LCOV - code coverage report
Current view: top level - lib/CodeGen - BranchFolding.cpp (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 717 759 94.5 %
Date: 2018-07-13 00:08:38 Functions: 42 49 85.7 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : //===- BranchFolding.cpp - Fold machine code branch instructions ----------===//
       2             : //
       3             : //                     The LLVM Compiler Infrastructure
       4             : //
       5             : // This file is distributed under the University of Illinois Open Source
       6             : // License. See LICENSE.TXT for details.
       7             : //
       8             : //===----------------------------------------------------------------------===//
       9             : //
      10             : // This pass forwards branches to unconditional branches to make them branch
      11             : // directly to the target block.  This pass often results in dead MBB's, which
      12             : // it then removes.
      13             : //
      14             : // Note that this pass must be run after register allocation, it cannot handle
      15             : // SSA form. It also must handle virtual registers for targets that emit virtual
      16             : // ISA (e.g. NVPTX).
      17             : //
      18             : //===----------------------------------------------------------------------===//
      19             : 
      20             : #include "BranchFolding.h"
      21             : #include "llvm/ADT/BitVector.h"
      22             : #include "llvm/ADT/DenseMap.h"
      23             : #include "llvm/ADT/STLExtras.h"
      24             : #include "llvm/ADT/SmallPtrSet.h"
      25             : #include "llvm/ADT/SmallSet.h"
      26             : #include "llvm/ADT/SmallVector.h"
      27             : #include "llvm/ADT/Statistic.h"
      28             : #include "llvm/CodeGen/Analysis.h"
      29             : #include "llvm/CodeGen/LivePhysRegs.h"
      30             : #include "llvm/CodeGen/MachineBasicBlock.h"
      31             : #include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
      32             : #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
      33             : #include "llvm/CodeGen/MachineFunction.h"
      34             : #include "llvm/CodeGen/MachineFunctionPass.h"
      35             : #include "llvm/CodeGen/MachineInstr.h"
      36             : #include "llvm/CodeGen/MachineInstrBuilder.h"
      37             : #include "llvm/CodeGen/MachineJumpTableInfo.h"
      38             : #include "llvm/CodeGen/MachineLoopInfo.h"
      39             : #include "llvm/CodeGen/MachineModuleInfo.h"
      40             : #include "llvm/CodeGen/MachineOperand.h"
      41             : #include "llvm/CodeGen/MachineRegisterInfo.h"
      42             : #include "llvm/CodeGen/TargetInstrInfo.h"
      43             : #include "llvm/CodeGen/TargetOpcodes.h"
      44             : #include "llvm/CodeGen/TargetPassConfig.h"
      45             : #include "llvm/CodeGen/TargetRegisterInfo.h"
      46             : #include "llvm/CodeGen/TargetSubtargetInfo.h"
      47             : #include "llvm/IR/DebugInfoMetadata.h"
      48             : #include "llvm/IR/DebugLoc.h"
      49             : #include "llvm/IR/Function.h"
      50             : #include "llvm/MC/LaneBitmask.h"
      51             : #include "llvm/MC/MCRegisterInfo.h"
      52             : #include "llvm/Pass.h"
      53             : #include "llvm/Support/BlockFrequency.h"
      54             : #include "llvm/Support/BranchProbability.h"
      55             : #include "llvm/Support/CommandLine.h"
      56             : #include "llvm/Support/Debug.h"
      57             : #include "llvm/Support/ErrorHandling.h"
      58             : #include "llvm/Support/raw_ostream.h"
      59             : #include "llvm/Target/TargetMachine.h"
      60             : #include <cassert>
      61             : #include <cstddef>
      62             : #include <iterator>
      63             : #include <numeric>
      64             : #include <vector>
      65             : 
      66             : using namespace llvm;
      67             : 
      68             : #define DEBUG_TYPE "branch-folder"
      69             : 
      70             : STATISTIC(NumDeadBlocks, "Number of dead blocks removed");
      71             : STATISTIC(NumBranchOpts, "Number of branches optimized");
      72             : STATISTIC(NumTailMerge , "Number of block tails merged");
      73             : STATISTIC(NumHoist     , "Number of times common instructions are hoisted");
      74             : STATISTIC(NumTailCalls,  "Number of tail calls optimized");
      75             : 
      76       99743 : static cl::opt<cl::boolOrDefault> FlagEnableTailMerge("enable-tail-merge",
      77       99743 :                               cl::init(cl::BOU_UNSET), cl::Hidden);
      78             : 
      79             : // Throttle for huge numbers of predecessors (compile speed problems)
      80             : static cl::opt<unsigned>
      81       99743 : TailMergeThreshold("tail-merge-threshold",
      82       99743 :           cl::desc("Max number of predecessors to consider tail merging"),
      83      299229 :           cl::init(150), cl::Hidden);
      84             : 
      85             : // Heuristic for tail merging (and, inversely, tail duplication).
      86             : // TODO: This should be replaced with a target query.
      87             : static cl::opt<unsigned>
      88       99743 : TailMergeSize("tail-merge-size",
      89       99743 :               cl::desc("Min number of instructions to consider tail merging"),
      90      299229 :               cl::init(3), cl::Hidden);
      91             : 
      92             : namespace {
      93             : 
      94             :   /// BranchFolderPass - Wrap branch folder in a machine function pass.
      95       19155 :   class BranchFolderPass : public MachineFunctionPass {
      96             :   public:
      97             :     static char ID;
      98             : 
      99       19259 :     explicit BranchFolderPass(): MachineFunctionPass(ID) {}
     100             : 
     101             :     bool runOnMachineFunction(MachineFunction &MF) override;
     102             : 
     103       19114 :     void getAnalysisUsage(AnalysisUsage &AU) const override {
     104             :       AU.addRequired<MachineBlockFrequencyInfo>();
     105             :       AU.addRequired<MachineBranchProbabilityInfo>();
     106             :       AU.addRequired<TargetPassConfig>();
     107       19114 :       MachineFunctionPass::getAnalysisUsage(AU);
     108       19114 :     }
     109             :   };
     110             : 
     111             : } // end anonymous namespace
     112             : 
     113             : char BranchFolderPass::ID = 0;
     114             : 
     115             : char &llvm::BranchFolderPassID = BranchFolderPass::ID;
     116             : 
     117      146610 : INITIALIZE_PASS(BranchFolderPass, DEBUG_TYPE,
     118             :                 "Control Flow Optimizer", false, false)
     119             : 
     120      184191 : bool BranchFolderPass::runOnMachineFunction(MachineFunction &MF) {
     121      184191 :   if (skipFunction(MF.getFunction()))
     122             :     return false;
     123             : 
     124      184035 :   TargetPassConfig *PassConfig = &getAnalysis<TargetPassConfig>();
     125             :   // TailMerge can create jump into if branches that make CFG irreducible for
     126             :   // HW that requires structurized CFG.
     127      548835 :   bool EnableTailMerge = !MF.getTarget().requiresStructuredCFG() &&
     128      180765 :                          PassConfig->getEnableTailMerge();
     129             :   BranchFolder::MBFIWrapper MBBFreqInfo(
     130      184035 :       getAnalysis<MachineBlockFrequencyInfo>());
     131             :   BranchFolder Folder(EnableTailMerge, /*CommonHoist=*/true, MBBFreqInfo,
     132      368070 :                       getAnalysis<MachineBranchProbabilityInfo>());
     133      368070 :   return Folder.OptimizeFunction(MF, MF.getSubtarget().getInstrInfo(),
     134      184035 :                                  MF.getSubtarget().getRegisterInfo(),
     135      184035 :                                  getAnalysisIfAvailable<MachineModuleInfo>());
     136             : }
     137             : 
     138      225003 : BranchFolder::BranchFolder(bool defaultEnableTailMerge, bool CommonHoist,
     139             :                            MBFIWrapper &FreqInfo,
     140             :                            const MachineBranchProbabilityInfo &ProbInfo,
     141      225003 :                            unsigned MinTailLength)
     142             :     : EnableHoistCommonCode(CommonHoist), MinCommonTailLength(MinTailLength),
     143      675009 :       MBBFreqInfo(FreqInfo), MBPI(ProbInfo) {
     144      225003 :   if (MinCommonTailLength == 0)
     145      218189 :     MinCommonTailLength = TailMergeSize;
     146      225003 :   switch (FlagEnableTailMerge) {
     147      224951 :   case cl::BOU_UNSET: EnableTailMerge = defaultEnableTailMerge; break;
     148           3 :   case cl::BOU_TRUE: EnableTailMerge = true; break;
     149          49 :   case cl::BOU_FALSE: EnableTailMerge = false; break;
     150             :   }
     151      225003 : }
     152             : 
     153       11783 : void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) {
     154             :   assert(MBB->pred_empty() && "MBB must be dead!");
     155             :   LLVM_DEBUG(dbgs() << "\nRemoving MBB: " << *MBB);
     156             : 
     157       11783 :   MachineFunction *MF = MBB->getParent();
     158             :   // drop all successors.
     159       26123 :   while (!MBB->succ_empty())
     160        7170 :     MBB->removeSuccessor(MBB->succ_end()-1);
     161             : 
     162             :   // Avoid matching if this pointer gets reused.
     163             :   TriedMerging.erase(MBB);
     164             : 
     165             :   // Remove the block.
     166             :   MF->erase(MBB);
     167       11783 :   EHScopeMembership.erase(MBB);
     168       11783 :   if (MLI)
     169             :     MLI->removeBlock(MBB);
     170       11783 : }
     171             : 
     172      225003 : bool BranchFolder::OptimizeFunction(MachineFunction &MF,
     173             :                                     const TargetInstrInfo *tii,
     174             :                                     const TargetRegisterInfo *tri,
     175             :                                     MachineModuleInfo *mmi,
     176             :                                     MachineLoopInfo *mli, bool AfterPlacement) {
     177      225003 :   if (!tii) return false;
     178             : 
     179      225003 :   TriedMerging.clear();
     180             : 
     181      225003 :   MachineRegisterInfo &MRI = MF.getRegInfo();
     182      225003 :   AfterBlockPlacement = AfterPlacement;
     183      225003 :   TII = tii;
     184      225003 :   TRI = tri;
     185      225003 :   MMI = mmi;
     186      225003 :   MLI = mli;
     187      225003 :   this->MRI = &MRI;
     188             : 
     189      450006 :   UpdateLiveIns = MRI.tracksLiveness() && TRI->trackLivenessAfterRegAlloc(MF);
     190      225003 :   if (!UpdateLiveIns)
     191        7962 :     MRI.invalidateLiveness();
     192             : 
     193             :   // Fix CFG.  The later algorithms expect it to be right.
     194             :   bool MadeChange = false;
     195      767743 :   for (MachineBasicBlock &MBB : MF) {
     196      542740 :     MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
     197             :     SmallVector<MachineOperand, 4> Cond;
     198      542740 :     if (!TII->analyzeBranch(MBB, TBB, FBB, Cond, true))
     199      314889 :       MadeChange |= MBB.CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
     200             :   }
     201             : 
     202             :   // Recalculate EH scope membership.
     203      450006 :   EHScopeMembership = getEHScopeMembership(MF);
     204             : 
     205             :   bool MadeChangeThisIteration = true;
     206      696113 :   while (MadeChangeThisIteration) {
     207      235555 :     MadeChangeThisIteration    = TailMergeBlocks(MF);
     208             :     // No need to clean up if tail merging does not change anything after the
     209             :     // block placement.
     210      235555 :     if (!AfterBlockPlacement || MadeChangeThisIteration)
     211      228741 :       MadeChangeThisIteration |= OptimizeBranches(MF);
     212      235555 :     if (EnableHoistCommonCode)
     213      192642 :       MadeChangeThisIteration |= HoistCommonCode(MF);
     214      235555 :     MadeChange |= MadeChangeThisIteration;
     215             :   }
     216             : 
     217             :   // See if any jump tables have become dead as the code generator
     218             :   // did its thing.
     219      225003 :   MachineJumpTableInfo *JTI = MF.getJumpTableInfo();
     220      225003 :   if (!JTI)
     221             :     return MadeChange;
     222             : 
     223             :   // Walk the function to find jump tables that are live.
     224         984 :   BitVector JTIsLive(JTI->getJumpTables().size());
     225        7218 :   for (const MachineBasicBlock &BB : MF) {
     226       72465 :     for (const MachineInstr &I : BB)
     227      591979 :       for (const MachineOperand &Op : I.operands()) {
     228      266483 :         if (!Op.isJTI()) continue;
     229             : 
     230             :         // Remember that this JT is live.
     231         820 :         JTIsLive.set(Op.getIndex());
     232             :       }
     233             :   }
     234             : 
     235             :   // Finally, remove dead jump tables.  This happens when the
     236             :   // indirect jump was unreachable (and thus deleted).
     237        1008 :   for (unsigned i = 0, e = JTIsLive.size(); i != e; ++i)
     238         516 :     if (!JTIsLive.test(i)) {
     239             :       JTI->RemoveJumpTable(i);
     240             :       MadeChange = true;
     241             :     }
     242             : 
     243             :   return MadeChange;
     244             : }
     245             : 
     246             : //===----------------------------------------------------------------------===//
     247             : //  Tail Merging of Blocks
     248             : //===----------------------------------------------------------------------===//
     249             : 
     250             : /// HashMachineInstr - Compute a hash value for MI and its operands.
     251      629751 : static unsigned HashMachineInstr(const MachineInstr &MI) {
     252      629751 :   unsigned Hash = MI.getOpcode();
     253     2947263 :   for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
     254     2317512 :     const MachineOperand &Op = MI.getOperand(i);
     255             : 
     256             :     // Merge in bits from the operand if easy. We can't use MachineOperand's
     257             :     // hash_code here because it's not deterministic and we sort by hash value
     258             :     // later.
     259             :     unsigned OperandHash = 0;
     260     2317512 :     switch (Op.getType()) {
     261     1490235 :     case MachineOperand::MO_Register:
     262     1490235 :       OperandHash = Op.getReg();
     263     1490235 :       break;
     264      421018 :     case MachineOperand::MO_Immediate:
     265      421018 :       OperandHash = Op.getImm();
     266      421018 :       break;
     267      117152 :     case MachineOperand::MO_MachineBasicBlock:
     268      117152 :       OperandHash = Op.getMBB()->getNumber();
     269      117152 :       break;
     270         406 :     case MachineOperand::MO_FrameIndex:
     271             :     case MachineOperand::MO_ConstantPoolIndex:
     272             :     case MachineOperand::MO_JumpTableIndex:
     273         406 :       OperandHash = Op.getIndex();
     274         406 :       break;
     275      173599 :     case MachineOperand::MO_GlobalAddress:
     276             :     case MachineOperand::MO_ExternalSymbol:
     277             :       // Global address / external symbol are too hard, don't bother, but do
     278             :       // pull in the offset.
     279      347198 :       OperandHash = Op.getOffset();
     280      173599 :       break;
     281             :     default:
     282             :       break;
     283             :     }
     284             : 
     285     2317512 :     Hash += ((OperandHash << 3) | Op.getType()) << (i & 31);
     286             :   }
     287      629751 :   return Hash;
     288             : }
     289             : 
     290             : /// HashEndOfMBB - Hash the last instruction in the MBB.
     291      635705 : static unsigned HashEndOfMBB(const MachineBasicBlock &MBB) {
     292             :   MachineBasicBlock::const_iterator I = MBB.getLastNonDebugInstr();
     293      635705 :   if (I == MBB.end())
     294             :     return 0;
     295             : 
     296      629751 :   return HashMachineInstr(*I);
     297             : }
     298             : 
     299             : ///  Whether MI should be counted as an instruction when calculating common tail.
     300             : static bool countsAsInstruction(const MachineInstr &MI) {
     301     3385700 :   return !(MI.isDebugValue() || MI.isCFIInstruction());
     302             : }
     303             : 
     304             : /// ComputeCommonTailLength - Given two machine basic blocks, compute the number
     305             : /// of instructions they actually have in common together at their end.  Return
     306             : /// iterators for the first shared instruction in each block.
     307      671699 : static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1,
     308             :                                         MachineBasicBlock *MBB2,
     309             :                                         MachineBasicBlock::iterator &I1,
     310             :                                         MachineBasicBlock::iterator &I2) {
     311      671699 :   I1 = MBB1->end();
     312      671699 :   I2 = MBB2->end();
     313             : 
     314             :   unsigned TailLen = 0;
     315     4060142 :   while (I1 != MBB1->begin() && I2 != MBB2->begin()) {
     316             :     --I1; --I2;
     317             :     // Skip debugging pseudos; necessary to avoid changing the code.
     318             :     while (!countsAsInstruction(*I1)) {
     319      159034 :       if (I1==MBB1->begin()) {
     320             :         while (!countsAsInstruction(*I2)) {
     321         280 :           if (I2==MBB2->begin()) {
     322             :             // I1==DBG at begin; I2==DBG at begin
     323             :             goto SkipTopCFIAndReturn;
     324             :           }
     325             :           --I2;
     326             :         }
     327             :         ++I2;
     328             :         // I1==DBG at begin; I2==non-DBG, or first of DBGs not at begin
     329             :         goto SkipTopCFIAndReturn;
     330             :       }
     331             :       --I1;
     332             :     }
     333             :     // I1==first (untested) non-DBG preceding known match
     334             :     while (!countsAsInstruction(*I2)) {
     335      158785 :       if (I2==MBB2->begin()) {
     336             :         ++I1;
     337             :         // I1==non-DBG, or first of DBGs not at begin; I2==DBG at begin
     338             :         goto SkipTopCFIAndReturn;
     339             :       }
     340             :       --I2;
     341             :     }
     342             :     // I1, I2==first (untested) non-DBGs preceding known match
     343     2386096 :     if (!I1->isIdenticalTo(*I2) ||
     344             :         // FIXME: This check is dubious. It's used to get around a problem where
     345             :         // people incorrectly expect inline asm directives to remain in the same
     346             :         // relative order. This is untenable because normal compiler
     347             :         // optimizations (like this one) may reorder and/or merge these
     348             :         // directives.
     349             :         I1->isInlineAsm()) {
     350             :       ++I1; ++I2;
     351             :       break;
     352             :     }
     353      969769 :     ++TailLen;
     354             :   }
     355             :   // Back past possible debugging pseudos at beginning of block.  This matters
     356             :   // when one block differs from the other only by whether debugging pseudos
     357             :   // are present at the beginning. (This way, the various checks later for
     358             :   // I1==MBB1->begin() work as expected.)
     359      864070 :   if (I1 == MBB1->begin() && I2 != MBB2->begin()) {
     360             :     --I2;
     361             :     while (I2->isDebugInstr()) {
     362          28 :       if (I2 == MBB2->begin())
     363             :         return TailLen;
     364             :       --I2;
     365             :     }
     366             :     ++I2;
     367             :   }
     368      832360 :   if (I2 == MBB2->begin() && I1 != MBB1->begin()) {
     369             :     --I1;
     370             :     while (I1->isDebugInstr()) {
     371          34 :       if (I1 == MBB1->begin())
     372             :         return TailLen;
     373             :       --I1;
     374             :     }
     375             :     ++I1;
     376             :   }
     377             : 
     378         107 : SkipTopCFIAndReturn:
     379             :   // Ensure that I1 and I2 do not point to a CFI_INSTRUCTION. This can happen if
     380             :   // I1 and I2 are non-identical when compared and then one or both of them ends
     381             :   // up pointing to a CFI instruction after being incremented. For example:
     382             :   /*
     383             :     BB1:
     384             :     ...
     385             :     INSTRUCTION_A
     386             :     ADD32ri8  <- last common instruction
     387             :     ...
     388             :     BB2:
     389             :     ...
     390             :     INSTRUCTION_B
     391             :     CFI_INSTRUCTION
     392             :     ADD32ri8  <- last common instruction
     393             :     ...
     394             :   */
     395             :   // When INSTRUCTION_A and INSTRUCTION_B are compared as not equal, after
     396             :   // incrementing the iterators, I1 will point to ADD, however I2 will point to
     397             :   // the CFI instruction. Later on, this leads to BB2 being 'hacked off' at the
     398             :   // wrong place (in ReplaceTailWithBranchTo()) which results in losing this CFI
     399             :   // instruction.
     400     1197405 :   while (I1 != MBB1->end() && I1->isCFIInstruction()) {
     401             :     ++I1;
     402             :   }
     403             : 
     404     1197399 :   while (I2 != MBB2->end() && I2->isCFIInstruction()) {
     405             :     ++I2;
     406             :   }
     407             : 
     408             :   return TailLen;
     409             : }
     410             : 
     411       13400 : void BranchFolder::replaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
     412             :                                            MachineBasicBlock &NewDest) {
     413       13400 :   if (UpdateLiveIns) {
     414             :     // OldInst should always point to an instruction.
     415       13377 :     MachineBasicBlock &OldMBB = *OldInst->getParent();
     416       13377 :     LiveRegs.clear();
     417       13377 :     LiveRegs.addLiveOuts(OldMBB);
     418             :     // Move backward to the place where will insert the jump.
     419       13377 :     MachineBasicBlock::iterator I = OldMBB.end();
     420             :     do {
     421             :       --I;
     422       63766 :       LiveRegs.stepBackward(*I);
     423       63766 :     } while (I != OldInst);
     424             : 
     425             :     // Merging the tails may have switched some undef operand to non-undef ones.
     426             :     // Add IMPLICIT_DEFS into OldMBB as necessary to have a definition of the
     427             :     // register.
     428       36669 :     for (MachineBasicBlock::RegisterMaskPair P : NewDest.liveins()) {
     429             :       // We computed the liveins with computeLiveIn earlier and should only see
     430             :       // full registers:
     431             :       assert(P.LaneMask == LaneBitmask::getAll() &&
     432             :              "Can only handle full register.");
     433             :       MCPhysReg Reg = P.PhysReg;
     434       23292 :       if (!LiveRegs.available(*MRI, Reg))
     435       23291 :         continue;
     436           1 :       DebugLoc DL;
     437           2 :       BuildMI(OldMBB, OldInst, DL, TII->get(TargetOpcode::IMPLICIT_DEF), Reg);
     438             :     }
     439             :   }
     440             : 
     441       13400 :   TII->ReplaceTailWithBranchTo(OldInst, &NewDest);
     442             :   ++NumTailMerge;
     443       13400 : }
     444             : 
     445        3474 : MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB,
     446             :                                             MachineBasicBlock::iterator BBI1,
     447             :                                             const BasicBlock *BB) {
     448        3474 :   if (!TII->isLegalToSplitMBBAt(CurMBB, BBI1))
     449             :     return nullptr;
     450             : 
     451        3474 :   MachineFunction &MF = *CurMBB.getParent();
     452             : 
     453             :   // Create the fall-through block.
     454        3474 :   MachineFunction::iterator MBBI = CurMBB.getIterator();
     455        3474 :   MachineBasicBlock *NewMBB = MF.CreateMachineBasicBlock(BB);
     456        3474 :   CurMBB.getParent()->insert(++MBBI, NewMBB);
     457             : 
     458             :   // Move all the successors of this block to the specified block.
     459        3474 :   NewMBB->transferSuccessors(&CurMBB);
     460             : 
     461             :   // Add an edge from CurMBB to NewMBB for the fall-through.
     462        3474 :   CurMBB.addSuccessor(NewMBB);
     463             : 
     464             :   // Splice the code over.
     465             :   NewMBB->splice(NewMBB->end(), &CurMBB, BBI1, CurMBB.end());
     466             : 
     467             :   // NewMBB belongs to the same loop as CurMBB.
     468        3474 :   if (MLI)
     469          16 :     if (MachineLoop *ML = MLI->getLoopFor(&CurMBB))
     470          32 :       ML->addBasicBlockToLoop(NewMBB, MLI->getBase());
     471             : 
     472             :   // NewMBB inherits CurMBB's block frequency.
     473        3474 :   MBBFreqInfo.setBlockFreq(NewMBB, MBBFreqInfo.getBlockFreq(&CurMBB));
     474             : 
     475        3474 :   if (UpdateLiveIns)
     476        3465 :     computeAndAddLiveIns(LiveRegs, *NewMBB);
     477             : 
     478             :   // Add the new block to the EH scope.
     479        3474 :   const auto &EHScopeI = EHScopeMembership.find(&CurMBB);
     480        3474 :   if (EHScopeI != EHScopeMembership.end()) {
     481           0 :     auto n = EHScopeI->second;
     482           0 :     EHScopeMembership[NewMBB] = n;
     483             :   }
     484             : 
     485             :   return NewMBB;
     486             : }
     487             : 
     488             : /// EstimateRuntime - Make a rough estimate for how long it will take to run
     489             : /// the specified code.
     490        8948 : static unsigned EstimateRuntime(MachineBasicBlock::iterator I,
     491             :                                 MachineBasicBlock::iterator E) {
     492             :   unsigned Time = 0;
     493       33518 :   for (; I != E; ++I) {
     494        3853 :     if (!countsAsInstruction(*I))
     495        3853 :       continue;
     496       20717 :     if (I->isCall())
     497         745 :       Time += 10;
     498       36252 :     else if (I->mayLoad() || I->mayStore())
     499        7055 :       Time += 2;
     500             :     else
     501       12917 :       ++Time;
     502             :   }
     503        8948 :   return Time;
     504             : }
     505             : 
     506             : // CurMBB needs to add an unconditional branch to SuccMBB (we removed these
     507             : // branches temporarily for tail merging).  In the case where CurMBB ends
     508             : // with a conditional branch to the next block, optimize by reversing the
     509             : // test and conditionally branching to SuccMBB instead.
     510      234676 : static void FixTail(MachineBasicBlock *CurMBB, MachineBasicBlock *SuccBB,
     511             :                     const TargetInstrInfo *TII) {
     512      234676 :   MachineFunction *MF = CurMBB->getParent();
     513             :   MachineFunction::iterator I = std::next(MachineFunction::iterator(CurMBB));
     514      234676 :   MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
     515             :   SmallVector<MachineOperand, 4> Cond;
     516      234676 :   DebugLoc dl = CurMBB->findBranchDebugLoc();
     517      234676 :   if (I != MF->end() && !TII->analyzeBranch(*CurMBB, TBB, FBB, Cond, true)) {
     518             :     MachineBasicBlock *NextBB = &*I;
     519      231866 :     if (TBB == NextBB && !Cond.empty() && !FBB) {
     520      101602 :       if (!TII->reverseBranchCondition(Cond)) {
     521      101602 :         TII->removeBranch(*CurMBB);
     522      203204 :         TII->insertBranch(*CurMBB, SuccBB, nullptr, Cond, dl);
     523             :         return;
     524             :       }
     525             :     }
     526             :   }
     527      133074 :   TII->insertBranch(*CurMBB, SuccBB, nullptr,
     528      266148 :                     SmallVector<MachineOperand, 0>(), dl);
     529             : }
     530             : 
     531             : bool
     532           0 : BranchFolder::MergePotentialsElt::operator<(const MergePotentialsElt &o) const {
     533      499548 :   if (getHash() < o.getHash())
     534             :     return true;
     535      212878 :   if (getHash() > o.getHash())
     536             :     return false;
     537      160589 :   if (getBlock()->getNumber() < o.getBlock()->getNumber())
     538             :     return true;
     539       53115 :   if (getBlock()->getNumber() > o.getBlock()->getNumber())
     540             :     return false;
     541             :   // _GLIBCXX_DEBUG checks strict weak ordering, which involves comparing
     542             :   // an object with itself.
     543             : #ifndef _GLIBCXX_DEBUG
     544           0 :   llvm_unreachable("Predecessor appears twice");
     545             : #else
     546             :   return false;
     547             : #endif
     548             : }
     549             : 
     550             : BlockFrequency
     551     1404275 : BranchFolder::MBFIWrapper::getBlockFreq(const MachineBasicBlock *MBB) const {
     552     1404275 :   auto I = MergedBBFreq.find(MBB);
     553             : 
     554     1404275 :   if (I != MergedBBFreq.end())
     555        4876 :     return I->second;
     556             : 
     557     1399399 :   return MBFI.getBlockFreq(MBB);
     558             : }
     559             : 
     560           0 : void BranchFolder::MBFIWrapper::setBlockFreq(const MachineBasicBlock *MBB,
     561             :                                              BlockFrequency F) {
     562       18258 :   MergedBBFreq[MBB] = F;
     563           0 : }
     564             : 
     565             : raw_ostream &
     566           0 : BranchFolder::MBFIWrapper::printBlockFreq(raw_ostream &OS,
     567             :                                           const MachineBasicBlock *MBB) const {
     568           0 :   return MBFI.printBlockFreq(OS, getBlockFreq(MBB));
     569             : }
     570             : 
     571             : raw_ostream &
     572           0 : BranchFolder::MBFIWrapper::printBlockFreq(raw_ostream &OS,
     573             :                                           const BlockFrequency Freq) const {
     574           0 :   return MBFI.printBlockFreq(OS, Freq);
     575             : }
     576             : 
     577           0 : void BranchFolder::MBFIWrapper::view(const Twine &Name, bool isSimple) {
     578           0 :   MBFI.view(Name, isSimple);
     579           0 : }
     580             : 
     581             : uint64_t
     582        1809 : BranchFolder::MBFIWrapper::getEntryFreq() const {
     583        1809 :   return MBFI.getEntryFreq();
     584             : }
     585             : 
     586             : /// CountTerminators - Count the number of terminators in the given
     587             : /// block and set I to the position of the first non-terminator, if there
     588             : /// is one, or MBB->end() otherwise.
     589        4857 : static unsigned CountTerminators(MachineBasicBlock *MBB,
     590             :                                  MachineBasicBlock::iterator &I) {
     591        4857 :   I = MBB->end();
     592             :   unsigned NumTerms = 0;
     593             :   while (true) {
     594        7421 :     if (I == MBB->begin()) {
     595           1 :       I = MBB->end();
     596           1 :       break;
     597             :     }
     598             :     --I;
     599        6138 :     if (!I->isTerminator()) break;
     600        1282 :     ++NumTerms;
     601             :   }
     602        4857 :   return NumTerms;
     603             : }
     604             : 
     605             : /// A no successor, non-return block probably ends in unreachable and is cold.
     606             : /// Also consider a block that ends in an indirect branch to be a return block,
     607             : /// since many targets use plain indirect branches to return.
     608      122579 : static bool blockEndsInUnreachable(const MachineBasicBlock *MBB) {
     609      122579 :   if (!MBB->succ_empty())
     610             :     return false;
     611      108816 :   if (MBB->empty())
     612             :     return true;
     613      111296 :   return !(MBB->back().isReturn() || MBB->back().isIndirectBranch());
     614             : }
     615             : 
     616             : /// ProfitableToMerge - Check if two machine basic blocks have a common tail
     617             : /// and decide if it would be profitable to merge those tails.  Return the
     618             : /// length of the common tail and iterators to the first common instruction
     619             : /// in each block.
     620             : /// MBB1, MBB2      The blocks to check
     621             : /// MinCommonTailLength  Minimum size of tail block to be merged.
     622             : /// CommonTailLen   Out parameter to record the size of the shared tail between
     623             : ///                 MBB1 and MBB2
     624             : /// I1, I2          Iterator references that will be changed to point to the first
     625             : ///                 instruction in the common tail shared by MBB1,MBB2
     626             : /// SuccBB          A common successor of MBB1, MBB2 which are in a canonical form
     627             : ///                 relative to SuccBB
     628             : /// PredBB          The layout predecessor of SuccBB, if any.
     629             : /// EHScopeMembership  map from block to EH scope #.
     630             : /// AfterPlacement  True if we are merging blocks after layout. Stricter
     631             : ///                 thresholds apply to prevent undoing tail-duplication.
     632             : static bool
     633      671765 : ProfitableToMerge(MachineBasicBlock *MBB1, MachineBasicBlock *MBB2,
     634             :                   unsigned MinCommonTailLength, unsigned &CommonTailLen,
     635             :                   MachineBasicBlock::iterator &I1,
     636             :                   MachineBasicBlock::iterator &I2, MachineBasicBlock *SuccBB,
     637             :                   MachineBasicBlock *PredBB,
     638             :                   DenseMap<const MachineBasicBlock *, int> &EHScopeMembership,
     639             :                   bool AfterPlacement) {
     640             :   // It is never profitable to tail-merge blocks from two different EH scopes.
     641      671765 :   if (!EHScopeMembership.empty()) {
     642          89 :     auto EHScope1 = EHScopeMembership.find(MBB1);
     643             :     assert(EHScope1 != EHScopeMembership.end());
     644          89 :     auto EHScope2 = EHScopeMembership.find(MBB2);
     645             :     assert(EHScope2 != EHScopeMembership.end());
     646          89 :     if (EHScope1->second != EHScope2->second)
     647          66 :       return false;
     648             :   }
     649             : 
     650      671699 :   CommonTailLen = ComputeCommonTailLength(MBB1, MBB2, I1, I2);
     651      671699 :   if (CommonTailLen == 0)
     652             :     return false;
     653             :   LLVM_DEBUG(dbgs() << "Common tail length of " << printMBBReference(*MBB1)
     654             :                     << " and " << printMBBReference(*MBB2) << " is "
     655             :                     << CommonTailLen << '\n');
     656             : 
     657             :   // It's almost always profitable to merge any number of non-terminator
     658             :   // instructions with the block that falls through into the common successor.
     659             :   // This is true only for a single successor. For multiple successors, we are
     660             :   // trading a conditional branch for an unconditional one.
     661             :   // TODO: Re-visit successor size for non-layout tail merging.
     662      402123 :   if ((MBB1 == PredBB || MBB2 == PredBB) &&
     663        1353 :       (!AfterPlacement || MBB1->succ_size() == 1)) {
     664             :     MachineBasicBlock::iterator I;
     665        4857 :     unsigned NumTerms = CountTerminators(MBB1 == PredBB ? MBB2 : MBB1, I);
     666        4857 :     if (CommonTailLen > NumTerms)
     667        4489 :       return true;
     668             :   }
     669             : 
     670             :   // If these are identical non-return blocks with no successors, merge them.
     671             :   // Such blocks are typically cold calls to noreturn functions like abort, and
     672             :   // are unlikely to become a fallthrough target after machine block placement.
     673             :   // Tail merging these blocks is unlikely to create additional unconditional
     674             :   // branches, and will reduce the size of this cold code.
     675      306761 :   if (I1 == MBB1->begin() && I2 == MBB2->begin() &&
     676      520213 :       blockEndsInUnreachable(MBB1) && blockEndsInUnreachable(MBB2))
     677             :     return true;
     678             : 
     679             :   // If one of the blocks can be completely merged and happens to be in
     680             :   // a position where the other could fall through into it, merge any number
     681             :   // of instructions, because it can be done without a branch.
     682             :   // TODO: If the blocks are not adjacent, move one of them so that they are?
     683      396664 :   if (MBB1->isLayoutSuccessor(MBB2) && I2 == MBB2->begin())
     684             :     return true;
     685      403947 :   if (MBB2->isLayoutSuccessor(MBB1) && I1 == MBB1->begin())
     686             :     return true;
     687             : 
     688             :   // If both blocks are identical and end in a branch, merge them unless they
     689             :   // both have a fallthrough predecessor and successor.
     690             :   // We can only do this after block placement because it depends on whether
     691             :   // there are fallthroughs, and we don't know until after layout.
     692      396840 :   if (AfterPlacement && I1 == MBB1->begin() && I2 == MBB2->begin()) {
     693         137 :     auto BothFallThrough = [](MachineBasicBlock *MBB) {
     694         137 :       if (MBB->succ_size() != 0 && !MBB->canFallThrough())
     695             :         return false;
     696             :       MachineFunction::iterator I(MBB);
     697           0 :       MachineFunction *MF = MBB->getParent();
     698           0 :       return (MBB != &*MF->begin()) && std::prev(I)->canFallThrough();
     699             :     };
     700         137 :     if (!BothFallThrough(MBB1) || !BothFallThrough(MBB2))
     701             :       return true;
     702             :   }
     703             : 
     704             :   // If both blocks have an unconditional branch temporarily stripped out,
     705             :   // count that as an additional common instruction for the following
     706             :   // heuristics. This heuristic is only accurate for single-succ blocks, so to
     707             :   // make sure that during layout merging and duplicating don't crash, we check
     708             :   // for that when merging during layout.
     709      393331 :   unsigned EffectiveTailLen = CommonTailLen;
     710      444889 :   if (SuccBB && MBB1 != PredBB && MBB2 != PredBB &&
     711       28354 :       (MBB1->succ_size() == 1 || !AfterPlacement) &&
     712      418524 :       !MBB1->back().isBarrier() &&
     713             :       !MBB2->back().isBarrier())
     714       25193 :     ++EffectiveTailLen;
     715             : 
     716             :   // Check if the common tail is long enough to be worthwhile.
     717      393331 :   if (EffectiveTailLen >= MinCommonTailLength)
     718             :     return true;
     719             : 
     720             :   // If we are optimizing for code size, 2 instructions in common is enough if
     721             :   // we don't have to split a block.  At worst we will be introducing 1 new
     722             :   // branch instruction, which is likely to be smaller than the 2
     723             :   // instructions that would be deleted in the merge.
     724      248998 :   MachineFunction *MF = MBB1->getParent();
     725      249064 :   return EffectiveTailLen >= 2 && MF->getFunction().optForSize() &&
     726          50 :          (I1 == MBB1->begin() || I2 == MBB2->begin());
     727             : }
     728             : 
     729      214627 : unsigned BranchFolder::ComputeSameTails(unsigned CurHash,
     730             :                                         unsigned MinCommonTailLength,
     731             :                                         MachineBasicBlock *SuccBB,
     732             :                                         MachineBasicBlock *PredBB) {
     733             :   unsigned maxCommonTailLength = 0U;
     734      214627 :   SameTails.clear();
     735             :   MachineBasicBlock::iterator TrialBBI1, TrialBBI2;
     736             :   MPIterator HighestMPIter = std::prev(MergePotentials.end());
     737             :   for (MPIterator CurMPIter = std::prev(MergePotentials.end()),
     738             :                   B = MergePotentials.begin();
     739      478656 :        CurMPIter != B && CurMPIter->getHash() == CurHash; --CurMPIter) {
     740      888647 :     for (MPIterator I = std::prev(CurMPIter); I->getHash() == CurHash; --I) {
     741             :       unsigned CommonTailLen;
     742      671765 :       if (ProfitableToMerge(CurMPIter->getBlock(), I->getBlock(),
     743             :                             MinCommonTailLength,
     744             :                             CommonTailLen, TrialBBI1, TrialBBI2,
     745             :                             SuccBB, PredBB,
     746             :                             EHScopeMembership,
     747      671765 :                             AfterBlockPlacement)) {
     748      153151 :         if (CommonTailLen > maxCommonTailLength) {
     749             :           SameTails.clear();
     750             :           maxCommonTailLength = CommonTailLen;
     751             :           HighestMPIter = CurMPIter;
     752        6119 :           SameTails.push_back(SameTailElt(CurMPIter, TrialBBI1));
     753             :         }
     754      169577 :         if (HighestMPIter == CurMPIter &&
     755       16426 :             CommonTailLen == maxCommonTailLength)
     756       14879 :           SameTails.push_back(SameTailElt(I, TrialBBI2));
     757             :       }
     758      671765 :       if (I == B)
     759             :         break;
     760             :     }
     761             :   }
     762      214627 :   return maxCommonTailLength;
     763             : }
     764             : 
     765      208972 : void BranchFolder::RemoveBlocksWithHash(unsigned CurHash,
     766             :                                         MachineBasicBlock *SuccBB,
     767             :                                         MachineBasicBlock *PredBB) {
     768             :   MPIterator CurMPIter, B;
     769             :   for (CurMPIter = std::prev(MergePotentials.end()),
     770             :       B = MergePotentials.begin();
     771      446844 :        CurMPIter->getHash() == CurHash; --CurMPIter) {
     772             :     // Put the unconditional branch back, if we need one.
     773      250780 :     MachineBasicBlock *CurMBB = CurMPIter->getBlock();
     774      250780 :     if (SuccBB && CurMBB != PredBB)
     775      128630 :       FixTail(CurMBB, SuccBB, TII);
     776      250780 :     if (CurMPIter == B)
     777             :       break;
     778             :   }
     779      208972 :   if (CurMPIter->getHash() != CurHash)
     780             :     CurMPIter++;
     781             :   MergePotentials.erase(CurMPIter, MergePotentials.end());
     782      208972 : }
     783             : 
     784        3474 : bool BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB,
     785             :                                              MachineBasicBlock *SuccBB,
     786             :                                              unsigned maxCommonTailLength,
     787             :                                              unsigned &commonTailIndex) {
     788        3474 :   commonTailIndex = 0;
     789             :   unsigned TimeEstimate = ~0U;
     790       15896 :   for (unsigned i = 0, e = SameTails.size(); i != e; ++i) {
     791             :     // Use PredBB if possible; that doesn't require a new branch.
     792       21318 :     if (SameTails[i].getBlock() == PredBB) {
     793        1711 :       commonTailIndex = i;
     794        1711 :       break;
     795             :     }
     796             :     // Otherwise, make a (fairly bogus) choice based on estimate of
     797             :     // how long it will take the various blocks to execute.
     798             :     unsigned t = EstimateRuntime(SameTails[i].getBlock()->begin(),
     799        8948 :                                  SameTails[i].getTailStartPos());
     800        8948 :     if (t <= TimeEstimate) {
     801             :       TimeEstimate = t;
     802        8637 :       commonTailIndex = i;
     803             :     }
     804             :   }
     805             : 
     806             :   MachineBasicBlock::iterator BBI =
     807        6948 :     SameTails[commonTailIndex].getTailStartPos();
     808             :   MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
     809             : 
     810             :   LLVM_DEBUG(dbgs() << "\nSplitting " << printMBBReference(*MBB) << ", size "
     811             :                     << maxCommonTailLength);
     812             : 
     813             :   // If the split block unconditionally falls-thru to SuccBB, it will be
     814             :   // merged. In control flow terms it should then take SuccBB's name. e.g. If
     815             :   // SuccBB is an inner loop, the common tail is still part of the inner loop.
     816        5612 :   const BasicBlock *BB = (SuccBB && MBB->succ_size() == 1) ?
     817             :     SuccBB->getBasicBlock() : MBB->getBasicBlock();
     818        3474 :   MachineBasicBlock *newMBB = SplitMBBAt(*MBB, BBI, BB);
     819        3474 :   if (!newMBB) {
     820             :     LLVM_DEBUG(dbgs() << "... failed!");
     821             :     return false;
     822             :   }
     823             : 
     824        3474 :   SameTails[commonTailIndex].setBlock(newMBB);
     825             :   SameTails[commonTailIndex].setTailStartPos(newMBB->begin());
     826             : 
     827             :   // If we split PredBB, newMBB is the new predecessor.
     828        3474 :   if (PredBB == MBB)
     829        1711 :     PredBB = newMBB;
     830             : 
     831             :   return true;
     832             : }
     833             : 
     834             : static void
     835       13400 : mergeOperations(MachineBasicBlock::iterator MBBIStartPos,
     836             :                 MachineBasicBlock &MBBCommon) {
     837       13400 :   MachineBasicBlock *MBB = MBBIStartPos->getParent();
     838             :   // Note CommonTailLen does not necessarily matches the size of
     839             :   // the common BB nor all its instructions because of debug
     840             :   // instructions differences.
     841             :   unsigned CommonTailLen = 0;
     842       77204 :   for (auto E = MBB->end(); MBBIStartPos != E; ++MBBIStartPos)
     843       63804 :     ++CommonTailLen;
     844             : 
     845       13400 :   MachineBasicBlock::reverse_iterator MBBI = MBB->rbegin();
     846             :   MachineBasicBlock::reverse_iterator MBBIE = MBB->rend();
     847       13400 :   MachineBasicBlock::reverse_iterator MBBICommon = MBBCommon.rbegin();
     848             :   MachineBasicBlock::reverse_iterator MBBIECommon = MBBCommon.rend();
     849             : 
     850       77204 :   while (CommonTailLen--) {
     851             :     assert(MBBI != MBBIE && "Reached BB end within common tail length!");
     852             :     (void)MBBIE;
     853             : 
     854        3153 :     if (!countsAsInstruction(*MBBI)) {
     855             :       ++MBBI;
     856        3153 :       continue;
     857             :     }
     858             : 
     859       63735 :     while ((MBBICommon != MBBIECommon) && !countsAsInstruction(*MBBICommon))
     860             :       ++MBBICommon;
     861             : 
     862             :     assert(MBBICommon != MBBIECommon &&
     863             :            "Reached BB end within common tail length!");
     864             :     assert(MBBICommon->isIdenticalTo(*MBBI) && "Expected matching MIIs!");
     865             : 
     866             :     // Merge MMOs from memory operations in the common block.
     867      110367 :     if (MBBICommon->mayLoad() || MBBICommon->mayStore())
     868       16338 :       MBBICommon->setMemRefs(MBBICommon->mergeMemRefsWith(*MBBI));
     869             :     // Drop undef flags if they aren't present in all merged instructions.
     870      382541 :     for (unsigned I = 0, E = MBBICommon->getNumOperands(); I != E; ++I) {
     871      321890 :       MachineOperand &MO = MBBICommon->getOperand(I);
     872      553814 :       if (MO.isReg() && MO.isUndef()) {
     873         223 :         const MachineOperand &OtherMO = MBBI->getOperand(I);
     874         223 :         if (!OtherMO.isUndef())
     875             :           MO.setIsUndef(false);
     876             :       }
     877             :     }
     878             : 
     879             :     ++MBBI;
     880             :     ++MBBICommon;
     881             :   }
     882       13400 : }
     883             : 
     884        5655 : void BranchFolder::mergeCommonTails(unsigned commonTailIndex) {
     885        5655 :   MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
     886             : 
     887       11310 :   std::vector<MachineBasicBlock::iterator> NextCommonInsts(SameTails.size());
     888       68475 :   for (unsigned int i = 0 ; i != SameTails.size() ; ++i) {
     889       19055 :     if (i != commonTailIndex) {
     890       26800 :       NextCommonInsts[i] = SameTails[i].getTailStartPos();
     891       13400 :       mergeOperations(SameTails[i].getTailStartPos(), *MBB);
     892             :     } else {
     893             :       assert(SameTails[i].getTailStartPos() == MBB->begin() &&
     894             :           "MBB is not a common tail only block");
     895             :     }
     896             :   }
     897             : 
     898       31294 :   for (auto &MI : *MBB) {
     899        1073 :     if (!countsAsInstruction(MI))
     900        1073 :       continue;
     901             :     DebugLoc DL = MI.getDebugLoc();
     902      276508 :     for (unsigned int i = 0 ; i < NextCommonInsts.size() ; i++) {
     903       79562 :       if (i == commonTailIndex)
     904       18911 :         continue;
     905             : 
     906             :       auto &Pos = NextCommonInsts[i];
     907             :       assert(Pos != SameTails[i].getBlock()->end() &&
     908             :           "Reached BB end within common tail");
     909             :       while (!countsAsInstruction(*Pos)) {
     910             :         ++Pos;
     911             :         assert(Pos != SameTails[i].getBlock()->end() &&
     912             :             "Reached BB end within common tail");
     913             :       }
     914             :       assert(MI.isIdenticalTo(*Pos) && "Expected matching MIIs!");
     915      121302 :       DL = DILocation::getMergedLocation(DL, Pos->getDebugLoc());
     916      121302 :       NextCommonInsts[i] = ++Pos;
     917             :     }
     918       18911 :     MI.setDebugLoc(DL);
     919             :   }
     920             : 
     921        5655 :   if (UpdateLiveIns) {
     922        5632 :     LivePhysRegs NewLiveIns(*TRI);
     923        5632 :     computeLiveIns(NewLiveIns, *MBB);
     924        5632 :     LiveRegs.init(*TRI);
     925             : 
     926             :     // The flag merging may lead to some register uses no longer using the
     927             :     // <undef> flag, add IMPLICIT_DEFs in the predecessors as necessary.
     928       12450 :     for (MachineBasicBlock *Pred : MBB->predecessors()) {
     929             :       LiveRegs.clear();
     930        6818 :       LiveRegs.addLiveOuts(*Pred);
     931        6818 :       MachineBasicBlock::iterator InsertBefore = Pred->getFirstTerminator();
     932      193906 :       for (unsigned Reg : NewLiveIns) {
     933       93544 :         if (!LiveRegs.available(*MRI, Reg))
     934       93507 :           continue;
     935          37 :         DebugLoc DL;
     936          74 :         BuildMI(*Pred, InsertBefore, DL, TII->get(TargetOpcode::IMPLICIT_DEF),
     937          37 :                 Reg);
     938             :       }
     939             :     }
     940             : 
     941        5632 :     MBB->clearLiveIns();
     942        5632 :     addLiveIns(*MBB, NewLiveIns);
     943             :   }
     944        5655 : }
     945             : 
     946             : // See if any of the blocks in MergePotentials (which all have SuccBB as a
     947             : // successor, or all have no successor if it is null) can be tail-merged.
     948             : // If there is a successor, any blocks in MergePotentials that are not
     949             : // tail-merged and are not immediately before Succ must have an unconditional
     950             : // branch to Succ added (but the predecessor/successor lists need no
     951             : // adjustment). The lone predecessor of Succ that falls through into Succ,
     952             : // if any, is given in PredBB.
     953             : // MinCommonTailLength - Except for the special cases below, tail-merge if
     954             : // there are at least this many instructions in common.
     955      174181 : bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB,
     956             :                                       MachineBasicBlock *PredBB,
     957             :                                       unsigned MinCommonTailLength) {
     958             :   bool MadeChange = false;
     959             : 
     960             :   LLVM_DEBUG(
     961             :       dbgs() << "\nTryTailMergeBlocks: ";
     962             :       for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i) dbgs()
     963             :       << printMBBReference(*MergePotentials[i].getBlock())
     964             :       << (i == e - 1 ? "" : ", ");
     965             :       dbgs() << "\n"; if (SuccBB) {
     966             :         dbgs() << "  with successor " << printMBBReference(*SuccBB) << '\n';
     967             :         if (PredBB)
     968             :           dbgs() << "  which has fall-through from "
     969             :                  << printMBBReference(*PredBB) << "\n";
     970             :       } dbgs() << "Looking for common tails of at least "
     971             :                << MinCommonTailLength << " instruction"
     972             :                << (MinCommonTailLength == 1 ? "" : "s") << '\n';);
     973             : 
     974             :   // Sort by hash value so that blocks with identical end sequences sort
     975             :   // together.
     976             :   array_pod_sort(MergePotentials.begin(), MergePotentials.end());
     977             : 
     978             :   // Walk through equivalence sets looking for actual exact matches.
     979      777616 :   while (MergePotentials.size() > 1) {
     980      214627 :     unsigned CurHash = MergePotentials.back().getHash();
     981             : 
     982             :     // Build SameTails, identifying the set of blocks with this hash code
     983             :     // and with the maximum number of instructions in common.
     984      214627 :     unsigned maxCommonTailLength = ComputeSameTails(CurHash,
     985             :                                                     MinCommonTailLength,
     986      214627 :                                                     SuccBB, PredBB);
     987             : 
     988             :     // If we didn't find any pair that has at least MinCommonTailLength
     989             :     // instructions in common, remove all blocks with this hash code and retry.
     990      423599 :     if (SameTails.empty()) {
     991      208972 :       RemoveBlocksWithHash(CurHash, SuccBB, PredBB);
     992      417944 :       continue;
     993             :     }
     994             : 
     995             :     // If one of the blocks is the entire common tail (and not the entry
     996             :     // block, which we can't jump to), we can treat all blocks with this same
     997             :     // tail at once.  Use PredBB if that is one of the possibilities, as that
     998             :     // will not introduce any extra branches.
     999             :     MachineBasicBlock *EntryBB =
    1000        5655 :         &MergePotentials.front().getBlock()->getParent()->front();
    1001        5655 :     unsigned commonTailIndex = SameTails.size();
    1002             :     // If there are two blocks, check to see if one can be made to fall through
    1003             :     // into the other.
    1004        4428 :     if (SameTails.size() == 2 &&
    1005       10137 :         SameTails[0].getBlock()->isLayoutSuccessor(SameTails[1].getBlock()) &&
    1006          54 :         SameTails[1].tailIsWholeBlock())
    1007          21 :       commonTailIndex = 1;
    1008       10041 :     else if (SameTails.size() == 2 &&
    1009        4407 :              SameTails[1].getBlock()->isLayoutSuccessor(
    1010        7337 :                                                      SameTails[0].getBlock()) &&
    1011        1703 :              SameTails[0].tailIsWholeBlock())
    1012         685 :       commonTailIndex = 0;
    1013             :     else {
    1014             :       // Otherwise just pick one, favoring the fall-through predecessor if
    1015             :       // there is one.
    1016       41619 :       for (unsigned i = 0, e = SameTails.size(); i != e; ++i) {
    1017       15884 :         MachineBasicBlock *MBB = SameTails[i].getBlock();
    1018       15902 :         if (MBB == EntryBB && SameTails[i].tailIsWholeBlock())
    1019           2 :           continue;
    1020       15882 :         if (MBB == PredBB) {
    1021        2498 :           commonTailIndex = i;
    1022        2498 :           break;
    1023             :         }
    1024       13384 :         if (SameTails[i].tailIsWholeBlock())
    1025        3996 :           commonTailIndex = i;
    1026             :       }
    1027             :     }
    1028             : 
    1029       15201 :     if (commonTailIndex == SameTails.size() ||
    1030        6423 :         (SameTails[commonTailIndex].getBlock() == PredBB &&
    1031             :          !SameTails[commonTailIndex].tailIsWholeBlock())) {
    1032             :       // None of the blocks consist entirely of the common tail.
    1033             :       // Split a block so that one does.
    1034        3474 :       if (!CreateCommonTailOnlyBlock(PredBB, SuccBB,
    1035             :                                      maxCommonTailLength, commonTailIndex)) {
    1036           0 :         RemoveBlocksWithHash(CurHash, SuccBB, PredBB);
    1037           0 :         continue;
    1038             :       }
    1039             :     }
    1040             : 
    1041        5655 :     MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
    1042             : 
    1043             :     // Recompute common tail MBB's edge weights and block frequency.
    1044        5655 :     setCommonTailEdgeWeights(*MBB);
    1045             : 
    1046             :     // Merge debug locations, MMOs and undef flags across identical instructions
    1047             :     // for common tail.
    1048        5655 :     mergeCommonTails(commonTailIndex);
    1049             : 
    1050             :     // MBB is common tail.  Adjust all other BB's to jump to this one.
    1051             :     // Traversal must be forwards so erases work.
    1052             :     LLVM_DEBUG(dbgs() << "\nUsing common tail in " << printMBBReference(*MBB)
    1053             :                       << " for ");
    1054       30365 :     for (unsigned int i=0, e = SameTails.size(); i != e; ++i) {
    1055       19055 :       if (commonTailIndex == i)
    1056        5655 :         continue;
    1057             :       LLVM_DEBUG(dbgs() << printMBBReference(*SameTails[i].getBlock())
    1058             :                         << (i == e - 1 ? "" : ", "));
    1059             :       // Hack the end off BB i, making it jump to BB commonTailIndex instead.
    1060       26800 :       replaceTailWithBranchTo(SameTails[i].getTailStartPos(), *MBB);
    1061             :       // BB i is no longer a predecessor of SuccBB; remove it from the worklist.
    1062       13400 :       MergePotentials.erase(SameTails[i].getMPIter());
    1063             :     }
    1064             :     LLVM_DEBUG(dbgs() << "\n");
    1065             :     // We leave commonTailIndex in the worklist in case there are other blocks
    1066             :     // that match it with a smaller number of instructions.
    1067             :     MadeChange = true;
    1068             :   }
    1069      174181 :   return MadeChange;
    1070             : }
    1071             : 
    1072      235555 : bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
    1073             :   bool MadeChange = false;
    1074      235555 :   if (!EnableTailMerge) return MadeChange;
    1075             : 
    1076             :   // First find blocks with no successors.
    1077             :   // Block placement does not create new tail merging opportunities for these
    1078             :   // blocks.
    1079      216351 :   if (!AfterBlockPlacement) {
    1080      209148 :     MergePotentials.clear();
    1081      846820 :     for (MachineBasicBlock &MBB : MF) {
    1082     1275354 :       if (MergePotentials.size() == TailMergeThreshold)
    1083             :         break;
    1084     1273441 :       if (!TriedMerging.count(&MBB) && MBB.succ_empty())
    1085      466960 :         MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(MBB), &MBB));
    1086             :     }
    1087             : 
    1088             :     // If this is a large problem, avoid visiting the same basic blocks
    1089             :     // multiple times.
    1090      418296 :     if (MergePotentials.size() == TailMergeThreshold)
    1091         755 :       for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
    1092        1500 :         TriedMerging.insert(MergePotentials[i].getBlock());
    1093             : 
    1094             :     // See if we can do any tail merging on those.
    1095      418296 :     if (MergePotentials.size() >= 2)
    1096       11012 :       MadeChange |= TryTailMergeBlocks(nullptr, nullptr, MinCommonTailLength);
    1097             :   }
    1098             : 
    1099             :   // Look at blocks (IBB) with multiple predecessors (PBB).
    1100             :   // We change each predecessor to a canonical form, by
    1101             :   // (1) temporarily removing any unconditional branch from the predecessor
    1102             :   // to IBB, and
    1103             :   // (2) alter conditional branches so they branch to the other block
    1104             :   // not IBB; this may require adding back an unconditional branch to IBB
    1105             :   // later, where there wasn't one coming in.  E.g.
    1106             :   //   Bcc IBB
    1107             :   //   fallthrough to QBB
    1108             :   // here becomes
    1109             :   //   Bncc QBB
    1110             :   // with a conceptual B to IBB after that, which never actually exists.
    1111             :   // With those changes, we see whether the predecessors' tails match,
    1112             :   // and merge them if so.  We change things out of canonical form and
    1113             :   // back to the way they were later in the process.  (OptimizeBranches
    1114             :   // would undo some of this, but we can't use it, because we'd get into
    1115             :   // a compile-time infinite loop repeatedly doing and undoing the same
    1116             :   // transformations.)
    1117             : 
    1118             :   for (MachineFunction::iterator I = std::next(MF.begin()), E = MF.end();
    1119      835657 :        I != E; ++I) {
    1120     1049222 :     if (I->pred_size() < 2) continue;
    1121             :     SmallPtrSet<MachineBasicBlock *, 8> UniquePreds;
    1122             :     MachineBasicBlock *IBB = &*I;
    1123             :     MachineBasicBlock *PredBB = &*std::prev(I);
    1124      194999 :     MergePotentials.clear();
    1125             :     MachineLoop *ML;
    1126             : 
    1127             :     // Bail if merging after placement and IBB is the loop header because
    1128             :     // -- If merging predecessors that belong to the same loop as IBB, the
    1129             :     // common tail of merged predecessors may become the loop top if block
    1130             :     // placement is called again and the predecessors may branch to this common
    1131             :     // tail and require more branches. This can be relaxed if
    1132             :     // MachineBlockPlacement::findBestLoopTop is more flexible.
    1133             :     // --If merging predecessors that do not belong to the same loop as IBB, the
    1134             :     // loop info of IBB's loop and the other loops may be affected. Calling the
    1135             :     // block placement again may make big change to the layout and eliminate the
    1136             :     // reason to do tail merging here.
    1137      194999 :     if (AfterBlockPlacement && MLI) {
    1138             :       ML = MLI->getLoopFor(IBB);
    1139       24612 :       if (ML && IBB == ML->getHeader())
    1140             :         continue;
    1141             :     }
    1142             : 
    1143      647299 :     for (MachineBasicBlock *PBB : I->predecessors()) {
    1144      915826 :       if (MergePotentials.size() == TailMergeThreshold)
    1145             :         break;
    1146             : 
    1147      457909 :       if (TriedMerging.count(PBB))
    1148       54922 :         continue;
    1149             : 
    1150             :       // Skip blocks that loop to themselves, can't tail merge these.
    1151      455688 :       if (PBB == IBB)
    1152        8644 :         continue;
    1153             : 
    1154             :       // Visit each predecessor only once.
    1155      447044 :       if (!UniquePreds.insert(PBB).second)
    1156           0 :         continue;
    1157             : 
    1158             :       // Skip blocks which may jump to a landing pad. Can't tail merge these.
    1159      447044 :       if (PBB->hasEHPadSuccessor())
    1160       39084 :         continue;
    1161             : 
    1162             :       // After block placement, only consider predecessors that belong to the
    1163             :       // same loop as IBB.  The reason is the same as above when skipping loop
    1164             :       // header.
    1165      407960 :       if (AfterBlockPlacement && MLI)
    1166      118001 :         if (ML != MLI->getLoopFor(PBB))
    1167        2684 :           continue;
    1168             : 
    1169      405276 :       MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
    1170             :       SmallVector<MachineOperand, 4> Cond;
    1171      405276 :       if (!TII->analyzeBranch(*PBB, TBB, FBB, Cond, true)) {
    1172             :         // Failing case: IBB is the target of a cbr, and we cannot reverse the
    1173             :         // branch.
    1174             :         SmallVector<MachineOperand, 4> NewCond(Cond);
    1175      402293 :         if (!Cond.empty() && TBB == IBB) {
    1176      105953 :           if (TII->reverseBranchCondition(NewCond))
    1177          68 :             continue;
    1178             :           // This is the QBB case described above
    1179      105885 :           if (!FBB) {
    1180      100685 :             auto Next = ++PBB->getIterator();
    1181      100685 :             if (Next != MF.end())
    1182      100685 :               FBB = &*Next;
    1183             :           }
    1184             :         }
    1185             : 
    1186             :         // Failing case: the only way IBB can be reached from PBB is via
    1187             :         // exception handling.  Happens for landing pads.  Would be nice to have
    1188             :         // a bit in the edge so we didn't have to do all this.
    1189      402225 :         if (IBB->isEHPad()) {
    1190           0 :           MachineFunction::iterator IP = ++PBB->getIterator();
    1191             :           MachineBasicBlock *PredNextBB = nullptr;
    1192           0 :           if (IP != MF.end())
    1193             :             PredNextBB = &*IP;
    1194           0 :           if (!TBB) {
    1195           0 :             if (IBB != PredNextBB)      // fallthrough
    1196           0 :               continue;
    1197           0 :           } else if (FBB) {
    1198           0 :             if (TBB != IBB && FBB != IBB)   // cbr then ubr
    1199           0 :               continue;
    1200           0 :           } else if (Cond.empty()) {
    1201           0 :             if (TBB != IBB)               // ubr
    1202           0 :               continue;
    1203             :           } else {
    1204           0 :             if (TBB != IBB && IBB != PredNextBB)  // cbr
    1205           0 :               continue;
    1206             :           }
    1207             :         }
    1208             : 
    1209             :         // Remove the unconditional branch at the end, if any.
    1210      402225 :         if (TBB && (Cond.empty() || FBB)) {
    1211      241088 :           DebugLoc dl = PBB->findBranchDebugLoc();
    1212      241088 :           TII->removeBranch(*PBB);
    1213      241088 :           if (!Cond.empty())
    1214             :             // reinsert conditional branch only, for now
    1215      217140 :             TII->insertBranch(*PBB, (TBB == IBB) ? FBB : TBB, nullptr,
    1216      108570 :                               NewCond, dl);
    1217             :         }
    1218             : 
    1219      804450 :         MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(*PBB), PBB));
    1220             :       }
    1221             :     }
    1222             : 
    1223             :     // If this is a large problem, avoid visiting the same basic blocks multiple
    1224             :     // times.
    1225      378780 :     if (MergePotentials.size() == TailMergeThreshold)
    1226         308 :       for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
    1227         608 :         TriedMerging.insert(MergePotentials[i].getBlock());
    1228             : 
    1229      378780 :     if (MergePotentials.size() >= 2)
    1230      163169 :       MadeChange |= TryTailMergeBlocks(IBB, PredBB, MinCommonTailLength);
    1231             : 
    1232             :     // Reinsert an unconditional branch if needed. The 1 below can occur as a
    1233             :     // result of removing blocks in TryTailMergeBlocks.
    1234             :     PredBB = &*std::prev(I); // this may have been changed in TryTailMergeBlocks
    1235      543576 :     if (MergePotentials.size() == 1 &&
    1236      164796 :         MergePotentials.begin()->getBlock() != PredBB)
    1237      106046 :       FixTail(MergePotentials.begin()->getBlock(), IBB, TII);
    1238             :   }
    1239             : 
    1240             :   return MadeChange;
    1241             : }
    1242             : 
    1243        5655 : void BranchFolder::setCommonTailEdgeWeights(MachineBasicBlock &TailMBB) {
    1244       11310 :   SmallVector<BlockFrequency, 2> EdgeFreqLs(TailMBB.succ_size());
    1245             :   BlockFrequency AccumulatedMBBFreq;
    1246             : 
    1247             :   // Aggregate edge frequency of successor edge j:
    1248             :   //  edgeFreq(j) = sum (freq(bb) * edgeProb(bb, j)),
    1249             :   //  where bb is a basic block that is in SameTails.
    1250       24710 :   for (const auto &Src : SameTails) {
    1251             :     const MachineBasicBlock *SrcMBB = Src.getBlock();
    1252       19055 :     BlockFrequency BlockFreq = MBBFreqInfo.getBlockFreq(SrcMBB);
    1253       19055 :     AccumulatedMBBFreq += BlockFreq;
    1254             : 
    1255             :     // It is not necessary to recompute edge weights if TailBB has less than two
    1256             :     // successors.
    1257       19055 :     if (TailMBB.succ_size() <= 1)
    1258       17703 :       continue;
    1259             : 
    1260             :     auto EdgeFreq = EdgeFreqLs.begin();
    1261             : 
    1262        2704 :     for (auto SuccI = TailMBB.succ_begin(), SuccE = TailMBB.succ_end();
    1263        4056 :          SuccI != SuccE; ++SuccI, ++EdgeFreq)
    1264        2704 :       *EdgeFreq += BlockFreq * MBPI.getEdgeProbability(SrcMBB, *SuccI);
    1265             :   }
    1266             : 
    1267        5655 :   MBBFreqInfo.setBlockFreq(&TailMBB, AccumulatedMBBFreq);
    1268             : 
    1269        5655 :   if (TailMBB.succ_size() <= 1)
    1270             :     return;
    1271             : 
    1272             :   auto SumEdgeFreq =
    1273             :       std::accumulate(EdgeFreqLs.begin(), EdgeFreqLs.end(), BlockFrequency(0))
    1274             :           .getFrequency();
    1275             :   auto EdgeFreq = EdgeFreqLs.begin();
    1276             : 
    1277         412 :   if (SumEdgeFreq > 0) {
    1278         824 :     for (auto SuccI = TailMBB.succ_begin(), SuccE = TailMBB.succ_end();
    1279        1236 :          SuccI != SuccE; ++SuccI, ++EdgeFreq) {
    1280             :       auto Prob = BranchProbability::getBranchProbability(
    1281         824 :           EdgeFreq->getFrequency(), SumEdgeFreq);
    1282         824 :       TailMBB.setSuccProbability(SuccI, Prob);
    1283             :     }
    1284             :   }
    1285             : }
    1286             : 
    1287             : //===----------------------------------------------------------------------===//
    1288             : //  Branch Optimization
    1289             : //===----------------------------------------------------------------------===//
    1290             : 
    1291      228741 : bool BranchFolder::OptimizeBranches(MachineFunction &MF) {
    1292             :   bool MadeChange = false;
    1293             : 
    1294             :   // Make sure blocks are numbered in order
    1295      228741 :   MF.RenumberBlocks();
    1296             :   // Renumbering blocks alters EH scope membership, recalculate it.
    1297      457482 :   EHScopeMembership = getEHScopeMembership(MF);
    1298             : 
    1299             :   for (MachineFunction::iterator I = std::next(MF.begin()), E = MF.end();
    1300      733639 :        I != E; ) {
    1301             :     MachineBasicBlock *MBB = &*I++;
    1302      504898 :     MadeChange |= OptimizeBlock(MBB);
    1303             : 
    1304             :     // If it is dead, remove it.
    1305      504898 :     if (MBB->pred_empty()) {
    1306       11783 :       RemoveDeadBlock(MBB);
    1307             :       MadeChange = true;
    1308             :       ++NumDeadBlocks;
    1309             :     }
    1310             :   }
    1311             : 
    1312      228741 :   return MadeChange;
    1313             : }
    1314             : 
    1315             : // Blocks should be considered empty if they contain only debug info;
    1316             : // else the debug info would affect codegen.
    1317             : static bool IsEmptyBlock(MachineBasicBlock *MBB) {
    1318     2136510 :   return MBB->getFirstNonDebugInstr() == MBB->end();
    1319             : }
    1320             : 
    1321             : // Blocks with only debug info and branches should be considered the same
    1322             : // as blocks with only branches.
    1323      139373 : static bool IsBranchOnlyBlock(MachineBasicBlock *MBB) {
    1324      139373 :   MachineBasicBlock::iterator I = MBB->getFirstNonDebugInstr();
    1325             :   assert(I != MBB->end() && "empty block!");
    1326      139373 :   return I->isBranch();
    1327             : }
    1328             : 
    1329             : /// IsBetterFallthrough - Return true if it would be clearly better to
    1330             : /// fall-through to MBB1 than to fall through into MBB2.  This has to return
    1331             : /// a strict ordering, returning true for both (MBB1,MBB2) and (MBB2,MBB1) will
    1332             : /// result in infinite loops.
    1333        4276 : static bool IsBetterFallthrough(MachineBasicBlock *MBB1,
    1334             :                                 MachineBasicBlock *MBB2) {
    1335             :   // Right now, we use a simple heuristic.  If MBB2 ends with a call, and
    1336             :   // MBB1 doesn't, we prefer to fall through into MBB1.  This allows us to
    1337             :   // optimize branches that branch to either a return block or an assert block
    1338             :   // into a fallthrough to the return.
    1339        4276 :   MachineBasicBlock::iterator MBB1I = MBB1->getLastNonDebugInstr();
    1340        4276 :   MachineBasicBlock::iterator MBB2I = MBB2->getLastNonDebugInstr();
    1341        8541 :   if (MBB1I == MBB1->end() || MBB2I == MBB2->end())
    1342             :     return false;
    1343             : 
    1344             :   // If there is a clear successor ordering we make sure that one block
    1345             :   // will fall through to the next
    1346        4265 :   if (MBB1->isSuccessor(MBB2)) return true;
    1347        4230 :   if (MBB2->isSuccessor(MBB1)) return false;
    1348             : 
    1349        5020 :   return MBB2I->isCall() && !MBB1I->isCall();
    1350             : }
    1351             : 
    1352             : /// getBranchDebugLoc - Find and return, if any, the DebugLoc of the branch
    1353             : /// instructions on the block.
    1354       15871 : static DebugLoc getBranchDebugLoc(MachineBasicBlock &MBB) {
    1355       15871 :   MachineBasicBlock::iterator I = MBB.getLastNonDebugInstr();
    1356       31742 :   if (I != MBB.end() && I->isBranch())
    1357             :     return I->getDebugLoc();
    1358        2176 :   return DebugLoc();
    1359             : }
    1360             : 
    1361         322 : static void copyDebugInfoToPredecessor(const TargetInstrInfo *TII,
    1362             :                                        MachineBasicBlock &MBB,
    1363             :                                        MachineBasicBlock &PredMBB) {
    1364         322 :   auto InsertBefore = PredMBB.getFirstTerminator();
    1365         326 :   for (MachineInstr &MI : MBB.instrs())
    1366           4 :     if (MI.isDebugValue()) {
    1367           4 :       TII->duplicate(PredMBB, InsertBefore, MI);
    1368             :       LLVM_DEBUG(dbgs() << "Copied debug value from empty block to pred: "
    1369             :                         << MI);
    1370             :     }
    1371         322 : }
    1372             : 
    1373         117 : static void copyDebugInfoToSuccessor(const TargetInstrInfo *TII,
    1374             :                                      MachineBasicBlock &MBB,
    1375             :                                      MachineBasicBlock &SuccMBB) {
    1376         117 :   auto InsertBefore = SuccMBB.SkipPHIsAndLabels(SuccMBB.begin());
    1377         117 :   for (MachineInstr &MI : MBB.instrs())
    1378           0 :     if (MI.isDebugValue()) {
    1379           0 :       TII->duplicate(SuccMBB, InsertBefore, MI);
    1380             :       LLVM_DEBUG(dbgs() << "Copied debug value from empty block to succ: "
    1381             :                         << MI);
    1382             :     }
    1383         117 : }
    1384             : 
    1385             : // Try to salvage DBG_VALUE instructions from an otherwise empty block. If such
    1386             : // a basic block is removed we would lose the debug information unless we have
    1387             : // copied the information to a predecessor/successor.
    1388             : //
    1389             : // TODO: This function only handles some simple cases. An alternative would be
    1390             : // to run a heavier analysis, such as the LiveDebugValues pass, before we do
    1391             : // branch folding.
    1392        4631 : static void salvageDebugInfoFromEmptyBlock(const TargetInstrInfo *TII,
    1393             :                                            MachineBasicBlock &MBB) {
    1394             :   assert(IsEmptyBlock(&MBB) && "Expected an empty block (except debug info).");
    1395             :   // If this MBB is the only predecessor of a successor it is legal to copy
    1396             :   // DBG_VALUE instructions to the beginning of the successor.
    1397        6470 :   for (MachineBasicBlock *SuccBB : MBB.successors())
    1398        1839 :     if (SuccBB->pred_size() == 1)
    1399         117 :       copyDebugInfoToSuccessor(TII, MBB, *SuccBB);
    1400             :   // If this MBB is the only successor of a predecessor it is legal to copy the
    1401             :   // DBG_VALUE instructions to the end of the predecessor (just before the
    1402             :   // terminators, assuming that the terminator isn't affecting the DBG_VALUE).
    1403        8984 :   for (MachineBasicBlock *PredBB : MBB.predecessors())
    1404        4353 :     if (PredBB->succ_size() == 1)
    1405         322 :       copyDebugInfoToPredecessor(TII, MBB, *PredBB);
    1406        4631 : }
    1407             : 
    1408      504898 : bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
    1409             :   bool MadeChange = false;
    1410      504898 :   MachineFunction &MF = *MBB->getParent();
    1411      538738 : ReoptimizeBlock:
    1412             : 
    1413      538738 :   MachineFunction::iterator FallThrough = MBB->getIterator();
    1414             :   ++FallThrough;
    1415             : 
    1416             :   // Make sure MBB and FallThrough belong to the same EH scope.
    1417             :   bool SameEHScope = true;
    1418      539399 :   if (!EHScopeMembership.empty() && FallThrough != MF.end()) {
    1419         539 :     auto MBBEHScope = EHScopeMembership.find(MBB);
    1420             :     assert(MBBEHScope != EHScopeMembership.end());
    1421         539 :     auto FallThroughEHScope = EHScopeMembership.find(&*FallThrough);
    1422             :     assert(FallThroughEHScope != EHScopeMembership.end());
    1423         539 :     SameEHScope = MBBEHScope->second == FallThroughEHScope->second;
    1424             :   }
    1425             : 
    1426             :   // If this block is empty, make everyone use its fall-through, not the block
    1427             :   // explicitly.  Landing pads should not do this since the landing-pad table
    1428             :   // points to this block.  Blocks with their addresses taken shouldn't be
    1429             :   // optimized away.
    1430      538738 :   if (IsEmptyBlock(MBB) && !MBB->isEHPad() && !MBB->hasAddressTaken() &&
    1431             :       SameEHScope) {
    1432        4631 :     salvageDebugInfoFromEmptyBlock(TII, *MBB);
    1433             :     // Dead block?  Leave for cleanup later.
    1434        4631 :     if (MBB->pred_empty()) return MadeChange;
    1435             : 
    1436        3836 :     if (FallThrough == MF.end()) {
    1437             :       // TODO: Simplify preds to not branch here if possible!
    1438        3630 :     } else if (FallThrough->isEHPad()) {
    1439             :       // Don't rewrite to a landing pad fallthough.  That could lead to the case
    1440             :       // where a BB jumps to more than one landing pad.
    1441             :       // TODO: Is it ever worth rewriting predecessors which don't already
    1442             :       // jump to a landing pad, and so can safely jump to the fallthrough?
    1443        3525 :     } else if (MBB->isSuccessor(&*FallThrough)) {
    1444             :       // Rewrite all predecessors of the old block to go to the fallthrough
    1445             :       // instead.
    1446        6187 :       while (!MBB->pred_empty()) {
    1447        2174 :         MachineBasicBlock *Pred = *(MBB->pred_end()-1);
    1448        2174 :         Pred->ReplaceUsesOfBlockWith(MBB, &*FallThrough);
    1449             :       }
    1450             :       // If MBB was the target of a jump table, update jump tables to go to the
    1451             :       // fallthrough instead.
    1452        1839 :       if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo())
    1453         232 :         MJTI->ReplaceMBBInJumpTables(MBB, &*FallThrough);
    1454             :       MadeChange = true;
    1455             :     }
    1456             :     return MadeChange;
    1457             :   }
    1458             : 
    1459             :   // Check to see if we can simplify the terminator of the block before this
    1460             :   // one.
    1461             :   MachineBasicBlock &PrevBB = *std::prev(MachineFunction::iterator(MBB));
    1462             : 
    1463      534107 :   MachineBasicBlock *PriorTBB = nullptr, *PriorFBB = nullptr;
    1464             :   SmallVector<MachineOperand, 4> PriorCond;
    1465             :   bool PriorUnAnalyzable =
    1466      534107 :       TII->analyzeBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, true);
    1467      534107 :   if (!PriorUnAnalyzable) {
    1468             :     // If the CFG for the prior block has extra edges, remove them.
    1469      516849 :     MadeChange |= PrevBB.CorrectExtraCFGEdges(PriorTBB, PriorFBB,
    1470      516849 :                                               !PriorCond.empty());
    1471             : 
    1472             :     // If the previous branch is conditional and both conditions go to the same
    1473             :     // destination, remove the branch, replacing it with an unconditional one or
    1474             :     // a fall-through.
    1475      516849 :     if (PriorTBB && PriorTBB == PriorFBB) {
    1476          14 :       DebugLoc dl = getBranchDebugLoc(PrevBB);
    1477          14 :       TII->removeBranch(PrevBB);
    1478             :       PriorCond.clear();
    1479          14 :       if (PriorTBB != MBB)
    1480           6 :         TII->insertBranch(PrevBB, PriorTBB, nullptr, PriorCond, dl);
    1481             :       MadeChange = true;
    1482             :       ++NumBranchOpts;
    1483             :       goto ReoptimizeBlock;
    1484             :     }
    1485             : 
    1486             :     // If the previous block unconditionally falls through to this block and
    1487             :     // this block has no other predecessors, move the contents of this block
    1488             :     // into the prior block. This doesn't usually happen when SimplifyCFG
    1489             :     // has been used, but it can happen if tail merging splits a fall-through
    1490             :     // predecessor of a block.
    1491             :     // This has to check PrevBB->succ_size() because EH edges are ignored by
    1492             :     // AnalyzeBranch.
    1493     1213913 :     if (PriorCond.empty() && !PriorTBB && MBB->pred_size() == 1 &&
    1494        3862 :         PrevBB.succ_size() == 1 &&
    1495      524489 :         !MBB->hasAddressTaken() && !MBB->isEHPad()) {
    1496             :       LLVM_DEBUG(dbgs() << "\nMerging into block: " << PrevBB
    1497             :                         << "From MBB: " << *MBB);
    1498             :       // Remove redundant DBG_VALUEs first.
    1499        3792 :       if (PrevBB.begin() != PrevBB.end()) {
    1500        3638 :         MachineBasicBlock::iterator PrevBBIter = PrevBB.end();
    1501             :         --PrevBBIter;
    1502        3638 :         MachineBasicBlock::iterator MBBIter = MBB->begin();
    1503             :         // Check if DBG_VALUE at the end of PrevBB is identical to the
    1504             :         // DBG_VALUE at the beginning of MBB.
    1505        1901 :         while (PrevBBIter != PrevBB.begin() && MBBIter != MBB->end()
    1506        3639 :                && PrevBBIter->isDebugInstr() && MBBIter->isDebugInstr()) {
    1507           1 :           if (!MBBIter->isIdenticalTo(*PrevBBIter))
    1508             :             break;
    1509             :           MachineInstr &DuplicateDbg = *MBBIter;
    1510             :           ++MBBIter; -- PrevBBIter;
    1511           1 :           DuplicateDbg.eraseFromParent();
    1512             :         }
    1513             :       }
    1514             :       PrevBB.splice(PrevBB.end(), MBB, MBB->begin(), MBB->end());
    1515        3792 :       PrevBB.removeSuccessor(PrevBB.succ_begin());
    1516             :       assert(PrevBB.succ_empty());
    1517        3792 :       PrevBB.transferSuccessors(MBB);
    1518             :       MadeChange = true;
    1519        3792 :       return MadeChange;
    1520             :     }
    1521             : 
    1522             :     // If the previous branch *only* branches to *this* block (conditional or
    1523             :     // not) remove the branch.
    1524      514422 :     if (PriorTBB == MBB && !PriorFBB) {
    1525         678 :       TII->removeBranch(PrevBB);
    1526             :       MadeChange = true;
    1527             :       ++NumBranchOpts;
    1528             :       goto ReoptimizeBlock;
    1529             :     }
    1530             : 
    1531             :     // If the prior block branches somewhere else on the condition and here if
    1532             :     // the condition is false, remove the uncond second branch.
    1533      512365 :     if (PriorFBB == MBB) {
    1534        2425 :       DebugLoc dl = getBranchDebugLoc(PrevBB);
    1535        2425 :       TII->removeBranch(PrevBB);
    1536        4850 :       TII->insertBranch(PrevBB, PriorTBB, nullptr, PriorCond, dl);
    1537             :       MadeChange = true;
    1538             :       ++NumBranchOpts;
    1539             :       goto ReoptimizeBlock;
    1540             :     }
    1541             : 
    1542             :     // If the prior block branches here on true and somewhere else on false, and
    1543             :     // if the branch condition is reversible, reverse the branch to create a
    1544             :     // fall-through.
    1545      509940 :     if (PriorTBB == MBB) {
    1546             :       SmallVector<MachineOperand, 4> NewPriorCond(PriorCond);
    1547         701 :       if (!TII->reverseBranchCondition(NewPriorCond)) {
    1548         697 :         DebugLoc dl = getBranchDebugLoc(PrevBB);
    1549         697 :         TII->removeBranch(PrevBB);
    1550        1394 :         TII->insertBranch(PrevBB, PriorFBB, nullptr, NewPriorCond, dl);
    1551             :         MadeChange = true;
    1552             :         ++NumBranchOpts;
    1553             :         goto ReoptimizeBlock;
    1554             :       }
    1555             :     }
    1556             : 
    1557             :     // If this block has no successors (e.g. it is a return block or ends with
    1558             :     // a call to a no-return function like abort or __cxa_throw) and if the pred
    1559             :     // falls through into this block, and if it would otherwise fall through
    1560             :     // into the block after this, move this block to the end of the function.
    1561             :     //
    1562             :     // We consider it more likely that execution will stay in the function (e.g.
    1563             :     // due to loops) than it is to exit it.  This asserts in loops etc, moving
    1564             :     // the assert condition out of the loop body.
    1565       57235 :     if (MBB->succ_empty() && !PriorCond.empty() && !PriorFBB &&
    1566      529945 :         MachineFunction::iterator(PriorTBB) == FallThrough &&
    1567        5949 :         !MBB->canFallThrough()) {
    1568             :       bool DoTransform = true;
    1569             : 
    1570             :       // We have to be careful that the succs of PredBB aren't both no-successor
    1571             :       // blocks.  If neither have successors and if PredBB is the second from
    1572             :       // last block in the function, we'd just keep swapping the two blocks for
    1573             :       // last.  Only do the swap if one is clearly better to fall through than
    1574             :       // the other.
    1575       10225 :       if (FallThrough == --MF.end() &&
    1576        4276 :           !IsBetterFallthrough(PriorTBB, MBB))
    1577             :         DoTransform = false;
    1578             : 
    1579             :       if (DoTransform) {
    1580             :         // Reverse the branch so we will fall through on the previous true cond.
    1581             :         SmallVector<MachineOperand, 4> NewPriorCond(PriorCond);
    1582        2317 :         if (!TII->reverseBranchCondition(NewPriorCond)) {
    1583             :           LLVM_DEBUG(dbgs() << "\nMoving MBB: " << *MBB
    1584             :                             << "To make fallthrough to: " << *PriorTBB << "\n");
    1585             : 
    1586        2317 :           DebugLoc dl = getBranchDebugLoc(PrevBB);
    1587        2317 :           TII->removeBranch(PrevBB);
    1588        4634 :           TII->insertBranch(PrevBB, MBB, nullptr, NewPriorCond, dl);
    1589             : 
    1590             :           // Move this block to the end of the function.
    1591        2317 :           MBB->moveAfter(&MF.back());
    1592             :           MadeChange = true;
    1593             :           ++NumBranchOpts;
    1594             :           return MadeChange;
    1595             :         }
    1596             :       }
    1597             :     }
    1598             :   }
    1599             : 
    1600     1407459 :   if (!IsEmptyBlock(MBB) && MBB->pred_size() == 1 &&
    1601      359111 :       MF.getFunction().optForSize()) {
    1602             :     // Changing "Jcc foo; foo: jmp bar;" into "Jcc bar;" might change the branch
    1603             :     // direction, thereby defeating careful block placement and regressing
    1604             :     // performance. Therefore, only consider this for optsize functions.
    1605        2856 :     MachineInstr &TailCall = *MBB->getFirstNonDebugInstr();
    1606        1428 :     if (TII->isUnconditionalTailCall(TailCall)) {
    1607          41 :       MachineBasicBlock *Pred = *MBB->pred_begin();
    1608          41 :       MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr;
    1609             :       SmallVector<MachineOperand, 4> PredCond;
    1610             :       bool PredAnalyzable =
    1611          41 :           !TII->analyzeBranch(*Pred, PredTBB, PredFBB, PredCond, true);
    1612             : 
    1613          68 :       if (PredAnalyzable && !PredCond.empty() && PredTBB == MBB &&
    1614          27 :           PredTBB != PredFBB) {
    1615             :         // The predecessor has a conditional branch to this block which consists
    1616             :         // of only a tail call. Try to fold the tail call into the conditional
    1617             :         // branch.
    1618          26 :         if (TII->canMakeTailCallConditional(PredCond, TailCall)) {
    1619             :           // TODO: It would be nice if analyzeBranch() could provide a pointer
    1620             :           // to the branch instruction so replaceBranchWithTailCall() doesn't
    1621             :           // have to search for it.
    1622          26 :           TII->replaceBranchWithTailCall(*Pred, PredCond, TailCall);
    1623             :           ++NumTailCalls;
    1624          26 :           Pred->removeSuccessor(MBB);
    1625             :           MadeChange = true;
    1626             :           return MadeChange;
    1627             :         }
    1628             :       }
    1629             :       // If the predecessor is falling through to this block, we could reverse
    1630             :       // the branch condition and fold the tail call into that. However, after
    1631             :       // that we might have to re-arrange the CFG to fall through to the other
    1632             :       // block and there is a high risk of regressing code size rather than
    1633             :       // improving it.
    1634             :     }
    1635             :   }
    1636             : 
    1637             :   // Analyze the branch in the current block.
    1638      524158 :   MachineBasicBlock *CurTBB = nullptr, *CurFBB = nullptr;
    1639             :   SmallVector<MachineOperand, 4> CurCond;
    1640             :   bool CurUnAnalyzable =
    1641      524158 :       TII->analyzeBranch(*MBB, CurTBB, CurFBB, CurCond, true);
    1642      524158 :   if (!CurUnAnalyzable) {
    1643             :     // If the CFG for the prior block has extra edges, remove them.
    1644      486680 :     MadeChange |= MBB->CorrectExtraCFGEdges(CurTBB, CurFBB, !CurCond.empty());
    1645             : 
    1646             :     // If this is a two-way branch, and the FBB branches to this block, reverse
    1647             :     // the condition so the single-basic-block loop is faster.  Instead of:
    1648             :     //    Loop: xxx; jcc Out; jmp Loop
    1649             :     // we want:
    1650             :     //    Loop: xxx; jncc Loop; jmp Out
    1651      486680 :     if (CurTBB && CurFBB && CurFBB == MBB && CurTBB != MBB) {
    1652             :       SmallVector<MachineOperand, 4> NewCond(CurCond);
    1653          35 :       if (!TII->reverseBranchCondition(NewCond)) {
    1654          35 :         DebugLoc dl = getBranchDebugLoc(*MBB);
    1655          35 :         TII->removeBranch(*MBB);
    1656          70 :         TII->insertBranch(*MBB, CurFBB, CurTBB, NewCond, dl);
    1657             :         MadeChange = true;
    1658             :         ++NumBranchOpts;
    1659             :         goto ReoptimizeBlock;
    1660             :       }
    1661             :     }
    1662             : 
    1663             :     // If this branch is the only thing in its block, see if we can forward
    1664             :     // other blocks across it.
    1665      896333 :     if (CurTBB && CurCond.empty() && !CurFBB &&
    1666      150419 :         IsBranchOnlyBlock(MBB) && CurTBB != MBB &&
    1667      497329 :         !MBB->hasAddressTaken() && !MBB->isEHPad()) {
    1668        5333 :       DebugLoc dl = getBranchDebugLoc(*MBB);
    1669             :       // This block may contain just an unconditional branch.  Because there can
    1670             :       // be 'non-branch terminators' in the block, try removing the branch and
    1671             :       // then seeing if the block is empty.
    1672        5333 :       TII->removeBranch(*MBB);
    1673             :       // If the only things remaining in the block are debug info, remove these
    1674             :       // as well, so this will behave the same as an empty block in non-debug
    1675             :       // mode.
    1676        5333 :       if (IsEmptyBlock(MBB)) {
    1677             :         // Make the block empty, losing the debug info (we could probably
    1678             :         // improve this in some cases.)
    1679             :         MBB->erase(MBB->begin(), MBB->end());
    1680             :       }
    1681             :       // If this block is just an unconditional branch to CurTBB, we can
    1682             :       // usually completely eliminate the block.  The only case we cannot
    1683             :       // completely eliminate the block is when the block before this one
    1684             :       // falls through into MBB and we can't understand the prior block's branch
    1685             :       // condition.
    1686        5333 :       if (MBB->empty()) {
    1687        5333 :         bool PredHasNoFallThrough = !PrevBB.canFallThrough();
    1688        5335 :         if (PredHasNoFallThrough || !PriorUnAnalyzable ||
    1689           2 :             !PrevBB.isSuccessor(MBB)) {
    1690             :           // If the prior block falls through into us, turn it into an
    1691             :           // explicit branch to us to make updates simpler.
    1692       10026 :           if (!PredHasNoFallThrough && PrevBB.isSuccessor(MBB) &&
    1693       15357 :               PriorTBB != MBB && PriorFBB != MBB) {
    1694        5013 :             if (!PriorTBB) {
    1695             :               assert(PriorCond.empty() && !PriorFBB &&
    1696             :                      "Bad branch analysis");
    1697        2176 :               PriorTBB = MBB;
    1698             :             } else {
    1699             :               assert(!PriorFBB && "Machine CFG out of date!");
    1700        2837 :               PriorFBB = MBB;
    1701             :             }
    1702        5013 :             DebugLoc pdl = getBranchDebugLoc(PrevBB);
    1703        5013 :             TII->removeBranch(PrevBB);
    1704       10026 :             TII->insertBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, pdl);
    1705             :           }
    1706             : 
    1707             :           // Iterate through all the predecessors, revectoring each in-turn.
    1708             :           size_t PI = 0;
    1709             :           bool DidChange = false;
    1710             :           bool HasBranchToSelf = false;
    1711       12375 :           while(PI != MBB->pred_size()) {
    1712        7044 :             MachineBasicBlock *PMBB = *(MBB->pred_begin() + PI);
    1713        7044 :             if (PMBB == MBB) {
    1714             :               // If this block has an uncond branch to itself, leave it.
    1715           0 :               ++PI;
    1716             :               HasBranchToSelf = true;
    1717             :             } else {
    1718             :               DidChange = true;
    1719        7044 :               PMBB->ReplaceUsesOfBlockWith(MBB, CurTBB);
    1720             :               // If this change resulted in PMBB ending in a conditional
    1721             :               // branch where both conditions go to the same destination,
    1722             :               // change this to an unconditional branch (and fix the CFG).
    1723        7044 :               MachineBasicBlock *NewCurTBB = nullptr, *NewCurFBB = nullptr;
    1724             :               SmallVector<MachineOperand, 4> NewCurCond;
    1725        7044 :               bool NewCurUnAnalyzable = TII->analyzeBranch(
    1726        7044 :                   *PMBB, NewCurTBB, NewCurFBB, NewCurCond, true);
    1727        7044 :               if (!NewCurUnAnalyzable && NewCurTBB && NewCurTBB == NewCurFBB) {
    1728          37 :                 DebugLoc pdl = getBranchDebugLoc(*PMBB);
    1729          37 :                 TII->removeBranch(*PMBB);
    1730             :                 NewCurCond.clear();
    1731          74 :                 TII->insertBranch(*PMBB, NewCurTBB, nullptr, NewCurCond, pdl);
    1732             :                 MadeChange = true;
    1733             :                 ++NumBranchOpts;
    1734          37 :                 PMBB->CorrectExtraCFGEdges(NewCurTBB, nullptr, false);
    1735             :               }
    1736             :             }
    1737             :           }
    1738             : 
    1739             :           // Change any jumptables to go to the new MBB.
    1740        5331 :           if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo())
    1741         161 :             MJTI->ReplaceMBBInJumpTables(MBB, CurTBB);
    1742        5331 :           if (DidChange) {
    1743             :             ++NumBranchOpts;
    1744             :             MadeChange = true;
    1745        5331 :             if (!HasBranchToSelf) return MadeChange;
    1746             :           }
    1747             :         }
    1748             :       }
    1749             : 
    1750             :       // Add the branch back if the block is more than just an uncond branch.
    1751           4 :       TII->insertBranch(*MBB, CurTBB, nullptr, CurCond, dl);
    1752             :     }
    1753             :   }
    1754             : 
    1755             :   // If the prior block doesn't fall through into this block, and if this
    1756             :   // block doesn't fall through into some other block, see if we can find a
    1757             :   // place to move this block where a fall-through will happen.
    1758      518792 :   if (!PrevBB.canFallThrough()) {
    1759             :     // Now we know that there was no fall-through into this block, check to
    1760             :     // see if it has a fall-through into its successor.
    1761      160601 :     bool CurFallsThru = MBB->canFallThrough();
    1762             : 
    1763      160601 :     if (!MBB->isEHPad()) {
    1764             :       // Check all the predecessors of this block.  If one of them has no fall
    1765             :       // throughs, move this block right after it.
    1766      138932 :       for (MachineBasicBlock *PredBB : MBB->predecessors()) {
    1767             :         // Analyze the branch at the end of the pred.
    1768       88947 :         MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr;
    1769             :         SmallVector<MachineOperand, 4> PredCond;
    1770      123286 :         if (PredBB != MBB && !PredBB->canFallThrough() &&
    1771       64105 :             !TII->analyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true) &&
    1772      108718 :             (!CurFallsThru || !CurTBB || !CurFBB) &&
    1773       19757 :             (!CurFallsThru || MBB->getNumber() >= PredBB->getNumber())) {
    1774             :           // If the current block doesn't fall through, just move it.
    1775             :           // If the current block can fall through and does not end with a
    1776             :           // conditional branch, we need to append an unconditional jump to
    1777             :           // the (current) next block.  To avoid a possible compile-time
    1778             :           // infinite loop, move blocks only backward in this case.
    1779             :           // Also, if there are already 2 branches here, we cannot add a third;
    1780             :           // this means we have the case
    1781             :           // Bcc next
    1782             :           // B elsewhere
    1783             :           // next:
    1784       28456 :           if (CurFallsThru) {
    1785             :             MachineBasicBlock *NextBB = &*std::next(MBB->getIterator());
    1786             :             CurCond.clear();
    1787       56103 :             TII->insertBranch(*MBB, NextBB, nullptr, CurCond, DebugLoc());
    1788             :           }
    1789       28456 :           MBB->moveAfter(PredBB);
    1790             :           MadeChange = true;
    1791             :           goto ReoptimizeBlock;
    1792             :         }
    1793             :       }
    1794             :     }
    1795             : 
    1796      132145 :     if (!CurFallsThru) {
    1797             :       // Check all successors to see if we can move this block before it.
    1798      133278 :       for (MachineBasicBlock *SuccBB : MBB->successors()) {
    1799             :         // Analyze the branch at the end of the block before the succ.
    1800       61789 :         MachineFunction::iterator SuccPrev = --SuccBB->getIterator();
    1801             : 
    1802             :         // If this block doesn't already fall-through to that successor, and if
    1803             :         // the succ doesn't already have a block that can fall through into it,
    1804             :         // and if the successor isn't an EH destination, we can arrange for the
    1805             :         // fallthrough to happen.
    1806      123087 :         if (SuccBB != MBB && &*SuccPrev != MBB &&
    1807      127562 :             !SuccPrev->canFallThrough() && !CurUnAnalyzable &&
    1808        1705 :             !SuccBB->isEHPad()) {
    1809        1535 :           MBB->moveBefore(SuccBB);
    1810             :           MadeChange = true;
    1811             :           goto ReoptimizeBlock;
    1812             :         }
    1813             :       }
    1814             : 
    1815             :       // Okay, there is no really great place to put this block.  If, however,
    1816             :       // the block before this one would be a fall-through if this block were
    1817             :       // removed, move this block to the end of the function. There is no real
    1818             :       // advantage in "falling through" to an EH block, so we don't want to
    1819             :       // perform this transformation for that case.
    1820             :       //
    1821             :       // Also, Windows EH introduced the possibility of an arbitrary number of
    1822             :       // successors to a given block.  The analyzeBranch call does not consider
    1823             :       // exception handling and so we can get in a state where a block
    1824             :       // containing a call is followed by multiple EH blocks that would be
    1825             :       // rotated infinitely at the end of the function if the transformation
    1826             :       // below were performed for EH "FallThrough" blocks.  Therefore, even if
    1827             :       // that appears not to be happening anymore, we should assume that it is
    1828             :       // possible and not remove the "!FallThrough()->isEHPad" condition below.
    1829       71489 :       MachineBasicBlock *PrevTBB = nullptr, *PrevFBB = nullptr;
    1830             :       SmallVector<MachineOperand, 4> PrevCond;
    1831       60653 :       if (FallThrough != MF.end() &&
    1832       77914 :           !FallThrough->isEHPad() &&
    1833      103548 :           !TII->analyzeBranch(PrevBB, PrevTBB, PrevFBB, PrevCond, true) &&
    1834       14798 :           PrevBB.isSuccessor(&*FallThrough)) {
    1835        3334 :         MBB->moveAfter(&MF.back());
    1836             :         MadeChange = true;
    1837             :         return MadeChange;
    1838             :       }
    1839             :     }
    1840             :   }
    1841             : 
    1842             :   return MadeChange;
    1843             : }
    1844             : 
    1845             : //===----------------------------------------------------------------------===//
    1846             : //  Hoist Common Code
    1847             : //===----------------------------------------------------------------------===//
    1848             : 
    1849           0 : bool BranchFolder::HoistCommonCode(MachineFunction &MF) {
    1850             :   bool MadeChange = false;
    1851      799118 :   for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ) {
    1852             :     MachineBasicBlock *MBB = &*I++;
    1853      606476 :     MadeChange |= HoistCommonCodeInSuccs(MBB);
    1854             :   }
    1855             : 
    1856           0 :   return MadeChange;
    1857             : }
    1858             : 
    1859             : /// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
    1860             : /// its 'true' successor.
    1861             : static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
    1862             :                                          MachineBasicBlock *TrueBB) {
    1863      168518 :   for (MachineBasicBlock *SuccBB : BB->successors())
    1864      168490 :     if (SuccBB != TrueBB)
    1865             :       return SuccBB;
    1866             :   return nullptr;
    1867             : }
    1868             : 
    1869             : template <class Container>
    1870      114405 : static void addRegAndItsAliases(unsigned Reg, const TargetRegisterInfo *TRI,
    1871             :                                 Container &Set) {
    1872      228810 :   if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
    1873     1303420 :     for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
    1874      537553 :       Set.insert(*AI);
    1875             :   } else {
    1876         248 :     Set.insert(Reg);
    1877             :   }
    1878      114405 : }
    1879             : 
    1880             : /// findHoistingInsertPosAndDeps - Find the location to move common instructions
    1881             : /// in successors to. The location is usually just before the terminator,
    1882             : /// however if the terminator is a conditional branch and its previous
    1883             : /// instruction is the flag setting instruction, the previous instruction is
    1884             : /// the preferred location. This function also gathers uses and defs of the
    1885             : /// instructions from the insertion point to the end of the block. The data is
    1886             : /// used by HoistCommonCodeInSuccs to ensure safety.
    1887             : static
    1888       35820 : MachineBasicBlock::iterator findHoistingInsertPosAndDeps(MachineBasicBlock *MBB,
    1889             :                                                   const TargetInstrInfo *TII,
    1890             :                                                   const TargetRegisterInfo *TRI,
    1891             :                                                   SmallSet<unsigned,4> &Uses,
    1892             :                                                   SmallSet<unsigned,4> &Defs) {
    1893       35820 :   MachineBasicBlock::iterator Loc = MBB->getFirstTerminator();
    1894       35820 :   if (!TII->isUnpredicatedTerminator(*Loc))
    1895             :     return MBB->end();
    1896             : 
    1897      186304 :   for (const MachineOperand &MO : Loc->operands()) {
    1898       75795 :     if (!MO.isReg())
    1899       39010 :       continue;
    1900       36785 :     unsigned Reg = MO.getReg();
    1901       36785 :     if (!Reg)
    1902           0 :       continue;
    1903       36785 :     if (MO.isUse()) {
    1904       36020 :       addRegAndItsAliases(Reg, TRI, Uses);
    1905             :     } else {
    1906         765 :       if (!MO.isDead())
    1907             :         // Don't try to hoist code in the rare case the terminator defines a
    1908             :         // register that is later used.
    1909             :         return MBB->end();
    1910             : 
    1911             :       // If the terminator defines a register, make sure we don't hoist
    1912             :       // the instruction whose def might be clobbered by the terminator.
    1913         212 :       addRegAndItsAliases(Reg, TRI, Defs);
    1914             :     }
    1915             :   }
    1916             : 
    1917             :   if (Uses.empty())
    1918           0 :     return Loc;
    1919             :   // If the terminator is the only instruction in the block and Uses is not
    1920             :   // empty (or we would have returned above), we can still safely hoist
    1921             :   // instructions just before the terminator as long as the Defs/Uses are not
    1922             :   // violated (which is checked in HoistCommonCodeInSuccs).
    1923       35267 :   if (Loc == MBB->begin())
    1924         489 :     return Loc;
    1925             : 
    1926             :   // The terminator is probably a conditional branch, try not to separate the
    1927             :   // branch from condition setting instruction.
    1928             :   MachineBasicBlock::iterator PI =
    1929       34778 :     skipDebugInstructionsBackward(std::prev(Loc), MBB->begin());
    1930             : 
    1931             :   bool IsDef = false;
    1932      223312 :   for (const MachineOperand &MO : PI->operands()) {
    1933             :     // If PI has a regmask operand, it is probably a call. Separate away.
    1934      124771 :     if (MO.isRegMask())
    1935           2 :       return Loc;
    1936      317654 :     if (!MO.isReg() || MO.isUse())
    1937      184830 :       continue;
    1938       32354 :     unsigned Reg = MO.getReg();
    1939       32354 :     if (!Reg)
    1940           0 :       continue;
    1941       32354 :     if (Uses.count(Reg)) {
    1942             :       IsDef = true;
    1943       30502 :       break;
    1944             :     }
    1945             :   }
    1946             :   if (!IsDef)
    1947             :     // The condition setting instruction is not just before the conditional
    1948             :     // branch.
    1949        4274 :     return Loc;
    1950             : 
    1951             :   // Be conservative, don't insert instruction above something that may have
    1952             :   // side-effects. And since it's potentially bad to separate flag setting
    1953             :   // instruction from the conditional branch, just abort the optimization
    1954             :   // completely.
    1955             :   // Also avoid moving code above predicated instruction since it's hard to
    1956             :   // reason about register liveness with predicated instruction.
    1957       30502 :   bool DontMoveAcrossStore = true;
    1958       59046 :   if (!PI->isSafeToMove(nullptr, DontMoveAcrossStore) || TII->isPredicated(*PI))
    1959             :     return MBB->end();
    1960             : 
    1961             :   // Find out what registers are live. Note this routine is ignoring other live
    1962             :   // registers which are only used by instructions in successor blocks.
    1963      210496 :   for (const MachineOperand &MO : PI->operands()) {
    1964       90977 :     if (!MO.isReg())
    1965       24604 :       continue;
    1966       79447 :     unsigned Reg = MO.getReg();
    1967       79447 :     if (!Reg)
    1968        1544 :       continue;
    1969       77903 :     if (MO.isUse()) {
    1970       48431 :       addRegAndItsAliases(Reg, TRI, Uses);
    1971             :     } else {
    1972       29472 :       if (Uses.erase(Reg)) {
    1973       57092 :         if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
    1974       59138 :           for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs)
    1975        2114 :             Uses.erase(*SubRegs); // Use sub-registers to be conservative
    1976             :         }
    1977             :       }
    1978       29472 :       addRegAndItsAliases(Reg, TRI, Defs);
    1979             :     }
    1980             :   }
    1981             : 
    1982       28542 :   return PI;
    1983             : }
    1984             : 
    1985      606476 : bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
    1986      606476 :   MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
    1987             :   SmallVector<MachineOperand, 4> Cond;
    1988      606476 :   if (TII->analyzeBranch(*MBB, TBB, FBB, Cond, true) || !TBB || Cond.empty())
    1989             :     return false;
    1990             : 
    1991      234971 :   if (!FBB) FBB = findFalseBlock(MBB, TBB);
    1992      118655 :   if (!FBB)
    1993             :     // Malformed bcc? True and false blocks are the same?
    1994             :     return false;
    1995             : 
    1996             :   // Restrict the optimization to cases where MBB is the only predecessor,
    1997             :   // it is an obvious win.
    1998      156137 :   if (TBB->pred_size() > 1 || FBB->pred_size() > 1)
    1999             :     return false;
    2000             : 
    2001             :   // Find a suitable position to hoist the common instructions to. Also figure
    2002             :   // out which registers are used or defined by instructions from the insertion
    2003             :   // point to the end of the block.
    2004       35820 :   SmallSet<unsigned, 4> Uses, Defs;
    2005             :   MachineBasicBlock::iterator Loc =
    2006       35820 :     findHoistingInsertPosAndDeps(MBB, TII, TRI, Uses, Defs);
    2007       35820 :   if (Loc == MBB->end())
    2008             :     return false;
    2009             : 
    2010             :   bool HasDups = false;
    2011       33307 :   SmallSet<unsigned, 4> ActiveDefsSet, AllDefsSet;
    2012       66614 :   MachineBasicBlock::iterator TIB = TBB->begin();
    2013       66614 :   MachineBasicBlock::iterator FIB = FBB->begin();
    2014             :   MachineBasicBlock::iterator TIE = TBB->end();
    2015             :   MachineBasicBlock::iterator FIE = FBB->end();
    2016       66817 :   while (TIB != TIE && FIB != FIE) {
    2017             :     // Skip dbg_value instructions. These do not count.
    2018       33025 :     TIB = skipDebugInstructionsForward(TIB, TIE);
    2019       33025 :     FIB = skipDebugInstructionsForward(FIB, FIE);
    2020       66050 :     if (TIB == TIE || FIB == FIE)
    2021             :       break;
    2022             : 
    2023       33025 :     if (!TIB->isIdenticalTo(*FIB, MachineInstr::CheckKillDead))
    2024             :       break;
    2025             : 
    2026         898 :     if (TII->isPredicated(*TIB))
    2027             :       // Hard to reason about register liveness with predicated instruction.
    2028             :       break;
    2029             : 
    2030             :     bool IsSafe = true;
    2031        4046 :     for (MachineOperand &MO : TIB->operands()) {
    2032             :       // Don't attempt to hoist instructions with register masks.
    2033        1879 :       if (MO.isRegMask()) {
    2034             :         IsSafe = false;
    2035          80 :         break;
    2036             :       }
    2037        1865 :       if (!MO.isReg())
    2038        1625 :         continue;
    2039        1269 :       unsigned Reg = MO.getReg();
    2040        1269 :       if (!Reg)
    2041         433 :         continue;
    2042         836 :       if (MO.isDef()) {
    2043         456 :         if (Uses.count(Reg)) {
    2044             :           // Avoid clobbering a register that's used by the instruction at
    2045             :           // the point of insertion.
    2046             :           IsSafe = false;
    2047             :           break;
    2048             :         }
    2049             : 
    2050         432 :         if (Defs.count(Reg) && !MO.isDead()) {
    2051             :           // Don't hoist the instruction if the def would be clobber by the
    2052             :           // instruction at the point insertion. FIXME: This is overly
    2053             :           // conservative. It should be possible to hoist the instructions
    2054             :           // in BB2 in the following example:
    2055             :           // BB1:
    2056             :           // r1, eflag = op1 r2, r3
    2057             :           // brcc eflag
    2058             :           //
    2059             :           // BB2:
    2060             :           // r1 = op2, ...
    2061             :           //    = op3, killed r1
    2062             :           IsSafe = false;
    2063             :           break;
    2064             :         }
    2065         380 :       } else if (!ActiveDefsSet.count(Reg)) {
    2066         370 :         if (Defs.count(Reg)) {
    2067             :           // Use is defined by the instruction at the point of insertion.
    2068             :           IsSafe = false;
    2069             :           break;
    2070             :         }
    2071             : 
    2072         370 :         if (MO.isKill() && Uses.count(Reg))
    2073             :           // Kills a register that's read by the instruction at the point of
    2074             :           // insertion. Remove the kill marker.
    2075             :           MO.setIsKill(false);
    2076             :       }
    2077             :     }
    2078             :     if (!IsSafe)
    2079             :       break;
    2080             : 
    2081         368 :     bool DontMoveAcrossStore = true;
    2082         368 :     if (!TIB->isSafeToMove(nullptr, DontMoveAcrossStore))
    2083             :       break;
    2084             : 
    2085             :     // Remove kills from ActiveDefsSet, these registers had short live ranges.
    2086         825 :     for (const MachineOperand &MO : TIB->operands()) {
    2087        1057 :       if (!MO.isReg() || !MO.isUse() || !MO.isKill())
    2088         682 :         continue;
    2089          16 :       unsigned Reg = MO.getReg();
    2090          16 :       if (!Reg)
    2091           0 :         continue;
    2092          16 :       if (!AllDefsSet.count(Reg)) {
    2093          14 :         continue;
    2094             :       }
    2095           2 :       if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
    2096          28 :         for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
    2097          12 :           ActiveDefsSet.erase(*AI);
    2098             :       } else {
    2099           0 :         ActiveDefsSet.erase(Reg);
    2100             :       }
    2101             :     }
    2102             : 
    2103             :     // Track local defs so we can update liveins.
    2104         825 :     for (const MachineOperand &MO : TIB->operands()) {
    2105         987 :       if (!MO.isReg() || !MO.isDef() || MO.isDead())
    2106         215 :         continue;
    2107         135 :       unsigned Reg = MO.getReg();
    2108         270 :       if (!Reg || TargetRegisterInfo::isVirtualRegister(Reg))
    2109           0 :         continue;
    2110         135 :       addRegAndItsAliases(Reg, TRI, ActiveDefsSet);
    2111         135 :       addRegAndItsAliases(Reg, TRI, AllDefsSet);
    2112             :     }
    2113             : 
    2114             :     HasDups = true;
    2115             :     ++TIB;
    2116             :     ++FIB;
    2117             :   }
    2118             : 
    2119       33307 :   if (!HasDups)
    2120             :     return false;
    2121             : 
    2122          95 :   MBB->splice(Loc, TBB, TBB->begin(), TIB);
    2123          95 :   FBB->erase(FBB->begin(), FIB);
    2124             : 
    2125          95 :   if (UpdateLiveIns) {
    2126          89 :     recomputeLiveIns(*TBB);
    2127          89 :     recomputeLiveIns(*FBB);
    2128             :   }
    2129             : 
    2130             :   ++NumHoist;
    2131             :   return true;
    2132      299229 : }

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