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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.
*/
#ifndef DFGScoreBoard_h
#define DFGScoreBoard_h
#if ENABLE(DFG_JIT)
#include <dfg/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(Graph& graph, uint32_t firstTemporary)
: m_graph(graph)
, m_firstTemporary(firstTemporary)
{
}
#if DFG_CONSISTENCY_CHECK
~ScoreBoard()
{
// Every VirtualRegister that was allocated should now be free.
ASSERT(m_used.size() == m_free.size());
// For every entry in the free list, the use count of the virtual register should be zero.
// * By using the virtual register numbers from m_free, we are checking that all values
// in m_free are < m_used.size(), and correspond to an allocated VirtualRegsiter.
// * By setting m_used to a non-zero value after checking it, we are checking that all
// entries in m_free are unique (otherwise the second test of m_used will fail).
for (size_t i = 0; i < m_free.size(); ++i) {
uint32_t virtualRegister = m_free[i];
ASSERT(!m_used[virtualRegister]);
m_used[virtualRegister] = 1;
}
}
#endif
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]);
return (VirtualRegister)(m_firstTemporary + index);
}
// Allocate a new VirtualRegister, and add a corresponding entry to m_used.
size_t next = allocatedCount();
m_used.append(0);
return (VirtualRegister)(m_firstTemporary + next);
}
// Increment the usecount for the VirtualRegsiter associated with 'child',
// if it reaches the node's refcount, free the VirtualRegsiter.
void use(NodeIndex child)
{
if (child == NoNode)
return;
// Find the virtual register number for this child, increment its use count.
Node& node = m_graph[child];
uint32_t index = node.virtualRegister - m_firstTemporary;
if (node.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);
}
}
unsigned allocatedCount()
{
// m_used contains an entry for every allocated VirtualRegister.
return m_used.size();
}
private:
// The graph, so we can get refCounts for nodes, to determine when values are dead.
Graph& m_graph;
// The first VirtualRegsiter to be used as a temporary.
uint32_t m_firstTemporary;
// 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
#endif
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