llvm-project/llvm/lib/Target/PowerPC/PPCMachineBasicBlockUtils.h

//==-- PPCMachineBasicBlockUtils.h - Functions for common MBB operations ---==//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines utility functions for commonly used operations on
// MachineBasicBlock's.
// NOTE: Include this file after defining DEBUG_TYPE so that the debug messages
//       can be emitted for the pass that is using this.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_LIB_TARGET_PPC_MACHINE_BASIC_BLOCK_UTILS_H
#define LLVM_LIB_TARGET_PPC_MACHINE_BASIC_BLOCK_UTILS_H

#include "PPCInstrInfo.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"

#ifndef DEBUG_TYPE
#define DEBUG_TYPE "ppc-generic-mbb-utilities"
#endif

using namespace llvm;

/// Given a basic block \p Successor that potentially contains PHIs, this
/// function will look for any incoming values in the PHIs that are supposed to
/// be coming from \p OrigMBB but whose definition is actually in \p NewMBB.
/// Any such PHIs will be updated to reflect reality.
static void updatePHIs(MachineBasicBlock *Successor, MachineBasicBlock *OrigMBB,
                       MachineBasicBlock *NewMBB, MachineRegisterInfo *MRI) {
  for (auto &MI : Successor->instrs()) {
    if (!MI.isPHI())
      continue;
    // This is a really ugly-looking loop, but it was pillaged directly from
    // MachineBasicBlock::transferSuccessorsAndUpdatePHIs().
    for (unsigned i = 2, e = MI.getNumOperands()+1; i != e; i += 2) {
      MachineOperand &MO = MI.getOperand(i);
      if (MO.getMBB() == OrigMBB) {
        // Check if the instruction is actualy defined in NewMBB.
        if (MI.getOperand(i-1).isReg()) {
          MachineInstr *DefMI = MRI->getVRegDef(MI.getOperand(i-1).getReg());
          if (DefMI->getParent() == NewMBB || !OrigMBB->isSuccessor(Successor)) {
            MO.setMBB(NewMBB);
            break;
          }
        }
      }
    }
  }
}

/// Given a basic block \p Successor that potentially contains PHIs, this
/// function will look for PHIs that have an incoming value from \p OrigMBB
/// and will add the same incoming value from \p NewMBB.
/// NOTE: This should only be used if \p NewMBB is an immediate dominator of
/// \p OrigMBB.
static void addIncomingValuesToPHIs(MachineBasicBlock *Successor,
                                    MachineBasicBlock *OrigMBB,
                                    MachineBasicBlock *NewMBB,
                                    MachineRegisterInfo *MRI) {
  assert(OrigMBB->isSuccessor(NewMBB) && "NewMBB must be a sucessor of OrigMBB");
  for (auto &MI : Successor->instrs()) {
    if (!MI.isPHI())
      continue;
    // This is a really ugly-looking loop, but it was pillaged directly from
    // MachineBasicBlock::transferSuccessorsAndUpdatePHIs().
    for (unsigned i = 2, e = MI.getNumOperands()+1; i != e; i += 2) {
      MachineOperand &MO = MI.getOperand(i);
      if (MO.getMBB() == OrigMBB) {
        MachineInstrBuilder MIB(*MI.getParent()->getParent(), &MI);
        MIB.addReg(MI.getOperand(i-1).getReg()).addMBB(NewMBB);
        break;
      }
    }
  }
}

struct BlockSplitInfo {
  MachineInstr *OrigBranch;
  MachineInstr *SplitBefore;
  MachineInstr *SplitCond;
  bool InvertNewBranch;
  bool InvertOrigBranch;
  bool BranchToFallThrough;
  const MachineBranchProbabilityInfo *MBPI;
  MachineInstr *MIToDelete;
  MachineInstr *NewCond;
  bool allInstrsInSameMBB() {
    if (!OrigBranch || !SplitBefore || !SplitCond)
      return false;
    MachineBasicBlock *MBB = OrigBranch->getParent();
    if (SplitBefore->getParent() != MBB ||
        SplitCond->getParent() != MBB)
      return false;
    if (MIToDelete && MIToDelete->getParent() != MBB)
      return false;
    if (NewCond && NewCond->getParent() != MBB)
      return false;
    return true;
  }
};

/// Splits a MachineBasicBlock to branch before \p SplitBefore. The original
/// branch is \p OrigBranch. The target of the new branch can either be the same
/// as the target of the original branch or the fallthrough successor of the
/// original block as determined by \p BranchToFallThrough. The branch
/// conditions will be inverted according to \p InvertNewBranch and
/// \p InvertOrigBranch. If an instruction that previously fed the branch is to
/// be deleted, it is provided in \p MIToDelete and \p NewCond will be used as
/// the branch condition. The branch probabilities will be set if the
/// MachineBranchProbabilityInfo isn't null.
static bool splitMBB(BlockSplitInfo &BSI) {
  assert(BSI.allInstrsInSameMBB() &&
         "All instructions must be in the same block.");

  MachineBasicBlock *ThisMBB = BSI.OrigBranch->getParent();
  MachineFunction *MF = ThisMBB->getParent();
  MachineRegisterInfo *MRI = &MF->getRegInfo();
  assert(MRI->isSSA() && "Can only do this while the function is in SSA form.");
  if (ThisMBB->succ_size() != 2) {
    DEBUG(dbgs() << "Don't know how to handle blocks that don't have exactly"
                 << " two succesors.\n");
    return false;
  }

  const PPCInstrInfo *TII = MF->getSubtarget<PPCSubtarget>().getInstrInfo();
  unsigned OrigBROpcode = BSI.OrigBranch->getOpcode();
  unsigned InvertedOpcode =
    OrigBROpcode == PPC::BC ? PPC::BCn :
    OrigBROpcode == PPC::BCn ? PPC::BC :
    OrigBROpcode == PPC::BCLR ? PPC::BCLRn : PPC::BCLR;
  unsigned NewBROpcode = BSI.InvertNewBranch ? InvertedOpcode : OrigBROpcode;
  MachineBasicBlock *OrigTarget = BSI.OrigBranch->getOperand(1).getMBB();
  MachineBasicBlock *OrigFallThrough =
    OrigTarget == *ThisMBB->succ_begin() ? *ThisMBB->succ_rbegin() :
    *ThisMBB->succ_begin();
  MachineBasicBlock *NewBRTarget =
    BSI.BranchToFallThrough ? OrigFallThrough : OrigTarget;
  BranchProbability ProbToNewTarget =
    !BSI.MBPI ? BranchProbability::getUnknown() :
    BSI.MBPI->getEdgeProbability(ThisMBB, NewBRTarget);

  // Create a new basic block.
  MachineBasicBlock::iterator InsertPoint = BSI.SplitBefore;
  const BasicBlock *LLVM_BB = ThisMBB->getBasicBlock();
  MachineFunction::iterator It = ThisMBB->getIterator();
  MachineBasicBlock *NewMBB = MF->CreateMachineBasicBlock(LLVM_BB);
  MF->insert(++It, NewMBB);

  // Move everything after SplitBefore into the new block.
  NewMBB->splice(NewMBB->end(), ThisMBB, InsertPoint, ThisMBB->end());
  NewMBB->transferSuccessors(ThisMBB);

  // Add the two successors to ThisMBB. The probabilities come from the
  // existing blocks if available.
  ThisMBB->addSuccessor(NewBRTarget, ProbToNewTarget);
  ThisMBB->addSuccessor(NewMBB, ProbToNewTarget.getCompl());

  // Add the branches to ThisMBB.
  BuildMI(*ThisMBB, ThisMBB->end(), BSI.SplitBefore->getDebugLoc(),
          TII->get(NewBROpcode)).addReg(BSI.SplitCond->getOperand(0).getReg())
          .addMBB(NewBRTarget);
  BuildMI(*ThisMBB, ThisMBB->end(), BSI.SplitBefore->getDebugLoc(),
          TII->get(PPC::B)).addMBB(NewMBB);
  if (BSI.MIToDelete)
    BSI.MIToDelete->eraseFromParent();

  // Change the condition on the original branch and invert it if requested.
  auto FirstTerminator = NewMBB->getFirstTerminator();
  if (BSI.NewCond) {
    assert(FirstTerminator->getOperand(0).isReg() &&
           "Can't update condition of unconditional branch.");
    FirstTerminator->getOperand(0).setReg(BSI.NewCond->getOperand(0).getReg());
  }
  if (BSI.InvertOrigBranch)
    FirstTerminator->setDesc(TII->get(InvertedOpcode));

  // If any of the PHIs in the successors of NewMBB reference values that
  // now come from NewMBB, they need to be updated.
  for (auto *Succ : NewMBB->successors()) {
    updatePHIs(Succ, ThisMBB, NewMBB, MRI);
  }
  addIncomingValuesToPHIs(NewBRTarget, ThisMBB, NewMBB, MRI);

  DEBUG(dbgs() << "After splitting, ThisMBB:\n"; ThisMBB->dump());
  DEBUG(dbgs() << "NewMBB:\n"; NewMBB->dump());
  DEBUG(dbgs() << "New branch-to block:\n"; NewBRTarget->dump());
  return true;
}


#endif