lib/Target/AVR/AVRRegisterInfo.cpp

   1 //===-- AVRRegisterInfo.cpp - AVR Register Information --------------------===//
   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 // This file contains the AVR implementation of the TargetRegisterInfo class.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "AVRRegisterInfo.h"
  14
  15 #include "llvm/ADT/BitVector.h"
  16 #include "llvm/CodeGen/MachineFrameInfo.h"
  17 #include "llvm/CodeGen/MachineFunction.h"
  18 #include "llvm/CodeGen/MachineInstrBuilder.h"
  19 #include "llvm/CodeGen/MachineRegisterInfo.h"
  20 #include "llvm/IR/Function.h"
  21 #include "llvm/CodeGen/TargetFrameLowering.h"
  22
  23 #include "AVR.h"
  24 #include "AVRInstrInfo.h"
  25 #include "AVRTargetMachine.h"
  26 #include "MCTargetDesc/AVRMCTargetDesc.h"
  27
  28 #define GET_REGINFO_TARGET_DESC
  29 #include "AVRGenRegisterInfo.inc"
  30
  31 namespace llvm {
  32
  33 AVRRegisterInfo::AVRRegisterInfo() : AVRGenRegisterInfo(0) {}
  34
  35 const uint16_t *
  36 AVRRegisterInfo::getCalleeSavedRegs(const MachineFunction *MF) const {
  37   CallingConv::ID CC = MF->getFunction().getCallingConv();
  38
  39   return ((CC == CallingConv::AVR_INTR || CC == CallingConv::AVR_SIGNAL)
  40               ? CSR_Interrupts_SaveList
  41               : CSR_Normal_SaveList);
  42 }
  43
  44 const uint32_t *
  45 AVRRegisterInfo::getCallPreservedMask(const MachineFunction &MF,
  46                                       CallingConv::ID CC) const {
  47   return ((CC == CallingConv::AVR_INTR || CC == CallingConv::AVR_SIGNAL)
  48               ? CSR_Interrupts_RegMask
  49               : CSR_Normal_RegMask);
  50 }
  51
  52 BitVector AVRRegisterInfo::getReservedRegs(const MachineFunction &MF) const {
  53   BitVector Reserved(getNumRegs());
  54
  55   // Reserve the intermediate result registers r1 and r2
  56   // The result of instructions like 'mul' is always stored here.
  57   Reserved.set(AVR::R0);
  58   Reserved.set(AVR::R1);
  59   Reserved.set(AVR::R1R0);
  60
  61   //  Reserve the stack pointer.
  62   Reserved.set(AVR::SPL);
  63   Reserved.set(AVR::SPH);
  64   Reserved.set(AVR::SP);
  65
  66   // We tenatively reserve the frame pointer register r29:r28 because the
  67   // function may require one, but we cannot tell until register allocation
  68   // is complete, which can be too late.
  69   //
  70   // Instead we just unconditionally reserve the Y register.
  71   //
  72   // TODO: Write a pass to enumerate functions which reserved the Y register
  73   //       but didn't end up needing a frame pointer. In these, we can
  74   //       convert one or two of the spills inside to use the Y register.
  75   Reserved.set(AVR::R28);
  76   Reserved.set(AVR::R29);
  77   Reserved.set(AVR::R29R28);
  78
  79   return Reserved;
  80 }
  81
  82 const TargetRegisterClass *
  83 AVRRegisterInfo::getLargestLegalSuperClass(const TargetRegisterClass *RC,
  84                                            const MachineFunction &MF) const {
  85   const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
  86   if (TRI->isTypeLegalForClass(*RC, MVT::i16)) {
  87     return &AVR::DREGSRegClass;
  88   }
  89
  90   if (TRI->isTypeLegalForClass(*RC, MVT::i8)) {
  91     return &AVR::GPR8RegClass;
  92   }
  93
  94   llvm_unreachable("Invalid register size");
  95 }
  96
  97 /// Fold a frame offset shared between two add instructions into a single one.
  98 static void foldFrameOffset(MachineBasicBlock::iterator &II, int &Offset, unsigned DstReg) {
  99   MachineInstr &MI = *II;
 100   int Opcode = MI.getOpcode();
 101
 102   // Don't bother trying if the next instruction is not an add or a sub.
 103   if ((Opcode != AVR::SUBIWRdK) && (Opcode != AVR::ADIWRdK)) {
 104     return;
 105   }
 106
 107   // Check that DstReg matches with next instruction, otherwise the instruction
 108   // is not related to stack address manipulation.
 109   if (DstReg != MI.getOperand(0).getReg()) {
 110     return;
 111   }
 112
 113   // Add the offset in the next instruction to our offset.
 114   switch (Opcode) {
 115   case AVR::SUBIWRdK:
 116     Offset += -MI.getOperand(2).getImm();
 117     break;
 118   case AVR::ADIWRdK:
 119     Offset += MI.getOperand(2).getImm();
 120     break;
 121   }
 122
 123   // Finally remove the instruction.
 124   II++;
 125   MI.eraseFromParent();
 126 }
 127
 128 void AVRRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
 129                                           int SPAdj, unsigned FIOperandNum,
 130                                           RegScavenger *RS) const {
 131   assert(SPAdj == 0 && "Unexpected SPAdj value");
 132
 133   MachineInstr &MI = *II;
 134   DebugLoc dl = MI.getDebugLoc();
 135   MachineBasicBlock &MBB = *MI.getParent();
 136   const MachineFunction &MF = *MBB.getParent();
 137   const AVRTargetMachine &TM = (const AVRTargetMachine &)MF.getTarget();
 138   const TargetInstrInfo &TII = *TM.getSubtargetImpl()->getInstrInfo();
 139   const MachineFrameInfo &MFI = MF.getFrameInfo();
 140   const TargetFrameLowering *TFI = TM.getSubtargetImpl()->getFrameLowering();
 141   int FrameIndex = MI.getOperand(FIOperandNum).getIndex();
 142   int Offset = MFI.getObjectOffset(FrameIndex);
 143
 144   // Add one to the offset because SP points to an empty slot.
 145   Offset += MFI.getStackSize() - TFI->getOffsetOfLocalArea() + 1;
 146   // Fold incoming offset.
 147   Offset += MI.getOperand(FIOperandNum + 1).getImm();
 148
 149   // This is actually "load effective address" of the stack slot
 150   // instruction. We have only two-address instructions, thus we need to
 151   // expand it into move + add.
 152   if (MI.getOpcode() == AVR::FRMIDX) {
 153     MI.setDesc(TII.get(AVR::MOVWRdRr));
 154     MI.getOperand(FIOperandNum).ChangeToRegister(AVR::R29R28, false);
 155     MI.RemoveOperand(2);
 156
 157     assert(Offset > 0 && "Invalid offset");
 158
 159     // We need to materialize the offset via an add instruction.
 160     unsigned Opcode;
 161     Register DstReg = MI.getOperand(0).getReg();
 162     assert(DstReg != AVR::R29R28 && "Dest reg cannot be the frame pointer");
 163
 164     II++; // Skip over the FRMIDX (and now MOVW) instruction.
 165
 166     // Generally, to load a frame address two add instructions are emitted that
 167     // could get folded into a single one:
 168     //  movw    r31:r30, r29:r28
 169     //  adiw    r31:r30, 29
 170     //  adiw    r31:r30, 16
 171     // to:
 172     //  movw    r31:r30, r29:r28
 173     //  adiw    r31:r30, 45
 174     if (II != MBB.end())
 175       foldFrameOffset(II, Offset, DstReg);
 176
 177     // Select the best opcode based on DstReg and the offset size.
 178     switch (DstReg) {
 179     case AVR::R25R24:
 180     case AVR::R27R26:
 181     case AVR::R31R30: {
 182       if (isUInt<6>(Offset)) {
 183         Opcode = AVR::ADIWRdK;
 184         break;
 185       }
 186       LLVM_FALLTHROUGH;
 187     }
 188     default: {
 189       // This opcode will get expanded into a pair of subi/sbci.
 190       Opcode = AVR::SUBIWRdK;
 191       Offset = -Offset;
 192       break;
 193     }
 194     }
 195
 196     MachineInstr *New = BuildMI(MBB, II, dl, TII.get(Opcode), DstReg)
 197                             .addReg(DstReg, RegState::Kill)
 198                             .addImm(Offset);
 199     New->getOperand(3).setIsDead();
 200
 201     return;
 202   }
 203
 204   // If the offset is too big we have to adjust and restore the frame pointer
 205   // to materialize a valid load/store with displacement.
 206   //:TODO: consider using only one adiw/sbiw chain for more than one frame index
 207   if (Offset > 62) {
 208     unsigned AddOpc = AVR::ADIWRdK, SubOpc = AVR::SBIWRdK;
 209     int AddOffset = Offset - 63 + 1;
 210
 211     // For huge offsets where adiw/sbiw cannot be used use a pair of subi/sbci.
 212     if ((Offset - 63 + 1) > 63) {
 213       AddOpc = AVR::SUBIWRdK;
 214       SubOpc = AVR::SUBIWRdK;
 215       AddOffset = -AddOffset;
 216     }
 217
 218     // It is possible that the spiller places this frame instruction in between
 219     // a compare and branch, invalidating the contents of SREG set by the
 220     // compare instruction because of the add/sub pairs. Conservatively save and
 221     // restore SREG before and after each add/sub pair.
 222     BuildMI(MBB, II, dl, TII.get(AVR::INRdA), AVR::R0).addImm(0x3f);
 223
 224     MachineInstr *New = BuildMI(MBB, II, dl, TII.get(AddOpc), AVR::R29R28)
 225                             .addReg(AVR::R29R28, RegState::Kill)
 226                             .addImm(AddOffset);
 227     New->getOperand(3).setIsDead();
 228
 229     // Restore SREG.
 230     BuildMI(MBB, std::next(II), dl, TII.get(AVR::OUTARr))
 231         .addImm(0x3f)
 232         .addReg(AVR::R0, RegState::Kill);
 233
 234     // No need to set SREG as dead here otherwise if the next instruction is a
 235     // cond branch it will be using a dead register.
 236     BuildMI(MBB, std::next(II), dl, TII.get(SubOpc), AVR::R29R28)
 237         .addReg(AVR::R29R28, RegState::Kill)
 238         .addImm(Offset - 63 + 1);
 239
 240     Offset = 62;
 241   }
 242
 243   MI.getOperand(FIOperandNum).ChangeToRegister(AVR::R29R28, false);
 244   assert(isUInt<6>(Offset) && "Offset is out of range");
 245   MI.getOperand(FIOperandNum + 1).ChangeToImmediate(Offset);
 246 }
 247
 248 Register AVRRegisterInfo::getFrameRegister(const MachineFunction &MF) const {
 249   const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
 250   if (TFI->hasFP(MF)) {
 251     // The Y pointer register
 252     return AVR::R28;
 253   }
 254
 255   return AVR::SP;
 256 }
 257
 258 const TargetRegisterClass *
 259 AVRRegisterInfo::getPointerRegClass(const MachineFunction &MF,
 260                                     unsigned Kind) const {
 261   // FIXME: Currently we're using avr-gcc as reference, so we restrict
 262   // ptrs to Y and Z regs. Though avr-gcc has buggy implementation
 263   // of memory constraint, so we can fix it and bit avr-gcc here ;-)
 264   return &AVR::PTRDISPREGSRegClass;
 265 }
 266
 267 void AVRRegisterInfo::splitReg(unsigned Reg,
 268                                unsigned &LoReg,
 269                                unsigned &HiReg) const {
 270     assert(AVR::DREGSRegClass.contains(Reg) && "can only split 16-bit registers");
 271
 272     LoReg = getSubReg(Reg, AVR::sub_lo);
 273     HiReg = getSubReg(Reg, AVR::sub_hi);
 274 }
 275
 276 bool AVRRegisterInfo::shouldCoalesce(MachineInstr *MI,
 277                                      const TargetRegisterClass *SrcRC,
 278                                      unsigned SubReg,
 279                                      const TargetRegisterClass *DstRC,
 280                                      unsigned DstSubReg,
 281                                      const TargetRegisterClass *NewRC,
 282                                      LiveIntervals &LIS) const {
 283   if(this->getRegClass(AVR::PTRDISPREGSRegClassID)->hasSubClassEq(NewRC)) {
 284     return false;
 285   }
 286
 287   return TargetRegisterInfo::shouldCoalesce(MI, SrcRC, SubReg, DstRC, DstSubReg, NewRC, LIS);
 288 }
 289
 290 } // end of namespace llvm