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 llvm { 30 void initializeHexagonCFGOptimizerPass(PassRegistry&); 31 } 32 33 34 namespace { 35 36 class HexagonCFGOptimizer : public MachineFunctionPass { 37 38 private: 39 const HexagonTargetMachine& QTM; 40 const HexagonSubtarget &QST; 41 42 void InvertAndChangeJumpTarget(MachineInstr*, MachineBasicBlock*); 43 44 public: 45 static char ID; 46 HexagonCFGOptimizer(const HexagonTargetMachine& TM) 47 : MachineFunctionPass(ID), QTM(TM), QST(*TM.getSubtargetImpl()) { 48 initializeHexagonCFGOptimizerPass(*PassRegistry::getPassRegistry()); 49 } 50 51 const char *getPassName() const { 52 return "Hexagon CFG Optimizer"; 53 } 54 bool runOnMachineFunction(MachineFunction &Fn); 55 }; 56 57 58 char HexagonCFGOptimizer::ID = 0; 59 60 static bool IsConditionalBranch(int Opc) { 61 return (Opc == Hexagon::JMP_t) || (Opc == Hexagon::JMP_f) 62 || (Opc == Hexagon::JMP_tnew_t) || (Opc == Hexagon::JMP_fnew_t); 63 } 64 65 66 static bool IsUnconditionalJump(int Opc) { 67 return (Opc == Hexagon::JMP); 68 } 69 70 71 void 72 HexagonCFGOptimizer::InvertAndChangeJumpTarget(MachineInstr* MI, 73 MachineBasicBlock* NewTarget) { 74 const HexagonInstrInfo *QII = QTM.getInstrInfo(); 75 int NewOpcode = 0; 76 switch(MI->getOpcode()) { 77 case Hexagon::JMP_t: 78 NewOpcode = Hexagon::JMP_f; 79 break; 80 81 case Hexagon::JMP_f: 82 NewOpcode = Hexagon::JMP_t; 83 break; 84 85 case Hexagon::JMP_tnew_t: 86 NewOpcode = Hexagon::JMP_fnew_t; 87 break; 88 89 case Hexagon::JMP_fnew_t: 90 NewOpcode = Hexagon::JMP_tnew_t; 91 break; 92 93 default: 94 llvm_unreachable("Cannot handle this case"); 95 } 96 97 MI->setDesc(QII->get(NewOpcode)); 98 MI->getOperand(1).setMBB(NewTarget); 99 } 100 101 102 bool HexagonCFGOptimizer::runOnMachineFunction(MachineFunction &Fn) { 103 104 // Loop over all of the basic blocks. 105 for (MachineFunction::iterator MBBb = Fn.begin(), MBBe = Fn.end(); 106 MBBb != MBBe; ++MBBb) { 107 MachineBasicBlock* MBB = MBBb; 108 109 // Traverse the basic block. 110 MachineBasicBlock::iterator MII = MBB->getFirstTerminator(); 111 if (MII != MBB->end()) { 112 MachineInstr *MI = MII; 113 int Opc = MI->getOpcode(); 114 if (IsConditionalBranch(Opc)) { 115 116 // 117 // (Case 1) Transform the code if the following condition occurs: 118 // BB1: if (p0) jump BB3 119 // ...falls-through to BB2 ... 120 // BB2: jump BB4 121 // ...next block in layout is BB3... 122 // BB3: ... 123 // 124 // Transform this to: 125 // BB1: if (!p0) jump BB4 126 // Remove BB2 127 // BB3: ... 128 // 129 // (Case 2) A variation occurs when BB3 contains a JMP to BB4: 130 // BB1: if (p0) jump BB3 131 // ...falls-through to BB2 ... 132 // BB2: jump BB4 133 // ...other basic blocks ... 134 // BB4: 135 // ...not a fall-thru 136 // BB3: ... 137 // jump BB4 138 // 139 // Transform this to: 140 // BB1: if (!p0) jump BB4 141 // Remove BB2 142 // BB3: ... 143 // BB4: ... 144 // 145 unsigned NumSuccs = MBB->succ_size(); 146 MachineBasicBlock::succ_iterator SI = MBB->succ_begin(); 147 MachineBasicBlock* FirstSucc = *SI; 148 MachineBasicBlock* SecondSucc = *(++SI); 149 MachineBasicBlock* LayoutSucc = NULL; 150 MachineBasicBlock* JumpAroundTarget = NULL; 151 152 if (MBB->isLayoutSuccessor(FirstSucc)) { 153 LayoutSucc = FirstSucc; 154 JumpAroundTarget = SecondSucc; 155 } else if (MBB->isLayoutSuccessor(SecondSucc)) { 156 LayoutSucc = SecondSucc; 157 JumpAroundTarget = FirstSucc; 158 } else { 159 // Odd case...cannot handle. 160 } 161 162 // The target of the unconditional branch must be JumpAroundTarget. 163 // TODO: If not, we should not invert the unconditional branch. 164 MachineBasicBlock* CondBranchTarget = NULL; 165 if ((MI->getOpcode() == Hexagon::JMP_t) || 166 (MI->getOpcode() == Hexagon::JMP_f)) { 167 CondBranchTarget = MI->getOperand(1).getMBB(); 168 } 169 170 if (!LayoutSucc || (CondBranchTarget != JumpAroundTarget)) { 171 continue; 172 } 173 174 if ((NumSuccs == 2) && LayoutSucc && (LayoutSucc->pred_size() == 1)) { 175 176 // Ensure that BB2 has one instruction -- an unconditional jump. 177 if ((LayoutSucc->size() == 1) && 178 IsUnconditionalJump(LayoutSucc->front().getOpcode())) { 179 MachineBasicBlock* UncondTarget = 180 LayoutSucc->front().getOperand(0).getMBB(); 181 // Check if the layout successor of BB2 is BB3. 182 bool case1 = LayoutSucc->isLayoutSuccessor(JumpAroundTarget); 183 bool case2 = JumpAroundTarget->isSuccessor(UncondTarget) && 184 JumpAroundTarget->size() >= 1 && 185 IsUnconditionalJump(JumpAroundTarget->back().getOpcode()) && 186 JumpAroundTarget->pred_size() == 1 && 187 JumpAroundTarget->succ_size() == 1; 188 189 if (case1 || case2) { 190 InvertAndChangeJumpTarget(MI, UncondTarget); 191 MBB->removeSuccessor(JumpAroundTarget); 192 MBB->addSuccessor(UncondTarget); 193 194 // Remove the unconditional branch in LayoutSucc. 195 LayoutSucc->erase(LayoutSucc->begin()); 196 LayoutSucc->removeSuccessor(UncondTarget); 197 LayoutSucc->addSuccessor(JumpAroundTarget); 198 199 // This code performs the conversion for case 2, which moves 200 // the block to the fall-thru case (BB3 in the code above). 201 if (case2 && !case1) { 202 JumpAroundTarget->moveAfter(LayoutSucc); 203 // only move a block if it doesn't have a fall-thru. otherwise 204 // the CFG will be incorrect. 205 if (!UncondTarget->canFallThrough()) { 206 UncondTarget->moveAfter(JumpAroundTarget); 207 } 208 } 209 210 // 211 // Correct live-in information. Is used by post-RA scheduler 212 // The live-in to LayoutSucc is now all values live-in to 213 // JumpAroundTarget. 214 // 215 std::vector<unsigned> OrigLiveIn(LayoutSucc->livein_begin(), 216 LayoutSucc->livein_end()); 217 std::vector<unsigned> NewLiveIn(JumpAroundTarget->livein_begin(), 218 JumpAroundTarget->livein_end()); 219 for (unsigned i = 0; i < OrigLiveIn.size(); ++i) { 220 LayoutSucc->removeLiveIn(OrigLiveIn[i]); 221 } 222 for (unsigned i = 0; i < NewLiveIn.size(); ++i) { 223 LayoutSucc->addLiveIn(NewLiveIn[i]); 224 } 225 } 226 } 227 } 228 } 229 } 230 } 231 return true; 232 } 233 } 234 235 236 //===----------------------------------------------------------------------===// 237 // Public Constructor Functions 238 //===----------------------------------------------------------------------===// 239 240 static void initializePassOnce(PassRegistry &Registry) { 241 PassInfo *PI = new PassInfo("Hexagon CFG Optimizer", "hexagon-cfg", 242 &HexagonCFGOptimizer::ID, 0, false, false); 243 Registry.registerPass(*PI, true); 244 } 245 246 void llvm::initializeHexagonCFGOptimizerPass(PassRegistry &Registry) { 247 CALL_ONCE_INITIALIZATION(initializePassOnce) 248 } 249 250 FunctionPass *llvm::createHexagonCFGOptimizer(const HexagonTargetMachine &TM) { 251 return new HexagonCFGOptimizer(TM); 252 } 253
