1 //===- HexagonCFGOptimizer.cpp - CFG optimizations ------------------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 9 #include "Hexagon.h" 10 #include "MCTargetDesc/HexagonMCTargetDesc.h" 11 #include "llvm/CodeGen/MachineBasicBlock.h" 12 #include "llvm/CodeGen/MachineFunction.h" 13 #include "llvm/CodeGen/MachineFunctionPass.h" 14 #include "llvm/CodeGen/MachineInstr.h" 15 #include "llvm/CodeGen/MachineOperand.h" 16 #include "llvm/CodeGen/TargetInstrInfo.h" 17 #include "llvm/CodeGen/TargetSubtargetInfo.h" 18 #include "llvm/Pass.h" 19 #include "llvm/Support/ErrorHandling.h" 20 #include <cassert> 21 #include <vector> 22 23 using namespace llvm; 24 25 #define DEBUG_TYPE "hexagon_cfg" 26 27 namespace llvm { 28 29 FunctionPass *createHexagonCFGOptimizer(); 30 void initializeHexagonCFGOptimizerPass(PassRegistry&); 31 32 } // end namespace llvm 33 34 namespace { 35 36 class HexagonCFGOptimizer : public MachineFunctionPass { 37 private: 38 void InvertAndChangeJumpTarget(MachineInstr &, MachineBasicBlock *); 39 bool isOnFallThroughPath(MachineBasicBlock *MBB); 40 41 public: 42 static char ID; 43 44 HexagonCFGOptimizer() : MachineFunctionPass(ID) { 45 initializeHexagonCFGOptimizerPass(*PassRegistry::getPassRegistry()); 46 } 47 48 StringRef getPassName() const override { return "Hexagon CFG Optimizer"; } 49 bool runOnMachineFunction(MachineFunction &Fn) override; 50 51 MachineFunctionProperties getRequiredProperties() const override { 52 return MachineFunctionProperties().set( 53 MachineFunctionProperties::Property::NoVRegs); 54 } 55 }; 56 57 } // end anonymous namespace 58 59 char HexagonCFGOptimizer::ID = 0; 60 61 static bool IsConditionalBranch(int Opc) { 62 switch (Opc) { 63 case Hexagon::J2_jumpt: 64 case Hexagon::J2_jumptpt: 65 case Hexagon::J2_jumpf: 66 case Hexagon::J2_jumpfpt: 67 case Hexagon::J2_jumptnew: 68 case Hexagon::J2_jumpfnew: 69 case Hexagon::J2_jumptnewpt: 70 case Hexagon::J2_jumpfnewpt: 71 return true; 72 } 73 return false; 74 } 75 76 static bool IsUnconditionalJump(int Opc) { 77 return (Opc == Hexagon::J2_jump); 78 } 79 80 void HexagonCFGOptimizer::InvertAndChangeJumpTarget( 81 MachineInstr &MI, MachineBasicBlock *NewTarget) { 82 const TargetInstrInfo *TII = 83 MI.getParent()->getParent()->getSubtarget().getInstrInfo(); 84 int NewOpcode = 0; 85 switch (MI.getOpcode()) { 86 case Hexagon::J2_jumpt: 87 NewOpcode = Hexagon::J2_jumpf; 88 break; 89 case Hexagon::J2_jumpf: 90 NewOpcode = Hexagon::J2_jumpt; 91 break; 92 case Hexagon::J2_jumptnewpt: 93 NewOpcode = Hexagon::J2_jumpfnewpt; 94 break; 95 case Hexagon::J2_jumpfnewpt: 96 NewOpcode = Hexagon::J2_jumptnewpt; 97 break; 98 default: 99 llvm_unreachable("Cannot handle this case"); 100 } 101 102 MI.setDesc(TII->get(NewOpcode)); 103 MI.getOperand(1).setMBB(NewTarget); 104 } 105 106 bool HexagonCFGOptimizer::isOnFallThroughPath(MachineBasicBlock *MBB) { 107 if (MBB->canFallThrough()) 108 return true; 109 for (MachineBasicBlock *PB : MBB->predecessors()) 110 if (PB->isLayoutSuccessor(MBB) && PB->canFallThrough()) 111 return true; 112 return false; 113 } 114 115 bool HexagonCFGOptimizer::runOnMachineFunction(MachineFunction &Fn) { 116 if (skipFunction(Fn.getFunction())) 117 return false; 118 119 // Loop over all of the basic blocks. 120 for (MachineBasicBlock &MBB : Fn) { 121 // Traverse the basic block. 122 MachineBasicBlock::iterator MII = MBB.getFirstTerminator(); 123 if (MII != MBB.end()) { 124 MachineInstr &MI = *MII; 125 int Opc = MI.getOpcode(); 126 if (IsConditionalBranch(Opc)) { 127 // (Case 1) Transform the code if the following condition occurs: 128 // BB1: if (p0) jump BB3 129 // ...falls-through to BB2 ... 130 // BB2: jump BB4 131 // ...next block in layout is BB3... 132 // BB3: ... 133 // 134 // Transform this to: 135 // BB1: if (!p0) jump BB4 136 // Remove BB2 137 // BB3: ... 138 // 139 // (Case 2) A variation occurs when BB3 contains a JMP to BB4: 140 // BB1: if (p0) jump BB3 141 // ...falls-through to BB2 ... 142 // BB2: jump BB4 143 // ...other basic blocks ... 144 // BB4: 145 // ...not a fall-thru 146 // BB3: ... 147 // jump BB4 148 // 149 // Transform this to: 150 // BB1: if (!p0) jump BB4 151 // Remove BB2 152 // BB3: ... 153 // BB4: ... 154 unsigned NumSuccs = MBB.succ_size(); 155 MachineBasicBlock::succ_iterator SI = MBB.succ_begin(); 156 MachineBasicBlock* FirstSucc = *SI; 157 MachineBasicBlock* SecondSucc = *(++SI); 158 MachineBasicBlock* LayoutSucc = nullptr; 159 MachineBasicBlock* JumpAroundTarget = nullptr; 160 161 if (MBB.isLayoutSuccessor(FirstSucc)) { 162 LayoutSucc = FirstSucc; 163 JumpAroundTarget = SecondSucc; 164 } else if (MBB.isLayoutSuccessor(SecondSucc)) { 165 LayoutSucc = SecondSucc; 166 JumpAroundTarget = FirstSucc; 167 } else { 168 // Odd case...cannot handle. 169 } 170 171 // The target of the unconditional branch must be JumpAroundTarget. 172 // TODO: If not, we should not invert the unconditional branch. 173 MachineBasicBlock* CondBranchTarget = nullptr; 174 if (MI.getOpcode() == Hexagon::J2_jumpt || 175 MI.getOpcode() == Hexagon::J2_jumpf) { 176 CondBranchTarget = MI.getOperand(1).getMBB(); 177 } 178 179 if (!LayoutSucc || (CondBranchTarget != JumpAroundTarget)) { 180 continue; 181 } 182 183 if ((NumSuccs == 2) && LayoutSucc && (LayoutSucc->pred_size() == 1)) { 184 // Ensure that BB2 has one instruction -- an unconditional jump. 185 if ((LayoutSucc->size() == 1) && 186 IsUnconditionalJump(LayoutSucc->front().getOpcode())) { 187 assert(JumpAroundTarget && "jump target is needed to process second basic block"); 188 MachineBasicBlock* UncondTarget = 189 LayoutSucc->front().getOperand(0).getMBB(); 190 // Check if the layout successor of BB2 is BB3. 191 bool case1 = LayoutSucc->isLayoutSuccessor(JumpAroundTarget); 192 bool case2 = JumpAroundTarget->isSuccessor(UncondTarget) && 193 !JumpAroundTarget->empty() && 194 IsUnconditionalJump(JumpAroundTarget->back().getOpcode()) && 195 JumpAroundTarget->pred_size() == 1 && 196 JumpAroundTarget->succ_size() == 1; 197 198 if (case1 || case2) { 199 InvertAndChangeJumpTarget(MI, UncondTarget); 200 MBB.replaceSuccessor(JumpAroundTarget, UncondTarget); 201 202 // Remove the unconditional branch in LayoutSucc. 203 LayoutSucc->erase(LayoutSucc->begin()); 204 LayoutSucc->replaceSuccessor(UncondTarget, JumpAroundTarget); 205 206 // This code performs the conversion for case 2, which moves 207 // the block to the fall-thru case (BB3 in the code above). 208 if (case2 && !case1) { 209 JumpAroundTarget->moveAfter(LayoutSucc); 210 // only move a block if it doesn't have a fall-thru. otherwise 211 // the CFG will be incorrect. 212 if (!isOnFallThroughPath(UncondTarget)) 213 UncondTarget->moveAfter(JumpAroundTarget); 214 } 215 216 // Correct live-in information. Is used by post-RA scheduler 217 // The live-in to LayoutSucc is now all values live-in to 218 // JumpAroundTarget. 219 std::vector<MachineBasicBlock::RegisterMaskPair> OrigLiveIn( 220 LayoutSucc->livein_begin(), LayoutSucc->livein_end()); 221 std::vector<MachineBasicBlock::RegisterMaskPair> NewLiveIn( 222 JumpAroundTarget->livein_begin(), 223 JumpAroundTarget->livein_end()); 224 for (const auto &OrigLI : OrigLiveIn) 225 LayoutSucc->removeLiveIn(OrigLI.PhysReg); 226 for (const auto &NewLI : NewLiveIn) 227 LayoutSucc->addLiveIn(NewLI); 228 } 229 } 230 } 231 } 232 } 233 } 234 return true; 235 } 236 237 //===----------------------------------------------------------------------===// 238 // Public Constructor Functions 239 //===----------------------------------------------------------------------===// 240 241 INITIALIZE_PASS(HexagonCFGOptimizer, "hexagon-cfg", "Hexagon CFG Optimizer", 242 false, false) 243 244 FunctionPass *llvm::createHexagonCFGOptimizer() { 245 return new HexagonCFGOptimizer(); 246 } 247