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//===- MachinePostDominators.cpp -Machine Post Dominator Calculation ------===// 
// 
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 
// See https://llvm.org/LICENSE.txt for license information. 
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 
// 
//===----------------------------------------------------------------------===// 
// 
// This file implements simple dominator construction algorithms for finding 
// post dominators on machine functions. 
// 
//===----------------------------------------------------------------------===// 
 
#include "llvm/CodeGen/MachinePostDominators.h" 
#include "llvm/InitializePasses.h" 
 
using namespace llvm; 
 
namespace llvm { 
template class DominatorTreeBase<MachineBasicBlock, true>; // PostDomTreeBase 
 
extern bool VerifyMachineDomInfo; 
} // namespace llvm 
 
char MachinePostDominatorTree::ID = 0; 
 
//declare initializeMachinePostDominatorTreePass 
INITIALIZE_PASS(MachinePostDominatorTree, "machinepostdomtree", 
                "MachinePostDominator Tree Construction", true, true) 
 
MachinePostDominatorTree::MachinePostDominatorTree() 
    : MachineFunctionPass(ID), PDT(nullptr) { 
  initializeMachinePostDominatorTreePass(*PassRegistry::getPassRegistry()); 
} 
 
FunctionPass *MachinePostDominatorTree::createMachinePostDominatorTreePass() { 
  return new MachinePostDominatorTree(); 
} 
 
bool MachinePostDominatorTree::runOnMachineFunction(MachineFunction &F) { 
  PDT = std::make_unique<PostDomTreeT>(); 
  PDT->recalculate(F); 
  return false; 
} 
 
void MachinePostDominatorTree::getAnalysisUsage(AnalysisUsage &AU) const { 
  AU.setPreservesAll(); 
  MachineFunctionPass::getAnalysisUsage(AU); 
} 
 
MachineBasicBlock *MachinePostDominatorTree::findNearestCommonDominator( 
    ArrayRef<MachineBasicBlock *> Blocks) const { 
  assert(!Blocks.empty()); 
 
  MachineBasicBlock *NCD = Blocks.front(); 
  for (MachineBasicBlock *BB : Blocks.drop_front()) { 
    NCD = PDT->findNearestCommonDominator(NCD, BB); 
 
    // Stop when the root is reached. 
    if (PDT->isVirtualRoot(PDT->getNode(NCD))) 
      return nullptr; 
  } 
 
  return NCD; 
} 
 
void MachinePostDominatorTree::verifyAnalysis() const { 
  if (PDT && VerifyMachineDomInfo) 
    if (!PDT->verify(PostDomTreeT::VerificationLevel::Basic)) { 
      errs() << "MachinePostDominatorTree verification failed\n"; 
 
      abort(); 
    } 
} 
 
void MachinePostDominatorTree::print(llvm::raw_ostream &OS, 
                                     const Module *M) const { 
  PDT->print(OS); 
}