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/*
* Copyright (C) 2015-2023 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.
*/
#include "config.h"
#include "DFGMovHintRemovalPhase.h"
#if ENABLE(DFG_JIT)
#include "DFGEpoch.h"
#include "DFGForAllKills.h"
#include "DFGGraph.h"
#include "DFGInsertionSet.h"
#include "DFGMayExit.h"
#include "DFGPhase.h"
#include "JSCJSValueInlines.h"
#include "OperandsInlines.h"
namespace JSC { namespace DFG {
namespace {
namespace DFGMovHintRemovalPhaseInternal {
static constexpr bool verbose = false;
}
class MovHintRemovalPhase : public Phase {
public:
MovHintRemovalPhase(Graph& graph)
: Phase(graph, "MovHint removal"_s)
, m_insertionSet(graph)
, m_state(OperandsLike, graph.block(0)->variablesAtHead)
, m_changed(false)
{
}
bool run()
{
dataLogIf(DFGMovHintRemovalPhaseInternal::verbose, "Graph before MovHint removal:\n", m_graph);
for (BasicBlock* block : m_graph.blocksInNaturalOrder())
handleBlock(block);
m_insertionSet.execute(m_graph.block(0));
return m_changed;
}
private:
void handleBlock(BasicBlock* block)
{
dataLogLnIf(DFGMovHintRemovalPhaseInternal::verbose, "Handing block ", pointerDump(block));
// A MovHint is unnecessary if the local dies before it is used. We answer this question by
// maintaining the current exit epoch, and associating an epoch with each local. When a
// local dies, it gets the current exit epoch. If a MovHint occurs in the same epoch as its
// local, then it means there was no exit between the local's death and the MovHint - i.e.
// the MovHint is unnecessary.
Epoch currentEpoch = Epoch::first();
m_state.fill(Epoch());
m_graph.forAllLiveInBytecode(
block->terminal()->origin.forExit,
[&] (Operand reg) {
m_state.operand(reg) = currentEpoch;
});
dataLogLnIf(DFGMovHintRemovalPhaseInternal::verbose, " Locals at ", block->terminal()->origin.forExit, ": ", m_state);
// Assume that blocks after we exit.
currentEpoch.bump();
for (unsigned nodeIndex = block->size(); nodeIndex--;) {
Node* node = block->at(nodeIndex);
if (node->op() == MovHint) {
Epoch localEpoch = m_state.operand(node->unlinkedOperand());
dataLogLnIf(DFGMovHintRemovalPhaseInternal::verbose, " At ", node, " (", node->unlinkedOperand(), "): current = ", currentEpoch, ", local = ", localEpoch);
if (!localEpoch || localEpoch == currentEpoch) {
// Now, MovHint will put bottom value to dead locals. This means that if you insert a new DFG node which introduce
// a new OSR exit, then it gets confused with the already-determined-dead locals. So this phase runs at very end of
// DFG pipeline, and we do not insert a node having a new OSR exit (if it is existing OSR exit, or if it does not exit,
// then it is totally fine).
node->setOpAndDefaultFlags(ZombieHint);
UseKind useKind = node->child1().useKind();
Node* constant = m_constants.ensure(static_cast<std::underlying_type_t<UseKind>>(useKind), [&]() -> Node* {
return m_insertionSet.insertBottomConstantForUse(0, m_graph.block(0)->at(0)->origin, useKind).node();
}).iterator->value;
node->child1() = Edge(constant, useKind);
m_changed = true;
}
m_state.operand(node->unlinkedOperand()) = Epoch();
}
if (mayExit(m_graph, node) != DoesNotExit)
currentEpoch.bump();
if (nodeIndex) {
forAllKilledOperands(
m_graph, block->at(nodeIndex - 1), node,
[&] (Operand operand) {
// This function is a bit sloppy - it might claim to kill a local even if
// it's still live after. We need to protect against that.
if (!!m_state.operand(operand))
return;
dataLogLnIf(DFGMovHintRemovalPhaseInternal::verbose, " Killed operand at ", node, ": ", operand);
m_state.operand(operand) = currentEpoch;
});
}
}
}
InsertionSet m_insertionSet;
UncheckedKeyHashMap<std::underlying_type_t<UseKind>, Node*, WTF::IntHash<std::underlying_type_t<UseKind>>, WTF::UnsignedWithZeroKeyHashTraits<std::underlying_type_t<UseKind>>> m_constants;
Operands<Epoch> m_state;
bool m_changed;
};
} // anonymous namespace
bool performMovHintRemoval(Graph& graph)
{
return runPhase<MovHintRemovalPhase>(graph);
}
} } // namespace JSC::DFG
#endif // ENABLE(DFG_JIT)
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