[Interpreter] Ensure we always have an outer register allocation scope.

test/unittests/interpreter/bytecode-register-allocator-unittest.cc

+// Copyright 2014 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/v8.h"
+
+#include "src/interpreter/bytecode-array-builder.h"
+#include "src/interpreter/bytecode-register-allocator.h"
+#include "test/unittests/test-utils.h"
+
+namespace v8 {
+namespace internal {
+namespace interpreter {
+
+class BytecodeRegisterAllocatorTest : public TestWithIsolateAndZone {
+ public:
+  BytecodeRegisterAllocatorTest() {}
+  ~BytecodeRegisterAllocatorTest() override {}
+};
+
+
+TEST_F(BytecodeRegisterAllocatorTest, TemporariesRecycled) {
+  BytecodeArrayBuilder builder(isolate(), zone());
+  builder.set_parameter_count(0);
+  builder.set_locals_count(0);
+  builder.set_context_count(0);
+
+  int first;
+  {
+    BytecodeRegisterAllocator temporaries(&builder);
+    first = temporaries.NewRegister().index();
+    temporaries.NewRegister();
+    temporaries.NewRegister();
+    temporaries.NewRegister();
+  }
+
+  int second;
+  {
+    BytecodeRegisterAllocator temporaries(&builder);
+    second = temporaries.NewRegister().index();
+  }
+
+  CHECK_EQ(first, second);
+}
+
+
+TEST_F(BytecodeRegisterAllocatorTest, ConsecutiveRegisters) {
+  BytecodeArrayBuilder builder(isolate(), zone());
+  builder.set_parameter_count(0);
+  builder.set_locals_count(0);
+  builder.set_context_count(0);
+
+  BytecodeRegisterAllocator temporaries(&builder);
+  temporaries.PrepareForConsecutiveAllocations(4);
+  Register reg0 = temporaries.NextConsecutiveRegister();
+  Register other = temporaries.NewRegister();
+  Register reg1 = temporaries.NextConsecutiveRegister();
+  Register reg2 = temporaries.NextConsecutiveRegister();
+  Register reg3 = temporaries.NextConsecutiveRegister();
+  USE(other);
+
+  CHECK(Register::AreContiguous(reg0, reg1, reg2, reg3));
+}
+
+}  // namespace interpreter
+}  // namespace internal
+}  // namespace v8