JavaScriptCore-7601.1.46.3.tar.gz

[apple/javascriptcore.git] / dfg / DFGMovHintRemovalPhase.cpp

diff --git a/dfg/DFGMovHintRemovalPhase.cpp b/dfg/DFGMovHintRemovalPhase.cpp
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+/*
+ * Copyright (C) 2015 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. 
+ */
+
+#include "config.h"
+#include "DFGMovHintRemovalPhase.h"
+
+#if ENABLE(DFG_JIT)
+
+#include "BytecodeLivenessAnalysisInlines.h"
+#include "DFGEpoch.h"
+#include "DFGForAllKills.h"
+#include "DFGGraph.h"
+#include "DFGInsertionSet.h"
+#include "DFGMayExit.h"
+#include "DFGPhase.h"
+#include "JSCInlines.h"
+#include "OperandsInlines.h"
+
+namespace JSC { namespace DFG {
+
+namespace {
+
+bool verbose = false;
+
+class MovHintRemovalPhase : public Phase {
+public:
+    MovHintRemovalPhase(Graph& graph)
+        : Phase(graph, "MovHint removal")
+        , m_state(OperandsLike, graph.block(0)->variablesAtHead)
+        , m_changed(false)
+    {
+    }
+    
+    bool run()
+    {
+        if (verbose) {
+            dataLog("Graph before MovHint removal:\n");
+            m_graph.dump();
+        }
+        
+        for (BasicBlock* block : m_graph.blocksInNaturalOrder())
+            handleBlock(block);
+        
+        return m_changed;
+    }
+
+private:
+    void handleBlock(BasicBlock* block)
+    {
+        if (verbose)
+            dataLog("Handing block ", pointerDump(block), "\n");
+        
+        // A MovHint is unnecessary if the local dies before it is used. We answer this question by
+        // maintaining the current exit epoch, and associating an epoch with each local. When a
+        // local dies, it gets the current exit epoch. If a MovHint occurs in the same epoch as its
+        // local, then it means there was no exit between the local's death and the MovHint - i.e.
+        // the MovHint is unnecessary.
+        
+        Epoch currentEpoch = Epoch::first();
+        
+        m_state.fill(Epoch());
+        m_graph.forAllLiveInBytecode(
+            block->terminal()->origin.forExit,
+            [&] (VirtualRegister reg) {
+                m_state.operand(reg) = currentEpoch;
+            });
+        
+        if (verbose)
+            dataLog("    Locals: ", m_state, "\n");
+        
+        // Assume that blocks after us exit.
+        currentEpoch.bump();
+        
+        for (unsigned nodeIndex = block->size(); nodeIndex--;) {
+            Node* node = block->at(nodeIndex);
+            
+            if (node->op() == MovHint) {
+                Epoch localEpoch = m_state.operand(node->unlinkedLocal());
+                if (verbose)
+                    dataLog("    At ", node, ": current = ", currentEpoch, ", local = ", localEpoch, "\n");
+                if (!localEpoch || localEpoch == currentEpoch) {
+                    node->setOpAndDefaultFlags(ZombieHint);
+                    node->child1() = Edge();
+                    m_changed = true;
+                }
+                m_state.operand(node->unlinkedLocal()) = Epoch();
+            }
+            
+            if (mayExit(m_graph, node))
+                currentEpoch.bump();
+            
+            if (nodeIndex) {
+                forAllKilledOperands(
+                    m_graph, block->at(nodeIndex - 1), node,
+                    [&] (VirtualRegister reg) {
+                        // This function is a bit sloppy - it might claim to kill a local even if
+                        // it's still live after. We need to protect against that.
+                        if (!!m_state.operand(reg))
+                            return;
+                        
+                        if (verbose)
+                            dataLog("    Killed operand at ", node, ": ", reg, "\n");
+                        m_state.operand(reg) = currentEpoch;
+                    });
+            }
+        }
+    }
+    
+    Operands<Epoch> m_state;
+    bool m_changed;
+};
+
+} // anonymous namespace
+    
+bool performMovHintRemoval(Graph& graph)
+{
+    SamplingRegion samplingRegion("DFG MovHint Removal Phase");
+    return runPhase<MovHintRemovalPhase>(graph);
+}
+
+} } // namespace JSC::DFG
+
+#endif // ENABLE(DFG_JIT)
+