JavaScriptCore-903.tar.gz

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

diff --git a/dfg/DFGScoreBoard.h b/dfg/DFGScoreBoard.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 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());
+        // Every entry in the used list should be available in the free list.
+        for (size_t i = 0; i < m_used.size(); ++i)
+            ASSERT(m_free.contains(i));
+        // For every entry in the used list the use count of the virtual register should be zero.
+        for (size_t i = 0; i < m_free.size(); ++i)
+            ASSERT(!m_used[i]);
+    }
+#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();
+    }
+
+#ifndef NDEBUG
+    void dump()
+    {
+        printf("    USED: [ ");
+        for (unsigned i = 0; i < m_used.size(); ++i) {
+            if (!m_free.contains(i))
+                printf("%d:%d ", m_firstTemporary + i, m_used[i]);
+        }
+        printf("]\n");
+
+        printf("    FREE: [ ");
+        for (unsigned i = 0; i < m_used.size(); ++i) {
+            if (m_free.contains(i)) {
+                ASSERT(!m_used[i]);
+                printf("%d ", m_firstTemporary + i);
+            }
+        }
+        printf("]\n");
+    }
+
+#endif
+
+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