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/MachineBranchProbabilityInfo.h" 13 #include "llvm/CodeGen/MachineFunction.h" 14 #include "llvm/CodeGen/MachineFunctionPass.h" 15 #include "llvm/CodeGen/MachineInstr.h" 16 #include "llvm/CodeGen/MachineOperand.h" 17 #include "llvm/CodeGen/TargetInstrInfo.h" 18 #include "llvm/CodeGen/TargetSubtargetInfo.h" 19 #include "llvm/Pass.h" 20 #include "llvm/Support/ErrorHandling.h" 21 #include <cassert> 22 #include <vector> 23 24 using namespace llvm; 25 26 #define DEBUG_TYPE "hexagon_cfg" 27 28 namespace llvm { 29 30 FunctionPass *createHexagonCFGOptimizer(); 31 void initializeHexagonCFGOptimizerPass(PassRegistry&); 32 33 } // end namespace llvm 34 35 namespace { 36 37 class HexagonCFGOptimizer : public MachineFunctionPass { 38 private: 39 void InvertAndChangeJumpTarget(MachineInstr &, MachineBasicBlock *); 40 bool isOnFallThroughPath(MachineBasicBlock *MBB); 41 42 public: 43 static char ID; 44 45 HexagonCFGOptimizer() : MachineFunctionPass(ID) { 46 initializeHexagonCFGOptimizerPass(*PassRegistry::getPassRegistry()); 47 } 48 49 StringRef getPassName() const override { return "Hexagon CFG Optimizer"; } 50 bool runOnMachineFunction(MachineFunction &Fn) override; 51 52 MachineFunctionProperties getRequiredProperties() const override { 53 return MachineFunctionProperties().set( 54 MachineFunctionProperties::Property::NoVRegs); 55 } 56 }; 57 58 } // end anonymous namespace 59 60 char HexagonCFGOptimizer::ID = 0; 61 62 static bool IsConditionalBranch(int Opc) { 63 switch (Opc) { 64 case Hexagon::J2_jumpt: 65 case Hexagon::J2_jumptpt: 66 case Hexagon::J2_jumpf: 67 case Hexagon::J2_jumpfpt: 68 case Hexagon::J2_jumptnew: 69 case Hexagon::J2_jumpfnew: 70 case Hexagon::J2_jumptnewpt: 71 case Hexagon::J2_jumpfnewpt: 72 return true; 73 } 74 return false; 75 } 76 77 static bool IsUnconditionalJump(int Opc) { 78 return (Opc == Hexagon::J2_jump); 79 } 80 81 void HexagonCFGOptimizer::InvertAndChangeJumpTarget( 82 MachineInstr &MI, MachineBasicBlock *NewTarget) { 83 const TargetInstrInfo *TII = 84 MI.getParent()->getParent()->getSubtarget().getInstrInfo(); 85 int NewOpcode = 0; 86 switch (MI.getOpcode()) { 87 case Hexagon::J2_jumpt: 88 NewOpcode = Hexagon::J2_jumpf; 89 break; 90 case Hexagon::J2_jumpf: 91 NewOpcode = Hexagon::J2_jumpt; 92 break; 93 case Hexagon::J2_jumptnewpt: 94 NewOpcode = Hexagon::J2_jumpfnewpt; 95 break; 96 case Hexagon::J2_jumpfnewpt: 97 NewOpcode = Hexagon::J2_jumptnewpt; 98 break; 99 default: 100 llvm_unreachable("Cannot handle this case"); 101 } 102 103 MI.setDesc(TII->get(NewOpcode)); 104 MI.getOperand(1).setMBB(NewTarget); 105 } 106 107 bool HexagonCFGOptimizer::isOnFallThroughPath(MachineBasicBlock *MBB) { 108 if (MBB->canFallThrough()) 109 return true; 110 for (MachineBasicBlock *PB : MBB->predecessors()) 111 if (PB->isLayoutSuccessor(MBB) && PB->canFallThrough()) 112 return true; 113 return false; 114 } 115 116 bool HexagonCFGOptimizer::runOnMachineFunction(MachineFunction &Fn) { 117 if (skipFunction(Fn.getFunction())) 118 return false; 119 120 // Loop over all of the basic blocks. 121 for (MachineFunction::iterator MBBb = Fn.begin(), MBBe = Fn.end(); 122 MBBb != MBBe; ++MBBb) { 123 MachineBasicBlock *MBB = &*MBBb; 124 125 // Traverse the basic block. 126 MachineBasicBlock::iterator MII = MBB->getFirstTerminator(); 127 if (MII != MBB->end()) { 128 MachineInstr &MI = *MII; 129 int Opc = MI.getOpcode(); 130 if (IsConditionalBranch(Opc)) { 131 // (Case 1) Transform the code if the following condition occurs: 132 // BB1: if (p0) jump BB3 133 // ...falls-through to BB2 ... 134 // BB2: jump BB4 135 // ...next block in layout is BB3... 136 // BB3: ... 137 // 138 // Transform this to: 139 // BB1: if (!p0) jump BB4 140 // Remove BB2 141 // BB3: ... 142 // 143 // (Case 2) A variation occurs when BB3 contains a JMP to BB4: 144 // BB1: if (p0) jump BB3 145 // ...falls-through to BB2 ... 146 // BB2: jump BB4 147 // ...other basic blocks ... 148 // BB4: 149 // ...not a fall-thru 150 // BB3: ... 151 // jump BB4 152 // 153 // Transform this to: 154 // BB1: if (!p0) jump BB4 155 // Remove BB2 156 // BB3: ... 157 // BB4: ... 158 unsigned NumSuccs = MBB->succ_size(); 159 MachineBasicBlock::succ_iterator SI = MBB->succ_begin(); 160 MachineBasicBlock* FirstSucc = *SI; 161 MachineBasicBlock* SecondSucc = *(++SI); 162 MachineBasicBlock* LayoutSucc = nullptr; 163 MachineBasicBlock* JumpAroundTarget = nullptr; 164 165 if (MBB->isLayoutSuccessor(FirstSucc)) { 166 LayoutSucc = FirstSucc; 167 JumpAroundTarget = SecondSucc; 168 } else if (MBB->isLayoutSuccessor(SecondSucc)) { 169 LayoutSucc = SecondSucc; 170 JumpAroundTarget = FirstSucc; 171 } else { 172 // Odd case...cannot handle. 173 } 174 175 // The target of the unconditional branch must be JumpAroundTarget. 176 // TODO: If not, we should not invert the unconditional branch. 177 MachineBasicBlock* CondBranchTarget = nullptr; 178 if (MI.getOpcode() == Hexagon::J2_jumpt || 179 MI.getOpcode() == Hexagon::J2_jumpf) { 180 CondBranchTarget = MI.getOperand(1).getMBB(); 181 } 182 183 if (!LayoutSucc || (CondBranchTarget != JumpAroundTarget)) { 184 continue; 185 } 186 187 if ((NumSuccs == 2) && LayoutSucc && (LayoutSucc->pred_size() == 1)) { 188 // Ensure that BB2 has one instruction -- an unconditional jump. 189 if ((LayoutSucc->size() == 1) && 190 IsUnconditionalJump(LayoutSucc->front().getOpcode())) { 191 assert(JumpAroundTarget && "jump target is needed to process second basic block"); 192 MachineBasicBlock* UncondTarget = 193 LayoutSucc->front().getOperand(0).getMBB(); 194 // Check if the layout successor of BB2 is BB3. 195 bool case1 = LayoutSucc->isLayoutSuccessor(JumpAroundTarget); 196 bool case2 = JumpAroundTarget->isSuccessor(UncondTarget) && 197 !JumpAroundTarget->empty() && 198 IsUnconditionalJump(JumpAroundTarget->back().getOpcode()) && 199 JumpAroundTarget->pred_size() == 1 && 200 JumpAroundTarget->succ_size() == 1; 201 202 if (case1 || case2) { 203 InvertAndChangeJumpTarget(MI, UncondTarget); 204 MBB->replaceSuccessor(JumpAroundTarget, UncondTarget); 205 206 // Remove the unconditional branch in LayoutSucc. 207 LayoutSucc->erase(LayoutSucc->begin()); 208 LayoutSucc->replaceSuccessor(UncondTarget, JumpAroundTarget); 209 210 // This code performs the conversion for case 2, which moves 211 // the block to the fall-thru case (BB3 in the code above). 212 if (case2 && !case1) { 213 JumpAroundTarget->moveAfter(LayoutSucc); 214 // only move a block if it doesn't have a fall-thru. otherwise 215 // the CFG will be incorrect. 216 if (!isOnFallThroughPath(UncondTarget)) 217 UncondTarget->moveAfter(JumpAroundTarget); 218 } 219 220 // Correct live-in information. Is used by post-RA scheduler 221 // The live-in to LayoutSucc is now all values live-in to 222 // JumpAroundTarget. 223 std::vector<MachineBasicBlock::RegisterMaskPair> OrigLiveIn( 224 LayoutSucc->livein_begin(), LayoutSucc->livein_end()); 225 std::vector<MachineBasicBlock::RegisterMaskPair> NewLiveIn( 226 JumpAroundTarget->livein_begin(), 227 JumpAroundTarget->livein_end()); 228 for (const auto &OrigLI : OrigLiveIn) 229 LayoutSucc->removeLiveIn(OrigLI.PhysReg); 230 for (const auto &NewLI : NewLiveIn) 231 LayoutSucc->addLiveIn(NewLI); 232 } 233 } 234 } 235 } 236 } 237 } 238 return true; 239 } 240 241 //===----------------------------------------------------------------------===// 242 // Public Constructor Functions 243 //===----------------------------------------------------------------------===// 244 245 INITIALIZE_PASS(HexagonCFGOptimizer, "hexagon-cfg", "Hexagon CFG Optimizer", 246 false, false) 247 248 FunctionPass *llvm::createHexagonCFGOptimizer() { 249 return new HexagonCFGOptimizer(); 250 } 251