/*

 * Copyright (c) 2017, 2019, 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.amd64;

import static jdk.vm.ci.amd64.AMD64.k7;

import static jdk.vm.ci.amd64.AMD64.rax;

import static jdk.vm.ci.amd64.AMD64.rcx;

import static jdk.vm.ci.amd64.AMD64.rdx;

import static jdk.vm.ci.code.ValueUtil.asRegister;

import static org.graalvm.compiler.lir.LIRInstruction.OperandFlag.ILLEGAL;

import static org.graalvm.compiler.lir.LIRInstruction.OperandFlag.REG;

import java.util.EnumSet;

import org.graalvm.compiler.asm.Label;

import org.graalvm.compiler.asm.amd64.AMD64Address;

import org.graalvm.compiler.asm.amd64.AMD64Address.Scale;

import org.graalvm.compiler.asm.amd64.AMD64Assembler.ConditionFlag;

import org.graalvm.compiler.asm.amd64.AMD64MacroAssembler;

import org.graalvm.compiler.core.common.LIRKind;

import org.graalvm.compiler.lir.LIRInstructionClass;

import org.graalvm.compiler.lir.Opcode;

import org.graalvm.compiler.lir.asm.CompilationResultBuilder;

import org.graalvm.compiler.lir.gen.LIRGeneratorTool;

import jdk.vm.ci.amd64.AMD64;

import jdk.vm.ci.amd64.AMD64.CPUFeature;

import jdk.vm.ci.amd64.AMD64Kind;

import jdk.vm.ci.code.Register;

import jdk.vm.ci.code.TargetDescription;

import jdk.vm.ci.meta.JavaKind;

import jdk.vm.ci.meta.Value;

/**

 * Emits code which compares two arrays lexicographically. If the CPU supports any vector

 * instructions specialized code is emitted to leverage these instructions.

 */

@Opcode("ARRAY_COMPARE_TO")

public final class AMD64ArrayCompareToOp extends AMD64LIRInstruction {

    public static final LIRInstructionClass<AMD64ArrayCompareToOp> TYPE = LIRInstructionClass.create(AMD64ArrayCompareToOp.class);

    private final JavaKind kind1;

    private final JavaKind kind2;

    private final int array1BaseOffset;

    private final int array2BaseOffset;

    @Def({REG}) protected Value resultValue;

    @Alive({REG}) protected Value array1Value;

    @Alive({REG}) protected Value array2Value;

    @Use({REG}) protected Value length1Value;

    @Use({REG}) protected Value length2Value;

    @Temp({REG}) protected Value length1ValueTemp;

    @Temp({REG}) protected Value length2ValueTemp;

    @Temp({REG}) protected Value temp1;

    @Temp({REG}) protected Value temp2;

    @Temp({REG, ILLEGAL}) protected Value vectorTemp1;

    public AMD64ArrayCompareToOp(LIRGeneratorTool tool, JavaKind kind1, JavaKind kind2, Value result, Value array1, Value array2, Value length1, Value length2) {

        super(TYPE);

        this.kind1 = kind1;

        this.kind2 = kind2;

        // Both offsets should be the same but better be safe than sorry.

        this.array1BaseOffset = tool.getProviders().getMetaAccess().getArrayBaseOffset(kind1);

        this.array2BaseOffset = tool.getProviders().getMetaAccess().getArrayBaseOffset(kind2);

        this.resultValue = result;

        this.array1Value = array1;

        this.array2Value = array2;

        /*

         * The length values are inputs but are also killed like temporaries so need both Use and

         * Temp annotations, which will only work with fixed registers.

         */

        this.length1Value = length1;

        this.length2Value = length2;

        this.length1ValueTemp = length1;

        this.length2ValueTemp = length2;

        // Allocate some temporaries.

        this.temp1 = tool.newVariable(LIRKind.unknownReference(tool.target().arch.getWordKind()));

        this.temp2 = tool.newVariable(LIRKind.unknownReference(tool.target().arch.getWordKind()));

        // We only need the vector temporaries if we generate SSE code.

        if (supportsSSE42(tool.target())) {

            this.vectorTemp1 = tool.newVariable(LIRKind.value(AMD64Kind.DOUBLE));

        } else {

            this.vectorTemp1 = Value.ILLEGAL;

        }

    }

    private static boolean supportsSSE42(TargetDescription target) {

        AMD64 arch = (AMD64) target.arch;

        return arch.getFeatures().contains(CPUFeature.SSE4_2);

    }

    private static boolean supportsAVX2(TargetDescription target) {

        AMD64 arch = (AMD64) target.arch;

        return arch.getFeatures().contains(CPUFeature.AVX2);

    }

    private static boolean supportsAVX512VLBW(TargetDescription target) {

        EnumSet<CPUFeature> features = ((AMD64) target.arch).getFeatures();

        return features.contains(CPUFeature.AVX512BW) && features.contains(CPUFeature.AVX512VL);

    }

    @Override

    public void emitCode(CompilationResultBuilder crb, AMD64MacroAssembler masm) {

        Register result = asRegister(resultValue);

        Register str1 = asRegister(temp1);

        Register str2 = asRegister(temp2);

        // Load array base addresses.

        masm.leaq(str1, new AMD64Address(asRegister(array1Value), array1BaseOffset));

        masm.leaq(str2, new AMD64Address(asRegister(array2Value), array2BaseOffset));

        Register cnt1 = asRegister(length1Value);

        Register cnt2 = asRegister(length2Value);

        // Checkstyle: stop

        Label LENGTH_DIFF_LABEL = new Label();

        Label POP_LABEL = new Label();

        Label DONE_LABEL = new Label();

        Label WHILE_HEAD_LABEL = new Label();

        Label COMPARE_WIDE_VECTORS_LOOP_FAILED = new Label(); // used only _LP64 && AVX3

        int stride, stride2;

        int adr_stride = -1;

        int adr_stride1 = -1;

        int adr_stride2 = -1;

        // Checkstyle: resume

        int stride2x2 = 0x40;

        AMD64Address.Scale scale = null;

        AMD64Address.Scale scale1 = null;

        AMD64Address.Scale scale2 = null;

        // if (ae != StrIntrinsicNode::LL) {

        if (!(kind1 == JavaKind.Byte && kind2 == JavaKind.Byte)) {

            stride2x2 = 0x20;

        }

        // if (ae == StrIntrinsicNode::LU || ae == StrIntrinsicNode::UL) {

        if (kind1 != kind2) {

            masm.shrl(cnt2, 1);

        }

        // Compute the minimum of the string lengths and the

        // difference of the string lengths (stack).

        // Do the conditional move stuff

        masm.movl(result, cnt1);

        masm.subl(cnt1, cnt2);

        masm.push(cnt1);

        masm.cmovl(ConditionFlag.LessEqual, cnt2, result);    // cnt2 = min(cnt1, cnt2)

        // Is the minimum length zero?

        masm.testl(cnt2, cnt2);

        masm.jcc(ConditionFlag.Zero, LENGTH_DIFF_LABEL);

        // if (ae == StrIntrinsicNode::LL) {

        if (kind1 == JavaKind.Byte && kind2 == JavaKind.Byte) {

            // Load first bytes

            masm.movzbl(result, new AMD64Address(str1, 0));  // result = str1[0]

            masm.movzbl(cnt1, new AMD64Address(str2, 0));    // cnt1 = str2[0]

            // } else if (ae == StrIntrinsicNode::UU) {

        } else if (kind1 == JavaKind.Char && kind2 == JavaKind.Char) {

            // Load first characters

            masm.movzwl(result, new AMD64Address(str1, 0));

            masm.movzwl(cnt1, new AMD64Address(str2, 0));

        } else {

            masm.movzbl(result, new AMD64Address(str1, 0));

            masm.movzwl(cnt1, new AMD64Address(str2, 0));

        }

        masm.subl(result, cnt1);

        masm.jcc(ConditionFlag.NotZero, POP_LABEL);

        // if (ae == StrIntrinsicNode::UU) {

        if (kind1 == JavaKind.Char && kind2 == JavaKind.Char) {

            // Divide length by 2 to get number of chars

            masm.shrl(cnt2, 1);

        }

        masm.cmpl(cnt2, 1);

        masm.jcc(ConditionFlag.Equal, LENGTH_DIFF_LABEL);

        // Check if the strings start at the same location and setup scale and stride

        // if (ae == StrIntrinsicNode::LL || ae == StrIntrinsicNode::UU) {

        if (kind1 == kind2) {

            masm.cmpptr(str1, str2);

            masm.jcc(ConditionFlag.Equal, LENGTH_DIFF_LABEL);

            // if (ae == StrIntrinsicNode::LL) {

            if (kind1 == JavaKind.Byte && kind2 == JavaKind.Byte) {

                scale = AMD64Address.Scale.Times1;

                stride = 16;

            } else {

                scale = AMD64Address.Scale.Times2;

                stride = 8;

            }

        } else {

            scale1 = AMD64Address.Scale.Times1;

            scale2 = AMD64Address.Scale.Times2;

            // scale not used

            stride = 8;

        }

        // if (UseAVX >= 2 && UseSSE42Intrinsics) {

        if (supportsAVX2(crb.target) && supportsSSE42(crb.target)) {

            Register vec1 = asRegister(vectorTemp1, AMD64Kind.DOUBLE);

            // Checkstyle: stop

            Label COMPARE_WIDE_VECTORS = new Label();

            Label VECTOR_NOT_EQUAL = new Label();

            Label COMPARE_WIDE_TAIL = new Label();

            Label COMPARE_SMALL_STR = new Label();

            Label COMPARE_WIDE_VECTORS_LOOP = new Label();

            Label COMPARE_16_CHARS = new Label();

            Label COMPARE_INDEX_CHAR = new Label();

            Label COMPARE_WIDE_VECTORS_LOOP_AVX2 = new Label();

            Label COMPARE_TAIL_LONG = new Label();

            Label COMPARE_WIDE_VECTORS_LOOP_AVX3 = new Label();  // used only _LP64 && AVX3

            // Checkstyle: resume

            int pcmpmask = 0x19;

            // if (ae == StrIntrinsicNode::LL) {

            if (kind1 == JavaKind.Byte && kind2 == JavaKind.Byte) {

                pcmpmask &= ~0x01;

            }

            // Setup to compare 16-chars (32-bytes) vectors,

            // start from first character again because it has aligned address.

            // if (ae == StrIntrinsicNode::LL) {

            if (kind1 == JavaKind.Byte && kind2 == JavaKind.Byte) {

                stride2 = 32;

            } else {

                stride2 = 16;

            }

            // if (ae == StrIntrinsicNode::LL || ae == StrIntrinsicNode::UU) {

            if (kind1 == kind2) {

                adr_stride = stride << scale.log2;

            } else {

                adr_stride1 = 8;  // stride << scale1;

                adr_stride2 = 16; // stride << scale2;

            }

            assert result.equals(rax) && cnt2.equals(rdx) && cnt1.equals(rcx) : "pcmpestri";

            // rax and rdx are used by pcmpestri as elements counters

            masm.movl(result, cnt2);

            masm.andl(cnt2, ~(stride2 - 1));   // cnt2 holds the vector count

            masm.jcc(ConditionFlag.Zero, COMPARE_TAIL_LONG);

            // fast path : compare first 2 8-char vectors.

            masm.bind(COMPARE_16_CHARS);

            // if (ae == StrIntrinsicNode::LL || ae == StrIntrinsicNode::UU) {

            if (kind1 == kind2) {

                masm.movdqu(vec1, new AMD64Address(str1, 0));

            } else {

                masm.pmovzxbw(vec1, new AMD64Address(str1, 0));

            }

            masm.pcmpestri(vec1, new AMD64Address(str2, 0), pcmpmask);

            masm.jccb(ConditionFlag.Below, COMPARE_INDEX_CHAR);

            // if (ae == StrIntrinsicNode::LL || ae == StrIntrinsicNode::UU) {

            if (kind1 == kind2) {

                masm.movdqu(vec1, new AMD64Address(str1, adr_stride));

                masm.pcmpestri(vec1, new AMD64Address(str2, adr_stride), pcmpmask);

            } else {

                masm.pmovzxbw(vec1, new AMD64Address(str1, adr_stride1));

                masm.pcmpestri(vec1, new AMD64Address(str2, adr_stride2), pcmpmask);

            }

            masm.jccb(ConditionFlag.AboveEqual, COMPARE_WIDE_VECTORS);

            masm.addl(cnt1, stride);

            // Compare the characters at index in cnt1

            masm.bind(COMPARE_INDEX_CHAR); // cnt1 has the offset of the mismatching character

            loadNextElements(masm, result, cnt2, str1, str2, scale, scale1, scale2, cnt1);

            masm.subl(result, cnt2);

            masm.jmp(POP_LABEL);

            // Setup the registers to start vector comparison loop

            masm.bind(COMPARE_WIDE_VECTORS);

            // if (ae == StrIntrinsicNode::LL || ae == StrIntrinsicNode::UU) {

            if (kind1 == kind2) {

                masm.leaq(str1, new AMD64Address(str1, result, scale));

                masm.leaq(str2, new AMD64Address(str2, result, scale));

            } else {

                masm.leaq(str1, new AMD64Address(str1, result, scale1));

                masm.leaq(str2, new AMD64Address(str2, result, scale2));

            }

            masm.subl(result, stride2);

            masm.subl(cnt2, stride2);

            masm.jcc(ConditionFlag.Zero, COMPARE_WIDE_TAIL);

            masm.negq(result);

            // In a loop, compare 16-chars (32-bytes) at once using (vpxor+vptest)

            masm.bind(COMPARE_WIDE_VECTORS_LOOP);

            // if (VM_Version::supports_avx512vlbw()) { // trying 64 bytes fast loop

            if (supportsAVX512VLBW(crb.target)) {

                masm.cmpl(cnt2, stride2x2);

                masm.jccb(ConditionFlag.Below, COMPARE_WIDE_VECTORS_LOOP_AVX2);

                masm.testl(cnt2, stride2x2 - 1);   // cnt2 holds the vector count

                // means we cannot subtract by 0x40

                masm.jccb(ConditionFlag.NotZero, COMPARE_WIDE_VECTORS_LOOP_AVX2);

                masm.bind(COMPARE_WIDE_VECTORS_LOOP_AVX3); // the hottest loop

                // if (ae == StrIntrinsicNode::LL || ae == StrIntrinsicNode::UU) {

                if (kind1 == kind2) {

                    masm.evmovdqu64(vec1, new AMD64Address(str1, result, scale));

                    // k7 == 11..11, if operands equal, otherwise k7 has some 0

                    masm.evpcmpeqb(k7, vec1, new AMD64Address(str2, result, scale));

                } else {

                    masm.evpmovzxbw(vec1, new AMD64Address(str1, result, scale1));

                    // k7 == 11..11, if operands equal, otherwise k7 has some 0

                    masm.evpcmpeqb(k7, vec1, new AMD64Address(str2, result, scale2));

                }

                masm.kortestq(k7, k7);

                masm.jcc(ConditionFlag.AboveEqual, COMPARE_WIDE_VECTORS_LOOP_FAILED);     // miscompare

                masm.addq(result, stride2x2);  // update since we already compared at this addr

                masm.subl(cnt2, stride2x2);      // and sub the size too

                masm.jccb(ConditionFlag.NotZero, COMPARE_WIDE_VECTORS_LOOP_AVX3);

                masm.vpxor(vec1, vec1, vec1);

                masm.jmpb(COMPARE_WIDE_TAIL);

            }

            masm.bind(COMPARE_WIDE_VECTORS_LOOP_AVX2);

            // if (ae == StrIntrinsicNode::LL || ae == StrIntrinsicNode::UU) {

            if (kind1 == kind2) {

                masm.vmovdqu(vec1, new AMD64Address(str1, result, scale));

                masm.vpxor(vec1, vec1, new AMD64Address(str2, result, scale));

            } else {

                masm.vpmovzxbw(vec1, new AMD64Address(str1, result, scale1));

                masm.vpxor(vec1, vec1, new AMD64Address(str2, result, scale2));

            }

            masm.vptest(vec1, vec1);

            masm.jcc(ConditionFlag.NotZero, VECTOR_NOT_EQUAL);

            masm.addq(result, stride2);

            masm.subl(cnt2, stride2);

            masm.jcc(ConditionFlag.NotZero, COMPARE_WIDE_VECTORS_LOOP);

            // clean upper bits of YMM registers

            masm.vpxor(vec1, vec1, vec1);

            // compare wide vectors tail

            masm.bind(COMPARE_WIDE_TAIL);

            masm.testq(result, result);

            masm.jcc(ConditionFlag.Zero, LENGTH_DIFF_LABEL);

            masm.movl(result, stride2);

            masm.movl(cnt2, result);

            masm.negq(result);

            masm.jmp(COMPARE_WIDE_VECTORS_LOOP_AVX2);

            // Identifies the mismatching (higher or lower)16-bytes in the 32-byte vectors.

            masm.bind(VECTOR_NOT_EQUAL);

            // clean upper bits of YMM registers

            masm.vpxor(vec1, vec1, vec1);

            // if (ae == StrIntrinsicNode::LL || ae == StrIntrinsicNode::UU) {

            if (kind1 == kind2) {

                masm.leaq(str1, new AMD64Address(str1, result, scale));

                masm.leaq(str2, new AMD64Address(str2, result, scale));

            } else {

                masm.leaq(str1, new AMD64Address(str1, result, scale1));

                masm.leaq(str2, new AMD64Address(str2, result, scale2));

            }

            masm.jmp(COMPARE_16_CHARS);

            // Compare tail chars, length between 1 to 15 chars

            masm.bind(COMPARE_TAIL_LONG);

            masm.movl(cnt2, result);

            masm.cmpl(cnt2, stride);

            masm.jcc(ConditionFlag.Less, COMPARE_SMALL_STR);

            // if (ae == StrIntrinsicNode::LL || ae == StrIntrinsicNode::UU) {

            if (kind1 == kind2) {

                masm.movdqu(vec1, new AMD64Address(str1, 0));

            } else {

                masm.pmovzxbw(vec1, new AMD64Address(str1, 0));

            }

            masm.pcmpestri(vec1, new AMD64Address(str2, 0), pcmpmask);

            masm.jcc(ConditionFlag.Below, COMPARE_INDEX_CHAR);

            masm.subq(cnt2, stride);

            masm.jcc(ConditionFlag.Zero, LENGTH_DIFF_LABEL);

            // if (ae == StrIntrinsicNode::LL || ae == StrIntrinsicNode::UU) {

            if (kind1 == kind2) {

                masm.leaq(str1, new AMD64Address(str1, result, scale));

                masm.leaq(str2, new AMD64Address(str2, result, scale));

            } else {

                masm.leaq(str1, new AMD64Address(str1, result, scale1));

                masm.leaq(str2, new AMD64Address(str2, result, scale2));

            }

            masm.negq(cnt2);

            masm.jmpb(WHILE_HEAD_LABEL);

            masm.bind(COMPARE_SMALL_STR);

        } else if (supportsSSE42(crb.target)) {

            Register vec1 = asRegister(vectorTemp1, AMD64Kind.DOUBLE);

            // Checkstyle: stop

            Label COMPARE_WIDE_VECTORS = new Label();

            Label VECTOR_NOT_EQUAL = new Label();

            Label COMPARE_TAIL = new Label();

            // Checkstyle: resume

            int pcmpmask = 0x19;

            // Setup to compare 8-char (16-byte) vectors,

            // start from first character again because it has aligned address.

            masm.movl(result, cnt2);

            masm.andl(cnt2, ~(stride - 1));   // cnt2 holds the vector count

            // if (ae == StrIntrinsicNode::LL) {

            if (kind1 == JavaKind.Byte && kind2 == JavaKind.Byte) {

                pcmpmask &= ~0x01;

            }

            masm.jcc(ConditionFlag.Zero, COMPARE_TAIL);

            // if (ae == StrIntrinsicNode::LL || ae == StrIntrinsicNode::UU) {

            if (kind1 == kind2) {

                masm.leaq(str1, new AMD64Address(str1, result, scale));

                masm.leaq(str2, new AMD64Address(str2, result, scale));

            } else {

                masm.leaq(str1, new AMD64Address(str1, result, scale1));

                masm.leaq(str2, new AMD64Address(str2, result, scale2));

            }

            masm.negq(result);

            // pcmpestri

            // inputs:

            // vec1- substring

            // rax - negative string length (elements count)

            // mem - scanned string

            // rdx - string length (elements count)

            // pcmpmask - cmp mode: 11000 (string compare with negated result)

            // + 00 (unsigned bytes) or + 01 (unsigned shorts)

            // outputs:

            // rcx - first mismatched element index

            assert result.equals(rax) && cnt2.equals(rdx) && cnt1.equals(rcx) : "pcmpestri";

            masm.bind(COMPARE_WIDE_VECTORS);

            // if (ae == StrIntrinsicNode::LL || ae == StrIntrinsicNode::UU) {

            if (kind1 == kind2) {

                masm.movdqu(vec1, new AMD64Address(str1, result, scale));

                masm.pcmpestri(vec1, new AMD64Address(str2, result, scale), pcmpmask);

            } else {

                masm.pmovzxbw(vec1, new AMD64Address(str1, result, scale1));

                masm.pcmpestri(vec1, new AMD64Address(str2, result, scale2), pcmpmask);

            }

            // After pcmpestri cnt1(rcx) contains mismatched element index

            masm.jccb(ConditionFlag.Below, VECTOR_NOT_EQUAL);  // CF==1

            masm.addq(result, stride);

            masm.subq(cnt2, stride);

            masm.jccb(ConditionFlag.NotZero, COMPARE_WIDE_VECTORS);

            // compare wide vectors tail

            masm.testq(result, result);

            masm.jcc(ConditionFlag.Zero, LENGTH_DIFF_LABEL);

            masm.movl(cnt2, stride);

            masm.movl(result, stride);

            masm.negq(result);

            // if (ae == StrIntrinsicNode::LL || ae == StrIntrinsicNode::UU) {

            if (kind1 == kind2) {

                masm.movdqu(vec1, new AMD64Address(str1, result, scale));

                masm.pcmpestri(vec1, new AMD64Address(str2, result, scale), pcmpmask);

            } else {

                masm.pmovzxbw(vec1, new AMD64Address(str1, result, scale1));

                masm.pcmpestri(vec1, new AMD64Address(str2, result, scale2), pcmpmask);

            }

            masm.jccb(ConditionFlag.AboveEqual, LENGTH_DIFF_LABEL);

            // Mismatched characters in the vectors

            masm.bind(VECTOR_NOT_EQUAL);

            masm.addq(cnt1, result);

            loadNextElements(masm, result, cnt2, str1, str2, scale, scale1, scale2, cnt1);

            masm.subl(result, cnt2);

            masm.jmpb(POP_LABEL);

            masm.bind(COMPARE_TAIL); // limit is zero

            masm.movl(cnt2, result);

            // Fallthru to tail compare

        }

        // Shift str2 and str1 to the end of the arrays, negate min

        // if (ae == StrIntrinsicNode::LL || ae == StrIntrinsicNode::UU) {

        if (kind1 == kind2) {

            masm.leaq(str1, new AMD64Address(str1, cnt2, scale));

            masm.leaq(str2, new AMD64Address(str2, cnt2, scale));

        } else {

            masm.leaq(str1, new AMD64Address(str1, cnt2, scale1));

            masm.leaq(str2, new AMD64Address(str2, cnt2, scale2));

        }

        masm.decrementl(cnt2);  // first character was compared already

        masm.negq(cnt2);

        // Compare the rest of the elements

        masm.bind(WHILE_HEAD_LABEL);

        loadNextElements(masm, result, cnt1, str1, str2, scale, scale1, scale2, cnt2);

        masm.subl(result, cnt1);

        masm.jccb(ConditionFlag.NotZero, POP_LABEL);

        masm.incrementq(cnt2, 1);

        masm.jccb(ConditionFlag.NotZero, WHILE_HEAD_LABEL);

        // Strings are equal up to min length. Return the length difference.

        masm.bind(LENGTH_DIFF_LABEL);

        masm.pop(result);

        // if (ae == StrIntrinsicNode::UU) {

        if (kind1 == JavaKind.Char && kind2 == JavaKind.Char) {

            // Divide diff by 2 to get number of chars

            masm.sarl(result, 1);

        }

        masm.jmpb(DONE_LABEL);