--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/graal/GraalCompiler/src/com/sun/c1x/opt/NullCheckEliminator.java	Wed Apr 27 11:50:44 2011 +0200
@@ -0,0 +1,599 @@
+/*
+ * 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.opt;
+
+import java.util.*;
+
+import com.sun.c1x.*;
+import com.sun.c1x.graph.*;
+import com.sun.c1x.ir.*;
+import com.sun.c1x.util.*;
+import com.sun.c1x.value.FrameState.*;
+import com.sun.cri.ci.*;
+
+/**
+ * This class implements a data-flow analysis to remove redundant null checks
+ * and deoptimization info for instructions that cannot ever produce {@code NullPointerException}s.
+ *
+ * This implementation uses an optimistic dataflow analysis by attempting to visit all predecessors
+ * of a block before visiting the block itself. For this purpose it uses the block numbers computed by
+ * the {@link BlockMap} during graph construction, which may not actually be
+ * a valid reverse post-order number (due to inlining and any previous optimizations).
+ *
+ * When loops are encountered, or if the blocks are not visited in the optimal order, this implementation
+ * will fall back to performing an iterative data flow analysis where it maintains a set
+ * of incoming non-null instructions and a set of locally produced outgoing non-null instructions
+ * and iterates the dataflow equations to a fixed point. Basically, for block b,
+ * out(b) = in(b) U local_out(b) and in(b) = intersect(out(pred)). After a fixed point is
+ * reached, the resulting incoming sets are used to visit instructions with uneliminated null checks
+ * a second time.
+ *
+ * Note that the iterative phase is actually optional, because the first pass is conservative.
+ * Iteration can be disabled by setting {@link C1XOptions#OptIterativeNCE} to
+ * {@code false}. Iteration is rarely necessary for acyclic graphs.
+ *
+ * @author Ben L. Titzer
+ */
+public class NullCheckEliminator extends DefaultValueVisitor {
+
+    private static class IfEdge {
+        final BlockBegin ifBlock;
+        final BlockBegin succ;
+        final Value checked;
+
+        IfEdge(BlockBegin i, BlockBegin s, Value c) {
+            this.ifBlock = i;
+            this.succ = s;
+            this.checked = c;
+        }
+    }
+
+    private static class BlockInfo {
+        // used in first pass
+        final BlockBegin block;
+        boolean marked;
+        CiBitMap localOut;
+        CiBitMap localExcept;
+        List<Value> localUses;
+        // used in iteration and flow sensitivity
+        IfEdge ifEdge;
+        CiBitMap localIn;
+
+        BlockInfo(BlockBegin b) {
+            this.block = b;
+        }
+    }
+
+    private static class ValueInfo {
+        final Value value;
+        final int globalIndex;
+
+        ValueInfo(Value value, int index) {
+            this.value = value;
+            globalIndex = index;
+        }
+    }
+
+    final IR ir;
+    final BlockWorkList workList = new BlockWorkList();
+
+    final ArrayList<BlockInfo> blockInfos = new ArrayList<BlockInfo>(5);
+    final ArrayList<ValueInfo> valueInfos = new ArrayList<ValueInfo>(5);
+    final ArrayList<BlockInfo> remainingUses = new ArrayList<BlockInfo>(5);
+
+    // maps used only in iteration
+    boolean requiresIteration;
+    int maximumIndex;
+
+    CiBitMap currentBitMap;
+    List<Value> currentUses;
+
+    /**
+     * Creates a new null check eliminator for the specified IR and performs the optimization.
+     * @param ir the IR
+     */
+    public NullCheckEliminator(IR ir) {
+        this.ir = ir;
+        optimize();
+    }
+
+    private void optimize() {
+        if (C1XOptions.PrintTimers) {
+            C1XTimers.NCE.start();
+        }
+        BlockInfo start = getBlockInfo(ir.startBlock);
+        mark(start);
+        processBlock(start);
+        while (!workList.isEmpty()) {
+            processBlock(getBlockInfo(workList.removeFromWorkList()));
+        }
+        if (requiresIteration && C1XOptions.OptIterativeNCE) {
+            // there was a loop, or blocks were not visited in reverse post-order;
+            // iteration is required to compute the in sets for a second pass
+            iterate();
+        }
+        clearInfo();
+        if (C1XOptions.PrintTimers) {
+            C1XTimers.NCE.stop();
+        }
+    }
+
+    private void processBlock(BlockInfo info) {
+        BlockBegin block = info.block;
+        // first pass on a block
+        computeLocalInSet(info);
+        // process any phis in the block
+        block.stateBefore().forEachPhi(block, new PhiProcedure() {
+            public boolean doPhi(Phi phi) {
+                visitPhi(phi);
+                return true;
+            }
+        });
+
+        // now visit the instructions in order
+        for (Instruction i = block.next(); i != null; i = i.next()) {
+            i.accept(this);
+        }
+        if (!currentUses.isEmpty()) {
+            // remember any localUses in this block for later iterative processing
+            info.localUses = currentUses;
+            remainingUses.add(info);
+        }
+        queueSuccessors(block.end().successors());
+        queueSuccessors(block.exceptionHandlerBlocks());
+    }
+
+    private void queueSuccessors(List<BlockBegin> successorList) {
+        for (BlockBegin succ : successorList) {
+            BlockInfo info = getBlockInfo(succ);
+            if (!isMarked(info)) {
+                workList.addSorted(succ, succ.depthFirstNumber());
+                mark(info);
+            }
+        }
+    }
+
+    private void computeLocalInSet(BlockInfo info) {
+        BlockBegin block = info.block;
+        // compute the initial {in} set based on the {localOut} sets of predecessors, if possible
+        currentBitMap = null;
+        currentUses = new ArrayList<Value>();
+        if (block.numberOfPreds() == 0) {
+            // no predecessors => start block
+            assert block == ir.startBlock : "block without predecessors should be start block";
+            currentBitMap = newBitMap();
+        } else {
+            // block has at least one predecessor
+            for (BlockBegin pred : block.predecessors()) {
+                if (getPredecessorMap(pred, block.isExceptionEntry()) == null) {
+                    // one of the predecessors of this block has not been visited,
+                    // we have to be conservative and start with nothing known
+                    currentBitMap = newBitMap();
+                    requiresIteration = true;
+                }
+            }
+            if (currentBitMap == null) {
+                // all the predecessors have been visited, compute the intersection of their {localOut} sets
+                for (BlockBegin pred : block.predecessors()) {
+                    BlockInfo predInfo = getBlockInfo(pred);
+                    CiBitMap predMap = getPredecessorMap(predInfo, block.isExceptionEntry());
+                    currentBitMap = intersectLocalOut(predInfo, currentBitMap, predMap, block);
+                }
+            }
+        }
+        assert currentBitMap != null : "current bitmap should be computed one or the other way";
+        // if there are exception handlers for this block, then clone {in} and put it in {localExcept}
+        if (block.numberOfExceptionHandlers() > 0) {
+            info.localExcept = currentBitMap.copy();
+        }
+        info.localOut = currentBitMap;
+    }
+
+    private CiBitMap intersectLocalOut(BlockInfo pred, CiBitMap current, CiBitMap predMap, BlockBegin succ) {
+        predMap = intersectFlowSensitive(pred, predMap, succ);
+        if (current == null) {
+            current = predMap.copy();
+        } else {
+            current.setIntersect(predMap);
+        }
+        return current;
+    }
+
+    private CiBitMap intersectFlowSensitive(BlockInfo pred, CiBitMap n, BlockBegin succ) {
+        if (C1XOptions.OptFlowSensitiveNCE) {
+            // check to see if there is an if edge between these two blocks
+            if (pred.ifEdge != null && pred.ifEdge.succ == succ) {
+                // if there is a special edge between pred and block, add the checked instruction
+                n = n.copy();
+                setValue(pred.ifEdge.checked, n);
+            }
+        }
+        return n;
+    }
+
+    private void iterate() {
+        // the previous phase calculated all the {localOut} sets; use iteration to
+        // calculate the {in} sets
+        if (remainingUses.size() > 0) {
+            // only perform iterative flow analysis if there are checks remaining to eliminate
+            C1XMetrics.NullCheckIterations++;
+            clearMarked();
+            // start off by propagating a new set to the start block
+            propagate(getBlockInfo(ir.startBlock), newBitMap(), ir.startBlock);
+            while (!workList.isEmpty()) {
+                BlockInfo block = getBlockInfo(workList.removeFromWorkList());
+                unmark(block);
+                iterateBlock(block);
+            }
+            // now that the fixed point is reached, reprocess any remaining localUses
+            currentUses = null; // the list won't be needed this time
+            for (BlockInfo info : remainingUses) {
+                reprocessUses(info.localIn, info.localUses);
+            }
+        }
+    }
+
+    private void iterateBlock(BlockInfo info) {
+        CiBitMap prevMap = info.localIn;
+        assert prevMap != null : "how did the block get on the worklist without an initial in map?";
+        CiBitMap localOut = info.localOut;
+        CiBitMap out;
+        // copy larger and do union with smaller
+        if (localOut.size() > prevMap.size()) {
+            out = localOut.copy();
+            out.setUnion(prevMap);
+        } else {
+            out = prevMap.copy();
+            out.setUnion(localOut);
+        }
+        propagateSuccessors(info, out, info.block.end().successors()); // propagate {in} U {localOut} to successors
+        propagateSuccessors(info, prevMap, info.block.exceptionHandlerBlocks()); // propagate {in} to exception handlers
+    }
+
+    private void propagateSuccessors(BlockInfo block, CiBitMap out, List<BlockBegin> successorList) {
+        for (BlockBegin succ : successorList) {
+            propagate(block, out, succ);
+        }
+    }
+
+    private void propagate(BlockInfo pred, CiBitMap bitMap, BlockBegin succ) {
+        boolean changed;
+        BlockInfo succInfo = getBlockInfo(succ);
+        if (succInfo.localIn == null) {
+            // this is the first time this block is being iterated
+            succInfo.localIn = bitMap.copy();
+            propagateFlowSensitive(pred, succInfo.localIn, succ, false);
+            changed = true;
+        } else {
+            // perform intersection with previous map
+            bitMap = propagateFlowSensitive(pred, bitMap, succ, true);
+            changed = succInfo.localIn.setIntersect(bitMap);
+        }
+        if (changed && !isMarked(succInfo)) {
+            mark(succInfo);
+            workList.addSorted(succ, succ.depthFirstNumber());
+        }
+    }
+
+    private CiBitMap propagateFlowSensitive(BlockInfo pred, CiBitMap bitMap, BlockBegin succ, boolean copy) {
+        if (C1XOptions.OptFlowSensitiveNCE) {
+            if (pred.ifEdge != null && pred.ifEdge.succ == succ) {
+                if (copy) {
+                    bitMap = bitMap.copy();
+                }
+                // there is a special if edge between these blocks, add the checked instruction
+                setValue(pred.ifEdge.checked, bitMap);
+            }
+        }
+        return bitMap;
+    }
+
+    private void reprocessUses(CiBitMap in, List<Value> uses) {
+        // iterate over each of the use instructions again, using the input bitmap
+        // and the hash sets
+        assert in != null;
+        currentBitMap = in;
+        for (Value i : uses) {
+            i.accept(this);
+        }
+    }
+
+    private boolean processUse(Value use, Value object, boolean implicitCheck) {
+        if (object.isNonNull()) {
+            // the object itself is known for sure to be non-null, so clear the flag.
+            // the flag is usually cleared in the constructor of the using instruction, but
+            // later optimizations may more reveal more non-null objects
+            use.eliminateNullCheck();
+            return true;
+        } else {
+            // check if the object is non-null in the bitmap or hashset
+            if (checkValue(object, currentBitMap)) {
+                // the object is non-null at this site
+                use.eliminateNullCheck();
+                return true;
+            } else {
+                if (implicitCheck) {
+                    // the object will be non-null after executing this instruction
+                    setValue(object, currentBitMap);
+                }
+                if (currentUses != null) {
+                    currentUses.add(use); // record a use for potential later iteration
+                }
+            }
+        }
+        return false;
+    }
+
+    private boolean isNonNullOnEdge(BlockBegin pred, BlockBegin succ, Value i) {
+        if (C1XOptions.OptFlowSensitiveNCE) {
+            IfEdge e = getBlockInfo(pred).ifEdge;
+            if (e != null && e.succ == succ && e.checked == i) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    @Override
+    public void visitPhi(Phi phi) {
+        for (int j = 0; j < phi.inputCount(); j++) {
+            Value operand = phi.inputAt(j);
+            if (processUse(phi, operand, false)) {
+                continue;
+            }
+            if (C1XOptions.OptFlowSensitiveNCE) {
+                BlockBegin phiBlock = phi.block();
+                if (!phiBlock.isExceptionEntry() && isNonNullOnEdge(phiBlock.predecessors().get(j), phiBlock, operand)) {
+                    continue;
+                }
+            }
+            return;
+        }
+        // all inputs are non-null
+        phi.setFlag(Value.Flag.NonNull);
+    }
+
+    @Override
+    public void visitLoadPointer(LoadPointer i) {
+        Value pointer = i.pointer();
+        if (pointer != null) {
+            processUse(i, pointer, true);
+        }
+    }
+
+    @Override
+    public void visitUnsafeCast(UnsafeCast i) {
+        if (processUse(i, i.value(), false)) {
+            // if the object is non null, the result of the cast is as well
+            i.setFlag(Value.Flag.NonNull);
+        }
+    }
+
+    @Override
+    public void visitLoadField(LoadField i) {
+        Value object = i.object();
+        if (object != null) {
+            processUse(i, object, true);
+        }
+    }
+
+    @Override
+    public void visitStorePointer(StorePointer i) {
+        Value pointer = i.pointer();
+        if (pointer != null) {
+            processUse(i, pointer, true);
+        }
+    }
+
+    @Override
+    public void visitStoreField(StoreField i) {
+        Value object = i.object();
+        if (object != null) {
+            processUse(i, object, true);
+        }
+    }
+
+    @Override
+    public void visitArrayLength(ArrayLength i) {
+        processUse(i, i.array(), true);
+    }
+
+    @Override
+    public void visitLoadIndexed(LoadIndexed i) {
+        processUse(i, i.array(), true);
+    }
+
+    @Override
+    public void visitStoreIndexed(StoreIndexed i) {
+        processUse(i, i.array(), true);
+    }
+
+    @Override
+    public void visitNullCheck(NullCheck i) {
+        processUse(i, i.object(), true);
+    }
+
+    @Override
+    public void visitInvoke(Invoke i) {
+        if (!i.isStatic()) {
+            processUse(i, i.receiver(), true);
+        }
+    }
+
+    @Override
+    public void visitCheckCast(CheckCast i) {
+        if (processUse(i, i.object(), false)) {
+            // if the object is non null, the result of the cast is as well
+            i.setFlag(Value.Flag.NonNull);
+        }
+    }
+
+    @Override
+    public void visitInstanceOf(InstanceOf i) {
+        processUse(i, i.object(), false); // instanceof can check faster if object is non-null
+    }
+
+    @Override
+    public void visitMonitorEnter(MonitorEnter i) {
+        processUse(i, i.object(), true);
+    }
+
+    @Override
+    public void visitIntrinsic(Intrinsic i) {
+        if (!i.isStatic()) {
+            processUse(i, i.receiver(), true);
+        }
+    }
+
+    @Override
+    public void visitIf(If i) {
+        if (C1XOptions.OptFlowSensitiveNCE) {
+            if (i.trueSuccessor() != i.falseSuccessor()) {
+                // if the two successors are different, then we may learn something on one branch
+                Value x = i.x();
+                if (x.kind == CiKind.Object) {
+                    // this is a comparison of object references
+                    Value y = i.y();
+                    if (processUse(i, x, false)) {
+                        // x is known to be non-null
+                        compareAgainstNonNull(i, y);
+                    } else if (processUse(i, y, false)) {
+                        // y is known to be non-null
+                        compareAgainstNonNull(i, x);
+                    } else if (x.isNullConstant()) {
+                        // x is the null constant
+                        compareAgainstNull(i, y);
+                    } else if (y.isNullConstant()) {
+                        // y is the null constaint
+                        compareAgainstNull(i, x);
+                    }
+                }
+                // XXX: also check (x instanceof T) tests
+            }
+        }
+    }
+
+    private void compareAgainstNonNull(If i, Value use) {
+        if (i.condition() == Condition.EQ) {
+            propagateNonNull(i, use, i.trueSuccessor());
+        }
+    }
+
+    private void compareAgainstNull(If i, Value use) {
+        if (i.condition() == Condition.EQ) {
+            propagateNonNull(i, use, i.falseSuccessor());
+        } else if (i.condition() == Condition.NE) {
+            propagateNonNull(i, use, i.trueSuccessor());
+        }
+    }
+
+    private void propagateNonNull(If i, Value use, BlockBegin succ) {
+        BlockInfo info = getBlockInfo(i.begin());
+        if (info.ifEdge == null) {
+            // Only use one if edge.
+            info.ifEdge = new IfEdge(i.begin(), succ, use);
+        }
+    }
+
+    private ValueInfo getValueInfo(Value value) {
+        Object info = value.optInfo;
+        if (info instanceof ValueInfo) {
+            return (ValueInfo) info;
+        }
+        C1XMetrics.NullCheckIdsAssigned++;
+        ValueInfo ninfo = new ValueInfo(value, maximumIndex++);
+        value.optInfo = ninfo;
+        valueInfos.add(ninfo);
+        return ninfo;
+    }
+
+    private BlockInfo getBlockInfo(BlockBegin block) {
+        Object info = block.optInfo;
+        if (info instanceof BlockInfo) {
+            return (BlockInfo) info;
+        }
+        BlockInfo ninfo = new BlockInfo(block);
+        block.optInfo = ninfo;
+        blockInfos.add(ninfo);
+        return ninfo;
+    }
+
+    private void setValue(Value value, CiBitMap bitmap) {
+        int index = getValueInfo(value).globalIndex;
+        bitmap.grow(index + 1);
+        bitmap.set(index);
+        if (value instanceof UnsafeCast) {
+            // An unsafe cast is just an alias
+            setValue(((UnsafeCast) value).value(), bitmap);
+        }
+    }
+
+    private boolean checkValue(Value value, CiBitMap bitmap) {
+        Object info = value.optInfo;
+        return info instanceof ValueInfo && bitmap.getDefault(((ValueInfo) info).globalIndex);
+    }
+
+    private boolean isMarked(BlockInfo block) {
+        return block.marked;
+    }
+
+    private void mark(BlockInfo block) {
+        block.marked = true;
+    }
+
+    private void unmark(BlockInfo block) {
+        block.marked = false;
+    }
+
+    private void clearInfo() {
+        // be a good citizen and clear all the information added to nodes
+        // (also avoids confusing a later application of this same optimization)
+        for (BlockInfo info : blockInfos) {
+            assert info.block.optInfo instanceof BlockInfo : "inconsistent block information";
+            info.block.optInfo = null;
+        }
+        for (ValueInfo info : valueInfos) {
+            assert info.value.optInfo instanceof ValueInfo : "inconsistent value information";
+            info.value.optInfo = null;
+        }
+    }
+
+    private void clearMarked() {
+        for (BlockInfo info : blockInfos) {
+            info.marked = false;
+        }
+    }
+
+    private CiBitMap newBitMap() {
+        return new CiBitMap(maximumIndex > 32 ? maximumIndex : 32);
+    }
+
+    private CiBitMap getPredecessorMap(BlockBegin pred, boolean exceptionBlock) {
+        BlockInfo predInfo = getBlockInfo(pred);
+        return exceptionBlock ? predInfo.localExcept : predInfo.localOut;
+    }
+
+    private CiBitMap getPredecessorMap(BlockInfo predInfo, boolean exceptionBlock) {
+        return exceptionBlock ? predInfo.localExcept : predInfo.localOut;
+    }
+}