[wasm] Add support to construct 'exnref' type globals.

R=ahaas@chromium.org
TEST=mjsunit/wasm/exceptions-global
BUG=v8:8091

Change-Id: I9eb4c92cca087719afda2da5d11c206aaed28c95
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1771788Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63414}

src/wasm/wasm-js.cc

@@ -1223,6 +1223,9 @@ bool GetValueType(Isolate* isolate, MaybeLocal<Value> maybe,
   } else if (enabled_features.anyref &&
              string->StringEquals(v8_str(isolate, "anyfunc"))) {
     *type = i::wasm::kWasmFuncRef;
+  } else if (enabled_features.eh &&
+             string->StringEquals(v8_str(isolate, "exnref"))) {
+    *type = i::wasm::kWasmExnRef;
   } else {
     // Unrecognized type.
     *type = i::wasm::kWasmStmt;
@@ -1337,7 +1340,8 @@ void WebAssemblyGlobal(const v8::FunctionCallbackInfo<v8::Value>& args) {
       global_obj->SetF64(f64_value);
       break;
     }
-    case i::wasm::kWasmAnyRef: {
+    case i::wasm::kWasmAnyRef:
+    case i::wasm::kWasmExnRef: {
       if (args.Length() < 2) {
         // When no inital value is provided, we have to use the WebAssembly
         // default value 'null', and not the JS default value 'undefined'.

test/mjsunit/wasm/exceptions-global.js

@@ -115,10 +115,8 @@ load("test/mjsunit/wasm/wasm-module-builder.js");
   assertThrowsEquals(() => instance.exports.rethrow_exnref(), exception2);
 })();
 
-// TODO(mstarzinger): Add the following test once proposal makes it clear how
-// far interaction with the mutable globals proposal is intended to go.
 // Test loading an imported mutable "exnref" being changed from the outside.
-/*(function TestGlobalExnRefGetImportedMutableAndRethrow() {
+(function TestGlobalExnRefGetImportedMutableAndRethrow() {
   print(arguments.callee.name);
   let builder = new WasmModuleBuilder();
   let g_index = builder.addImportedGlobal("m", "exn", kWasmExnRef, true);
@@ -135,7 +133,7 @@ load("test/mjsunit/wasm/wasm-module-builder.js");
   assertThrowsEquals(() => instance.exports.rethrow_exnref(), exception1);
   let exception2 = mutable_global.value = "an even fancier exception";
   assertThrowsEquals(() => instance.exports.rethrow_exnref(), exception2);
-})();*/
+})();
 
 // Test custom initialization index for a global "exnref" variable.
 (function TestGlobalExnRefInitIndex() {