JavaScriptCore-7600.1.4.9.tar.gz

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

diff --git a/dfg/DFGLivenessAnalysisPhase.cpp b/dfg/DFGLivenessAnalysisPhase.cpp
new file mode 100644 (file)
index 0000000..b3131a4
--- /dev/null
+++ b/dfg/DFGLivenessAnalysisPhase.cpp
@@ -0,0 +1,167 @@
+/*
+ * Copyright (C) 2013 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 "DFGLivenessAnalysisPhase.h"
+
+#if ENABLE(DFG_JIT)
+
+#include "DFGBasicBlockInlines.h"
+#include "DFGGraph.h"
+#include "DFGInsertionSet.h"
+#include "DFGPhase.h"
+#include "JSCInlines.h"
+
+namespace JSC { namespace DFG {
+
+class LivenessAnalysisPhase : public Phase {
+public:
+    LivenessAnalysisPhase(Graph& graph)
+        : Phase(graph, "liveness analysis")
+    {
+    }
+    
+    bool run()
+    {
+        ASSERT(m_graph.m_form == SSA);
+        
+        // Liveness is a backwards analysis; the roots are the blocks that
+        // end in a terminal (Return/Throw/ThrowReferenceError). For now, we
+        // use a fixpoint formulation since liveness is a rapid analysis with
+        // convergence guaranteed after O(connectivity).
+        
+        // Start by assuming that everything is dead.
+        for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
+            BasicBlock* block = m_graph.block(blockIndex);
+            if (!block)
+                continue;
+            block->ssa->liveAtHead.clear();
+            block->ssa->liveAtTail.clear();
+        }
+        
+        do {
+            m_changed = false;
+            for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;)
+                process(blockIndex);
+        } while (m_changed);
+        
+        if (!m_graph.block(0)->ssa->liveAtHead.isEmpty()) {
+            startCrashing();
+            dataLog(
+                "Bad liveness analysis result: live at root is not empty: ",
+                nodeListDump(m_graph.block(0)->ssa->liveAtHead), "\n");
+            dataLog("IR at time of error:\n");
+            m_graph.dump();
+            CRASH();
+        }
+        
+        return true;
+    }
+
+private:
+    void process(BlockIndex blockIndex)
+    {
+        BasicBlock* block = m_graph.block(blockIndex);
+        if (!block)
+            return;
+        
+        // FIXME: It's likely that this can be improved, for static analyses that use
+        // HashSets. https://bugs.webkit.org/show_bug.cgi?id=118455
+        m_live = block->ssa->liveAtTail;
+        
+        for (unsigned nodeIndex = block->size(); nodeIndex--;) {
+            Node* node = block->at(nodeIndex);
+            
+            // Given an Upsilon:
+            //
+            //    n: Upsilon(@x, ^p)
+            //
+            // We say that it def's @p and @n and uses @x.
+            //
+            // Given a Phi:
+            //
+            //    p: Phi()
+            //
+            // We say nothing. It's neither a use nor a def.
+            //
+            // Given a node:
+            //
+            //    n: Thingy(@a, @b, @c)
+            //
+            // We say that it def's @n and uses @a, @b, @c.
+            
+            switch (node->op()) {
+            case Upsilon: {
+                Node* phi = node->phi();
+                m_live.remove(phi);
+                m_live.remove(node);
+                m_live.add(node->child1().node());
+                break;
+            }
+                
+            case Phi: {
+                break;
+            }
+                
+            default:
+                m_live.remove(node);
+                DFG_NODE_DO_TO_CHILDREN(m_graph, node, addChildUse);
+                break;
+            }
+        }
+        
+        if (m_live == block->ssa->liveAtHead)
+            return;
+        
+        m_changed = true;
+        block->ssa->liveAtHead = m_live;
+        for (unsigned i = block->predecessors.size(); i--;)
+            block->predecessors[i]->ssa->liveAtTail.add(m_live.begin(), m_live.end());
+    }
+    
+    void addChildUse(Node*, Edge& edge)
+    {
+        addChildUse(edge);
+    }
+    
+    void addChildUse(Edge& edge)
+    {
+        edge.setKillStatus(m_live.add(edge.node()).isNewEntry ? DoesKill : DoesNotKill);
+    }
+    
+    bool m_changed;
+    HashSet<Node*> m_live;
+};
+
+bool performLivenessAnalysis(Graph& graph)
+{
+    SamplingRegion samplingRegion("DFG Liveness Analysis Phase");
+    return runPhase<LivenessAnalysisPhase>(graph);
+}
+
+} } // namespace JSC::DFG
+
+#endif // ENABLE(DFG_JIT)
+