1 //=- MachineLoopUtils.cpp - Functions for manipulating loops ----------------=// 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 "llvm/CodeGen/MachineLoopUtils.h" 10 #include "llvm/CodeGen/MachineBasicBlock.h" 11 #include "llvm/CodeGen/MachineRegisterInfo.h" 12 #include "llvm/CodeGen/TargetInstrInfo.h" 13 using namespace llvm; 14 15 namespace { 16 // MI's parent and BB are clones of each other. Find the equivalent copy of MI 17 // in BB. 18 MachineInstr &findEquivalentInstruction(MachineInstr &MI, 19 MachineBasicBlock *BB) { 20 MachineBasicBlock *PB = MI.getParent(); 21 unsigned Offset = std::distance(PB->instr_begin(), MachineBasicBlock::instr_iterator(MI)); 22 return *std::next(BB->instr_begin(), Offset); 23 } 24 } // namespace 25 26 MachineBasicBlock *llvm::PeelSingleBlockLoop(LoopPeelDirection Direction, 27 MachineBasicBlock *Loop, 28 MachineRegisterInfo &MRI, 29 const TargetInstrInfo *TII) { 30 MachineFunction &MF = *Loop->getParent(); 31 MachineBasicBlock *Preheader = *Loop->pred_begin(); 32 if (Preheader == Loop) 33 Preheader = *std::next(Loop->pred_begin()); 34 MachineBasicBlock *Exit = *Loop->succ_begin(); 35 if (Exit == Loop) 36 Exit = *std::next(Loop->succ_begin()); 37 38 MachineBasicBlock *NewBB = MF.CreateMachineBasicBlock(Loop->getBasicBlock()); 39 if (Direction == LPD_Front) 40 MF.insert(Loop->getIterator(), NewBB); 41 else 42 MF.insert(std::next(Loop->getIterator()), NewBB); 43 44 DenseMap<Register, Register> Remaps; 45 auto InsertPt = NewBB->end(); 46 for (MachineInstr &MI : *Loop) { 47 MachineInstr *NewMI = MF.CloneMachineInstr(&MI); 48 NewBB->insert(InsertPt, NewMI); 49 for (MachineOperand &MO : NewMI->defs()) { 50 Register OrigR = MO.getReg(); 51 if (OrigR.isPhysical()) 52 continue; 53 Register &R = Remaps[OrigR]; 54 R = MRI.createVirtualRegister(MRI.getRegClass(OrigR)); 55 MO.setReg(R); 56 57 if (Direction == LPD_Back) { 58 // Replace all uses outside the original loop with the new register. 59 // FIXME: is the use_iterator stable enough to mutate register uses 60 // while iterating? 61 SmallVector<MachineOperand *, 4> Uses; 62 for (auto &Use : MRI.use_operands(OrigR)) 63 if (Use.getParent()->getParent() != Loop) 64 Uses.push_back(&Use); 65 for (auto *Use : Uses) { 66 const TargetRegisterClass *ConstrainRegClass = 67 MRI.constrainRegClass(R, MRI.getRegClass(Use->getReg())); 68 assert(ConstrainRegClass && 69 "Expected a valid constrained register class!"); 70 (void)ConstrainRegClass; 71 Use->setReg(R); 72 } 73 } 74 } 75 } 76 77 for (auto I = NewBB->getFirstNonPHI(); I != NewBB->end(); ++I) 78 for (MachineOperand &MO : I->uses()) 79 if (MO.isReg() && Remaps.count(MO.getReg())) 80 MO.setReg(Remaps[MO.getReg()]); 81 82 for (auto I = NewBB->begin(); I->isPHI(); ++I) { 83 MachineInstr &MI = *I; 84 unsigned LoopRegIdx = 3, InitRegIdx = 1; 85 if (MI.getOperand(2).getMBB() != Preheader) 86 std::swap(LoopRegIdx, InitRegIdx); 87 MachineInstr &OrigPhi = findEquivalentInstruction(MI, Loop); 88 assert(OrigPhi.isPHI()); 89 if (Direction == LPD_Front) { 90 // When peeling front, we are only left with the initial value from the 91 // preheader. 92 Register R = MI.getOperand(LoopRegIdx).getReg(); 93 if (Remaps.count(R)) 94 R = Remaps[R]; 95 OrigPhi.getOperand(InitRegIdx).setReg(R); 96 MI.removeOperand(LoopRegIdx + 1); 97 MI.removeOperand(LoopRegIdx + 0); 98 } else { 99 // When peeling back, the initial value is the loop-carried value from 100 // the original loop. 101 Register LoopReg = OrigPhi.getOperand(LoopRegIdx).getReg(); 102 MI.getOperand(LoopRegIdx).setReg(LoopReg); 103 MI.removeOperand(InitRegIdx + 1); 104 MI.removeOperand(InitRegIdx + 0); 105 } 106 } 107 108 DebugLoc DL; 109 if (Direction == LPD_Front) { 110 Preheader->ReplaceUsesOfBlockWith(Loop, NewBB); 111 NewBB->addSuccessor(Loop); 112 Loop->replacePhiUsesWith(Preheader, NewBB); 113 Preheader->updateTerminator(Loop); 114 TII->removeBranch(*NewBB); 115 TII->insertBranch(*NewBB, Loop, nullptr, {}, DL); 116 } else { 117 Loop->replaceSuccessor(Exit, NewBB); 118 Exit->replacePhiUsesWith(Loop, NewBB); 119 NewBB->addSuccessor(Exit); 120 121 MachineBasicBlock *TBB = nullptr, *FBB = nullptr; 122 SmallVector<MachineOperand, 4> Cond; 123 bool CanAnalyzeBr = !TII->analyzeBranch(*Loop, TBB, FBB, Cond); 124 (void)CanAnalyzeBr; 125 assert(CanAnalyzeBr && "Must be able to analyze the loop branch!"); 126 TII->removeBranch(*Loop); 127 TII->insertBranch(*Loop, TBB == Exit ? NewBB : TBB, 128 FBB == Exit ? NewBB : FBB, Cond, DL); 129 if (TII->removeBranch(*NewBB) > 0) 130 TII->insertBranch(*NewBB, Exit, nullptr, {}, DL); 131 } 132 133 return NewBB; 134 } 135