LCOV - code coverage report
Current view: top level - lib/CodeGen - BranchFolding.cpp (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 857 905 94.7 %
Date: 2017-09-14 15:23:50 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/SmallPtrSet.h"
      23             : #include "llvm/ADT/SmallSet.h"
      24             : #include "llvm/ADT/SmallVector.h"
      25             : #include "llvm/ADT/Statistic.h"
      26             : #include "llvm/ADT/STLExtras.h"
      27             : #include "llvm/CodeGen/Analysis.h"
      28             : #include "llvm/CodeGen/MachineBasicBlock.h"
      29             : #include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
      30             : #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
      31             : #include "llvm/CodeGen/MachineFunction.h"
      32             : #include "llvm/CodeGen/MachineFunctionPass.h"
      33             : #include "llvm/CodeGen/MachineInstr.h"
      34             : #include "llvm/CodeGen/MachineInstrBuilder.h"
      35             : #include "llvm/CodeGen/MachineJumpTableInfo.h"
      36             : #include "llvm/CodeGen/MachineLoopInfo.h"
      37             : #include "llvm/CodeGen/MachineModuleInfo.h"
      38             : #include "llvm/CodeGen/MachineOperand.h"
      39             : #include "llvm/CodeGen/MachineRegisterInfo.h"
      40             : #include "llvm/CodeGen/TargetPassConfig.h"
      41             : #include "llvm/IR/DebugInfoMetadata.h"
      42             : #include "llvm/IR/DebugLoc.h"
      43             : #include "llvm/IR/Function.h"
      44             : #include "llvm/MC/MCRegisterInfo.h"
      45             : #include "llvm/Pass.h"
      46             : #include "llvm/Support/BlockFrequency.h"
      47             : #include "llvm/Support/BranchProbability.h"
      48             : #include "llvm/Support/CommandLine.h"
      49             : #include "llvm/Support/Debug.h"
      50             : #include "llvm/Support/ErrorHandling.h"
      51             : #include "llvm/Support/raw_ostream.h"
      52             : #include "llvm/Target/TargetInstrInfo.h"
      53             : #include "llvm/Target/TargetMachine.h"
      54             : #include "llvm/Target/TargetRegisterInfo.h"
      55             : #include "llvm/Target/TargetSubtargetInfo.h"
      56             : #include <cassert>
      57             : #include <cstddef>
      58             : #include <iterator>
      59             : #include <numeric>
      60             : #include <vector>
      61             : 
      62             : using namespace llvm;
      63             : 
      64             : #define DEBUG_TYPE "branch-folder"
      65             : 
      66             : STATISTIC(NumDeadBlocks, "Number of dead blocks removed");
      67             : STATISTIC(NumBranchOpts, "Number of branches optimized");
      68             : STATISTIC(NumTailMerge , "Number of block tails merged");
      69             : STATISTIC(NumHoist     , "Number of times common instructions are hoisted");
      70             : STATISTIC(NumTailCalls,  "Number of tail calls optimized");
      71             : 
      72       72306 : static cl::opt<cl::boolOrDefault> FlagEnableTailMerge("enable-tail-merge",
      73      144612 :                               cl::init(cl::BOU_UNSET), cl::Hidden);
      74             : 
      75             : // Throttle for huge numbers of predecessors (compile speed problems)
      76             : static cl::opt<unsigned>
      77       72306 : TailMergeThreshold("tail-merge-threshold",
      78      216918 :           cl::desc("Max number of predecessors to consider tail merging"),
      79      289224 :           cl::init(150), cl::Hidden);
      80             : 
      81             : // Heuristic for tail merging (and, inversely, tail duplication).
      82             : // TODO: This should be replaced with a target query.
      83             : static cl::opt<unsigned>
      84       72306 : TailMergeSize("tail-merge-size",
      85      216918 :           cl::desc("Min number of instructions to consider tail merging"),
      86      289224 :                               cl::init(3), cl::Hidden);
      87             : 
      88             : namespace {
      89             : 
      90             :   /// BranchFolderPass - Wrap branch folder in a machine function pass.
      91       15517 :   class BranchFolderPass : public MachineFunctionPass {
      92             :   public:
      93             :     static char ID;
      94             : 
      95       15616 :     explicit BranchFolderPass(): MachineFunctionPass(ID) {}
      96             : 
      97             :     bool runOnMachineFunction(MachineFunction &MF) override;
      98             : 
      99       15563 :     void getAnalysisUsage(AnalysisUsage &AU) const override {
     100       15563 :       AU.addRequired<MachineBlockFrequencyInfo>();
     101       15563 :       AU.addRequired<MachineBranchProbabilityInfo>();
     102       15563 :       AU.addRequired<TargetPassConfig>();
     103       15563 :       MachineFunctionPass::getAnalysisUsage(AU);
     104       15563 :     }
     105             :   };
     106             : 
     107             : } // end anonymous namespace
     108             : 
     109             : char BranchFolderPass::ID = 0;
     110             : char &llvm::BranchFolderPassID = BranchFolderPass::ID;
     111             : 
     112      151199 : INITIALIZE_PASS(BranchFolderPass, DEBUG_TYPE,
     113             :                 "Control Flow Optimizer", false, false)
     114             : 
     115      135734 : bool BranchFolderPass::runOnMachineFunction(MachineFunction &MF) {
     116      135734 :   if (skipFunction(*MF.getFunction()))
     117             :     return false;
     118             : 
     119      135677 :   TargetPassConfig *PassConfig = &getAnalysis<TargetPassConfig>();
     120             :   // TailMerge can create jump into if branches that make CFG irreducible for
     121             :   // HW that requires structurized CFG.
     122      404974 :   bool EnableTailMerge = !MF.getTarget().requiresStructuredCFG() &&
     123      269297 :                          PassConfig->getEnableTailMerge();
     124             :   BranchFolder::MBFIWrapper MBBFreqInfo(
     125      271354 :       getAnalysis<MachineBlockFrequencyInfo>());
     126             :   BranchFolder Folder(EnableTailMerge, /*CommonHoist=*/true, MBBFreqInfo,
     127      271354 :                       getAnalysis<MachineBranchProbabilityInfo>());
     128      271354 :   return Folder.OptimizeFunction(MF, MF.getSubtarget().getInstrInfo(),
     129      135677 :                                  MF.getSubtarget().getRegisterInfo(),
     130      135677 :                                  getAnalysisIfAvailable<MachineModuleInfo>());
     131             : }
     132             : 
     133      169251 : BranchFolder::BranchFolder(bool defaultEnableTailMerge, bool CommonHoist,
     134             :                            MBFIWrapper &FreqInfo,
     135             :                            const MachineBranchProbabilityInfo &ProbInfo,
     136      169251 :                            unsigned MinTailLength)
     137             :     : EnableHoistCommonCode(CommonHoist), MinCommonTailLength(MinTailLength),
     138     1015506 :       MBBFreqInfo(FreqInfo), MBPI(ProbInfo) {
     139      169251 :   if (MinCommonTailLength == 0)
     140      163286 :     MinCommonTailLength = TailMergeSize;
     141      169251 :   switch (FlagEnableTailMerge) {
     142      169197 :   case cl::BOU_UNSET: EnableTailMerge = defaultEnableTailMerge; break;
     143           3 :   case cl::BOU_TRUE: EnableTailMerge = true; break;
     144          51 :   case cl::BOU_FALSE: EnableTailMerge = false; break;
     145             :   }
     146      169251 : }
     147             : 
     148       10298 : void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) {
     149             :   assert(MBB->pred_empty() && "MBB must be dead!");
     150             :   DEBUG(dbgs() << "\nRemoving MBB: " << *MBB);
     151             : 
     152       10298 :   MachineFunction *MF = MBB->getParent();
     153             :   // drop all successors.
     154       22428 :   while (!MBB->succ_empty())
     155       12130 :     MBB->removeSuccessor(MBB->succ_end()-1);
     156             : 
     157             :   // Avoid matching if this pointer gets reused.
     158       20596 :   TriedMerging.erase(MBB);
     159             : 
     160             :   // Remove the block.
     161       10298 :   MF->erase(MBB);
     162       10298 :   FuncletMembership.erase(MBB);
     163       10298 :   if (MLI)
     164         284 :     MLI->removeBlock(MBB);
     165       10298 : }
     166             : 
     167      169251 : bool BranchFolder::OptimizeFunction(MachineFunction &MF,
     168             :                                     const TargetInstrInfo *tii,
     169             :                                     const TargetRegisterInfo *tri,
     170             :                                     MachineModuleInfo *mmi,
     171             :                                     MachineLoopInfo *mli, bool AfterPlacement) {
     172      169251 :   if (!tii) return false;
     173             : 
     174      169251 :   TriedMerging.clear();
     175             : 
     176      169251 :   MachineRegisterInfo &MRI = MF.getRegInfo();
     177      169251 :   AfterBlockPlacement = AfterPlacement;
     178      169251 :   TII = tii;
     179      169251 :   TRI = tri;
     180      169251 :   MMI = mmi;
     181      169251 :   MLI = mli;
     182      169251 :   this->MRI = &MRI;
     183             : 
     184      169251 :   UpdateLiveIns = MRI.tracksLiveness() && TRI->trackLivenessAfterRegAlloc(MF);
     185      169251 :   if (!UpdateLiveIns)
     186             :     MRI.invalidateLiveness();
     187             : 
     188             :   // Fix CFG.  The later algorithms expect it to be right.
     189      169251 :   bool MadeChange = false;
     190      968183 :   for (MachineBasicBlock &MBB : MF) {
     191      460430 :     MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
     192      920860 :     SmallVector<MachineOperand, 4> Cond;
     193      460430 :     if (!TII->analyzeBranch(MBB, TBB, FBB, Cond, true))
     194      289288 :       MadeChange |= MBB.CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
     195             :   }
     196             : 
     197             :   // Recalculate funclet membership.
     198      338502 :   FuncletMembership = getFuncletMembership(MF);
     199             : 
     200      169251 :   bool MadeChangeThisIteration = true;
     201      526001 :   while (MadeChangeThisIteration) {
     202      178375 :     MadeChangeThisIteration    = TailMergeBlocks(MF);
     203             :     // No need to clean up if tail merging does not change anything after the
     204             :     // block placement.
     205      178375 :     if (!AfterBlockPlacement || MadeChangeThisIteration)
     206      172410 :       MadeChangeThisIteration |= OptimizeBranches(MF);
     207      178375 :     if (EnableHoistCommonCode)
     208      143127 :       MadeChangeThisIteration |= HoistCommonCode(MF);
     209      178375 :     MadeChange |= MadeChangeThisIteration;
     210             :   }
     211             : 
     212             :   // See if any jump tables have become dead as the code generator
     213             :   // did its thing.
     214      169251 :   MachineJumpTableInfo *JTI = MF.getJumpTableInfo();
     215      169251 :   if (!JTI)
     216             :     return MadeChange;
     217             : 
     218             :   // Walk the function to find jump tables that are live.
     219         876 :   BitVector JTIsLive(JTI->getJumpTables().size());
     220        7579 :   for (const MachineBasicBlock &BB : MF) {
     221      133338 :     for (const MachineInstr &I : BB)
     222      296526 :       for (const MachineOperand &Op : I.operands()) {
     223      242387 :         if (!Op.isJTI()) continue;
     224             : 
     225             :         // Remember that this JT is live.
     226         737 :         JTIsLive.set(Op.getIndex());
     227             :       }
     228             :   }
     229             : 
     230             :   // Finally, remove dead jump tables.  This happens when the
     231             :   // indirect jump was unreachable (and thus deleted).
     232         902 :   for (unsigned i = 0, e = JTIsLive.size(); i != e; ++i)
     233         464 :     if (!JTIsLive.test(i)) {
     234           0 :       JTI->RemoveJumpTable(i);
     235           0 :       MadeChange = true;
     236             :     }
     237             : 
     238         438 :   return MadeChange;
     239             : }
     240             : 
     241             : //===----------------------------------------------------------------------===//
     242             : //  Tail Merging of Blocks
     243             : //===----------------------------------------------------------------------===//
     244             : 
     245             : /// HashMachineInstr - Compute a hash value for MI and its operands.
     246      538963 : static unsigned HashMachineInstr(const MachineInstr &MI) {
     247     1077926 :   unsigned Hash = MI.getOpcode();
     248     2470966 :   for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
     249     3864006 :     const MachineOperand &Op = MI.getOperand(i);
     250             : 
     251             :     // Merge in bits from the operand if easy. We can't use MachineOperand's
     252             :     // hash_code here because it's not deterministic and we sort by hash value
     253             :     // later.
     254     1932003 :     unsigned OperandHash = 0;
     255     1932003 :     switch (Op.getType()) {
     256     1190233 :     case MachineOperand::MO_Register:
     257     1190233 :       OperandHash = Op.getReg();
     258     1190233 :       break;
     259      367918 :     case MachineOperand::MO_Immediate:
     260      367918 :       OperandHash = Op.getImm();
     261      367918 :       break;
     262      104243 :     case MachineOperand::MO_MachineBasicBlock:
     263      104243 :       OperandHash = Op.getMBB()->getNumber();
     264      104243 :       break;
     265         343 :     case MachineOperand::MO_FrameIndex:
     266             :     case MachineOperand::MO_ConstantPoolIndex:
     267             :     case MachineOperand::MO_JumpTableIndex:
     268         343 :       OperandHash = Op.getIndex();
     269         343 :       break;
     270      162883 :     case MachineOperand::MO_GlobalAddress:
     271             :     case MachineOperand::MO_ExternalSymbol:
     272             :       // Global address / external symbol are too hard, don't bother, but do
     273             :       // pull in the offset.
     274      162883 :       OperandHash = Op.getOffset();
     275      162883 :       break;
     276             :     default:
     277             :       break;
     278             :     }
     279             : 
     280     1932003 :     Hash += ((OperandHash << 3) | Op.getType()) << (i & 31);
     281             :   }
     282      538963 :   return Hash;
     283             : }
     284             : 
     285             : /// HashEndOfMBB - Hash the last instruction in the MBB.
     286      544149 : static unsigned HashEndOfMBB(const MachineBasicBlock &MBB) {
     287      544149 :   MachineBasicBlock::const_iterator I = MBB.getLastNonDebugInstr();
     288     1088298 :   if (I == MBB.end())
     289             :     return 0;
     290             : 
     291      538963 :   return HashMachineInstr(*I);
     292             : }
     293             : 
     294             : /// ComputeCommonTailLength - Given two machine basic blocks, compute the number
     295             : /// of instructions they actually have in common together at their end.  Return
     296             : /// iterators for the first shared instruction in each block.
     297      629188 : static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1,
     298             :                                         MachineBasicBlock *MBB2,
     299             :                                         MachineBasicBlock::iterator &I1,
     300             :                                         MachineBasicBlock::iterator &I2) {
     301      629188 :   I1 = MBB1->end();
     302      629188 :   I2 = MBB2->end();
     303             : 
     304      629188 :   unsigned TailLen = 0;
     305     6502501 :   while (I1 != MBB1->begin() && I2 != MBB2->begin()) {
     306     1279485 :     --I1; --I2;
     307             :     // Skip debugging pseudos; necessary to avoid changing the code.
     308     2559366 :     while (I1->isDebugValue()) {
     309         460 :       if (I1==MBB1->begin()) {
     310         126 :         while (I2->isDebugValue()) {
     311          70 :           if (I2==MBB2->begin())
     312             :             // I1==DBG at begin; I2==DBG at begin
     313             :             return TailLen;
     314             :           --I2;
     315             :         }
     316          28 :         ++I2;
     317             :         // I1==DBG at begin; I2==non-DBG, or first of DBGs not at begin
     318          28 :         return TailLen;
     319             :       }
     320             :       --I1;
     321             :     }
     322             :     // I1==first (untested) non-DBG preceding known match
     323     2559286 :     while (I2->isDebugValue()) {
     324         396 :       if (I2==MBB2->begin()) {
     325           8 :         ++I1;
     326             :         // I1==non-DBG, or first of DBGs not at begin; I2==DBG at begin
     327           8 :         return TailLen;
     328             :       }
     329             :       --I2;
     330             :     }
     331             :     // I1, I2==first (untested) non-DBGs preceding known match
     332     3432375 :     if (!I1->isIdenticalTo(*I2) ||
     333             :         // FIXME: This check is dubious. It's used to get around a problem where
     334             :         // people incorrectly expect inline asm directives to remain in the same
     335             :         // relative order. This is untenable because normal compiler
     336             :         // optimizations (like this one) may reorder and/or merge these
     337             :         // directives.
     338     1746970 :         I1->isInlineAsm()) {
     339      406096 :       ++I1; ++I2;
     340             :       break;
     341             :     }
     342      873349 :     ++TailLen;
     343             :   }
     344             :   // Back past possible debugging pseudos at beginning of block.  This matters
     345             :   // when one block differs from the other only by whether debugging pseudos
     346             :   // are present at the beginning. (This way, the various checks later for
     347             :   // I1==MBB1->begin() work as expected.)
     348     1639292 :   if (I1 == MBB1->begin() && I2 != MBB2->begin()) {
     349             :     --I2;
     350      127580 :     while (I2->isDebugValue()) {
     351          14 :       if (I2 == MBB2->begin())
     352             :         return TailLen;
     353             :       --I2;
     354             :     }
     355             :     ++I2;
     356             :   }
     357     1576830 :   if (I2 == MBB2->begin() && I1 != MBB1->begin()) {
     358             :     --I1;
     359       65108 :     while (I1->isDebugValue()) {
     360           0 :       if (I1 == MBB1->begin())
     361             :         return TailLen;
     362             :       --I1;
     363             :     }
     364             :     ++I1;
     365             :   }
     366             :   return TailLen;
     367             : }
     368             : 
     369       11749 : void BranchFolder::replaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
     370             :                                            MachineBasicBlock &NewDest) {
     371       11749 :   if (UpdateLiveIns) {
     372             :     // OldInst should always point to an instruction.
     373       11736 :     MachineBasicBlock &OldMBB = *OldInst->getParent();
     374       23472 :     LiveRegs.clear();
     375       11736 :     LiveRegs.addLiveOuts(OldMBB);
     376             :     // Move backward to the place where will insert the jump.
     377       11736 :     MachineBasicBlock::iterator I = OldMBB.end();
     378             :     do {
     379       54527 :       --I;
     380      109054 :       LiveRegs.stepBackward(*I);
     381       54527 :     } while (I != OldInst);
     382             : 
     383             :     // Merging the tails may have switched some undef operand to non-undef ones.
     384             :     // Add IMPLICIT_DEFS into OldMBB as necessary to have a definition of the
     385             :     // register.
     386       43841 :     for (MachineBasicBlock::RegisterMaskPair P : NewDest.liveins()) {
     387             :       // We computed the liveins with computeLiveIn earlier and should only see
     388             :       // full registers:
     389             :       assert(P.LaneMask == LaneBitmask::getAll() &&
     390             :              "Can only handle full register.");
     391       20369 :       MCPhysReg Reg = P.PhysReg;
     392       20369 :       if (!LiveRegs.available(*MRI, Reg))
     393       20368 :         continue;
     394           2 :       DebugLoc DL;
     395           2 :       BuildMI(OldMBB, OldInst, DL, TII->get(TargetOpcode::IMPLICIT_DEF), Reg);
     396             :     }
     397             :   }
     398             : 
     399       11749 :   TII->ReplaceTailWithBranchTo(OldInst, &NewDest);
     400       11749 :   ++NumTailMerge;
     401       11749 : }
     402             : 
     403        3096 : MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB,
     404             :                                             MachineBasicBlock::iterator BBI1,
     405             :                                             const BasicBlock *BB) {
     406        3096 :   if (!TII->isLegalToSplitMBBAt(CurMBB, BBI1))
     407             :     return nullptr;
     408             : 
     409        3096 :   MachineFunction &MF = *CurMBB.getParent();
     410             : 
     411             :   // Create the fall-through block.
     412        6192 :   MachineFunction::iterator MBBI = CurMBB.getIterator();
     413        3096 :   MachineBasicBlock *NewMBB = MF.CreateMachineBasicBlock(BB);
     414        9288 :   CurMBB.getParent()->insert(++MBBI, NewMBB);
     415             : 
     416             :   // Move all the successors of this block to the specified block.
     417        3096 :   NewMBB->transferSuccessors(&CurMBB);
     418             : 
     419             :   // Add an edge from CurMBB to NewMBB for the fall-through.
     420        3096 :   CurMBB.addSuccessor(NewMBB);
     421             : 
     422             :   // Splice the code over.
     423        9288 :   NewMBB->splice(NewMBB->end(), &CurMBB, BBI1, CurMBB.end());
     424             : 
     425             :   // NewMBB belongs to the same loop as CurMBB.
     426        3096 :   if (MLI)
     427         780 :     if (MachineLoop *ML = MLI->getLoopFor(&CurMBB))
     428          22 :       ML->addBasicBlockToLoop(NewMBB, MLI->getBase());
     429             : 
     430             :   // NewMBB inherits CurMBB's block frequency.
     431        6192 :   MBBFreqInfo.setBlockFreq(NewMBB, MBBFreqInfo.getBlockFreq(&CurMBB));
     432             : 
     433        3096 :   if (UpdateLiveIns)
     434        3087 :     computeAndAddLiveIns(LiveRegs, *NewMBB);
     435             : 
     436             :   // Add the new block to the funclet.
     437        3096 :   const auto &FuncletI = FuncletMembership.find(&CurMBB);
     438        9288 :   if (FuncletI != FuncletMembership.end()) {
     439           0 :     auto n = FuncletI->second;
     440           0 :     FuncletMembership[NewMBB] = n;
     441             :   }
     442             : 
     443             :   return NewMBB;
     444             : }
     445             : 
     446             : /// EstimateRuntime - Make a rough estimate for how long it will take to run
     447             : /// the specified code.
     448        7615 : static unsigned EstimateRuntime(MachineBasicBlock::iterator I,
     449             :                                 MachineBasicBlock::iterator E) {
     450        7615 :   unsigned Time = 0;
     451       21186 :   for (; I != E; ++I) {
     452       27142 :     if (I->isDebugValue())
     453          21 :       continue;
     454       27100 :     if (I->isCall())
     455         482 :       Time += 10;
     456       23622 :     else if (I->mayLoad() || I->mayStore())
     457        3016 :       Time += 2;
     458             :     else
     459       10052 :       ++Time;
     460             :   }
     461        7615 :   return Time;
     462             : }
     463             : 
     464             : // CurMBB needs to add an unconditional branch to SuccMBB (we removed these
     465             : // branches temporarily for tail merging).  In the case where CurMBB ends
     466             : // with a conditional branch to the next block, optimize by reversing the
     467             : // test and conditionally branching to SuccMBB instead.
     468      213834 : static void FixTail(MachineBasicBlock *CurMBB, MachineBasicBlock *SuccBB,
     469             :                     const TargetInstrInfo *TII) {
     470      213834 :   MachineFunction *MF = CurMBB->getParent();
     471      427668 :   MachineFunction::iterator I = std::next(MachineFunction::iterator(CurMBB));
     472      213834 :   MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
     473      336363 :   SmallVector<MachineOperand, 4> Cond;
     474      336363 :   DebugLoc dl = CurMBB->findBranchDebugLoc();
     475      213834 :   if (I != MF->end() && !TII->analyzeBranch(*CurMBB, TBB, FBB, Cond, true)) {
     476      211352 :     MachineBasicBlock *NextBB = &*I;
     477      211352 :     if (TBB == NextBB && !Cond.empty() && !FBB) {
     478       91307 :       if (!TII->reverseBranchCondition(Cond)) {
     479       91305 :         TII->removeBranch(*CurMBB);
     480      182610 :         TII->insertBranch(*CurMBB, SuccBB, nullptr, Cond, dl);
     481       91305 :         return;
     482             :       }
     483             :     }
     484             :   }
     485      122529 :   TII->insertBranch(*CurMBB, SuccBB, nullptr,
     486      367587 :                     SmallVector<MachineOperand, 0>(), dl);
     487             : }
     488             : 
     489             : bool
     490           0 : BranchFolder::MergePotentialsElt::operator<(const MergePotentialsElt &o) const {
     491      458299 :   if (getHash() < o.getHash())
     492             :     return true;
     493      247705 :   if (getHash() > o.getHash())
     494             :     return false;
     495      145603 :   if (getBlock()->getNumber() < o.getBlock()->getNumber())
     496             :     return true;
     497       47665 :   if (getBlock()->getNumber() > o.getBlock()->getNumber())
     498             :     return false;
     499             :   // _GLIBCXX_DEBUG checks strict weak ordering, which involves comparing
     500             :   // an object with itself.
     501             : #ifndef _GLIBCXX_DEBUG
     502           0 :   llvm_unreachable("Predecessor appears twice");
     503             : #else
     504             :   return false;
     505             : #endif
     506             : }
     507             : 
     508             : BlockFrequency
     509     1444910 : BranchFolder::MBFIWrapper::getBlockFreq(const MachineBasicBlock *MBB) const {
     510     1444910 :   auto I = MergedBBFreq.find(MBB);
     511             : 
     512     2889820 :   if (I != MergedBBFreq.end())
     513        4428 :     return I->second;
     514             : 
     515     1440482 :   return MBFI.getBlockFreq(MBB);
     516             : }
     517             : 
     518           0 : void BranchFolder::MBFIWrapper::setBlockFreq(const MachineBasicBlock *MBB,
     519             :                                              BlockFrequency F) {
     520       16366 :   MergedBBFreq[MBB] = F;
     521           0 : }
     522             : 
     523             : raw_ostream &
     524           0 : BranchFolder::MBFIWrapper::printBlockFreq(raw_ostream &OS,
     525             :                                           const MachineBasicBlock *MBB) const {
     526           0 :   return MBFI.printBlockFreq(OS, getBlockFreq(MBB));
     527             : }
     528             : 
     529             : raw_ostream &
     530           0 : BranchFolder::MBFIWrapper::printBlockFreq(raw_ostream &OS,
     531             :                                           const BlockFrequency Freq) const {
     532           0 :   return MBFI.printBlockFreq(OS, Freq);
     533             : }
     534             : 
     535           0 : void BranchFolder::MBFIWrapper::view(const Twine &Name, bool isSimple) {
     536           0 :   MBFI.view(Name, isSimple);
     537           0 : }
     538             : 
     539             : uint64_t
     540        1559 : BranchFolder::MBFIWrapper::getEntryFreq() const {
     541        1559 :   return MBFI.getEntryFreq();
     542             : }
     543             : 
     544             : /// CountTerminators - Count the number of terminators in the given
     545             : /// block and set I to the position of the first non-terminator, if there
     546             : /// is one, or MBB->end() otherwise.
     547        5077 : static unsigned CountTerminators(MachineBasicBlock *MBB,
     548             :                                  MachineBasicBlock::iterator &I) {
     549        5077 :   I = MBB->end();
     550        5077 :   unsigned NumTerms = 0;
     551             :   while (true) {
     552       13778 :     if (I == MBB->begin()) {
     553           2 :       I = MBB->end();
     554           2 :       break;
     555             :     }
     556        6283 :     --I;
     557       12566 :     if (!I->isTerminator()) break;
     558        1208 :     ++NumTerms;
     559             :   }
     560        5077 :   return NumTerms;
     561             : }
     562             : 
     563             : /// A no successor, non-return block probably ends in unreachable and is cold.
     564             : /// Also consider a block that ends in an indirect branch to be a return block,
     565             : /// since many targets use plain indirect branches to return.
     566      119595 : static bool blockEndsInUnreachable(const MachineBasicBlock *MBB) {
     567      119595 :   if (!MBB->succ_empty())
     568             :     return false;
     569      106509 :   if (MBB->empty())
     570             :     return true;
     571      213534 :   return !(MBB->back().isReturn() || MBB->back().isIndirectBranch());
     572             : }
     573             : 
     574             : /// ProfitableToMerge - Check if two machine basic blocks have a common tail
     575             : /// and decide if it would be profitable to merge those tails.  Return the
     576             : /// length of the common tail and iterators to the first common instruction
     577             : /// in each block.
     578             : /// MBB1, MBB2      The blocks to check
     579             : /// MinCommonTailLength  Minimum size of tail block to be merged.
     580             : /// CommonTailLen   Out parameter to record the size of the shared tail between
     581             : ///                 MBB1 and MBB2
     582             : /// I1, I2          Iterator references that will be changed to point to the first
     583             : ///                 instruction in the common tail shared by MBB1,MBB2
     584             : /// SuccBB          A common successor of MBB1, MBB2 which are in a canonical form
     585             : ///                 relative to SuccBB
     586             : /// PredBB          The layout predecessor of SuccBB, if any.
     587             : /// FuncletMembership  map from block to funclet #.
     588             : /// AfterPlacement  True if we are merging blocks after layout. Stricter
     589             : ///                 thresholds apply to prevent undoing tail-duplication.
     590             : static bool
     591      629252 : ProfitableToMerge(MachineBasicBlock *MBB1, MachineBasicBlock *MBB2,
     592             :                   unsigned MinCommonTailLength, unsigned &CommonTailLen,
     593             :                   MachineBasicBlock::iterator &I1,
     594             :                   MachineBasicBlock::iterator &I2, MachineBasicBlock *SuccBB,
     595             :                   MachineBasicBlock *PredBB,
     596             :                   DenseMap<const MachineBasicBlock *, int> &FuncletMembership,
     597             :                   bool AfterPlacement) {
     598             :   // It is never profitable to tail-merge blocks from two different funclets.
     599      629252 :   if (!FuncletMembership.empty()) {
     600          92 :     auto Funclet1 = FuncletMembership.find(MBB1);
     601             :     assert(Funclet1 != FuncletMembership.end());
     602          92 :     auto Funclet2 = FuncletMembership.find(MBB2);
     603             :     assert(Funclet2 != FuncletMembership.end());
     604          92 :     if (Funclet1->second != Funclet2->second)
     605          64 :       return false;
     606             :   }
     607             : 
     608      629188 :   CommonTailLen = ComputeCommonTailLength(MBB1, MBB2, I1, I2);
     609      629188 :   if (CommonTailLen == 0)
     610             :     return false;
     611             :   DEBUG(dbgs() << "Common tail length of BB#" << MBB1->getNumber()
     612             :                << " and BB#" << MBB2->getNumber() << " is " << CommonTailLen
     613             :                << '\n');
     614             : 
     615             :   // It's almost always profitable to merge any number of non-terminator
     616             :   // instructions with the block that falls through into the common successor.
     617             :   // This is true only for a single successor. For multiple successors, we are
     618             :   // trading a conditional branch for an unconditional one.
     619             :   // TODO: Re-visit successor size for non-layout tail merging.
     620      368296 :   if ((MBB1 == PredBB || MBB2 == PredBB) &&
     621        1898 :       (!AfterPlacement || MBB1->succ_size() == 1)) {
     622        5077 :     MachineBasicBlock::iterator I;
     623        5077 :     unsigned NumTerms = CountTerminators(MBB1 == PredBB ? MBB2 : MBB1, I);
     624        5077 :     if (CommonTailLen > NumTerms)
     625        4729 :       return true;
     626             :   }
     627             : 
     628             :   // If these are identical non-return blocks with no successors, merge them.
     629             :   // Such blocks are typically cold calls to noreturn functions like abort, and
     630             :   // are unlikely to become a fallthrough target after machine block placement.
     631             :   // Tail merging these blocks is unlikely to create additional unconditional
     632             :   // branches, and will reduce the size of this cold code.
     633     1212836 :   if (I1 == MBB1->begin() && I2 == MBB2->begin() &&
     634      483162 :       blockEndsInUnreachable(MBB1) && blockEndsInUnreachable(MBB2))
     635             :     return true;
     636             : 
     637             :   // If one of the blocks can be completely merged and happens to be in
     638             :   // a position where the other could fall through into it, merge any number
     639             :   // of instructions, because it can be done without a branch.
     640             :   // TODO: If the blocks are not adjacent, move one of them so that they are?
     641      363972 :   if (MBB1->isLayoutSuccessor(MBB2) && I2 == MBB2->begin())
     642             :     return true;
     643      376554 :   if (MBB2->isLayoutSuccessor(MBB1) && I1 == MBB1->begin())
     644             :     return true;
     645             : 
     646             :   // If both blocks are identical and end in a branch, merge them unless they
     647             :   // both have a fallthrough predecessor and successor.
     648             :   // We can only do this after block placement because it depends on whether
     649             :   // there are fallthroughs, and we don't know until after layout.
     650      371060 :   if (AfterPlacement && I1 == MBB1->begin() && I2 == MBB2->begin()) {
     651         126 :     auto BothFallThrough = [](MachineBasicBlock *MBB) {
     652         126 :       if (MBB->succ_size() != 0 && !MBB->canFallThrough())
     653             :         return false;
     654           0 :       MachineFunction::iterator I(MBB);
     655           0 :       MachineFunction *MF = MBB->getParent();
     656           0 :       return (MBB != &*MF->begin()) && std::prev(I)->canFallThrough();
     657             :     };
     658         126 :     if (!BothFallThrough(MBB1) || !BothFallThrough(MBB2))
     659             :       return true;
     660             :   }
     661             : 
     662             :   // If both blocks have an unconditional branch temporarily stripped out,
     663             :   // count that as an additional common instruction for the following
     664             :   // heuristics. This heuristic is only accurate for single-succ blocks, so to
     665             :   // make sure that during layout merging and duplicating don't crash, we check
     666             :   // for that when merging during layout.
     667      360466 :   unsigned EffectiveTailLen = CommonTailLen;
     668      406185 :   if (SuccBB && MBB1 != PredBB && MBB2 != PredBB &&
     669       48021 :       (MBB1->succ_size() == 1 || !AfterPlacement) &&
     670      427687 :       !MBB1->back().isBarrier() &&
     671       44814 :       !MBB2->back().isBarrier())
     672       22407 :     ++EffectiveTailLen;
     673             : 
     674             :   // Check if the common tail is long enough to be worthwhile.
     675      360466 :   if (EffectiveTailLen >= MinCommonTailLength)
     676             :     return true;
     677             : 
     678             :   // If we are optimizing for code size, 2 instructions in common is enough if
     679             :   // we don't have to split a block.  At worst we will be introducing 1 new
     680             :   // branch instruction, which is likely to be smaller than the 2
     681             :   // instructions that would be deleted in the merge.
     682      245062 :   MachineFunction *MF = MBB1->getParent();
     683      245129 :   return EffectiveTailLen >= 2 && MF->getFunction()->optForSize() &&
     684         238 :          (I1 == MBB1->begin() || I2 == MBB2->begin());
     685             : }
     686             : 
     687      195935 : unsigned BranchFolder::ComputeSameTails(unsigned CurHash,
     688             :                                         unsigned MinCommonTailLength,
     689             :                                         MachineBasicBlock *SuccBB,
     690             :                                         MachineBasicBlock *PredBB) {
     691      195935 :   unsigned maxCommonTailLength = 0U;
     692      391870 :   SameTails.clear();
     693      391870 :   MachineBasicBlock::iterator TrialBBI1, TrialBBI2;
     694      587805 :   MPIterator HighestMPIter = std::prev(MergePotentials.end());
     695      587805 :   for (MPIterator CurMPIter = std::prev(MergePotentials.end()),
     696      391870 :                   B = MergePotentials.begin();
     697      437030 :        CurMPIter != B && CurMPIter->getHash() == CurHash; --CurMPIter) {
     698     1073752 :     for (MPIterator I = std::prev(CurMPIter); I->getHash() == CurHash; --I) {
     699             :       unsigned CommonTailLen;
     700      629252 :       if (ProfitableToMerge(CurMPIter->getBlock(), I->getBlock(),
     701             :                             MinCommonTailLength,
     702             :                             CommonTailLen, TrialBBI1, TrialBBI2,
     703             :                             SuccBB, PredBB,
     704             :                             FuncletMembership,
     705      629252 :                             AfterBlockPlacement)) {
     706      123259 :         if (CommonTailLen > maxCommonTailLength) {
     707       10988 :           SameTails.clear();
     708        5494 :           maxCommonTailLength = CommonTailLen;
     709        5494 :           HighestMPIter = CurMPIter;
     710       16482 :           SameTails.push_back(SameTailElt(CurMPIter, TrialBBI1));
     711             :         }
     712      137948 :         if (HighestMPIter == CurMPIter &&
     713       14689 :             CommonTailLen == maxCommonTailLength)
     714       39792 :           SameTails.push_back(SameTailElt(I, TrialBBI2));
     715             :       }
     716      629252 :       if (I == B)
     717             :         break;
     718             :     }
     719             :   }
     720      195935 :   return maxCommonTailLength;
     721             : }
     722             : 
     723      190848 : void BranchFolder::RemoveBlocksWithHash(unsigned CurHash,
     724             :                                         MachineBasicBlock *SuccBB,
     725             :                                         MachineBasicBlock *PredBB) {
     726      190848 :   MPIterator CurMPIter, B;
     727      763392 :   for (CurMPIter = std::prev(MergePotentials.end()),
     728      190848 :       B = MergePotentials.begin();
     729      407881 :        CurMPIter->getHash() == CurHash; --CurMPIter) {
     730             :     // Put the unconditional branch back, if we need one.
     731      228404 :     MachineBasicBlock *CurMBB = CurMPIter->getBlock();
     732      228404 :     if (SuccBB && CurMBB != PredBB)
     733      114153 :       FixTail(CurMBB, SuccBB, TII);
     734      228404 :     if (CurMPIter == B)
     735             :       break;
     736             :   }
     737      190848 :   if (CurMPIter->getHash() != CurHash)
     738      179477 :     CurMPIter++;
     739      954240 :   MergePotentials.erase(CurMPIter, MergePotentials.end());
     740      190848 : }
     741             : 
     742        3096 : bool BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB,
     743             :                                              MachineBasicBlock *SuccBB,
     744             :                                              unsigned maxCommonTailLength,
     745             :                                              unsigned &commonTailIndex) {
     746        3096 :   commonTailIndex = 0;
     747        3096 :   unsigned TimeEstimate = ~0U;
     748       13807 :   for (unsigned i = 0, e = SameTails.size(); i != e; ++i) {
     749             :     // Use PredBB if possible; that doesn't require a new branch.
     750       27774 :     if (SameTails[i].getBlock() == PredBB) {
     751        1643 :       commonTailIndex = i;
     752        1643 :       break;
     753             :     }
     754             :     // Otherwise, make a (fairly bogus) choice based on estimate of
     755             :     // how long it will take the various blocks to execute.
     756       22845 :     unsigned t = EstimateRuntime(SameTails[i].getBlock()->begin(),
     757       15230 :                                  SameTails[i].getTailStartPos());
     758        7615 :     if (t <= TimeEstimate) {
     759        7432 :       TimeEstimate = t;
     760        7432 :       commonTailIndex = i;
     761             :     }
     762             :   }
     763             : 
     764             :   MachineBasicBlock::iterator BBI =
     765        6192 :     SameTails[commonTailIndex].getTailStartPos();
     766        6192 :   MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
     767             : 
     768             :   DEBUG(dbgs() << "\nSplitting BB#" << MBB->getNumber() << ", size "
     769             :                << maxCommonTailLength);
     770             : 
     771             :   // If the split block unconditionally falls-thru to SuccBB, it will be
     772             :   // merged. In control flow terms it should then take SuccBB's name. e.g. If
     773             :   // SuccBB is an inner loop, the common tail is still part of the inner loop.
     774        5023 :   const BasicBlock *BB = (SuccBB && MBB->succ_size() == 1) ?
     775        3096 :     SuccBB->getBasicBlock() : MBB->getBasicBlock();
     776        3096 :   MachineBasicBlock *newMBB = SplitMBBAt(*MBB, BBI, BB);
     777        3096 :   if (!newMBB) {
     778             :     DEBUG(dbgs() << "... failed!");
     779             :     return false;
     780             :   }
     781             : 
     782        9288 :   SameTails[commonTailIndex].setBlock(newMBB);
     783        6192 :   SameTails[commonTailIndex].setTailStartPos(newMBB->begin());
     784             : 
     785             :   // If we split PredBB, newMBB is the new predecessor.
     786        3096 :   if (PredBB == MBB)
     787        1643 :     PredBB = newMBB;
     788             : 
     789             :   return true;
     790             : }
     791             : 
     792             : static void
     793       11749 : mergeOperations(MachineBasicBlock::iterator MBBIStartPos,
     794             :                 MachineBasicBlock &MBBCommon) {
     795       11749 :   MachineBasicBlock *MBB = MBBIStartPos->getParent();
     796             :   // Note CommonTailLen does not necessarily matches the size of
     797             :   // the common BB nor all its instructions because of debug
     798             :   // instructions differences.
     799       11749 :   unsigned CommonTailLen = 0;
     800       78052 :   for (auto E = MBB->end(); MBBIStartPos != E; ++MBBIStartPos)
     801       54554 :     ++CommonTailLen;
     802             : 
     803       11749 :   MachineBasicBlock::reverse_iterator MBBI = MBB->rbegin();
     804       11749 :   MachineBasicBlock::reverse_iterator MBBIE = MBB->rend();
     805       11749 :   MachineBasicBlock::reverse_iterator MBBICommon = MBBCommon.rbegin();
     806       11749 :   MachineBasicBlock::reverse_iterator MBBIECommon = MBBCommon.rend();
     807             : 
     808       66303 :   while (CommonTailLen--) {
     809             :     assert(MBBI != MBBIE && "Reached BB end within common tail length!");
     810             :     (void)MBBIE;
     811             : 
     812      109173 :     if (MBBI->isDebugValue()) {
     813          65 :       ++MBBI;
     814          65 :       continue;
     815             :     }
     816             : 
     817      163626 :     while ((MBBICommon != MBBIECommon) && MBBICommon->isDebugValue())
     818             :       ++MBBICommon;
     819             : 
     820             :     assert(MBBICommon != MBBIECommon &&
     821             :            "Reached BB end within common tail length!");
     822             :     assert(MBBICommon->isIdenticalTo(*MBBI) && "Expected matching MIIs!");
     823             : 
     824             :     // Merge MMOs from memory operations in the common block.
     825       98806 :     if (MBBICommon->mayLoad() || MBBICommon->mayStore())
     826       43422 :       MBBICommon->setMemRefs(MBBICommon->mergeMemRefsWith(*MBBI));
     827             :     // Drop undef flags if they aren't present in all merged instructions.
     828      377111 :     for (unsigned I = 0, E = MBBICommon->getNumOperands(); I != E; ++I) {
     829      536266 :       MachineOperand &MO = MBBICommon->getOperand(I);
     830      453740 :       if (MO.isReg() && MO.isUndef()) {
     831         430 :         const MachineOperand &OtherMO = MBBI->getOperand(I);
     832         215 :         if (!OtherMO.isUndef())
     833             :           MO.setIsUndef(false);
     834             :       }
     835             :     }
     836             : 
     837       54489 :     ++MBBI;
     838             :     ++MBBICommon;
     839             :   }
     840       11749 : }
     841             : 
     842        5087 : void BranchFolder::mergeCommonTails(unsigned commonTailIndex) {
     843       15261 :   MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
     844             : 
     845       20348 :   std::vector<MachineBasicBlock::iterator> NextCommonInsts(SameTails.size());
     846       43846 :   for (unsigned int i = 0 ; i != SameTails.size() ; ++i) {
     847       16836 :     if (i != commonTailIndex) {
     848       35247 :       NextCommonInsts[i] = SameTails[i].getTailStartPos();
     849       11749 :       mergeOperations(SameTails[i].getTailStartPos(), *MBB);
     850             :     } else {
     851             :       assert(SameTails[i].getTailStartPos() == MBB->begin() &&
     852             :           "MBB is not a common tail only block");
     853             :     }
     854             :   }
     855             : 
     856       54004 :   for (auto &MI : *MBB) {
     857       16828 :     if (MI.isDebugValue())
     858          53 :       continue;
     859       33550 :     DebugLoc DL = MI.getDebugLoc();
     860      247342 :     for (unsigned int i = 0 ; i < NextCommonInsts.size() ; i++) {
     861       71264 :       if (i == commonTailIndex)
     862       16775 :         continue;
     863             : 
     864      108978 :       auto &Pos = NextCommonInsts[i];
     865             :       assert(Pos != SameTails[i].getBlock()->end() &&
     866             :           "Reached BB end within common tail");
     867      109102 :       while (Pos->isDebugValue()) {
     868             :         ++Pos;
     869             :         assert(Pos != SameTails[i].getBlock()->end() &&
     870             :             "Reached BB end within common tail");
     871             :       }
     872             :       assert(MI.isIdenticalTo(*Pos) && "Expected matching MIIs!");
     873      326934 :       DL = DILocation::getMergedLocation(DL, Pos->getDebugLoc());
     874      108978 :       NextCommonInsts[i] = ++Pos;
     875             :     }
     876       50325 :     MI.setDebugLoc(DL);
     877             :   }
     878             : 
     879        5087 :   if (UpdateLiveIns) {
     880       15222 :     LivePhysRegs NewLiveIns(*TRI);
     881        5074 :     computeLiveIns(NewLiveIns, *MBB);
     882             : 
     883             :     // The flag merging may lead to some register uses no longer using the
     884             :     // <undef> flag, add IMPLICIT_DEFs in the predecessors as necessary.
     885       16697 :     for (MachineBasicBlock *Pred : MBB->predecessors()) {
     886       13098 :       LiveRegs.init(*TRI);
     887        6549 :       LiveRegs.addLiveOuts(*Pred);
     888        6549 :       MachineBasicBlock::iterator InsertBefore = Pred->getFirstTerminator();
     889       81680 :       for (unsigned Reg : NewLiveIns) {
     890       62033 :         if (!LiveRegs.available(*MRI, Reg))
     891       62004 :           continue;
     892          58 :         DebugLoc DL;
     893          58 :         BuildMI(*Pred, InsertBefore, DL, TII->get(TargetOpcode::IMPLICIT_DEF),
     894          58 :                 Reg);
     895             :       }
     896             :     }
     897             : 
     898        5074 :     MBB->clearLiveIns();
     899        5074 :     addLiveIns(*MBB, NewLiveIns);
     900             :   }
     901        5087 : }
     902             : 
     903             : // See if any of the blocks in MergePotentials (which all have SuccBB as a
     904             : // successor, or all have no successor if it is null) can be tail-merged.
     905             : // If there is a successor, any blocks in MergePotentials that are not
     906             : // tail-merged and are not immediately before Succ must have an unconditional
     907             : // branch to Succ added (but the predecessor/successor lists need no
     908             : // adjustment). The lone predecessor of Succ that falls through into Succ,
     909             : // if any, is given in PredBB.
     910             : // MinCommonTailLength - Except for the special cases below, tail-merge if
     911             : // there are at least this many instructions in common.
     912      159500 : bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB,
     913             :                                       MachineBasicBlock *PredBB,
     914             :                                       unsigned MinCommonTailLength) {
     915      159500 :   bool MadeChange = false;
     916             : 
     917             :   DEBUG(dbgs() << "\nTryTailMergeBlocks: ";
     918             :         for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
     919             :           dbgs() << "BB#" << MergePotentials[i].getBlock()->getNumber()
     920             :                  << (i == e-1 ? "" : ", ");
     921             :         dbgs() << "\n";
     922             :         if (SuccBB) {
     923             :           dbgs() << "  with successor BB#" << SuccBB->getNumber() << '\n';
     924             :           if (PredBB)
     925             :             dbgs() << "  which has fall-through from BB#"
     926             :                    << PredBB->getNumber() << "\n";
     927             :         }
     928             :         dbgs() << "Looking for common tails of at least "
     929             :                << MinCommonTailLength << " instruction"
     930             :                << (MinCommonTailLength == 1 ? "" : "s") << '\n';
     931             :        );
     932             : 
     933             :   // Sort by hash value so that blocks with identical end sequences sort
     934             :   // together.
     935      478500 :   array_pod_sort(MergePotentials.begin(), MergePotentials.end());
     936             : 
     937             :   // Walk through equivalence sets looking for actual exact matches.
     938      710870 :   while (MergePotentials.size() > 1) {
     939      391870 :     unsigned CurHash = MergePotentials.back().getHash();
     940             : 
     941             :     // Build SameTails, identifying the set of blocks with this hash code
     942             :     // and with the maximum number of instructions in common.
     943      195935 :     unsigned maxCommonTailLength = ComputeSameTails(CurHash,
     944             :                                                     MinCommonTailLength,
     945      195935 :                                                     SuccBB, PredBB);
     946             : 
     947             :     // If we didn't find any pair that has at least MinCommonTailLength
     948             :     // instructions in common, remove all blocks with this hash code and retry.
     949      582718 :     if (SameTails.empty()) {
     950      190848 :       RemoveBlocksWithHash(CurHash, SuccBB, PredBB);
     951      381696 :       continue;
     952             :     }
     953             : 
     954             :     // If one of the blocks is the entire common tail (and not the entry
     955             :     // block, which we can't jump to), we can treat all blocks with this same
     956             :     // tail at once.  Use PredBB if that is one of the possibilities, as that
     957             :     // will not introduce any extra branches.
     958             :     MachineBasicBlock *EntryBB =
     959       15261 :         &MergePotentials.front().getBlock()->getParent()->front();
     960       10174 :     unsigned commonTailIndex = SameTails.size();
     961             :     // If there are two blocks, check to see if one can be made to fall through
     962             :     // into the other.
     963        9127 :     if (SameTails.size() == 2 &&
     964       13225 :         SameTails[0].getBlock()->isLayoutSuccessor(SameTails[1].getBlock()) &&
     965         116 :         SameTails[1].tailIsWholeBlock())
     966          16 :       commonTailIndex = 1;
     967        9095 :     else if (SameTails.size() == 2 &&
     968       12072 :              SameTails[1].getBlock()->isLayoutSuccessor(
     969       14663 :                                                      SameTails[0].getBlock()) &&
     970        3088 :              SameTails[0].tailIsWholeBlock())
     971         616 :       commonTailIndex = 0;
     972             :     else {
     973             :       // Otherwise just pick one, favoring the fall-through predecessor if
     974             :       // there is one.
     975       36377 :       for (unsigned i = 0, e = SameTails.size(); i != e; ++i) {
     976       41850 :         MachineBasicBlock *MBB = SameTails[i].getBlock();
     977       13971 :         if (MBB == EntryBB && SameTails[i].tailIsWholeBlock())
     978           1 :           continue;
     979       13949 :         if (MBB == PredBB) {
     980        2444 :           commonTailIndex = i;
     981        2444 :           break;
     982             :         }
     983       23010 :         if (SameTails[i].tailIsWholeBlock())
     984        3541 :           commonTailIndex = i;
     985             :       }
     986             :     }
     987             : 
     988       13808 :     if (commonTailIndex == SameTails.size() ||
     989       13382 :         (SameTails[commonTailIndex].getBlock() == PredBB &&
     990        4960 :          !SameTails[commonTailIndex].tailIsWholeBlock())) {
     991             :       // None of the blocks consist entirely of the common tail.
     992             :       // Split a block so that one does.
     993        3096 :       if (!CreateCommonTailOnlyBlock(PredBB, SuccBB,
     994             :                                      maxCommonTailLength, commonTailIndex)) {
     995           0 :         RemoveBlocksWithHash(CurHash, SuccBB, PredBB);
     996           0 :         continue;
     997             :       }
     998             :     }
     999             : 
    1000       15261 :     MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
    1001             : 
    1002             :     // Recompute common tail MBB's edge weights and block frequency.
    1003        5087 :     setCommonTailEdgeWeights(*MBB);
    1004             : 
    1005             :     // Merge debug locations, MMOs and undef flags across identical instructions
    1006             :     // for common tail.
    1007        5087 :     mergeCommonTails(commonTailIndex);
    1008             : 
    1009             :     // MBB is common tail.  Adjust all other BB's to jump to this one.
    1010             :     // Traversal must be forwards so erases work.
    1011             :     DEBUG(dbgs() << "\nUsing common tail in BB#" << MBB->getNumber()
    1012             :                  << " for ");
    1013       27010 :     for (unsigned int i=0, e = SameTails.size(); i != e; ++i) {
    1014       16836 :       if (commonTailIndex == i)
    1015        5087 :         continue;
    1016             :       DEBUG(dbgs() << "BB#" << SameTails[i].getBlock()->getNumber()
    1017             :                    << (i == e-1 ? "" : ", "));
    1018             :       // Hack the end off BB i, making it jump to BB commonTailIndex instead.
    1019       23498 :       replaceTailWithBranchTo(SameTails[i].getTailStartPos(), *MBB);
    1020             :       // BB i is no longer a predecessor of SuccBB; remove it from the worklist.
    1021       46996 :       MergePotentials.erase(SameTails[i].getMPIter());
    1022             :     }
    1023             :     DEBUG(dbgs() << "\n");
    1024             :     // We leave commonTailIndex in the worklist in case there are other blocks
    1025             :     // that match it with a smaller number of instructions.
    1026        5087 :     MadeChange = true;
    1027             :   }
    1028      159500 :   return MadeChange;
    1029             : }
    1030             : 
    1031      178375 : bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
    1032      178375 :   bool MadeChange = false;
    1033      178375 :   if (!EnableTailMerge) return MadeChange;
    1034             : 
    1035             :   // First find blocks with no successors.
    1036             :   // Block placement does not create new tail merging opportunities for these
    1037             :   // blocks.
    1038      161133 :   if (!AfterBlockPlacement) {
    1039      309674 :     MergePotentials.clear();
    1040     1004865 :     for (MachineBasicBlock &MBB : MF) {
    1041     1621062 :       if (MergePotentials.size() == TailMergeThreshold)
    1042             :         break;
    1043     1079343 :       if (!TriedMerging.count(&MBB) && MBB.succ_empty())
    1044      530595 :         MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(MBB), &MBB));
    1045             :     }
    1046             : 
    1047             :     // If this is a large problem, avoid visiting the same basic blocks
    1048             :     // multiple times.
    1049      464511 :     if (MergePotentials.size() == TailMergeThreshold)
    1050         755 :       for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
    1051        1500 :         TriedMerging.insert(MergePotentials[i].getBlock());
    1052             : 
    1053             :     // See if we can do any tail merging on those.
    1054      309674 :     if (MergePotentials.size() >= 2)
    1055        9423 :       MadeChange |= TryTailMergeBlocks(nullptr, nullptr, MinCommonTailLength);
    1056             :   }
    1057             : 
    1058             :   // Look at blocks (IBB) with multiple predecessors (PBB).
    1059             :   // We change each predecessor to a canonical form, by
    1060             :   // (1) temporarily removing any unconditional branch from the predecessor
    1061             :   // to IBB, and
    1062             :   // (2) alter conditional branches so they branch to the other block
    1063             :   // not IBB; this may require adding back an unconditional branch to IBB
    1064             :   // later, where there wasn't one coming in.  E.g.
    1065             :   //   Bcc IBB
    1066             :   //   fallthrough to QBB
    1067             :   // here becomes
    1068             :   //   Bncc QBB
    1069             :   // with a conceptual B to IBB after that, which never actually exists.
    1070             :   // With those changes, we see whether the predecessors' tails match,
    1071             :   // and merge them if so.  We change things out of canonical form and
    1072             :   // back to the way they were later in the process.  (OptimizeBranches
    1073             :   // would undo some of this, but we can't use it, because we'd get into
    1074             :   // a compile-time infinite loop repeatedly doing and undoing the same
    1075             :   // transformations.)
    1076             : 
    1077      483399 :   for (MachineFunction::iterator I = std::next(MF.begin()), E = MF.end();
    1078      727364 :        I != E; ++I) {
    1079     1525304 :     if (I->pred_size() < 2) continue;
    1080      351546 :     SmallPtrSet<MachineBasicBlock *, 8> UniquePreds;
    1081      178157 :     MachineBasicBlock *IBB = &*I;
    1082      356314 :     MachineBasicBlock *PredBB = &*std::prev(I);
    1083      356314 :     MergePotentials.clear();
    1084             :     MachineLoop *ML;
    1085             : 
    1086             :     // Bail if merging after placement and IBB is the loop header because
    1087             :     // -- If merging predecessors that belong to the same loop as IBB, the
    1088             :     // common tail of merged predecessors may become the loop top if block
    1089             :     // placement is called again and the predecessors may branch to this common
    1090             :     // tail and require more branches. This can be relaxed if
    1091             :     // MachineBlockPlacement::findBestLoopTop is more flexible.
    1092             :     // --If merging predecessors that do not belong to the same loop as IBB, the
    1093             :     // loop info of IBB's loop and the other loops may be affected. Calling the
    1094             :     // block placement again may make big change to the layout and eliminate the
    1095             :     // reason to do tail merging here.
    1096      178157 :     if (AfterBlockPlacement && MLI) {
    1097      111802 :       ML = MLI->getLoopFor(IBB);
    1098       21880 :       if (ML && IBB == ML->getHeader())
    1099             :         continue;
    1100             :     }
    1101             : 
    1102      936842 :     for (MachineBasicBlock *PBB : I->predecessors()) {
    1103     1250034 :       if (MergePotentials.size() == TailMergeThreshold)
    1104             :         break;
    1105             : 
    1106      416675 :       if (TriedMerging.count(PBB))
    1107       47736 :         continue;
    1108             : 
    1109             :       // Skip blocks that loop to themselves, can't tail merge these.
    1110      415541 :       if (PBB == IBB)
    1111        7593 :         continue;
    1112             : 
    1113             :       // Visit each predecessor only once.
    1114      407948 :       if (!UniquePreds.insert(PBB).second)
    1115           0 :         continue;
    1116             : 
    1117             :       // Skip blocks which may jump to a landing pad. Can't tail merge these.
    1118      407948 :       if (PBB->hasEHPadSuccessor())
    1119       35772 :         continue;
    1120             : 
    1121             :       // After block placement, only consider predecessors that belong to the
    1122             :       // same loop as IBB.  The reason is the same as above when skipping loop
    1123             :       // header.
    1124      372176 :       if (AfterBlockPlacement && MLI)
    1125      221662 :         if (ML != MLI->getLoopFor(PBB))
    1126        2040 :           continue;
    1127             : 
    1128      370136 :       MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
    1129      740209 :       SmallVector<MachineOperand, 4> Cond;
    1130      370136 :       if (!TII->analyzeBranch(*PBB, TBB, FBB, Cond, true)) {
    1131             :         // Failing case: IBB is the target of a cbr, and we cannot reverse the
    1132             :         // branch.
    1133      734631 :         SmallVector<MachineOperand, 4> NewCond(Cond);
    1134      367347 :         if (!Cond.empty() && TBB == IBB) {
    1135       95017 :           if (TII->reverseBranchCondition(NewCond))
    1136         126 :             continue;
    1137             :           // This is the QBB case described above
    1138       94954 :           if (!FBB) {
    1139      270396 :             auto Next = ++PBB->getIterator();
    1140       90132 :             if (Next != MF.end())
    1141       90132 :               FBB = &*Next;
    1142             :           }
    1143             :         }
    1144             : 
    1145             :         // Failing case: the only way IBB can be reached from PBB is via
    1146             :         // exception handling.  Happens for landing pads.  Would be nice to have
    1147             :         // a bit in the edge so we didn't have to do all this.
    1148      367284 :         if (IBB->isEHPad()) {
    1149           0 :           MachineFunction::iterator IP = ++PBB->getIterator();
    1150           0 :           MachineBasicBlock *PredNextBB = nullptr;
    1151           0 :           if (IP != MF.end())
    1152           0 :             PredNextBB = &*IP;
    1153           0 :           if (!TBB) {
    1154           0 :             if (IBB != PredNextBB)      // fallthrough
    1155           0 :               continue;
    1156           0 :           } else if (FBB) {
    1157           0 :             if (TBB != IBB && FBB != IBB)   // cbr then ubr
    1158           0 :               continue;
    1159           0 :           } else if (Cond.empty()) {
    1160           0 :             if (TBB != IBB)               // ubr
    1161           0 :               continue;
    1162             :           } else {
    1163           0 :             if (TBB != IBB && IBB != PredNextBB)  // cbr
    1164           0 :               continue;
    1165             :           }
    1166             :         }
    1167             : 
    1168             :         // Remove the unconditional branch at the end, if any.
    1169      367284 :         if (TBB && (Cond.empty() || FBB)) {
    1170      439520 :           DebugLoc dl = PBB->findBranchDebugLoc();
    1171      219760 :           TII->removeBranch(*PBB);
    1172      219760 :           if (!Cond.empty())
    1173             :             // reinsert conditional branch only, for now
    1174      194976 :             TII->insertBranch(*PBB, (TBB == IBB) ? FBB : TBB, nullptr,
    1175       97488 :                               NewCond, dl);
    1176             :         }
    1177             : 
    1178     1101852 :         MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(*PBB), PBB));
    1179             :       }
    1180             :     }
    1181             : 
    1182             :     // If this is a large problem, avoid visiting the same basic blocks multiple
    1183             :     // times.
    1184      520167 :     if (MergePotentials.size() == TailMergeThreshold)
    1185         157 :       for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
    1186         308 :         TriedMerging.insert(MergePotentials[i].getBlock());
    1187             : 
    1188      346778 :     if (MergePotentials.size() >= 2)
    1189      150077 :       MadeChange |= TryTailMergeBlocks(IBB, PredBB, MinCommonTailLength);
    1190             : 
    1191             :     // Reinsert an unconditional branch if needed. The 1 below can occur as a
    1192             :     // result of removing blocks in TryTailMergeBlocks.
    1193      346778 :     PredBB = &*std::prev(I); // this may have been changed in TryTailMergeBlocks
    1194      498041 :     if (MergePotentials.size() == 1 &&
    1195      302526 :         MergePotentials.begin()->getBlock() != PredBB)
    1196      199362 :       FixTail(MergePotentials.begin()->getBlock(), IBB, TII);
    1197             :   }
    1198             : 
    1199             :   return MadeChange;
    1200             : }
    1201             : 
    1202        5087 : void BranchFolder::setCommonTailEdgeWeights(MachineBasicBlock &TailMBB) {
    1203       15635 :   SmallVector<BlockFrequency, 2> EdgeFreqLs(TailMBB.succ_size());
    1204        5087 :   BlockFrequency AccumulatedMBBFreq;
    1205             : 
    1206             :   // Aggregate edge frequency of successor edge j:
    1207             :   //  edgeFreq(j) = sum (freq(bb) * edgeProb(bb, j)),
    1208             :   //  where bb is a basic block that is in SameTails.
    1209       37184 :   for (const auto &Src : SameTails) {
    1210       16836 :     const MachineBasicBlock *SrcMBB = Src.getBlock();
    1211       16836 :     BlockFrequency BlockFreq = MBBFreqInfo.getBlockFreq(SrcMBB);
    1212       16836 :     AccumulatedMBBFreq += BlockFreq;
    1213             : 
    1214             :     // It is not necessary to recompute edge weights if TailBB has less than two
    1215             :     // successors.
    1216       16836 :     if (TailMBB.succ_size() <= 1)
    1217       15581 :       continue;
    1218             : 
    1219        1255 :     auto EdgeFreq = EdgeFreqLs.begin();
    1220             : 
    1221        5020 :     for (auto SuccI = TailMBB.succ_begin(), SuccE = TailMBB.succ_end();
    1222        3765 :          SuccI != SuccE; ++SuccI, ++EdgeFreq)
    1223        2510 :       *EdgeFreq += BlockFreq * MBPI.getEdgeProbability(SrcMBB, *SuccI);
    1224             :   }
    1225             : 
    1226       10174 :   MBBFreqInfo.setBlockFreq(&TailMBB, AccumulatedMBBFreq);
    1227             : 
    1228        5087 :   if (TailMBB.succ_size() <= 1)
    1229        4713 :     return;
    1230             : 
    1231             :   auto SumEdgeFreq =
    1232        1870 :       std::accumulate(EdgeFreqLs.begin(), EdgeFreqLs.end(), BlockFrequency(0))
    1233         374 :           .getFrequency();
    1234         374 :   auto EdgeFreq = EdgeFreqLs.begin();
    1235             : 
    1236         374 :   if (SumEdgeFreq > 0) {
    1237        1492 :     for (auto SuccI = TailMBB.succ_begin(), SuccE = TailMBB.succ_end();
    1238        1119 :          SuccI != SuccE; ++SuccI, ++EdgeFreq) {
    1239             :       auto Prob = BranchProbability::getBranchProbability(
    1240         746 :           EdgeFreq->getFrequency(), SumEdgeFreq);
    1241         746 :       TailMBB.setSuccProbability(SuccI, Prob);
    1242             :     }
    1243             :   }
    1244             : }
    1245             : 
    1246             : //===----------------------------------------------------------------------===//
    1247             : //  Branch Optimization
    1248             : //===----------------------------------------------------------------------===//
    1249             : 
    1250      172410 : bool BranchFolder::OptimizeBranches(MachineFunction &MF) {
    1251      172410 :   bool MadeChange = false;
    1252             : 
    1253             :   // Make sure blocks are numbered in order
    1254      172410 :   MF.RenumberBlocks();
    1255             :   // Renumbering blocks alters funclet membership, recalculate it.
    1256      344820 :   FuncletMembership = getFuncletMembership(MF);
    1257             : 
    1258      517230 :   for (MachineFunction::iterator I = std::next(MF.begin()), E = MF.end();
    1259      632804 :        I != E; ) {
    1260     1381182 :     MachineBasicBlock *MBB = &*I++;
    1261      460394 :     MadeChange |= OptimizeBlock(MBB);
    1262             : 
    1263             :     // If it is dead, remove it.
    1264      460394 :     if (MBB->pred_empty()) {
    1265       10298 :       RemoveDeadBlock(MBB);
    1266       10298 :       MadeChange = true;
    1267             :       ++NumDeadBlocks;
    1268             :     }
    1269             :   }
    1270             : 
    1271      172410 :   return MadeChange;
    1272             : }
    1273             : 
    1274             : // Blocks should be considered empty if they contain only debug info;
    1275             : // else the debug info would affect codegen.
    1276             : static bool IsEmptyBlock(MachineBasicBlock *MBB) {
    1277     1956130 :   return MBB->getFirstNonDebugInstr() == MBB->end();
    1278             : }
    1279             : 
    1280             : // Blocks with only debug info and branches should be considered the same
    1281             : // as blocks with only branches.
    1282      128647 : static bool IsBranchOnlyBlock(MachineBasicBlock *MBB) {
    1283      128647 :   MachineBasicBlock::iterator I = MBB->getFirstNonDebugInstr();
    1284             :   assert(I != MBB->end() && "empty block!");
    1285      257294 :   return I->isBranch();
    1286             : }
    1287             : 
    1288             : /// IsBetterFallthrough - Return true if it would be clearly better to
    1289             : /// fall-through to MBB1 than to fall through into MBB2.  This has to return
    1290             : /// a strict ordering, returning true for both (MBB1,MBB2) and (MBB2,MBB1) will
    1291             : /// result in infinite loops.
    1292        3269 : static bool IsBetterFallthrough(MachineBasicBlock *MBB1,
    1293             :                                 MachineBasicBlock *MBB2) {
    1294             :   // Right now, we use a simple heuristic.  If MBB2 ends with a call, and
    1295             :   // MBB1 doesn't, we prefer to fall through into MBB1.  This allows us to
    1296             :   // optimize branches that branch to either a return block or an assert block
    1297             :   // into a fallthrough to the return.
    1298        3269 :   MachineBasicBlock::iterator MBB1I = MBB1->getLastNonDebugInstr();
    1299        3269 :   MachineBasicBlock::iterator MBB2I = MBB2->getLastNonDebugInstr();
    1300       13062 :   if (MBB1I == MBB1->end() || MBB2I == MBB2->end())
    1301             :     return false;
    1302             : 
    1303             :   // If there is a clear successor ordering we make sure that one block
    1304             :   // will fall through to the next
    1305        3262 :   if (MBB1->isSuccessor(MBB2)) return true;
    1306        3256 :   if (MBB2->isSuccessor(MBB1)) return false;
    1307             : 
    1308        7810 :   return MBB2I->isCall() && !MBB1I->isCall();
    1309             : }
    1310             : 
    1311             : /// getBranchDebugLoc - Find and return, if any, the DebugLoc of the branch
    1312             : /// instructions on the block.
    1313       14659 : static DebugLoc getBranchDebugLoc(MachineBasicBlock &MBB) {
    1314       14659 :   MachineBasicBlock::iterator I = MBB.getLastNonDebugInstr();
    1315       58636 :   if (I != MBB.end() && I->isBranch())
    1316       12591 :     return I->getDebugLoc();
    1317        2068 :   return DebugLoc();
    1318             : }
    1319             : 
    1320      460394 : bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
    1321      460394 :   bool MadeChange = false;
    1322      460394 :   MachineFunction &MF = *MBB->getParent();
    1323      493703 : ReoptimizeBlock:
    1324             : 
    1325      987406 :   MachineFunction::iterator FallThrough = MBB->getIterator();
    1326      493703 :   ++FallThrough;
    1327             : 
    1328             :   // Make sure MBB and FallThrough belong to the same funclet.
    1329      493703 :   bool SameFunclet = true;
    1330      988009 :   if (!FuncletMembership.empty() && FallThrough != MF.end()) {
    1331         493 :     auto MBBFunclet = FuncletMembership.find(MBB);
    1332             :     assert(MBBFunclet != FuncletMembership.end());
    1333         986 :     auto FallThroughFunclet = FuncletMembership.find(&*FallThrough);
    1334             :     assert(FallThroughFunclet != FuncletMembership.end());
    1335         493 :     SameFunclet = MBBFunclet->second == FallThroughFunclet->second;
    1336             :   }
    1337             : 
    1338             :   // If this block is empty, make everyone use its fall-through, not the block
    1339             :   // explicitly.  Landing pads should not do this since the landing-pad table
    1340             :   // points to this block.  Blocks with their addresses taken shouldn't be
    1341             :   // optimized away.
    1342      493703 :   if (IsEmptyBlock(MBB) && !MBB->isEHPad() && !MBB->hasAddressTaken() &&
    1343             :       SameFunclet) {
    1344             :     // Dead block?  Leave for cleanup later.
    1345        4159 :     if (MBB->pred_empty()) return MadeChange;
    1346             : 
    1347        3566 :     if (FallThrough == MF.end()) {
    1348             :       // TODO: Simplify preds to not branch here if possible!
    1349        3388 :     } else if (FallThrough->isEHPad()) {
    1350             :       // Don't rewrite to a landing pad fallthough.  That could lead to the case
    1351             :       // where a BB jumps to more than one landing pad.
    1352             :       // TODO: Is it ever worth rewriting predecessors which don't already
    1353             :       // jump to a landing pad, and so can safely jump to the fallthrough?
    1354        3274 :     } else if (MBB->isSuccessor(&*FallThrough)) {
    1355             :       // Rewrite all predecessors of the old block to go to the fallthrough
    1356             :       // instead.
    1357        4822 :       while (!MBB->pred_empty()) {
    1358        3410 :         MachineBasicBlock *Pred = *(MBB->pred_end()-1);
    1359        1705 :         Pred->ReplaceUsesOfBlockWith(MBB, &*FallThrough);
    1360             :       }
    1361             :       // If MBB was the target of a jump table, update jump tables to go to the
    1362             :       // fallthrough instead.
    1363        1412 :       if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo())
    1364         228 :         MJTI->ReplaceMBBInJumpTables(MBB, &*FallThrough);
    1365             :       MadeChange = true;
    1366             :     }
    1367             :     return MadeChange;
    1368             :   }
    1369             : 
    1370             :   // Check to see if we can simplify the terminator of the block before this
    1371             :   // one.
    1372      979088 :   MachineBasicBlock &PrevBB = *std::prev(MachineFunction::iterator(MBB));
    1373             : 
    1374      489544 :   MachineBasicBlock *PriorTBB = nullptr, *PriorFBB = nullptr;
    1375      489544 :   SmallVector<MachineOperand, 4> PriorCond;
    1376             :   bool PriorUnAnalyzable =
    1377      489544 :       TII->analyzeBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, true);
    1378      489544 :   if (!PriorUnAnalyzable) {
    1379             :     // If the CFG for the prior block has extra edges, remove them.
    1380      474924 :     MadeChange |= PrevBB.CorrectExtraCFGEdges(PriorTBB, PriorFBB,
    1381      474924 :                                               !PriorCond.empty());
    1382             : 
    1383             :     // If the previous branch is conditional and both conditions go to the same
    1384             :     // destination, remove the branch, replacing it with an unconditional one or
    1385             :     // a fall-through.
    1386      474924 :     if (PriorTBB && PriorTBB == PriorFBB) {
    1387          28 :       DebugLoc dl = getBranchDebugLoc(PrevBB);
    1388          14 :       TII->removeBranch(PrevBB);
    1389          14 :       PriorCond.clear();
    1390          14 :       if (PriorTBB != MBB)
    1391           6 :         TII->insertBranch(PrevBB, PriorTBB, nullptr, PriorCond, dl);
    1392          14 :       MadeChange = true;
    1393          14 :       ++NumBranchOpts;
    1394             :       goto ReoptimizeBlock;
    1395             :     }
    1396             : 
    1397             :     // If the previous block unconditionally falls through to this block and
    1398             :     // this block has no other predecessors, move the contents of this block
    1399             :     // into the prior block. This doesn't usually happen when SimplifyCFG
    1400             :     // has been used, but it can happen if tail merging splits a fall-through
    1401             :     // predecessor of a block.
    1402             :     // This has to check PrevBB->succ_size() because EH edges are ignored by
    1403             :     // AnalyzeBranch.
    1404     1124001 :     if (PriorCond.empty() && !PriorTBB && MBB->pred_size() == 1 &&
    1405       94548 :         PrevBB.succ_size() == 1 &&
    1406      482202 :         !MBB->hasAddressTaken() && !MBB->isEHPad()) {
    1407             :       DEBUG(dbgs() << "\nMerging into block: " << PrevBB
    1408             :                    << "From MBB: " << *MBB);
    1409             :       // Remove redundant DBG_VALUEs first.
    1410       10848 :       if (PrevBB.begin() != PrevBB.end()) {
    1411        3522 :         MachineBasicBlock::iterator PrevBBIter = PrevBB.end();
    1412        3522 :         --PrevBBIter;
    1413        3522 :         MachineBasicBlock::iterator MBBIter = MBB->begin();
    1414             :         // Check if DBG_VALUE at the end of PrevBB is identical to the
    1415             :         // DBG_VALUE at the beginning of MBB.
    1416       10469 :         while (PrevBBIter != PrevBB.begin() && MBBIter != MBB->end()
    1417        6947 :                && PrevBBIter->isDebugValue() && MBBIter->isDebugValue()) {
    1418           2 :           if (!MBBIter->isIdenticalTo(*PrevBBIter))
    1419             :             break;
    1420           1 :           MachineInstr &DuplicateDbg = *MBBIter;
    1421           2 :           ++MBBIter; -- PrevBBIter;
    1422           1 :           DuplicateDbg.eraseFromParent();
    1423             :         }
    1424             :       }
    1425       14464 :       PrevBB.splice(PrevBB.end(), MBB, MBB->begin(), MBB->end());
    1426        3616 :       PrevBB.removeSuccessor(PrevBB.succ_begin());
    1427             :       assert(PrevBB.succ_empty());
    1428        3616 :       PrevBB.transferSuccessors(MBB);
    1429        3616 :       MadeChange = true;
    1430      459851 :       return MadeChange;
    1431             :     }
    1432             : 
    1433             :     // If the previous branch *only* branches to *this* block (conditional or
    1434             :     // not) remove the branch.
    1435      472548 :     if (PriorTBB == MBB && !PriorFBB) {
    1436         667 :       TII->removeBranch(PrevBB);
    1437         667 :       MadeChange = true;
    1438             :       ++NumBranchOpts;
    1439             :       goto ReoptimizeBlock;
    1440             :     }
    1441             : 
    1442             :     // If the prior block branches somewhere else on the condition and here if
    1443             :     // the condition is false, remove the uncond second branch.
    1444      470627 :     if (PriorFBB == MBB) {
    1445        5158 :       DebugLoc dl = getBranchDebugLoc(PrevBB);
    1446        2579 :       TII->removeBranch(PrevBB);
    1447        5158 :       TII->insertBranch(PrevBB, PriorTBB, nullptr, PriorCond, dl);
    1448        2579 :       MadeChange = true;
    1449        2579 :       ++NumBranchOpts;
    1450             :       goto ReoptimizeBlock;
    1451             :     }
    1452             : 
    1453             :     // If the prior block branches here on true and somewhere else on false, and
    1454             :     // if the branch condition is reversible, reverse the branch to create a
    1455             :     // fall-through.
    1456      468048 :     if (PriorTBB == MBB) {
    1457         605 :       SmallVector<MachineOperand, 4> NewPriorCond(PriorCond);
    1458         587 :       if (!TII->reverseBranchCondition(NewPriorCond)) {
    1459        1138 :         DebugLoc dl = getBranchDebugLoc(PrevBB);
    1460         569 :         TII->removeBranch(PrevBB);
    1461        1138 :         TII->insertBranch(PrevBB, PriorFBB, nullptr, NewPriorCond, dl);
    1462         569 :         MadeChange = true;
    1463         569 :         ++NumBranchOpts;
    1464             :         goto ReoptimizeBlock;
    1465             :       }
    1466             :     }
    1467             : 
    1468             :     // If this block has no successors (e.g. it is a return block or ends with
    1469             :     // a call to a no-return function like abort or __cxa_throw) and if the pred
    1470             :     // falls through into this block, and if it would otherwise fall through
    1471             :     // into the block after this, move this block to the end of the function.
    1472             :     //
    1473             :     // We consider it more likely that execution will stay in the function (e.g.
    1474             :     // due to loops) than it is to exit it.  This asserts in loops etc, moving
    1475             :     // the assert condition out of the loop body.
    1476      519539 :     if (MBB->succ_empty() && !PriorCond.empty() && !PriorFBB &&
    1477      499374 :         MachineFunction::iterator(PriorTBB) == FallThrough &&
    1478        5207 :         !MBB->canFallThrough()) {
    1479        5207 :       bool DoTransform = true;
    1480             : 
    1481             :       // We have to be careful that the succs of PredBB aren't both no-successor
    1482             :       // blocks.  If neither have successors and if PredBB is the second from
    1483             :       // last block in the function, we'd just keep swapping the two blocks for
    1484             :       // last.  Only do the swap if one is clearly better to fall through than
    1485             :       // the other.
    1486       13683 :       if (FallThrough == --MF.end() &&
    1487        3269 :           !IsBetterFallthrough(PriorTBB, MBB))
    1488             :         DoTransform = false;
    1489             : 
    1490             :       if (DoTransform) {
    1491             :         // Reverse the branch so we will fall through on the previous true cond.
    1492        2391 :         SmallVector<MachineOperand, 4> NewPriorCond(PriorCond);
    1493        2391 :         if (!TII->reverseBranchCondition(NewPriorCond)) {
    1494             :           DEBUG(dbgs() << "\nMoving MBB: " << *MBB
    1495             :                        << "To make fallthrough to: " << *PriorTBB << "\n");
    1496             : 
    1497        4782 :           DebugLoc dl = getBranchDebugLoc(PrevBB);
    1498        2391 :           TII->removeBranch(PrevBB);
    1499        4782 :           TII->insertBranch(PrevBB, MBB, nullptr, NewPriorCond, dl);
    1500             : 
    1501             :           // Move this block to the end of the function.
    1502        2391 :           MBB->moveAfter(&MF.back());
    1503        2391 :           MadeChange = true;
    1504        2391 :           ++NumBranchOpts;
    1505        2391 :           return MadeChange;
    1506             :         }
    1507             :       }
    1508             :     }
    1509             :   }
    1510             : 
    1511     1287779 :   if (!IsEmptyBlock(MBB) && MBB->pred_size() == 1 &&
    1512      328374 :       MF.getFunction()->optForSize()) {
    1513             :     // Changing "Jcc foo; foo: jmp bar;" into "Jcc bar;" might change the branch
    1514             :     // direction, thereby defeating careful block placement and regressing
    1515             :     // performance. Therefore, only consider this for optsize functions.
    1516        2634 :     MachineInstr &TailCall = *MBB->getFirstNonDebugInstr();
    1517        1317 :     if (TII->isUnconditionalTailCall(TailCall)) {
    1518          35 :       MachineBasicBlock *Pred = *MBB->pred_begin();
    1519          35 :       MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr;
    1520          46 :       SmallVector<MachineOperand, 4> PredCond;
    1521             :       bool PredAnalyzable =
    1522          35 :           !TII->analyzeBranch(*Pred, PredTBB, PredFBB, PredCond, true);
    1523             : 
    1524          60 :       if (PredAnalyzable && !PredCond.empty() && PredTBB == MBB &&
    1525          25 :           PredTBB != PredFBB) {
    1526             :         // The predecessor has a conditional branch to this block which consists
    1527             :         // of only a tail call. Try to fold the tail call into the conditional
    1528             :         // branch.
    1529          24 :         if (TII->canMakeTailCallConditional(PredCond, TailCall)) {
    1530             :           // TODO: It would be nice if analyzeBranch() could provide a pointer
    1531             :           // to the branch instruction so replaceBranchWithTailCall() doesn't
    1532             :           // have to search for it.
    1533          24 :           TII->replaceBranchWithTailCall(*Pred, PredCond, TailCall);
    1534          24 :           ++NumTailCalls;
    1535          24 :           Pred->removeSuccessor(MBB);
    1536          24 :           MadeChange = true;
    1537          48 :           return MadeChange;
    1538             :         }
    1539             :       }
    1540             :       // If the predecessor is falling through to this block, we could reverse
    1541             :       // the branch condition and fold the tail call into that. However, after
    1542             :       // that we might have to re-arrange the CFG to fall through to the other
    1543             :       // block and there is a high risk of regressing code size rather than
    1544             :       // improving it.
    1545             :     }
    1546             :   }
    1547             : 
    1548             :   // Analyze the branch in the current block.
    1549      479684 :   MachineBasicBlock *CurTBB = nullptr, *CurFBB = nullptr;
    1550      479684 :   SmallVector<MachineOperand, 4> CurCond;
    1551             :   bool CurUnAnalyzable =
    1552      479684 :       TII->analyzeBranch(*MBB, CurTBB, CurFBB, CurCond, true);
    1553      479684 :   if (!CurUnAnalyzable) {
    1554             :     // If the CFG for the prior block has extra edges, remove them.
    1555      447400 :     MadeChange |= MBB->CorrectExtraCFGEdges(CurTBB, CurFBB, !CurCond.empty());
    1556             : 
    1557             :     // If this is a two-way branch, and the FBB branches to this block, reverse
    1558             :     // the condition so the single-basic-block loop is faster.  Instead of:
    1559             :     //    Loop: xxx; jcc Out; jmp Loop
    1560             :     // we want:
    1561             :     //    Loop: xxx; jncc Loop; jmp Out
    1562      447400 :     if (CurTBB && CurFBB && CurFBB == MBB && CurTBB != MBB) {
    1563          28 :       SmallVector<MachineOperand, 4> NewCond(CurCond);
    1564          28 :       if (!TII->reverseBranchCondition(NewCond)) {
    1565          56 :         DebugLoc dl = getBranchDebugLoc(*MBB);
    1566          28 :         TII->removeBranch(*MBB);
    1567          56 :         TII->insertBranch(*MBB, CurFBB, CurTBB, NewCond, dl);
    1568          28 :         MadeChange = true;
    1569          28 :         ++NumBranchOpts;
    1570             :         goto ReoptimizeBlock;
    1571             :       }
    1572             :     }
    1573             : 
    1574             :     // If this branch is the only thing in its block, see if we can forward
    1575             :     // other blocks across it.
    1576      822691 :     if (CurTBB && CurCond.empty() && !CurFBB &&
    1577      138282 :         IsBranchOnlyBlock(MBB) && CurTBB != MBB &&
    1578      456700 :         !MBB->hasAddressTaken() && !MBB->isEHPad()) {
    1579        4656 :       DebugLoc dl = getBranchDebugLoc(*MBB);
    1580             :       // This block may contain just an unconditional branch.  Because there can
    1581             :       // be 'non-branch terminators' in the block, try removing the branch and
    1582             :       // then seeing if the block is empty.
    1583        4654 :       TII->removeBranch(*MBB);
    1584             :       // If the only things remaining in the block are debug info, remove these
    1585             :       // as well, so this will behave the same as an empty block in non-debug
    1586             :       // mode.
    1587        4654 :       if (IsEmptyBlock(MBB)) {
    1588             :         // Make the block empty, losing the debug info (we could probably
    1589             :         // improve this in some cases.)
    1590        9308 :         MBB->erase(MBB->begin(), MBB->end());
    1591             :       }
    1592             :       // If this block is just an unconditional branch to CurTBB, we can
    1593             :       // usually completely eliminate the block.  The only case we cannot
    1594             :       // completely eliminate the block is when the block before this one
    1595             :       // falls through into MBB and we can't understand the prior block's branch
    1596             :       // condition.
    1597        4654 :       if (MBB->empty()) {
    1598        4654 :         bool PredHasNoFallThrough = !PrevBB.canFallThrough();
    1599        4656 :         if (PredHasNoFallThrough || !PriorUnAnalyzable ||
    1600           2 :             !PrevBB.isSuccessor(MBB)) {
    1601             :           // If the prior block falls through into us, turn it into an
    1602             :           // explicit branch to us to make updates simpler.
    1603        8826 :           if (!PredHasNoFallThrough && PrevBB.isSuccessor(MBB) &&
    1604       13467 :               PriorTBB != MBB && PriorFBB != MBB) {
    1605        4402 :             if (!PriorTBB) {
    1606             :               assert(PriorCond.empty() && !PriorFBB &&
    1607             :                      "Bad branch analysis");
    1608        2068 :               PriorTBB = MBB;
    1609             :             } else {
    1610             :               assert(!PriorFBB && "Machine CFG out of date!");
    1611        2334 :               PriorFBB = MBB;
    1612             :             }
    1613        8804 :             DebugLoc pdl = getBranchDebugLoc(PrevBB);
    1614        4402 :             TII->removeBranch(PrevBB);
    1615        8804 :             TII->insertBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, pdl);
    1616             :           }
    1617             : 
    1618             :           // Iterate through all the predecessors, revectoring each in-turn.
    1619             :           size_t PI = 0;
    1620             :           bool DidChange = false;
    1621             :           bool HasBranchToSelf = false;
    1622       10882 :           while(PI != MBB->pred_size()) {
    1623       18690 :             MachineBasicBlock *PMBB = *(MBB->pred_begin() + PI);
    1624        6230 :             if (PMBB == MBB) {
    1625             :               // If this block has an uncond branch to itself, leave it.
    1626           0 :               ++PI;
    1627           0 :               HasBranchToSelf = true;
    1628             :             } else {
    1629        6230 :               DidChange = true;
    1630        6230 :               PMBB->ReplaceUsesOfBlockWith(MBB, CurTBB);
    1631             :               // If this change resulted in PMBB ending in a conditional
    1632             :               // branch where both conditions go to the same destination,
    1633             :               // change this to an unconditional branch (and fix the CFG).
    1634        6230 :               MachineBasicBlock *NewCurTBB = nullptr, *NewCurFBB = nullptr;
    1635       12460 :               SmallVector<MachineOperand, 4> NewCurCond;
    1636        6230 :               bool NewCurUnAnalyzable = TII->analyzeBranch(
    1637        6230 :                   *PMBB, NewCurTBB, NewCurFBB, NewCurCond, true);
    1638        6230 :               if (!NewCurUnAnalyzable && NewCurTBB && NewCurTBB == NewCurFBB) {
    1639          44 :                 DebugLoc pdl = getBranchDebugLoc(*PMBB);
    1640          22 :                 TII->removeBranch(*PMBB);
    1641          22 :                 NewCurCond.clear();
    1642          44 :                 TII->insertBranch(*PMBB, NewCurTBB, nullptr, NewCurCond, pdl);
    1643          22 :                 MadeChange = true;
    1644          22 :                 ++NumBranchOpts;
    1645          22 :                 PMBB->CorrectExtraCFGEdges(NewCurTBB, nullptr, false);
    1646             :               }
    1647             :             }
    1648             :           }
    1649             : 
    1650             :           // Change any jumptables to go to the new MBB.
    1651        4652 :           if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo())
    1652          95 :             MJTI->ReplaceMBBInJumpTables(MBB, CurTBB);
    1653        4652 :           if (DidChange) {
    1654        4652 :             ++NumBranchOpts;
    1655        4652 :             MadeChange = true;
    1656        9304 :             if (!HasBranchToSelf) return MadeChange;
    1657             :           }
    1658             :         }
    1659             :       }
    1660             : 
    1661             :       // Add the branch back if the block is more than just an uncond branch.
    1662           4 :       TII->insertBranch(*MBB, CurTBB, nullptr, CurCond, dl);
    1663             :     }
    1664             :   }
    1665             : 
    1666             :   // If the prior block doesn't fall through into this block, and if this
    1667             :   // block doesn't fall through into some other block, see if we can find a
    1668             :   // place to move this block where a fall-through will happen.
    1669      475004 :   if (!PrevBB.canFallThrough()) {
    1670             :     // Now we know that there was no fall-through into this block, check to
    1671             :     // see if it has a fall-through into its successor.
    1672      148765 :     bool CurFallsThru = MBB->canFallThrough();
    1673             : 
    1674      148765 :     if (!MBB->isEHPad()) {
    1675             :       // Check all the predecessors of this block.  If one of them has no fall
    1676             :       // throughs, move this block right after it.
    1677      197421 :       for (MachineBasicBlock *PredBB : MBB->predecessors()) {
    1678             :         // Analyze the branch at the end of the pred.
    1679       81591 :         MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr;
    1680      135298 :         SmallVector<MachineOperand, 4> PredCond;
    1681      114869 :         if (PredBB != MBB && !PredBB->canFallThrough() &&
    1682       62414 :             !TII->analyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true) &&
    1683      100760 :             (!CurFallsThru || !CurTBB || !CurFBB) &&
    1684       19143 :             (!CurFallsThru || MBB->getNumber() >= PredBB->getNumber())) {
    1685             :           // If the current block doesn't fall through, just move it.
    1686             :           // If the current block can fall through and does not end with a
    1687             :           // conditional branch, we need to append an unconditional jump to
    1688             :           // the (current) next block.  To avoid a possible compile-time
    1689             :           // infinite loop, move blocks only backward in this case.
    1690             :           // Also, if there are already 2 branches here, we cannot add a third;
    1691             :           // this means we have the case
    1692             :           // Bcc next
    1693             :           // B elsewhere
    1694             :           // next:
    1695       27884 :           if (CurFallsThru) {
    1696       36342 :             MachineBasicBlock *NextBB = &*std::next(MBB->getIterator());
    1697       18171 :             CurCond.clear();
    1698       72684 :             TII->insertBranch(*MBB, NextBB, nullptr, CurCond, DebugLoc());
    1699             :           }
    1700       27884 :           MBB->moveAfter(PredBB);
    1701       27884 :           MadeChange = true;
    1702       27884 :           goto ReoptimizeBlock;
    1703             :         }
    1704             :       }
    1705             :     }
    1706             : 
    1707      120881 :     if (!CurFallsThru) {
    1708             :       // Check all successors to see if we can move this block before it.
    1709      185440 :       for (MachineBasicBlock *SuccBB : MBB->successors()) {
    1710             :         // Analyze the branch at the end of the block before the succ.
    1711      165780 :         MachineFunction::iterator SuccPrev = --SuccBB->getIterator();
    1712             : 
    1713             :         // If this block doesn't already fall-through to that successor, and if
    1714             :         // the succ doesn't already have a block that can fall through into it,
    1715             :         // and if the successor isn't an EH destination, we can arrange for the
    1716             :         // fallthrough to happen.
    1717      110009 :         if (SuccBB != MBB && &*SuccPrev != MBB &&
    1718      114513 :             !SuccPrev->canFallThrough() && !CurUnAnalyzable &&
    1719        1733 :             !SuccBB->isEHPad()) {
    1720        1568 :           MBB->moveBefore(SuccBB);
    1721        1568 :           MadeChange = true;
    1722        1568 :           goto ReoptimizeBlock;
    1723             :         }
    1724             :       }
    1725             : 
    1726             :       // Okay, there is no really great place to put this block.  If, however,
    1727             :       // the block before this one would be a fall-through if this block were
    1728             :       // removed, move this block to the end of the function. There is no real
    1729             :       // advantage in "falling through" to an EH block, so we don't want to
    1730             :       // perform this transformation for that case.
    1731             :       //
    1732             :       // Also, Windows EH introduced the possibility of an arbitrary number of
    1733             :       // successors to a given block.  The analyzeBranch call does not consider
    1734             :       // exception handling and so we can get in a state where a block
    1735             :       // containing a call is followed by multiple EH blocks that would be
    1736             :       // rotated infinitely at the end of the function if the transformation
    1737             :       // below were performed for EH "FallThrough" blocks.  Therefore, even if
    1738             :       // that appears not to be happening anymore, we should assume that it is
    1739             :       // possible and not remove the "!FallThrough()->isEHPad" condition below.
    1740       64306 :       MachineBasicBlock *PrevTBB = nullptr, *PrevFBB = nullptr;
    1741      125858 :       SmallVector<MachineOperand, 4> PrevCond;
    1742      119270 :       if (FallThrough != MF.end() &&
    1743       70513 :           !FallThrough->isEHPad() &&
    1744       93171 :           !TII->analyzeBranch(PrevBB, PrevTBB, PrevFBB, PrevCond, true) &&
    1745       13316 :           PrevBB.isSuccessor(&*FallThrough)) {
    1746        2754 :         MBB->moveAfter(&MF.back());
    1747        2754 :         MadeChange = true;
    1748        5508 :         return MadeChange;
    1749             :       }
    1750             :     }
    1751             :   }
    1752             : 
    1753             :   return MadeChange;
    1754             : }
    1755             : 
    1756             : //===----------------------------------------------------------------------===//
    1757             : //  Hoist Common Code
    1758             : //===----------------------------------------------------------------------===//
    1759             : 
    1760           0 : bool BranchFolder::HoistCommonCode(MachineFunction &MF) {
    1761      143127 :   bool MadeChange = false;
    1762      286254 :   for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ) {
    1763     1550214 :     MachineBasicBlock *MBB = &*I++;
    1764      516738 :     MadeChange |= HoistCommonCodeInSuccs(MBB);
    1765             :   }
    1766             : 
    1767           0 :   return MadeChange;
    1768             : }
    1769             : 
    1770             : /// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
    1771             : /// its 'true' successor.
    1772             : static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
    1773             :                                          MachineBasicBlock *TrueBB) {
    1774      253417 :   for (MachineBasicBlock *SuccBB : BB->successors())
    1775      149877 :     if (SuccBB != TrueBB)
    1776             :       return SuccBB;
    1777             :   return nullptr;
    1778             : }
    1779             : 
    1780             : template <class Container>
    1781       90531 : static void addRegAndItsAliases(unsigned Reg, const TargetRegisterInfo *TRI,
    1782             :                                 Container &Set) {
    1783      181062 :   if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
    1784      739034 :     for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
    1785      279071 :       Set.insert(*AI);
    1786             :   } else {
    1787          85 :     Set.insert(Reg);
    1788             :   }
    1789       90531 : }
    1790             : 
    1791             : /// findHoistingInsertPosAndDeps - Find the location to move common instructions
    1792             : /// in successors to. The location is usually just before the terminator,
    1793             : /// however if the terminator is a conditional branch and its previous
    1794             : /// instruction is the flag setting instruction, the previous instruction is
    1795             : /// the preferred location. This function also gathers uses and defs of the
    1796             : /// instructions from the insertion point to the end of the block. The data is
    1797             : /// used by HoistCommonCodeInSuccs to ensure safety.
    1798             : static
    1799       31712 : MachineBasicBlock::iterator findHoistingInsertPosAndDeps(MachineBasicBlock *MBB,
    1800             :                                                   const TargetInstrInfo *TII,
    1801             :                                                   const TargetRegisterInfo *TRI,
    1802             :                                                   SmallSet<unsigned,4> &Uses,
    1803             :                                                   SmallSet<unsigned,4> &Defs) {
    1804       31712 :   MachineBasicBlock::iterator Loc = MBB->getFirstTerminator();
    1805       63424 :   if (!TII->isUnpredicatedTerminator(*Loc))
    1806             :     return MBB->end();
    1807             : 
    1808      129781 :   for (const MachineOperand &MO : Loc->operands()) {
    1809       66674 :     if (!MO.isReg())
    1810       34364 :       continue;
    1811       32310 :     unsigned Reg = MO.getReg();
    1812       32310 :     if (!Reg)
    1813           0 :       continue;
    1814       32310 :     if (MO.isUse()) {
    1815       31884 :       addRegAndItsAliases(Reg, TRI, Uses);
    1816             :     } else {
    1817         426 :       if (!MO.isDead())
    1818             :         // Don't try to hoist code in the rare case the terminator defines a
    1819             :         // register that is later used.
    1820             :         return MBB->end();
    1821             : 
    1822             :       // If the terminator defines a register, make sure we don't hoist
    1823             :       // the instruction whose def might be clobbered by the terminator.
    1824         109 :       addRegAndItsAliases(Reg, TRI, Defs);
    1825             :     }
    1826             :   }
    1827             : 
    1828           0 :   if (Uses.empty())
    1829           0 :     return Loc;
    1830       62790 :   if (Loc == MBB->begin())
    1831             :     return MBB->end();
    1832             : 
    1833             :   // The terminator is probably a conditional branch, try not to separate the
    1834             :   // branch from condition setting instruction.
    1835             :   MachineBasicBlock::iterator PI =
    1836       92757 :     skipDebugInstructionsBackward(std::prev(Loc), MBB->begin());
    1837             : 
    1838       30919 :   bool IsDef = false;
    1839      158568 :   for (const MachineOperand &MO : PI->operands()) {
    1840             :     // If PI has a regmask operand, it is probably a call. Separate away.
    1841      120428 :     if (MO.isRegMask())
    1842           4 :       return Loc;
    1843      307437 :     if (!MO.isReg() || MO.isUse())
    1844      190292 :       continue;
    1845       25278 :     unsigned Reg = MO.getReg();
    1846       25278 :     if (!Reg)
    1847           0 :       continue;
    1848       25278 :     if (Uses.count(Reg)) {
    1849       23694 :       IsDef = true;
    1850       23694 :       break;
    1851             :     }
    1852             :   }
    1853             :   if (!IsDef)
    1854             :     // The condition setting instruction is not just before the conditional
    1855             :     // branch.
    1856        7221 :     return Loc;
    1857             : 
    1858             :   // Be conservative, don't insert instruction above something that may have
    1859             :   // side-effects. And since it's potentially bad to separate flag setting
    1860             :   // instruction from the conditional branch, just abort the optimization
    1861             :   // completely.
    1862             :   // Also avoid moving code above predicated instruction since it's hard to
    1863             :   // reason about register liveness with predicated instruction.
    1864       23694 :   bool DontMoveAcrossStore = true;
    1865       67808 :   if (!PI->isSafeToMove(nullptr, DontMoveAcrossStore) || TII->isPredicated(*PI))
    1866             :     return MBB->end();
    1867             : 
    1868             : 
    1869             :   // Find out what registers are live. Note this routine is ignoring other live
    1870             :   // registers which are only used by instructions in successor blocks.
    1871      208911 :   for (const MachineOperand &MO : PI->operands()) {
    1872       71373 :     if (!MO.isReg())
    1873       24955 :       continue;
    1874       59583 :     unsigned Reg = MO.getReg();
    1875       59583 :     if (!Reg)
    1876        1375 :       continue;
    1877       58208 :     if (MO.isUse()) {
    1878       35311 :       addRegAndItsAliases(Reg, TRI, Uses);
    1879             :     } else {
    1880       22897 :       if (Uses.erase(Reg)) {
    1881       44118 :         if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
    1882       46336 :           for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs)
    1883        4544 :             Uses.erase(*SubRegs); // Use sub-registers to be conservative
    1884             :         }
    1885             :       }
    1886       22897 :       addRegAndItsAliases(Reg, TRI, Defs);
    1887             :     }
    1888             :   }
    1889             : 
    1890       22055 :   return PI;
    1891             : }
    1892             : 
    1893      516738 : bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
    1894      516738 :   MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
    1895     1033476 :   SmallVector<MachineOperand, 4> Cond;
    1896      516738 :   if (TII->analyzeBranch(*MBB, TBB, FBB, Cond, true) || !TBB || Cond.empty())
    1897             :     return false;
    1898             : 
    1899      209261 :   if (!FBB) FBB = findFalseBlock(MBB, TBB);
    1900      105760 :   if (!FBB)
    1901             :     // Malformed bcc? True and false blocks are the same?
    1902             :     return false;
    1903             : 
    1904             :   // Restrict the optimization to cases where MBB is the only predecessor,
    1905             :   // it is an obvious win.
    1906      244639 :   if (TBB->pred_size() > 1 || FBB->pred_size() > 1)
    1907             :     return false;
    1908             : 
    1909             :   // Find a suitable position to hoist the common instructions to. Also figure
    1910             :   // out which registers are used or defined by instructions from the insertion
    1911             :   // point to the end of the block.
    1912       95136 :   SmallSet<unsigned, 4> Uses, Defs;
    1913             :   MachineBasicBlock::iterator Loc =
    1914       31712 :     findHoistingInsertPosAndDeps(MBB, TII, TRI, Uses, Defs);
    1915       63424 :   if (Loc == MBB->end())
    1916             :     return false;
    1917             : 
    1918       29280 :   bool HasDups = false;
    1919       87840 :   SmallVector<unsigned, 4> LocalDefs, LocalKills;
    1920       87840 :   SmallSet<unsigned, 4> ActiveDefsSet, AllDefsSet;
    1921       58560 :   MachineBasicBlock::iterator TIB = TBB->begin();
    1922       58560 :   MachineBasicBlock::iterator FIB = FBB->begin();
    1923       58560 :   MachineBasicBlock::iterator TIE = TBB->end();
    1924       58560 :   MachineBasicBlock::iterator FIE = FBB->end();
    1925       58801 :   while (TIB != TIE && FIB != FIE) {
    1926             :     // Skip dbg_value instructions. These do not count.
    1927       28988 :     TIB = skipDebugInstructionsForward(TIB, TIE);
    1928       28988 :     FIB = skipDebugInstructionsForward(FIB, FIE);
    1929       57976 :     if (TIB == TIE || FIB == FIE)
    1930             :       break;
    1931             : 
    1932       57976 :     if (!TIB->isIdenticalTo(*FIB, MachineInstr::CheckKillDead))
    1933             :       break;
    1934             : 
    1935        1134 :     if (TII->isPredicated(*TIB))
    1936             :       // Hard to reason about register liveness with predicated instruction.
    1937             :       break;
    1938             : 
    1939         567 :     bool IsSafe = true;
    1940        3644 :     for (MachineOperand &MO : TIB->operands()) {
    1941             :       // Don't attempt to hoist instructions with register masks.
    1942        2587 :       if (MO.isRegMask()) {
    1943             :         IsSafe = false;
    1944          77 :         break;
    1945             :       }
    1946        2565 :       if (!MO.isReg())
    1947        2363 :         continue;
    1948        1714 :       unsigned Reg = MO.getReg();
    1949        1714 :       if (!Reg)
    1950         661 :         continue;
    1951        1053 :       if (MO.isDef()) {
    1952         575 :         if (Uses.count(Reg)) {
    1953             :           // Avoid clobbering a register that's used by the instruction at
    1954             :           // the point of insertion.
    1955             :           IsSafe = false;
    1956             :           break;
    1957             :         }
    1958             : 
    1959         577 :         if (Defs.count(Reg) && !MO.isDead()) {
    1960             :           // Don't hoist the instruction if the def would be clobber by the
    1961             :           // instruction at the point insertion. FIXME: This is overly
    1962             :           // conservative. It should be possible to hoist the instructions
    1963             :           // in BB2 in the following example:
    1964             :           // BB1:
    1965             :           // r1, eflag = op1 r2, r3
    1966             :           // brcc eflag
    1967             :           //
    1968             :           // BB2:
    1969             :           // r1 = op2, ...
    1970             :           //    = op3, r1<kill>
    1971             :           IsSafe = false;
    1972             :           break;
    1973             :         }
    1974         478 :       } else if (!ActiveDefsSet.count(Reg)) {
    1975         467 :         if (Defs.count(Reg)) {
    1976             :           // Use is defined by the instruction at the point of insertion.
    1977             :           IsSafe = false;
    1978             :           break;
    1979             :         }
    1980             : 
    1981         467 :         if (MO.isKill() && Uses.count(Reg))
    1982             :           // Kills a register that's read by the instruction at the point of
    1983             :           // insertion. Remove the kill marker.
    1984             :           MO.setIsKill(false);
    1985             :       }
    1986             :     }
    1987             :     if (!IsSafe)
    1988             :       break;
    1989             : 
    1990         490 :     bool DontMoveAcrossStore = true;
    1991         490 :     if (!TIB->isSafeToMove(nullptr, DontMoveAcrossStore))
    1992             :       break;
    1993             : 
    1994             :     // Remove kills from ActiveDefsSet, these registers had short live ranges.
    1995         694 :     for (const MachineOperand &MO : TIB->operands()) {
    1996        1185 :       if (!MO.isReg() || !MO.isUse() || !MO.isKill())
    1997         764 :         continue;
    1998          26 :       unsigned Reg = MO.getReg();
    1999          26 :       if (!Reg)
    2000           0 :         continue;
    2001          50 :       if (!AllDefsSet.count(Reg)) {
    2002          24 :         LocalKills.push_back(Reg);
    2003          24 :         continue;
    2004             :       }
    2005           4 :       if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
    2006          28 :         for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
    2007          12 :           ActiveDefsSet.erase(*AI);
    2008             :       } else {
    2009           0 :         ActiveDefsSet.erase(Reg);
    2010             :       }
    2011             :     }
    2012             : 
    2013             :     // Track local defs so we can update liveins.
    2014         694 :     for (const MachineOperand &MO : TIB->operands()) {
    2015        1135 :       if (!MO.isReg() || !MO.isDef() || MO.isDead())
    2016         462 :         continue;
    2017         165 :       unsigned Reg = MO.getReg();
    2018         495 :       if (!Reg || TargetRegisterInfo::isVirtualRegister(Reg))
    2019           0 :         continue;
    2020         165 :       LocalDefs.push_back(Reg);
    2021         165 :       addRegAndItsAliases(Reg, TRI, ActiveDefsSet);
    2022         165 :       addRegAndItsAliases(Reg, TRI, AllDefsSet);
    2023             :     }
    2024             : 
    2025         149 :     HasDups = true;
    2026         149 :     ++TIB;
    2027         149 :     ++FIB;
    2028             :   }
    2029             : 
    2030       29280 :   if (!HasDups)
    2031             :     return false;
    2032             : 
    2033         348 :   MBB->splice(Loc, TBB, TBB->begin(), TIB);
    2034         348 :   FBB->erase(FBB->begin(), FIB);
    2035             : 
    2036             :   // Update livein's.
    2037         116 :   bool ChangedLiveIns = false;
    2038         397 :   for (unsigned i = 0, e = LocalDefs.size(); i != e; ++i) {
    2039         330 :     unsigned Def = LocalDefs[i];
    2040         165 :     if (ActiveDefsSet.count(Def)) {
    2041         330 :       TBB->addLiveIn(Def);
    2042         330 :       FBB->addLiveIn(Def);
    2043         165 :       ChangedLiveIns = true;
    2044             :     }
    2045             :   }
    2046         372 :   for (unsigned K : LocalKills) {
    2047          24 :     TBB->removeLiveIn(K);
    2048          24 :     FBB->removeLiveIn(K);
    2049          24 :     ChangedLiveIns = true;
    2050             :   }
    2051             : 
    2052         116 :   if (ChangedLiveIns) {
    2053         116 :     TBB->sortUniqueLiveIns();
    2054         116 :     FBB->sortUniqueLiveIns();
    2055             :   }
    2056             : 
    2057             :   ++NumHoist;
    2058             :   return true;
    2059      216918 : }

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