[builtins] support exception handling in TFJ builtins

test/cctest/test-code-stub-assembler.cc

 // Copyright 2015 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.
 
 #include "src/base/utils/random-number-generator.h"
 #include "src/ic/stub-cache.h"
 #include "src/isolate.h"
 #include "test/cctest/compiler/code-assembler-tester.h"
 #include "test/cctest/compiler/function-tester.h"
 
@@ skipping 1322 matching lines @@
       queried_existing = true;
     }
 
     Handle<Code> expected_handler(handler, isolate);
     ft.CheckTrue(receiver, name, expected_handler);
   }
   // Ensure we performed both kind of queries.
   CHECK(queried_existing && queried_non_existing);
 }
 
+TEST(BranchIfException) {
+  typedef CodeStubAssembler::Label Label;
+  // typedef CodeStubAssembler::Variable Variable;
+  Isolate* isolate(CcTest::InitIsolateOnce());
+
+  VoidDescriptor descriptor(isolate);
+  CodeStubAssemblerTester m(isolate, descriptor);
+
+  Node* context = m.HeapConstant(Handle<Context>(isolate->native_context()));
+  Node* to_string_tag =
+      m.HeapConstant(isolate->factory()->to_string_tag_symbol());
+
+  Label exception_handler(&m);
+  Callable to_string = CodeFactory::ToString(isolate);
+  Node* string = m.CallStub(to_string, context, to_string_tag);
+  m.BranchIfException(string, &exception_handler);
+  m.Return(string);
+
+  m.Bind(&exception_handler);
+  m.Return(m.SmiConstant(Smi::FromInt(-1)));
+
+  Handle<Code> code = m.GenerateCode();
+  CHECK(!code.is_null());
+
+  // Emulate TFJ builtin
+  code->set_flags(Code::ComputeFlags(Code::BUILTIN));
+
+  FunctionTester ft(code, 0);
+  MaybeHandle<Object> result = ft.Call();
+  CHECK_EQ(-1, Handle<Smi>::cast(result.ToHandleChecked())->value());
+}
+
+TEST(BranchIfException2) {
+  typedef CodeStubAssembler::Label Label;
+  // typedef CodeStubAssembler::Variable Variable;
+  Isolate* isolate(CcTest::InitIsolateOnce());
+
+  VoidDescriptor descriptor(isolate);
+  CodeStubAssemblerTester m(isolate, descriptor);
+
+  Node* context = m.HeapConstant(Handle<Context>(isolate->native_context()));
+  Node* to_string_tag =
+      m.HeapConstant(isolate->factory()->to_string_tag_symbol());
+
+  Label exception_handler(&m);
+  Callable to_string = CodeFactory::ToString(isolate);
+  Node* string = m.CallStub(to_string, context, to_string_tag);
+  m.BranchIfException(string, &exception_handler);
+  m.Return(string);
+
+  m.Bind(&exception_handler);
+  m.Return(string);

[caitp, 2016/08/18 03:08:57]

The fact that this test passes is very surprising to me. An op like
`GetException()` or something would be very nice, and would read easier.

I haven't started working on something like that yet, as I'm not certain how it
would even work. I'd prefer that to defining a Variable and passing it to
BranchIfException() though.

+
+  Handle<Code> code = m.GenerateCode();
+  CHECK(!code.is_null());
+
+  // Emulate TFJ builtin
+  code->set_flags(Code::ComputeFlags(Code::BUILTIN));
+
+  FunctionTester ft(code, 0);
+  Handle<Object> result = ft.Call().ToHandleChecked();
+
+  // Should be a TypeError
+  CHECK(result->IsJSObject());
+
+  Handle<Object> constructor =
+      Object::GetPropertyOrElement(result,
+                                   isolate->factory()->constructor_string())
+          .ToHandleChecked();
+  CHECK(constructor->SameValue(*isolate->type_error_function()));
+}
+
 }  // namespace internal
 }  // namespace v8