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/*
* Copyright (C) 2011 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
#if ENABLE(DFG_JIT)
#include "DFGGraph.h"
#include <wtf/Vector.h>
namespace JSC { namespace DFG {
// === ScoreBoard ===
//
// This class is used in performing a virtual register allocation over the graph.
// VirtualRegisters are allocated to nodes, with a used count for each virtual
// register tracking the lifespan of the value; after the final use of a node
// the VirtualRegister associated is freed such that it can be reused for
// another node.
class ScoreBoard {
public:
ScoreBoard(unsigned nextMachineLocal)
: m_highWatermark(nextMachineLocal + 1)
, m_used(nextMachineLocal, max())
{
m_free.reserveInitialCapacity(nextMachineLocal);
}
~ScoreBoard()
{
assertClear();
}
void sortFree()
{
std::sort(m_free.begin(), m_free.end());
}
void assertClear()
{
if (!ASSERT_ENABLED)
return;
// For every entry in the used list the use count of the virtual register should be zero, or max, due to it being a preserved local.
for (size_t i = 0; i < m_used.size(); ++i)
RELEASE_ASSERT(!m_used[i] || m_used[i] == max());
// For every entry in the free list, the use count should be zero.
for (size_t i = 0; i < m_free.size(); ++i)
RELEASE_ASSERT(!m_used[m_free[i]]);
// There must not be duplicates in the free list.
for (size_t i = 0; i < m_free.size(); ++i) {
for (size_t j = i + 1; j < m_free.size(); ++j)
RELEASE_ASSERT(m_free[i] != m_free[j]);
}
}
VirtualRegister allocate()
{
// Do we have any VirtualRegsiters in the free list, that were used by
// prior nodes, but are now available?
if (!m_free.isEmpty()) {
uint32_t index = m_free.last();
m_free.removeLast();
// Use count must have hit zero for it to have been added to the free list!
ASSERT(!m_used[index]);
m_highWatermark = std::max(m_highWatermark, static_cast<unsigned>(index) + 1);
return virtualRegisterForLocal(index);
}
// Allocate a new VirtualRegister, and add a corresponding entry to m_used.
size_t next = m_used.size();
m_used.append(0);
m_highWatermark = std::max(m_highWatermark, static_cast<unsigned>(next) + 1);
return virtualRegisterForLocal(next);
}
// Increment the usecount for the VirtualRegister associated with 'child',
// if it reaches the node's refcount, free the VirtualRegister.
void use(Node* child)
{
if (!child)
return;
ASSERT(!child->isTuple());
// Find the virtual register number for this child, increment its use count.
uint32_t index = child->virtualRegister().toLocal();
ASSERT(m_used[index] != max());
if (child->refCount() == ++m_used[index]) {
// If the use count in the scoreboard reaches the use count for the node,
// then this was its last use; the virtual register is now free.
// Clear the use count & add to the free list.
m_used[index] = 0;
m_free.append(index);
}
}
void use(Edge child)
{
use(child.node());
}
void useIfHasResult(Edge child)
{
if (!child)
return;
if (!child->hasResult())
return;
use(child);
}
unsigned highWatermark()
{
return m_highWatermark;
}
#ifndef NDEBUG
void dump()
{
dataLogF(" USED: [ ");
for (unsigned i = 0; i < m_used.size(); ++i) {
if (!m_free.contains(i)) {
dataLogF("%d:", i);
if (m_used[i] == max())
dataLogF("local ");
else
dataLogF("%d ", m_used[i]);
}
}
dataLogF("]\n");
dataLogF(" FREE: [ ");
for (unsigned i = 0; i < m_used.size(); ++i) {
if (m_free.contains(i) && m_used[i] != max()) {
ASSERT(!m_used[i]);
dataLogF("%d ", i);
}
}
dataLogF("]\n");
}
#endif
private:
static uint32_t max() { return std::numeric_limits<uint32_t>::max(); }
// The size of the span of virtual registers that this code block will use.
unsigned m_highWatermark;
// For every virtual register that has been allocated (either currently alive, or in
// the free list), we keep a count of the number of remaining uses until it is dead
// (0, in the case of entries in the free list). Since there is an entry for every
// allocated VirtualRegister, the length of this array conveniently provides the
// next available VirtualRegister number.
Vector<uint32_t, 64> m_used;
// A free list of VirtualRegsiters no longer alive.
Vector<uint32_t, 64> m_free;
};
} } // namespace JSC::DFG
#endif
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