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/*
* Copyright (C) 2024 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
#include "ExpressionInfo.h"
namespace JSC {
template<typename RemapFunc>
void ExpressionInfo::Encoder::remap(Vector<unsigned>&& adjustmentLabelPoints, RemapFunc remapFunc)
{
if (!adjustmentLabelPoints.size())
return; // Nothing to adjust.
// Pad the end with a value that exceeds all other bytecodeIndexes.
// This way, currentLabel below will always has a meaningful value
// to compare instPC against.
adjustmentLabelPoints.append(UINT_MAX);
ExpressionInfo::Decoder decoder(m_expressionInfoEncodedInfo);
unsigned numEncodedInfo = m_expressionInfoEncodedInfo.size();
// These are the types of adjustments that we need to handle:
// 1. bytecode got inserted before a LabelPoint.
// 2. bytecode got inserted after the LabelPoint.
// 3. bytecode got deleted after the LabelPoint.
//
// This means that we only need to do a remap of InstPC for the following:
//
// a. the EncodedInfo Entry at a LabelPoint InstPC (due to (1) above).
//
// In this case, the InstPC increased. Our remap will add a delta for the increment.
// Since our EncodedInfo are expressed as deltas from the previous Entry, once an
// adjustment has been applied, subsequent entries will just pick it up for free.
//
// b. the EncodedInfo Entry right after the LabelPoint InstPC (due to (2) and (3) above).
//
// Inserting / Removing bytecode after the LabelPoint affects the InstPC of bytecode
// that follows the LabelPoint starting with the bytecode immediately after. There may
// or may not be any ExpressionInfo Entry for these bytecode. However, we can just be
// conservative, and go ahead to compute the remap for the next Entry anyway. After
// that, our delta cummulation scheme takes care of the rest.
//
// There's also a chance that the next Entry is already beyond the next LabelPoint.
// This is also fine because our remap is computed based on the absolute value of its
// InstPC, not its relative value. Hence, there is no adjusment error: we'll always
// get the correct remapped InstPC value.
//
// c. the EncodedInfo Entry that start with an AbsInstPC.
//
// Above, we pointed out that because our EncodedInfo are expressed as deltas from
// the previous Entry, adjustments are picked up for free. There is one exception:
// AbsInstPC. AbsInstPC does not build on cummulative deltas. So, whenever we see an
// AbsInstPC, we must also remap it.
unsigned adjustmentIndex = 0;
InstPC currentLabel = adjustmentLabelPoints[adjustmentIndex];
bool needToAdjustLabelAfter = false;
unsigned cummulativeDelta = 0;
while (decoder.decode() != IterationStatus::Done) {
bool isAbsInstPC = decoder.currentInfo()->isAbsInstPC();
bool needRemap = isAbsInstPC;
InstPC instPC = decoder.instPC();
if (instPC >= currentLabel) {
needToAdjustLabelAfter = true;
needRemap = true;
currentLabel = adjustmentLabelPoints[++adjustmentIndex];
} else if (needToAdjustLabelAfter) {
needToAdjustLabelAfter = false;
needRemap = true;
}
unsigned instPCDelta;
if (needRemap) {
if (isAbsInstPC)
cummulativeDelta = 0;
instPCDelta = remapFunc(instPC) - instPC - cummulativeDelta;
if (instPCDelta || isAbsInstPC) {
adjustInstPC(decoder.currentInfo(), instPCDelta);
// adjustInstPC() may have resized and reallocated m_expressionInfoEncodedInfo.
// So, we need to re-compute endInfo. info will be re-computed at the top of the loop.
decoder.recacheInfo(m_expressionInfoEncodedInfo);
cummulativeDelta += instPCDelta;
}
}
}
m_numberOfEncodedInfoExtensions = m_expressionInfoEncodedInfo.size() - numEncodedInfo;
// Now, let's remap the Chapter startInstPCs. Their startEncodedInfoIndex will not change because
// the above remap algorithm does in place remapping.
for (auto& chapter : m_expressionInfoChapters)
chapter.startInstPC = remapFunc(chapter.startInstPC);
}
} // namespace JSC
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