LCOV - code coverage report
Current view: top level - lib/CodeGen - MachineSSAUpdater.cpp (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 86 100 86.0 %
Date: 2018-06-17 00:07:59 Functions: 13 15 86.7 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : //===- MachineSSAUpdater.cpp - Unstructured SSA Update Tool ---------------===//
       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 file implements the MachineSSAUpdater class. It's based on SSAUpdater
      11             : // class in lib/Transforms/Utils.
      12             : //
      13             : //===----------------------------------------------------------------------===//
      14             : 
      15             : #include "llvm/CodeGen/MachineSSAUpdater.h"
      16             : #include "llvm/ADT/DenseMap.h"
      17             : #include "llvm/ADT/SmallVector.h"
      18             : #include "llvm/CodeGen/MachineBasicBlock.h"
      19             : #include "llvm/CodeGen/MachineFunction.h"
      20             : #include "llvm/CodeGen/MachineInstr.h"
      21             : #include "llvm/CodeGen/MachineInstrBuilder.h"
      22             : #include "llvm/CodeGen/MachineOperand.h"
      23             : #include "llvm/CodeGen/MachineRegisterInfo.h"
      24             : #include "llvm/CodeGen/TargetInstrInfo.h"
      25             : #include "llvm/CodeGen/TargetOpcodes.h"
      26             : #include "llvm/CodeGen/TargetSubtargetInfo.h"
      27             : #include "llvm/IR/DebugLoc.h"
      28             : #include "llvm/Support/Debug.h"
      29             : #include "llvm/Support/ErrorHandling.h"
      30             : #include "llvm/Support/raw_ostream.h"
      31             : #include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
      32             : #include <utility>
      33             : 
      34             : using namespace llvm;
      35             : 
      36             : #define DEBUG_TYPE "machine-ssaupdater"
      37             : 
      38             : using AvailableValsTy = DenseMap<MachineBasicBlock *, unsigned>;
      39             : 
      40             : static AvailableValsTy &getAvailableVals(void *AV) {
      41             :   return *static_cast<AvailableValsTy*>(AV);
      42             : }
      43             : 
      44        3525 : MachineSSAUpdater::MachineSSAUpdater(MachineFunction &MF,
      45        3525 :                                      SmallVectorImpl<MachineInstr*> *NewPHI)
      46        3525 :   : InsertedPHIs(NewPHI), TII(MF.getSubtarget().getInstrInfo()),
      47        7050 :     MRI(&MF.getRegInfo()) {}
      48             : 
      49        7050 : MachineSSAUpdater::~MachineSSAUpdater() {
      50        4226 :   delete static_cast<AvailableValsTy*>(AV);
      51        3525 : }
      52             : 
      53             : /// Initialize - Reset this object to get ready for a new set of SSA
      54             : /// updates.  ProtoValue is the value used to name PHI nodes.
      55        1247 : void MachineSSAUpdater::Initialize(unsigned V) {
      56        1247 :   if (!AV)
      57        1402 :     AV = new AvailableValsTy();
      58             :   else
      59         546 :     getAvailableVals(AV).clear();
      60             : 
      61        1247 :   VR = V;
      62        2494 :   VRC = MRI->getRegClass(VR);
      63        1247 : }
      64             : 
      65             : /// HasValueForBlock - Return true if the MachineSSAUpdater already has a value for
      66             : /// the specified block.
      67          56 : bool MachineSSAUpdater::HasValueForBlock(MachineBasicBlock *BB) const {
      68         112 :   return getAvailableVals(AV).count(BB);
      69             : }
      70             : 
      71             : /// AddAvailableValue - Indicate that a rewritten value is available in the
      72             : /// specified block with the specified value.
      73        2905 : void MachineSSAUpdater::AddAvailableValue(MachineBasicBlock *BB, unsigned V) {
      74        5810 :   getAvailableVals(AV)[BB] = V;
      75        2905 : }
      76             : 
      77             : /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
      78             : /// live at the end of the specified block.
      79           0 : unsigned MachineSSAUpdater::GetValueAtEndOfBlock(MachineBasicBlock *BB) {
      80           0 :   return GetValueAtEndOfBlockInternal(BB);
      81             : }
      82             : 
      83             : static
      84          30 : unsigned LookForIdenticalPHI(MachineBasicBlock *BB,
      85             :         SmallVectorImpl<std::pair<MachineBasicBlock *, unsigned>> &PredValues) {
      86          30 :   if (BB->empty())
      87             :     return 0;
      88             : 
      89          30 :   MachineBasicBlock::iterator I = BB->begin();
      90             :   if (!I->isPHI())
      91             :     return 0;
      92             : 
      93             :   AvailableValsTy AVals;
      94          36 :   for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
      95          78 :     AVals[PredValues[i].first] = PredValues[i].second;
      96          13 :   while (I != BB->end() && I->isPHI()) {
      97             :     bool Same = true;
      98          26 :     for (unsigned i = 1, e = I->getNumOperands(); i != e; i += 2) {
      99          38 :       unsigned SrcReg = I->getOperand(i).getReg();
     100          38 :       MachineBasicBlock *SrcBB = I->getOperand(i+1).getMBB();
     101          19 :       if (AVals[SrcBB] != SrcReg) {
     102             :         Same = false;
     103           3 :         break;
     104             :       }
     105             :     }
     106             :     if (Same)
     107           7 :       return I->getOperand(0).getReg();
     108             :     ++I;
     109             :   }
     110             :   return 0;
     111             : }
     112             : 
     113             : /// InsertNewDef - Insert an empty PHI or IMPLICIT_DEF instruction which define
     114             : /// a value of the given register class at the start of the specified basic
     115             : /// block. It returns the virtual register defined by the instruction.
     116             : static
     117          42 : MachineInstrBuilder InsertNewDef(unsigned Opcode,
     118             :                            MachineBasicBlock *BB, MachineBasicBlock::iterator I,
     119             :                            const TargetRegisterClass *RC,
     120             :                            MachineRegisterInfo *MRI,
     121             :                            const TargetInstrInfo *TII) {
     122          42 :   unsigned NewVR = MRI->createVirtualRegister(RC);
     123         126 :   return BuildMI(*BB, I, DebugLoc(), TII->get(Opcode), NewVR);
     124             : }
     125             : 
     126             : /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
     127             : /// is live in the middle of the specified block.
     128             : ///
     129             : /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
     130             : /// important case: if there is a definition of the rewritten value after the
     131             : /// 'use' in BB.  Consider code like this:
     132             : ///
     133             : ///      X1 = ...
     134             : ///   SomeBB:
     135             : ///      use(X)
     136             : ///      X2 = ...
     137             : ///      br Cond, SomeBB, OutBB
     138             : ///
     139             : /// In this case, there are two values (X1 and X2) added to the AvailableVals
     140             : /// set by the client of the rewriter, and those values are both live out of
     141             : /// their respective blocks.  However, the use of X happens in the *middle* of
     142             : /// a block.  Because of this, we need to insert a new PHI node in SomeBB to
     143             : /// merge the appropriate values, and this value isn't live out of the block.
     144          56 : unsigned MachineSSAUpdater::GetValueInMiddleOfBlock(MachineBasicBlock *BB) {
     145             :   // If there is no definition of the renamed variable in this block, just use
     146             :   // GetValueAtEndOfBlock to do our work.
     147          56 :   if (!HasValueForBlock(BB))
     148          19 :     return GetValueAtEndOfBlockInternal(BB);
     149             : 
     150             :   // If there are no predecessors, just return undef.
     151          37 :   if (BB->pred_empty()) {
     152             :     // Insert an implicit_def to represent an undef value.
     153           0 :     MachineInstr *NewDef = InsertNewDef(TargetOpcode::IMPLICIT_DEF,
     154             :                                         BB, BB->getFirstTerminator(),
     155           0 :                                         VRC, MRI, TII);
     156           0 :     return NewDef->getOperand(0).getReg();
     157             :   }
     158             : 
     159             :   // Otherwise, we have the hard case.  Get the live-in values for each
     160             :   // predecessor.
     161             :   SmallVector<std::pair<MachineBasicBlock*, unsigned>, 8> PredValues;
     162             :   unsigned SingularValue = 0;
     163             : 
     164             :   bool isFirstPred = true;
     165             :   for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
     166         384 :          E = BB->pred_end(); PI != E; ++PI) {
     167         347 :     MachineBasicBlock *PredBB = *PI;
     168         347 :     unsigned PredVal = GetValueAtEndOfBlockInternal(PredBB);
     169         347 :     PredValues.push_back(std::make_pair(PredBB, PredVal));
     170             : 
     171             :     // Compute SingularValue.
     172         347 :     if (isFirstPred) {
     173             :       SingularValue = PredVal;
     174             :       isFirstPred = false;
     175         310 :     } else if (PredVal != SingularValue)
     176             :       SingularValue = 0;
     177             :   }
     178             : 
     179             :   // Otherwise, if all the merged values are the same, just use it.
     180          37 :   if (SingularValue != 0)
     181             :     return SingularValue;
     182             : 
     183             :   // If an identical PHI is already in BB, just reuse it.
     184          30 :   unsigned DupPHI = LookForIdenticalPHI(BB, PredValues);
     185          30 :   if (DupPHI)
     186             :     return DupPHI;
     187             : 
     188             :   // Otherwise, we do need a PHI: insert one now.
     189          46 :   MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->begin();
     190             :   MachineInstrBuilder InsertedPHI = InsertNewDef(TargetOpcode::PHI, BB,
     191          23 :                                                  Loc, VRC, MRI, TII);
     192             : 
     193             :   // Fill in all the predecessors of the PHI.
     194         347 :   for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
     195         972 :     InsertedPHI.addReg(PredValues[i].second).addMBB(PredValues[i].first);
     196             : 
     197             :   // See if the PHI node can be merged to a single value.  This can happen in
     198             :   // loop cases when we get a PHI of itself and one other value.
     199          23 :   if (unsigned ConstVal = InsertedPHI->isConstantValuePHI()) {
     200           0 :     InsertedPHI->eraseFromParent();
     201           0 :     return ConstVal;
     202             :   }
     203             : 
     204             :   // If the client wants to know about all new instructions, tell it.
     205          23 :   if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
     206             : 
     207             :   LLVM_DEBUG(dbgs() << "  Inserted PHI: " << *InsertedPHI << "\n");
     208          23 :   return InsertedPHI->getOperand(0).getReg();
     209             : }
     210             : 
     211             : static
     212             : MachineBasicBlock *findCorrespondingPred(const MachineInstr *MI,
     213             :                                          MachineOperand *U) {
     214          17 :   for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
     215          34 :     if (&MI->getOperand(i) == U)
     216          16 :       return MI->getOperand(i+1).getMBB();
     217             :   }
     218             : 
     219           0 :   llvm_unreachable("MachineOperand::getParent() failure?");
     220             : }
     221             : 
     222             : /// RewriteUse - Rewrite a use of the symbolic value.  This handles PHI nodes,
     223             : /// which use their value in the corresponding predecessor.
     224          64 : void MachineSSAUpdater::RewriteUse(MachineOperand &U) {
     225          64 :   MachineInstr *UseMI = U.getParent();
     226             :   unsigned NewVR = 0;
     227             :   if (UseMI->isPHI()) {
     228             :     MachineBasicBlock *SourceBB = findCorrespondingPred(UseMI, &U);
     229           8 :     NewVR = GetValueAtEndOfBlockInternal(SourceBB);
     230             :   } else {
     231          56 :     NewVR = GetValueInMiddleOfBlock(UseMI->getParent());
     232             :   }
     233             : 
     234          64 :   U.setReg(NewVR);
     235          64 : }
     236             : 
     237             : /// SSAUpdaterTraits<MachineSSAUpdater> - Traits for the SSAUpdaterImpl
     238             : /// template, specialized for MachineSSAUpdater.
     239             : namespace llvm {
     240             : 
     241             : template<>
     242             : class SSAUpdaterTraits<MachineSSAUpdater> {
     243             : public:
     244             :   using BlkT = MachineBasicBlock;
     245             :   using ValT = unsigned;
     246             :   using PhiT = MachineInstr;
     247             :   using BlkSucc_iterator = MachineBasicBlock::succ_iterator;
     248             : 
     249             :   static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return BB->succ_begin(); }
     250             :   static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return BB->succ_end(); }
     251             : 
     252             :   /// Iterator for PHI operands.
     253             :   class PHI_iterator {
     254             :   private:
     255             :     MachineInstr *PHI;
     256             :     unsigned idx;
     257             :  
     258             :   public:
     259             :     explicit PHI_iterator(MachineInstr *P) // begin iterator
     260             :       : PHI(P), idx(1) {}
     261             :     PHI_iterator(MachineInstr *P, bool) // end iterator
     262          11 :       : PHI(P), idx(PHI->getNumOperands()) {}
     263             : 
     264           0 :     PHI_iterator &operator++() { idx += 2; return *this; } 
     265             :     bool operator==(const PHI_iterator& x) const { return idx == x.idx; }
     266             :     bool operator!=(const PHI_iterator& x) const { return !operator==(x); }
     267             : 
     268          22 :     unsigned getIncomingValue() { return PHI->getOperand(idx).getReg(); }
     269             : 
     270             :     MachineBasicBlock *getIncomingBlock() {
     271          22 :       return PHI->getOperand(idx+1).getMBB();
     272             :     }
     273             :   };
     274             : 
     275             :   static inline PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
     276             : 
     277             :   static inline PHI_iterator PHI_end(PhiT *PHI) {
     278             :     return PHI_iterator(PHI, true);
     279             :   }
     280             : 
     281             :   /// FindPredecessorBlocks - Put the predecessors of BB into the Preds
     282             :   /// vector.
     283             :   static void FindPredecessorBlocks(MachineBasicBlock *BB,
     284             :                                     SmallVectorImpl<MachineBasicBlock*> *Preds){
     285             :     for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
     286         144 :            E = BB->pred_end(); PI != E; ++PI)
     287          89 :       Preds->push_back(*PI);
     288             :   }
     289             : 
     290             :   /// GetUndefVal - Create an IMPLICIT_DEF instruction with a new register.
     291             :   /// Add it into the specified block and return the register.
     292           0 :   static unsigned GetUndefVal(MachineBasicBlock *BB,
     293             :                               MachineSSAUpdater *Updater) {
     294             :     // Insert an implicit_def to represent an undef value.
     295           0 :     MachineInstr *NewDef = InsertNewDef(TargetOpcode::IMPLICIT_DEF,
     296             :                                         BB, BB->getFirstTerminator(),
     297             :                                         Updater->VRC, Updater->MRI,
     298           0 :                                         Updater->TII);
     299           0 :     return NewDef->getOperand(0).getReg();
     300             :   }
     301             : 
     302             :   /// CreateEmptyPHI - Create a PHI instruction that defines a new register.
     303             :   /// Add it into the specified block and return the register.
     304          19 :   static unsigned CreateEmptyPHI(MachineBasicBlock *BB, unsigned NumPreds,
     305             :                                  MachineSSAUpdater *Updater) {
     306          38 :     MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->begin();
     307          38 :     MachineInstr *PHI = InsertNewDef(TargetOpcode::PHI, BB, Loc,
     308             :                                      Updater->VRC, Updater->MRI,
     309          38 :                                      Updater->TII);
     310          19 :     return PHI->getOperand(0).getReg();
     311             :   }
     312             : 
     313             :   /// AddPHIOperand - Add the specified value as an operand of the PHI for
     314             :   /// the specified predecessor block.
     315          49 :   static void AddPHIOperand(MachineInstr *PHI, unsigned Val,
     316             :                             MachineBasicBlock *Pred) {
     317         147 :     MachineInstrBuilder(*Pred->getParent(), PHI).addReg(Val).addMBB(Pred);
     318          49 :   }
     319             : 
     320             :   /// InstrIsPHI - Check if an instruction is a PHI.
     321             :   static MachineInstr *InstrIsPHI(MachineInstr *I) {
     322          19 :     if (I && I->isPHI())
     323             :       return I;
     324             :     return nullptr;
     325             :   }
     326             : 
     327             :   /// ValueIsPHI - Check if the instruction that defines the specified register
     328             :   /// is a PHI instruction.
     329          19 :   static MachineInstr *ValueIsPHI(unsigned Val, MachineSSAUpdater *Updater) {
     330          38 :     return InstrIsPHI(Updater->MRI->getVRegDef(Val));
     331             :   }
     332             : 
     333             :   /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
     334             :   /// operands, i.e., it was just added.
     335             :   static MachineInstr *ValueIsNewPHI(unsigned Val, MachineSSAUpdater *Updater) {
     336          19 :     MachineInstr *PHI = ValueIsPHI(Val, Updater);
     337          19 :     if (PHI && PHI->getNumOperands() <= 1)
     338             :       return PHI;
     339             :     return nullptr;
     340             :   }
     341             : 
     342             :   /// GetPHIValue - For the specified PHI instruction, return the register
     343             :   /// that it defines.
     344             :   static unsigned GetPHIValue(MachineInstr *PHI) {
     345           0 :     return PHI->getOperand(0).getReg();
     346             :   }
     347             : };
     348             : 
     349             : } // end namespace llvm
     350             : 
     351             : /// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
     352             : /// for the specified BB and if so, return it.  If not, construct SSA form by
     353             : /// first calculating the required placement of PHIs and then inserting new
     354             : /// PHIs where needed.
     355         374 : unsigned MachineSSAUpdater::GetValueAtEndOfBlockInternal(MachineBasicBlock *BB){
     356         374 :   AvailableValsTy &AvailableVals = getAvailableVals(AV);
     357         374 :   if (unsigned V = AvailableVals[BB])
     358             :     return V;
     359             : 
     360          33 :   SSAUpdaterImpl<MachineSSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
     361          33 :   return Impl.GetValue(BB);
     362             : }

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