[wasm] Fix missing default value for anyref local.

R=titzer@chromium.org
TEST=mjsunit/wasm/anyref

Change-Id: Ia79c78038f6cc92f657ee1b48474323bde981155
Reviewed-on: https://chromium-review.googlesource.com/1201784Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55583}

src/wasm/function-body-decoder.cc

@@ -597,6 +597,7 @@ class WasmGraphBuildingInterface {
         return builder_->Float64Constant(0);
       case kWasmS128:
         return builder_->S128Zero();
+      case kWasmAnyRef:
       case kWasmExceptRef:
         return builder_->RefNull();
       default:

test/mjsunit/wasm/anyref.js

@@ -76,7 +76,6 @@ load("test/mjsunit/wasm/wasm-module-builder.js");
       .addBody([kExprRefNull])
       .exportFunc();
 
-
   const instance = builder.instantiate();
 
   assertEquals(null, instance.exports.main());
@@ -98,5 +97,17 @@ load("test/mjsunit/wasm/wasm-module-builder.js");
   assertEquals(0, instance.exports.main(undefined));
   assertEquals(1, instance.exports.main(null));
   assertEquals(0, instance.exports.main(print));
+})();
 
+(function testAnyRefLocalDefaultValue() {
+  print(arguments.callee.name);
+  const builder = new WasmModuleBuilder();
+  builder.addFunction('main', kSig_r_v)
+      .addBody([kExprGetLocal, 0])
+      .addLocals({anyref_count: 1})
+      .exportFunc();
+
+  const instance = builder.instantiate();
+
+  assertEquals(null, instance.exports.main());
 })();

test/mjsunit/wasm/wasm-module-builder.js

@@ -569,6 +569,9 @@ class WasmModuleBuilder {
             if (l.s128_count > 0) {
               local_decls.push({count: l.s128_count, type: kWasmS128});
             }
+            if (l.anyref_count > 0) {
+              local_decls.push({count: l.anyref_count, type: kWasmAnyRef});
+            }
             if (l.except_count > 0) {
               local_decls.push({count: l.except_count, type: kWasmExceptRef});
             }