Imported WebKit commit 2ea9d364d0f6efa8fa64acf19f451504c59be0e4 (http://svn.webkit.org/repository/webkit/trunk@104285)

1 files changed, 143 insertions, 0 deletions

diff --git a/Source/JavaScriptCore/dfg/DFGVariableAccessData.h b/Source/JavaScriptCore/dfg/DFGVariableAccessData.h
new file mode 100644
index 000000000..3cc53748a
--- /dev/null
+++ b/Source/JavaScriptCore/dfg/DFGVariableAccessData.h
@@ -0,0 +1,143 @@
+/*
+ * 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 DFGVariableAccessData_h
+#define DFGVariableAccessData_h
+
+#include "DFGOperands.h"
+#include "PredictedType.h"
+#include "VirtualRegister.h"
+#include <wtf/Platform.h>
+#include <wtf/UnionFind.h>
+
+namespace JSC { namespace DFG {
+
+class VariableAccessData : public UnionFind<VariableAccessData> {
+public:
+    enum Ballot { VoteValue, VoteDouble };
+
+    VariableAccessData()
+        : m_local(static_cast<VirtualRegister>(std::numeric_limits<int>::min()))
+        , m_prediction(PredictNone)
+        , m_shouldUseDoubleFormat(false)
+    {
+        clearVotes();
+    }
+    
+    VariableAccessData(VirtualRegister local)
+        : m_local(local)
+        , m_prediction(PredictNone)
+        , m_shouldUseDoubleFormat(false)
+    {
+        clearVotes();
+    }
+    
+    VirtualRegister local()
+    {
+        ASSERT(m_local == find()->m_local);
+        return m_local;
+    }
+    
+    int operand()
+    {
+        return static_cast<int>(local());
+    }
+    
+    bool predict(PredictedType prediction)
+    {
+        return mergePrediction(find()->m_prediction, prediction);
+    }
+    
+    PredictedType prediction()
+    {
+        return find()->m_prediction;
+    }
+    
+    void clearVotes()
+    {
+        ASSERT(find() == this);
+        m_votes[VoteValue] = 0;
+        m_votes[VoteDouble] = 0;
+    }
+    
+    void vote(Ballot ballot)
+    {
+        ASSERT(static_cast<unsigned>(ballot) < 2);
+        m_votes[ballot]++;
+    }
+    
+    double doubleVoteRatio()
+    {
+        ASSERT(find() == this);
+        return static_cast<double>(m_votes[VoteDouble]) / m_votes[VoteValue];
+    }
+    
+    bool shouldUseDoubleFormatAccordingToVote()
+    {
+        // FIXME: make this work for arguments.
+        return !operandIsArgument(operand()) && ((isNumberPrediction(prediction()) && doubleVoteRatio() >= Options::doubleVoteRatioForDoubleFormat) || isDoublePrediction(prediction()));
+    }
+    
+    bool shouldUseDoubleFormat()
+    {
+        ASSERT(find() == this);
+        return m_shouldUseDoubleFormat;
+    }
+    
+    bool tallyVotesForShouldUseDoubleFormat()
+    {
+        ASSERT(find() == this);
+        
+        bool newValueOfShouldUseDoubleFormat = shouldUseDoubleFormatAccordingToVote();
+        if (!newValueOfShouldUseDoubleFormat) {
+            // We monotonically convert to double. Hence, if the fixpoint leads us to conclude that we should
+            // switch back to int, we instead ignore this and stick with double.
+            return false;
+        }
+        
+        if (m_shouldUseDoubleFormat)
+            return false;
+        
+        m_shouldUseDoubleFormat = true;
+        mergePrediction(m_prediction, PredictDouble);
+        return true;
+    }
+    
+private:
+    // This is slightly space-inefficient, since anything we're unified with
+    // will have the same operand and should have the same prediction. But
+    // putting them here simplifies the code, and we don't expect DFG space
+    // usage for variable access nodes do be significant.
+
+    VirtualRegister m_local;
+    PredictedType m_prediction;
+    
+    float m_votes[2];
+    bool m_shouldUseDoubleFormat;
+};
+
+} } // namespace JSC::DFG
+
+#endif // DFGVariableAccessData_h