Coverage Report

Created: 2017-10-03 07:32

/Users/buildslave/jenkins/sharedspace/clang-stage2-coverage-R@2/llvm/lib/Target/PowerPC/PPCBranchSelector.cpp
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//===-- PPCBranchSelector.cpp - Emit long conditional branches ------------===//
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//
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//                     The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file contains a pass that scans a machine function to determine which
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// conditional branches need more than 16 bits of displacement to reach their
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// target basic block.  It does this in two passes; a calculation of basic block
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// positions pass, and a branch pseudo op to machine branch opcode pass.  This
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// pass should be run last, just before the assembly printer.
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//
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//===----------------------------------------------------------------------===//
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#include "MCTargetDesc/PPCPredicates.h"
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#include "PPC.h"
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#include "PPCInstrBuilder.h"
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#include "PPCInstrInfo.h"
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#include "PPCSubtarget.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/Support/MathExtras.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Target/TargetSubtargetInfo.h"
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using namespace llvm;
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#define DEBUG_TYPE "ppc-branch-select"
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STATISTIC(NumExpanded, "Number of branches expanded to long format");
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namespace llvm {
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  void initializePPCBSelPass(PassRegistry&);
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}
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namespace {
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  struct PPCBSel : public MachineFunctionPass {
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    static char ID;
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    PPCBSel() : MachineFunctionPass(ID) {
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      initializePPCBSelPass(*PassRegistry::getPassRegistry());
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    }
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    // The sizes of the basic blocks in the function (the first
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    // element of the pair); the second element of the pair is the amount of the
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    // size that is due to potential padding.
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    std::vector<std::pair<unsigned, unsigned>> BlockSizes;
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    bool runOnMachineFunction(MachineFunction &Fn) override;
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    MachineFunctionProperties getRequiredProperties() const override {
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      return MachineFunctionProperties().set(
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          MachineFunctionProperties::Property::NoVRegs);
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    }
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    StringRef getPassName() const override { return "PowerPC Branch Selector"; }
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  };
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  char PPCBSel::ID = 0;
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}
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INITIALIZE_PASS(PPCBSel, "ppc-branch-select", "PowerPC Branch Selector",
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                false, false)
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/// createPPCBranchSelectionPass - returns an instance of the Branch Selection
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/// Pass
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///
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FunctionPass *llvm::createPPCBranchSelectionPass() {
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  return new PPCBSel();
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}
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bool PPCBSel::runOnMachineFunction(MachineFunction &Fn) {
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  const PPCInstrInfo *TII =
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      static_cast<const PPCInstrInfo *>(Fn.getSubtarget().getInstrInfo());
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  // Give the blocks of the function a dense, in-order, numbering.
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  Fn.RenumberBlocks();
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  BlockSizes.resize(Fn.getNumBlockIDs());
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  auto GetAlignmentAdjustment =
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    [](MachineBasicBlock &MBB, unsigned Offset) -> unsigned {
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    unsigned Align = MBB.getAlignment();
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    if (!Align)
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      return 0;
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    unsigned AlignAmt = 1 << Align;
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    unsigned ParentAlign = MBB.getParent()->getAlignment();
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    if (Align <= ParentAlign)
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      return OffsetToAlignment(Offset, AlignAmt);
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    // The alignment of this MBB is larger than the function's alignment, so we
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    // can't tell whether or not it will insert nops. Assume that it will.
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    return AlignAmt + OffsetToAlignment(Offset, AlignAmt);
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  };
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  // We need to be careful about the offset of the first block in the function
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  // because it might not have the function's alignment. This happens because,
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  // under the ELFv2 ABI, for functions which require a TOC pointer, we add a
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  // two-instruction sequence to the start of the function.
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  // Note: This needs to be synchronized with the check in
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  // PPCLinuxAsmPrinter::EmitFunctionBodyStart.
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  unsigned InitialOffset = 0;
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  if (Fn.getSubtarget<PPCSubtarget>().isELFv2ABI() &&
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      !Fn.getRegInfo().use_empty(PPC::X2))
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    InitialOffset = 8;
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  // Measure each MBB and compute a size for the entire function.
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  unsigned FuncSize = InitialOffset;
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  for (MachineFunction::iterator MFI = Fn.begin(), E = Fn.end(); MFI != E;
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++MFI11.9k
) {
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    MachineBasicBlock *MBB = &*MFI;
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    // The end of the previous block may have extra nops if this block has an
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    // alignment requirement.
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    if (
MBB->getNumber() > 011.9k
) {
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      unsigned AlignExtra = GetAlignmentAdjustment(*MBB, FuncSize);
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      auto &BS = BlockSizes[MBB->getNumber()-1];
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      BS.first += AlignExtra;
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      BS.second = AlignExtra;
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      FuncSize += AlignExtra;
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    }
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    unsigned BlockSize = 0;
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    for (MachineInstr &MI : *MBB)
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      BlockSize += TII->getInstSizeInBytes(MI);
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    BlockSizes[MBB->getNumber()].first = BlockSize;
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    FuncSize += BlockSize;
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  }
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  // If the entire function is smaller than the displacement of a branch field,
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  // we know we don't need to shrink any branches in this function.  This is a
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  // common case.
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  if (
FuncSize < (1 << 15)7.48k
) {
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    BlockSizes.clear();
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    return false;
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  }
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0
  
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  // For each conditional branch, if the offset to its destination is larger
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  // than the offset field allows, transform it into a long branch sequence
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  // like this:
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  //   short branch:
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  //     bCC MBB
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  //   long branch:
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  //     b!CC $PC+8
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  //     b MBB
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  //
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  bool MadeChange = true;
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  bool EverMadeChange = false;
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  while (
MadeChange0
) {
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    // Iteratively expand branches until we reach a fixed point.
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    MadeChange = false;
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    for (MachineFunction::iterator MFI = Fn.begin(), E = Fn.end(); MFI != E;
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++MFI0
) {
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      MachineBasicBlock &MBB = *MFI;
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      unsigned MBBStartOffset = 0;
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      for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
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I != E0
;
++I0
) {
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        MachineBasicBlock *Dest = nullptr;
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        if (
I->getOpcode() == PPC::BCC && 0
!I->getOperand(2).isImm()0
)
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          Dest = I->getOperand(2).getMBB();
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        else 
if (0
(I->getOpcode() == PPC::BC || 0
I->getOpcode() == PPC::BCn0
) &&
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                 !I->getOperand(1).isImm())
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          Dest = I->getOperand(1).getMBB();
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        else 
if (0
(I->getOpcode() == PPC::BDNZ8 || 0
I->getOpcode() == PPC::BDNZ0
||
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I->getOpcode() == PPC::BDZ80
||
I->getOpcode() == PPC::BDZ0
) &&
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                 !I->getOperand(0).isImm())
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          Dest = I->getOperand(0).getMBB();
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0
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        if (
!Dest0
) {
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          MBBStartOffset += TII->getInstSizeInBytes(*I);
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          continue;
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        }
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        // Determine the offset from the current branch to the destination
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        // block.
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        int BranchSize;
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        if (
Dest->getNumber() <= MBB.getNumber()0
) {
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          // If this is a backwards branch, the delta is the offset from the
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          // start of this block to this branch, plus the sizes of all blocks
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          // from this block to the dest.
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          BranchSize = MBBStartOffset;
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          for (unsigned i = Dest->getNumber(), e = MBB.getNumber(); 
i != e0
;
++i0
)
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            BranchSize += BlockSizes[i].first;
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        } else {
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          // Otherwise, add the size of the blocks between this block and the
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          // dest to the number of bytes left in this block.
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          BranchSize = -MBBStartOffset;
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0
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          for (unsigned i = MBB.getNumber(), e = Dest->getNumber(); 
i != e0
;
++i0
)
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            BranchSize += BlockSizes[i].first;
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        }
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0
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        // If this branch is in range, ignore it.
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        if (
isInt<16>(BranchSize)0
) {
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          MBBStartOffset += 4;
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          continue;
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        }
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        // Otherwise, we have to expand it to a long branch.
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        MachineInstr &OldBranch = *I;
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        DebugLoc dl = OldBranch.getDebugLoc();
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        if (
I->getOpcode() == PPC::BCC0
) {
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          // The BCC operands are:
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          // 0. PPC branch predicate
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          // 1. CR register
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          // 2. Target MBB
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          PPC::Predicate Pred = (PPC::Predicate)I->getOperand(0).getImm();
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          unsigned CRReg = I->getOperand(1).getReg();
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          // Jump over the uncond branch inst (i.e. $PC+8) on opposite condition.
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          BuildMI(MBB, I, dl, TII->get(PPC::BCC))
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            .addImm(PPC::InvertPredicate(Pred)).addReg(CRReg).addImm(2);
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        } else 
if (0
I->getOpcode() == PPC::BC0
) {
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          unsigned CRBit = I->getOperand(0).getReg();
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          BuildMI(MBB, I, dl, TII->get(PPC::BCn)).addReg(CRBit).addImm(2);
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        } else 
if (0
I->getOpcode() == PPC::BCn0
) {
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          unsigned CRBit = I->getOperand(0).getReg();
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          BuildMI(MBB, I, dl, TII->get(PPC::BC)).addReg(CRBit).addImm(2);
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        } else 
if (0
I->getOpcode() == PPC::BDNZ0
) {
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          BuildMI(MBB, I, dl, TII->get(PPC::BDZ)).addImm(2);
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        } else 
if (0
I->getOpcode() == PPC::BDNZ80
) {
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          BuildMI(MBB, I, dl, TII->get(PPC::BDZ8)).addImm(2);
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        } else 
if (0
I->getOpcode() == PPC::BDZ0
) {
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          BuildMI(MBB, I, dl, TII->get(PPC::BDNZ)).addImm(2);
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        } else 
if (0
I->getOpcode() == PPC::BDZ80
) {
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          BuildMI(MBB, I, dl, TII->get(PPC::BDNZ8)).addImm(2);
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        } else {
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           llvm_unreachable("Unhandled branch type!");
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        }
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        // Uncond branch to the real destination.
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        I = BuildMI(MBB, I, dl, TII->get(PPC::B)).addMBB(Dest);
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0
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        // Remove the old branch from the function.
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        OldBranch.eraseFromParent();
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0
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        // Remember that this instruction is 8-bytes, increase the size of the
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        // block by 4, remember to iterate.
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        BlockSizes[MBB.getNumber()].first += 4;
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        MBBStartOffset += 8;
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        ++NumExpanded;
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        MadeChange = true;
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      }
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    }
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if (0
MadeChange0
) {
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      // If we're going to iterate again, make sure we've updated our
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      // padding-based contributions to the block sizes.
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      unsigned Offset = InitialOffset;
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      for (MachineFunction::iterator MFI = Fn.begin(), E = Fn.end(); MFI != E;
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++MFI0
) {
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        MachineBasicBlock *MBB = &*MFI;
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0
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0
        if (
MBB->getNumber() > 00
) {
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          auto &BS = BlockSizes[MBB->getNumber()-1];
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          BS.first -= BS.second;
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          Offset -= BS.second;
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0
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          unsigned AlignExtra = GetAlignmentAdjustment(*MBB, Offset);
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0
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0
          BS.first += AlignExtra;
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0
          BS.second = AlignExtra;
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0
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0
          Offset += AlignExtra;
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0
        }
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0
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0
        Offset += BlockSizes[MBB->getNumber()].first;
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0
      }
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0
    }
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0
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0
    EverMadeChange |= MadeChange;
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0
  }
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0
  
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0
  BlockSizes.clear();
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  return true;
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}