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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 DFGAliasTracker_h
#define DFGAliasTracker_h
#if ENABLE(DFG_JIT)
#include <dfg/DFGGraph.h>
#include <wtf/Vector.h>
namespace JSC { namespace DFG {
// === AliasTracker ===
//
// This class id used to detect aliasing property accesses, which we may
// be able to speculatively optimize (for example removing redundant loads
// where we know a getter will not be called, or optimizing puts to arrays
// where we know the value being written to in within length and is not a
// hole value). In time, this should be more than a 1-deep buffer!
class AliasTracker {
public:
AliasTracker(Graph& graph)
: m_graph(graph)
, m_candidateAliasGetByVal(NoNode)
{
}
NodeIndex lookupGetByVal(NodeIndex base, NodeIndex property)
{
// Try to detect situations where a GetByVal follows another GetByVal to the same
// property; in these cases, we may be able to omit the subsequent get on the
// speculative path, where we know conditions hold to make this safe (for example,
// on the speculative path we will not have allowed getter access).
if (m_candidateAliasGetByVal != NoNode) {
Node& possibleAlias = m_graph[m_candidateAliasGetByVal];
ASSERT(possibleAlias.op == GetByVal);
// This check ensures the accesses alias, provided that the subscript is an
// integer index (this is good enough; the speculative path will only generate
// optimized accesses to handle integer subscripts).
if (possibleAlias.child1 == base && equalIgnoringLaterNumericConversion(possibleAlias.child2, property))
return m_candidateAliasGetByVal;
}
return NoNode;
}
void recordGetByVal(NodeIndex getByVal)
{
m_candidateAliasGetByVal = getByVal;
}
void recordPutByVal(NodeIndex putByVal)
{
ASSERT_UNUSED(putByVal, m_graph[putByVal].op == PutByVal || m_graph[putByVal].op == PutByValAlias);
m_candidateAliasGetByVal = NoNode;
}
void recordGetById(NodeIndex getById)
{
ASSERT_UNUSED(getById, m_graph[getById].op == GetById);
m_candidateAliasGetByVal = NoNode;
}
void recordPutById(NodeIndex putById)
{
ASSERT_UNUSED(putById, m_graph[putById].op == PutById);
m_candidateAliasGetByVal = NoNode;
}
void recordPutByIdDirect(NodeIndex putByVal)
{
ASSERT_UNUSED(putByVal, m_graph[putByVal].op == PutByIdDirect);
m_candidateAliasGetByVal = NoNode;
}
private:
// This method returns true for arguments:
// - (X, X)
// - (X, ValueToNumber(X))
// - (X, ValueToInt32(X))
// - (X, NumberToInt32(X))
bool equalIgnoringLaterNumericConversion(NodeIndex op1, NodeIndex op2)
{
if (op1 == op2)
return true;
Node& node2 = m_graph[op2];
return (node2.op == ValueToNumber || node2.op == ValueToInt32 || node2.op == NumberToInt32) && op1 == node2.child1;
}
// The graph, to look up potentially aliasing nodes.
Graph& m_graph;
// Currently a 1-deep buffer!
NodeIndex m_candidateAliasGetByVal;
};
} } // namespace JSC::DFG
#endif
#endif