--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/graal/GraalCompiler/src/com/sun/c1x/alloc/ControlFlowOptimizer.java	Sat May 21 17:46:54 2011 +0200
@@ -0,0 +1,260 @@
+/*
+ * 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.graph.*;
+import com.sun.c1x.ir.*;
+import com.sun.c1x.lir.*;
+import com.sun.c1x.util.*;
+import com.sun.cri.ci.*;
+
+/**
+ * This class performs basic optimizations on the control flow graph after LIR generation.
+ */
+final class ControlFlowOptimizer {
+
+    /**
+     * Performs control flow optimizations on the given IR graph.
+     * @param ir the IR graph that should be optimized
+     */
+    public static void optimize(IR ir) {
+        ControlFlowOptimizer optimizer = new ControlFlowOptimizer(ir);
+        List<LIRBlock> code = ir.linearScanOrder();
+        optimizer.reorderShortLoops(code);
+        optimizer.deleteEmptyBlocks(code);
+        optimizer.deleteUnnecessaryJumps(code);
+        optimizer.deleteJumpsToReturn(code);
+    }
+
+    private final IR ir;
+
+    private ControlFlowOptimizer(IR ir) {
+        this.ir = ir;
+    }
+
+    private void reorderShortLoop(List<LIRBlock> code, LIRBlock headerBlock, int headerIdx) {
+        int i = headerIdx + 1;
+        int maxEnd = Math.min(headerIdx + C1XOptions.MaximumShortLoopSize, code.size());
+        while (i < maxEnd && code.get(i).loopDepth() >= headerBlock.loopDepth()) {
+            i++;
+        }
+
+        if (i == code.size() || code.get(i).loopDepth() < headerBlock.loopDepth()) {
+            int endIdx = i - 1;
+            LIRBlock endBlock = code.get(endIdx);
+
+            if (endBlock.numberOfSux() == 1 && endBlock.suxAt(0) == headerBlock) {
+                // short loop from headerIdx to endIdx found . reorder blocks such that
+                // the headerBlock is the last block instead of the first block of the loop
+
+                for (int j = headerIdx; j < endIdx; j++) {
+                    code.set(j, code.get(j + 1));
+                }
+                code.set(endIdx, headerBlock);
+            }
+        }
+    }
+
+    private void reorderShortLoops(List<LIRBlock> code) {
+        for (int i = code.size() - 1; i >= 0; i--) {
+            LIRBlock block = code.get(i);
+
+            if (block.isLinearScanLoopHeader()) {
+                reorderShortLoop(code, block, i);
+            }
+        }
+
+        assert verify(code);
+    }
+
+    // only blocks with exactly one successor can be deleted. Such blocks
+    // must always end with an unconditional branch to this successor
+    private boolean canDeleteBlock(LIRBlock block) {
+        if (block.numberOfSux() != 1 ||
+            block == ir.startBlock ||
+            block.suxAt(0) == block) {
+            return false;
+        }
+
+        List<LIRInstruction> instructions = block.lir().instructionsList();
+
+        assert instructions.size() >= 2 : "block must have label and branch";
+        assert instructions.get(0).code == LIROpcode.Label : "first instruction must always be a label";
+        assert instructions.get(instructions.size() - 1) instanceof LIRBranch : "last instruction must always be a branch";
+        assert ((LIRBranch) instructions.get(instructions.size() - 1)).cond() == Condition.TRUE : "branch must be unconditional";
+        assert ((LIRBranch) instructions.get(instructions.size() - 1)).block() == block.suxAt(0) : "branch target must be the successor";
+
+        // block must have exactly one successor
+
+        return instructions.size() == 2 && instructions.get(instructions.size() - 1).info == null;
+    }
+
+    private void deleteEmptyBlocks(List<LIRBlock> code) {
+        int oldPos = 0;
+        int newPos = 0;
+        int numBlocks = code.size();
+
+        while (oldPos < numBlocks) {
+            LIRBlock block = code.get(oldPos);
+
+            if (canDeleteBlock(block)) {
+                LIRBlock newTarget = block.suxAt(0);
+
+                // update the block references in any branching LIR instructions
+                for (LIRBlock pred : block.blockPredecessors()) {
+                    for (LIRInstruction instr : pred.lir().instructionsList()) {
+                        if (instr instanceof LIRBranch) {
+                            ((LIRBranch) instr).substitute(block, newTarget);
+                        } else if (instr instanceof LIRTableSwitch) {
+                            ((LIRTableSwitch) instr).substitute(block, newTarget);
+                        }
+                    }
+                }
+
+                // adjust successor and predecessor lists
+                block.replaceWith(newTarget);
+                C1XMetrics.BlocksDeleted++;
+            } else {
+                // adjust position of this block in the block list if blocks before
+                // have been deleted
+                if (newPos != oldPos) {
+                    code.set(newPos, code.get(oldPos));
+                }
+                newPos++;
+            }
+            oldPos++;
+        }
+        assert verify(code);
+        Util.truncate(code, newPos);
+
+        assert verify(code);
+    }
+
+    private void deleteUnnecessaryJumps(List<LIRBlock> code) {
+        // skip the last block because there a branch is always necessary
+        for (int i = code.size() - 2; i >= 0; i--) {
+            LIRBlock block = code.get(i);
+            List<LIRInstruction> instructions = block.lir().instructionsList();
+
+            LIRInstruction lastOp = instructions.get(instructions.size() - 1);
+            if (lastOp.code == LIROpcode.Branch) {
+                assert lastOp instanceof LIRBranch : "branch must be of type LIRBranch";
+                LIRBranch lastBranch = (LIRBranch) lastOp;
+
+                assert lastBranch.block() != null : "last branch must always have a block as target";
+                assert lastBranch.label() == lastBranch.block().label() : "must be equal";
+
+                if (lastBranch.info == null) {
+                    if (lastBranch.block() == code.get(i + 1)) {
+                        // delete last branch instruction
+                        Util.truncate(instructions, instructions.size() - 1);
+
+                    } else {
+                        LIRInstruction prevOp = instructions.get(instructions.size() - 2);
+                        if (prevOp.code == LIROpcode.Branch || prevOp.code == LIROpcode.CondFloatBranch) {
+                            assert prevOp instanceof LIRBranch : "branch must be of type LIRBranch";
+                            LIRBranch prevBranch = (LIRBranch) prevOp;
+
+                            if (prevBranch.block() == code.get(i + 1) && prevBranch.info == null) {
+                                // eliminate a conditional branch to the immediate successor
+                                prevBranch.changeBlock(lastBranch.block());
+                                prevBranch.negateCondition();
+                                Util.truncate(instructions, instructions.size() - 1);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
+        assert verify(code);
+    }
+
+    private void deleteJumpsToReturn(List<LIRBlock> code) {
+        for (int i = code.size() - 1; i >= 0; i--) {
+            LIRBlock block = code.get(i);
+            List<LIRInstruction> curInstructions = block.lir().instructionsList();
+            LIRInstruction curLastOp = curInstructions.get(curInstructions.size() - 1);
+
+            assert curInstructions.get(0).code == LIROpcode.Label : "first instruction must always be a label";
+            if (curInstructions.size() == 2 && curLastOp.code == LIROpcode.Return) {
+                // the block contains only a label and a return
+                // if a predecessor ends with an unconditional jump to this block, then the jump
+                // can be replaced with a return instruction
+                //
+                // Note: the original block with only a return statement cannot be deleted completely
+                // because the predecessors might have other (conditional) jumps to this block.
+                // this may lead to unnecesary return instructions in the final code
+
+                assert curLastOp.info == null : "return instructions do not have debug information";
+
+                assert curLastOp instanceof LIROp1 : "return must be LIROp1";
+                CiValue returnOpr = ((LIROp1) curLastOp).operand();
+
+                for (int j = block.numberOfPreds() - 1; j >= 0; j--) {
+                    LIRBlock pred = block.predAt(j);
+                    List<LIRInstruction> predInstructions = pred.lir().instructionsList();
+                    LIRInstruction predLastOp = predInstructions.get(predInstructions.size() - 1);
+
+                    if (predLastOp.code == LIROpcode.Branch) {
+                        assert predLastOp instanceof LIRBranch : "branch must be LIRBranch";
+                        LIRBranch predLastBranch = (LIRBranch) predLastOp;
+
+                        if (predLastBranch.block() == block && predLastBranch.cond() == Condition.TRUE && predLastBranch.info == null) {
+                            // replace the jump to a return with a direct return
+                            // Note: currently the edge between the blocks is not deleted
+                            predInstructions.set(predInstructions.size() - 1, new LIROp1(LIROpcode.Return, returnOpr));
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    private boolean verify(List<LIRBlock> code) {
+        for (LIRBlock block : code) {
+            List<LIRInstruction> instructions = block.lir().instructionsList();
+
+            for (LIRInstruction instr : instructions) {
+                if (instr instanceof LIRBranch) {
+                    LIRBranch opBranch = (LIRBranch) instr;
+                    assert opBranch.block() == null || code.contains(opBranch.block()) : "missing successor branch from: " + block + " to: " + opBranch.block();
+                    assert opBranch.unorderedBlock() == null || code.contains(opBranch.unorderedBlock()) : "missing successor branch from: " + block + " to: " + opBranch.unorderedBlock();
+                }
+            }
+
+            for (LIRBlock sux : block.blockSuccessors()) {
+                assert code.contains(sux) : "missing successor from: " + block + "to: " + sux;
+            }
+
+            for (LIRBlock pred : block.blockPredecessors()) {
+                assert code.contains(pred) : "missing predecessor from: " + block + "to: " + pred;
+            }
+        }
+
+        return true;
+    }
+}