1 files changed, 84 insertions, 0 deletions
diff --git a/js/src/frontend/JumpList.h b/js/src/frontend/JumpList.h
new file mode 100644
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+++ b/js/src/frontend/JumpList.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef frontend_JumpList_h
+#define frontend_JumpList_h
+
+#include <stddef.h>  // ptrdiff_t
+
+#include "frontend/BytecodeOffset.h"  // BytecodeOffset
+#include "js/TypeDecls.h"             // jsbytecode
+
+namespace js {
+namespace frontend {
+
+// Linked list of jump instructions that need to be patched. The linked list is
+// stored in the bytes of the incomplete bytecode that will be patched, so no
+// extra memory is needed, and patching the instructions destroys the list.
+//
+// Example:
+//
+//     JumpList brList;
+//     if (!emitJump(JSOp::JumpIfFalse, &brList)) {
+//         return false;
+//     }
+//     ...
+//     JumpTarget label;
+//     if (!emitJumpTarget(&label)) {
+//         return false;
+//     }
+//     ...
+//     if (!emitJump(JSOp::Goto, &brList)) {
+//         return false;
+//     }
+//     ...
+//     patchJumpsToTarget(brList, label);
+//
+//                      +-> (the delta is END_OF_LIST_DELTA (=0) for the last
+//                      |    item)
+//                      |
+//                      |
+//    JumpIfFalse .. <+ +                +-+   JumpIfFalse ..
+//    ..              |                  |     ..
+//  label:            |                  +-> label:
+//    JumpTarget      |                  |     JumpTarget
+//    ..              |                  |     ..
+//    Goto .. <+ +----+                  +-+   Goto .. <+
+//             |                                   |
+//             |                                   |
+//             +                                   +
+//           brList                              brList
+//
+//       |                                  ^
+//       +------- patchJumpsToTarget -------+
+//
+
+// Offset of a jump target instruction, used for patching jump instructions.
+struct JumpTarget {
+  BytecodeOffset offset = BytecodeOffset::invalidOffset();
+};
+
+struct JumpList {
+  // Delta value for pre-patchJumpsToTarget that marks the end of the link.
+  static const ptrdiff_t END_OF_LIST_DELTA = 0;
+
+  // -1 is used to mark the end of jump lists.
+  JumpList() : offset(BytecodeOffset::invalidOffset()) {}
+
+  BytecodeOffset offset;
+
+  // Add a jump instruction to the list.
+  void push(jsbytecode* code, BytecodeOffset jumpOffset);
+
+  // Patch all jump instructions in this list to jump to `target`.  This
+  // clobbers the list.
+  void patchAll(jsbytecode* code, JumpTarget target);
+};
+
+} /* namespace frontend */
+} /* namespace js */
+
+#endif /* frontend_JumpList_h */