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/*
* Copyright (C) 2015 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. AND ITS CONTRIBUTORS ``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 ITS 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.
*/
#include "config.h"
#include "DFGCopyBarrierOptimizationPhase.h"
#if ENABLE(DFG_JIT)
#include "DFGClobberize.h"
#include "DFGDoesGC.h"
#include "DFGGraph.h"
#include "DFGPhase.h"
#include "JSCInlines.h"
namespace JSC { namespace DFG {
namespace {
bool verbose = false;
class CopyBarrierOptimizationPhase : public Phase {
public:
CopyBarrierOptimizationPhase(Graph& graph)
: Phase(graph, "copy barrier optimization")
{
}
bool run()
{
if (verbose) {
dataLog("Starting copy barrier optimization:\n");
m_graph.dump();
}
// First convert all GetButterfly nodes into GetButterflyReadOnly.
for (BasicBlock* block : m_graph.blocksInNaturalOrder()) {
for (Node* node : *block) {
if (node->op() == GetButterfly)
node->setOp(GetButterflyReadOnly);
}
}
// Anytime we use a GetButterflyReadOnly in a setting that may write to the heap, or if we're in a
// new epoch, convert it to a GetButterfly. The epoch gets incremented at basic block boundaries,
// anytime we GC, and anytime a barrier on the butterfly may be executed. We traverse the program
// in pre-order so that we always see uses after defs. Note that this is a fixpoint because if we
// turn a GetButterflyReadOnly into a GetButterfly, then we've introduced a butterfly reallocation.
bool changed = true;
Epoch currentEpoch = Epoch::first();
m_graph.clearEpochs();
while (changed) {
changed = false;
for (BasicBlock* block : m_graph.blocksInPreOrder()) {
currentEpoch.bump();
for (Node* node : *block) {
bool writesToHeap = writesOverlap(m_graph, node, Heap);
bool reallocatesButterfly = false;
if (doesGC(m_graph, node) || writesOverlap(m_graph, node, JSObject_butterfly))
reallocatesButterfly = true;
else {
// This is not an exhaustive list of things that will execute copy barriers. Most
// things that execute copy barriers also do GC or have writes that overlap the
// butterfly heap, and we catch that above.
switch (node->op()) {
case GetButterfly:
case MultiPutByOffset:
reallocatesButterfly = true;
break;
default:
break;
}
}
m_graph.doToChildren(
node,
[&] (Edge edge) {
if (edge->op() != GetButterflyReadOnly)
return;
if (writesToHeap || currentEpoch != edge->epoch()) {
changed = true;
edge->setOp(GetButterfly);
}
});
if (reallocatesButterfly)
currentEpoch.bump();
node->setEpoch(currentEpoch);
}
}
}
// This phase always thinks that it changes the graph. That's OK, because it's a late phase.
return true;
}
};
} // anonymous namespace
bool performCopyBarrierOptimization(Graph& graph)
{
SamplingRegion samplingRegion("DFG Copy Barrier Optimization Phase");
return runPhase<CopyBarrierOptimizationPhase>(graph);
}
} } // namespace JSC::DFG
#endif // ENABLE(DFG_JIT)
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