/*===================== 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
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IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.


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

#define DEBUG_TYPE "gen-simplification"
#include "Compiler/CISACodeGen/GenSimplification.h"
#include "Compiler/CISACodeGen/ShaderCodeGen.hpp"
#include "Compiler/CodeGenContextWrapper.hpp"
#include "Compiler/MetaDataUtilsWrapper.h"
#include "Compiler/IGCPassSupport.h"
#include "common/LLVMWarningsPush.hpp"
#include <llvm/Pass.h>
#include <llvm/ADT/APInt.h>
#include <llvm/ADT/SmallVector.h>
#include <llvm/IR/InstVisitor.h>
#include <llvm/IR/Instruction.h>
#include <llvm/Support/raw_ostream.h>
#include "common/LLVMWarningsPop.hpp"
#include "Probe/Assertion.h"

using namespace llvm;
using namespace IGC;
using namespace IGC::IGCMD;

namespace {

    class GenSimplification : public FunctionPass,
        public InstVisitor<GenSimplification> {
        bool Changed;

    public:
        static char ID;

        GenSimplification() : FunctionPass(ID), Changed(false) {
            initializeGenSimplificationPass(*PassRegistry::getPassRegistry());
        }

        bool runOnFunction(Function&) override;

        void getAnalysisUsage(AnalysisUsage& AU) const override {
            AU.setPreservesCFG();
            AU.addRequired<CodeGenContextWrapper>();
            AU.addRequired<MetaDataUtilsWrapper>();
        }
        void visitPHINode(PHINode&);
        void visitExtractElement(ExtractElementInst&);

    private:
        bool simplifyVectorPHINodeCase1(PHINode&) const;
        bool simplifyVectorPHINodeCase2(PHINode&) const;
    };

} // End anonymous namespace

char GenSimplification::ID = 0;

#define PASS_FLAG     "igc-shuffle-simplification"
#define PASS_DESC     "Gen Simplification"
#define PASS_CFG_ONLY false
#define PASS_ANALYSIS false
namespace IGC {
    IGC_INITIALIZE_PASS_BEGIN(GenSimplification, PASS_FLAG, PASS_DESC, PASS_CFG_ONLY, PASS_ANALYSIS)
        IGC_INITIALIZE_PASS_DEPENDENCY(CodeGenContextWrapper)
        IGC_INITIALIZE_PASS_DEPENDENCY(MetaDataUtilsWrapper)
        IGC_INITIALIZE_PASS_END(GenSimplification, PASS_FLAG, PASS_DESC, PASS_CFG_ONLY, PASS_ANALYSIS)
}

FunctionPass* IGC::createGenSimplificationPass() {
    return new GenSimplification();
}

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

    Changed = false;
    visit(F);

    return Changed;
}

bool GenSimplification::simplifyVectorPHINodeCase1(PHINode& PN) const {
    IGC_ASSERT(isa<VectorType>(PN.getType()));

    // Check all users are 'bitcast'.
    Type* Ty = nullptr;
    for (auto* U : PN.users()) {
        auto BC = dyn_cast<BitCastInst>(U);
        if (!BC)
            return false;
        if (Ty && Ty != BC->getType())
            return false;
        Ty = BC->getType();
    }
    // Check all operands are constant or 'bitcast' from the same type.
    for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
        auto V = PN.getIncomingValue(i);
        if (isa<Constant>(V))
            continue;
        auto BC = dyn_cast<BitCastInst>(V);
        if (!BC)
            return false;
        if (BC->getSrcTy() != Ty)
            return false;
    }

    IRBuilder<> IRB(&PN);
    // Form a phi-node of type 'Ty'.
    PHINode* NewPN = IRB.CreatePHI(Ty, PN.getNumIncomingValues());
    for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
        auto V = PN.getIncomingValue(i);
        if (auto BC = dyn_cast<BitCastInst>(V)) {
            V = BC->getOperand(0);
        }
        else {
            IGC_ASSERT(isa<Constant>(V));
            V = IRB.CreateBitCast(V, Ty);
        }
        NewPN->addIncoming(V, PN.getIncomingBlock(i));
    }
    for (auto* U : PN.users()) {
        auto BC = cast<BitCastInst>(U);
        BC->replaceAllUsesWith(NewPN);
    }

    return true;
}

bool GenSimplification::simplifyVectorPHINodeCase2(PHINode& PN) const {
    IGC_ASSERT(isa<VectorType>(PN.getType()));

    // Check all users are 'extractelement' with constant indices.
    for (auto* U : PN.users()) {
        auto EEI = dyn_cast<ExtractElementInst>(U);
        if (!EEI)
            return false;
        ConstantInt* Idx = dyn_cast<ConstantInt>(EEI->getIndexOperand());
        if (!Idx)
            return false;
    }

    Type* Ty = PN.getType();
    Type* EltTy = Ty->getScalarType();
    unsigned NumElts = (unsigned)cast<VectorType>(Ty)->getNumElements();

    SmallVector<Value*, 8> Lanes;
    SmallVector<SmallVector<Value*, 8>, 4> Values;

    // Check all operands are constants or chains of 'insertelement'.
    for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
        auto V = PN.getIncomingValue(i);
        // Refill lanes.
        Lanes.clear();
        Lanes.resize(NumElts);
        std::fill(Lanes.begin(), Lanes.end(), UndefValue::get(EltTy));
        // Constant
        if (auto C = dyn_cast<Constant>(V)) {
            for (unsigned j = 0; j != NumElts; ++j) {
                auto Elt = C->getAggregateElement(j);
                if (!Elt)
                    return false;
                Lanes[j] = Elt;
            }
            Values.push_back(Lanes);
            continue;
        }
        // Or chain of 'insertelement'.
        APInt IdxMask(NumElts, 0); // Variable length bit mask.
        while (auto IEI = dyn_cast<InsertElementInst>(V)) {
            ConstantInt* Idx = dyn_cast<ConstantInt>(IEI->getOperand(2));
            if (!Idx)
                return false;
            unsigned j = unsigned(Idx->getZExtValue());
            // Skip if 'j' is already populated.
            if (!IdxMask[j]) {
                Lanes[j] = IEI->getOperand(1);
                IdxMask.setBit(j);
            }
            // Move next.
            V = IEI->getOperand(0);
        }
        if (!isa<UndefValue>(V))
            return false;
        Values.push_back(Lanes);
    }

    IRBuilder<> IRB(&PN);
    // Form scalar phi-nodes of type 'EltTy'.
    for (unsigned j = 0; j != NumElts; ++j) {
        PHINode* NewPN = IRB.CreatePHI(EltTy, PN.getNumIncomingValues());
        for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
            auto V = Values[i][j];
            NewPN->addIncoming(V, PN.getIncomingBlock(i));
        }
        for (auto* U : PN.users()) {
            auto EEI = cast<ExtractElementInst>(U);
            auto Idx = cast<ConstantInt>(EEI->getIndexOperand());
            if (Idx->getZExtValue() != j)
                continue;
            EEI->replaceAllUsesWith(NewPN);
        }
    }

    return true;
}

void GenSimplification::visitPHINode(PHINode& PN) {
    VectorType* VTy = dyn_cast<VectorType>(PN.getType());
    if (!VTy)
        return;

    Changed |= simplifyVectorPHINodeCase1(PN) || simplifyVectorPHINodeCase2(PN);
}

void GenSimplification::visitExtractElement(ExtractElementInst& EEI) {
    // Skip non-2-element vector.
    Value* Vec = EEI.getVectorOperand();
    VectorType* VTy = cast<VectorType>(Vec->getType());
    if (VTy->getNumElements() != 2)
        return;

    // Skip if the index is not zero-extended from a boolean value.
    ZExtInst* ZEI = dyn_cast<ZExtInst>(EEI.getIndexOperand());
    if (!ZEI || !ZEI->getOperand(0)->getType()->isIntegerTy(1))
        return;
    Value* Cond = ZEI->getOperand(0);

    // Collect all scalar values forming this 2-element vector.
    SmallVector<Value*, 2> Values(2);
    unsigned Mask = 0;
    InsertElementInst* IEI = nullptr;
    while ((IEI = dyn_cast<InsertElementInst>(Vec))) {
        ConstantInt* Idx = dyn_cast<ConstantInt>(IEI->getOperand(2));
        if (!Idx)
            return;
        unsigned i = unsigned(Idx->getZExtValue());
        if (i != 0 && i != 1)
            return;
        Values[i] = IEI->getOperand(1);
        Mask |= (1U << i);
        // Early quit if all elements are collected.
        if (Mask == 3)
            break;
        Vec = IEI->getOperand(0);
    }
    // Skip if one of them could not be collected.
    if (Values[0] == nullptr || Values[1] == nullptr)
        return;
    // Convert such an extractelement into select.
    IRBuilder<> IRB(&EEI);
    Value* NewVal = IRB.CreateSelect(Cond, Values[1], Values[0]);
    EEI.replaceAllUsesWith(NewVal);
    Changed = true;
}
