123.4));
+  assertEquals(0, instance.exports.main(undefined));
+  assertEquals(1, instance.exports.main(null));
+  assertEquals(0, instance.exports.main(print));
+})();