/*===================== begin_copyright_notice ==================================

Copyright (c) 2017 Intel Corporation

Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be included
in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.


======================= end_copyright_notice ==================================*/

#include "common/LLVMWarningsPush.hpp"
#include <llvm/Transforms/Utils/Cloning.h>
#include <llvm/Transforms/Utils/BasicBlockUtils.h>
#include <llvm/Transforms/Utils/LoopUtils.h>
#include "common/LLVMWarningsPop.hpp"

#include "common/LLVMUtils.h"

#include "Compiler/CISACodeGen/ShaderCodeGen.hpp"
#include "Compiler/CISACodeGen/helper.h"
#include "Compiler/CustomLoopOpt.hpp"
#include "Compiler/IGCPassSupport.h"
#include "Compiler/MetaDataUtilsWrapper.h"


using namespace llvm;
using namespace IGC;

#define PASS_FLAG     "igc-custom-loop-opt"
#define PASS_DESC     "IGC Custom Loop Opt"
#define PASS_CFG_ONLY false
#define PASS_ANALYSIS false
IGC_INITIALIZE_PASS_BEGIN(CustomLoopVersioning, PASS_FLAG, PASS_DESC, PASS_CFG_ONLY, PASS_ANALYSIS)
IGC_INITIALIZE_PASS_DEPENDENCY(CodeGenContextWrapper)
IGC_INITIALIZE_PASS_DEPENDENCY(MetaDataUtilsWrapper);
IGC_INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass);
IGC_INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass);
IGC_INITIALIZE_PASS_DEPENDENCY(LCSSAWrapperPass)
IGC_INITIALIZE_PASS_END(CustomLoopVersioning, PASS_FLAG, PASS_DESC, PASS_CFG_ONLY, PASS_ANALYSIS)

char CustomLoopVersioning::ID = 0;

CustomLoopVersioning::CustomLoopVersioning() : FunctionPass(ID)
{
    initializeCustomLoopVersioningPass(*PassRegistry::getPassRegistry());
}

bool CustomLoopVersioning::isCBLoad(Value* val, unsigned& bufId, unsigned& offset)
{
    LoadInst* ld = dyn_cast<LoadInst>(val);
    if (!ld)
        return false;

    unsigned as = ld->getPointerAddressSpace();
    bool directBuf = false;
    BufferType bufType = DecodeAS4GFXResource(as, directBuf, bufId);
    if (!(bufType == CONSTANT_BUFFER && directBuf))
        return false;

    Value* ptr = ld->getPointerOperand();
    if (IntToPtrInst* itop = dyn_cast<IntToPtrInst>(ptr))
    {
        ConstantInt* ci = dyn_cast<ConstantInt>(
            itop->getOperand(0));
        if (ci)
        {
            offset = int_cast<unsigned>(ci->getZExtValue());
            return true;
        }
    }
    if (ConstantExpr* itop = dyn_cast<ConstantExpr>(ptr))
    {
        if (itop->getOpcode() == Instruction::IntToPtr)
        {
            offset = int_cast<unsigned>(
                cast<ConstantInt>(itop->getOperand(0))->getZExtValue());
            return true;
        }
    }
    return false;
}

bool CustomLoopVersioning::runOnFunction(Function& F)
{
    // Skip non-kernel function.                                                  
    IGCMD::MetaDataUtils *mdu = getAnalysis<MetaDataUtilsWrapper>().getMetaDataUtils();
    auto FII = mdu->findFunctionsInfoItem(&F);
    if (FII == mdu->end_FunctionsInfo())
        return false;

    m_cgCtx = getAnalysis<CodeGenContextWrapper>().getCodeGenContext();
    m_LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
    m_DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
    m_function = &F;

    bool changed = false;
    for (auto& LI : *m_LI)
    {
        Loop* L = &(*LI);

        // only check while loop with single BB loop body
        if (L->isSafeToClone() && L->getLoopDepth() == 1 &&
            L->getNumBlocks() == 1 && L->getNumBackEdges() == 1 &&
            L->getHeader() == L->getExitingBlock() &&
            L->getLoopPreheader() && L->isLCSSAForm(*m_DT))
        {
            changed = processLoop(L);
            if (changed)
                break;
        }
    }

    if (changed)
    {
        m_cgCtx->getModuleMetaData()->psInfo.hasVersionedLoop = true;
        DumpLLVMIR(m_cgCtx, "customloop");
    }
    return changed;
}

//
// float t = ...;
// float nextT = t * CB_Load;
// [loop] while (t < loop_range_y)
// {
//     float val0 = max(t, loop_range_x);
//     float val1 = min(nextT, loop_range_y);
//     ...
//     t = nextT;
//     nextT *= CB_Load;
// }
//
// pre_header:
//   %cb = load float, float addrspace(65538)* ...
//   %nextT_start = fmul float %t_start, %cb
//
// loop_header:
//   %t = phi float [ %t_start, %then409 ], [ %nextT, %break_cont ]
//   %nextT = phi float [ %nextT_start, %then409 ], [ %res_s588, %break_cont ]
//   %cond = fcmp ult float %t, %loop_range_y
//   br i1 %cond, label %break_cont, label %after_loop
//
// loop_body:
//   %206 = call float @llvm.maxnum.f32(float %loop_range_x, float %t)
//   %207 = call float @llvm.minnum.f32(float %loop_range_y, float %nextT)
//   ...
//   %258 = load float, float addrspace(65538)* ...
//   %res_s588 = fmul float %nextT, %258
//   br label %loop_entry
//   
// 
bool CustomLoopVersioning::detectLoop(Loop* loop,
    Value* &var_range_x, Value* &var_range_y,
    LoadInst* &var_CBLoad_preHdr,
    Value* &var_t_preHdr,
    Value* &var_nextT_preHdr)
{
    BasicBlock* preHdr = loop->getLoopPreheader();
    BasicBlock* header = loop->getHeader();
    BasicBlock* body = loop->getLoopLatch();

    Instruction* i0 = body->getFirstNonPHI();
    Instruction* i1 = GetNextInstruction(i0);

    CallInst* imax = dyn_cast<CallInst>(i0);
    CallInst* imin = i1 ? dyn_cast<CallInst>(i1) : nullptr;

    if (!(imax && GetOpCode(imax) == llvm_max &&
          imin && GetOpCode(imin) == llvm_min))
    {
        return false;
    }

    CallInst* interval_x = dyn_cast<CallInst>(imax->getArgOperand(0));
    CallInst* interval_y = dyn_cast<CallInst>(imin->getArgOperand(0));

    if (!(interval_x && GetOpCode(interval_x) == llvm_max) ||
        !(interval_y && GetOpCode(interval_y) == llvm_min))
    {
        return false;
    }
    var_range_x = interval_x;
    var_range_y = interval_y;

    PHINode* var_t;
    PHINode* var_nextT;

    var_t = dyn_cast<PHINode>(imax->getArgOperand(1));
    var_nextT = dyn_cast<PHINode>(imin->getArgOperand(1));
    if (var_t == nullptr || var_nextT == nullptr)
    {
        return false;
    }

    if (var_t->getParent() != header || var_nextT->getParent() != header)
    {
        return false;
    }

    // check for "nextT = t * CB_Load" before loop
    BinaryOperator* fmul = dyn_cast<BinaryOperator>(
        var_nextT->getIncomingValueForBlock(preHdr));
    if (!fmul)
    {
        return false;
    }
    if (fmul->getOperand(0) !=
        var_t->getIncomingValueForBlock(preHdr))
    {
        return false;
    }
    var_t_preHdr = var_t->getIncomingValueForBlock(preHdr);
    var_nextT_preHdr = var_nextT->getIncomingValueForBlock(preHdr);

    unsigned bufId, cbOffset;
    if (!isCBLoad(fmul->getOperand(1), bufId, cbOffset))
    {
        return false;
    }
    var_CBLoad_preHdr = cast<LoadInst>(fmul->getOperand(1));

    // check for "t = nextT" inside loop
    if (var_t->getIncomingValueForBlock(body) != var_nextT)
    {
        return false;
    }

    fmul = dyn_cast<BinaryOperator>(
        var_nextT->getIncomingValueForBlock(body));
    if (!fmul)
    {
        return false;
    }

    // check for "nextT *= CB_Load" inside loop
    Value* src0 = fmul->getOperand(0);
    if (src0 != var_nextT)
    {
        return false;
    }

    unsigned bufId2, cbOffset2;
    if (!isCBLoad(fmul->getOperand(1), bufId2, cbOffset2))
    {
        return false;
    }
    if (bufId != bufId2 || cbOffset != cbOffset2)
    {
        return false;
    }

    BranchInst* br = cast<BranchInst>(body->getTerminator());
    if (!br->isConditional())
    {
        return false;
    }

    // check for "while (t < loop_range_y)"
    FCmpInst* fcmp = dyn_cast<FCmpInst>(br->getCondition());
    if (!fcmp || fcmp->getOperand(0) != var_nextT)
    {
        return false;
    }

    if (fcmp->getOperand(1) != interval_y)
    {
        return false;
    }

    return true;
}

// while (t < loop_range_y)
//     float val0 = max(t, loop_range_x);
//     float val1 = min(nextT, loop_range_y);
// -->
// while (t < loop_range_x)
//     float val0 = loop_range_x;
//     float val1 = nextT;
void CustomLoopVersioning::rewriteLoopSeg1(Loop* loop,
    Value* interval_x, Value* interval_y)
{
    BasicBlock* header = loop->getHeader();
    BasicBlock* body = loop->getLoopLatch();

    BranchInst* br = cast<BranchInst>(header->getTerminator());
    FCmpInst* fcmp = dyn_cast<FCmpInst>(br->getCondition());
    assert(fcmp && fcmp->getOperand(1) == interval_y);

    fcmp->setOperand(1, interval_x);

    Instruction* i0 = body->getFirstNonPHI();
    Instruction* i1 = GetNextInstruction(i0);

    IntrinsicInst* imax = cast<IntrinsicInst>(i0);
    IntrinsicInst* imin = cast<IntrinsicInst>(i1);
    assert(imax && imin);

    imax->replaceAllUsesWith(interval_x);
    imin->replaceAllUsesWith(imin->getArgOperand(1));
}

void CustomLoopVersioning::hoistSeg2Invariant(Loop* loop,
    Instruction* fmul, Value* cbLoad)
{
    BasicBlock* preHdr = loop->getLoopPreheader();
    BasicBlock* body = loop->getLoopLatch();

    // detecting loop invariant and move it to header:
    //   %211 = call float @llvm.fabs.f32(float %210)
    //   %212 = call float @llvm.log2.f32(float %211)
    //   %res_s465 = fmul float %165, %212
    //   %213 = call float @llvm.exp2.f32(float %res_s465)
    IntrinsicInst* intrin_abs = nullptr;
    IntrinsicInst* intrin_log2 = nullptr;
    Instruction* fmul_log2 = nullptr;
    Value* fmul_log2_opnd = nullptr;

    for (auto* UI : fmul->users())
    {
        IntrinsicInst* intrin = dyn_cast<IntrinsicInst>(UI);
        if (intrin->getIntrinsicID() == Intrinsic::fabs &&
            intrin->getNumUses() == 1)
        {
            intrin_abs = intrin;
            break;
        }
    }

    if (intrin_abs && intrin_abs->getParent() == body)
    {
        IntrinsicInst* intrin = dyn_cast<IntrinsicInst>(
            *intrin_abs->users().begin());
        if (intrin &&
            intrin->getIntrinsicID() == Intrinsic::log2 &&
            intrin->getNumUses() == 1)
        {
            intrin_log2 = intrin;
        }
    }

    if (intrin_log2 && intrin_log2->getParent() == body)
    {
        Instruction* fmul = dyn_cast<Instruction>(
            *intrin_log2->users().begin());
        if (fmul &&
            fmul->getOpcode() == Instruction::FMul &&
            fmul->getNumUses() == 1)
        {
            unsigned id = fmul->getOperand(0) == intrin_log2 ? 1 : 0;
            // make sure another operand is coming from out of loop
            Instruction* i = dyn_cast<Instruction>(fmul->getOperand(id));
            if (i && !loop->contains(i->getParent()))
            {
                fmul_log2 = fmul;
                fmul_log2_opnd = fmul->getOperand(id);
            }
        }
    }

    if (fmul_log2 && fmul_log2->getParent() == body)
    {
        IntrinsicInst* intrin = dyn_cast<IntrinsicInst>(
            *fmul_log2->users().begin());
        if (intrin &&
            intrin->getIntrinsicID() == Intrinsic::exp2)
        {
            IRBuilder<> irb(preHdr->getFirstNonPHI());
            irb.setFastMathFlags(fmul_log2->getFastMathFlags());

            Function* flog =
                Intrinsic::getDeclaration(m_function->getParent(),
                    llvm::Intrinsic::log2, intrin_log2->getType());
            Function* fexp =
                Intrinsic::getDeclaration(m_function->getParent(),
                    llvm::Intrinsic::exp2, intrin_log2->getType());
            Value* v = irb.CreateCall(flog, cbLoad);
            v = irb.CreateFMul(fmul_log2_opnd, v);
            v = irb.CreateCall(fexp, v);
            intrin->replaceAllUsesWith(v);
        }
    }
    fmul->replaceAllUsesWith(cbLoad);
}

// while (t < loop_range_y)
//     float val0 = max(t, loop_range_x);
//     float val1 = min(nextT, loop_range_y);
// -->
// while (t < loop_range_y/CB_Load)
//     float val0 = t;
//     float val1 = next;
void CustomLoopVersioning::rewriteLoopSeg2(Loop* loop,
    Value* interval_y, Value* cbLoad)
{
    BasicBlock* header = loop->getHeader();
    BasicBlock* body = loop->getLoopLatch();

    BranchInst* br = cast<BranchInst>(header->getTerminator());
    FCmpInst* fcmp = dyn_cast<FCmpInst>(br->getCondition());
    assert(fcmp && fcmp->getOperand(1) == interval_y);

    Instruction* v = BinaryOperator::Create(Instruction::FDiv,
        interval_y, cbLoad, "", fcmp);
    v->setFast(true);
    fcmp->setOperand(1, v);

    Instruction* i0 = body->getFirstNonPHI();
    Instruction* i1 = GetNextInstruction(i0);

    IntrinsicInst* imax = cast<IntrinsicInst>(i0);
    IntrinsicInst* imin = cast<IntrinsicInst>(i1);
    assert(imax && imin);

    // find
    //   %206 = call float @llvm.maxnum.f32()
    //   %207 = call float @llvm.minnum.f32()
    //   %209 = fdiv float 1.000000e+00, % 206
    //   %210 = fmul float %207, % 209
    Instruction* fmul = nullptr;
    for (auto* max_Users : imax->users())
    {
        if (Instruction* fdiv = dyn_cast<BinaryOperator>(max_Users))
        {
            if (ConstantFP *cf = dyn_cast<ConstantFP>(fdiv->getOperand(0)))
            {
                if (cf->isExactlyValue(1.0))
                {
                    for (auto* UI : fdiv->users())
                    {
                        if ((fmul = dyn_cast<BinaryOperator>(UI)))
                        {
                            if (fmul->getOperand(0) == imin ||
                                (fmul->getOperand(1) == imin &&
                                    fmul->getParent() == body))
                            {
                                // find val1/val0
                                hoistSeg2Invariant(loop, fmul, cbLoad);

                                break;
                            }
                        }
                    }
                }
            }
        }
    }

    imax->replaceAllUsesWith(imax->getArgOperand(1));
    imin->replaceAllUsesWith(imin->getArgOperand(1));
}

//     float val0 = max(t, loop_range_x);
//     float val1 = min(nextT, loop_range_y);
// -->
//     float val0 = t;
//     float val1 = loop_range_y;
void CustomLoopVersioning::rewriteLoopSeg3(BasicBlock* bb,
    Value* interval_y)
{
    Instruction* i0 = bb->getFirstNonPHI();
    Instruction* i1 = GetNextInstruction(i0);

    IntrinsicInst* imax = cast<IntrinsicInst>(i0);
    IntrinsicInst* imin = cast<IntrinsicInst>(i1);
    assert(imax && imin);

    imax->replaceAllUsesWith(imax->getArgOperand(1));
    imin->replaceAllUsesWith(interval_y);

    auto II = bb->begin();
    auto IE = BasicBlock::iterator(bb->getFirstNonPHI());

    while (II != IE)
    {
        PHINode* PN = cast<PHINode>(II);

        assert(PN->getNumIncomingValues() == 2);
        for (unsigned i = 0; i < PN->getNumIncomingValues(); i++)
        {
            if (PN->getIncomingBlock(i) != bb)
            {
                PN->replaceAllUsesWith(PN->getIncomingValue(i));
            }
        }
        ++II;
        PN->eraseFromParent();
    }
}

void CustomLoopVersioning::linkLoops(
    Loop* loopSeg1, Loop* loopSeg2,
    BasicBlock* afterLoop)
{
    // we are handling do/while loop
    assert(loopSeg1->getHeader() == loopSeg1->getLoopLatch());
    assert(loopSeg2->getHeader() == loopSeg2->getLoopLatch());

    BasicBlock* seg1Body = loopSeg1->getLoopLatch();
    BasicBlock* seg2PreHdr = loopSeg2->getLoopPreheader();
    BasicBlock* seg2Body = loopSeg2->getLoopLatch();

    BranchInst* br = cast<BranchInst>(seg1Body->getTerminator());
    unsigned idx = br->getSuccessor(0) == afterLoop ? 0 : 1;
    br->setSuccessor(idx, loopSeg2->getLoopPreheader());

    auto II_1 = seg1Body->begin(), II_2 = seg2Body->begin();
    auto IE_2 = BasicBlock::iterator(seg2Body->getFirstNonPHI());

    for (; II_2 != IE_2; ++II_2, ++II_1)
    {
        PHINode* PN2 = cast<PHINode>(II_2);
        PHINode* PN1 = cast<PHINode>(II_1);
        Value* liveOut = nullptr;

        for (unsigned i = 0; i < PN1->getNumIncomingValues(); i++)
        {
            if (PN1->getIncomingBlock(i) == seg1Body)
            {
                liveOut = PN1->getIncomingValue(i);
                break;
            }
        }

        assert(liveOut != nullptr);
        for (unsigned i = 0; i < PN2->getNumIncomingValues(); i++)
        {

            if (PN2->getIncomingBlock(i) != seg2Body)
            {
                PN2->setIncomingValue(i, liveOut);
                PN2->setIncomingBlock(i, seg2PreHdr);
            }
        }
    }

}

bool CustomLoopVersioning::processLoop(Loop* loop)
{
    Value* var_range_x;
    Value* var_range_y;
    LoadInst* var_CBLoad_preHdr;
    Value* var_t_preHdr;
    Value* var_nextT_preHdr;
    bool found = false;

    found = detectLoop(loop, var_range_x, var_range_y,
        var_CBLoad_preHdr, var_t_preHdr, var_nextT_preHdr);

    if (!found)
        return false;

    const SmallVectorImpl<Instruction*>& liveOut =
        llvm::findDefsUsedOutsideOfLoop(loop);

    BasicBlock* preHdr = loop->getLoopPreheader();

    // apply the transformation
    BasicBlock* PH = llvm::SplitBlock(preHdr, preHdr->getTerminator(), m_DT, m_LI);

    // create loop seg 1 and insert before orig loop
    SmallVector<BasicBlock *, 8> seg1Blocks;
    Loop* loopSeg1 = llvm::cloneLoopWithPreheader(
        PH, preHdr, loop, m_vmapToSeg1, ".seg1", m_LI, m_DT, seg1Blocks);
    llvm::remapInstructionsInBlocks(seg1Blocks, m_vmapToSeg1);

    // create the check for fast loop
    // if (CB_Load > 1.0 &&
    //     loop_range_x * CB_Load < loop_range_y)
    //     fast version;
    // else
    //     orig version;
    preHdr->getTerminator()->eraseFromParent();

    IRBuilder<> irb(preHdr);
    FastMathFlags FMF;
    FMF.setFast();
    irb.setFastMathFlags(FMF);
    Value* cond0 = irb.CreateFCmpOGT(
        var_CBLoad_preHdr, ConstantFP::get(irb.getFloatTy(), 1.0));

    Value* cond1 = irb.CreateFCmpOLT(
        irb.CreateFMul(var_range_x, var_CBLoad_preHdr),
        var_range_y);


    irb.CreateCondBr(irb.CreateAnd(cond0, cond1),
        loopSeg1->getLoopPreheader(),
        loop->getLoopPreheader());

    BasicBlock* afterLoop = loop->getExitBlock();
    assert(afterLoop && "No single successor to loop exit block");

    // create loop seg 2 and insert before orig loop (after loop seg 1)
    SmallVector<BasicBlock *, 8> seg2Blocks;
    Loop* loopSeg2 = llvm::cloneLoopWithPreheader(
        PH, loopSeg1->getHeader(), loop, m_vmapToSeg2, ".seg2", m_LI, m_DT, seg2Blocks);
    llvm::remapInstructionsInBlocks(seg2Blocks, m_vmapToSeg2);

    // rewrite loop seg 1
    rewriteLoopSeg1(loopSeg1, var_range_x, var_range_y);

    // link loop seg1 to loop seg2
    linkLoops(loopSeg1, loopSeg2, afterLoop);

    // create seg3 after seg2 before changing loop2 body
    SmallVector<BasicBlock *, 8> seg3Blocks;
    Loop* loopSeg3 = llvm::cloneLoopWithPreheader(
        PH, loopSeg2->getHeader(), loop, m_vmapToSeg3, ".seg3", m_LI, m_DT, seg3Blocks);
    llvm::remapInstructionsInBlocks(seg3Blocks, m_vmapToSeg3);
    BasicBlock* bbSeg3 = loopSeg3->getLoopLatch();

    // rewrite loop seg2
    rewriteLoopSeg2(loopSeg2, var_range_y, var_CBLoad_preHdr);

    // link seg2 -> seg3 -> after_loop
    linkLoops(loopSeg2, loopSeg3, afterLoop);

    bbSeg3->getTerminator()->eraseFromParent();
    BranchInst::Create(afterLoop, bbSeg3);

    rewriteLoopSeg3(bbSeg3, var_range_y);

    addPhiNodes(liveOut, loopSeg1, loopSeg2, bbSeg3, loop);

    return true;
}

void CustomLoopVersioning::addPhiNodes(
    const SmallVectorImpl<Instruction*> &liveOuts,
    Loop* loopSeg1, Loop* loopSeg2, BasicBlock* bbSeg3, Loop* origLoop)
{
    BasicBlock* phiBB = origLoop->getExitBlock();
    assert(phiBB && "No single successor to loop exit block");

    for (auto* Inst : liveOuts)
    {
        Value* seg3Val = m_vmapToSeg3[Inst];
        PHINode* phi;

        phi = PHINode::Create(Inst->getType(), 2, "", &phiBB->front());
        SmallVector<Instruction*, 8> instToDel;
        for (auto* User : Inst->users())
        {
            PHINode* pu = dyn_cast<PHINode>(User);
            if (pu && pu->getParent() == phiBB)
            {
                // replace LCSSA phi with newly created phi node
                pu->replaceAllUsesWith(phi);
                instToDel.push_back(pu);
            }
        }
        for (auto* I : instToDel)
        {
            I->eraseFromParent();
        }
        phi->addIncoming(seg3Val, bbSeg3);
        phi->addIncoming(Inst, origLoop->getExitingBlock());
    }
}


// This pass is mostly forked from LoopSimplification pass
class LoopCanonicalization : public llvm::FunctionPass
{
public:
    static char ID;

    LoopCanonicalization();

    void getAnalysisUsage(llvm::AnalysisUsage& AU) const
    {
        AU.addRequired<llvm::LoopInfoWrapperPass>();
        AU.addRequired<llvm::DominatorTreeWrapperPass>();
        AU.addRequiredID(llvm::LCSSAID);
        AU.addPreservedID(LCSSAID);
    }

    bool runOnFunction(Function& F);
    bool processLoop(Loop* loop, DominatorTree *DT, LoopInfo *LI, bool PreserveLCSSA);
    bool processOneLoop(Loop* loop, DominatorTree *DT, LoopInfo *LI, bool PreserveLCSSA);


    llvm::StringRef getPassName() const
    {
        return "IGC loop canonicalization";
    }

private:
    CodeGenContext * m_cgCtx;
    llvm::LoopInfo* m_LI;
    llvm::DominatorTree* m_DT;
    llvm::Function* m_function;
};
#undef PASS_FLAG
#undef PASS_DESC
#undef PASS_CFG_ONLY
#undef PASS_ANALYSIS
#define PASS_FLAG     "igc-loop-canonicalization"
#define PASS_DESC     "IGC Loop canonicalization"
#define PASS_CFG_ONLY false
#define PASS_ANALYSIS false
IGC_INITIALIZE_PASS_BEGIN(LoopCanonicalization, PASS_FLAG, PASS_DESC, PASS_CFG_ONLY, PASS_ANALYSIS)
IGC_INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass);
IGC_INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass);
IGC_INITIALIZE_PASS_DEPENDENCY(LCSSAWrapperPass)
IGC_INITIALIZE_PASS_END(LoopCanonicalization, PASS_FLAG, PASS_DESC, PASS_CFG_ONLY, PASS_ANALYSIS)


char LoopCanonicalization::ID = 0;

LoopCanonicalization::LoopCanonicalization() : FunctionPass(ID)
{
    initializeLoopCanonicalizationPass(*PassRegistry::getPassRegistry());
}
/// \brief This method is called when the specified loop has more than one
/// backedge in it.
///
/// If this occurs, revector all of these backedges to target a new basic block
/// and have that block branch to the loop header.  This ensures that loops
/// have exactly one backedge.
static BasicBlock *insertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader,
    DominatorTree *DT, LoopInfo *LI) {
    assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");

    // Get information about the loop
    BasicBlock *Header = L->getHeader();
    Function *F = Header->getParent();

    // Unique backedge insertion currently depends on having a preheader.
    if(!Preheader)
        return nullptr;

    // The header is not an EH pad; preheader insertion should ensure this.
    assert(!Header->isEHPad() && "Can't insert backedge to EH pad");

    // Figure out which basic blocks contain back-edges to the loop header.
    std::vector<BasicBlock*> BackedgeBlocks;
    for(pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I) {
        BasicBlock *P = *I;

        // Indirectbr edges cannot be split, so we must fail if we find one.
        if(isa<IndirectBrInst>(P->getTerminator()))
            return nullptr;

        if(P != Preheader) BackedgeBlocks.push_back(P);
    }

    // Create and insert the new backedge block...
    BasicBlock *BEBlock = BasicBlock::Create(Header->getContext(),
        Header->getName() + ".backedge", F);
    BranchInst *BETerminator = BranchInst::Create(Header, BEBlock);
    BETerminator->setDebugLoc(Header->getFirstNonPHI()->getDebugLoc());

    // Move the new backedge block to right after the last backedge block.
    Function::iterator InsertPos = ++BackedgeBlocks.back()->getIterator();
    F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);

    // Now that the block has been inserted into the function, create PHI nodes in
    // the backedge block which correspond to any PHI nodes in the header block.
    for(BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
        PHINode *PN = cast<PHINode>(I);
        PHINode *NewPN = PHINode::Create(PN->getType(), BackedgeBlocks.size(),
            PN->getName() + ".be", BETerminator);

        // Loop over the PHI node, moving all entries except the one for the
        // preheader over to the new PHI node.
        unsigned PreheaderIdx = ~0U;
        bool HasUniqueIncomingValue = true;
        Value *UniqueValue = nullptr;
        for(unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
            BasicBlock *IBB = PN->getIncomingBlock(i);
            Value *IV = PN->getIncomingValue(i);
            if(IBB == Preheader) {
                PreheaderIdx = i;
            }
            else {
                NewPN->addIncoming(IV, IBB);
                if(HasUniqueIncomingValue) {
                    if(!UniqueValue)
                        UniqueValue = IV;
                    else if(UniqueValue != IV)
                        HasUniqueIncomingValue = false;
                }
            }
        }

        // Delete all of the incoming values from the old PN except the preheader's
        assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
        if(PreheaderIdx != 0) {
            PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
            PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
        }
        // Nuke all entries except the zero'th.
        for(unsigned i = 0, e = PN->getNumIncomingValues() - 1; i != e; ++i)
            PN->removeIncomingValue(e - i, false);

        // Finally, add the newly constructed PHI node as the entry for the BEBlock.
        PN->addIncoming(NewPN, BEBlock);

        // As an optimization, if all incoming values in the new PhiNode (which is a
        // subset of the incoming values of the old PHI node) have the same value,
        // eliminate the PHI Node.
        if(HasUniqueIncomingValue) {
            NewPN->replaceAllUsesWith(UniqueValue);
            BEBlock->getInstList().erase(NewPN);
        }
    }

    // Now that all of the PHI nodes have been inserted and adjusted, modify the
    // backedge blocks to jump to the BEBlock instead of the header.
    // If one of the backedges has llvm.loop metadata attached, we remove
    // it from the backedge and add it to BEBlock.
    unsigned LoopMDKind = BEBlock->getContext().getMDKindID("llvm.loop");
    MDNode *LoopMD = nullptr;
    for(unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
        IGCLLVM::TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
        if(!LoopMD)
            LoopMD = TI->getMetadata(LoopMDKind);
        TI->setMetadata(LoopMDKind, nullptr);
        for(unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
            if(TI->getSuccessor(Op) == Header)
                TI->setSuccessor(Op, BEBlock);
    }
    BEBlock->getTerminator()->setMetadata(LoopMDKind, LoopMD);

    //===--- Update all analyses which we must preserve now -----------------===//

    // Update Loop Information - we know that this block is now in the current
    // loop and all parent loops.
    L->addBasicBlockToLoop(BEBlock, *LI);

    // Update dominator information
    DT->splitBlock(BEBlock);

    return BEBlock;
}

bool LoopCanonicalization::runOnFunction(llvm::Function& F)
{
    bool Changed = false;
    LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
    DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
    bool PreserveLCSSA = mustPreserveAnalysisID(LCSSAID);

    // Simplify each loop nest in the function.
    for(LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
        Changed |= processLoop(*I, DT, LI, PreserveLCSSA);
    return Changed;
}

bool LoopCanonicalization::processLoop(llvm::Loop* L, DominatorTree *DT, LoopInfo *LI, bool PreserveLCSSA)
{
    bool changed = false;
    // Worklist maintains our depth-first queue of loops in this nest to process.
    SmallVector<Loop *, 4> Worklist;
    Worklist.push_back(L);

    // Walk the worklist from front to back, pushing newly found sub loops onto
    // the back. This will let us process loops from back to front in depth-first
    // order. We can use this simple process because loops form a tree.
    for(unsigned Idx = 0; Idx != Worklist.size(); ++Idx) {
        Loop *L2 = Worklist[Idx];
        Worklist.append(L2->begin(), L2->end());
    }

    while(!Worklist.empty())
        changed |= processOneLoop(Worklist.pop_back_val(), DT, LI, PreserveLCSSA);
    return changed;
}

// Do basic loop canonicalization to ensure correctness. We need a single header and single latch
bool LoopCanonicalization::processOneLoop(Loop* L, DominatorTree *DT, LoopInfo *LI, bool PreserveLCSSA)
{
    bool changed = false;
    // Does the loop already have a preheader?  If so, don't insert one.
    BasicBlock *Preheader = L->getLoopPreheader();
    if(!Preheader) {
        Preheader = InsertPreheaderForLoop(L, DT, LI, PreserveLCSSA);
        if(Preheader) {
            changed = true;
        }
    }

    // If the header has more than two predecessors at this point (from the
    // preheader and from multiple backedges), we must adjust the loop.
    BasicBlock *LoopLatch = L->getLoopLatch();
    if(!LoopLatch) {
        // If we either couldn't, or didn't want to, identify nesting of the loops,
        // insert a new block that all backedges target, then make it jump to the
        // loop header.
        LoopLatch = insertUniqueBackedgeBlock(L, Preheader, DT, LI);
        if(LoopLatch) {
            changed = true;
        }
    }
    return changed;
}

namespace IGC
{
FunctionPass* createLoopCanonicalization()
{
    return new LoopCanonicalization();
}
}

