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