/*
 * Copyright (c) 2015, 2018, 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 org.graalvm.compiler.lir.alloc.lsra;

import static jdk.vm.ci.code.ValueUtil.asRegister;
import static jdk.vm.ci.code.ValueUtil.asStackSlot;
import static jdk.vm.ci.code.ValueUtil.isRegister;
import static jdk.vm.ci.code.ValueUtil.isStackSlot;
import static org.graalvm.compiler.lir.LIRValueUtil.asVariable;
import static org.graalvm.compiler.lir.LIRValueUtil.isVariable;
import static org.graalvm.compiler.lir.debug.LIRGenerationDebugContext.getSourceForOperandFromDebugContext;

import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.BitSet;
import java.util.EnumSet;

import jdk.internal.vm.compiler.collections.EconomicSet;
import jdk.internal.vm.compiler.collections.Equivalence;
import org.graalvm.compiler.core.common.LIRKind;
import org.graalvm.compiler.core.common.PermanentBailoutException;
import org.graalvm.compiler.core.common.alloc.ComputeBlockOrder;
import org.graalvm.compiler.core.common.cfg.AbstractBlockBase;
import org.graalvm.compiler.core.common.util.BitMap2D;
import org.graalvm.compiler.debug.Assertions;
import org.graalvm.compiler.debug.DebugContext;
import org.graalvm.compiler.debug.GraalError;
import org.graalvm.compiler.debug.Indent;
import org.graalvm.compiler.lir.InstructionValueConsumer;
import org.graalvm.compiler.lir.LIRInstruction;
import org.graalvm.compiler.lir.LIRInstruction.OperandFlag;
import org.graalvm.compiler.lir.LIRInstruction.OperandMode;
import org.graalvm.compiler.lir.StandardOp.LoadConstantOp;
import org.graalvm.compiler.lir.StandardOp.ValueMoveOp;
import org.graalvm.compiler.lir.ValueConsumer;
import org.graalvm.compiler.lir.alloc.lsra.Interval.RegisterPriority;
import org.graalvm.compiler.lir.alloc.lsra.Interval.SpillState;
import org.graalvm.compiler.lir.alloc.lsra.LinearScan.BlockData;
import org.graalvm.compiler.lir.gen.LIRGenerationResult;
import org.graalvm.compiler.lir.phases.AllocationPhase.AllocationContext;

import jdk.vm.ci.code.Register;
import jdk.vm.ci.code.RegisterArray;
import jdk.vm.ci.code.StackSlot;
import jdk.vm.ci.code.TargetDescription;
import jdk.vm.ci.meta.AllocatableValue;
import jdk.vm.ci.meta.Constant;
import jdk.vm.ci.meta.JavaConstant;
import jdk.vm.ci.meta.Value;
import jdk.vm.ci.meta.ValueKind;

public class LinearScanLifetimeAnalysisPhase extends LinearScanAllocationPhase {

    protected final LinearScan allocator;
    protected final DebugContext debug;

    
Params:
linearScan – /**
     * @param linearScan
     */
    protected LinearScanLifetimeAnalysisPhase(LinearScan linearScan) {
        allocator = linearScan;
        debug = allocator.getDebug();
    }

    @Override
    protected void run(TargetDescription target, LIRGenerationResult lirGenRes, AllocationContext context) {
        numberInstructions();
        debug.dump(DebugContext.VERBOSE_LEVEL, lirGenRes.getLIR(), "Before register allocation");
        computeLocalLiveSets();
        computeGlobalLiveSets();
        buildIntervals(Assertions.detailedAssertionsEnabled(allocator.getOptions()));
    }

    
Bit set for each variable that is contained in each loop.
/**
     * Bit set for each variable that is contained in each loop.
     */
    private BitMap2D intervalInLoop;

    boolean isIntervalInLoop(int interval, int loop) {
        return intervalInLoop.at(interval, loop);
    }

    
Numbers all instructions in all blocks. The numbering follows the linear scan order. /**
     * Numbers all instructions in all blocks. The numbering follows the
     * {@linkplain ComputeBlockOrder linear scan order}.
     */
    protected void numberInstructions() {

        allocator.initIntervals();

        ValueConsumer setVariableConsumer = (value, mode, flags) -> {
            if (isVariable(value)) {
                allocator.getOrCreateInterval(asVariable(value));
            }
        };

        // Assign IDs to LIR nodes and build a mapping, lirOps, from ID to LIRInstruction node.
        int numInstructions = 0;
        for (AbstractBlockBase<?> block : allocator.sortedBlocks()) {
            numInstructions += allocator.getLIR().getLIRforBlock(block).size();
        }

        // initialize with correct length
        allocator.initOpIdMaps(numInstructions);

        int opId = 0;
        int index = 0;
        for (AbstractBlockBase<?> block : allocator.sortedBlocks()) {
            allocator.initBlockData(block);

            ArrayList<LIRInstruction> instructions = allocator.getLIR().getLIRforBlock(block);

            int numInst = instructions.size();
            for (int j = 0; j < numInst; j++) {
                LIRInstruction op = instructions.get(j);
                op.setId(opId);

                allocator.putOpIdMaps(index, op, block);
                assert allocator.instructionForId(opId) == op : "must match";

                op.visitEachTemp(setVariableConsumer);
                op.visitEachOutput(setVariableConsumer);

                index++;
                opId += 2; // numbering of lirOps by two
            }
        }
        assert index == numInstructions : "must match";
        assert (index << 1) == opId : "must match: " + (index << 1);
    }

    
Computes local live sets (i.e. BlockData.liveGen and BlockData.liveKill) separately for each block. /**
     * Computes local live sets (i.e. {@link BlockData#liveGen} and {@link BlockData#liveKill})
     * separately for each block.
     */
    @SuppressWarnings("try")
    void computeLocalLiveSets() {
        int liveSize = allocator.liveSetSize();

        intervalInLoop = new BitMap2D(allocator.operandSize(), allocator.numLoops());

        try {
            final BitSet liveGenScratch = new BitSet(liveSize);
            final BitSet liveKillScratch = new BitSet(liveSize);
            // iterate all blocks
            for (final AbstractBlockBase<?> block : allocator.sortedBlocks()) {
                try (Indent indent = debug.logAndIndent("compute local live sets for block %s", block)) {

                    liveGenScratch.clear();
                    liveKillScratch.clear();

                    ArrayList<LIRInstruction> instructions = allocator.getLIR().getLIRforBlock(block);
                    int numInst = instructions.size();

                    ValueConsumer useConsumer = (operand, mode, flags) -> {
                        if (isVariable(operand)) {
                            int operandNum = allocator.operandNumber(operand);
                            if (!liveKillScratch.get(operandNum)) {
                                liveGenScratch.set(operandNum);
                                if (debug.isLogEnabled()) {
                                    debug.log("liveGen for operand %d(%s)", operandNum, operand);
                                }
                            }
                            if (block.getLoop() != null) {
                                intervalInLoop.setBit(operandNum, block.getLoop().getIndex());
                            }
                        }

                        if (allocator.detailedAsserts) {
                            verifyInput(block, liveKillScratch, operand);
                        }
                    };
                    ValueConsumer stateConsumer = (operand, mode, flags) -> {
                        if (LinearScan.isVariableOrRegister(operand)) {
                            int operandNum = allocator.operandNumber(operand);
                            if (!liveKillScratch.get(operandNum)) {
                                liveGenScratch.set(operandNum);
                                if (debug.isLogEnabled()) {
                                    debug.log("liveGen in state for operand %d(%s)", operandNum, operand);
                                }
                            }
                        }
                    };
                    ValueConsumer defConsumer = (operand, mode, flags) -> {
                        if (isVariable(operand)) {
                            int varNum = allocator.operandNumber(operand);
                            liveKillScratch.set(varNum);
                            if (debug.isLogEnabled()) {
                                debug.log("liveKill for operand %d(%s)", varNum, operand);
                            }
                            if (block.getLoop() != null) {
                                intervalInLoop.setBit(varNum, block.getLoop().getIndex());
                            }
                        }

                        if (allocator.detailedAsserts) {
                            /*
                             * Fixed intervals are never live at block boundaries, so they need not
                             * be processed in live sets. Process them only in debug mode so that
                             * this can be checked
                             */
                            verifyTemp(liveKillScratch, operand);
                        }
                    };

                    // iterate all instructions of the block
                    for (int j = 0; j < numInst; j++) {
                        final LIRInstruction op = instructions.get(j);

                        try (Indent indent2 = debug.logAndIndent("handle op %d: %s", op.id(), op)) {
                            op.visitEachInput(useConsumer);
                            op.visitEachAlive(useConsumer);
                            /*
                             * Add uses of live locals from interpreter's point of view for proper
                             * debug information generation.
                             */
                            op.visitEachState(stateConsumer);
                            op.visitEachTemp(defConsumer);
                            op.visitEachOutput(defConsumer);
                        }
                    } // end of instruction iteration

                    BlockData blockSets = allocator.getBlockData(block);
                    blockSets.liveGen = trimClone(liveGenScratch);
                    blockSets.liveKill = trimClone(liveKillScratch);
                    // sticky size, will get non-sticky in computeGlobalLiveSets
                    blockSets.liveIn = new BitSet(0);
                    blockSets.liveOut = new BitSet(0);

                    if (debug.isLogEnabled()) {
                        debug.log("liveGen  B%d %s", block.getId(), blockSets.liveGen);
                        debug.log("liveKill B%d %s", block.getId(), blockSets.liveKill);
                    }

                }
            } // end of block iteration
        } catch (OutOfMemoryError oom) {
            throw new PermanentBailoutException(oom, "Out-of-memory during live set allocation of size %d", liveSize);
        }
    }

    private void verifyTemp(BitSet liveKill, Value operand) {
        /*
         * Fixed intervals are never live at block boundaries, so they need not be processed in live
         * sets. Process them only in debug mode so that this can be checked
         */
        if (isRegister(operand)) {
            if (allocator.isProcessed(operand)) {
                liveKill.set(allocator.operandNumber(operand));
            }
        }
    }

    private void verifyInput(AbstractBlockBase<?> block, BitSet liveKill, Value operand) {
        /*
         * Fixed intervals are never live at block boundaries, so they need not be processed in live
         * sets. This is checked by these assertions to be sure about it. The entry block may have
         * incoming values in registers, which is ok.
         */
        if (isRegister(operand) && block != allocator.getLIR().getControlFlowGraph().getStartBlock()) {
            if (allocator.isProcessed(operand)) {
                assert liveKill.get(allocator.operandNumber(operand)) : "using fixed register " + asRegister(operand) + " that is not defined in this block " + block;
            }
        }
    }

    
Performs a backward dataflow analysis to compute global live sets (i.e. BlockData.liveIn and BlockData.liveOut) for each block. /**
     * Performs a backward dataflow analysis to compute global live sets (i.e.
     * {@link BlockData#liveIn} and {@link BlockData#liveOut}) for each block.
     */
    @SuppressWarnings("try")
    protected void computeGlobalLiveSets() {
        try (Indent indent = debug.logAndIndent("compute global live sets")) {
            int numBlocks = allocator.blockCount();
            boolean changeOccurred;
            boolean changeOccurredInBlock;
            int iterationCount = 0;
            BitSet scratch = new BitSet(allocator.liveSetSize()); // scratch set for calculations

            /*
             * Perform a backward dataflow analysis to compute liveOut and liveIn for each block.
             * The loop is executed until a fixpoint is reached (no changes in an iteration).
             */
            do {
                changeOccurred = false;

                try (Indent indent2 = debug.logAndIndent("new iteration %d", iterationCount)) {

                    // iterate all blocks in reverse order
                    for (int i = numBlocks - 1; i >= 0; i--) {
                        AbstractBlockBase<?> block = allocator.blockAt(i);
                        BlockData blockSets = allocator.getBlockData(block);

                        changeOccurredInBlock = false;

                        /*
                         * liveOut(block) is the union of liveIn(sux), for successors sux of block.
                         */
                        int n = block.getSuccessorCount();
                        if (n > 0) {
                            scratch.clear();
                            // block has successors
                            if (n > 0) {
                                for (AbstractBlockBase<?> successor : block.getSuccessors()) {
                                    scratch.or(allocator.getBlockData(successor).liveIn);
                                }
                            }

                            if (!blockSets.liveOut.equals(scratch)) {
                                blockSets.liveOut = trimClone(scratch);

                                changeOccurred = true;
                                changeOccurredInBlock = true;
                            }
                        }

                        if (iterationCount == 0 || changeOccurredInBlock) {
                            /*
                             * liveIn(block) is the union of liveGen(block) with (liveOut(block) &
                             * !liveKill(block)).
                             *
                             * Note: liveIn has to be computed only in first iteration or if liveOut
                             * has changed!
                             *
                             * Note: liveIn set can only grow, never shrink. No need to clear it.
                             */
                            BitSet liveIn = blockSets.liveIn;
                            /*
                             * BitSet#or will call BitSet#ensureSize (since the bit set is of length
                             * 0 initially) and set sticky to false
                             */
                            liveIn.or(blockSets.liveOut);
                            liveIn.andNot(blockSets.liveKill);
                            liveIn.or(blockSets.liveGen);

                            liveIn.clone(); // trimToSize()

                            if (debug.isLogEnabled()) {
                                debug.log("block %d: livein = %s,  liveout = %s", block.getId(), liveIn, blockSets.liveOut);
                            }
                        }
                    }
                    iterationCount++;

                    if (changeOccurred && iterationCount > 50) {
                        /*
                         * Very unlikely, should never happen: If it happens we cannot guarantee it
                         * won't happen again.
                         */
                        throw new PermanentBailoutException("too many iterations in computeGlobalLiveSets");
                    }
                }
            } while (changeOccurred);

            if (Assertions.detailedAssertionsEnabled(allocator.getOptions())) {
                verifyLiveness();
            }

            // check that the liveIn set of the first block is empty
            AbstractBlockBase<?> startBlock = allocator.getLIR().getControlFlowGraph().getStartBlock();
            if (allocator.getBlockData(startBlock).liveIn.cardinality() != 0) {
                if (Assertions.detailedAssertionsEnabled(allocator.getOptions())) {
                    reportFailure(numBlocks);
                }
                // bailout if this occurs in product mode.
                throw new GraalError("liveIn set of first block must be empty: " + allocator.getBlockData(startBlock).liveIn);
            }
        }
    }

    
Creates a trimmed copy a bit set. BitSet.clone() cannot be used since it will not trim the array if the bit set is sticky. /**
     * Creates a trimmed copy a bit set.
     *
     * {@link BitSet#clone()} cannot be used since it will not {@linkplain BitSet#trimToSize trim}
     * the array if the bit set is {@linkplain BitSet#sizeIsSticky sticky}.
     */
    @SuppressWarnings("javadoc")
    private static BitSet trimClone(BitSet set) {
        BitSet trimmedSet = new BitSet(0); // zero-length words array, sticky
        trimmedSet.or(set); // words size ensured to be words-in-use of set,
                            // also makes it non-sticky
        return trimmedSet;
    }

    @SuppressWarnings("try")
    protected void reportFailure(int numBlocks) {
        try (DebugContext.Scope s = debug.forceLog()) {
            try (Indent indent = debug.logAndIndent("report failure")) {

                BitSet startBlockLiveIn = allocator.getBlockData(allocator.getLIR().getControlFlowGraph().getStartBlock()).liveIn;
                try (Indent indent2 = debug.logAndIndent("Error: liveIn set of first block must be empty (when this fails, variables are used before they are defined):")) {
                    for (int operandNum = startBlockLiveIn.nextSetBit(0); operandNum >= 0; operandNum = startBlockLiveIn.nextSetBit(operandNum + 1)) {
                        Interval interval = allocator.intervalFor(operandNum);
                        if (interval != null) {
                            Value operand = interval.operand;
                            debug.log("var %d; operand=%s; node=%s", operandNum, operand, getSourceForOperandFromDebugContext(debug, operand));
                        } else {
                            debug.log("var %d; missing operand", operandNum);
                        }
                    }
                }

                // print some additional information to simplify debugging
                for (int operandNum = startBlockLiveIn.nextSetBit(0); operandNum >= 0; operandNum = startBlockLiveIn.nextSetBit(operandNum + 1)) {
                    Interval interval = allocator.intervalFor(operandNum);
                    Value operand = null;
                    Object valueForOperandFromDebugContext = null;
                    if (interval != null) {
                        operand = interval.operand;
                        valueForOperandFromDebugContext = getSourceForOperandFromDebugContext(debug, operand);
                    }
                    try (Indent indent2 = debug.logAndIndent("---- Detailed information for var %d; operand=%s; node=%s ----", operandNum, operand, valueForOperandFromDebugContext)) {

                        ArrayDeque<AbstractBlockBase<?>> definedIn = new ArrayDeque<>();
                        EconomicSet<AbstractBlockBase<?>> usedIn = EconomicSet.create(Equivalence.IDENTITY);
                        for (AbstractBlockBase<?> block : allocator.sortedBlocks()) {
                            if (allocator.getBlockData(block).liveGen.get(operandNum)) {
                                usedIn.add(block);
                                try (Indent indent3 = debug.logAndIndent("used in block B%d", block.getId())) {
                                    for (LIRInstruction ins : allocator.getLIR().getLIRforBlock(block)) {
                                        try (Indent indent4 = debug.logAndIndent("%d: %s", ins.id(), ins)) {
                                            ins.forEachState((liveStateOperand, mode, flags) -> {
                                                debug.log("operand=%s", liveStateOperand);
                                                return liveStateOperand;
                                            });
                                        }
                                    }
                                }
                            }
                            if (allocator.getBlockData(block).liveKill.get(operandNum)) {
                                definedIn.add(block);
                                try (Indent indent3 = debug.logAndIndent("defined in block B%d", block.getId())) {
                                    for (LIRInstruction ins : allocator.getLIR().getLIRforBlock(block)) {
                                        debug.log("%d: %s", ins.id(), ins);
                                    }
                                }
                            }
                        }

                        int[] hitCount = new int[numBlocks];

                        while (!definedIn.isEmpty()) {
                            AbstractBlockBase<?> block = definedIn.removeFirst();
                            usedIn.remove(block);
                            for (AbstractBlockBase<?> successor : block.getSuccessors()) {
                                if (successor.isLoopHeader()) {
                                    if (!block.isLoopEnd()) {
                                        definedIn.add(successor);
                                    }
                                } else {
                                    if (++hitCount[successor.getId()] == successor.getPredecessorCount()) {
                                        definedIn.add(successor);
                                    }
                                }
                            }
                        }
                        try (Indent indent3 = debug.logAndIndent("**** offending usages are in: ")) {
                            for (AbstractBlockBase<?> block : usedIn) {
                                debug.log("B%d", block.getId());
                            }
                        }
                    }
                }
            }
        } catch (Throwable e) {
            throw debug.handle(e);
        }
    }

    protected void verifyLiveness() {
        /*
         * Check that fixed intervals are not live at block boundaries (live set must be empty at
         * fixed intervals).
         */
        for (AbstractBlockBase<?> block : allocator.sortedBlocks()) {
            for (int j = 0; j <= allocator.maxRegisterNumber(); j++) {
                assert !allocator.getBlockData(block).liveIn.get(j) : "liveIn  set of fixed register must be empty";
                assert !allocator.getBlockData(block).liveOut.get(j) : "liveOut set of fixed register must be empty";
                assert !allocator.getBlockData(block).liveGen.get(j) : "liveGen set of fixed register must be empty";
            }
        }
    }

    protected void addUse(AllocatableValue operand, int from, int to, RegisterPriority registerPriority, ValueKind<?> kind, boolean detailedAsserts) {
        if (!allocator.isProcessed(operand)) {
            return;
        }

        Interval interval = allocator.getOrCreateInterval(operand);
        if (!kind.equals(LIRKind.Illegal)) {
            interval.setKind(kind);
        }

        interval.addRange(from, to);

        // Register use position at even instruction id.
        interval.addUsePos(to & ~1, registerPriority, detailedAsserts);

        if (debug.isLogEnabled()) {
            debug.log("add use: %s, from %d to %d (%s)", interval, from, to, registerPriority.name());
        }
    }

    protected void addTemp(AllocatableValue operand, int tempPos, RegisterPriority registerPriority, ValueKind<?> kind, boolean detailedAsserts) {
        if (!allocator.isProcessed(operand)) {
            return;
        }

        Interval interval = allocator.getOrCreateInterval(operand);
        if (!kind.equals(LIRKind.Illegal)) {
            interval.setKind(kind);
        }

        interval.addRange(tempPos, tempPos + 1);
        interval.addUsePos(tempPos, registerPriority, detailedAsserts);
        interval.addMaterializationValue(null);

        if (debug.isLogEnabled()) {
            debug.log("add temp: %s tempPos %d (%s)", interval, tempPos, RegisterPriority.MustHaveRegister.name());
        }
    }

    protected void addDef(AllocatableValue operand, LIRInstruction op, RegisterPriority registerPriority, ValueKind<?> kind, boolean detailedAsserts) {
        if (!allocator.isProcessed(operand)) {
            return;
        }
        int defPos = op.id();

        Interval interval = allocator.getOrCreateInterval(operand);
        if (!kind.equals(LIRKind.Illegal)) {
            interval.setKind(kind);
        }

        Range r = interval.first();
        if (r.from <= defPos) {
            /*
             * Update the starting point (when a range is first created for a use, its start is the
             * beginning of the current block until a def is encountered).
             */
            r.from = defPos;
            interval.addUsePos(defPos, registerPriority, detailedAsserts);

        } else {
            /*
             * Dead value - make vacuous interval also add register priority for dead intervals
             */
            interval.addRange(defPos, defPos + 1);
            interval.addUsePos(defPos, registerPriority, detailedAsserts);
            if (debug.isLogEnabled()) {
                debug.log("Warning: def of operand %s at %d occurs without use", operand, defPos);
            }
        }

        changeSpillDefinitionPos(op, operand, interval, defPos);
        if (registerPriority == RegisterPriority.None && interval.spillState().ordinal() <= SpillState.StartInMemory.ordinal() && isStackSlot(operand)) {
            // detection of method-parameters and roundfp-results
            interval.setSpillState(SpillState.StartInMemory);
        }
        interval.addMaterializationValue(getMaterializedValue(op, operand, interval));

        if (debug.isLogEnabled()) {
            debug.log("add def: %s defPos %d (%s)", interval, defPos, registerPriority.name());
        }
    }

    
Optimizes moves related to incoming stack based arguments. The interval for the destination
of such moves is assigned the stack slot (which is in the caller's frame) as its spill slot.
/**
     * Optimizes moves related to incoming stack based arguments. The interval for the destination
     * of such moves is assigned the stack slot (which is in the caller's frame) as its spill slot.
     */
    protected void handleMethodArguments(LIRInstruction op) {
        if (ValueMoveOp.isValueMoveOp(op)) {
            ValueMoveOp move = ValueMoveOp.asValueMoveOp(op);
            if (optimizeMethodArgument(move.getInput())) {
                StackSlot slot = asStackSlot(move.getInput());
                if (Assertions.detailedAssertionsEnabled(allocator.getOptions())) {
                    assert op.id() > 0 : "invalid id";
                    assert allocator.blockForId(op.id()).getPredecessorCount() == 0 : "move from stack must be in first block";
                    assert isVariable(move.getResult()) : "result of move must be a variable";

                    if (debug.isLogEnabled()) {
                        debug.log("found move from stack slot %s to %s", slot, move.getResult());
                    }
                }

                Interval interval = allocator.intervalFor(move.getResult());
                interval.setSpillSlot(slot);
                interval.assignLocation(slot);
            }
        }
    }

    protected void addRegisterHint(final LIRInstruction op, final Value targetValue, OperandMode mode, EnumSet<OperandFlag> flags, final boolean hintAtDef) {
        if (flags.contains(OperandFlag.HINT) && LinearScan.isVariableOrRegister(targetValue)) {

            op.forEachRegisterHint(targetValue, mode, (registerHint, valueMode, valueFlags) -> {
                if (LinearScan.isVariableOrRegister(registerHint)) {
                    Interval from = allocator.getOrCreateInterval((AllocatableValue) registerHint);
                    Interval to = allocator.getOrCreateInterval((AllocatableValue) targetValue);

                    /* hints always point from def to use */
                    if (hintAtDef) {
                        to.setLocationHint(from);
                    } else {
                        from.setLocationHint(to);
                    }
                    if (debug.isLogEnabled()) {
                        debug.log("operation at opId %d: added hint from interval %d to %d", op.id(), from.operandNumber, to.operandNumber);
                    }

                    return registerHint;
                }
                return null;
            });
        }
    }

    
Eliminates moves from register to stack if the stack slot is known to be correct.
Params:
op – 
operand – /**
     * Eliminates moves from register to stack if the stack slot is known to be correct.
     *
     * @param op
     * @param operand
     */
    protected void changeSpillDefinitionPos(LIRInstruction op, AllocatableValue operand, Interval interval, int defPos) {
        assert interval.isSplitParent() : "can only be called for split parents";

        switch (interval.spillState()) {
            case NoDefinitionFound:
                assert interval.spillDefinitionPos() == -1 : "must no be set before";
                interval.setSpillDefinitionPos(defPos);
                interval.setSpillState(SpillState.NoSpillStore);
                break;

            case NoSpillStore:
                assert defPos <= interval.spillDefinitionPos() : "positions are processed in reverse order when intervals are created";
                if (defPos < interval.spillDefinitionPos() - 2) {
                    // second definition found, so no spill optimization possible for this interval
                    interval.setSpillState(SpillState.NoOptimization);
                } else {
                    // two consecutive definitions (because of two-operand LIR form)
                    assert allocator.blockForId(defPos) == allocator.blockForId(interval.spillDefinitionPos()) : "block must be equal";
                }
                break;

            case NoOptimization:
                // nothing to do
                break;

            default:
                throw GraalError.shouldNotReachHere("other states not allowed at this time");
        }
    }

    private static boolean optimizeMethodArgument(Value value) {
        /*
         * Object method arguments that are passed on the stack are currently not optimized because
         * this requires that the runtime visits method arguments during stack walking.
         */
        return isStackSlot(value) && asStackSlot(value).isInCallerFrame() && LIRKind.isValue(value);
    }

    
Determines the register priority for an instruction's output/result operand.
/**
     * Determines the register priority for an instruction's output/result operand.
     */
    protected RegisterPriority registerPriorityOfOutputOperand(LIRInstruction op) {
        if (ValueMoveOp.isValueMoveOp(op)) {
            ValueMoveOp move = ValueMoveOp.asValueMoveOp(op);
            if (optimizeMethodArgument(move.getInput())) {
                return RegisterPriority.None;
            }
        }

        // all other operands require a register
        return RegisterPriority.MustHaveRegister;
    }

    
Determines the priority which with an instruction's input operand will be allocated a
register.
/**
     * Determines the priority which with an instruction's input operand will be allocated a
     * register.
     */
    protected static RegisterPriority registerPriorityOfInputOperand(EnumSet<OperandFlag> flags) {
        if (flags.contains(OperandFlag.STACK)) {
            return RegisterPriority.ShouldHaveRegister;
        }
        // all other operands require a register
        return RegisterPriority.MustHaveRegister;
    }

    @SuppressWarnings("try")
    protected void buildIntervals(boolean detailedAsserts) {

        try (Indent indent = debug.logAndIndent("build intervals")) {
            InstructionValueConsumer outputConsumer = (op, operand, mode, flags) -> {
                if (LinearScan.isVariableOrRegister(operand)) {
                    addDef((AllocatableValue) operand, op, registerPriorityOfOutputOperand(op), operand.getValueKind(), detailedAsserts);
                    addRegisterHint(op, operand, mode, flags, true);
                }
            };

            InstructionValueConsumer tempConsumer = (op, operand, mode, flags) -> {
                if (LinearScan.isVariableOrRegister(operand)) {
                    addTemp((AllocatableValue) operand, op.id(), RegisterPriority.MustHaveRegister, operand.getValueKind(), detailedAsserts);
                    addRegisterHint(op, operand, mode, flags, false);
                }
            };

            InstructionValueConsumer aliveConsumer = (op, operand, mode, flags) -> {
                if (LinearScan.isVariableOrRegister(operand)) {
                    RegisterPriority p = registerPriorityOfInputOperand(flags);
                    int opId = op.id();
                    int blockFrom = allocator.getFirstLirInstructionId((allocator.blockForId(opId)));
                    addUse((AllocatableValue) operand, blockFrom, opId + 1, p, operand.getValueKind(), detailedAsserts);
                    addRegisterHint(op, operand, mode, flags, false);
                }
            };

            InstructionValueConsumer inputConsumer = (op, operand, mode, flags) -> {
                if (LinearScan.isVariableOrRegister(operand)) {
                    int opId = op.id();
                    int blockFrom = allocator.getFirstLirInstructionId((allocator.blockForId(opId)));
                    RegisterPriority p = registerPriorityOfInputOperand(flags);
                    addUse((AllocatableValue) operand, blockFrom, opId, p, operand.getValueKind(), detailedAsserts);
                    addRegisterHint(op, operand, mode, flags, false);
                }
            };

            InstructionValueConsumer stateProc = (op, operand, mode, flags) -> {
                if (LinearScan.isVariableOrRegister(operand)) {
                    int opId = op.id();
                    int blockFrom = allocator.getFirstLirInstructionId((allocator.blockForId(opId)));
                    addUse((AllocatableValue) operand, blockFrom, opId + 1, RegisterPriority.None, operand.getValueKind(), detailedAsserts);
                }
            };

            // create a list with all caller-save registers (cpu, fpu, xmm)
            RegisterArray callerSaveRegs = allocator.getRegisterAllocationConfig().getRegisterConfig().getCallerSaveRegisters();

            // iterate all blocks in reverse order
            for (int i = allocator.blockCount() - 1; i >= 0; i--) {

                AbstractBlockBase<?> block = allocator.blockAt(i);
                try (Indent indent2 = debug.logAndIndent("handle block %d", block.getId())) {

                    ArrayList<LIRInstruction> instructions = allocator.getLIR().getLIRforBlock(block);
                    final int blockFrom = allocator.getFirstLirInstructionId(block);
                    int blockTo = allocator.getLastLirInstructionId(block);

                    assert blockFrom == instructions.get(0).id();
                    assert blockTo == instructions.get(instructions.size() - 1).id();

                    // Update intervals for operands live at the end of this block;
                    BitSet live = allocator.getBlockData(block).liveOut;
                    for (int operandNum = live.nextSetBit(0); operandNum >= 0; operandNum = live.nextSetBit(operandNum + 1)) {
                        assert live.get(operandNum) : "should not stop here otherwise";
                        AllocatableValue operand = allocator.intervalFor(operandNum).operand;
                        if (debug.isLogEnabled()) {
                            debug.log("live in %d: %s", operandNum, operand);
                        }

                        addUse(operand, blockFrom, blockTo + 2, RegisterPriority.None, LIRKind.Illegal, detailedAsserts);

                        /*
                         * Add special use positions for loop-end blocks when the interval is used
                         * anywhere inside this loop. It's possible that the block was part of a
                         * non-natural loop, so it might have an invalid loop index.
                         */
                        if (block.isLoopEnd() && block.getLoop() != null && isIntervalInLoop(operandNum, block.getLoop().getIndex())) {
                            allocator.intervalFor(operandNum).addUsePos(blockTo + 1, RegisterPriority.LiveAtLoopEnd, detailedAsserts);
                        }
                    }

                    /*
                     * Iterate all instructions of the block in reverse order. definitions of
                     * intervals are processed before uses.
                     */
                    for (int j = instructions.size() - 1; j >= 0; j--) {
                        final LIRInstruction op = instructions.get(j);
                        final int opId = op.id();

                        try (Indent indent3 = debug.logAndIndent("handle inst %d: %s", opId, op)) {

                            // add a temp range for each register if operation destroys
                            // caller-save registers
                            if (op.destroysCallerSavedRegisters()) {
                                for (Register r : callerSaveRegs) {
                                    if (allocator.attributes(r).isAllocatable()) {
                                        addTemp(r.asValue(), opId, RegisterPriority.None, LIRKind.Illegal, detailedAsserts);
                                    }
                                }
                                if (debug.isLogEnabled()) {
                                    debug.log("operation destroys all caller-save registers");
                                }
                            }

                            op.visitEachOutput(outputConsumer);
                            op.visitEachTemp(tempConsumer);
                            op.visitEachAlive(aliveConsumer);
                            op.visitEachInput(inputConsumer);

                            /*
                             * Add uses of live locals from interpreter's point of view for proper
                             * debug information generation. Treat these operands as temp values (if
                             * the live range is extended to a call site, the value would be in a
                             * register at the call otherwise).
                             */
                            op.visitEachState(stateProc);

                            // special steps for some instructions (especially moves)
                            handleMethodArguments(op);

                        }

                    } // end of instruction iteration
                }
            } // end of block iteration

            /*
             * Add the range [0, 1] to all fixed intervals. the register allocator need not handle
             * unhandled fixed intervals.
             */
            for (Interval interval : allocator.intervals()) {
                if (interval != null && isRegister(interval.operand)) {
                    interval.addRange(0, 1);
                }
            }
        }
    }

    
Returns a value for a interval definition, which can be used for re-materialization.
Params:
op – An instruction which defines a value
operand – The destination operand of the instruction
interval – The interval for this defined value.
Returns:
Returns the value which is moved to the instruction and which can be reused at all reload-locations in case the interval of this instruction is spilled. Currently this can only be a JavaConstant./**
     * Returns a value for a interval definition, which can be used for re-materialization.
     *
     * @param op An instruction which defines a value
     * @param operand The destination operand of the instruction
     * @param interval The interval for this defined value.
     * @return Returns the value which is moved to the instruction and which can be reused at all
     *         reload-locations in case the interval of this instruction is spilled. Currently this
     *         can only be a {@link JavaConstant}.
     */
    protected Constant getMaterializedValue(LIRInstruction op, Value operand, Interval interval) {
        if (LoadConstantOp.isLoadConstantOp(op)) {
            LoadConstantOp move = LoadConstantOp.asLoadConstantOp(op);

            if (!allocator.neverSpillConstants()) {
                /*
                 * Check if the interval has any uses which would accept an stack location (priority
                 * == ShouldHaveRegister). Rematerialization of such intervals can result in a
                 * degradation, because rematerialization always inserts a constant load, even if
                 * the value is not needed in a register.
                 */
                Interval.UsePosList usePosList = interval.usePosList();
                int numUsePos = usePosList.size();
                for (int useIdx = 0; useIdx < numUsePos; useIdx++) {
                    Interval.RegisterPriority priority = usePosList.registerPriority(useIdx);
                    if (priority == Interval.RegisterPriority.ShouldHaveRegister) {
                        return null;
                    }
                }
            }
            return move.getConstant();
        }
        return null;
    }
}