[wasm][anyref] Implement ref.is_null

R=titzer@chromium.org

Bug: v8:7581
Change-Id: I30482ddb95a5c8501f1764922cc579855c209fdf
Reviewed-on: https://chromium-review.googlesource.com/998162
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52502}

src/compiler/wasm-compiler.cc

@@ -811,6 +811,8 @@ Node* WasmGraphBuilder::Unop(wasm::WasmOpcode opcode, Node* input,
       return jsgraph()->machine()->Is32()
                  ? BuildCcallConvertFloat(input, position, opcode)
                  : BuildIntConvertFloat(input, position, opcode);
+    case wasm::kExprRefIsNull:
+      return graph()->NewNode(m->WordEqual(), input, anyref_null_node_);
     case wasm::kExprI32AsmjsLoadMem8S:
       return BuildAsmjsLoadMem(MachineType::Int8(), input);
     case wasm::kExprI32AsmjsLoadMem8U:

test/mjsunit/wasm/anyref.js

@@ -81,3 +81,22 @@ load("test/mjsunit/wasm/wasm-module-builder.js");
 
   assertEquals(null, instance.exports.main());
 })();
+
+(function testAnyRefIsNull() {
+  print(arguments.callee.name);
+  const builder = new WasmModuleBuilder();
+  builder.addFunction('main', kSig_i_r)
+      .addBody([kExprGetLocal, 0, kExprRefIsNull])
+      .exportFunc();
+
+  const instance = builder.instantiate();
+
+  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));
+
+})();

test/mjsunit/wasm/wasm-constants.js

@@ -135,6 +135,7 @@ let kSig_v_f = makeSig([kWasmF32], []);
 let kSig_f_f = makeSig([kWasmF32], [kWasmF32]);
 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_r_v = makeSig([], [kWasmAnyRef]);
 
@@ -250,6 +251,7 @@ let kExprF64Lt = 0x63;
 let kExprF64Gt = 0x64;
 let kExprF64Le = 0x65;
 let kExprF64Ge = 0x66;
+let kExprRefIsNull = 0xd1;
 let kExprI32Clz = 0x67;
 let kExprI32Ctz = 0x68;
 let kExprI32Popcnt = 0x69;