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 "llvm/CodeGen/MachineBasicBlock.h" 11 #include "llvm/CodeGen/MachineBranchProbabilityInfo.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 (MachineFunction::iterator MBBb = Fn.begin(), MBBe = Fn.end(); 121 MBBb != MBBe; ++MBBb) { 122 MachineBasicBlock *MBB = &*MBBb; 123 124 // Traverse the basic block. 125 MachineBasicBlock::iterator MII = MBB->getFirstTerminator(); 126 if (MII != MBB->end()) { 127 MachineInstr &MI = *MII; 128 int Opc = MI.getOpcode(); 129 if (IsConditionalBranch(Opc)) { 130 // (Case 1) Transform the code if the following condition occurs: 131 // BB1: if (p0) jump BB3 132 // ...falls-through to BB2 ... 133 // BB2: jump BB4 134 // ...next block in layout is BB3... 135 // BB3: ... 136 // 137 // Transform this to: 138 // BB1: if (!p0) jump BB4 139 // Remove BB2 140 // BB3: ... 141 // 142 // (Case 2) A variation occurs when BB3 contains a JMP to BB4: 143 // BB1: if (p0) jump BB3 144 // ...falls-through to BB2 ... 145 // BB2: jump BB4 146 // ...other basic blocks ... 147 // BB4: 148 // ...not a fall-thru 149 // BB3: ... 150 // jump BB4 151 // 152 // Transform this to: 153 // BB1: if (!p0) jump BB4 154 // Remove BB2 155 // BB3: ... 156 // BB4: ... 157 unsigned NumSuccs = MBB->succ_size(); 158 MachineBasicBlock::succ_iterator SI = MBB->succ_begin(); 159 MachineBasicBlock* FirstSucc = *SI; 160 MachineBasicBlock* SecondSucc = *(++SI); 161 MachineBasicBlock* LayoutSucc = nullptr; 162 MachineBasicBlock* JumpAroundTarget = nullptr; 163 164 if (MBB->isLayoutSuccessor(FirstSucc)) { 165 LayoutSucc = FirstSucc; 166 JumpAroundTarget = SecondSucc; 167 } else if (MBB->isLayoutSuccessor(SecondSucc)) { 168 LayoutSucc = SecondSucc; 169 JumpAroundTarget = FirstSucc; 170 } else { 171 // Odd case...cannot handle. 172 } 173 174 // The target of the unconditional branch must be JumpAroundTarget. 175 // TODO: If not, we should not invert the unconditional branch. 176 MachineBasicBlock* CondBranchTarget = nullptr; 177 if (MI.getOpcode() == Hexagon::J2_jumpt || 178 MI.getOpcode() == Hexagon::J2_jumpf) { 179 CondBranchTarget = MI.getOperand(1).getMBB(); 180 } 181 182 if (!LayoutSucc || (CondBranchTarget != JumpAroundTarget)) { 183 continue; 184 } 185 186 if ((NumSuccs == 2) && LayoutSucc && (LayoutSucc->pred_size() == 1)) { 187 // Ensure that BB2 has one instruction -- an unconditional jump. 188 if ((LayoutSucc->size() == 1) && 189 IsUnconditionalJump(LayoutSucc->front().getOpcode())) { 190 assert(JumpAroundTarget && "jump target is needed to process second basic block"); 191 MachineBasicBlock* UncondTarget = 192 LayoutSucc->front().getOperand(0).getMBB(); 193 // Check if the layout successor of BB2 is BB3. 194 bool case1 = LayoutSucc->isLayoutSuccessor(JumpAroundTarget); 195 bool case2 = JumpAroundTarget->isSuccessor(UncondTarget) && 196 !JumpAroundTarget->empty() && 197 IsUnconditionalJump(JumpAroundTarget->back().getOpcode()) && 198 JumpAroundTarget->pred_size() == 1 && 199 JumpAroundTarget->succ_size() == 1; 200 201 if (case1 || case2) { 202 InvertAndChangeJumpTarget(MI, UncondTarget); 203 MBB->replaceSuccessor(JumpAroundTarget, UncondTarget); 204 205 // Remove the unconditional branch in LayoutSucc. 206 LayoutSucc->erase(LayoutSucc->begin()); 207 LayoutSucc->replaceSuccessor(UncondTarget, JumpAroundTarget); 208 209 // This code performs the conversion for case 2, which moves 210 // the block to the fall-thru case (BB3 in the code above). 211 if (case2 && !case1) { 212 JumpAroundTarget->moveAfter(LayoutSucc); 213 // only move a block if it doesn't have a fall-thru. otherwise 214 // the CFG will be incorrect. 215 if (!isOnFallThroughPath(UncondTarget)) 216 UncondTarget->moveAfter(JumpAroundTarget); 217 } 218 219 // Correct live-in information. Is used by post-RA scheduler 220 // The live-in to LayoutSucc is now all values live-in to 221 // JumpAroundTarget. 222 std::vector<MachineBasicBlock::RegisterMaskPair> OrigLiveIn( 223 LayoutSucc->livein_begin(), LayoutSucc->livein_end()); 224 std::vector<MachineBasicBlock::RegisterMaskPair> NewLiveIn( 225 JumpAroundTarget->livein_begin(), 226 JumpAroundTarget->livein_end()); 227 for (const auto &OrigLI : OrigLiveIn) 228 LayoutSucc->removeLiveIn(OrigLI.PhysReg); 229 for (const auto &NewLI : NewLiveIn) 230 LayoutSucc->addLiveIn(NewLI); 231 } 232 } 233 } 234 } 235 } 236 } 237 return true; 238 } 239 240 //===----------------------------------------------------------------------===// 241 // Public Constructor Functions 242 //===----------------------------------------------------------------------===// 243 244 INITIALIZE_PASS(HexagonCFGOptimizer, "hexagon-cfg", "Hexagon CFG Optimizer", 245 false, false) 246 247 FunctionPass *llvm::createHexagonCFGOptimizer() { 248 return new HexagonCFGOptimizer(); 249 } 250