includes: move Label out of assembler.h.

src/label.h

Index: src/label.h
diff --git a/src/label.h b/src/label.h
new file mode 100644
index 0000000000000000000000000000000000000000..e77a2afcc19a83b2e7151ce0ecb39c4e5738e7b4
--- /dev/null
+++ b/src/label.h
@@ -0,0 +1,92 @@
+// 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.
+
+#ifndef V8_LABEL_H_
+#define V8_LABEL_H_
+
+#include "src/base/macros.h"
+
+namespace v8 {
+namespace internal {
+
+// -----------------------------------------------------------------------------
+// Labels represent pc locations; they are typically jump or call targets.
+// After declaration, a label can be freely used to denote known or (yet)
+// unknown pc location. Assembler::bind() is used to bind a label to the
+// current pc. A label can be bound only once.
+
+class Label {
+ public:
+  enum Distance { kNear, kFar };
+
+  INLINE(Label()) {
+    Unuse();
+    UnuseNear();
+  }
+
+  INLINE(~Label()) {
+    DCHECK(!is_linked());
+    DCHECK(!is_near_linked());
+  }
+
+  INLINE(void Unuse()) { pos_ = 0; }
+  INLINE(void UnuseNear()) { near_link_pos_ = 0; }
+
+  INLINE(bool is_bound() const) { return pos_ < 0; }
+  INLINE(bool is_unused() const) { return pos_ == 0 && near_link_pos_ == 0; }
+  INLINE(bool is_linked() const) { return pos_ > 0; }
+  INLINE(bool is_near_linked() const) { return near_link_pos_ > 0; }
+
+  // Returns the position of bound or linked labels. Cannot be used
+  // for unused labels.
+  int pos() const {
+    if (pos_ < 0) return -pos_ - 1;
+    if (pos_ > 0) return pos_ - 1;
+    UNREACHABLE();
+    return 0;
+  }
+
+  int near_link_pos() const { return near_link_pos_ - 1; }
+
+ private:
+  // pos_ encodes both the binding state (via its sign)
+  // and the binding position (via its value) of a label.
+  //
+  // pos_ <  0  bound label, pos() returns the jump target position
+  // pos_ == 0  unused label
+  // pos_ >  0  linked label, pos() returns the last reference position
+  int pos_;
+
+  // Behaves like |pos_| in the "> 0" case, but for near jumps to this label.
+  int near_link_pos_;
+
+  void bind_to(int pos) {
+    pos_ = -pos - 1;
+    DCHECK(is_bound());
+  }
+  void link_to(int pos, Distance distance = kFar) {
+    if (distance == kNear) {
+      near_link_pos_ = pos + 1;
+      DCHECK(is_near_linked());
+    } else {
+      pos_ = pos + 1;
+      DCHECK(is_linked());
+    }
+  }
+
+  friend class Assembler;
+  friend class Displacement;
+  friend class RegExpMacroAssemblerIrregexp;
+
+#if V8_TARGET_ARCH_ARM64
+  // On ARM64, the Assembler keeps track of pointers to Labels to resolve
+  // branches to distant targets. Copying labels would confuse the Assembler.
+  DISALLOW_COPY_AND_ASSIGN(Label);  // NOLINT
+#endif
+};
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_LABEL_H_