LCOV - code coverage report
Current view: top level - lib/CodeGen - BranchFolding.cpp (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 712 750 94.9 %
Date: 2018-02-20 03:34:22 Functions: 39 46 84.8 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : //===- BranchFolding.cpp - Fold machine code branch instructions ----------===//
       2             : //
       3             : //                     The LLVM Compiler Infrastructure
       4             : //
       5             : // This file is distributed under the University of Illinois Open Source
       6             : // License. See LICENSE.TXT for details.
       7             : //
       8             : //===----------------------------------------------------------------------===//
       9             : //
      10             : // This pass forwards branches to unconditional branches to make them branch
      11             : // directly to the target block.  This pass often results in dead MBB's, which
      12             : // it then removes.
      13             : //
      14             : // Note that this pass must be run after register allocation, it cannot handle
      15             : // SSA form. It also must handle virtual registers for targets that emit virtual
      16             : // ISA (e.g. NVPTX).
      17             : //
      18             : //===----------------------------------------------------------------------===//
      19             : 
      20             : #include "BranchFolding.h"
      21             : #include "llvm/ADT/BitVector.h"
      22             : #include "llvm/ADT/DenseMap.h"
      23             : #include "llvm/ADT/STLExtras.h"
      24             : #include "llvm/ADT/SmallPtrSet.h"
      25             : #include "llvm/ADT/SmallSet.h"
      26             : #include "llvm/ADT/SmallVector.h"
      27             : #include "llvm/ADT/Statistic.h"
      28             : #include "llvm/CodeGen/Analysis.h"
      29             : #include "llvm/CodeGen/LivePhysRegs.h"
      30             : #include "llvm/CodeGen/MachineBasicBlock.h"
      31             : #include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
      32             : #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
      33             : #include "llvm/CodeGen/MachineFunction.h"
      34             : #include "llvm/CodeGen/MachineFunctionPass.h"
      35             : #include "llvm/CodeGen/MachineInstr.h"
      36             : #include "llvm/CodeGen/MachineInstrBuilder.h"
      37             : #include "llvm/CodeGen/MachineJumpTableInfo.h"
      38             : #include "llvm/CodeGen/MachineLoopInfo.h"
      39             : #include "llvm/CodeGen/MachineModuleInfo.h"
      40             : #include "llvm/CodeGen/MachineOperand.h"
      41             : #include "llvm/CodeGen/MachineRegisterInfo.h"
      42             : #include "llvm/CodeGen/TargetInstrInfo.h"
      43             : #include "llvm/CodeGen/TargetOpcodes.h"
      44             : #include "llvm/CodeGen/TargetPassConfig.h"
      45             : #include "llvm/CodeGen/TargetRegisterInfo.h"
      46             : #include "llvm/CodeGen/TargetSubtargetInfo.h"
      47             : #include "llvm/IR/DebugInfoMetadata.h"
      48             : #include "llvm/IR/DebugLoc.h"
      49             : #include "llvm/IR/Function.h"
      50             : #include "llvm/MC/LaneBitmask.h"
      51             : #include "llvm/MC/MCRegisterInfo.h"
      52             : #include "llvm/Pass.h"
      53             : #include "llvm/Support/BlockFrequency.h"
      54             : #include "llvm/Support/BranchProbability.h"
      55             : #include "llvm/Support/CommandLine.h"
      56             : #include "llvm/Support/Debug.h"
      57             : #include "llvm/Support/ErrorHandling.h"
      58             : #include "llvm/Support/raw_ostream.h"
      59             : #include "llvm/Target/TargetMachine.h"
      60             : #include <cassert>
      61             : #include <cstddef>
      62             : #include <iterator>
      63             : #include <numeric>
      64             : #include <vector>
      65             : 
      66             : using namespace llvm;
      67             : 
      68             : #define DEBUG_TYPE "branch-folder"
      69             : 
      70             : STATISTIC(NumDeadBlocks, "Number of dead blocks removed");
      71             : STATISTIC(NumBranchOpts, "Number of branches optimized");
      72             : STATISTIC(NumTailMerge , "Number of block tails merged");
      73             : STATISTIC(NumHoist     , "Number of times common instructions are hoisted");
      74             : STATISTIC(NumTailCalls,  "Number of tail calls optimized");
      75             : 
      76       97303 : static cl::opt<cl::boolOrDefault> FlagEnableTailMerge("enable-tail-merge",
      77       97303 :                               cl::init(cl::BOU_UNSET), cl::Hidden);
      78             : 
      79             : // Throttle for huge numbers of predecessors (compile speed problems)
      80             : static cl::opt<unsigned>
      81       97303 : TailMergeThreshold("tail-merge-threshold",
      82       97303 :           cl::desc("Max number of predecessors to consider tail merging"),
      83      291909 :           cl::init(150), cl::Hidden);
      84             : 
      85             : // Heuristic for tail merging (and, inversely, tail duplication).
      86             : // TODO: This should be replaced with a target query.
      87             : static cl::opt<unsigned>
      88       97303 : TailMergeSize("tail-merge-size",
      89       97303 :               cl::desc("Min number of instructions to consider tail merging"),
      90      291909 :               cl::init(3), cl::Hidden);
      91             : 
      92             : namespace {
      93             : 
      94             :   /// BranchFolderPass - Wrap branch folder in a machine function pass.
      95       17295 :   class BranchFolderPass : public MachineFunctionPass {
      96             :   public:
      97             :     static char ID;
      98             : 
      99       17395 :     explicit BranchFolderPass(): MachineFunctionPass(ID) {}
     100             : 
     101             :     bool runOnMachineFunction(MachineFunction &MF) override;
     102             : 
     103       17292 :     void getAnalysisUsage(AnalysisUsage &AU) const override {
     104             :       AU.addRequired<MachineBlockFrequencyInfo>();
     105             :       AU.addRequired<MachineBranchProbabilityInfo>();
     106             :       AU.addRequired<TargetPassConfig>();
     107       17292 :       MachineFunctionPass::getAnalysisUsage(AU);
     108       17292 :     }
     109             :   };
     110             : 
     111             : } // end anonymous namespace
     112             : 
     113             : char BranchFolderPass::ID = 0;
     114             : 
     115             : char &llvm::BranchFolderPassID = BranchFolderPass::ID;
     116             : 
     117      134608 : INITIALIZE_PASS(BranchFolderPass, DEBUG_TYPE,
     118             :                 "Control Flow Optimizer", false, false)
     119             : 
     120      159587 : bool BranchFolderPass::runOnMachineFunction(MachineFunction &MF) {
     121      159587 :   if (skipFunction(MF.getFunction()))
     122             :     return false;
     123             : 
     124      159476 :   TargetPassConfig *PassConfig = &getAnalysis<TargetPassConfig>();
     125             :   // TailMerge can create jump into if branches that make CFG irreducible for
     126             :   // HW that requires structurized CFG.
     127      476239 :   bool EnableTailMerge = !MF.getTarget().requiresStructuredCFG() &&
     128      157287 :                          PassConfig->getEnableTailMerge();
     129             :   BranchFolder::MBFIWrapper MBBFreqInfo(
     130      159476 :       getAnalysis<MachineBlockFrequencyInfo>());
     131             :   BranchFolder Folder(EnableTailMerge, /*CommonHoist=*/true, MBBFreqInfo,
     132      318952 :                       getAnalysis<MachineBranchProbabilityInfo>());
     133      318952 :   return Folder.OptimizeFunction(MF, MF.getSubtarget().getInstrInfo(),
     134      159476 :                                  MF.getSubtarget().getRegisterInfo(),
     135      159476 :                                  getAnalysisIfAvailable<MachineModuleInfo>());
     136             : }
     137             : 
     138      196602 : BranchFolder::BranchFolder(bool defaultEnableTailMerge, bool CommonHoist,
     139             :                            MBFIWrapper &FreqInfo,
     140             :                            const MachineBranchProbabilityInfo &ProbInfo,
     141      196602 :                            unsigned MinTailLength)
     142             :     : EnableHoistCommonCode(CommonHoist), MinCommonTailLength(MinTailLength),
     143      589806 :       MBBFreqInfo(FreqInfo), MBPI(ProbInfo) {
     144      196602 :   if (MinCommonTailLength == 0)
     145      190272 :     MinCommonTailLength = TailMergeSize;
     146      196602 :   switch (FlagEnableTailMerge) {
     147      196548 :   case cl::BOU_UNSET: EnableTailMerge = defaultEnableTailMerge; break;
     148           3 :   case cl::BOU_TRUE: EnableTailMerge = true; break;
     149          51 :   case cl::BOU_FALSE: EnableTailMerge = false; break;
     150             :   }
     151      196602 : }
     152             : 
     153       10846 : void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) {
     154             :   assert(MBB->pred_empty() && "MBB must be dead!");
     155             :   DEBUG(dbgs() << "\nRemoving MBB: " << *MBB);
     156             : 
     157       10846 :   MachineFunction *MF = MBB->getParent();
     158             :   // drop all successors.
     159       23870 :   while (!MBB->succ_empty())
     160        6512 :     MBB->removeSuccessor(MBB->succ_end()-1);
     161             : 
     162             :   // Avoid matching if this pointer gets reused.
     163             :   TriedMerging.erase(MBB);
     164             : 
     165             :   // Remove the block.
     166             :   MF->erase(MBB);
     167       10846 :   FuncletMembership.erase(MBB);
     168       10846 :   if (MLI)
     169             :     MLI->removeBlock(MBB);
     170       10846 : }
     171             : 
     172      196602 : bool BranchFolder::OptimizeFunction(MachineFunction &MF,
     173             :                                     const TargetInstrInfo *tii,
     174             :                                     const TargetRegisterInfo *tri,
     175             :                                     MachineModuleInfo *mmi,
     176             :                                     MachineLoopInfo *mli, bool AfterPlacement) {
     177      196602 :   if (!tii) return false;
     178             : 
     179      196602 :   TriedMerging.clear();
     180             : 
     181      196602 :   MachineRegisterInfo &MRI = MF.getRegInfo();
     182      196602 :   AfterBlockPlacement = AfterPlacement;
     183      196602 :   TII = tii;
     184      196602 :   TRI = tri;
     185      196602 :   MMI = mmi;
     186      196602 :   MLI = mli;
     187      196602 :   this->MRI = &MRI;
     188             : 
     189      393204 :   UpdateLiveIns = MRI.tracksLiveness() && TRI->trackLivenessAfterRegAlloc(MF);
     190      196602 :   if (!UpdateLiveIns)
     191        6363 :     MRI.invalidateLiveness();
     192             : 
     193             :   // Fix CFG.  The later algorithms expect it to be right.
     194             :   bool MadeChange = false;
     195      696221 :   for (MachineBasicBlock &MBB : MF) {
     196      499619 :     MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
     197             :     SmallVector<MachineOperand, 4> Cond;
     198      499619 :     if (!TII->analyzeBranch(MBB, TBB, FBB, Cond, true))
     199      301025 :       MadeChange |= MBB.CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
     200             :   }
     201             : 
     202             :   // Recalculate funclet membership.
     203      393204 :   FuncletMembership = getFuncletMembership(MF);
     204             : 
     205             :   bool MadeChangeThisIteration = true;
     206      608618 :   while (MadeChangeThisIteration) {
     207      206008 :     MadeChangeThisIteration    = TailMergeBlocks(MF);
     208             :     // No need to clean up if tail merging does not change anything after the
     209             :     // block placement.
     210      206008 :     if (!AfterBlockPlacement || MadeChangeThisIteration)
     211      199678 :       MadeChangeThisIteration |= OptimizeBranches(MF);
     212      206008 :     if (EnableHoistCommonCode)
     213      167115 :       MadeChangeThisIteration |= HoistCommonCode(MF);
     214      206008 :     MadeChange |= MadeChangeThisIteration;
     215             :   }
     216             : 
     217             :   // See if any jump tables have become dead as the code generator
     218             :   // did its thing.
     219      196602 :   MachineJumpTableInfo *JTI = MF.getJumpTableInfo();
     220      196602 :   if (!JTI)
     221             :     return MadeChange;
     222             : 
     223             :   // Walk the function to find jump tables that are live.
     224         924 :   BitVector JTIsLive(JTI->getJumpTables().size());
     225        6984 :   for (const MachineBasicBlock &BB : MF) {
     226       70941 :     for (const MachineInstr &I : BB)
     227      585093 :       for (const MachineOperand &Op : I.operands()) {
     228      263598 :         if (!Op.isJTI()) continue;
     229             : 
     230             :         // Remember that this JT is live.
     231         775 :         JTIsLive.set(Op.getIndex());
     232             :       }
     233             :   }
     234             : 
     235             :   // Finally, remove dead jump tables.  This happens when the
     236             :   // indirect jump was unreachable (and thus deleted).
     237         948 :   for (unsigned i = 0, e = JTIsLive.size(); i != e; ++i)
     238         486 :     if (!JTIsLive.test(i)) {
     239             :       JTI->RemoveJumpTable(i);
     240             :       MadeChange = true;
     241             :     }
     242             : 
     243             :   return MadeChange;
     244             : }
     245             : 
     246             : //===----------------------------------------------------------------------===//
     247             : //  Tail Merging of Blocks
     248             : //===----------------------------------------------------------------------===//
     249             : 
     250             : /// HashMachineInstr - Compute a hash value for MI and its operands.
     251      583167 : static unsigned HashMachineInstr(const MachineInstr &MI) {
     252      583167 :   unsigned Hash = MI.getOpcode();
     253     2770119 :   for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
     254     2186952 :     const MachineOperand &Op = MI.getOperand(i);
     255             : 
     256             :     // Merge in bits from the operand if easy. We can't use MachineOperand's
     257             :     // hash_code here because it's not deterministic and we sort by hash value
     258             :     // later.
     259             :     unsigned OperandHash = 0;
     260     2186952 :     switch (Op.getType()) {
     261     1405419 :     case MachineOperand::MO_Register:
     262     1405419 :       OperandHash = Op.getReg();
     263     1405419 :       break;
     264      394415 :     case MachineOperand::MO_Immediate:
     265      394415 :       OperandHash = Op.getImm();
     266      394415 :       break;
     267      111016 :     case MachineOperand::MO_MachineBasicBlock:
     268      111016 :       OperandHash = Op.getMBB()->getNumber();
     269      111016 :       break;
     270         393 :     case MachineOperand::MO_FrameIndex:
     271             :     case MachineOperand::MO_ConstantPoolIndex:
     272             :     case MachineOperand::MO_JumpTableIndex:
     273         393 :       OperandHash = Op.getIndex();
     274         393 :       break;
     275      165862 :     case MachineOperand::MO_GlobalAddress:
     276             :     case MachineOperand::MO_ExternalSymbol:
     277             :       // Global address / external symbol are too hard, don't bother, but do
     278             :       // pull in the offset.
     279      331724 :       OperandHash = Op.getOffset();
     280      165862 :       break;
     281             :     default:
     282             :       break;
     283             :     }
     284             : 
     285     2186952 :     Hash += ((OperandHash << 3) | Op.getType()) << (i & 31);
     286             :   }
     287      583167 :   return Hash;
     288             : }
     289             : 
     290             : /// HashEndOfMBB - Hash the last instruction in the MBB.
     291      588775 : static unsigned HashEndOfMBB(const MachineBasicBlock &MBB) {
     292             :   MachineBasicBlock::const_iterator I = MBB.getLastNonDebugInstr();
     293      588775 :   if (I == MBB.end())
     294             :     return 0;
     295             : 
     296      583167 :   return HashMachineInstr(*I);
     297             : }
     298             : 
     299             : /// ComputeCommonTailLength - Given two machine basic blocks, compute the number
     300             : /// of instructions they actually have in common together at their end.  Return
     301             : /// iterators for the first shared instruction in each block.
     302      814469 : static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1,
     303             :                                         MachineBasicBlock *MBB2,
     304             :                                         MachineBasicBlock::iterator &I1,
     305             :                                         MachineBasicBlock::iterator &I2) {
     306      814469 :   I1 = MBB1->end();
     307      814469 :   I2 = MBB2->end();
     308             : 
     309             :   unsigned TailLen = 0;
     310     4080666 :   while (I1 != MBB1->begin() && I2 != MBB2->begin()) {
     311             :     --I1; --I2;
     312             :     // Skip debugging pseudos; necessary to avoid changing the code.
     313     1472233 :     while (I1->isDebugValue()) {
     314         300 :       if (I1==MBB1->begin()) {
     315         107 :         while (I2->isDebugValue()) {
     316          67 :           if (I2==MBB2->begin())
     317             :             // I1==DBG at begin; I2==DBG at begin
     318             :             return TailLen;
     319             :           --I2;
     320             :         }
     321             :         ++I2;
     322             :         // I1==DBG at begin; I2==non-DBG, or first of DBGs not at begin
     323          40 :         return TailLen;
     324             :       }
     325             :       --I1;
     326             :     }
     327             :     // I1==first (untested) non-DBG preceding known match
     328     1472188 :     while (I2->isDebugValue()) {
     329         258 :       if (I2==MBB2->begin()) {
     330             :         ++I1;
     331             :         // I1==non-DBG, or first of DBGs not at begin; I2==DBG at begin
     332           3 :         return TailLen;
     333             :       }
     334             :       --I2;
     335             :     }
     336             :     // I1, I2==first (untested) non-DBGs preceding known match
     337     2353123 :     if (!I1->isIdenticalTo(*I2) ||
     338             :         // FIXME: This check is dubious. It's used to get around a problem where
     339             :         // people incorrectly expect inline asm directives to remain in the same
     340             :         // relative order. This is untenable because normal compiler
     341             :         // optimizations (like this one) may reorder and/or merge these
     342             :         // directives.
     343             :         I1->isInlineAsm()) {
     344             :       ++I1; ++I2;
     345             :       break;
     346             :     }
     347      881079 :     ++TailLen;
     348             :   }
     349             :   // Back past possible debugging pseudos at beginning of block.  This matters
     350             :   // when one block differs from the other only by whether debugging pseudos
     351             :   // are present at the beginning. (This way, the various checks later for
     352             :   // I1==MBB1->begin() work as expected.)
     353     1005922 :   if (I1 == MBB1->begin() && I2 != MBB2->begin()) {
     354             :     --I2;
     355       64060 :     while (I2->isDebugValue()) {
     356          10 :       if (I2 == MBB2->begin())
     357             :         return TailLen;
     358             :       --I2;
     359             :     }
     360             :     ++I2;
     361             :   }
     362      973921 :   if (I2 == MBB2->begin() && I1 != MBB1->begin()) {
     363             :     --I1;
     364       32058 :     while (I1->isDebugValue()) {
     365           5 :       if (I1 == MBB1->begin())
     366             :         return TailLen;
     367             :       --I1;
     368             :     }
     369             :     ++I1;
     370             :   }
     371             :   return TailLen;
     372             : }
     373             : 
     374       12296 : void BranchFolder::replaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
     375             :                                            MachineBasicBlock &NewDest) {
     376       12296 :   if (UpdateLiveIns) {
     377             :     // OldInst should always point to an instruction.
     378       12283 :     MachineBasicBlock &OldMBB = *OldInst->getParent();
     379       12283 :     LiveRegs.clear();
     380       12283 :     LiveRegs.addLiveOuts(OldMBB);
     381             :     // Move backward to the place where will insert the jump.
     382       12283 :     MachineBasicBlock::iterator I = OldMBB.end();
     383             :     do {
     384             :       --I;
     385       56180 :       LiveRegs.stepBackward(*I);
     386       56180 :     } while (I != OldInst);
     387             : 
     388             :     // Merging the tails may have switched some undef operand to non-undef ones.
     389             :     // Add IMPLICIT_DEFS into OldMBB as necessary to have a definition of the
     390             :     // register.
     391       33918 :     for (MachineBasicBlock::RegisterMaskPair P : NewDest.liveins()) {
     392             :       // We computed the liveins with computeLiveIn earlier and should only see
     393             :       // full registers:
     394             :       assert(P.LaneMask == LaneBitmask::getAll() &&
     395             :              "Can only handle full register.");
     396             :       MCPhysReg Reg = P.PhysReg;
     397       21635 :       if (!LiveRegs.available(*MRI, Reg))
     398       21634 :         continue;
     399           1 :       DebugLoc DL;
     400           2 :       BuildMI(OldMBB, OldInst, DL, TII->get(TargetOpcode::IMPLICIT_DEF), Reg);
     401             :     }
     402             :   }
     403             : 
     404       12296 :   TII->ReplaceTailWithBranchTo(OldInst, &NewDest);
     405             :   ++NumTailMerge;
     406       12296 : }
     407             : 
     408        3460 : MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB,
     409             :                                             MachineBasicBlock::iterator BBI1,
     410             :                                             const BasicBlock *BB) {
     411        3460 :   if (!TII->isLegalToSplitMBBAt(CurMBB, BBI1))
     412             :     return nullptr;
     413             : 
     414        3460 :   MachineFunction &MF = *CurMBB.getParent();
     415             : 
     416             :   // Create the fall-through block.
     417        3460 :   MachineFunction::iterator MBBI = CurMBB.getIterator();
     418        3460 :   MachineBasicBlock *NewMBB = MF.CreateMachineBasicBlock(BB);
     419        3460 :   CurMBB.getParent()->insert(++MBBI, NewMBB);
     420             : 
     421             :   // Move all the successors of this block to the specified block.
     422        3460 :   NewMBB->transferSuccessors(&CurMBB);
     423             : 
     424             :   // Add an edge from CurMBB to NewMBB for the fall-through.
     425        3460 :   CurMBB.addSuccessor(NewMBB);
     426             : 
     427             :   // Splice the code over.
     428             :   NewMBB->splice(NewMBB->end(), &CurMBB, BBI1, CurMBB.end());
     429             : 
     430             :   // NewMBB belongs to the same loop as CurMBB.
     431        3460 :   if (MLI)
     432          12 :     if (MachineLoop *ML = MLI->getLoopFor(&CurMBB))
     433          24 :       ML->addBasicBlockToLoop(NewMBB, MLI->getBase());
     434             : 
     435             :   // NewMBB inherits CurMBB's block frequency.
     436        3460 :   MBBFreqInfo.setBlockFreq(NewMBB, MBBFreqInfo.getBlockFreq(&CurMBB));
     437             : 
     438        3460 :   if (UpdateLiveIns)
     439        3451 :     computeAndAddLiveIns(LiveRegs, *NewMBB);
     440             : 
     441             :   // Add the new block to the funclet.
     442        3460 :   const auto &FuncletI = FuncletMembership.find(&CurMBB);
     443        3460 :   if (FuncletI != FuncletMembership.end()) {
     444           0 :     auto n = FuncletI->second;
     445           0 :     FuncletMembership[NewMBB] = n;
     446             :   }
     447             : 
     448             :   return NewMBB;
     449             : }
     450             : 
     451             : /// EstimateRuntime - Make a rough estimate for how long it will take to run
     452             : /// the specified code.
     453        8330 : static unsigned EstimateRuntime(MachineBasicBlock::iterator I,
     454             :                                 MachineBasicBlock::iterator E) {
     455             :   unsigned Time = 0;
     456       26576 :   for (; I != E; ++I) {
     457       18246 :     if (I->isDebugValue())
     458          30 :       continue;
     459       18216 :     if (I->isCall())
     460        1148 :       Time += 10;
     461       30865 :     else if (I->mayLoad() || I->mayStore())
     462        3952 :       Time += 2;
     463             :     else
     464       13116 :       ++Time;
     465             :   }
     466        8330 :   return Time;
     467             : }
     468             : 
     469             : // CurMBB needs to add an unconditional branch to SuccMBB (we removed these
     470             : // branches temporarily for tail merging).  In the case where CurMBB ends
     471             : // with a conditional branch to the next block, optimize by reversing the
     472             : // test and conditionally branching to SuccMBB instead.
     473      224217 : static void FixTail(MachineBasicBlock *CurMBB, MachineBasicBlock *SuccBB,
     474             :                     const TargetInstrInfo *TII) {
     475      224217 :   MachineFunction *MF = CurMBB->getParent();
     476             :   MachineFunction::iterator I = std::next(MachineFunction::iterator(CurMBB));
     477      224217 :   MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
     478             :   SmallVector<MachineOperand, 4> Cond;
     479      224217 :   DebugLoc dl = CurMBB->findBranchDebugLoc();
     480      224217 :   if (I != MF->end() && !TII->analyzeBranch(*CurMBB, TBB, FBB, Cond, true)) {
     481             :     MachineBasicBlock *NextBB = &*I;
     482      221638 :     if (TBB == NextBB && !Cond.empty() && !FBB) {
     483       96478 :       if (!TII->reverseBranchCondition(Cond)) {
     484       96476 :         TII->removeBranch(*CurMBB);
     485      192952 :         TII->insertBranch(*CurMBB, SuccBB, nullptr, Cond, dl);
     486             :         return;
     487             :       }
     488             :     }
     489             :   }
     490      127741 :   TII->insertBranch(*CurMBB, SuccBB, nullptr,
     491      255482 :                     SmallVector<MachineOperand, 0>(), dl);
     492             : }
     493             : 
     494             : bool
     495           0 : BranchFolder::MergePotentialsElt::operator<(const MergePotentialsElt &o) const {
     496      476767 :   if (getHash() < o.getHash())
     497             :     return true;
     498      203508 :   if (getHash() > o.getHash())
     499             :     return false;
     500      153376 :   if (getBlock()->getNumber() < o.getBlock()->getNumber())
     501             :     return true;
     502       50194 :   if (getBlock()->getNumber() > o.getBlock()->getNumber())
     503             :     return false;
     504             :   // _GLIBCXX_DEBUG checks strict weak ordering, which involves comparing
     505             :   // an object with itself.
     506             : #ifndef _GLIBCXX_DEBUG
     507           0 :   llvm_unreachable("Predecessor appears twice");
     508             : #else
     509             :   return false;
     510             : #endif
     511             : }
     512             : 
     513             : BlockFrequency
     514     1414894 : BranchFolder::MBFIWrapper::getBlockFreq(const MachineBasicBlock *MBB) const {
     515     1414894 :   auto I = MergedBBFreq.find(MBB);
     516             : 
     517     1414894 :   if (I != MergedBBFreq.end())
     518        4918 :     return I->second;
     519             : 
     520     1409976 :   return MBFI.getBlockFreq(MBB);
     521             : }
     522             : 
     523           0 : void BranchFolder::MBFIWrapper::setBlockFreq(const MachineBasicBlock *MBB,
     524             :                                              BlockFrequency F) {
     525       17904 :   MergedBBFreq[MBB] = F;
     526           0 : }
     527             : 
     528             : raw_ostream &
     529           0 : BranchFolder::MBFIWrapper::printBlockFreq(raw_ostream &OS,
     530             :                                           const MachineBasicBlock *MBB) const {
     531           0 :   return MBFI.printBlockFreq(OS, getBlockFreq(MBB));
     532             : }
     533             : 
     534             : raw_ostream &
     535           0 : BranchFolder::MBFIWrapper::printBlockFreq(raw_ostream &OS,
     536             :                                           const BlockFrequency Freq) const {
     537           0 :   return MBFI.printBlockFreq(OS, Freq);
     538             : }
     539             : 
     540           0 : void BranchFolder::MBFIWrapper::view(const Twine &Name, bool isSimple) {
     541           0 :   MBFI.view(Name, isSimple);
     542           0 : }
     543             : 
     544             : uint64_t
     545        1713 : BranchFolder::MBFIWrapper::getEntryFreq() const {
     546        1713 :   return MBFI.getEntryFreq();
     547             : }
     548             : 
     549             : /// CountTerminators - Count the number of terminators in the given
     550             : /// block and set I to the position of the first non-terminator, if there
     551             : /// is one, or MBB->end() otherwise.
     552        4555 : static unsigned CountTerminators(MachineBasicBlock *MBB,
     553             :                                  MachineBasicBlock::iterator &I) {
     554        4555 :   I = MBB->end();
     555             :   unsigned NumTerms = 0;
     556             :   while (true) {
     557        7029 :     if (I == MBB->begin()) {
     558           1 :       I = MBB->end();
     559           1 :       break;
     560             :     }
     561             :     --I;
     562        5791 :     if (!I->isTerminator()) break;
     563        1237 :     ++NumTerms;
     564             :   }
     565        4555 :   return NumTerms;
     566             : }
     567             : 
     568             : /// A no successor, non-return block probably ends in unreachable and is cold.
     569             : /// Also consider a block that ends in an indirect branch to be a return block,
     570             : /// since many targets use plain indirect branches to return.
     571      120063 : static bool blockEndsInUnreachable(const MachineBasicBlock *MBB) {
     572      120063 :   if (!MBB->succ_empty())
     573             :     return false;
     574      106555 :   if (MBB->empty())
     575             :     return true;
     576      106845 :   return !(MBB->back().isReturn() || MBB->back().isIndirectBranch());
     577             : }
     578             : 
     579             : /// ProfitableToMerge - Check if two machine basic blocks have a common tail
     580             : /// and decide if it would be profitable to merge those tails.  Return the
     581             : /// length of the common tail and iterators to the first common instruction
     582             : /// in each block.
     583             : /// MBB1, MBB2      The blocks to check
     584             : /// MinCommonTailLength  Minimum size of tail block to be merged.
     585             : /// CommonTailLen   Out parameter to record the size of the shared tail between
     586             : ///                 MBB1 and MBB2
     587             : /// I1, I2          Iterator references that will be changed to point to the first
     588             : ///                 instruction in the common tail shared by MBB1,MBB2
     589             : /// SuccBB          A common successor of MBB1, MBB2 which are in a canonical form
     590             : ///                 relative to SuccBB
     591             : /// PredBB          The layout predecessor of SuccBB, if any.
     592             : /// FuncletMembership  map from block to funclet #.
     593             : /// AfterPlacement  True if we are merging blocks after layout. Stricter
     594             : ///                 thresholds apply to prevent undoing tail-duplication.
     595             : static bool
     596      814533 : ProfitableToMerge(MachineBasicBlock *MBB1, MachineBasicBlock *MBB2,
     597             :                   unsigned MinCommonTailLength, unsigned &CommonTailLen,
     598             :                   MachineBasicBlock::iterator &I1,
     599             :                   MachineBasicBlock::iterator &I2, MachineBasicBlock *SuccBB,
     600             :                   MachineBasicBlock *PredBB,
     601             :                   DenseMap<const MachineBasicBlock *, int> &FuncletMembership,
     602             :                   bool AfterPlacement) {
     603             :   // It is never profitable to tail-merge blocks from two different funclets.
     604      814533 :   if (!FuncletMembership.empty()) {
     605          92 :     auto Funclet1 = FuncletMembership.find(MBB1);
     606             :     assert(Funclet1 != FuncletMembership.end());
     607          92 :     auto Funclet2 = FuncletMembership.find(MBB2);
     608             :     assert(Funclet2 != FuncletMembership.end());
     609          92 :     if (Funclet1->second != Funclet2->second)
     610          64 :       return false;
     611             :   }
     612             : 
     613      814469 :   CommonTailLen = ComputeCommonTailLength(MBB1, MBB2, I1, I2);
     614      814469 :   if (CommonTailLen == 0)
     615             :     return false;
     616             :   DEBUG(dbgs() << "Common tail length of " << printMBBReference(*MBB1)
     617             :                << " and " << printMBBReference(*MBB2) << " is " << CommonTailLen
     618             :                << '\n');
     619             : 
     620             :   // It's almost always profitable to merge any number of non-terminator
     621             :   // instructions with the block that falls through into the common successor.
     622             :   // This is true only for a single successor. For multiple successors, we are
     623             :   // trading a conditional branch for an unconditional one.
     624             :   // TODO: Re-visit successor size for non-layout tail merging.
     625      371025 :   if ((MBB1 == PredBB || MBB2 == PredBB) &&
     626        1355 :       (!AfterPlacement || MBB1->succ_size() == 1)) {
     627             :     MachineBasicBlock::iterator I;
     628        4555 :     unsigned NumTerms = CountTerminators(MBB1 == PredBB ? MBB2 : MBB1, I);
     629        4555 :     if (CommonTailLen > NumTerms)
     630        4191 :       return true;
     631             :   }
     632             : 
     633             :   // If these are identical non-return blocks with no successors, merge them.
     634             :   // Such blocks are typically cold calls to noreturn functions like abort, and
     635             :   // are unlikely to become a fallthrough target after machine block placement.
     636             :   // Tail merging these blocks is unlikely to create additional unconditional
     637             :   // branches, and will reduce the size of this cold code.
     638      303752 :   if (I1 == MBB1->begin() && I2 == MBB2->begin() &&
     639      486897 :       blockEndsInUnreachable(MBB1) && blockEndsInUnreachable(MBB2))
     640             :     return true;
     641             : 
     642             :   // If one of the blocks can be completely merged and happens to be in
     643             :   // a position where the other could fall through into it, merge any number
     644             :   // of instructions, because it can be done without a branch.
     645             :   // TODO: If the blocks are not adjacent, move one of them so that they are?
     646      366993 :   if (MBB1->isLayoutSuccessor(MBB2) && I2 == MBB2->begin())
     647             :     return true;
     648      373540 :   if (MBB2->isLayoutSuccessor(MBB1) && I1 == MBB1->begin())
     649             :     return true;
     650             : 
     651             :   // If both blocks are identical and end in a branch, merge them unless they
     652             :   // both have a fallthrough predecessor and successor.
     653             :   // We can only do this after block placement because it depends on whether
     654             :   // there are fallthroughs, and we don't know until after layout.
     655      368646 :   if (AfterPlacement && I1 == MBB1->begin() && I2 == MBB2->begin()) {
     656         150 :     auto BothFallThrough = [](MachineBasicBlock *MBB) {
     657         150 :       if (MBB->succ_size() != 0 && !MBB->canFallThrough())
     658             :         return false;
     659             :       MachineFunction::iterator I(MBB);
     660           4 :       MachineFunction *MF = MBB->getParent();
     661           8 :       return (MBB != &*MF->begin()) && std::prev(I)->canFallThrough();
     662             :     };
     663         148 :     if (!BothFallThrough(MBB1) || !BothFallThrough(MBB2))
     664             :       return true;
     665             :   }
     666             : 
     667             :   // If both blocks have an unconditional branch temporarily stripped out,
     668             :   // count that as an additional common instruction for the following
     669             :   // heuristics. This heuristic is only accurate for single-succ blocks, so to
     670             :   // make sure that during layout merging and duplicating don't crash, we check
     671             :   // for that when merging during layout.
     672      363660 :   unsigned EffectiveTailLen = CommonTailLen;
     673      414647 :   if (SuccBB && MBB1 != PredBB && MBB2 != PredBB &&
     674       28016 :       (MBB1->succ_size() == 1 || !AfterPlacement) &&
     675      388538 :       !MBB1->back().isBarrier() &&
     676             :       !MBB2->back().isBarrier())
     677       24878 :     ++EffectiveTailLen;
     678             : 
     679             :   // Check if the common tail is long enough to be worthwhile.
     680      363660 :   if (EffectiveTailLen >= MinCommonTailLength)
     681             :     return true;
     682             : 
     683             :   // If we are optimizing for code size, 2 instructions in common is enough if
     684             :   // we don't have to split a block.  At worst we will be introducing 1 new
     685             :   // branch instruction, which is likely to be smaller than the 2
     686             :   // instructions that would be deleted in the merge.
     687      245510 :   MachineFunction *MF = MBB1->getParent();
     688      245575 :   return EffectiveTailLen >= 2 && MF->getFunction().optForSize() &&
     689          50 :          (I1 == MBB1->begin() || I2 == MBB2->begin());
     690             : }
     691             : 
     692      204755 : unsigned BranchFolder::ComputeSameTails(unsigned CurHash,
     693             :                                         unsigned MinCommonTailLength,
     694             :                                         MachineBasicBlock *SuccBB,
     695             :                                         MachineBasicBlock *PredBB) {
     696             :   unsigned maxCommonTailLength = 0U;
     697      204755 :   SameTails.clear();
     698             :   MachineBasicBlock::iterator TrialBBI1, TrialBBI2;
     699             :   MPIterator HighestMPIter = std::prev(MergePotentials.end());
     700             :   for (MPIterator CurMPIter = std::prev(MergePotentials.end()),
     701             :                   B = MergePotentials.begin();
     702      461590 :        CurMPIter != B && CurMPIter->getHash() == CurHash; --CurMPIter) {
     703     1026101 :     for (MPIterator I = std::prev(CurMPIter); I->getHash() == CurHash; --I) {
     704             :       unsigned CommonTailLen;
     705      814533 :       if (ProfitableToMerge(CurMPIter->getBlock(), I->getBlock(),
     706             :                             MinCommonTailLength,
     707             :                             CommonTailLen, TrialBBI1, TrialBBI2,
     708             :                             SuccBB, PredBB,
     709             :                             FuncletMembership,
     710      814533 :                             AfterBlockPlacement)) {
     711      125540 :         if (CommonTailLen > maxCommonTailLength) {
     712             :           SameTails.clear();
     713             :           maxCommonTailLength = CommonTailLen;
     714             :           HighestMPIter = CurMPIter;
     715        5914 :           SameTails.push_back(SameTailElt(CurMPIter, TrialBBI1));
     716             :         }
     717      140625 :         if (HighestMPIter == CurMPIter &&
     718       15085 :             CommonTailLen == maxCommonTailLength)
     719       13649 :           SameTails.push_back(SameTailElt(I, TrialBBI2));
     720             :       }
     721      814533 :       if (I == B)
     722             :         break;
     723             :     }
     724             :   }
     725      204755 :   return maxCommonTailLength;
     726             : }
     727             : 
     728      199263 : void BranchFolder::RemoveBlocksWithHash(unsigned CurHash,
     729             :                                         MachineBasicBlock *SuccBB,
     730             :                                         MachineBasicBlock *PredBB) {
     731             :   MPIterator CurMPIter, B;
     732             :   for (CurMPIter = std::prev(MergePotentials.end()),
     733             :       B = MergePotentials.begin();
     734      426780 :        CurMPIter->getHash() == CurHash; --CurMPIter) {
     735             :     // Put the unconditional branch back, if we need one.
     736      239710 :     MachineBasicBlock *CurMBB = CurMPIter->getBlock();
     737      239710 :     if (SuccBB && CurMBB != PredBB)
     738      117356 :       FixTail(CurMBB, SuccBB, TII);
     739      239710 :     if (CurMPIter == B)
     740             :       break;
     741             :   }
     742      199263 :   if (CurMPIter->getHash() != CurHash)
     743             :     CurMPIter++;
     744             :   MergePotentials.erase(CurMPIter, MergePotentials.end());
     745      199263 : }
     746             : 
     747        3460 : bool BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB,
     748             :                                              MachineBasicBlock *SuccBB,
     749             :                                              unsigned maxCommonTailLength,
     750             :                                              unsigned &commonTailIndex) {
     751        3460 :   commonTailIndex = 0;
     752             :   unsigned TimeEstimate = ~0U;
     753       15250 :   for (unsigned i = 0, e = SameTails.size(); i != e; ++i) {
     754             :     // Use PredBB if possible; that doesn't require a new branch.
     755       20130 :     if (SameTails[i].getBlock() == PredBB) {
     756        1735 :       commonTailIndex = i;
     757        1735 :       break;
     758             :     }
     759             :     // Otherwise, make a (fairly bogus) choice based on estimate of
     760             :     // how long it will take the various blocks to execute.
     761             :     unsigned t = EstimateRuntime(SameTails[i].getBlock()->begin(),
     762        8330 :                                  SameTails[i].getTailStartPos());
     763        8330 :     if (t <= TimeEstimate) {
     764             :       TimeEstimate = t;
     765        8077 :       commonTailIndex = i;
     766             :     }
     767             :   }
     768             : 
     769             :   MachineBasicBlock::iterator BBI =
     770        6920 :     SameTails[commonTailIndex].getTailStartPos();
     771             :   MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
     772             : 
     773             :   DEBUG(dbgs() << "\nSplitting " << printMBBReference(*MBB) << ", size "
     774             :                << maxCommonTailLength);
     775             : 
     776             :   // If the split block unconditionally falls-thru to SuccBB, it will be
     777             :   // merged. In control flow terms it should then take SuccBB's name. e.g. If
     778             :   // SuccBB is an inner loop, the common tail is still part of the inner loop.
     779        5739 :   const BasicBlock *BB = (SuccBB && MBB->succ_size() == 1) ?
     780             :     SuccBB->getBasicBlock() : MBB->getBasicBlock();
     781        3460 :   MachineBasicBlock *newMBB = SplitMBBAt(*MBB, BBI, BB);
     782        3460 :   if (!newMBB) {
     783             :     DEBUG(dbgs() << "... failed!");
     784             :     return false;
     785             :   }
     786             : 
     787        3460 :   SameTails[commonTailIndex].setBlock(newMBB);
     788             :   SameTails[commonTailIndex].setTailStartPos(newMBB->begin());
     789             : 
     790             :   // If we split PredBB, newMBB is the new predecessor.
     791        3460 :   if (PredBB == MBB)
     792        1735 :     PredBB = newMBB;
     793             : 
     794             :   return true;
     795             : }
     796             : 
     797             : static void
     798       12296 : mergeOperations(MachineBasicBlock::iterator MBBIStartPos,
     799             :                 MachineBasicBlock &MBBCommon) {
     800       12296 :   MachineBasicBlock *MBB = MBBIStartPos->getParent();
     801             :   // Note CommonTailLen does not necessarily matches the size of
     802             :   // the common BB nor all its instructions because of debug
     803             :   // instructions differences.
     804             :   unsigned CommonTailLen = 0;
     805       68503 :   for (auto E = MBB->end(); MBBIStartPos != E; ++MBBIStartPos)
     806       56207 :     ++CommonTailLen;
     807             : 
     808       12296 :   MachineBasicBlock::reverse_iterator MBBI = MBB->rbegin();
     809             :   MachineBasicBlock::reverse_iterator MBBIE = MBB->rend();
     810       12296 :   MachineBasicBlock::reverse_iterator MBBICommon = MBBCommon.rbegin();
     811             :   MachineBasicBlock::reverse_iterator MBBIECommon = MBBCommon.rend();
     812             : 
     813       68503 :   while (CommonTailLen--) {
     814             :     assert(MBBI != MBBIE && "Reached BB end within common tail length!");
     815             :     (void)MBBIE;
     816             : 
     817       56363 :     if (MBBI->isDebugValue()) {
     818             :       ++MBBI;
     819         156 :       continue;
     820             :     }
     821             : 
     822      112340 :     while ((MBBICommon != MBBIECommon) && MBBICommon->isDebugValue())
     823             :       ++MBBICommon;
     824             : 
     825             :     assert(MBBICommon != MBBIECommon &&
     826             :            "Reached BB end within common tail length!");
     827             :     assert(MBBICommon->isIdenticalTo(*MBBI) && "Expected matching MIIs!");
     828             : 
     829             :     // Merge MMOs from memory operations in the common block.
     830      101508 :     if (MBBICommon->mayLoad() || MBBICommon->mayStore())
     831       14983 :       MBBICommon->setMemRefs(MBBICommon->mergeMemRefsWith(*MBBI));
     832             :     // Drop undef flags if they aren't present in all merged instructions.
     833      356207 :     for (unsigned I = 0, E = MBBICommon->getNumOperands(); I != E; ++I) {
     834      300156 :       MachineOperand &MO = MBBICommon->getOperand(I);
     835      515419 :       if (MO.isReg() && MO.isUndef()) {
     836         197 :         const MachineOperand &OtherMO = MBBI->getOperand(I);
     837         197 :         if (!OtherMO.isUndef())
     838             :           MO.setIsUndef(false);
     839             :       }
     840             :     }
     841             : 
     842             :     ++MBBI;
     843             :     ++MBBICommon;
     844             :   }
     845       12296 : }
     846             : 
     847        5492 : void BranchFolder::mergeCommonTails(unsigned commonTailIndex) {
     848        5492 :   MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
     849             : 
     850       10984 :   std::vector<MachineBasicBlock::iterator> NextCommonInsts(SameTails.size());
     851       64348 :   for (unsigned int i = 0 ; i != SameTails.size() ; ++i) {
     852       17788 :     if (i != commonTailIndex) {
     853       24592 :       NextCommonInsts[i] = SameTails[i].getTailStartPos();
     854       12296 :       mergeOperations(SameTails[i].getTailStartPos(), *MBB);
     855             :     } else {
     856             :       assert(SameTails[i].getTailStartPos() == MBB->begin() &&
     857             :           "MBB is not a common tail only block");
     858             :     }
     859             :   }
     860             : 
     861       28785 :   for (auto &MI : *MBB) {
     862       17801 :     if (MI.isDebugValue())
     863         135 :       continue;
     864             :     DebugLoc DL = MI.getDebugLoc();
     865      256483 :     for (unsigned int i = 0 ; i < NextCommonInsts.size() ; i++) {
     866       73717 :       if (i == commonTailIndex)
     867       17666 :         continue;
     868             : 
     869             :       auto &Pos = NextCommonInsts[i];
     870             :       assert(Pos != SameTails[i].getBlock()->end() &&
     871             :           "Reached BB end within common tail");
     872       56200 :       while (Pos->isDebugValue()) {
     873             :         ++Pos;
     874             :         assert(Pos != SameTails[i].getBlock()->end() &&
     875             :             "Reached BB end within common tail");
     876             :       }
     877             :       assert(MI.isIdenticalTo(*Pos) && "Expected matching MIIs!");
     878      112102 :       DL = DILocation::getMergedLocation(DL, Pos->getDebugLoc());
     879      112102 :       NextCommonInsts[i] = ++Pos;
     880             :     }
     881       17666 :     MI.setDebugLoc(DL);
     882             :   }
     883             : 
     884        5492 :   if (UpdateLiveIns) {
     885        5479 :     LivePhysRegs NewLiveIns(*TRI);
     886        5479 :     computeLiveIns(NewLiveIns, *MBB);
     887             : 
     888             :     // The flag merging may lead to some register uses no longer using the
     889             :     // <undef> flag, add IMPLICIT_DEFs in the predecessors as necessary.
     890       11896 :     for (MachineBasicBlock *Pred : MBB->predecessors()) {
     891        6417 :       LiveRegs.init(*TRI);
     892        6417 :       LiveRegs.addLiveOuts(*Pred);
     893        6417 :       MachineBasicBlock::iterator InsertBefore = Pred->getFirstTerminator();
     894      138281 :       for (unsigned Reg : NewLiveIns) {
     895       65932 :         if (!LiveRegs.available(*MRI, Reg))
     896       65911 :           continue;
     897          21 :         DebugLoc DL;
     898          42 :         BuildMI(*Pred, InsertBefore, DL, TII->get(TargetOpcode::IMPLICIT_DEF),
     899          21 :                 Reg);
     900             :       }
     901             :     }
     902             : 
     903        5479 :     MBB->clearLiveIns();
     904        5479 :     addLiveIns(*MBB, NewLiveIns);
     905             :   }
     906        5492 : }
     907             : 
     908             : // See if any of the blocks in MergePotentials (which all have SuccBB as a
     909             : // successor, or all have no successor if it is null) can be tail-merged.
     910             : // If there is a successor, any blocks in MergePotentials that are not
     911             : // tail-merged and are not immediately before Succ must have an unconditional
     912             : // branch to Succ added (but the predecessor/successor lists need no
     913             : // adjustment). The lone predecessor of Succ that falls through into Succ,
     914             : // if any, is given in PredBB.
     915             : // MinCommonTailLength - Except for the special cases below, tail-merge if
     916             : // there are at least this many instructions in common.
     917      165758 : bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB,
     918             :                                       MachineBasicBlock *PredBB,
     919             :                                       unsigned MinCommonTailLength) {
     920             :   bool MadeChange = false;
     921             : 
     922             :   DEBUG(dbgs() << "\nTryTailMergeBlocks: ";
     923             :         for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i) dbgs()
     924             :         << printMBBReference(*MergePotentials[i].getBlock())
     925             :         << (i == e - 1 ? "" : ", ");
     926             :         dbgs() << "\n"; if (SuccBB) {
     927             :           dbgs() << "  with successor " << printMBBReference(*SuccBB) << '\n';
     928             :           if (PredBB)
     929             :             dbgs() << "  which has fall-through from "
     930             :                    << printMBBReference(*PredBB) << "\n";
     931             :         } dbgs() << "Looking for common tails of at least "
     932             :                  << MinCommonTailLength << " instruction"
     933             :                  << (MinCommonTailLength == 1 ? "" : "s") << '\n';);
     934             : 
     935             :   // Sort by hash value so that blocks with identical end sequences sort
     936             :   // together.
     937             :   array_pod_sort(MergePotentials.begin(), MergePotentials.end());
     938             : 
     939             :   // Walk through equivalence sets looking for actual exact matches.
     940      741026 :   while (MergePotentials.size() > 1) {
     941      204755 :     unsigned CurHash = MergePotentials.back().getHash();
     942             : 
     943             :     // Build SameTails, identifying the set of blocks with this hash code
     944             :     // and with the maximum number of instructions in common.
     945      204755 :     unsigned maxCommonTailLength = ComputeSameTails(CurHash,
     946             :                                                     MinCommonTailLength,
     947      204755 :                                                     SuccBB, PredBB);
     948             : 
     949             :     // If we didn't find any pair that has at least MinCommonTailLength
     950             :     // instructions in common, remove all blocks with this hash code and retry.
     951      404018 :     if (SameTails.empty()) {
     952      199263 :       RemoveBlocksWithHash(CurHash, SuccBB, PredBB);
     953      398526 :       continue;
     954             :     }
     955             : 
     956             :     // If one of the blocks is the entire common tail (and not the entry
     957             :     // block, which we can't jump to), we can treat all blocks with this same
     958             :     // tail at once.  Use PredBB if that is one of the possibilities, as that
     959             :     // will not introduce any extra branches.
     960             :     MachineBasicBlock *EntryBB =
     961        5492 :         &MergePotentials.front().getBlock()->getParent()->front();
     962        5492 :     unsigned commonTailIndex = SameTails.size();
     963             :     // If there are two blocks, check to see if one can be made to fall through
     964             :     // into the other.
     965        4418 :     if (SameTails.size() == 2 &&
     966        9969 :         SameTails[0].getBlock()->isLayoutSuccessor(SameTails[1].getBlock()) &&
     967          59 :         SameTails[1].tailIsWholeBlock())
     968          16 :       commonTailIndex = 1;
     969        9878 :     else if (SameTails.size() == 2 &&
     970        4402 :              SameTails[1].getBlock()->isLayoutSuccessor(
     971        7138 :                                                      SameTails[0].getBlock()) &&
     972        1662 :              SameTails[0].tailIsWholeBlock())
     973         651 :       commonTailIndex = 0;
     974             :     else {
     975             :       // Otherwise just pick one, favoring the fall-through predecessor if
     976             :       // there is one.
     977       39031 :       for (unsigned i = 0, e = SameTails.size(); i != e; ++i) {
     978       14762 :         MachineBasicBlock *MBB = SameTails[i].getBlock();
     979       14781 :         if (MBB == EntryBB && SameTails[i].tailIsWholeBlock())
     980           1 :           continue;
     981       14761 :         if (MBB == PredBB) {
     982        2484 :           commonTailIndex = i;
     983        2484 :           break;
     984             :         }
     985       12277 :         if (SameTails[i].tailIsWholeBlock())
     986        3678 :           commonTailIndex = i;
     987             :       }
     988             :     }
     989             : 
     990       14751 :     if (commonTailIndex == SameTails.size() ||
     991        6282 :         (SameTails[commonTailIndex].getBlock() == PredBB &&
     992             :          !SameTails[commonTailIndex].tailIsWholeBlock())) {
     993             :       // None of the blocks consist entirely of the common tail.
     994             :       // Split a block so that one does.
     995        3460 :       if (!CreateCommonTailOnlyBlock(PredBB, SuccBB,
     996             :                                      maxCommonTailLength, commonTailIndex)) {
     997           0 :         RemoveBlocksWithHash(CurHash, SuccBB, PredBB);
     998           0 :         continue;
     999             :       }
    1000             :     }
    1001             : 
    1002        5492 :     MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
    1003             : 
    1004             :     // Recompute common tail MBB's edge weights and block frequency.
    1005        5492 :     setCommonTailEdgeWeights(*MBB);
    1006             : 
    1007             :     // Merge debug locations, MMOs and undef flags across identical instructions
    1008             :     // for common tail.
    1009        5492 :     mergeCommonTails(commonTailIndex);
    1010             : 
    1011             :     // MBB is common tail.  Adjust all other BB's to jump to this one.
    1012             :     // Traversal must be forwards so erases work.
    1013             :     DEBUG(dbgs() << "\nUsing common tail in " << printMBBReference(*MBB)
    1014             :                  << " for ");
    1015       28772 :     for (unsigned int i=0, e = SameTails.size(); i != e; ++i) {
    1016       17788 :       if (commonTailIndex == i)
    1017        5492 :         continue;
    1018             :       DEBUG(dbgs() << printMBBReference(*SameTails[i].getBlock())
    1019             :                    << (i == e - 1 ? "" : ", "));
    1020             :       // Hack the end off BB i, making it jump to BB commonTailIndex instead.
    1021       24592 :       replaceTailWithBranchTo(SameTails[i].getTailStartPos(), *MBB);
    1022             :       // BB i is no longer a predecessor of SuccBB; remove it from the worklist.
    1023       12296 :       MergePotentials.erase(SameTails[i].getMPIter());
    1024             :     }
    1025             :     DEBUG(dbgs() << "\n");
    1026             :     // We leave commonTailIndex in the worklist in case there are other blocks
    1027             :     // that match it with a smaller number of instructions.
    1028             :     MadeChange = true;
    1029             :   }
    1030      165758 :   return MadeChange;
    1031             : }
    1032             : 
    1033      206008 : bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
    1034             :   bool MadeChange = false;
    1035      206008 :   if (!EnableTailMerge) return MadeChange;
    1036             : 
    1037             :   // First find blocks with no successors.
    1038             :   // Block placement does not create new tail merging opportunities for these
    1039             :   // blocks.
    1040      188629 :   if (!AfterBlockPlacement) {
    1041      181907 :     MergePotentials.clear();
    1042      767430 :     for (MachineBasicBlock &MBB : MF) {
    1043     1171056 :       if (MergePotentials.size() == TailMergeThreshold)
    1044             :         break;
    1045     1169691 :       if (!TriedMerging.count(&MBB) && MBB.succ_empty())
    1046      409366 :         MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(MBB), &MBB));
    1047             :     }
    1048             : 
    1049             :     // If this is a large problem, avoid visiting the same basic blocks
    1050             :     // multiple times.
    1051      363814 :     if (MergePotentials.size() == TailMergeThreshold)
    1052         755 :       for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
    1053        1500 :         TriedMerging.insert(MergePotentials[i].getBlock());
    1054             : 
    1055             :     // See if we can do any tail merging on those.
    1056      363814 :     if (MergePotentials.size() >= 2)
    1057        9826 :       MadeChange |= TryTailMergeBlocks(nullptr, nullptr, MinCommonTailLength);
    1058             :   }
    1059             : 
    1060             :   // Look at blocks (IBB) with multiple predecessors (PBB).
    1061             :   // We change each predecessor to a canonical form, by
    1062             :   // (1) temporarily removing any unconditional branch from the predecessor
    1063             :   // to IBB, and
    1064             :   // (2) alter conditional branches so they branch to the other block
    1065             :   // not IBB; this may require adding back an unconditional branch to IBB
    1066             :   // later, where there wasn't one coming in.  E.g.
    1067             :   //   Bcc IBB
    1068             :   //   fallthrough to QBB
    1069             :   // here becomes
    1070             :   //   Bncc QBB
    1071             :   // with a conceptual B to IBB after that, which never actually exists.
    1072             :   // With those changes, we see whether the predecessors' tails match,
    1073             :   // and merge them if so.  We change things out of canonical form and
    1074             :   // back to the way they were later in the process.  (OptimizeBranches
    1075             :   // would undo some of this, but we can't use it, because we'd get into
    1076             :   // a compile-time infinite loop repeatedly doing and undoing the same
    1077             :   // transformations.)
    1078             : 
    1079             :   for (MachineFunction::iterator I = std::next(MF.begin()), E = MF.end();
    1080      780648 :        I != E; ++I) {
    1081     1003276 :     if (I->pred_size() < 2) continue;
    1082             :     SmallPtrSet<MachineBasicBlock *, 8> UniquePreds;
    1083             :     MachineBasicBlock *IBB = &*I;
    1084             :     MachineBasicBlock *PredBB = &*std::prev(I);
    1085      186146 :     MergePotentials.clear();
    1086             :     MachineLoop *ML;
    1087             : 
    1088             :     // Bail if merging after placement and IBB is the loop header because
    1089             :     // -- If merging predecessors that belong to the same loop as IBB, the
    1090             :     // common tail of merged predecessors may become the loop top if block
    1091             :     // placement is called again and the predecessors may branch to this common
    1092             :     // tail and require more branches. This can be relaxed if
    1093             :     // MachineBlockPlacement::findBestLoopTop is more flexible.
    1094             :     // --If merging predecessors that do not belong to the same loop as IBB, the
    1095             :     // loop info of IBB's loop and the other loops may be affected. Calling the
    1096             :     // block placement again may make big change to the layout and eliminate the
    1097             :     // reason to do tail merging here.
    1098      186146 :     if (AfterBlockPlacement && MLI) {
    1099             :       ML = MLI->getLoopFor(IBB);
    1100       24710 :       if (ML && IBB == ML->getHeader())
    1101             :         continue;
    1102             :     }
    1103             : 
    1104      617275 :     for (MachineBasicBlock *PBB : I->predecessors()) {
    1105      873032 :       if (MergePotentials.size() == TailMergeThreshold)
    1106             :         break;
    1107             : 
    1108      436513 :       if (TriedMerging.count(PBB))
    1109       50704 :         continue;
    1110             : 
    1111             :       // Skip blocks that loop to themselves, can't tail merge these.
    1112      435379 :       if (PBB == IBB)
    1113        8051 :         continue;
    1114             : 
    1115             :       // Visit each predecessor only once.
    1116      427328 :       if (!UniquePreds.insert(PBB).second)
    1117           0 :         continue;
    1118             : 
    1119             :       // Skip blocks which may jump to a landing pad. Can't tail merge these.
    1120      427328 :       if (PBB->hasEHPadSuccessor())
    1121       37921 :         continue;
    1122             : 
    1123             :       // After block placement, only consider predecessors that belong to the
    1124             :       // same loop as IBB.  The reason is the same as above when skipping loop
    1125             :       // header.
    1126      389407 :       if (AfterBlockPlacement && MLI)
    1127      115775 :         if (ML != MLI->getLoopFor(PBB))
    1128        2399 :           continue;
    1129             : 
    1130      387008 :       MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
    1131             :       SmallVector<MachineOperand, 4> Cond;
    1132      387008 :       if (!TII->analyzeBranch(*PBB, TBB, FBB, Cond, true)) {
    1133             :         // Failing case: IBB is the target of a cbr, and we cannot reverse the
    1134             :         // branch.
    1135             :         SmallVector<MachineOperand, 4> NewCond(Cond);
    1136      384157 :         if (!Cond.empty() && TBB == IBB) {
    1137      100633 :           if (TII->reverseBranchCondition(NewCond))
    1138          65 :             continue;
    1139             :           // This is the QBB case described above
    1140      100568 :           if (!FBB) {
    1141       95626 :             auto Next = ++PBB->getIterator();
    1142       95626 :             if (Next != MF.end())
    1143       95626 :               FBB = &*Next;
    1144             :           }
    1145             :         }
    1146             : 
    1147             :         // Failing case: the only way IBB can be reached from PBB is via
    1148             :         // exception handling.  Happens for landing pads.  Would be nice to have
    1149             :         // a bit in the edge so we didn't have to do all this.
    1150      384092 :         if (IBB->isEHPad()) {
    1151           0 :           MachineFunction::iterator IP = ++PBB->getIterator();
    1152             :           MachineBasicBlock *PredNextBB = nullptr;
    1153           0 :           if (IP != MF.end())
    1154             :             PredNextBB = &*IP;
    1155           0 :           if (!TBB) {
    1156           0 :             if (IBB != PredNextBB)      // fallthrough
    1157           0 :               continue;
    1158           0 :           } else if (FBB) {
    1159           0 :             if (TBB != IBB && FBB != IBB)   // cbr then ubr
    1160           0 :               continue;
    1161           0 :           } else if (Cond.empty()) {
    1162           0 :             if (TBB != IBB)               // ubr
    1163           0 :               continue;
    1164             :           } else {
    1165           0 :             if (TBB != IBB && IBB != PredNextBB)  // cbr
    1166           0 :               continue;
    1167             :           }
    1168             :         }
    1169             : 
    1170             :         // Remove the unconditional branch at the end, if any.
    1171      384092 :         if (TBB && (Cond.empty() || FBB)) {
    1172      230444 :           DebugLoc dl = PBB->findBranchDebugLoc();
    1173      230444 :           TII->removeBranch(*PBB);
    1174      230444 :           if (!Cond.empty())
    1175             :             // reinsert conditional branch only, for now
    1176      206268 :             TII->insertBranch(*PBB, (TBB == IBB) ? FBB : TBB, nullptr,
    1177      103134 :                               NewCond, dl);
    1178             :         }
    1179             : 
    1180      768184 :         MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(*PBB), PBB));
    1181             :       }
    1182             :     }
    1183             : 
    1184             :     // If this is a large problem, avoid visiting the same basic blocks multiple
    1185             :     // times.
    1186      361524 :     if (MergePotentials.size() == TailMergeThreshold)
    1187         157 :       for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
    1188         308 :         TriedMerging.insert(MergePotentials[i].getBlock());
    1189             : 
    1190      361524 :     if (MergePotentials.size() >= 2)
    1191      155932 :       MadeChange |= TryTailMergeBlocks(IBB, PredBB, MinCommonTailLength);
    1192             : 
    1193             :     // Reinsert an unconditional branch if needed. The 1 below can occur as a
    1194             :     // result of removing blocks in TryTailMergeBlocks.
    1195             :     PredBB = &*std::prev(I); // this may have been changed in TryTailMergeBlocks
    1196      518556 :     if (MergePotentials.size() == 1 &&
    1197      157032 :         MergePotentials.begin()->getBlock() != PredBB)
    1198      106861 :       FixTail(MergePotentials.begin()->getBlock(), IBB, TII);
    1199             :   }
    1200             : 
    1201             :   return MadeChange;
    1202             : }
    1203             : 
    1204        5492 : void BranchFolder::setCommonTailEdgeWeights(MachineBasicBlock &TailMBB) {
    1205       10984 :   SmallVector<BlockFrequency, 2> EdgeFreqLs(TailMBB.succ_size());
    1206             :   BlockFrequency AccumulatedMBBFreq;
    1207             : 
    1208             :   // Aggregate edge frequency of successor edge j:
    1209             :   //  edgeFreq(j) = sum (freq(bb) * edgeProb(bb, j)),
    1210             :   //  where bb is a basic block that is in SameTails.
    1211       23280 :   for (const auto &Src : SameTails) {
    1212             :     const MachineBasicBlock *SrcMBB = Src.getBlock();
    1213       17788 :     BlockFrequency BlockFreq = MBBFreqInfo.getBlockFreq(SrcMBB);
    1214       17788 :     AccumulatedMBBFreq += BlockFreq;
    1215             : 
    1216             :     // It is not necessary to recompute edge weights if TailBB has less than two
    1217             :     // successors.
    1218       17788 :     if (TailMBB.succ_size() <= 1)
    1219       16512 :       continue;
    1220             : 
    1221             :     auto EdgeFreq = EdgeFreqLs.begin();
    1222             : 
    1223        2552 :     for (auto SuccI = TailMBB.succ_begin(), SuccE = TailMBB.succ_end();
    1224        3828 :          SuccI != SuccE; ++SuccI, ++EdgeFreq)
    1225        2552 :       *EdgeFreq += BlockFreq * MBPI.getEdgeProbability(SrcMBB, *SuccI);
    1226             :   }
    1227             : 
    1228        5492 :   MBBFreqInfo.setBlockFreq(&TailMBB, AccumulatedMBBFreq);
    1229             : 
    1230        5492 :   if (TailMBB.succ_size() <= 1)
    1231             :     return;
    1232             : 
    1233             :   auto SumEdgeFreq =
    1234             :       std::accumulate(EdgeFreqLs.begin(), EdgeFreqLs.end(), BlockFrequency(0))
    1235             :           .getFrequency();
    1236             :   auto EdgeFreq = EdgeFreqLs.begin();
    1237             : 
    1238         382 :   if (SumEdgeFreq > 0) {
    1239         764 :     for (auto SuccI = TailMBB.succ_begin(), SuccE = TailMBB.succ_end();
    1240        1146 :          SuccI != SuccE; ++SuccI, ++EdgeFreq) {
    1241             :       auto Prob = BranchProbability::getBranchProbability(
    1242         764 :           EdgeFreq->getFrequency(), SumEdgeFreq);
    1243         764 :       TailMBB.setSuccProbability(SuccI, Prob);
    1244             :     }
    1245             :   }
    1246             : }
    1247             : 
    1248             : //===----------------------------------------------------------------------===//
    1249             : //  Branch Optimization
    1250             : //===----------------------------------------------------------------------===//
    1251             : 
    1252      199678 : bool BranchFolder::OptimizeBranches(MachineFunction &MF) {
    1253             :   bool MadeChange = false;
    1254             : 
    1255             :   // Make sure blocks are numbered in order
    1256      199678 :   MF.RenumberBlocks();
    1257             :   // Renumbering blocks alters funclet membership, recalculate it.
    1258      399356 :   FuncletMembership = getFuncletMembership(MF);
    1259             : 
    1260             :   for (MachineFunction::iterator I = std::next(MF.begin()), E = MF.end();
    1261      681491 :        I != E; ) {
    1262             :     MachineBasicBlock *MBB = &*I++;
    1263      481813 :     MadeChange |= OptimizeBlock(MBB);
    1264             : 
    1265             :     // If it is dead, remove it.
    1266      481813 :     if (MBB->pred_empty()) {
    1267       10846 :       RemoveDeadBlock(MBB);
    1268             :       MadeChange = true;
    1269             :       ++NumDeadBlocks;
    1270             :     }
    1271             :   }
    1272             : 
    1273      199678 :   return MadeChange;
    1274             : }
    1275             : 
    1276             : // Blocks should be considered empty if they contain only debug info;
    1277             : // else the debug info would affect codegen.
    1278             : static bool IsEmptyBlock(MachineBasicBlock *MBB) {
    1279     2040416 :   return MBB->getFirstNonDebugInstr() == MBB->end();
    1280             : }
    1281             : 
    1282             : // Blocks with only debug info and branches should be considered the same
    1283             : // as blocks with only branches.
    1284      133280 : static bool IsBranchOnlyBlock(MachineBasicBlock *MBB) {
    1285      133280 :   MachineBasicBlock::iterator I = MBB->getFirstNonDebugInstr();
    1286             :   assert(I != MBB->end() && "empty block!");
    1287      133280 :   return I->isBranch();
    1288             : }
    1289             : 
    1290             : /// IsBetterFallthrough - Return true if it would be clearly better to
    1291             : /// fall-through to MBB1 than to fall through into MBB2.  This has to return
    1292             : /// a strict ordering, returning true for both (MBB1,MBB2) and (MBB2,MBB1) will
    1293             : /// result in infinite loops.
    1294        3430 : static bool IsBetterFallthrough(MachineBasicBlock *MBB1,
    1295             :                                 MachineBasicBlock *MBB2) {
    1296             :   // Right now, we use a simple heuristic.  If MBB2 ends with a call, and
    1297             :   // MBB1 doesn't, we prefer to fall through into MBB1.  This allows us to
    1298             :   // optimize branches that branch to either a return block or an assert block
    1299             :   // into a fallthrough to the return.
    1300        3430 :   MachineBasicBlock::iterator MBB1I = MBB1->getLastNonDebugInstr();
    1301        3430 :   MachineBasicBlock::iterator MBB2I = MBB2->getLastNonDebugInstr();
    1302        6852 :   if (MBB1I == MBB1->end() || MBB2I == MBB2->end())
    1303             :     return false;
    1304             : 
    1305             :   // If there is a clear successor ordering we make sure that one block
    1306             :   // will fall through to the next
    1307        3422 :   if (MBB1->isSuccessor(MBB2)) return true;
    1308        3396 :   if (MBB2->isSuccessor(MBB1)) return false;
    1309             : 
    1310        4059 :   return MBB2I->isCall() && !MBB1I->isCall();
    1311             : }
    1312             : 
    1313             : /// getBranchDebugLoc - Find and return, if any, the DebugLoc of the branch
    1314             : /// instructions on the block.
    1315       15146 : static DebugLoc getBranchDebugLoc(MachineBasicBlock &MBB) {
    1316       15146 :   MachineBasicBlock::iterator I = MBB.getLastNonDebugInstr();
    1317       30292 :   if (I != MBB.end() && I->isBranch())
    1318             :     return I->getDebugLoc();
    1319        2111 :   return DebugLoc();
    1320             : }
    1321             : 
    1322      481813 : bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
    1323             :   bool MadeChange = false;
    1324      481813 :   MachineFunction &MF = *MBB->getParent();
    1325      514589 : ReoptimizeBlock:
    1326             : 
    1327      514589 :   MachineFunction::iterator FallThrough = MBB->getIterator();
    1328             :   ++FallThrough;
    1329             : 
    1330             :   // Make sure MBB and FallThrough belong to the same funclet.
    1331             :   bool SameFunclet = true;
    1332      515208 :   if (!FuncletMembership.empty() && FallThrough != MF.end()) {
    1333         503 :     auto MBBFunclet = FuncletMembership.find(MBB);
    1334             :     assert(MBBFunclet != FuncletMembership.end());
    1335         503 :     auto FallThroughFunclet = FuncletMembership.find(&*FallThrough);
    1336             :     assert(FallThroughFunclet != FuncletMembership.end());
    1337         503 :     SameFunclet = MBBFunclet->second == FallThroughFunclet->second;
    1338             :   }
    1339             : 
    1340             :   // If this block is empty, make everyone use its fall-through, not the block
    1341             :   // explicitly.  Landing pads should not do this since the landing-pad table
    1342             :   // points to this block.  Blocks with their addresses taken shouldn't be
    1343             :   // optimized away.
    1344      514589 :   if (IsEmptyBlock(MBB) && !MBB->isEHPad() && !MBB->hasAddressTaken() &&
    1345             :       SameFunclet) {
    1346             :     // Dead block?  Leave for cleanup later.
    1347        4362 :     if (MBB->pred_empty()) return MadeChange;
    1348             : 
    1349        3739 :     if (FallThrough == MF.end()) {
    1350             :       // TODO: Simplify preds to not branch here if possible!
    1351        3550 :     } else if (FallThrough->isEHPad()) {
    1352             :       // Don't rewrite to a landing pad fallthough.  That could lead to the case
    1353             :       // where a BB jumps to more than one landing pad.
    1354             :       // TODO: Is it ever worth rewriting predecessors which don't already
    1355             :       // jump to a landing pad, and so can safely jump to the fallthrough?
    1356        3430 :     } else if (MBB->isSuccessor(&*FallThrough)) {
    1357             :       // Rewrite all predecessors of the old block to go to the fallthrough
    1358             :       // instead.
    1359        5155 :       while (!MBB->pred_empty()) {
    1360        1827 :         MachineBasicBlock *Pred = *(MBB->pred_end()-1);
    1361        1827 :         Pred->ReplaceUsesOfBlockWith(MBB, &*FallThrough);
    1362             :       }
    1363             :       // If MBB was the target of a jump table, update jump tables to go to the
    1364             :       // fallthrough instead.
    1365        1501 :       if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo())
    1366         223 :         MJTI->ReplaceMBBInJumpTables(MBB, &*FallThrough);
    1367             :       MadeChange = true;
    1368             :     }
    1369             :     return MadeChange;
    1370             :   }
    1371             : 
    1372             :   // Check to see if we can simplify the terminator of the block before this
    1373             :   // one.
    1374             :   MachineBasicBlock &PrevBB = *std::prev(MachineFunction::iterator(MBB));
    1375             : 
    1376      510227 :   MachineBasicBlock *PriorTBB = nullptr, *PriorFBB = nullptr;
    1377             :   SmallVector<MachineOperand, 4> PriorCond;
    1378             :   bool PriorUnAnalyzable =
    1379      510227 :       TII->analyzeBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, true);
    1380      510227 :   if (!PriorUnAnalyzable) {
    1381             :     // If the CFG for the prior block has extra edges, remove them.
    1382      494919 :     MadeChange |= PrevBB.CorrectExtraCFGEdges(PriorTBB, PriorFBB,
    1383      494919 :                                               !PriorCond.empty());
    1384             : 
    1385             :     // If the previous branch is conditional and both conditions go to the same
    1386             :     // destination, remove the branch, replacing it with an unconditional one or
    1387             :     // a fall-through.
    1388      494919 :     if (PriorTBB && PriorTBB == PriorFBB) {
    1389           9 :       DebugLoc dl = getBranchDebugLoc(PrevBB);
    1390           9 :       TII->removeBranch(PrevBB);
    1391             :       PriorCond.clear();
    1392           9 :       if (PriorTBB != MBB)
    1393           6 :         TII->insertBranch(PrevBB, PriorTBB, nullptr, PriorCond, dl);
    1394             :       MadeChange = true;
    1395             :       ++NumBranchOpts;
    1396             :       goto ReoptimizeBlock;
    1397             :     }
    1398             : 
    1399             :     // If the previous block unconditionally falls through to this block and
    1400             :     // this block has no other predecessors, move the contents of this block
    1401             :     // into the prior block. This doesn't usually happen when SimplifyCFG
    1402             :     // has been used, but it can happen if tail merging splits a fall-through
    1403             :     // predecessor of a block.
    1404             :     // This has to check PrevBB->succ_size() because EH edges are ignored by
    1405             :     // AnalyzeBranch.
    1406     1168788 :     if (PriorCond.empty() && !PriorTBB && MBB->pred_size() == 1 &&
    1407        3753 :         PrevBB.succ_size() == 1 &&
    1408      502350 :         !MBB->hasAddressTaken() && !MBB->isEHPad()) {
    1409             :       DEBUG(dbgs() << "\nMerging into block: " << PrevBB
    1410             :                    << "From MBB: " << *MBB);
    1411             :       // Remove redundant DBG_VALUEs first.
    1412        3687 :       if (PrevBB.begin() != PrevBB.end()) {
    1413        3573 :         MachineBasicBlock::iterator PrevBBIter = PrevBB.end();
    1414             :         --PrevBBIter;
    1415        3573 :         MachineBasicBlock::iterator MBBIter = MBB->begin();
    1416             :         // Check if DBG_VALUE at the end of PrevBB is identical to the
    1417             :         // DBG_VALUE at the beginning of MBB.
    1418        1725 :         while (PrevBBIter != PrevBB.begin() && MBBIter != MBB->end()
    1419        5299 :                && PrevBBIter->isDebugValue() && MBBIter->isDebugValue()) {
    1420           1 :           if (!MBBIter->isIdenticalTo(*PrevBBIter))
    1421             :             break;
    1422             :           MachineInstr &DuplicateDbg = *MBBIter;
    1423             :           ++MBBIter; -- PrevBBIter;
    1424           1 :           DuplicateDbg.eraseFromParent();
    1425             :         }
    1426             :       }
    1427             :       PrevBB.splice(PrevBB.end(), MBB, MBB->begin(), MBB->end());
    1428        3687 :       PrevBB.removeSuccessor(PrevBB.succ_begin());
    1429             :       assert(PrevBB.succ_empty());
    1430        3687 :       PrevBB.transferSuccessors(MBB);
    1431             :       MadeChange = true;
    1432        3687 :       return MadeChange;
    1433             :     }
    1434             : 
    1435             :     // If the previous branch *only* branches to *this* block (conditional or
    1436             :     // not) remove the branch.
    1437      492481 :     if (PriorTBB == MBB && !PriorFBB) {
    1438         608 :       TII->removeBranch(PrevBB);
    1439             :       MadeChange = true;
    1440             :       ++NumBranchOpts;
    1441             :       goto ReoptimizeBlock;
    1442             :     }
    1443             : 
    1444             :     // If the prior block branches somewhere else on the condition and here if
    1445             :     // the condition is false, remove the uncond second branch.
    1446      490615 :     if (PriorFBB == MBB) {
    1447        2235 :       DebugLoc dl = getBranchDebugLoc(PrevBB);
    1448        2235 :       TII->removeBranch(PrevBB);
    1449        4470 :       TII->insertBranch(PrevBB, PriorTBB, nullptr, PriorCond, dl);
    1450             :       MadeChange = true;
    1451             :       ++NumBranchOpts;
    1452             :       goto ReoptimizeBlock;
    1453             :     }
    1454             : 
    1455             :     // If the prior block branches here on true and somewhere else on false, and
    1456             :     // if the branch condition is reversible, reverse the branch to create a
    1457             :     // fall-through.
    1458      488380 :     if (PriorTBB == MBB) {
    1459             :       SmallVector<MachineOperand, 4> NewPriorCond(PriorCond);
    1460         650 :       if (!TII->reverseBranchCondition(NewPriorCond)) {
    1461         632 :         DebugLoc dl = getBranchDebugLoc(PrevBB);
    1462         632 :         TII->removeBranch(PrevBB);
    1463        1264 :         TII->insertBranch(PrevBB, PriorFBB, nullptr, NewPriorCond, dl);
    1464             :         MadeChange = true;
    1465             :         ++NumBranchOpts;
    1466             :         goto ReoptimizeBlock;
    1467             :       }
    1468             :     }
    1469             : 
    1470             :     // If this block has no successors (e.g. it is a return block or ends with
    1471             :     // a call to a no-return function like abort or __cxa_throw) and if the pred
    1472             :     // falls through into this block, and if it would otherwise fall through
    1473             :     // into the block after this, move this block to the end of the function.
    1474             :     //
    1475             :     // We consider it more likely that execution will stay in the function (e.g.
    1476             :     // due to loops) than it is to exit it.  This asserts in loops etc, moving
    1477             :     // the assert condition out of the loop body.
    1478       53893 :     if (MBB->succ_empty() && !PriorCond.empty() && !PriorFBB &&
    1479      506764 :         MachineFunction::iterator(PriorTBB) == FallThrough &&
    1480        5390 :         !MBB->canFallThrough()) {
    1481             :       bool DoTransform = true;
    1482             : 
    1483             :       // We have to be careful that the succs of PredBB aren't both no-successor
    1484             :       // blocks.  If neither have successors and if PredBB is the second from
    1485             :       // last block in the function, we'd just keep swapping the two blocks for
    1486             :       // last.  Only do the swap if one is clearly better to fall through than
    1487             :       // the other.
    1488        8820 :       if (FallThrough == --MF.end() &&
    1489        3430 :           !IsBetterFallthrough(PriorTBB, MBB))
    1490             :         DoTransform = false;
    1491             : 
    1492             :       if (DoTransform) {
    1493             :         // Reverse the branch so we will fall through on the previous true cond.
    1494             :         SmallVector<MachineOperand, 4> NewPriorCond(PriorCond);
    1495        2450 :         if (!TII->reverseBranchCondition(NewPriorCond)) {
    1496             :           DEBUG(dbgs() << "\nMoving MBB: " << *MBB
    1497             :                        << "To make fallthrough to: " << *PriorTBB << "\n");
    1498             : 
    1499        2450 :           DebugLoc dl = getBranchDebugLoc(PrevBB);
    1500        2450 :           TII->removeBranch(PrevBB);
    1501        4900 :           TII->insertBranch(PrevBB, MBB, nullptr, NewPriorCond, dl);
    1502             : 
    1503             :           // Move this block to the end of the function.
    1504        2450 :           MBB->moveAfter(&MF.back());
    1505             :           MadeChange = true;
    1506             :           ++NumBranchOpts;
    1507             :           return MadeChange;
    1508             :         }
    1509             :       }
    1510             :     }
    1511             :   }
    1512             : 
    1513     1344068 :   if (!IsEmptyBlock(MBB) && MBB->pred_size() == 1 &&
    1514      342874 :       MF.getFunction().optForSize()) {
    1515             :     // Changing "Jcc foo; foo: jmp bar;" into "Jcc bar;" might change the branch
    1516             :     // direction, thereby defeating careful block placement and regressing
    1517             :     // performance. Therefore, only consider this for optsize functions.
    1518        2692 :     MachineInstr &TailCall = *MBB->getFirstNonDebugInstr();
    1519        1346 :     if (TII->isUnconditionalTailCall(TailCall)) {
    1520          35 :       MachineBasicBlock *Pred = *MBB->pred_begin();
    1521          35 :       MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr;
    1522             :       SmallVector<MachineOperand, 4> PredCond;
    1523             :       bool PredAnalyzable =
    1524          35 :           !TII->analyzeBranch(*Pred, PredTBB, PredFBB, PredCond, true);
    1525             : 
    1526          60 :       if (PredAnalyzable && !PredCond.empty() && PredTBB == MBB &&
    1527          25 :           PredTBB != PredFBB) {
    1528             :         // The predecessor has a conditional branch to this block which consists
    1529             :         // of only a tail call. Try to fold the tail call into the conditional
    1530             :         // branch.
    1531          24 :         if (TII->canMakeTailCallConditional(PredCond, TailCall)) {
    1532             :           // TODO: It would be nice if analyzeBranch() could provide a pointer
    1533             :           // to the branch instruction so replaceBranchWithTailCall() doesn't
    1534             :           // have to search for it.
    1535          24 :           TII->replaceBranchWithTailCall(*Pred, PredCond, TailCall);
    1536             :           ++NumTailCalls;
    1537          24 :           Pred->removeSuccessor(MBB);
    1538             :           MadeChange = true;
    1539             :           return MadeChange;
    1540             :         }
    1541             :       }
    1542             :       // If the predecessor is falling through to this block, we could reverse
    1543             :       // the branch condition and fold the tail call into that. However, after
    1544             :       // that we might have to re-arrange the CFG to fall through to the other
    1545             :       // block and there is a high risk of regressing code size rather than
    1546             :       // improving it.
    1547             :     }
    1548             :   }
    1549             : 
    1550             :   // Analyze the branch in the current block.
    1551      500582 :   MachineBasicBlock *CurTBB = nullptr, *CurFBB = nullptr;
    1552             :   SmallVector<MachineOperand, 4> CurCond;
    1553             :   bool CurUnAnalyzable =
    1554      500582 :       TII->analyzeBranch(*MBB, CurTBB, CurFBB, CurCond, true);
    1555      500582 :   if (!CurUnAnalyzable) {
    1556             :     // If the CFG for the prior block has extra edges, remove them.
    1557      466933 :     MadeChange |= MBB->CorrectExtraCFGEdges(CurTBB, CurFBB, !CurCond.empty());
    1558             : 
    1559             :     // If this is a two-way branch, and the FBB branches to this block, reverse
    1560             :     // the condition so the single-basic-block loop is faster.  Instead of:
    1561             :     //    Loop: xxx; jcc Out; jmp Loop
    1562             :     // we want:
    1563             :     //    Loop: xxx; jncc Loop; jmp Out
    1564      466933 :     if (CurTBB && CurFBB && CurFBB == MBB && CurTBB != MBB) {
    1565             :       SmallVector<MachineOperand, 4> NewCond(CurCond);
    1566          28 :       if (!TII->reverseBranchCondition(NewCond)) {
    1567          28 :         DebugLoc dl = getBranchDebugLoc(*MBB);
    1568          28 :         TII->removeBranch(*MBB);
    1569          56 :         TII->insertBranch(*MBB, CurFBB, CurTBB, NewCond, dl);
    1570             :         MadeChange = true;
    1571             :         ++NumBranchOpts;
    1572             :         goto ReoptimizeBlock;
    1573             :       }
    1574             :     }
    1575             : 
    1576             :     // If this branch is the only thing in its block, see if we can forward
    1577             :     // other blocks across it.
    1578      858270 :     if (CurTBB && CurCond.empty() && !CurFBB &&
    1579      143707 :         IsBranchOnlyBlock(MBB) && CurTBB != MBB &&
    1580      476964 :         !MBB->hasAddressTaken() && !MBB->isEHPad()) {
    1581        5013 :       DebugLoc dl = getBranchDebugLoc(*MBB);
    1582             :       // This block may contain just an unconditional branch.  Because there can
    1583             :       // be 'non-branch terminators' in the block, try removing the branch and
    1584             :       // then seeing if the block is empty.
    1585        5013 :       TII->removeBranch(*MBB);
    1586             :       // If the only things remaining in the block are debug info, remove these
    1587             :       // as well, so this will behave the same as an empty block in non-debug
    1588             :       // mode.
    1589        5013 :       if (IsEmptyBlock(MBB)) {
    1590             :         // Make the block empty, losing the debug info (we could probably
    1591             :         // improve this in some cases.)
    1592             :         MBB->erase(MBB->begin(), MBB->end());
    1593             :       }
    1594             :       // If this block is just an unconditional branch to CurTBB, we can
    1595             :       // usually completely eliminate the block.  The only case we cannot
    1596             :       // completely eliminate the block is when the block before this one
    1597             :       // falls through into MBB and we can't understand the prior block's branch
    1598             :       // condition.
    1599        5013 :       if (MBB->empty()) {
    1600        5013 :         bool PredHasNoFallThrough = !PrevBB.canFallThrough();
    1601        5015 :         if (PredHasNoFallThrough || !PriorUnAnalyzable ||
    1602           2 :             !PrevBB.isSuccessor(MBB)) {
    1603             :           // If the prior block falls through into us, turn it into an
    1604             :           // explicit branch to us to make updates simpler.
    1605        9536 :           if (!PredHasNoFallThrough && PrevBB.isSuccessor(MBB) &&
    1606       14536 :               PriorTBB != MBB && PriorFBB != MBB) {
    1607        4757 :             if (!PriorTBB) {
    1608             :               assert(PriorCond.empty() && !PriorFBB &&
    1609             :                      "Bad branch analysis");
    1610        2111 :               PriorTBB = MBB;
    1611             :             } else {
    1612             :               assert(!PriorFBB && "Machine CFG out of date!");
    1613        2646 :               PriorFBB = MBB;
    1614             :             }
    1615        4757 :             DebugLoc pdl = getBranchDebugLoc(PrevBB);
    1616        4757 :             TII->removeBranch(PrevBB);
    1617        9514 :             TII->insertBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, pdl);
    1618             :           }
    1619             : 
    1620             :           // Iterate through all the predecessors, revectoring each in-turn.
    1621             :           size_t PI = 0;
    1622             :           bool DidChange = false;
    1623             :           bool HasBranchToSelf = false;
    1624       11668 :           while(PI != MBB->pred_size()) {
    1625        6657 :             MachineBasicBlock *PMBB = *(MBB->pred_begin() + PI);
    1626        6657 :             if (PMBB == MBB) {
    1627             :               // If this block has an uncond branch to itself, leave it.
    1628           0 :               ++PI;
    1629             :               HasBranchToSelf = true;
    1630             :             } else {
    1631             :               DidChange = true;
    1632        6657 :               PMBB->ReplaceUsesOfBlockWith(MBB, CurTBB);
    1633             :               // If this change resulted in PMBB ending in a conditional
    1634             :               // branch where both conditions go to the same destination,
    1635             :               // change this to an unconditional branch (and fix the CFG).
    1636        6657 :               MachineBasicBlock *NewCurTBB = nullptr, *NewCurFBB = nullptr;
    1637             :               SmallVector<MachineOperand, 4> NewCurCond;
    1638        6657 :               bool NewCurUnAnalyzable = TII->analyzeBranch(
    1639        6657 :                   *PMBB, NewCurTBB, NewCurFBB, NewCurCond, true);
    1640        6657 :               if (!NewCurUnAnalyzable && NewCurTBB && NewCurTBB == NewCurFBB) {
    1641          22 :                 DebugLoc pdl = getBranchDebugLoc(*PMBB);
    1642          22 :                 TII->removeBranch(*PMBB);
    1643             :                 NewCurCond.clear();
    1644          44 :                 TII->insertBranch(*PMBB, NewCurTBB, nullptr, NewCurCond, pdl);
    1645             :                 MadeChange = true;
    1646             :                 ++NumBranchOpts;
    1647          22 :                 PMBB->CorrectExtraCFGEdges(NewCurTBB, nullptr, false);
    1648             :               }
    1649             :             }
    1650             :           }
    1651             : 
    1652             :           // Change any jumptables to go to the new MBB.
    1653        5011 :           if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo())
    1654          99 :             MJTI->ReplaceMBBInJumpTables(MBB, CurTBB);
    1655        5011 :           if (DidChange) {
    1656             :             ++NumBranchOpts;
    1657             :             MadeChange = true;
    1658        5011 :             if (!HasBranchToSelf) return MadeChange;
    1659             :           }
    1660             :         }
    1661             :       }
    1662             : 
    1663             :       // Add the branch back if the block is more than just an uncond branch.
    1664           4 :       TII->insertBranch(*MBB, CurTBB, nullptr, CurCond, dl);
    1665             :     }
    1666             :   }
    1667             : 
    1668             :   // If the prior block doesn't fall through into this block, and if this
    1669             :   // block doesn't fall through into some other block, see if we can find a
    1670             :   // place to move this block where a fall-through will happen.
    1671      495543 :   if (!PrevBB.canFallThrough()) {
    1672             :     // Now we know that there was no fall-through into this block, check to
    1673             :     // see if it has a fall-through into its successor.
    1674      153982 :     bool CurFallsThru = MBB->canFallThrough();
    1675             : 
    1676      153982 :     if (!MBB->isEHPad()) {
    1677             :       // Check all the predecessors of this block.  If one of them has no fall
    1678             :       // throughs, move this block right after it.
    1679      131388 :       for (MachineBasicBlock *PredBB : MBB->predecessors()) {
    1680             :         // Analyze the branch at the end of the pred.
    1681       84686 :         MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr;
    1682             :         SmallVector<MachineOperand, 4> PredCond;
    1683      118063 :         if (PredBB != MBB && !PredBB->canFallThrough() &&
    1684       62523 :             !TII->analyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true) &&
    1685      103927 :             (!CurFallsThru || !CurTBB || !CurFBB) &&
    1686       19227 :             (!CurFallsThru || MBB->getNumber() >= PredBB->getNumber())) {
    1687             :           // If the current block doesn't fall through, just move it.
    1688             :           // If the current block can fall through and does not end with a
    1689             :           // conditional branch, we need to append an unconditional jump to
    1690             :           // the (current) next block.  To avoid a possible compile-time
    1691             :           // infinite loop, move blocks only backward in this case.
    1692             :           // Also, if there are already 2 branches here, we cannot add a third;
    1693             :           // this means we have the case
    1694             :           // Bcc next
    1695             :           // B elsewhere
    1696             :           // next:
    1697       27834 :           if (CurFallsThru) {
    1698             :             MachineBasicBlock *NextBB = &*std::next(MBB->getIterator());
    1699             :             CurCond.clear();
    1700       54657 :             TII->insertBranch(*MBB, NextBB, nullptr, CurCond, DebugLoc());
    1701             :           }
    1702       27834 :           MBB->moveAfter(PredBB);
    1703             :           MadeChange = true;
    1704             :           goto ReoptimizeBlock;
    1705             :         }
    1706             :       }
    1707             :     }
    1708             : 
    1709      126148 :     if (!CurFallsThru) {
    1710             :       // Check all successors to see if we can move this block before it.
    1711      126696 :       for (MachineBasicBlock *SuccBB : MBB->successors()) {
    1712             :         // Analyze the branch at the end of the block before the succ.
    1713       58467 :         MachineFunction::iterator SuccPrev = --SuccBB->getIterator();
    1714             : 
    1715             :         // If this block doesn't already fall-through to that successor, and if
    1716             :         // the succ doesn't already have a block that can fall through into it,
    1717             :         // and if the successor isn't an EH destination, we can arrange for the
    1718             :         // fallthrough to happen.
    1719      116450 :         if (SuccBB != MBB && &*SuccPrev != MBB &&
    1720      120667 :             !SuccPrev->canFallThrough() && !CurUnAnalyzable &&
    1721        1596 :             !SuccBB->isEHPad()) {
    1722        1430 :           MBB->moveBefore(SuccBB);
    1723             :           MadeChange = true;
    1724             :           goto ReoptimizeBlock;
    1725             :         }
    1726             :       }
    1727             : 
    1728             :       // Okay, there is no really great place to put this block.  If, however,
    1729             :       // the block before this one would be a fall-through if this block were
    1730             :       // removed, move this block to the end of the function. There is no real
    1731             :       // advantage in "falling through" to an EH block, so we don't want to
    1732             :       // perform this transformation for that case.
    1733             :       //
    1734             :       // Also, Windows EH introduced the possibility of an arbitrary number of
    1735             :       // successors to a given block.  The analyzeBranch call does not consider
    1736             :       // exception handling and so we can get in a state where a block
    1737             :       // containing a call is followed by multiple EH blocks that would be
    1738             :       // rotated infinitely at the end of the function if the transformation
    1739             :       // below were performed for EH "FallThrough" blocks.  Therefore, even if
    1740             :       // that appears not to be happening anymore, we should assume that it is
    1741             :       // possible and not remove the "!FallThrough()->isEHPad" condition below.
    1742       68229 :       MachineBasicBlock *PrevTBB = nullptr, *PrevFBB = nullptr;
    1743             :       SmallVector<MachineOperand, 4> PrevCond;
    1744       58483 :       if (FallThrough != MF.end() &&
    1745       75346 :           !FallThrough->isEHPad() &&
    1746       99592 :           !TII->analyzeBranch(PrevBB, PrevTBB, PrevFBB, PrevCond, true) &&
    1747       14500 :           PrevBB.isSuccessor(&*FallThrough)) {
    1748        3112 :         MBB->moveAfter(&MF.back());
    1749             :         MadeChange = true;
    1750             :         return MadeChange;
    1751             :       }
    1752             :     }
    1753             :   }
    1754             : 
    1755             :   return MadeChange;
    1756             : }
    1757             : 
    1758             : //===----------------------------------------------------------------------===//
    1759             : //  Hoist Common Code
    1760             : //===----------------------------------------------------------------------===//
    1761             : 
    1762           0 : bool BranchFolder::HoistCommonCode(MachineFunction &MF) {
    1763             :   bool MadeChange = false;
    1764      725362 :   for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ) {
    1765             :     MachineBasicBlock *MBB = &*I++;
    1766      558247 :     MadeChange |= HoistCommonCodeInSuccs(MBB);
    1767             :   }
    1768             : 
    1769           0 :   return MadeChange;
    1770             : }
    1771             : 
    1772             : /// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
    1773             : /// its 'true' successor.
    1774             : static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
    1775             :                                          MachineBasicBlock *TrueBB) {
    1776      159010 :   for (MachineBasicBlock *SuccBB : BB->successors())
    1777      158973 :     if (SuccBB != TrueBB)
    1778             :       return SuccBB;
    1779             :   return nullptr;
    1780             : }
    1781             : 
    1782             : template <class Container>
    1783       97878 : static void addRegAndItsAliases(unsigned Reg, const TargetRegisterInfo *TRI,
    1784             :                                 Container &Set) {
    1785      195756 :   if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
    1786      812460 :     for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
    1787      308437 :       Set.insert(*AI);
    1788             :   } else {
    1789          85 :     Set.insert(Reg);
    1790             :   }
    1791       97878 : }
    1792             : 
    1793             : /// findHoistingInsertPosAndDeps - Find the location to move common instructions
    1794             : /// in successors to. The location is usually just before the terminator,
    1795             : /// however if the terminator is a conditional branch and its previous
    1796             : /// instruction is the flag setting instruction, the previous instruction is
    1797             : /// the preferred location. This function also gathers uses and defs of the
    1798             : /// instructions from the insertion point to the end of the block. The data is
    1799             : /// used by HoistCommonCodeInSuccs to ensure safety.
    1800             : static
    1801       33533 : MachineBasicBlock::iterator findHoistingInsertPosAndDeps(MachineBasicBlock *MBB,
    1802             :                                                   const TargetInstrInfo *TII,
    1803             :                                                   const TargetRegisterInfo *TRI,
    1804             :                                                   SmallSet<unsigned,4> &Uses,
    1805             :                                                   SmallSet<unsigned,4> &Defs) {
    1806       33533 :   MachineBasicBlock::iterator Loc = MBB->getFirstTerminator();
    1807       33533 :   if (!TII->isUnpredicatedTerminator(*Loc))
    1808             :     return MBB->end();
    1809             : 
    1810      173657 :   for (const MachineOperand &MO : Loc->operands()) {
    1811       70394 :     if (!MO.isReg())
    1812       36219 :       continue;
    1813       34175 :     unsigned Reg = MO.getReg();
    1814       34175 :     if (!Reg)
    1815           0 :       continue;
    1816       34175 :     if (MO.isUse()) {
    1817       33727 :       addRegAndItsAliases(Reg, TRI, Uses);
    1818             :     } else {
    1819         448 :       if (!MO.isDead())
    1820             :         // Don't try to hoist code in the rare case the terminator defines a
    1821             :         // register that is later used.
    1822             :         return MBB->end();
    1823             : 
    1824             :       // If the terminator defines a register, make sure we don't hoist
    1825             :       // the instruction whose def might be clobbered by the terminator.
    1826         116 :       addRegAndItsAliases(Reg, TRI, Defs);
    1827             :     }
    1828             :   }
    1829             : 
    1830             :   if (Uses.empty())
    1831           0 :     return Loc;
    1832       33201 :   if (Loc == MBB->begin())
    1833             :     return MBB->end();
    1834             : 
    1835             :   // The terminator is probably a conditional branch, try not to separate the
    1836             :   // branch from condition setting instruction.
    1837             :   MachineBasicBlock::iterator PI =
    1838             :     skipDebugInstructionsBackward(std::prev(Loc), MBB->begin());
    1839             : 
    1840             :   bool IsDef = false;
    1841      236031 :   for (const MachineOperand &MO : PI->operands()) {
    1842             :     // If PI has a regmask operand, it is probably a call. Separate away.
    1843      127069 :     if (MO.isRegMask())
    1844           2 :       return Loc;
    1845      325086 :     if (!MO.isReg() || MO.isUse())
    1846      200054 :       continue;
    1847       27040 :     unsigned Reg = MO.getReg();
    1848       27040 :     if (!Reg)
    1849           0 :       continue;
    1850       27040 :     if (Uses.count(Reg)) {
    1851             :       IsDef = true;
    1852       25404 :       break;
    1853             :     }
    1854             :   }
    1855             :   if (!IsDef)
    1856             :     // The condition setting instruction is not just before the conditional
    1857             :     // branch.
    1858        7299 :     return Loc;
    1859             : 
    1860             :   // Be conservative, don't insert instruction above something that may have
    1861             :   // side-effects. And since it's potentially bad to separate flag setting
    1862             :   // instruction from the conditional branch, just abort the optimization
    1863             :   // completely.
    1864             :   // Also avoid moving code above predicated instruction since it's hard to
    1865             :   // reason about register liveness with predicated instruction.
    1866       25404 :   bool DontMoveAcrossStore = true;
    1867       48946 :   if (!PI->isSafeToMove(nullptr, DontMoveAcrossStore) || TII->isPredicated(*PI))
    1868             :     return MBB->end();
    1869             : 
    1870             :   // Find out what registers are live. Note this routine is ignoring other live
    1871             :   // registers which are only used by instructions in successor blocks.
    1872      175014 :   for (const MachineOperand &MO : PI->operands()) {
    1873       75737 :     if (!MO.isReg())
    1874       22533 :       continue;
    1875       65196 :     unsigned Reg = MO.getReg();
    1876       65196 :     if (!Reg)
    1877        1451 :       continue;
    1878       63745 :     if (MO.isUse()) {
    1879       39362 :       addRegAndItsAliases(Reg, TRI, Uses);
    1880             :     } else {
    1881       24383 :       if (Uses.erase(Reg)) {
    1882       47084 :         if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
    1883       48946 :           for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs)
    1884        1916 :             Uses.erase(*SubRegs); // Use sub-registers to be conservative
    1885             :         }
    1886             :       }
    1887       24383 :       addRegAndItsAliases(Reg, TRI, Defs);
    1888             :     }
    1889             :   }
    1890             : 
    1891       23540 :   return PI;
    1892             : }
    1893             : 
    1894      558247 : bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
    1895      558247 :   MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
    1896             :   SmallVector<MachineOperand, 4> Cond;
    1897      558247 :   if (TII->analyzeBranch(*MBB, TBB, FBB, Cond, true) || !TBB || Cond.empty())
    1898             :     return false;
    1899             : 
    1900      221146 :   if (!FBB) FBB = findFalseBlock(MBB, TBB);
    1901      111672 :   if (!FBB)
    1902             :     // Malformed bcc? True and false blocks are the same?
    1903             :     return false;
    1904             : 
    1905             :   // Restrict the optimization to cases where MBB is the only predecessor,
    1906             :   // it is an obvious win.
    1907      146691 :   if (TBB->pred_size() > 1 || FBB->pred_size() > 1)
    1908             :     return false;
    1909             : 
    1910             :   // Find a suitable position to hoist the common instructions to. Also figure
    1911             :   // out which registers are used or defined by instructions from the insertion
    1912             :   // point to the end of the block.
    1913       33533 :   SmallSet<unsigned, 4> Uses, Defs;
    1914             :   MachineBasicBlock::iterator Loc =
    1915       33533 :     findHoistingInsertPosAndDeps(MBB, TII, TRI, Uses, Defs);
    1916       33533 :   if (Loc == MBB->end())
    1917             :     return false;
    1918             : 
    1919             :   bool HasDups = false;
    1920             :   SmallVector<unsigned, 4> LocalDefs, LocalKills;
    1921       30841 :   SmallSet<unsigned, 4> ActiveDefsSet, AllDefsSet;
    1922       61682 :   MachineBasicBlock::iterator TIB = TBB->begin();
    1923       61682 :   MachineBasicBlock::iterator FIB = FBB->begin();
    1924             :   MachineBasicBlock::iterator TIE = TBB->end();
    1925             :   MachineBasicBlock::iterator FIE = FBB->end();
    1926       61864 :   while (TIB != TIE && FIB != FIE) {
    1927             :     // Skip dbg_value instructions. These do not count.
    1928       30528 :     TIB = skipDebugInstructionsForward(TIB, TIE);
    1929       30528 :     FIB = skipDebugInstructionsForward(FIB, FIE);
    1930       30528 :     if (TIB == TIE || FIB == FIE)
    1931             :       break;
    1932             : 
    1933       30528 :     if (!TIB->isIdenticalTo(*FIB, MachineInstr::CheckKillDead))
    1934             :       break;
    1935             : 
    1936         872 :     if (TII->isPredicated(*TIB))
    1937             :       // Hard to reason about register liveness with predicated instruction.
    1938             :       break;
    1939             : 
    1940             :     bool IsSafe = true;
    1941        3890 :     for (MachineOperand &MO : TIB->operands()) {
    1942             :       // Don't attempt to hoist instructions with register masks.
    1943        1815 :       if (MO.isRegMask()) {
    1944             :         IsSafe = false;
    1945          88 :         break;
    1946             :       }
    1947        1793 :       if (!MO.isReg())
    1948        1581 :         continue;
    1949        1217 :       unsigned Reg = MO.getReg();
    1950        1217 :       if (!Reg)
    1951         429 :         continue;
    1952         788 :       if (MO.isDef()) {
    1953         448 :         if (Uses.count(Reg)) {
    1954             :           // Avoid clobbering a register that's used by the instruction at
    1955             :           // the point of insertion.
    1956             :           IsSafe = false;
    1957             :           break;
    1958             :         }
    1959             : 
    1960         438 :         if (Defs.count(Reg) && !MO.isDead()) {
    1961             :           // Don't hoist the instruction if the def would be clobber by the
    1962             :           // instruction at the point insertion. FIXME: This is overly
    1963             :           // conservative. It should be possible to hoist the instructions
    1964             :           // in BB2 in the following example:
    1965             :           // BB1:
    1966             :           // r1, eflag = op1 r2, r3
    1967             :           // brcc eflag
    1968             :           //
    1969             :           // BB2:
    1970             :           // r1 = op2, ...
    1971             :           //    = op3, killed r1
    1972             :           IsSafe = false;
    1973             :           break;
    1974             :         }
    1975         340 :       } else if (!ActiveDefsSet.count(Reg)) {
    1976         333 :         if (Defs.count(Reg)) {
    1977             :           // Use is defined by the instruction at the point of insertion.
    1978             :           IsSafe = false;
    1979             :           break;
    1980             :         }
    1981             : 
    1982         333 :         if (MO.isKill() && Uses.count(Reg))
    1983             :           // Kills a register that's read by the instruction at the point of
    1984             :           // insertion. Remove the kill marker.
    1985             :           MO.setIsKill(false);
    1986             :       }
    1987             :     }
    1988             :     if (!IsSafe)
    1989             :       break;
    1990             : 
    1991         348 :     bool DontMoveAcrossStore = true;
    1992         348 :     if (!TIB->isSafeToMove(nullptr, DontMoveAcrossStore))
    1993             :       break;
    1994             : 
    1995             :     // Remove kills from ActiveDefsSet, these registers had short live ranges.
    1996         869 :     for (const MachineOperand &MO : TIB->operands()) {
    1997        1118 :       if (!MO.isReg() || !MO.isUse() || !MO.isKill())
    1998         718 :         continue;
    1999          18 :       unsigned Reg = MO.getReg();
    2000          18 :       if (!Reg)
    2001           0 :         continue;
    2002          34 :       if (!AllDefsSet.count(Reg)) {
    2003          16 :         LocalKills.push_back(Reg);
    2004          16 :         continue;
    2005             :       }
    2006           2 :       if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
    2007          28 :         for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
    2008          12 :           ActiveDefsSet.erase(*AI);
    2009             :       } else {
    2010           0 :         ActiveDefsSet.erase(Reg);
    2011             :       }
    2012             :     }
    2013             : 
    2014             :     // Track local defs so we can update liveins.
    2015         869 :     for (const MachineOperand &MO : TIB->operands()) {
    2016        1059 :       if (!MO.isReg() || !MO.isDef() || MO.isDead())
    2017         448 :         continue;
    2018         145 :       unsigned Reg = MO.getReg();
    2019         290 :       if (!Reg || TargetRegisterInfo::isVirtualRegister(Reg))
    2020           0 :         continue;
    2021         145 :       LocalDefs.push_back(Reg);
    2022         145 :       addRegAndItsAliases(Reg, TRI, ActiveDefsSet);
    2023         145 :       addRegAndItsAliases(Reg, TRI, AllDefsSet);
    2024             :     }
    2025             : 
    2026             :     HasDups = true;
    2027             :     ++TIB;
    2028             :     ++FIB;
    2029             :   }
    2030             : 
    2031       30841 :   if (!HasDups)
    2032             :     return false;
    2033             : 
    2034         102 :   MBB->splice(Loc, TBB, TBB->begin(), TIB);
    2035         102 :   FBB->erase(FBB->begin(), FIB);
    2036             : 
    2037             :   // Update livein's.
    2038             :   bool ChangedLiveIns = false;
    2039         247 :   for (unsigned i = 0, e = LocalDefs.size(); i != e; ++i) {
    2040         290 :     unsigned Def = LocalDefs[i];
    2041         145 :     if (ActiveDefsSet.count(Def)) {
    2042         145 :       TBB->addLiveIn(Def);
    2043         145 :       FBB->addLiveIn(Def);
    2044             :       ChangedLiveIns = true;
    2045             :     }
    2046             :   }
    2047         134 :   for (unsigned K : LocalKills) {
    2048          16 :     TBB->removeLiveIn(K);
    2049          16 :     FBB->removeLiveIn(K);
    2050             :     ChangedLiveIns = true;
    2051             :   }
    2052             : 
    2053         102 :   if (ChangedLiveIns) {
    2054         102 :     TBB->sortUniqueLiveIns();
    2055         102 :     FBB->sortUniqueLiveIns();
    2056             :   }
    2057             : 
    2058             :   ++NumHoist;
    2059             :   return true;
    2060      291909 : }

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