--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/graal/GraalCompiler/src/com/sun/c1x/graph/CriticalEdgeFinder.java	Wed Apr 27 11:50:44 2011 +0200
@@ -0,0 +1,84 @@
+/*
+ * Copyright (c) 2009, 2010, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package com.sun.c1x.graph;
+
+import java.util.*;
+
+import com.sun.c1x.*;
+import com.sun.c1x.debug.*;
+import com.sun.c1x.ir.*;
+
+/**
+ * This class finds and splits "critical" edges in the control flow graph.
+ * An edge between two blocks {@code A} and {@code B} is "critical" if {@code A}
+ * has more than one successor and {@code B} has more than one predecessor. Such
+ * edges are split by adding a block between the two blocks.
+ *
+ * @author Thomas Wuerthinger
+ */
+public class CriticalEdgeFinder implements BlockClosure {
+
+    private final IR ir;
+
+    /**
+     * The graph edges represented as a map from source to target nodes.
+     * Using a linked hash map makes compilation tracing more deterministic and thus eases debugging.
+     */
+    private Map<BlockBegin, Set<BlockBegin>> edges = C1XOptions.DetailedAsserts ?
+                    new LinkedHashMap<BlockBegin, Set<BlockBegin>>() :
+                    new HashMap<BlockBegin, Set<BlockBegin>>();
+
+    public CriticalEdgeFinder(IR ir) {
+        this.ir = ir;
+    }
+
+    public void apply(BlockBegin block) {
+        if (block.numberOfSux() >= 2) {
+            for (BlockBegin succ : block.end().successors()) {
+                if (succ.numberOfPreds() >= 2) {
+                    // TODO: (tw) probably we don't have to make it a critical edge if succ only contains the _same_ predecessor multiple times.
+                    recordCriticalEdge(block, succ);
+                }
+            }
+        }
+    }
+
+    private void recordCriticalEdge(BlockBegin block, BlockBegin succ) {
+        if (!edges.containsKey(block)) {
+            edges.put(block, new HashSet<BlockBegin>());
+        }
+
+        edges.get(block).add(succ);
+    }
+
+    public void splitCriticalEdges() {
+        for (BlockBegin from : edges.keySet()) {
+            for (BlockBegin to : edges.get(from)) {
+                BlockBegin split = ir.splitEdge(from, to);
+                if (C1XOptions.PrintHIR) {
+                    TTY.println("Split edge between block %d and block %d, creating new block %d", from.blockID, to.blockID, split.blockID);
+                }
+            }
+        }
+    }
+}