JavaScriptCore-903.tar.gz

[apple/javascriptcore.git] / dfg / DFGAliasTracker.h

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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