lib/Target/Hexagon/HexagonCFGOptimizer.cpp

   1 //===-- HexagonCFGOptimizer.cpp - CFG optimizations -----------------------===//
   2 //                     The LLVM Compiler Infrastructure
   3 //
   4 // This file is distributed under the University of Illinois Open Source
   5 // License. See LICENSE.TXT for details.
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #define DEBUG_TYPE "hexagon_cfg"
  10 #include "Hexagon.h"
  11 #include "HexagonMachineFunctionInfo.h"
  12 #include "HexagonSubtarget.h"
  13 #include "HexagonTargetMachine.h"
  14 #include "llvm/CodeGen/MachineDominators.h"
  15 #include "llvm/CodeGen/MachineFunctionPass.h"
  16 #include "llvm/CodeGen/MachineInstrBuilder.h"
  17 #include "llvm/CodeGen/MachineLoopInfo.h"
  18 #include "llvm/CodeGen/MachineRegisterInfo.h"
  19 #include "llvm/CodeGen/Passes.h"
  20 #include "llvm/Support/Compiler.h"
  21 #include "llvm/Support/Debug.h"
  22 #include "llvm/Support/MathExtras.h"
  23 #include "llvm/Target/TargetInstrInfo.h"
  24 #include "llvm/Target/TargetMachine.h"
  25 #include "llvm/Target/TargetRegisterInfo.h"
  26
  27 using namespace llvm;
  28
  29 namespace {
  30
  31 class HexagonCFGOptimizer : public MachineFunctionPass {
  32
  33 private:
  34   HexagonTargetMachine& QTM;
  35   const HexagonSubtarget &QST;
  36
  37   void InvertAndChangeJumpTarget(MachineInstr*, MachineBasicBlock*);
  38
  39  public:
  40   static char ID;
  41   HexagonCFGOptimizer(HexagonTargetMachine& TM) : MachineFunctionPass(ID),
  42                                                   QTM(TM),
  43                                                   QST(*TM.getSubtargetImpl()) {}
  44
  45   const char *getPassName() const {
  46     return "Hexagon CFG Optimizer";
  47   }
  48   bool runOnMachineFunction(MachineFunction &Fn);
  49 };
  50
  51
  52 char HexagonCFGOptimizer::ID = 0;
  53
  54 static bool IsConditionalBranch(int Opc) {
  55   return (Opc == Hexagon::JMP_c) || (Opc == Hexagon::JMP_cNot)
  56     || (Opc == Hexagon::JMP_cdnPt) || (Opc == Hexagon::JMP_cdnNotPt);
  57 }
  58
  59
  60 static bool IsUnconditionalJump(int Opc) {
  61   return (Opc == Hexagon::JMP);
  62 }
  63
  64
  65 void
  66 HexagonCFGOptimizer::InvertAndChangeJumpTarget(MachineInstr* MI,
  67                                                MachineBasicBlock* NewTarget) {
  68   const HexagonInstrInfo *QII = QTM.getInstrInfo();
  69   int NewOpcode = 0;
  70   switch(MI->getOpcode()) {
  71   case Hexagon::JMP_c:
  72     NewOpcode = Hexagon::JMP_cNot;
  73     break;
  74
  75   case Hexagon::JMP_cNot:
  76     NewOpcode = Hexagon::JMP_c;
  77     break;
  78
  79   case Hexagon::JMP_cdnPt:
  80     NewOpcode = Hexagon::JMP_cdnNotPt;
  81     break;
  82
  83   case Hexagon::JMP_cdnNotPt:
  84     NewOpcode = Hexagon::JMP_cdnPt;
  85     break;
  86
  87   default:
  88     llvm_unreachable("Cannot handle this case");
  89   }
  90
  91   MI->setDesc(QII->get(NewOpcode));
  92   MI->getOperand(1).setMBB(NewTarget);
  93 }
  94
  95
  96 bool HexagonCFGOptimizer::runOnMachineFunction(MachineFunction &Fn) {
  97
  98   // Loop over all of the basic blocks.
  99   for (MachineFunction::iterator MBBb = Fn.begin(), MBBe = Fn.end();
 100        MBBb != MBBe; ++MBBb) {
 101     MachineBasicBlock* MBB = MBBb;
 102
 103     // Traverse the basic block.
 104     MachineBasicBlock::iterator MII = MBB->getFirstTerminator();
 105     if (MII != MBB->end()) {
 106       MachineInstr *MI = MII;
 107       int Opc = MI->getOpcode();
 108       if (IsConditionalBranch(Opc)) {
 109
 110         //
 111         // (Case 1) Transform the code if the following condition occurs:
 112         //   BB1: if (p0) jump BB3
 113         //   ...falls-through to BB2 ...
 114         //   BB2: jump BB4
 115         //   ...next block in layout is BB3...
 116         //   BB3: ...
 117         //
 118         //  Transform this to:
 119         //  BB1: if (!p0) jump BB4
 120         //  Remove BB2
 121         //  BB3: ...
 122         //
 123         // (Case 2) A variation occurs when BB3 contains a JMP to BB4:
 124         //   BB1: if (p0) jump BB3
 125         //   ...falls-through to BB2 ...
 126         //   BB2: jump BB4
 127         //   ...other basic blocks ...
 128         //   BB4:
 129         //   ...not a fall-thru
 130         //   BB3: ...
 131         //     jump BB4
 132         //
 133         // Transform this to:
 134         //   BB1: if (!p0) jump BB4
 135         //   Remove BB2
 136         //   BB3: ...
 137         //   BB4: ...
 138         //
 139         unsigned NumSuccs = MBB->succ_size();
 140         MachineBasicBlock::succ_iterator SI = MBB->succ_begin();
 141         MachineBasicBlock* FirstSucc = *SI;
 142         MachineBasicBlock* SecondSucc = *(++SI);
 143         MachineBasicBlock* LayoutSucc = NULL;
 144         MachineBasicBlock* JumpAroundTarget = NULL;
 145
 146         if (MBB->isLayoutSuccessor(FirstSucc)) {
 147           LayoutSucc = FirstSucc;
 148           JumpAroundTarget = SecondSucc;
 149         } else if (MBB->isLayoutSuccessor(SecondSucc)) {
 150           LayoutSucc = SecondSucc;
 151           JumpAroundTarget = FirstSucc;
 152         } else {
 153           // Odd case...cannot handle.
 154         }
 155
 156         // The target of the unconditional branch must be JumpAroundTarget.
 157         // TODO: If not, we should not invert the unconditional branch.
 158         MachineBasicBlock* CondBranchTarget = NULL;
 159         if ((MI->getOpcode() == Hexagon::JMP_c) ||
 160             (MI->getOpcode() == Hexagon::JMP_cNot)) {
 161           CondBranchTarget = MI->getOperand(1).getMBB();
 162         }
 163
 164         if (!LayoutSucc || (CondBranchTarget != JumpAroundTarget)) {
 165           continue;
 166         }
 167
 168         if ((NumSuccs == 2) && LayoutSucc && (LayoutSucc->pred_size() == 1)) {
 169
 170           // Ensure that BB2 has one instruction -- an unconditional jump.
 171           if ((LayoutSucc->size() == 1) &&
 172               IsUnconditionalJump(LayoutSucc->front().getOpcode())) {
 173             MachineBasicBlock* UncondTarget =
 174               LayoutSucc->front().getOperand(0).getMBB();
 175             // Check if the layout successor of BB2 is BB3.
 176             bool case1 = LayoutSucc->isLayoutSuccessor(JumpAroundTarget);
 177             bool case2 = JumpAroundTarget->isSuccessor(UncondTarget) &&
 178               JumpAroundTarget->size() >= 1 &&
 179               IsUnconditionalJump(JumpAroundTarget->back().getOpcode()) &&
 180               JumpAroundTarget->pred_size() == 1 &&
 181               JumpAroundTarget->succ_size() == 1;
 182
 183             if (case1 || case2) {
 184               InvertAndChangeJumpTarget(MI, UncondTarget);
 185               MBB->removeSuccessor(JumpAroundTarget);
 186               MBB->addSuccessor(UncondTarget);
 187
 188               // Remove the unconditional branch in LayoutSucc.
 189               LayoutSucc->erase(LayoutSucc->begin());
 190               LayoutSucc->removeSuccessor(UncondTarget);
 191               LayoutSucc->addSuccessor(JumpAroundTarget);
 192
 193               // This code performs the conversion for case 2, which moves
 194               // the block to the fall-thru case (BB3 in the code above).
 195               if (case2 && !case1) {
 196                 JumpAroundTarget->moveAfter(LayoutSucc);
 197                 // only move a block if it doesn't have a fall-thru. otherwise
 198                 // the CFG will be incorrect.
 199                 if (!UncondTarget->canFallThrough()) {
 200                   UncondTarget->moveAfter(JumpAroundTarget);
 201                 }
 202               }
 203
 204               //
 205               // Correct live-in information. Is used by post-RA scheduler
 206               // The live-in to LayoutSucc is now all values live-in to
 207               // JumpAroundTarget.
 208               //
 209               std::vector<unsigned> OrigLiveIn(LayoutSucc->livein_begin(),
 210                                                LayoutSucc->livein_end());
 211               std::vector<unsigned> NewLiveIn(JumpAroundTarget->livein_begin(),
 212                                               JumpAroundTarget->livein_end());
 213               for (unsigned i = 0; i < OrigLiveIn.size(); ++i) {
 214                 LayoutSucc->removeLiveIn(OrigLiveIn[i]);
 215               }
 216               for (unsigned i = 0; i < NewLiveIn.size(); ++i) {
 217                 LayoutSucc->addLiveIn(NewLiveIn[i]);
 218               }
 219             }
 220           }
 221         }
 222       }
 223     }
 224   }
 225   return true;
 226 }
 227 }
 228
 229
 230 //===----------------------------------------------------------------------===//
 231 //                         Public Constructor Functions
 232 //===----------------------------------------------------------------------===//
 233
 234 FunctionPass *llvm::createHexagonCFGOptimizer(HexagonTargetMachine &TM) {
 235   return new HexagonCFGOptimizer(TM);
 236 }