[wasm] Fix usages of ErrorThrower::Reify

ErrorThrower::Reify() should only be called if an error is actually set.
This CL introduces a Reset() method to replace the obsolete (now
disallowed) usages.

R=mtrofin@chromium.org
BUG=chromium:717056

Change-Id: I41b989a9c7b33591ee26ec6d43540a38289ab54f
Reviewed-on: https://chromium-review.googlesource.com/493506Reviewed-by: Mircea Trofin <mtrofin@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45039}

src/asmjs/asm-js.cc

@@ -335,7 +335,7 @@ MaybeHandle<Object> AsmJs::InstantiateAsmWasm(Isolate* isolate,
   MaybeHandle<Object> maybe_module_object =
       wasm::SyncInstantiate(isolate, &thrower, module, ffi_object, memory);
   if (maybe_module_object.is_null()) {
-    thrower.Reify();  // Ensure exceptions do not propagate.
+    thrower.Reset();  // Ensure exceptions do not propagate.
     return MaybeHandle<Object>();
   }
   DCHECK(!thrower.error());

src/wasm/wasm-js.cc

@@ -180,7 +180,7 @@ void WebAssemblyValidate(const v8::FunctionCallbackInfo<v8::Value>& args) {
       i::wasm::SyncValidate(reinterpret_cast<i::Isolate*>(isolate), bytes)) {
     return_value.Set(v8::True(isolate));
   } else {
-    if (thrower.wasm_error()) thrower.Reify();  // Clear error.
+    if (thrower.wasm_error()) thrower.Reset();  // Clear error.
     return_value.Set(v8::False(isolate));
   }
 }

src/wasm/wasm-result.cc

@@ -144,6 +144,11 @@ Handle<Object> ErrorThrower::Reify() {
   return exception;
 }
 
+void ErrorThrower::Reset() {
+  error_type_ = kNone;
+  error_msg_.clear();
+}
+
 ErrorThrower::ErrorThrower(ErrorThrower&& other)
     : isolate_(other.isolate_),
       context_(other.context_),

src/wasm/wasm-result.h

@@ -114,7 +114,11 @@ class V8_EXPORT_PRIVATE ErrorThrower {
                  result.error_offset());
   }
 
-  Handle<Object> Reify();
+  // Create and return exception object.
+  MUST_USE_RESULT Handle<Object> Reify();
+
+  // Reset any error which was set on this thrower.
+  void Reset();
 
   bool error() const { return error_type_ != kNone; }
   bool wasm_error() { return error_type_ >= kFirstWasmError; }

test/mjsunit/regress/wasm/regression-717056.js

+// Copyright 2017 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.
+
+// Check that stack overflow inside asm-wasm translation propagates correctly.
+
+function asm() {
+  'use asm';
+  return {};
+}
+
+function rec() {
+  asm();
+  rec();
+}
+assertThrows(() => rec(), RangeError);