--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/graal/com.oracle.max.graal.compiler/src/com/sun/c1x/alloc/EdgeMoveOptimizer.java	Wed Jun 08 08:42:25 2011 +0200
@@ -0,0 +1,298 @@
+/*
+ * 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.sun.c1x.alloc;
+
+import java.util.*;
+
+import com.sun.c1x.*;
+import com.sun.c1x.ir.*;
+import com.sun.c1x.lir.*;
+
+/**
+ * This class optimizes moves, particularly those that result from eliminating SSA form.
+ *
+ * When a block has more than one predecessor, and all predecessors end with
+ * the {@linkplain #same(LIRInstruction, LIRInstruction) same} sequence of
+ * {@linkplain LIROpcode#Move move} instructions, then these sequences
+ * can be replaced with a single copy of the sequence at the beginning of the block.
+ *
+ * Similarly, when a block has more than one successor, then same sequences of
+ * moves at the beginning of the successors can be placed once at the end of
+ * the block. But because the moves must be inserted before all branch
+ * instructions, this works only when there is exactly one conditional branch
+ * at the end of the block (because the moves must be inserted before all
+ * branches, but after all compares).
+ *
+ * This optimization affects all kind of moves (reg->reg, reg->stack and
+ * stack->reg). Because this optimization works best when a block contains only
+ * a few moves, it has a huge impact on the number of blocks that are totally
+ * empty.
+ *
+ * @author Christian Wimmer (original HotSpot implementation)
+ * @author Thomas Wuerthinger
+ * @author Doug Simon
+ */
+final class EdgeMoveOptimizer {
+
+    /**
+     * Optimizes moves on block edges.
+     *
+     * @param blockList a list of blocks whose moves should be optimized
+     */
+    public static void optimize(List<LIRBlock> blockList) {
+        EdgeMoveOptimizer optimizer = new EdgeMoveOptimizer();
+
+        // ignore the first block in the list (index 0 is not processed)
+        for (int i = blockList.size() - 1; i >= 1; i--) {
+            LIRBlock block = blockList.get(i);
+
+            if (block.numberOfPreds() > 1) {
+                optimizer.optimizeMovesAtBlockEnd(block);
+            }
+            if (block.numberOfSux() == 2) {
+                optimizer.optimizeMovesAtBlockBegin(block);
+            }
+        }
+    }
+
+    private final List<List<LIRInstruction>> edgeInstructionSeqences;
+
+    private EdgeMoveOptimizer() {
+        edgeInstructionSeqences = new ArrayList<List<LIRInstruction>>(4);
+    }
+
+    /**
+     * Determines if two operations are both {@linkplain LIROpcode#Move moves}
+     * that have the same {@linkplain LIROp1#operand() source} and {@linkplain LIROp1#result() destination}
+     * operands and they have the same {@linkplain LIRInstruction#info debug info}.
+     *
+     * @param op1 the first instruction to compare
+     * @param op2 the second instruction to compare
+     * @return {@code true} if {@code op1} and {@code op2} are the same by the above algorithm
+     */
+    private boolean same(LIRInstruction op1, LIRInstruction op2) {
+        assert op1 != null;
+        assert op2 != null;
+
+        if (op1.code == LIROpcode.Move && op2.code == LIROpcode.Move) {
+            assert op1 instanceof LIROp1 : "move must be LIROp1";
+            assert op2 instanceof LIROp1 : "move must be LIROp1";
+            LIROp1 move1 = (LIROp1) op1;
+            LIROp1 move2 = (LIROp1) op2;
+            if (move1.info == move2.info && move1.operand().equals(move2.operand()) && move1.result().equals(move2.result())) {
+                // these moves are exactly equal and can be optimized
+                return true;
+            }
+        }
+        return false;
+    }
+
+    /**
+     * Moves the longest {@linkplain #same common} subsequence at the end all
+     * predecessors of {@code block} to the start of {@code block}.
+     */
+    private void optimizeMovesAtBlockEnd(LIRBlock block) {
+        if (block.isPredecessor(block)) {
+            // currently we can't handle this correctly.
+            return;
+        }
+
+        // clear all internal data structures
+        edgeInstructionSeqences.clear();
+
+        int numPreds = block.numberOfPreds();
+        assert numPreds > 1 : "do not call otherwise";
+
+        // setup a list with the LIR instructions of all predecessors
+        for (int i = 0; i < numPreds; i++) {
+            LIRBlock pred = block.predAt(i);
+            assert pred != null;
+            assert pred.lir() != null;
+            List<LIRInstruction> predInstructions = pred.lir().instructionsList();
+
+            if (pred.numberOfSux() != 1) {
+                // this can happen with switch-statements where multiple edges are between
+                // the same blocks.
+                return;
+            }
+
+            assert pred.suxAt(0) == block : "invalid control flow";
+            assert predInstructions.get(predInstructions.size() - 1).code == LIROpcode.Branch : "block with successor must end with branch";
+            assert predInstructions.get(predInstructions.size() - 1) instanceof LIRBranch : "branch must be LIROpBranch";
+            assert ((LIRBranch) predInstructions.get(predInstructions.size() - 1)).cond() == Condition.TRUE : "block must end with unconditional branch";
+
+            if (predInstructions.get(predInstructions.size() - 1).info != null) {
+                // can not optimize instructions that have debug info
+                return;
+            }
+
+            // ignore the unconditional branch at the end of the block
+            List<LIRInstruction> seq = predInstructions.subList(0, predInstructions.size() - 1);
+            edgeInstructionSeqences.add(seq);
+        }
+
+        // process lir-instructions while all predecessors end with the same instruction
+        while (true) {
+            List<LIRInstruction> seq = edgeInstructionSeqences.get(0);
+            if (seq.isEmpty()) {
+                return;
+            }
+
+            LIRInstruction op = last(seq);
+            for (int i = 1; i < numPreds; ++i) {
+                List<LIRInstruction> otherSeq = edgeInstructionSeqences.get(i);
+                if (otherSeq.isEmpty() || !same(op, last(otherSeq))) {
+                    return;
+                }
+            }
+
+            // insert the instruction at the beginning of the current block
+            block.lir().insertBefore(1, op);
+
+            // delete the instruction at the end of all predecessors
+            for (int i = 0; i < numPreds; i++) {
+                seq = edgeInstructionSeqences.get(i);
+                removeLast(seq);
+            }
+        }
+    }
+
+    /**
+     * Moves the longest {@linkplain #same common} subsequence at the start of all
+     * successors of {@code block} to the end of {@code block} just prior to the
+     * branch instruction ending {@code block}.
+     */
+    private void optimizeMovesAtBlockBegin(LIRBlock block) {
+
+        edgeInstructionSeqences.clear();
+        int numSux = block.numberOfSux();
+
+        List<LIRInstruction> instructions = block.lir().instructionsList();
+
+        assert numSux == 2 : "method should not be called otherwise";
+        assert instructions.get(instructions.size() - 1).code == LIROpcode.Branch : "block with successor must end with branch block=B" + block.blockID();
+        assert instructions.get(instructions.size() - 1) instanceof LIRBranch : "branch must be LIROpBranch";
+        assert ((LIRBranch) instructions.get(instructions.size() - 1)).cond() == Condition.TRUE : "block must end with unconditional branch";
+
+        if (instructions.get(instructions.size() - 1).info != null) {
+            // cannot optimize instructions when debug info is needed
+            return;
+        }
+
+        LIRInstruction branch = instructions.get(instructions.size() - 2);
+        if (branch.info != null || (branch.code != LIROpcode.Branch && branch.code != LIROpcode.CondFloatBranch)) {
+            // not a valid case for optimization
+            // currently, only blocks that end with two branches (conditional branch followed
+            // by unconditional branch) are optimized
+            return;
+        }
+
+        // now it is guaranteed that the block ends with two branch instructions.
+        // the instructions are inserted at the end of the block before these two branches
+        int insertIdx = instructions.size() - 2;
+
+        if (C1XOptions.DetailedAsserts) {
+            for (int i = insertIdx - 1; i >= 0; i--) {
+                LIRInstruction op = instructions.get(i);
+                if ((op.code == LIROpcode.Branch || op.code == LIROpcode.CondFloatBranch) && ((LIRBranch) op).block() != null) {
+                    throw new Error("block with two successors can have only two branch instructions");
+                }
+            }
+        }
+
+        // setup a list with the lir-instructions of all successors
+        for (int i = 0; i < numSux; i++) {
+            LIRBlock sux = block.suxAt(i);
+            List<LIRInstruction> suxInstructions = sux.lir().instructionsList();
+
+            assert suxInstructions.get(0).code == LIROpcode.Label : "block must start with label";
+
+            if (sux.numberOfPreds() != 1) {
+                // this can happen with switch-statements where multiple edges are between
+                // the same blocks.
+                return;
+            }
+            assert sux.predAt(0) == block : "invalid control flow";
+
+            // ignore the label at the beginning of the block
+            List<LIRInstruction> seq = suxInstructions.subList(1, suxInstructions.size());
+            edgeInstructionSeqences.add(seq);
+        }
+
+        // process LIR instructions while all successors begin with the same instruction
+        while (true) {
+            List<LIRInstruction> seq = edgeInstructionSeqences.get(0);
+            if (seq.isEmpty()) {
+                return;
+            }
+
+            LIRInstruction op = first(seq);
+            for (int i = 1; i < numSux; i++) {
+                List<LIRInstruction> otherSeq = edgeInstructionSeqences.get(i);
+                if (otherSeq.isEmpty() || !same(op, first(otherSeq))) {
+                    // these instructions are different and cannot be optimized .
+                    // no further optimization possible
+                    return;
+                }
+            }
+
+            // insert instruction at end of current block
+            block.lir().insertBefore(insertIdx, op);
+            insertIdx++;
+
+            // delete the instructions at the beginning of all successors
+            for (int i = 0; i < numSux; i++) {
+                seq = edgeInstructionSeqences.get(i);
+                removeFirst(seq);
+            }
+        }
+    }
+
+    /**
+     * Gets the first element from a LIR instruction sequence.
+     */
+    private static LIRInstruction first(List<LIRInstruction> seq) {
+        return seq.get(0);
+    }
+
+    /**
+     * Gets the last element from a LIR instruction sequence.
+     */
+    private static LIRInstruction last(List<LIRInstruction> seq) {
+        return seq.get(seq.size() - 1);
+    }
+
+    /**
+     * Removes the first element from a LIR instruction sequence.
+     */
+    private static void removeFirst(List<LIRInstruction> seq) {
+        seq.remove(0);
+    }
+
+    /**
+     * Removes the last element from a LIR instruction sequence.
+     */
+    private static void removeLast(List<LIRInstruction> seq) {
+        seq.remove(seq.size() - 1);
+    }
+}