[wasm][anyref] Implement the RefNull opcode

R=titzer@chromium.org

Bug: v8:7581
Change-Id: I3a1fcffd3429907bcf9f92a904ab30568e6d4d07
Reviewed-on: https://chromium-review.googlesource.com/998914
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52501}

src/compiler/wasm-compiler.cc

@@ -97,12 +97,13 @@ bool ContainsSimd(wasm::FunctionSig* sig) {
 
 WasmGraphBuilder::WasmGraphBuilder(
     ModuleEnv* env, Zone* zone, JSGraph* jsgraph, Handle<Code> centry_stub,
-    wasm::FunctionSig* sig,
+    Handle<Oddball> anyref_null, wasm::FunctionSig* sig,
     compiler::SourcePositionTable* source_position_table,
     RuntimeExceptionSupport exception_support)
     : zone_(zone),
       jsgraph_(jsgraph),
       centry_stub_node_(jsgraph_->HeapConstant(centry_stub)),
+      anyref_null_node_(jsgraph_->HeapConstant(anyref_null)),
       env_(env),
       cur_buffer_(def_buffer_),
       cur_bufsize_(kDefaultBufferSize),
@@ -4664,7 +4665,8 @@ Handle<Code> CompileJSToWasmWrapper(Isolate* isolate, wasm::WasmModule* module,
   ModuleEnv env(module, use_trap_handler);
 
   WasmGraphBuilder builder(&env, &zone, &jsgraph,
-                           CEntryStub(isolate, 1).GetCode(), func->sig);
+                           CEntryStub(isolate, 1).GetCode(),
+                           isolate->factory()->null_value(), func->sig);
   builder.set_control_ptr(&control);
   builder.set_effect_ptr(&effect);
   builder.BuildJSToWasmWrapper(weak_instance, wasm_code);
@@ -4776,9 +4778,9 @@ Handle<Code> CompileWasmToJSWrapper(Isolate* isolate, Handle<JSReceiver> target,
                                    : nullptr;
 
   ModuleEnv env(nullptr, use_trap_handler);
-  WasmGraphBuilder builder(&env, &zone, &jsgraph,
-                           CEntryStub(isolate, 1).GetCode(), sig,
-                           source_position_table);
+  WasmGraphBuilder builder(
+      &env, &zone, &jsgraph, CEntryStub(isolate, 1).GetCode(),
+      isolate->factory()->null_value(), sig, source_position_table);
   builder.set_control_ptr(&control);
   builder.set_effect_ptr(&effect);
   builder.BuildWasmToJSWrapper(target, index);
@@ -4842,7 +4844,8 @@ Handle<Code> CompileWasmInterpreterEntry(Isolate* isolate, uint32_t func_index,
   Node* effect = nullptr;
 
   WasmGraphBuilder builder(nullptr, &zone, &jsgraph,
-                           CEntryStub(isolate, 1).GetCode(), sig);
+                           CEntryStub(isolate, 1).GetCode(),
+                           isolate->factory()->null_value(), sig);
   builder.set_control_ptr(&control);
   builder.set_effect_ptr(&effect);
   builder.BuildWasmInterpreterEntry(func_index);
@@ -4903,7 +4906,8 @@ Handle<Code> CompileCWasmEntry(Isolate* isolate, wasm::FunctionSig* sig) {
   Node* effect = nullptr;
 
   WasmGraphBuilder builder(nullptr, &zone, &jsgraph,
-                           CEntryStub(isolate, 1).GetCode(), sig);
+                           CEntryStub(isolate, 1).GetCode(),
+                           isolate->factory()->null_value(), sig);
   builder.set_control_ptr(&control);
   builder.set_effect_ptr(&effect);
   builder.BuildCWasmEntry();
@@ -4977,8 +4981,12 @@ SourcePositionTable* WasmCompilationUnit::BuildGraphForWasmFunction(
 
   SourcePositionTable* source_position_table =
       new (tf_.jsgraph_->zone()) SourcePositionTable(tf_.jsgraph_->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(env_, tf_.jsgraph_->zone(), tf_.jsgraph_,
-                           centry_stub_, func_body_.sig, source_position_table,
+                           centry_stub_, isolate_->factory()->null_value(),
+                           func_body_.sig, source_position_table,
                            wasm_compilation_data_.runtime_exception_support());
   tf_.graph_construction_result_ =
       wasm::BuildTFGraph(isolate_->allocator(), &builder, func_body_);

src/compiler/wasm-compiler.h

@@ -229,7 +229,8 @@ class WasmGraphBuilder {
   enum EnforceBoundsCheck : bool { kNeedsBoundsCheck, kCanOmitBoundsCheck };
 
   WasmGraphBuilder(ModuleEnv* env, Zone* zone, JSGraph* graph,
-                   Handle<Code> centry_stub, wasm::FunctionSig* sig,
+                   Handle<Code> centry_stub, Handle<Oddball> anyref_null,
+                   wasm::FunctionSig* sig,
                    compiler::SourcePositionTable* spt = nullptr,
                    RuntimeExceptionSupport res = kRuntimeExceptionSupport);
 
@@ -264,6 +265,7 @@ class WasmGraphBuilder {
   Node* IntPtrConstant(intptr_t value);
   Node* Float32Constant(float value);
   Node* Float64Constant(double value);
+  Node* RefNull() { return anyref_null_node_; }
   Node* HeapConstant(Handle<HeapObject> value);
   Node* Binop(wasm::WasmOpcode opcode, Node* left, Node* right,
               wasm::WasmCodePosition position = wasm::kNoCodePosition);
@@ -418,6 +420,7 @@ class WasmGraphBuilder {
   Zone* const zone_;
   JSGraph* const jsgraph_;
   Node* const centry_stub_node_;
+  Node* const anyref_null_node_;
   // env_ == nullptr means we're not compiling Wasm functions, such as for
   // wrappers or interpreter stubs.
   ModuleEnv* const env_ = nullptr;

src/wasm/baseline/liftoff-compiler.cc

@@ -928,7 +928,9 @@ class LiftoffCompiler {
     __ PushRegister(kWasmF64, reg);
   }
 
-  void RefNull(Decoder* decoder, Value* result) { UNIMPLEMENTED(); }
+  void RefNull(Decoder* decoder, Value* result) {
+    unsupported(decoder, "ref_null");
+  }
 
   void Drop(Decoder* decoder, const Value& value) {
     __ DropStackSlot(&__ cache_state()->stack_state.back());

src/wasm/function-body-decoder.cc

@@ -235,7 +235,7 @@ class WasmGraphBuildingInterface {
   }
 
   void RefNull(Decoder* decoder, Value* result) {
-    result->node = builder_->HeapConstant(Handle<HeapObject>::null());
+    result->node = builder_->RefNull();
   }
 
   void Drop(Decoder* decoder, const Value& value) {}

src/wasm/wasm-code-manager.cc

@@ -684,7 +684,7 @@ WasmCode* NativeModule::AddCode(
     RelocInfo::Mode mode = it.rinfo()->rmode();
     if (mode == RelocInfo::EMBEDDED_OBJECT) {
       Handle<HeapObject> p = it.rinfo()->target_object_handle(origin);
-      DCHECK_EQ(*p, p->GetIsolate()->heap()->undefined_value());
+      DCHECK(p->IsUndefined(p->GetIsolate()) || p->IsNull(p->GetIsolate()));
       it.rinfo()->set_target_object(*p, SKIP_WRITE_BARRIER, SKIP_ICACHE_FLUSH);
     } else if (RelocInfo::IsCodeTarget(mode)) {
       // rewrite code handles to direct pointers to the first instruction in the

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

@@ -270,13 +270,15 @@ void TestBuildingGraph(
     compiler::RuntimeExceptionSupport runtime_exception_support) {
   if (module) {
     compiler::WasmGraphBuilder builder(
-        module, zone, jsgraph, CEntryStub(jsgraph->isolate(), 1).GetCode(), sig,
-        source_position_table, runtime_exception_support);
+        module, zone, jsgraph, CEntryStub(jsgraph->isolate(), 1).GetCode(),
+        jsgraph->isolate()->factory()->null_value(), sig, source_position_table,
+        runtime_exception_support);
     TestBuildingGraphWithBuilder(&builder, zone, sig, start, end);
   } else {
     compiler::WasmGraphBuilder builder(
         nullptr, zone, jsgraph, CEntryStub(jsgraph->isolate(), 1).GetCode(),
-        sig, source_position_table, runtime_exception_support);
+        jsgraph->isolate()->factory()->null_value(), sig, source_position_table,
+        runtime_exception_support);
     TestBuildingGraphWithBuilder(&builder, zone, sig, start, end);
   }
 }

test/mjsunit/wasm/anyref.js

@@ -68,3 +68,16 @@ load("test/mjsunit/wasm/wasm-module-builder.js");
 
   instance.exports.main({hello: 'world'});
 })();
+
+(function testAnyRefNull() {
+  print(arguments.callee.name);
+  const builder = new WasmModuleBuilder();
+  builder.addFunction('main', kSig_r_v)
+      .addBody([kExprRefNull])
+      .exportFunc();
+
+
+  const instance = builder.instantiate();
+
+  assertEquals(null, instance.exports.main());
+})();

test/mjsunit/wasm/wasm-constants.js

@@ -136,6 +136,7 @@ let kSig_f_f = makeSig([kWasmF32], [kWasmF32]);
 let kSig_d_d = makeSig([kWasmF64], [kWasmF64]);
 let kSig_r_r = makeSig([kWasmAnyRef], [kWasmAnyRef]);
 let kSig_v_r = makeSig([kWasmAnyRef], []);
+let kSig_r_v = makeSig([], [kWasmAnyRef]);
 
 function makeSig(params, results) {
   return {params: params, results: results};
@@ -189,6 +190,7 @@ let kExprI32Const = 0x41;
 let kExprI64Const = 0x42;
 let kExprF32Const = 0x43;
 let kExprF64Const = 0x44;
+let kExprRefNull = 0xd0;
 let kExprI32LoadMem = 0x28;
 let kExprI64LoadMem = 0x29;
 let kExprF32LoadMem = 0x2a;