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

Copyright (c) 2017 Intel Corporation

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======================= end_copyright_notice ==================================*/
#include "Compiler/CISACodeGen/BlockCoalescing.hpp"
#include "Compiler/MetaDataApi/MetaDataApi.h"
#include "common/igc_regkeys.hpp"
#include "Compiler/IGCPassSupport.h"

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

char BlockCoalescing::ID = 0;
#define PASS_FLAG "BlockCoalescing"
#define PASS_DESCRIPTION "Mark empty blocks after deSSA"
#define PASS_CFG_ONLY true
#define PASS_ANALYSIS true
IGC_INITIALIZE_PASS_BEGIN(BlockCoalescing, PASS_FLAG, PASS_DESCRIPTION, PASS_CFG_ONLY, PASS_ANALYSIS)
IGC_INITIALIZE_PASS_DEPENDENCY(DeSSA)
IGC_INITIALIZE_PASS_DEPENDENCY(CodeGenPatternMatch)
IGC_INITIALIZE_PASS_DEPENDENCY(MetaDataUtilsWrapper)
IGC_INITIALIZE_PASS_END(BlockCoalescing, PASS_FLAG, PASS_DESCRIPTION, PASS_CFG_ONLY, PASS_ANALYSIS)

namespace IGC
{

BlockCoalescing::BlockCoalescing( ) : FunctionPass( ID ) 
{
    initializeBlockCoalescingPass( *PassRegistry::getPassRegistry( ) );
}

bool BlockCoalescing::runOnFunction(Function& F)
{

    MetaDataUtils *pMdUtils = getAnalysis<MetaDataUtilsWrapper>().getMetaDataUtils();
    if (pMdUtils->findFunctionsInfoItem(&F) == pMdUtils->end_FunctionsInfo())
    {
        return false;
    }

    // If De-SSA is disabled we cannot remove empty blocks as they might contain move instructions
    if(IGC_IS_FLAG_ENABLED(DisableEmptyBlockRemoval) || IGC_IS_FLAG_ENABLED(DisableDeSSA))
    {
        return false;
    }
    DeSSA* deSSA = &getAnalysis<DeSSA>();
    CodeGenPatternMatch* patternMatch = &getAnalysis<CodeGenPatternMatch>( );
    for(uint i = 0; i < patternMatch->m_numBlocks; i++)
    {
        SBasicBlock& block = patternMatch->m_blocks[i];
        // An empty block would have only one pattern matching the branch instruction
        if(block.m_dags.size() == 1)
        {
            if(BranchInst* br = dyn_cast<BranchInst>(block.m_dags[0].m_root))
            {
                if(br->isUnconditional())
                {
                    BasicBlock *succ = br->getSuccessor(0);
                    assert(succ && "Branch must have a successor!");
                    if (block.id >= patternMatch->GetBlockId(succ))
                    {
                        if (block.bb->getSinglePredecessor() == nullptr)
                        {
                            // do not remove this BB that goes backward, otherwise
                            // one back edge becomes two back edges, and the 
                            // control-flow reconverge point changes.
                            continue;
                        }
                        else if (IGC_GET_FLAG_VALUE(EnableVISAStructurizer) == FLAG_SCF_Aggressive)
                        {
                            // Do not remove the BB that goes backward, otherwise,
                            // a loop with break will end up with more than one exits,
                            // which will not be recognized as GEN while
                            continue;
                        }
                    }
                    
                    // Make sure that if there is any loop, one of BBs in the loop will
                    // not be in the m_emptyBlocks (eventually condense it to a single BB).
                    if (!hasEmptyBlockLoop(block.bb))
                    {
                        m_emptyBlocks.insert(block.bb);
                    }
                }                
            }
        }
    }
    for (auto &ConstI : patternMatch->ConstantPlacement)
    {
        m_emptyBlocks.erase(ConstI.second);
    }
    for(auto BBI = F.begin(), BBE = F.end(); BBI != BBE; BBI++)
    {
        BasicBlock* bb = &(*BBI);
        for(auto II = BBI->begin(), IE = BBI->end(); II != IE; II++)
        {
            PHINode *phi = dyn_cast<PHINode>(II);
            if(!phi)
            {
                break;
            }
            if(deSSA->isIsolated(phi))
            {
                m_emptyBlocks.erase(bb);
                for(pred_iterator PI = pred_begin(bb), PE = pred_end(bb); PI != PE; PI++)
                {
                    m_emptyBlocks.erase(*PI);
                }
            }
            for(unsigned int i = 0, numOperand = phi->getNumIncomingValues(); i != numOperand; i++ )
            {
                if(deSSA->getRootValue(phi->getOperand(i)) == nullptr || 
                   deSSA->getRootValue(phi->getOperand(i)) != deSSA->getRootValue(phi))
                {
                    if(!isa<UndefValue>(phi->getOperand(i)))
                    {
                        m_emptyBlocks.erase(phi->getIncomingBlock(i));
                    }
                }
            }
        }
    }
    return false;
}

// Check if EmptyBlock (not in m_emptyBlocks, and has single sucessor)
// could form a loop with BBs in m_emptyBlocks; if so, return true.
inline bool BlockCoalescing::hasEmptyBlockLoop(BasicBlock *EmptyBlock)
{
    BasicBlock *succ = EmptyBlock->getTerminator()->getSuccessor(0);

    // No loop formed by BBs in m_emptyBlock, so while will stop.
    //
    // If EmptyBlock would form a loop, it shall go to BBs in
    // m_emptyBlocks and one BB in m_emptyBlocks will goto succ.
    while (m_emptyBlocks.find(succ) != m_emptyBlocks.end())
    {
        succ = succ->getTerminator()->getSuccessor(0);
    }
    return (EmptyBlock == succ);
}

bool BlockCoalescing::IsEmptyBlock(BasicBlock* bb)
{
    return m_emptyBlocks.find(bb)!=m_emptyBlocks.end();
}

BasicBlock* BlockCoalescing::FollowEmptyBlock(BasicBlock* bb)
{
    BasicBlock* block = bb;
    while(IsEmptyBlock(block))
    {
        assert(block->getTerminator()->getNumSuccessors() == 1);
        block = block->getTerminator()->getSuccessor(0);
    }
    return block;
}

BasicBlock* BlockCoalescing::SkipEmptyBasicBlock(BasicBlock* bb)
{
    BasicBlock* block = bb;
    while(IsEmptyBlock(block))
    {
        assert(block->getTerminator()->getNumSuccessors() == 1);
        block = block->getNextNode();
    }
    return block;
}
}
