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// 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_
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