HPCC-Platform/ecl/hqlcpp/hqlcppcase.cpp

/*##############################################################################

    Copyright (C) 2011 HPCC Systems.

    All rights reserved. This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU Affero General Public License as
    published by the Free Software Foundation, either version 3 of the
    License, or (at your option) any later version.

    This program 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 Affero General Public License for more details.

    You should have received a copy of the GNU Affero General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
############################################################################## */
#include "jliball.hpp"
#include "hql.hpp"

#include "platform.h"
#include "jlib.hpp"
#include "jexcept.hpp"
#include "jmisc.hpp"

#include "hql.hpp"

#include "hqlfunc.hpp"

#include "hqlcpp.ipp"
#include "hqlwcpp.hpp"
#include "hqlutil.hpp"
#include "hqlcpputil.hpp"
#include "hqlcatom.hpp"
#include "hqlcerrors.hpp"

#define INTEGER_SEARCH_THRESHOLD                    30      // above this, a table search is generated.
#define MAX_NUM_NOBREAK_CASE                        80      // maximum number of case: without a break - compiler workaround
#define INLINE_COMPARE_THRESHOLD                    2       // above this, a loop is generated
#define SWITCH_TABLE_DENSITY_THRESHOLD              3       // % used before use array index.
#define MAX_NESTED_CASES                            8       // to stop C++ compiler running out of scopes.

//===========================================================================

static _ATOM searchDataTableAtom;
static _ATOM searchEStringTableAtom;
static _ATOM searchQStringTableAtom;
static _ATOM searchStringTableAtom;
static _ATOM searchVStringTableAtom;

//===========================================================================

MODULE_INIT(INIT_PRIORITY_STANDARD)
{
    searchDataTableAtom = createIdentifierAtom("searchDataTable");
    searchEStringTableAtom = createIdentifierAtom("searchEStringTable");
    searchQStringTableAtom = createIdentifierAtom("searchQStringTable");
    searchStringTableAtom = createIdentifierAtom("searchStringTable");
    searchVStringTableAtom = createIdentifierAtom("searchVStringTable");
    return true;
}
MODULE_EXIT()
{
}

//===========================================================================

//Case helper functions...
void cvtChooseListToPairs(HqlExprArray & target, IHqlExpression * from, unsigned base)
{
    unsigned max = from->numChildren();
    unsigned idx;
    target.ensure(max);
    for (idx = 0; idx < max; idx++)
    {
        IHqlExpression * v1 = createConstant(createIntValue(idx+base, LINK(unsignedType)));
        IHqlExpression * v2 = from->queryChild(idx);
        ITypeInfo * type = v2->queryType();
        target.append(* createValue(no_mapto, LINK(type), v1, LINK(v2)));
    }
}

void cvtIndexListToPairs(HqlExprArray & target, IHqlExpression * from)
{
    unsigned max = from->numChildren();
    unsigned idx;
    target.ensure(max);
    for (idx = 0; idx < max; idx++)
    {
        IHqlExpression * v1 = from->queryChild(idx);
        IHqlExpression * v2 = createConstant(createIntValue(idx+1, LINK(unsignedType)));
        ITypeInfo * type = v2->queryType();
        target.append(* createValue(no_mapto, LINK(type), LINK(v1), v2));
    }
}

void cvtInListToPairs(HqlExprArray & target, IHqlExpression * from, bool valueIfMatch)
{
    unsigned max = from->numChildren();
    unsigned idx;
    IHqlExpression * tValue = queryBoolExpr(valueIfMatch);
    ITypeInfo * type = queryBoolType();
    target.ensure(max);
    for (idx = 0; idx < max; idx++)
    {
        IHqlExpression * v1 = from->queryChild(idx);
        target.append(* createValue(no_mapto, LINK(type), LINK(v1), LINK(tValue)));
    }
}

IHqlExpression * createNotFoundValue()
{
    OwnedITypeInfo int4 = makeIntType(4, true);
    return createConstant(int4->castFrom(true, -1));
}

//===========================================================================

static int comparePair(IInterface * * left, IInterface * * right)
{
    IHqlExpression * lexpr = (IHqlExpression *)*left;
    IHqlExpression * rexpr = (IHqlExpression *)*right;

    return lexpr->queryChild(0)->queryValue()->compare(rexpr->queryChild(0)->queryValue());
}


HqlCppCaseInfo::HqlCppCaseInfo(HqlCppTranslator & _translator) : translator(_translator)
{
    complexCompare = false;
    constantCases = true;
    constantValues = true;
    indexType.setown(makeIntType(sizeof(int), true));
}

void HqlCppCaseInfo::addPair(IHqlExpression * expr)
{
    pairs.append(*LINK(expr));
    
    IHqlExpression * compareValue = expr->queryChild(0);
    if (!compareValue->queryValue())
        constantCases = false;
    if (!expr->queryChild(1)->queryValue())
        constantValues = false;

    if (cond && !complexCompare)
    {
        ITypeInfo * valueType = compareValue->queryType();
        if (valueType != cond->queryType())
            complexCompare = isCompare3Valued(compareValue->queryType());
    }

    updateResultType(expr->queryChild(1));

}

void HqlCppCaseInfo::addPairs(HqlExprArray & _pairs)
{
    pairs.ensure(_pairs.ordinality());
    ForEachItemIn(idx, _pairs)
        addPair(&_pairs.item(idx));
}

bool HqlCppCaseInfo::buildAssign(BuildCtx & ctx, const CHqlBoundTarget & target)
{
    if (pairs.ordinality() == 0)
    {
        translator.buildExprAssign(ctx, target, defaultValue);
    }
    else if (cond.get() && constantCases)
    {
        processBranches();

        BuildCtx subctx(ctx);
        CHqlBoundExpr test;
        buildSwitchCondition(ctx, test);

        if (complexCompare)
        {
            if ((pairs.ordinality() > INLINE_COMPARE_THRESHOLD) || (translator.getHints() & HintSize))
            {
                if (okToAlwaysEvaluateDefault() || hasLibraryChop())
                    buildLoopChopMap(subctx, target, test);
                else
                    buildGeneralAssign(subctx, target);
            }
            else 
            {
                if (okToAlwaysEvaluateDefault())
                    buildChop3Map(subctx, target, test);
                else
                    buildGeneralAssign(subctx, target);
            }
        }
        else
        {
            ITypeInfo * condType = test.queryType()->queryPromotedType();
            if (!queryBuildArrayLookup(subctx, target, test))
            {
                if (condType->getTypeCode() != type_real)
                {
                    OwnedHqlExpr search = test.getTranslatedExpr();
                    if (constantValues && (condType->getTypeCode() == type_int) && (pairs.ordinality() > INTEGER_SEARCH_THRESHOLD))
                        buildIntegerSearchMap(subctx, target, search);
                    else
                        buildSwitchMap(subctx, &target, test.expr);
                }
                else
                {
                    if (okToAlwaysEvaluateDefault() && pairs.ordinality() > 4)
                    {
                        translator.buildExprAssign(ctx, target, defaultValue);
                        buildChop2Map(subctx, target, test, 0, pairs.ordinality());
                    }
                    else
                        buildGeneralAssign(subctx, target);
                }
            }
        }
    }
    else
        buildGeneralAssign(ctx, target);

    return true;
}

bool HqlCppCaseInfo::buildReturn(BuildCtx & ctx)
{
    if (pairs.ordinality() == 0)
    {
        translator.buildReturn(ctx, defaultValue);
    }
    else if (cond.get() && constantCases)
    {
        processBranches();

        BuildCtx subctx(ctx);
        CHqlBoundExpr test;
        buildSwitchCondition(ctx, test);

        if (complexCompare)
        {
            buildGeneralReturn(subctx);
        }
        else
        {
            //if canBuildArrayLookup(test)
            //if use a lookup table to map value->constants
            if (test.queryType()->getTypeCode() != type_real)
                buildSwitchMap(subctx, NULL, test.expr);
            else
                buildGeneralReturn(subctx);
        }
    }
    else
        buildGeneralReturn(ctx);

    return true;
}

void HqlCppCaseInfo::buildChop3Map(BuildCtx & ctx, const CHqlBoundTarget & target, CHqlBoundExpr & test, IHqlExpression * temp, unsigned start, unsigned end)
{
    if ((end - start) <= 2)
        buildChop2Map(ctx, target, test, start, end);
    else
    {
        unsigned mid = (start + end) / 2;
        generateCompareVar(ctx, temp, test, queryCompare(mid));
        OwnedHqlExpr test1 = createValue(no_eq, LINK(temp), getZero());
        OwnedHqlExpr test2 = createValue(no_lt, LINK(temp), getZero());

        BuildCtx subctx(ctx);
        IHqlStmt * if1 = subctx.addFilter(test1);                   // if (test == 0)
        translator.buildExprAssign(subctx, target, queryReturn(mid));  //   target = value(n)
        subctx.selectElse(if1);                                                         // else
        IHqlStmt * if2 = subctx.addFilter(test2);                   //   if (test < 0)
        buildChop3Map(subctx, target, test, temp, start, mid);      //       repeat for start..mid
        subctx.selectElse(if2);                                                         //   else
        buildChop3Map(subctx, target, test, temp, mid+1, end);      //       repeat for min..end
    }
}


void HqlCppCaseInfo::buildChop3Map(BuildCtx & ctx, const CHqlBoundTarget & target, CHqlBoundExpr & test)
{
    //need to hack it because there is no signed integer type
    OwnedHqlExpr tempVar = ctx.getTempDeclare(indexType, NULL);

    translator.buildExprAssign(ctx, target, defaultValue);
    buildChop3Map(ctx, target, test, tempVar, 0, getNumPairs());
}

void HqlCppCaseInfo::buildChop2Map(BuildCtx & ctx, const CHqlBoundTarget & target, CHqlBoundExpr & test, unsigned start, unsigned end)
{
    BuildCtx subctx(ctx);
    
    if ((end - start) <= 3)             // (1,2,3) avg(2) cf. (2,2,3) avg(2.3)
    {
        //optimize the case where they all create the same value
        bool same = true;
        unsigned index;
        for (index=start+1; index < end; ++index)
        {
            if (queryReturn(index-1) != queryReturn(index))
            {
                same = false;
                break;
            }
        }
        
        if (same)
        {
            CompoundBuilder cb(no_or);
            for (index=start; index < end; ++index)
            {
                IHqlExpression * compare = queryCompare(index);
                IHqlExpression * cond  = createCompareExpr(no_eq, test.getTranslatedExpr(), LINK(compare));
                cb.addOperand(cond);
            }
            OwnedHqlExpr compound = cb.getCompound();
            translator.buildFilter(subctx, compound);
            translator.buildExprAssign(subctx, target, queryReturn(start));
        }
        else
        {
            IHqlStmt * stmt = NULL;
            for (index=start; index < end; ++index)
            {
                if (stmt)
                    subctx.selectElse(stmt);
                
                IHqlExpression * compare = queryCompare(index);
                OwnedHqlExpr cond  = createCompareExpr(no_eq, test.getTranslatedExpr(), LINK(compare));
                CHqlBoundExpr bound;
                translator.buildExpr(subctx, cond, bound);
                stmt = subctx.addFilter(bound.expr);
                translator.buildExprAssign(subctx, target, queryReturn(index));
            }
        }
    }
    else
    {
        unsigned mid = (start + end) / 2;
        
        IHqlExpression * compare = queryCompare(mid);
        OwnedHqlExpr cond  = createCompareExpr(no_lt, test.getTranslatedExpr(), LINK(compare));
        CHqlBoundExpr bound;
        translator.buildExpr(subctx, cond, bound);
        IHqlStmt * stmt = subctx.addFilter(bound.expr);

        buildChop2Map(subctx, target, test, start, mid);
        subctx.selectElse(stmt);
        buildChop2Map(subctx, target, test, mid, end);
    }
}

IHqlExpression * HqlCppCaseInfo::buildIndexedMap(BuildCtx & ctx, IHqlExpression * test, unsigned lower, unsigned upper)
{
    ITypeInfo * compareType = test->queryType()->queryPromotedType();
    type_t compareTypeCode = compareType->getTypeCode();

    HqlExprArray values;
    IHqlExpression * dft = queryActiveTableSelector();  // value doesn't matter as long as it will not occur
    unsigned num = (upper-lower+1);
    values.ensure(num);
    unsigned idx;
    for (idx = 0; idx < num; idx++)
        values.append(*LINK(dft));

    ForEachItemIn(idx2, pairs)
    {
        IHqlExpression & cur = pairs.item(idx2);
        IValue * value = cur.queryChild(0)->queryValue();
        unsigned replaceIndex;
        switch (compareTypeCode)
        {
        case type_int:
            replaceIndex = (int)value->getIntValue()-lower;
            break;
        case type_string:
            {
                StringBuffer temp;
                value->getStringValue(temp);
                replaceIndex = (int)(unsigned char)temp.charAt(0)-lower;
                break;
            }
        default:
            throwUnexpectedType(compareType);
        }

        IHqlExpression * mapTo = cur.queryChild(1);
        if (mapTo->getOperator() != no_constant)
            throwUnexpected();
        if (replaceIndex >= num)
            translator.reportWarning(HQLWRN_CaseCanNeverMatch, "CASE entry %d can never match the test condition", replaceIndex);
        else
            values.replace(*LINK(mapTo),replaceIndex);
    }

    //Now replace the placeholders with the default values.
    for (idx = 0; idx < num; idx++)
    {
        if (&values.item(idx) == dft)
            values.replace(*defaultValue.getLink(),idx);
    }

    // use a var string type to get better C++ generated...
    ITypeInfo * storeType = getArrayElementType(resultType);
    ITypeInfo * listType = makeArrayType(storeType, values.ordinality());
    OwnedHqlExpr lvalues = createValue(no_list, listType, values);

    CHqlBoundExpr boundTable;
    translator.buildExpr(ctx, lvalues, boundTable);
    IHqlExpression * tableIndex;
    switch (compareTypeCode)
    {
        case type_int:
            tableIndex = LINK(test);
            break;
        case type_string:
            tableIndex = createValue(no_index, makeCharType(), LINK(test), getZero());
            break;
        default:
            throwUnexpectedType(compareType);
    }

    ITypeInfo * retType = resultType;
    IHqlExpression * ret = createValue(no_index, LINK(retType), LINK(boundTable.expr), tableIndex);
    return createTranslatedOwned(ret);
}

void HqlCppCaseInfo::buildLoopChopMap(BuildCtx & ctx, const CHqlBoundTarget & target, CHqlBoundExpr & test)
{
    //Declare a table that contains all the strings...
    ITypeInfo * compareType = queryCompareType();
    type_t ctc = compareType->getTypeCode();

    OwnedHqlExpr values = createCompareList();
    CHqlBoundExpr boundTable;
    translator.buildExpr(ctx, values, boundTable);

    OwnedHqlExpr midVar = createVariable(LINK(indexType));

    if (hasLibraryChop())
    {
        ITypeInfo * tableEntryType = makeReferenceModifier(LINK(compareType));
        ITypeInfo * tableType = makePointerType(tableEntryType);
        HqlExprArray args;

        _ATOM func;
        switch (ctc)
        {
        case type_data: 
            func = searchDataTableAtom; 
            break;
        case type_varstring: 
            func = searchVStringTableAtom;
            break;
        case type_qstring:
            func = searchQStringTableAtom;
            break;
        case type_string:
            if (compareType->queryCharset()->queryName() == asciiAtom)
                func = searchStringTableAtom;
            else if (compareType->queryCharset()->queryName() == ebcdicAtom)
                func = searchEStringTableAtom;
            else
                UNIMPLEMENTED;
            break;
        case type_unicode:
            func = searchUnicodeTableAtom;
            break;
        case type_utf8:
            func = searchUtf8TableAtom;
            break;
        case type_varunicode:
            func = searchVUnicodeTableAtom;
            break;
        default:
            throwUnexpectedType(compareType);
        }
        args.append(*getSizetConstant(values->numChildren()));
        if ((ctc != type_varstring) && (ctc != type_varunicode))
            args.append(*getSizetConstant(values->queryChild(0)->queryType()->getStringLen()));
        args.append(*createValue(no_address, tableType, createValue(no_index, LINK(tableEntryType), LINK(boundTable.expr), getZero())));
        if ((ctc != type_varstring) && (ctc != type_varunicode))
            args.append(*translator.getBoundLength(test));
        args.append(*ensureIndexable(test.expr));
        if ((ctc==type_unicode) || (ctc == type_varunicode) || (ctc == type_utf8))
            args.append(*createConstant(compareType->queryLocale()->str()));

        OwnedHqlExpr call = translator.bindTranslatedFunctionCall(func, args);
        OwnedHqlExpr search = createTranslated(call);

        bool includeDefaultInResult = false;
        OwnedHqlExpr resultExpr = createResultsExpr(midVar, true, &includeDefaultInResult);

        OwnedHqlExpr simpleResult = queryCreateSimpleResultAssign(search, resultExpr);
        if (simpleResult)
            translator.buildExprAssign(ctx, target, simpleResult);
        else
        {
            ctx.addDeclare(midVar, NULL);
            translator.buildAssignToTemp(ctx, midVar, search);
            if (includeDefaultInResult)
            {
                translator.buildExprAssign(ctx, target, resultExpr);
            }
            else
            {
                OwnedHqlExpr compare = createBoolExpr(no_ne, LINK(midVar), createNotFoundValue());

                BuildCtx subctx(ctx);
                IHqlStmt * stmt = subctx.addFilter(compare);
                translator.buildExprAssign(subctx, target, resultExpr);
                subctx.selectElse(stmt);
                translator.buildExprAssign(subctx, target, defaultValue);
            }
        }
    }
    else
    {
#if 0
        //Keep this as a reminder of what was needed to fix qstrings.
        if (ctc == type_qstring)
        {
            Linked<ITypeInfo> compareType = queryCompareType();
            compareType.setown(makeArrayType(compareType.getLink()));
            table = createValue(no_typetransfer, compareType.getLink(), table);
        }
#endif

        OwnedHqlExpr resultExpr = createResultsExpr(midVar, false);
        //Now generate the code that performs the binary chop..
        ctx.addDeclare(midVar, NULL);
        OwnedHqlExpr compareVar = ctx.getTempDeclare(indexType, NULL);
        OwnedHqlExpr leftVar = ctx.getTempDeclare(indexType, NULL);
        OwnedHqlExpr rightVar = ctx.getTempDeclare(indexType, NULL);

        OwnedHqlExpr numPairs = getSizetConstant(getNumPairs());
        ctx.addAssign(leftVar, queryZero());
        ctx.addAssign(rightVar, numPairs);
        translator.buildExprAssign(ctx, target, defaultValue);

        OwnedHqlExpr loopc = createBoolExpr(no_lt, LINK(leftVar), LINK(rightVar));
        OwnedHqlExpr mid = createValue(no_div, createValue(no_add, LINK(leftVar), LINK(rightVar)), createConstant(indexType->castFrom(false, 2)));
        OwnedHqlExpr mid_p1 = createValue(no_add, LINK(indexType), LINK(midVar), createConstant(indexType->castFrom(false, 1)));
        OwnedHqlExpr curelem = createValue(no_index, LINK(compareType), boundTable.getTranslatedExpr(), createTranslated(mid_p1));
        OwnedHqlExpr test1 = createBoolExpr(no_lt, LINK(compareVar), getZero());
        OwnedHqlExpr test2 = createBoolExpr(no_gt, LINK(compareVar), getZero());

        OwnedHqlExpr order = createValue(no_order, LINK(indexType), test.getTranslatedExpr(), LINK(curelem));
        BuildCtx loopctx(ctx);
        loopctx.addLoop(loopc, NULL, true);
            translator.buildAssignToTemp(loopctx, midVar, mid);
            translator.buildAssignToTemp(loopctx, compareVar, order);

            BuildCtx subctx(loopctx);
            IHqlStmt * if1 = subctx.addFilter(test1);                                    // if (test < 0)
            translator.buildAssignToTemp(subctx, rightVar, midVar);                     //   right = mid;
            subctx.selectElse(if1);                                                                          // else
            IHqlStmt * if2 = subctx.addFilter(test2);                                    //     if (test > 0)
            translator.buildAssignToTemp(subctx, leftVar, mid_p1);                      //       left = mid + 1;
            subctx.selectElse(if2);                                                                          //     else
            //generate the default assignment...
            translator.buildExprAssign(subctx, target, resultExpr);
            subctx.addBreak();
    }
}

void HqlCppCaseInfo::buildIntegerSearchMap(BuildCtx & ctx, const CHqlBoundTarget & target, IHqlExpression * test)
{
    ITypeInfo * compareType = queryCompareType();

    HqlExprArray args;
    args.append(*createCompareList());
    args.append(*LINK(test));

    _ATOM func;
    if (compareType->isSigned())
    {
        if (compareType->getSize() > 4)
            func = searchTableInteger8Atom;
        else
            func = searchTableInteger4Atom;
    }
    else
    {
        if (compareType->getSize() > 4)
            func = searchTableUInteger8Atom;
        else
            func = searchTableUInteger4Atom;
    }

    OwnedHqlExpr search = translator.bindFunctionCall(func, args);

    OwnedHqlExpr midVar = createVariable(LINK(indexType));
    bool includeDefaultInResult = false;
    OwnedHqlExpr resultExpr = createResultsExpr(midVar, true, &includeDefaultInResult);

    OwnedHqlExpr simpleResult = queryCreateSimpleResultAssign(search, resultExpr);
    if (simpleResult)
        translator.buildExprAssign(ctx, target, simpleResult);
    else
    {
        ctx.addDeclare(midVar, NULL);
        translator.buildAssignToTemp(ctx, midVar, search);
        if (includeDefaultInResult)
        {
            translator.buildExprAssign(ctx, target, resultExpr);
        }
        else
        {
            OwnedHqlExpr compare = createBoolExpr(no_ne, LINK(midVar), createNotFoundValue());

            BuildCtx subctx(ctx);
            IHqlStmt * stmt = subctx.addFilter(compare);
            translator.buildExprAssign(subctx, target, resultExpr);
            subctx.selectElse(stmt);
            translator.buildExprAssign(subctx, target, defaultValue);
        }
    }
}

void HqlCppCaseInfo::buildSwitchCondition(BuildCtx & ctx, CHqlBoundExpr & bound)
{
    OwnedHqlExpr simpleCond = complexCompare ? getSimplifyCompareArg(cond) : LINK(cond);
    translator.buildCachedExpr(ctx, simpleCond, bound);
}

void HqlCppCaseInfo::buildSwitchMap(BuildCtx & ctx, const CHqlBoundTarget * target, IHqlExpression * test)
{
    bool isCharCompare = (test->queryType()->getTypeCode() == type_string);
    
    LinkedHqlExpr cond = test;
    if (isCharCompare)
        cond.setown(createValue(no_index, makeCharType(), LINK(test), getZero()));
    
    BuildCtx subctx(ctx);
    IHqlStmt * stmt = subctx.addSwitch(cond);
    
    // are all the comparisons against constant values?  If so we optimize it...
    unsigned sameCount = 0;
    ForEachItemIn(idx, pairs)
    {
        IHqlExpression & cur = pairs.item(idx);
        LinkedHqlExpr compare = cur.queryChild(0);
        IHqlExpression * branchValue = cur.queryChild(1);

        if (isCharCompare)
        {
            OwnedITypeInfo charType = makeCharType();
            IValue * cur = compare->queryValue();
            IValue * next = cur->castTo(charType);
            compare.setown(createConstant(next));
        }
        
        bool same = false;
        bool skip = false;
        if (idx != pairs.ordinality()-1)
        {
            IHqlExpression & next = pairs.item(idx+1);
            if (next.queryChild(1) == branchValue)
                same = true;
            //if save item is included twice, remove one so no error
            //from the case statement
            if (next.queryChild(0) == cur.queryChild(0))
            {
                skip = true;
#ifdef _DEBUG
                throwUnexpected();      // should have been removed as a duplicate 
#endif
            }
        }
        if (sameCount >= MAX_NUM_NOBREAK_CASE)
            same = false;

        if (!skip)
        {
            subctx.addCase(stmt, compare);
            
            // common up case labels that produce the same result
            if (!same)
            {
                sameCount = 1;
                if (target)
                    translator.buildExprAssign(subctx, *target, branchValue);
                else
                    translator.buildReturn(subctx, branchValue);
            }
            else
                sameCount++;
        }
    }
    
    if (target)
    {
        subctx.addDefault(stmt);
        translator.buildExprAssign(subctx, *target, defaultValue);
    }
    else
        translator.buildReturn(ctx, defaultValue);
}


void HqlCppCaseInfo::buildGeneralAssign(BuildCtx & ctx, const CHqlBoundTarget & target)
{
    unsigned max = pairs.ordinality();

    Owned<BuildCtx> subctx = new BuildCtx(ctx);
    CHqlBoundExpr pureCond;
    if (cond.get())
        translator.buildCachedExpr(*subctx, cond, pureCond);
    
    OwnedHqlExpr testMore;

    if (max > MAX_NESTED_CASES)
    {
        //Too many nested blocks cause the compiler indigestion...
        Owned<ITypeInfo> t = makeBoolType();
        testMore.setown(ctx.getTempDeclare(t, queryBoolExpr(false)));
    }

    for (unsigned idx = 0; idx < max; idx++)
    {
        IHqlExpression & cur = pairs.item(idx);
        IHqlExpression * curtest = cur.queryChild(0);
        IHqlExpression * curvalue = cur.queryChild(1);

        OwnedHqlExpr compare;
        if (!pureCond.expr)
            compare.setown(ensureExprType(curtest, queryBoolType()));
        else
            compare.setown(createBoolExpr(no_eq, pureCond.getTranslatedExpr(), LINK(curtest)));

        if (idx && ((idx % MAX_NESTED_CASES) == 0))
        {
            translator.buildAssignToTemp(*subctx,testMore,queryBoolExpr(true));
            subctx.setown(new BuildCtx(ctx));
            subctx->addFilter(testMore);
            translator.buildAssignToTemp(*subctx,testMore,queryBoolExpr(false));
        }

        IHqlStmt * test = translator.buildFilterViaExpr(*subctx, compare);
        translator.buildExprAssign(*subctx, target, curvalue);
        subctx->selectElse(test);
    }

    translator.buildExprAssign(*subctx, target, defaultValue);
}

void HqlCppCaseInfo::buildGeneralReturn(BuildCtx & ctx)
{
    unsigned max = pairs.ordinality();

    CHqlBoundExpr pureCond;
    if (cond.get())
        translator.buildCachedExpr(ctx, cond, pureCond);
    
    for (unsigned idx = 0; idx < max; idx++)
    {
        IHqlExpression & cur = pairs.item(idx);
        IHqlExpression * curtest = cur.queryChild(0);
        IHqlExpression * curvalue = cur.queryChild(1);

        OwnedHqlExpr compare;
        if (!pureCond.expr)
            compare.setown(ensureExprType(curtest, queryBoolType()));
        else
            compare.setown(createBoolExpr(no_eq, pureCond.getTranslatedExpr(), LINK(curtest)));

        BuildCtx subctx(ctx);
        translator.buildFilter(subctx, compare);
        translator.buildReturn(subctx, curvalue);
    }

    translator.buildReturn(ctx, defaultValue);
}

bool HqlCppCaseInfo::okToAlwaysEvaluateDefault()
{
    return defaultValue->isPure();
}

ITypeInfo * HqlCppCaseInfo::queryCompareType()
{
    return cond->queryType()->queryPromotedType();
}

IHqlExpression * HqlCppCaseInfo::createCompareList()
{
    //NB: All cases need to have the same type because they are stored in a table
    Linked<ITypeInfo> promoted = pairs.item(0).queryChild(0)->queryType();
    unsigned max = pairs.ordinality();
    for (unsigned idx1 = 1; idx1 < max; idx1++)
    {
        ITypeInfo * type = pairs.item(idx1).queryChild(0)->queryType();
        promoted.setown(getPromotedECLType(promoted, type));
    }

    HqlExprArray values;
    values.ensure(pairs.ordinality());
    ForEachItemIn(idx, pairs)
    {
        IHqlExpression & pair = pairs.item(idx);
        IHqlExpression * compare = pair.queryChild(0);
        values.append(*ensureExprType(compare, promoted));
    }

    Linked<ITypeInfo> compareType = queryCompareType();
    switch (compareType->getTypeCode())
    {
    case type_string:
    case type_data:
    case type_varstring:
    case type_qstring:
    case type_utf8:
        compareType.setown(makePointerType(makeCharType(false)));
        break;
    case type_unicode:
    case type_varunicode:
        compareType.setown(makePointerType(makeClassType("UChar")));
        break;
    }
    return createValue(no_list, makeArrayType(compareType.getLink()), values);
}


IHqlExpression * HqlCppCaseInfo::createResultsExpr(IHqlExpression * matchVar, bool canIncludeDefault, bool * includedDefault)
{
    if (includedDefault)
        *includedDefault = false;

    //Look at all the return results and see what relation we can create
    //This can generate one of the following:
    //1. A single value.
    //2. A function of the result. e.g., IN...
    //3. A lookup in another table. [ all values are constant ]
    //4. A nested map statement
    bool areSame = true;
    bool areLinear = true;
    bool areConstant = true;
    __int64 linearStart = 0;
    __int64 linearMultiple = 1;
    ITypeInfo * retType = resultType;

    switch (retType->getTypeCode())
    {
    case type_int:
    case type_boolean:
        break;
    case type_string:
    case type_data:
//      areConstant = false;        // a temporary hack to stop incorrect table being generated.
        areLinear = false;
        break;
    default:
        areLinear = false;
        break;
    }

    IHqlExpression * prevValue = NULL;
    HqlExprArray values;
    values.ensure(pairs.ordinality());
    ForEachItemIn(idx, pairs)
    {
        IHqlExpression & pair = pairs.item(idx);
        IHqlExpression * value = pair.queryChild(1);
        IValue * cvalue = value->queryValue();

        if (cvalue)
        {
            if (areLinear)
            {
                __int64 val = cvalue->getIntValue();
                if (idx == 0)
                    linearStart = val;
                else if (idx == 1)
                    linearMultiple = (val - linearStart);
                else if (val != linearStart + idx * linearMultiple)
                    areLinear = false;
            }
        }
        else
        {
            areConstant = false;
            areLinear = false;
        }
        
        if (idx > 0)
        {
            if (areSame && (prevValue != value))
                areSame = false;
        }

        values.append(*ensureExprType(value, resultType));
        prevValue = value;
    }

    if (areSame)
        return LINK(prevValue);

    if (areLinear)
    {
        IHqlExpression * ret = ensureExprType(matchVar, resultType);
        if (linearMultiple != 1)
            ret = createValue(no_mul, LINK(resultType), ret, createConstant(resultType->castFrom(true, linearMultiple)));
        if (linearStart != 0)
            ret = createValue(no_add, LINK(resultType), ret, createConstant(resultType->castFrom(true, linearStart)));
        return ret;
    }

    unsigned firstMatchEntry = 0;
    if (canIncludeDefault)
    {
        //If all the values are constant, then can add the default as an extra 0th entry, because -1 will be the index for the default
        if (areConstant && defaultValue->isConstant() && defaultValue->queryType() == values.item(0).queryType())
        {
            firstMatchEntry = 1;
            values.add(*LINK(defaultValue), 0);
            *includedDefault = true;
        }
    }

    // easy way to create a value list...
    ITypeInfo * storeType = getArrayElementType(retType);
    OwnedHqlExpr newlist = createValue(no_list, makeSetType(storeType), values);
    if (areConstant)
    {
        IHqlExpression * index = adjustValue(matchVar, 1+firstMatchEntry);
        return createValue(no_index, LINK(retType), LINK(newlist), index, createAttribute(noBoundCheckAtom));
    }

    //Need to generate a case (switch integer case 1: ..... )
    HqlExprArray choosePairs;
    cvtChooseListToPairs(choosePairs, newlist, 0);

    IHqlExpression * caseExpr = createOpenValue(no_case, LINK(retType));
    caseExpr->addOperand(LINK(matchVar));
    ForEachItemIn(idx2, choosePairs)
        caseExpr->addOperand(&choosePairs.item(idx2));
    choosePairs.kill(true);
    caseExpr->addOperand(LINK(defaultValue));
    return caseExpr->closeExpr();
}


void HqlCppCaseInfo::generateCompareVar(BuildCtx & ctx, IHqlExpression * target, CHqlBoundExpr & test, IHqlExpression * other)
{
    OwnedHqlExpr compare = createValue(no_order, test.getTranslatedExpr(), LINK(other));
    translator.buildAssignToTemp(ctx, target, compare);
}
    
unsigned HqlCppCaseInfo::getNumPairs()
{
    return pairs.ordinality();
}

bool HqlCppCaseInfo::hasLibraryChop()
{
    ITypeInfo * compareType = queryCompareType();
    type_t ctc = compareType->getTypeCode();

    return ((ctc == type_string) || (ctc == type_data) || (ctc == type_varstring) || (ctc == type_qstring) || (ctc == type_unicode) || (ctc == type_varunicode) || (ctc == type_utf8));
}

void HqlCppCaseInfo::processBranches()
{
    sortPairs();
    removeDuplicates();
    promoteTypes();
}

void HqlCppCaseInfo::promoteTypes()
{
    Owned<ITypeInfo> promoted = pairs.item(0).queryChild(0)->getType();

    unsigned max = pairs.ordinality();
    for (unsigned idx1 = 1; idx1 < max; idx1++)
    {
        ITypeInfo * type = pairs.item(idx1).queryChild(0)->queryType();

        if (isStringType(promoted) && isStringType(type))
        {
            if (promoted->getStringLen() != type->getStringLen())
            {
                promoted.setown(::getPromotedECLType(promoted, type));
                promoted.setown(getStretchedType(UNKNOWN_LENGTH, promoted));
            }
        }

        promoted.setown(::getPromotedECLType(promoted, type));
    }

    if (isStringType(promoted))
        promoted.setown(getStretchedType(UNKNOWN_LENGTH, promoted));
    ITypeInfo * testType = queryCompareType();
    if ((testType->queryCharset() != promoted->queryCharset()) || (testType->queryLocale() != promoted->queryLocale()))
        cond.setown(ensureExprType(cond, promoted));
}


bool HqlCppCaseInfo::canBuildArrayLookup(const CHqlBoundExpr & test)
{
    ITypeInfo * condType = test.queryType()->queryPromotedType();

    //MORE: Also support this for high density tables that don't start at 0... - checking upper and lower bounds
    unsigned bitSize = condType->getBitSize();
    if (constantValues && (bitSize && (bitSize <= 8) && !condType->isSigned()))
    {
        unsigned limit = (1 << bitSize);
        //use case if enough items, or above a certain density...
        if (pairs.ordinality() * 100 >= limit * SWITCH_TABLE_DENSITY_THRESHOLD)
        {
            if ((condType->getTypeCode() == type_int) || (condType->getTypeCode() == type_string))
                return true;
        }
    }
    return false;
}

bool HqlCppCaseInfo::queryBuildArrayLookup(BuildCtx & ctx, const CHqlBoundTarget & target, const CHqlBoundExpr & test)
{
    if (canBuildArrayLookup(test))
    {
        //MORE: Also support this for high density tables that don't start at 0... - checking upper and lower bounds
        ITypeInfo * condType = test.queryType()->queryPromotedType();
        unsigned bitSize = condType->getBitSize();
        unsigned limit = (1 << bitSize);

        BuildCtx subctx(ctx);
        OwnedHqlExpr ret = buildIndexedMap(subctx, test.expr, 0, limit-1);
        translator.buildExprAssign(ctx, target, ret);
        return true;
    }
    return false;
}

void HqlCppCaseInfo::removeDuplicates()
{
    unsigned num = pairs.ordinality();
    if (num > 1)
    {
        num--;
        while (num--)
        {
            IHqlExpression & cur = pairs.item(num);
            IHqlExpression & next = pairs.item(num+1);

            if (cur.queryChild(0) == next.queryChild(0))
            {
                if (cur.queryChild(1) == next.queryChild(1))
                    pairs.remove(num+1);
                else
                {
                    // we need to keep the first in the original list....  Horrid, but it works...
                    unsigned off1 = originalPairs.find(cur);
                    unsigned off2 = originalPairs.find(next);
                    assertex(off1 != NotFound && off2 !=  NotFound);
                    if (off1 < off2)
                        pairs.remove(num+1);
                    else
                        pairs.remove(num);
                }
            }
        }
    }
}


IHqlExpression * HqlCppCaseInfo::queryCreateSimpleResultAssign(IHqlExpression * search, IHqlExpression * resultExpr)
{
    IHqlExpression * trueExpr = queryBoolExpr(true);
    IHqlExpression * falseExpr = queryBoolExpr(false);
    if (resultExpr == trueExpr && defaultValue == falseExpr)
        return createBoolExpr(no_ne, LINK(search), createNotFoundValue());
    if (resultExpr == falseExpr && defaultValue == trueExpr)
        return createBoolExpr(no_eq, LINK(search), createNotFoundValue());
    return NULL;
}

IHqlExpression * HqlCppCaseInfo::queryCompare(unsigned index)
{
    return pairs.item(index).queryChild(0);
}


IHqlExpression * HqlCppCaseInfo::queryReturn(unsigned index)
{
    return pairs.item(index).queryChild(1);
}
        

void HqlCppCaseInfo::setCond(IHqlExpression * expr)
{
    cond.set(expr);
    if (isCompare3Valued(expr->queryType()))
        complexCompare = true;
}


void HqlCppCaseInfo::setDefault(IHqlExpression * expr)
{
    defaultValue.set(expr);
}

void HqlCppCaseInfo::sortPairs()
{
    appendArray(originalPairs, pairs);
    pairs.sort(comparePair);
}

void HqlCppCaseInfo::updateResultType(IHqlExpression * expr)
{
    ITypeInfo * curResultType = expr->queryType();
    if (resultType)
        resultType.setown(::getPromotedECLType(resultType, curResultType));
    else
        resultType.set(curResultType);
}