rangecheck.cpp

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

//

#include "jitpch.h"
#include "rangecheck.h"

// Max stack depth (path length) in walking the UD chain.
static const int MAX_SEARCH_DEPTH = 100;

// Max nodes to visit in the UD chain for the current method being compiled.
static const int MAX_VISIT_BUDGET = 8192;

// RangeCheck constructor.
RangeCheck::RangeCheck(Compiler* pCompiler)
    : m_pOverflowMap(nullptr)
    , m_pRangeMap(nullptr)
    , m_pSearchPath(nullptr)
#ifdef DEBUG
    , m_fMappedDefs(false)
    , m_pDefTable(nullptr)
#endif
    , m_pCompiler(pCompiler)
    , m_alloc(pCompiler->getAllocator(CMK_RangeCheck))
    , m_nVisitBudget(MAX_VISIT_BUDGET)
{
}

bool RangeCheck::IsOverBudget()
{
    return (m_nVisitBudget <= 0);
}

// Get the range map in which computed ranges are cached.
RangeCheck::RangeMap* RangeCheck::GetRangeMap()
{
    if (m_pRangeMap == nullptr)
    {
        m_pRangeMap = new (m_alloc) RangeMap(m_alloc);
    }
    return m_pRangeMap;
}

// Get the overflow map in which computed overflows are cached.
RangeCheck::OverflowMap* RangeCheck::GetOverflowMap()
{
    if (m_pOverflowMap == nullptr)
    {
        m_pOverflowMap = new (m_alloc) OverflowMap(m_alloc);
    }
    return m_pOverflowMap;
}

// Get the length of the array vn, if it is new.
int RangeCheck::GetArrLength(ValueNum vn)
{
    ValueNum arrRefVN = m_pCompiler->vnStore->GetArrForLenVn(vn);
    return m_pCompiler->vnStore->GetNewArrSize(arrRefVN);
}

// Check if the computed range is within bounds.
bool RangeCheck::BetweenBounds(Range& range, int lower, GenTree* upper)
{
#ifdef DEBUG
    if (m_pCompiler->verbose)
    {
        printf("%s BetweenBounds <%d, ", range.ToString(m_pCompiler->getAllocatorDebugOnly()), lower);
        Compiler::printTreeID(upper);
        printf(">\n");
    }
#endif // DEBUG

    ValueNumStore* vnStore = m_pCompiler->vnStore;

    // Get the VN for the upper limit.
    ValueNum uLimitVN = vnStore->VNConservativeNormalValue(upper->gtVNPair);

#ifdef DEBUG
    JITDUMP(FMT_VN " upper bound is: ", uLimitVN);
    if (m_pCompiler->verbose)
    {
        vnStore->vnDump(m_pCompiler, uLimitVN);
    }
    JITDUMP("\n");
#endif

    int arrSize = 0;

    if (vnStore->IsVNConstant(uLimitVN))
    {
        ssize_t  constVal  = -1;
        unsigned iconFlags = 0;

        if (m_pCompiler->optIsTreeKnownIntValue(true, upper, &constVal, &iconFlags))
        {
            arrSize = (int)constVal;
        }
    }
    else if (vnStore->IsVNArrLen(uLimitVN))
    {
        // Get the array reference from the length.
        ValueNum arrRefVN = vnStore->GetArrForLenVn(uLimitVN);
        // Check if array size can be obtained.
        arrSize = vnStore->GetNewArrSize(arrRefVN);
    }
    else if (!vnStore->IsVNCheckedBound(uLimitVN))
    {
        // If the upper limit is not length, then bail.
        return false;
    }

    JITDUMP("Array size is: %d\n", arrSize);

    // Upper limit: len + ucns (upper limit constant).
    if (range.UpperLimit().IsBinOpArray())
    {
        if (range.UpperLimit().vn != uLimitVN)
        {
            return false;
        }

        int ucns = range.UpperLimit().GetConstant();

        // Upper limit: Len + [0..n]
        if (ucns >= 0)
        {
            return false;
        }

        // Since upper limit is bounded by the array, return true if lower bound is good.
        if (range.LowerLimit().IsConstant() && range.LowerLimit().GetConstant() >= 0)
        {
            return true;
        }

        // Check if we have the array size allocated by new.
        if (arrSize <= 0)
        {
            return false;
        }

        // At this point,
        // upper limit = len + ucns. ucns < 0
        // lower limit = len + lcns.
        if (range.LowerLimit().IsBinOpArray())
        {
            int lcns = range.LowerLimit().GetConstant();
            if (lcns >= 0 || -lcns > arrSize)
            {
                return false;
            }
            return (range.LowerLimit().vn == uLimitVN && lcns <= ucns);
        }
    }
    // If upper limit is constant
    else if (range.UpperLimit().IsConstant())
    {
        if (arrSize <= 0)
        {
            return false;
        }
        int ucns = range.UpperLimit().GetConstant();
        if (ucns >= arrSize)
        {
            return false;
        }
        if (range.LowerLimit().IsConstant())
        {
            int lcns = range.LowerLimit().GetConstant();
            // Make sure lcns < ucns which is already less than arrSize.
            return (lcns >= 0 && lcns <= ucns);
        }
        if (range.LowerLimit().IsBinOpArray())
        {
            int lcns = range.LowerLimit().GetConstant();
            // len + lcns, make sure we don't subtract too much from len.
            if (lcns >= 0 || -lcns > arrSize)
            {
                return false;
            }
            // Make sure a.len + lcns <= ucns.
            return (range.LowerLimit().vn == uLimitVN && (arrSize + lcns) <= ucns);
        }
    }

    return false;
}

void RangeCheck::OptimizeRangeCheck(BasicBlock* block, GenTreeStmt* stmt, GenTree* treeParent)
{
    // Check if we are dealing with a bounds check node.
    if (treeParent->OperGet() != GT_COMMA)
    {
        return;
    }

    // If we are not looking at array bounds check, bail.
    GenTree* tree = treeParent->gtOp.gtOp1;
    if (!tree->OperIsBoundsCheck())
    {
        return;
    }

    GenTreeBoundsChk* bndsChk = tree->AsBoundsChk();
    m_pCurBndsChk             = bndsChk;
    GenTree* treeIndex        = bndsChk->gtIndex;

    // Take care of constant index first, like a[2], for example.
    ValueNum idxVn    = m_pCompiler->vnStore->VNConservativeNormalValue(treeIndex->gtVNPair);
    ValueNum arrLenVn = m_pCompiler->vnStore->VNConservativeNormalValue(bndsChk->gtArrLen->gtVNPair);
    int      arrSize  = 0;

    if (m_pCompiler->vnStore->IsVNConstant(arrLenVn))
    {
        ssize_t  constVal  = -1;
        unsigned iconFlags = 0;

        if (m_pCompiler->optIsTreeKnownIntValue(true, bndsChk->gtArrLen, &constVal, &iconFlags))
        {
            arrSize = (int)constVal;
        }
    }
    else
#ifdef FEATURE_SIMD
        if (tree->gtOper != GT_SIMD_CHK
#ifdef FEATURE_HW_INTRINSICS
            && tree->gtOper != GT_HW_INTRINSIC_CHK
#endif // FEATURE_HW_INTRINSICS
            )
#endif // FEATURE_SIMD
    {
        arrSize = GetArrLength(arrLenVn);
    }

    JITDUMP("ArrSize for lengthVN:%03X = %d\n", arrLenVn, arrSize);
    if (m_pCompiler->vnStore->IsVNConstant(idxVn) && (arrSize > 0))
    {
        ssize_t  idxVal    = -1;
        unsigned iconFlags = 0;
        if (!m_pCompiler->optIsTreeKnownIntValue(true, treeIndex, &idxVal, &iconFlags))
        {
            return;
        }

        JITDUMP("[RangeCheck::OptimizeRangeCheck] Is index %d in <0, arrLenVn " FMT_VN " sz:%d>.\n", idxVal, arrLenVn,
                arrSize);
        if ((idxVal < arrSize) && (idxVal >= 0))
        {
            JITDUMP("Removing range check\n");
            m_pCompiler->optRemoveRangeCheck(treeParent, stmt);
            return;
        }
    }

    GetRangeMap()->RemoveAll();
    GetOverflowMap()->RemoveAll();
    m_pSearchPath = new (m_alloc) SearchPath(m_alloc);

    // Get the range for this index.
    Range range = GetRange(block, treeIndex, false DEBUGARG(0));

    // If upper or lower limit is found to be unknown (top), or it was found to
    // be unknown because of over budget or a deep search, then return early.
    if (range.UpperLimit().IsUnknown() || range.LowerLimit().IsUnknown())
    {
        // Note: If we had stack depth too deep in the GetRange call, we'd be
        // too deep even in the DoesOverflow call. So return early.
        return;
    }

    if (DoesOverflow(block, treeIndex))
    {
        JITDUMP("Method determined to overflow.\n");
        return;
    }

    JITDUMP("Range value %s\n", range.ToString(m_pCompiler->getAllocatorDebugOnly()));
    m_pSearchPath->RemoveAll();
    Widen(block, treeIndex, &range);

    // If upper or lower limit is unknown, then return.
    if (range.UpperLimit().IsUnknown() || range.LowerLimit().IsUnknown())
    {
        return;
    }

    // Is the range between the lower and upper bound values.
    if (BetweenBounds(range, 0, bndsChk->gtArrLen))
    {
        JITDUMP("[RangeCheck::OptimizeRangeCheck] Between bounds\n");
        m_pCompiler->optRemoveRangeCheck(treeParent, stmt);
    }
    return;
}

void RangeCheck::Widen(BasicBlock* block, GenTree* tree, Range* pRange)
{
#ifdef DEBUG
    if (m_pCompiler->verbose)
    {
        printf("[RangeCheck::Widen] " FMT_BB ", \n", block->bbNum);
        Compiler::printTreeID(tree);
        printf("\n");
    }
#endif // DEBUG

    Range& range = *pRange;

    // Try to deduce the lower bound, if it is not known already.
    if (range.LowerLimit().IsDependent() || range.LowerLimit().IsUnknown())
    {
        // To determine the lower bound, ask if the loop increases monotonically.
        bool increasing = IsMonotonicallyIncreasing(tree, false);
        JITDUMP("IsMonotonicallyIncreasing %d", increasing);
        if (increasing)
        {
            GetRangeMap()->RemoveAll();
            *pRange = GetRange(block, tree, true DEBUGARG(0));
        }
    }
}

bool RangeCheck::IsBinOpMonotonicallyIncreasing(GenTreeOp* binop)
{
    assert(binop->OperIs(GT_ADD));

    GenTree* op1 = binop->gtGetOp1();
    GenTree* op2 = binop->gtGetOp2();

    JITDUMP("[RangeCheck::IsBinOpMonotonicallyIncreasing] [%06d], [%06d]\n", Compiler::dspTreeID(op1),
            Compiler::dspTreeID(op2));
    // Check if we have a var + const.
    if (op2->OperGet() == GT_LCL_VAR)
    {
        jitstd::swap(op1, op2);
    }
    if (op1->OperGet() != GT_LCL_VAR)
    {
        JITDUMP("Not monotonic because op1 is not lclVar.\n");
        return false;
    }
    switch (op2->OperGet())
    {
        case GT_LCL_VAR:
            // When adding two local variables, we also must ensure that any constant is non-negative.
            return IsMonotonicallyIncreasing(op1, true) && IsMonotonicallyIncreasing(op2, true);

        case GT_CNS_INT:
            return (op2->AsIntConCommon()->IconValue() >= 0) && IsMonotonicallyIncreasing(op1, false);

        default:
            JITDUMP("Not monotonic because expression is not recognized.\n");
            return false;
    }
}

// The parameter rejectNegativeConst is true when we are adding two local vars (see above)
bool RangeCheck::IsMonotonicallyIncreasing(GenTree* expr, bool rejectNegativeConst)
{
    JITDUMP("[RangeCheck::IsMonotonicallyIncreasing] [%06d]\n", Compiler::dspTreeID(expr));

    // Add hashtable entry for expr.
    bool alreadyPresent = !m_pSearchPath->Set(expr, nullptr, SearchPath::Overwrite);
    if (alreadyPresent)
    {
        return true;
    }

    // Remove hashtable entry for expr when we exit the present scope.
    auto                                         code = [this, expr] { m_pSearchPath->Remove(expr); };
    jitstd::utility::scoped_code<decltype(code)> finally(code);

    if (m_pSearchPath->GetCount() > MAX_SEARCH_DEPTH)
    {
        return false;
    }

    // If expr is constant, then it is not part of the dependency
    // loop which has to increase monotonically.
    ValueNum vn = expr->gtVNPair.GetConservative();
    if (m_pCompiler->vnStore->IsVNInt32Constant(vn))
    {
        if (rejectNegativeConst)
        {
            int cons = m_pCompiler->vnStore->ConstantValue<int>(vn);
            return (cons >= 0);
        }
        else
        {
            return true;
        }
    }
    // If the rhs expr is local, then try to find the def of the local.
    else if (expr->IsLocal())
    {
        BasicBlock* asgBlock;
        GenTreeOp*  asg = GetSsaDefAsg(expr->AsLclVarCommon(), &asgBlock);
        return (asg != nullptr) && IsMonotonicallyIncreasing(asg->gtGetOp2(), rejectNegativeConst);
    }
    else if (expr->OperGet() == GT_ADD)
    {
        return IsBinOpMonotonicallyIncreasing(expr->AsOp());
    }
    else if (expr->OperGet() == GT_PHI)
    {
        for (GenTreeArgList* args = expr->gtOp.gtOp1->AsArgList(); args != nullptr; args = args->Rest())
        {
            // If the arg is already in the path, skip.
            if (m_pSearchPath->Lookup(args->Current()))
            {
                continue;
            }
            if (!IsMonotonicallyIncreasing(args->Current(), rejectNegativeConst))
            {
                JITDUMP("Phi argument not monotonic\n");
                return false;
            }
        }
        return true;
    }
    JITDUMP("Unknown tree type\n");
    return false;
}

// Given a lclvar use, try to find the lclvar's defining assignment and its containing block.
GenTreeOp* RangeCheck::GetSsaDefAsg(GenTreeLclVarCommon* lclUse, BasicBlock** asgBlock)
{
    unsigned ssaNum = lclUse->GetSsaNum();

    if (ssaNum == SsaConfig::RESERVED_SSA_NUM)
    {
        return nullptr;
    }

    LclSsaVarDsc* ssaData = m_pCompiler->lvaTable[lclUse->GetLclNum()].GetPerSsaData(ssaNum);
    GenTree*      lclDef  = ssaData->m_defLoc.m_tree;

    if (lclDef == nullptr)
    {
        return nullptr;
    }

    // We have the def node but we also need the assignment node to get its source.
    // gtGetParent can be used to get the assignment node but it's rather expensive
    // and not strictly necessary here, there shouldn't be any other node between
    // the assignment node and its destination node.
    GenTree* asg = lclDef->gtNext;

    if (!asg->OperIs(GT_ASG) || (asg->gtGetOp1() != lclDef))
    {
        return nullptr;
    }

#ifdef DEBUG
    Location* loc = GetDef(lclUse);
    assert(loc->parent == asg);
    assert(loc->block == ssaData->m_defLoc.m_blk);
#endif

    *asgBlock = ssaData->m_defLoc.m_blk;
    return asg->AsOp();
}

#ifdef DEBUG
UINT64 RangeCheck::HashCode(unsigned lclNum, unsigned ssaNum)
{
    assert(ssaNum != SsaConfig::RESERVED_SSA_NUM);
    return UINT64(lclNum) << 32 | ssaNum;
}

// Get the def location of a given variable.
RangeCheck::Location* RangeCheck::GetDef(unsigned lclNum, unsigned ssaNum)
{
    Location* loc = nullptr;
    if (ssaNum == SsaConfig::RESERVED_SSA_NUM)
    {
        return nullptr;
    }
    if (!m_fMappedDefs)
    {
        MapMethodDefs();
    }
    // No defs.
    if (m_pDefTable == nullptr)
    {
        return nullptr;
    }
    m_pDefTable->Lookup(HashCode(lclNum, ssaNum), &loc);
    return loc;
}

RangeCheck::Location* RangeCheck::GetDef(GenTreeLclVarCommon* lcl)
{
    return GetDef(lcl->GetLclNum(), lcl->GetSsaNum());
}

// Add the def location to the hash table.
void RangeCheck::SetDef(UINT64 hash, Location* loc)
{
    if (m_pDefTable == nullptr)
    {
        m_pDefTable = new (m_alloc) VarToLocMap(m_alloc);
    }
#ifdef DEBUG
    Location* loc2;
    if (m_pDefTable->Lookup(hash, &loc2))
    {
        JITDUMP("Already have " FMT_BB ", [%06d], [%06d] for hash => %0I64X", loc2->block->bbNum,
                Compiler::dspTreeID(loc2->stmt), Compiler::dspTreeID(loc2->tree), hash);
        assert(false);
    }
#endif
    m_pDefTable->Set(hash, loc);
}
#endif

// Merge assertions on the edge flowing into the block about a variable.
void RangeCheck::MergeEdgeAssertions(GenTreeLclVarCommon* lcl, ASSERT_VALARG_TP assertions, Range* pRange)
{
    if (BitVecOps::IsEmpty(m_pCompiler->apTraits, assertions))
    {
        return;
    }

    if (lcl->gtSsaNum == SsaConfig::RESERVED_SSA_NUM)
    {
        return;
    }
    // Walk through the "assertions" to check if the apply.
    BitVecOps::Iter iter(m_pCompiler->apTraits, assertions);
    unsigned        index = 0;
    while (iter.NextElem(&index))
    {
        AssertionIndex assertionIndex = GetAssertionIndex(index);

        Compiler::AssertionDsc* curAssertion = m_pCompiler->optGetAssertion(assertionIndex);

        Limit      limit(Limit::keUndef);
        genTreeOps cmpOper = GT_NONE;

        LclSsaVarDsc* ssaData     = m_pCompiler->lvaTable[lcl->gtLclNum].GetPerSsaData(lcl->gtSsaNum);
        ValueNum      normalLclVN = m_pCompiler->vnStore->VNConservativeNormalValue(ssaData->m_vnPair);

        // Current assertion is of the form (i < len - cns) != 0
        if (curAssertion->IsCheckedBoundArithBound())
        {
            ValueNumStore::CompareCheckedBoundArithInfo info;

            // Get i, len, cns and < as "info."
            m_pCompiler->vnStore->GetCompareCheckedBoundArithInfo(curAssertion->op1.vn, &info);

            // If we don't have the same variable we are comparing against, bail.
            if (normalLclVN != info.cmpOp)
            {
                continue;
            }

            if ((info.arrOper != GT_ADD) && (info.arrOper != GT_SUB))
            {
                continue;
            }

            // If the operand that operates on the bound is not constant, then done.
            if (!m_pCompiler->vnStore->IsVNInt32Constant(info.arrOp))
            {
                continue;
            }

            int cons = m_pCompiler->vnStore->ConstantValue<int>(info.arrOp);
            limit    = Limit(Limit::keBinOpArray, info.vnBound, info.arrOper == GT_SUB ? -cons : cons);
            cmpOper  = (genTreeOps)info.cmpOper;
        }
        // Current assertion is of the form (i < len) != 0
        else if (curAssertion->IsCheckedBoundBound())
        {
            ValueNumStore::CompareCheckedBoundArithInfo info;

            // Get the info as "i", "<" and "len"
            m_pCompiler->vnStore->GetCompareCheckedBound(curAssertion->op1.vn, &info);

            // If we don't have the same variable we are comparing against, bail.
            if (normalLclVN != info.cmpOp)
            {
                continue;
            }

            limit   = Limit(Limit::keBinOpArray, info.vnBound, 0);
            cmpOper = (genTreeOps)info.cmpOper;
        }
        // Current assertion is of the form (i < 100) != 0
        else if (curAssertion->IsConstantBound())
        {
            ValueNumStore::ConstantBoundInfo info;

            // Get the info as "i", "<" and "100"
            m_pCompiler->vnStore->GetConstantBoundInfo(curAssertion->op1.vn, &info);

            // If we don't have the same variable we are comparing against, bail.
            if (normalLclVN != info.cmpOpVN)
            {
                continue;
            }

            limit   = Limit(Limit::keConstant, info.constVal);
            cmpOper = (genTreeOps)info.cmpOper;
        }
        // Current assertion is not supported, ignore it
        else
        {
            continue;
        }

        assert(limit.IsBinOpArray() || limit.IsConstant());

        // Make sure the assertion is of the form != 0 or == 0.
        if (curAssertion->op2.vn != m_pCompiler->vnStore->VNZeroForType(TYP_INT))
        {
            continue;
        }
#ifdef DEBUG
        if (m_pCompiler->verbose)
        {
            m_pCompiler->optPrintAssertion(curAssertion, assertionIndex);
        }
#endif

        ValueNum arrLenVN = m_pCompiler->vnStore->VNConservativeNormalValue(m_pCurBndsChk->gtArrLen->gtVNPair);

        if (m_pCompiler->vnStore->IsVNConstant(arrLenVN))
        {
            // Set arrLenVN to NoVN; this will make it match the "vn" recorded on
            // constant limits (where we explicitly track the constant and don't
            // redundantly store its VN in the "vn" field).
            arrLenVN = ValueNumStore::NoVN;
        }

        // During assertion prop we add assertions of the form:
        //
        //      (i < length) == 0
        //      (i < length) != 0
        //      (i < 100) == 0
        //      (i < 100) != 0
        //
        // At this point, we have detected that op1.vn is (i < length) or (i < length + cns) or
        // (i < 100) and the op2.vn is 0.
        //
        // Now, let us check if we are == 0 (i.e., op1 assertion is false) or != 0 (op1 assertion
        // is true.),
        //
        // If we have an assertion of the form == 0 (i.e., equals false), then reverse relop.
        // The relop has to be reversed because we have: (i < length) is false which is the same
        // as (i >= length).
        if (curAssertion->assertionKind == Compiler::OAK_EQUAL)
        {
            cmpOper = GenTree::ReverseRelop(cmpOper);
        }

        // Bounds are inclusive, so add -1 for upper bound when "<". But make sure we won't overflow.
        if (cmpOper == GT_LT && !limit.AddConstant(-1))
        {
            continue;
        }
        // Bounds are inclusive, so add +1 for lower bound when ">". But make sure we won't overflow.
        if (cmpOper == GT_GT && !limit.AddConstant(1))
        {
            continue;
        }

        // Doesn't tighten the current bound. So skip.
        if (pRange->uLimit.IsConstant() && limit.vn != arrLenVN)
        {
            continue;
        }

        // Check if the incoming limit from assertions tightens the existing upper limit.
        if (pRange->uLimit.IsBinOpArray() && (pRange->uLimit.vn == arrLenVN))
        {
            // We have checked the current range's (pRange's) upper limit is either of the form:
            //      length + cns
            //      and length == the bndsChkCandidate's arrLen
            //
            // We want to check if the incoming limit tightens the bound, and for that
            // we need to make sure that incoming limit is also on the same length (or
            // length + cns) and not some other length.

            if (limit.vn != arrLenVN)
            {
                JITDUMP("Array length VN did not match arrLen=" FMT_VN ", limit=" FMT_VN "\n", arrLenVN, limit.vn);
                continue;
            }

            int curCns = pRange->uLimit.cns;
            int limCns = (limit.IsBinOpArray()) ? limit.cns : 0;

            // Incoming limit doesn't tighten the existing upper limit.
            if (limCns >= curCns)
            {
                JITDUMP("Bound limit %d doesn't tighten current bound %d\n", limCns, curCns);
                continue;
            }
        }
        else
        {
            // Current range's upper bound is not "length + cns" and the
            // incoming limit is not on the same length as the bounds check candidate.
            // So we could skip this assertion. But in cases, of Dependent or Unknown
            // type of upper limit, the incoming assertion still tightens the upper
            // bound to a saner value. So do not skip the assertion.
        }

        // cmpOp (loop index i) cmpOper len +/- cns
        switch (cmpOper)
        {
            case GT_LT:
                pRange->uLimit = limit;
                break;

            case GT_GT:
                pRange->lLimit = limit;
                break;

            case GT_GE:
                pRange->lLimit = limit;
                break;

            case GT_LE:
                pRange->uLimit = limit;
                break;

            default:
                // All other 'cmpOper' kinds leave lLimit/uLimit unchanged
                break;
        }
        JITDUMP("The range after edge merging:");
        JITDUMP(pRange->ToString(m_pCompiler->getAllocatorDebugOnly()));
        JITDUMP("\n");
    }
}

// Merge assertions from the pred edges of the block, i.e., check for any assertions about "op's" value numbers for phi
// arguments. If not a phi argument, check if we assertions about local variables.
void RangeCheck::MergeAssertion(BasicBlock* block, GenTree* op, Range* pRange DEBUGARG(int indent))
{
    JITDUMP("Merging assertions from pred edges of " FMT_BB " for op [%06d] " FMT_VN "\n", block->bbNum,
            Compiler::dspTreeID(op), m_pCompiler->vnStore->VNConservativeNormalValue(op->gtVNPair));
    ASSERT_TP assertions = BitVecOps::UninitVal();

    // If we have a phi arg, we can get to the block from it and use its assertion out.
    if (op->gtOper == GT_PHI_ARG)
    {
        GenTreePhiArg* arg  = (GenTreePhiArg*)op;
        BasicBlock*    pred = arg->gtPredBB;
        if (pred->bbFallsThrough() && pred->bbNext == block)
        {
            assertions = pred->bbAssertionOut;
            JITDUMP("Merge assertions from pred " FMT_BB " edge: %s\n", pred->bbNum,
                    BitVecOps::ToString(m_pCompiler->apTraits, assertions));
        }
        else if ((pred->bbJumpKind == BBJ_COND || pred->bbJumpKind == BBJ_ALWAYS) && pred->bbJumpDest == block)
        {
            if (m_pCompiler->bbJtrueAssertionOut != nullptr)
            {
                assertions = m_pCompiler->bbJtrueAssertionOut[pred->bbNum];
                JITDUMP("Merge assertions from pred " FMT_BB " JTrue edge: %s\n", pred->bbNum,
                        BitVecOps::ToString(m_pCompiler->apTraits, assertions));
            }
        }
    }
    // Get assertions from bbAssertionIn.
    else if (op->IsLocal())
    {
        assertions = block->bbAssertionIn;
    }

    if (!BitVecOps::MayBeUninit(assertions))
    {
        // Perform the merge step to fine tune the range value.
        MergeEdgeAssertions(op->AsLclVarCommon(), assertions, pRange);
    }
}

// Compute the range for a binary operation.
Range RangeCheck::ComputeRangeForBinOp(BasicBlock* block, GenTreeOp* binop, bool monotonic DEBUGARG(int indent))
{
    assert(binop->OperIs(GT_ADD));

    GenTree* op1 = binop->gtGetOp1();
    GenTree* op2 = binop->gtGetOp2();

    Range* op1RangeCached = nullptr;
    Range  op1Range       = Limit(Limit::keUndef);
    // Check if the range value is already cached.
    if (!GetRangeMap()->Lookup(op1, &op1RangeCached))
    {
        // If we already have the op in the path, then, just rely on assertions, else
        // find the range.
        if (m_pSearchPath->Lookup(op1))
        {
            op1Range = Range(Limit(Limit::keDependent));
        }
        else
        {
            op1Range = GetRange(block, op1, monotonic DEBUGARG(indent));
        }
        MergeAssertion(block, op1, &op1Range DEBUGARG(indent + 1));
    }
    else
    {
        op1Range = *op1RangeCached;
    }

    Range* op2RangeCached;
    Range  op2Range = Limit(Limit::keUndef);
    // Check if the range value is already cached.
    if (!GetRangeMap()->Lookup(op2, &op2RangeCached))
    {
        // If we already have the op in the path, then, just rely on assertions, else
        // find the range.
        if (m_pSearchPath->Lookup(op2))
        {
            op2Range = Range(Limit(Limit::keDependent));
        }
        else
        {
            op2Range = GetRange(block, op2, monotonic DEBUGARG(indent));
        }
        MergeAssertion(block, op2, &op2Range DEBUGARG(indent + 1));
    }
    else
    {
        op2Range = *op2RangeCached;
    }

    Range r = RangeOps::Add(op1Range, op2Range);
    JITDUMP("BinOp add ranges %s %s = %s\n", op1Range.ToString(m_pCompiler->getAllocatorDebugOnly()),
            op2Range.ToString(m_pCompiler->getAllocatorDebugOnly()), r.ToString(m_pCompiler->getAllocatorDebugOnly()));
    return r;
}

// Compute the range for a local var definition.
Range RangeCheck::ComputeRangeForLocalDef(BasicBlock*          block,
                                          GenTreeLclVarCommon* lcl,
                                          bool monotonic DEBUGARG(int indent))
{
    BasicBlock* asgBlock;
    GenTreeOp*  asg = GetSsaDefAsg(lcl, &asgBlock);
    if (asg == nullptr)
    {
        return Range(Limit(Limit::keUnknown));
    }
#ifdef DEBUG
    if (m_pCompiler->verbose)
    {
        JITDUMP("----------------------------------------------------\n");
        m_pCompiler->gtDispTree(asg);
        JITDUMP("----------------------------------------------------\n");
    }
#endif
    assert(asg->OperIs(GT_ASG));
    Range range = GetRange(asgBlock, asg->gtGetOp2(), monotonic DEBUGARG(indent));
    if (!BitVecOps::MayBeUninit(block->bbAssertionIn))
    {
        JITDUMP("Merge assertions from " FMT_BB ":%s for assignment about [%06d]\n", block->bbNum,
                BitVecOps::ToString(m_pCompiler->apTraits, block->bbAssertionIn), Compiler::dspTreeID(asg->gtGetOp1()));
        MergeEdgeAssertions(asg->gtGetOp1()->AsLclVarCommon(), block->bbAssertionIn, &range);
        JITDUMP("done merging\n");
    }
    return range;
}

// https://msdn.microsoft.com/en-us/windows/apps/hh285054.aspx
// CLR throws IDS_EE_ARRAY_DIMENSIONS_EXCEEDED if array length is > INT_MAX.
// new byte[INT_MAX]; still throws OutOfMemoryException on my system with 32 GB RAM.
// I believe practical limits are still smaller than this number.
#define ARRLEN_MAX (0x7FFFFFFF)

// Get the limit's maximum possible value, treating array length to be ARRLEN_MAX.
bool RangeCheck::GetLimitMax(Limit& limit, int* pMax)
{
    int& max1 = *pMax;
    switch (limit.type)
    {
        case Limit::keConstant:
            max1 = limit.GetConstant();
            break;

        case Limit::keBinOpArray:
        {
            int tmp = GetArrLength(limit.vn);
            if (tmp <= 0)
            {
                tmp = ARRLEN_MAX;
            }
            if (IntAddOverflows(tmp, limit.GetConstant()))
            {
                return false;
            }
            max1 = tmp + limit.GetConstant();
        }
        break;

        default:
            return false;
    }
    return true;
}

// Check if the arithmetic overflows.
bool RangeCheck::AddOverflows(Limit& limit1, Limit& limit2)
{
    int max1;
    if (!GetLimitMax(limit1, &max1))
    {
        return true;
    }

    int max2;
    if (!GetLimitMax(limit2, &max2))
    {
        return true;
    }

    return IntAddOverflows(max1, max2);
}

// Does the bin operation overflow.
bool RangeCheck::DoesBinOpOverflow(BasicBlock* block, GenTreeOp* binop)
{
    GenTree* op1 = binop->gtGetOp1();
    GenTree* op2 = binop->gtGetOp2();

    if (!m_pSearchPath->Lookup(op1) && DoesOverflow(block, op1))
    {
        return true;
    }

    if (!m_pSearchPath->Lookup(op2) && DoesOverflow(block, op2))
    {
        return true;
    }

    // Get the cached ranges of op1
    Range* op1Range = nullptr;
    if (!GetRangeMap()->Lookup(op1, &op1Range))
    {
        return true;
    }
    // Get the cached ranges of op2
    Range* op2Range = nullptr;
    if (!GetRangeMap()->Lookup(op2, &op2Range))
    {
        return true;
    }

    // If dependent, check if we can use some assertions.
    if (op1Range->UpperLimit().IsDependent())
    {
        MergeAssertion(block, op1, op1Range DEBUGARG(0));
    }

    // If dependent, check if we can use some assertions.
    if (op2Range->UpperLimit().IsDependent())
    {
        MergeAssertion(block, op2, op2Range DEBUGARG(0));
    }

    JITDUMP("Checking bin op overflow %s %s\n", op1Range->ToString(m_pCompiler->getAllocatorDebugOnly()),
            op2Range->ToString(m_pCompiler->getAllocatorDebugOnly()));

    if (!AddOverflows(op1Range->UpperLimit(), op2Range->UpperLimit()))
    {
        return false;
    }
    return true;
}

// Check if the var definition the rhs involves arithmetic that overflows.
bool RangeCheck::DoesVarDefOverflow(GenTreeLclVarCommon* lcl)
{
    BasicBlock* asgBlock;
    GenTreeOp*  asg = GetSsaDefAsg(lcl, &asgBlock);
    return (asg == nullptr) || DoesOverflow(asgBlock, asg->gtGetOp2());
}

bool RangeCheck::DoesPhiOverflow(BasicBlock* block, GenTree* expr)
{
    for (GenTreeArgList* args = expr->gtOp.gtOp1->AsArgList(); args != nullptr; args = args->Rest())
    {
        GenTree* arg = args->Current();
        if (m_pSearchPath->Lookup(arg))
        {
            continue;
        }
        if (DoesOverflow(block, arg))
        {
            return true;
        }
    }
    return false;
}

bool RangeCheck::DoesOverflow(BasicBlock* block, GenTree* expr)
{
    bool overflows = false;
    if (!GetOverflowMap()->Lookup(expr, &overflows))
    {
        overflows = ComputeDoesOverflow(block, expr);
    }
    return overflows;
}

bool RangeCheck::ComputeDoesOverflow(BasicBlock* block, GenTree* expr)
{
    JITDUMP("Does overflow [%06d]?\n", Compiler::dspTreeID(expr));
    m_pSearchPath->Set(expr, block, SearchPath::Overwrite);

    bool overflows = true;

    if (m_pSearchPath->GetCount() > MAX_SEARCH_DEPTH)
    {
        overflows = true;
    }
    // If the definition chain resolves to a constant, it doesn't overflow.
    else if (m_pCompiler->vnStore->IsVNConstant(expr->gtVNPair.GetConservative()))
    {
        overflows = false;
    }
    else if (expr->OperGet() == GT_IND)
    {
        overflows = false;
    }
    else if (expr->OperGet() == GT_COMMA)
    {
        overflows = ComputeDoesOverflow(block, expr->gtEffectiveVal());
    }
    // Check if the var def has rhs involving arithmetic that overflows.
    else if (expr->IsLocal())
    {
        overflows = DoesVarDefOverflow(expr->AsLclVarCommon());
    }
    // Check if add overflows.
    else if (expr->OperGet() == GT_ADD)
    {
        overflows = DoesBinOpOverflow(block, expr->AsOp());
    }
    // Walk through phi arguments to check if phi arguments involve arithmetic that overflows.
    else if (expr->OperGet() == GT_PHI)
    {
        overflows = DoesPhiOverflow(block, expr);
    }
    else if (expr->OperGet() == GT_CAST)
    {
        GenTreeCast* castExpr = expr->AsCast();
        if (castExpr->CastToType() == TYP_UBYTE && castExpr->CastFromType() == TYP_INT)
        {
            overflows = false;
        }
    }

    GetOverflowMap()->Set(expr, overflows, OverflowMap::Overwrite);
    m_pSearchPath->Remove(expr);
    return overflows;
}

// Compute the range recursively by asking for the range of each variable in the dependency chain.
// eg.: c = a + b; ask range of "a" and "b" and add the results.
// If the result cannot be determined i.e., the dependency chain does not terminate in a value,
// but continues to loop, which will happen with phi nodes. We end the looping by calling the
// value as "dependent" (dep).
// If the loop is proven to be "monotonic", then make liberal decisions while merging phi node.
// eg.: merge((0, dep), (dep, dep)) = (0, dep)
Range RangeCheck::ComputeRange(BasicBlock* block, GenTree* expr, bool monotonic DEBUGARG(int indent))
{
    bool  newlyAdded = !m_pSearchPath->Set(expr, block, SearchPath::Overwrite);
    Range range      = Limit(Limit::keUndef);

    ValueNum vn = m_pCompiler->vnStore->VNConservativeNormalValue(expr->gtVNPair);

    // If we just added 'expr' in the current search path, then reduce the budget.
    if (newlyAdded)
    {
        // Assert that we are not re-entrant for a node which has been
        // visited and resolved before and not currently on the search path.
        noway_assert(!GetRangeMap()->Lookup(expr));
        m_nVisitBudget--;
    }
    // Prevent quadratic behavior.
    if (IsOverBudget())
    {
        // Set to unknown, since an Unknown range resolution, will stop further
        // searches. This is because anything that merges with Unknown will
        // yield Unknown. Unknown is lattice top.
        range = Range(Limit(Limit::keUnknown));
        JITDUMP("GetRange not tractable within max node visit budget.\n");
    }
    // Prevent unbounded recursion.
    else if (m_pSearchPath->GetCount() > MAX_SEARCH_DEPTH)
    {
        // Unknown is lattice top, anything that merges with Unknown will yield Unknown.
        range = Range(Limit(Limit::keUnknown));
        JITDUMP("GetRange not tractable within max stack depth.\n");
    }
    // TODO-CQ: The current implementation is reliant on integer storage types
    // for constants. It could use INT64. Still, representing ULONG constants
    // might require preserving the var_type whether it is a un/signed 64-bit.
    // JIT64 doesn't do anything for "long" either. No asm diffs.
    else if (expr->TypeGet() == TYP_LONG || expr->TypeGet() == TYP_ULONG)
    {
        range = Range(Limit(Limit::keUnknown));
        JITDUMP("GetRange long or ulong, setting to unknown value.\n");
    }
    // If VN is constant return range as constant.
    else if (m_pCompiler->vnStore->IsVNConstant(vn))
    {
        range = (m_pCompiler->vnStore->TypeOfVN(vn) == TYP_INT)
                    ? Range(Limit(Limit::keConstant, m_pCompiler->vnStore->ConstantValue<int>(vn)))
                    : Limit(Limit::keUnknown);
    }
    // If local, find the definition from the def map and evaluate the range for rhs.
    else if (expr->IsLocal())
    {
        range = ComputeRangeForLocalDef(block, expr->AsLclVarCommon(), monotonic DEBUGARG(indent + 1));
        MergeAssertion(block, expr, &range DEBUGARG(indent + 1));
    }
    // If add, then compute the range for the operands and add them.
    else if (expr->OperGet() == GT_ADD)
    {
        range = ComputeRangeForBinOp(block, expr->AsOp(), monotonic DEBUGARG(indent + 1));
    }
    // If phi, then compute the range for arguments, calling the result "dependent" when looping begins.
    else if (expr->OperGet() == GT_PHI)
    {
        for (GenTreeArgList* args = expr->gtOp.gtOp1->AsArgList(); args != nullptr; args = args->Rest())
        {
            Range argRange = Range(Limit(Limit::keUndef));
            if (m_pSearchPath->Lookup(args->Current()))
            {
                JITDUMP("PhiArg [%06d] is already being computed\n", Compiler::dspTreeID(args->Current()));
                argRange = Range(Limit(Limit::keDependent));
            }
            else
            {
                argRange = GetRange(block, args->Current(), monotonic DEBUGARG(indent + 1));
            }
            assert(!argRange.LowerLimit().IsUndef());
            assert(!argRange.UpperLimit().IsUndef());
            MergeAssertion(block, args->Current(), &argRange DEBUGARG(indent + 1));
            JITDUMP("Merging ranges %s %s:", range.ToString(m_pCompiler->getAllocatorDebugOnly()),
                    argRange.ToString(m_pCompiler->getAllocatorDebugOnly()));
            range = RangeOps::Merge(range, argRange, monotonic);
            JITDUMP("%s\n", range.ToString(m_pCompiler->getAllocatorDebugOnly()));
        }
    }
    else if (expr->OperIs(GT_CAST) || varTypeIsSmallInt(expr->TypeGet()))
    {
        var_types exprType = expr->OperIs(GT_CAST) ? expr->AsCast()->CastToType() : expr->TypeGet();

        switch (exprType)
        {
            case TYP_UBYTE:
                range = Range(Limit(Limit::keConstant, 0), Limit(Limit::keConstant, 255));
                break;
            case TYP_BYTE:
                range = Range(Limit(Limit::keConstant, -128), Limit(Limit::keConstant, 127));
                break;
            case TYP_USHORT:
                range = Range(Limit(Limit::keConstant, 0), Limit(Limit::keConstant, 65535));
                break;
            case TYP_SHORT:
                range = Range(Limit(Limit::keConstant, -32768), Limit(Limit::keConstant, 32767));
                break;
            default:
                range = Range(Limit(Limit::keUnknown));
                break;
        }

        JITDUMP("%s\n", range.ToString(m_pCompiler->getAllocatorDebugOnly()));
    }
    else
    {
        // The expression is not recognized, so the result is unknown.
        range = Range(Limit(Limit::keUnknown));
    }

    GetRangeMap()->Set(expr, new (m_alloc) Range(range), RangeMap::Overwrite);
    m_pSearchPath->Remove(expr);
    return range;
}

#ifdef DEBUG
void Indent(int indent)
{
    for (int i = 0; i < indent; ++i)
    {
        JITDUMP("   ");
    }
}
#endif

// Get the range, if it is already computed, use the cached range value, else compute it.
Range RangeCheck::GetRange(BasicBlock* block, GenTree* expr, bool monotonic DEBUGARG(int indent))
{
#ifdef DEBUG
    if (m_pCompiler->verbose)
    {
        Indent(indent);
        JITDUMP("[RangeCheck::GetRange] " FMT_BB, block->bbNum);
        m_pCompiler->gtDispTree(expr);
        Indent(indent);
        JITDUMP("{\n", expr);
    }
#endif

    Range* pRange = nullptr;
    Range  range =
        GetRangeMap()->Lookup(expr, &pRange) ? *pRange : ComputeRange(block, expr, monotonic DEBUGARG(indent));

#ifdef DEBUG
    if (m_pCompiler->verbose)
    {
        Indent(indent);
        JITDUMP("   %s Range [%06d] => %s\n", (pRange == nullptr) ? "Computed" : "Cached", Compiler::dspTreeID(expr),
                range.ToString(m_pCompiler->getAllocatorDebugOnly()));
        Indent(indent);
        JITDUMP("}\n", expr);
    }
#endif
    return range;
}

#ifdef DEBUG
// If this is a tree local definition add its location to the def map.
void RangeCheck::MapStmtDefs(const Location& loc)
{
    GenTreeLclVarCommon* tree = loc.tree;

    unsigned lclNum = tree->GetLclNum();
    unsigned ssaNum = tree->GetSsaNum();
    if (ssaNum == SsaConfig::RESERVED_SSA_NUM)
    {
        return;
    }

    // If useasg then get the correct ssaNum to add to the map.
    if (tree->gtFlags & GTF_VAR_USEASG)
    {
        unsigned ssaNum = m_pCompiler->GetSsaNumForLocalVarDef(tree);
        if (ssaNum != SsaConfig::RESERVED_SSA_NUM)
        {
            // To avoid ind(addr) use asgs
            if (loc.parent->OperIs(GT_ASG))
            {
                SetDef(HashCode(lclNum, ssaNum), new (m_alloc) Location(loc));
            }
        }
    }
    // If def get the location and store it against the variable's ssaNum.
    else if (tree->gtFlags & GTF_VAR_DEF)
    {
        if (loc.parent->OperGet() == GT_ASG)
        {
            SetDef(HashCode(lclNum, ssaNum), new (m_alloc) Location(loc));
        }
    }
}

struct MapMethodDefsData
{
    RangeCheck*  rc;
    BasicBlock*  block;
    GenTreeStmt* stmt;

    MapMethodDefsData(RangeCheck* rc, BasicBlock* block, GenTreeStmt* stmt) : rc(rc), block(block), stmt(stmt)
    {
    }
};

Compiler::fgWalkResult MapMethodDefsVisitor(GenTree** ptr, Compiler::fgWalkData* data)
{
    GenTree*           tree = *ptr;
    MapMethodDefsData* rcd  = ((MapMethodDefsData*)data->pCallbackData);

    if (tree->IsLocal())
    {
        rcd->rc->MapStmtDefs(RangeCheck::Location(rcd->block, rcd->stmt, tree->AsLclVarCommon(), data->parent));
    }

    return Compiler::WALK_CONTINUE;
}

void RangeCheck::MapMethodDefs()
{
    // First, gather where all definitions occur in the program and store it in a map.
    for (BasicBlock* block = m_pCompiler->fgFirstBB; block != nullptr; block = block->bbNext)
    {
        for (GenTreeStmt* stmt = block->firstStmt(); stmt != nullptr; stmt = stmt->getNextStmt())
        {
            MapMethodDefsData data(this, block, stmt);
            m_pCompiler->fgWalkTreePre(&stmt->gtStmtExpr, MapMethodDefsVisitor, &data, false, true);
        }
    }
    m_fMappedDefs = true;
}
#endif

// Entry point to range check optimizations.
void RangeCheck::OptimizeRangeChecks()
{
    if (m_pCompiler->fgSsaPassesCompleted == 0)
    {
        return;
    }
#ifdef DEBUG
    if (m_pCompiler->verbose)
    {
        JITDUMP("*************** In OptimizeRangeChecks()\n");
        JITDUMP("Blocks/trees before phase\n");
        m_pCompiler->fgDispBasicBlocks(true);
    }
#endif

    // Walk through trees looking for arrBndsChk node and check if it can be optimized.
    for (BasicBlock* block = m_pCompiler->fgFirstBB; block; block = block->bbNext)
    {
        for (GenTreeStmt* stmt = block->firstStmt(); stmt != nullptr; stmt = stmt->getNextStmt())
        {
            for (GenTree* tree = stmt->gtStmtList; tree; tree = tree->gtNext)
            {
                if (IsOverBudget())
                {
                    return;
                }
                OptimizeRangeCheck(block, stmt, tree);
            }
        }
    }
}