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/*========================== begin_copyright_notice ============================
Copyright (C) 2017-2021 Intel Corporation
SPDX-License-Identifier: MIT
============================= end_copyright_notice ===========================*/
#include "Compiler/CISACodeGen/BlockCoalescing.hpp"
#include "Compiler/MetaDataApi/MetaDataApi.h"
#include "common/igc_regkeys.hpp"
#include "Compiler/IGCPassSupport.h"
#include "Probe/Assertion.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 = nullptr;
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* const succ = br->getSuccessor(0);
IGC_ASSERT_MESSAGE(nullptr != 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))
{
IGC_ASSERT(block->getTerminator()->getNumSuccessors() == 1);
block = block->getTerminator()->getSuccessor(0);
}
return block;
}
BasicBlock* BlockCoalescing::SkipEmptyBasicBlock(BasicBlock* bb)
{
BasicBlock* block = bb;
while (IsEmptyBlock(block))
{
IGC_ASSERT(block->getTerminator()->getNumSuccessors() == 1);
block = block->getNextNode();
}
return block;
}
}
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