--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/graal/com.oracle.graal.lir/src/com/oracle/graal/lir/ControlFlowOptimizer.java	Thu Sep 06 18:07:15 2012 +0200
@@ -0,0 +1,141 @@
+/*
+ * Copyright (c) 2009, 2011, 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.oracle.graal.lir;
+
+import java.util.*;
+
+import com.oracle.graal.debug.*;
+import com.oracle.graal.lir.cfg.*;
+
+/**
+ * This class performs basic optimizations on the control flow graph after LIR generation.
+ */
+public final class ControlFlowOptimizer {
+
+    /**
+     * Performs control flow optimizations on the given LIR graph.
+     * @param blocks the blocks that should be optimized
+     */
+    public static void optimize(List<Block> blocks) {
+        ControlFlowOptimizer.deleteEmptyBlocks(blocks);
+        ControlFlowOptimizer.deleteUnnecessaryJumps(blocks);
+    }
+
+    private ControlFlowOptimizer() {
+    }
+
+    /**
+     * Checks whether a block can be deleted. Only blocks with exactly one successor and an
+     * unconditional branch to this successor are eligable.
+     * @param block the block checked for deletion
+     * @return whether the block can be deleted
+     */
+    private static boolean canDeleteBlock(Block block) {
+        if (block.numberOfSux() != 1 ||
+            block.numberOfPreds() == 0 ||
+            block.suxAt(0) == block) {
+            return false;
+        }
+
+        List<LIRInstruction> instructions = block.lir;
+
+        assert instructions.size() >= 2 : "block must have label and branch";
+        assert instructions.get(0) instanceof StandardOp.LabelOp : "first instruction must always be a label";
+        assert instructions.get(instructions.size() - 1) instanceof StandardOp.JumpOp : "last instruction must always be a branch";
+        assert ((StandardOp.JumpOp) instructions.get(instructions.size() - 1)).destination().label() == ((StandardOp.LabelOp) block.suxAt(0).lir.get(0)).getLabel() : "branch target must be the successor";
+
+        // Block must have exactly one successor.
+        return instructions.size() == 2 && !instructions.get(instructions.size() - 1).hasState();
+    }
+
+    private static void deleteEmptyBlocks(List<Block> blocks) {
+        assert verify(blocks);
+        Iterator<Block> iterator = blocks.iterator();
+        while (iterator.hasNext()) {
+            Block block = iterator.next();
+            if (canDeleteBlock(block)) {
+                // adjust successor and predecessor lists
+                Block other = block.suxAt(0);
+                for (Block pred : block.getPredecessors()) {
+                    Collections.replaceAll(pred.getSuccessors(), block, other);
+                }
+                for (int i = 0; i < other.getPredecessors().size(); i++) {
+                    if (other.getPredecessors().get(i) == block) {
+                        other.getPredecessors().remove(i);
+                        other.getPredecessors().addAll(i, block.getPredecessors());
+                    }
+                }
+                block.getSuccessors().clear();
+                block.getPredecessors().clear();
+                Debug.metric("BlocksDeleted").increment();
+                iterator.remove();
+            }
+        }
+        assert verify(blocks);
+    }
+
+    private static void deleteUnnecessaryJumps(List<Block> blocks) {
+        // skip the last block because there a branch is always necessary
+        for (int i = blocks.size() - 2; i >= 0; i--) {
+            Block block = blocks.get(i);
+            List<LIRInstruction> instructions = block.lir;
+
+            LIRInstruction lastOp = instructions.get(instructions.size() - 1);
+            if (lastOp instanceof StandardOp.JumpOp) {
+                StandardOp.JumpOp lastJump = (StandardOp.JumpOp) lastOp;
+
+                if (!lastOp.hasState()) {
+                    if (lastJump.destination().label() == ((StandardOp.LabelOp) blocks.get(i + 1).lir.get(0)).getLabel()) {
+                        // delete last branch instruction
+                        instructions.remove(instructions.size() - 1);
+                    } else {
+                        LIRInstruction prevOp = instructions.get(instructions.size() - 2);
+                        if (prevOp instanceof StandardOp.BranchOp) {
+                            StandardOp.BranchOp prevBranch = (StandardOp.BranchOp) prevOp;
+
+                            if (prevBranch.destination().label() == ((StandardOp.LabelOp) blocks.get(i + 1).lir.get(0)).getLabel() && !prevOp.hasState()) {
+                                // eliminate a conditional branch to the immediate successor
+                                prevBranch.negate(lastJump.destination());
+                                instructions.remove(instructions.size() - 1);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+        assert verify(blocks);
+    }
+
+    private static boolean verify(List<Block> code) {
+        for (Block block : code) {
+            for (Block sux : block.getSuccessors()) {
+                assert code.contains(sux) : "missing successor from: " + block + "to: " + sux;
+            }
+            for (Block pred : block.getPredecessors()) {
+                assert code.contains(pred) : "missing predecessor from: " + block + "to: " + pred;
+            }
+        }
+
+        return true;
+    }
+}