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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 */
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