lib/Target/ARM/ThumbRegisterInfo.cpp

   1 //===-- ThumbRegisterInfo.cpp - Thumb-1 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 Thumb-1 implementation of the TargetRegisterInfo
  10 // class.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "ThumbRegisterInfo.h"
  15 #include "ARMBaseInstrInfo.h"
  16 #include "ARMMachineFunctionInfo.h"
  17 #include "ARMSubtarget.h"
  18 #include "MCTargetDesc/ARMAddressingModes.h"
  19 #include "llvm/CodeGen/MachineConstantPool.h"
  20 #include "llvm/CodeGen/MachineFrameInfo.h"
  21 #include "llvm/CodeGen/MachineFunction.h"
  22 #include "llvm/CodeGen/MachineInstrBuilder.h"
  23 #include "llvm/CodeGen/MachineRegisterInfo.h"
  24 #include "llvm/CodeGen/RegisterScavenging.h"
  25 #include "llvm/IR/Constants.h"
  26 #include "llvm/IR/DerivedTypes.h"
  27 #include "llvm/IR/Function.h"
  28 #include "llvm/IR/LLVMContext.h"
  29 #include "llvm/Support/CommandLine.h"
  30 #include "llvm/Support/ErrorHandling.h"
  31 #include "llvm/CodeGen/TargetFrameLowering.h"
  32 #include "llvm/Target/TargetMachine.h"
  33
  34 namespace llvm {
  35 extern cl::opt<bool> ReuseFrameIndexVals;
  36 }
  37
  38 using namespace llvm;
  39
  40 ThumbRegisterInfo::ThumbRegisterInfo() : ARMBaseRegisterInfo() {}
  41
  42 const TargetRegisterClass *
  43 ThumbRegisterInfo::getLargestLegalSuperClass(const TargetRegisterClass *RC,
  44                                               const MachineFunction &MF) const {
  45   if (!MF.getSubtarget<ARMSubtarget>().isThumb1Only())
  46     return ARMBaseRegisterInfo::getLargestLegalSuperClass(RC, MF);
  47
  48   if (ARM::tGPRRegClass.hasSubClassEq(RC))
  49     return &ARM::tGPRRegClass;
  50   return ARMBaseRegisterInfo::getLargestLegalSuperClass(RC, MF);
  51 }
  52
  53 const TargetRegisterClass *
  54 ThumbRegisterInfo::getPointerRegClass(const MachineFunction &MF,
  55                                       unsigned Kind) const {
  56   if (!MF.getSubtarget<ARMSubtarget>().isThumb1Only())
  57     return ARMBaseRegisterInfo::getPointerRegClass(MF, Kind);
  58   return &ARM::tGPRRegClass;
  59 }
  60
  61 static void emitThumb1LoadConstPool(MachineBasicBlock &MBB,
  62                                     MachineBasicBlock::iterator &MBBI,
  63                                     const DebugLoc &dl, unsigned DestReg,
  64                                     unsigned SubIdx, int Val,
  65                                     ARMCC::CondCodes Pred, unsigned PredReg,
  66                                     unsigned MIFlags) {
  67   MachineFunction &MF = *MBB.getParent();
  68   const ARMSubtarget &STI = MF.getSubtarget<ARMSubtarget>();
  69   const TargetInstrInfo &TII = *STI.getInstrInfo();
  70   MachineConstantPool *ConstantPool = MF.getConstantPool();
  71   const Constant *C = ConstantInt::get(
  72           Type::getInt32Ty(MBB.getParent()->getFunction().getContext()), Val);
  73   unsigned Idx = ConstantPool->getConstantPoolIndex(C, 4);
  74
  75   BuildMI(MBB, MBBI, dl, TII.get(ARM::tLDRpci))
  76     .addReg(DestReg, getDefRegState(true), SubIdx)
  77     .addConstantPoolIndex(Idx).addImm(Pred).addReg(PredReg)
  78     .setMIFlags(MIFlags);
  79 }
  80
  81 static void emitThumb2LoadConstPool(MachineBasicBlock &MBB,
  82                                     MachineBasicBlock::iterator &MBBI,
  83                                     const DebugLoc &dl, unsigned DestReg,
  84                                     unsigned SubIdx, int Val,
  85                                     ARMCC::CondCodes Pred, unsigned PredReg,
  86                                     unsigned MIFlags) {
  87   MachineFunction &MF = *MBB.getParent();
  88   const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
  89   MachineConstantPool *ConstantPool = MF.getConstantPool();
  90   const Constant *C = ConstantInt::get(
  91            Type::getInt32Ty(MBB.getParent()->getFunction().getContext()), Val);
  92   unsigned Idx = ConstantPool->getConstantPoolIndex(C, 4);
  93
  94   BuildMI(MBB, MBBI, dl, TII.get(ARM::t2LDRpci))
  95       .addReg(DestReg, getDefRegState(true), SubIdx)
  96       .addConstantPoolIndex(Idx)
  97       .add(predOps(ARMCC::AL))
  98       .setMIFlags(MIFlags);
  99 }
 100
 101 /// emitLoadConstPool - Emits a load from constpool to materialize the
 102 /// specified immediate.
 103 void ThumbRegisterInfo::emitLoadConstPool(
 104     MachineBasicBlock &MBB, MachineBasicBlock::iterator &MBBI,
 105     const DebugLoc &dl, unsigned DestReg, unsigned SubIdx, int Val,
 106     ARMCC::CondCodes Pred, unsigned PredReg, unsigned MIFlags) const {
 107   MachineFunction &MF = *MBB.getParent();
 108   const ARMSubtarget &STI = MF.getSubtarget<ARMSubtarget>();
 109   if (STI.isThumb1Only()) {
 110     assert(
 111         (isARMLowRegister(DestReg) || Register::isVirtualRegister(DestReg)) &&
 112         "Thumb1 does not have ldr to high register");
 113     return emitThumb1LoadConstPool(MBB, MBBI, dl, DestReg, SubIdx, Val, Pred,
 114                                    PredReg, MIFlags);
 115   }
 116   return emitThumb2LoadConstPool(MBB, MBBI, dl, DestReg, SubIdx, Val, Pred,
 117                                  PredReg, MIFlags);
 118 }
 119
 120 /// emitThumbRegPlusImmInReg - Emits a series of instructions to materialize
 121 /// a destreg = basereg + immediate in Thumb code. Materialize the immediate
 122 /// in a register using mov / mvn sequences or load the immediate from a
 123 /// constpool entry.
 124 static void emitThumbRegPlusImmInReg(
 125     MachineBasicBlock &MBB, MachineBasicBlock::iterator &MBBI,
 126     const DebugLoc &dl, unsigned DestReg, unsigned BaseReg, int NumBytes,
 127     bool CanChangeCC, const TargetInstrInfo &TII,
 128     const ARMBaseRegisterInfo &MRI, unsigned MIFlags = MachineInstr::NoFlags) {
 129   MachineFunction &MF = *MBB.getParent();
 130   const ARMSubtarget &ST = MF.getSubtarget<ARMSubtarget>();
 131   bool isHigh = !isARMLowRegister(DestReg) ||
 132                 (BaseReg != 0 && !isARMLowRegister(BaseReg));
 133   bool isSub = false;
 134   // Subtract doesn't have high register version. Load the negative value
 135   // if either base or dest register is a high register. Also, if do not
 136   // issue sub as part of the sequence if condition register is to be
 137   // preserved.
 138   if (NumBytes < 0 && !isHigh && CanChangeCC) {
 139     isSub = true;
 140     NumBytes = -NumBytes;
 141   }
 142   unsigned LdReg = DestReg;
 143   if (DestReg == ARM::SP)
 144     assert(BaseReg == ARM::SP && "Unexpected!");
 145   if (!isARMLowRegister(DestReg) && !Register::isVirtualRegister(DestReg))
 146     LdReg = MF.getRegInfo().createVirtualRegister(&ARM::tGPRRegClass);
 147
 148   if (NumBytes <= 255 && NumBytes >= 0 && CanChangeCC) {
 149     BuildMI(MBB, MBBI, dl, TII.get(ARM::tMOVi8), LdReg)
 150         .add(t1CondCodeOp())
 151         .addImm(NumBytes)
 152         .setMIFlags(MIFlags);
 153   } else if (NumBytes < 0 && NumBytes >= -255 && CanChangeCC) {
 154     BuildMI(MBB, MBBI, dl, TII.get(ARM::tMOVi8), LdReg)
 155         .add(t1CondCodeOp())
 156         .addImm(NumBytes)
 157         .setMIFlags(MIFlags);
 158     BuildMI(MBB, MBBI, dl, TII.get(ARM::tRSB), LdReg)
 159         .add(t1CondCodeOp())
 160         .addReg(LdReg, RegState::Kill)
 161         .setMIFlags(MIFlags);
 162   } else if (ST.genExecuteOnly()) {
 163     BuildMI(MBB, MBBI, dl, TII.get(ARM::t2MOVi32imm), LdReg)
 164       .addImm(NumBytes).setMIFlags(MIFlags);
 165   } else
 166     MRI.emitLoadConstPool(MBB, MBBI, dl, LdReg, 0, NumBytes, ARMCC::AL, 0,
 167                           MIFlags);
 168
 169   // Emit add / sub.
 170   int Opc = (isSub) ? ARM::tSUBrr
 171                     : ((isHigh || !CanChangeCC) ? ARM::tADDhirr : ARM::tADDrr);
 172   MachineInstrBuilder MIB = BuildMI(MBB, MBBI, dl, TII.get(Opc), DestReg);
 173   if (Opc != ARM::tADDhirr)
 174     MIB = MIB.add(t1CondCodeOp());
 175   if (DestReg == ARM::SP || isSub)
 176     MIB.addReg(BaseReg).addReg(LdReg, RegState::Kill);
 177   else
 178     MIB.addReg(LdReg).addReg(BaseReg, RegState::Kill);
 179   MIB.add(predOps(ARMCC::AL));
 180 }
 181
 182 /// emitThumbRegPlusImmediate - Emits a series of instructions to materialize
 183 /// a destreg = basereg + immediate in Thumb code. Tries a series of ADDs or
 184 /// SUBs first, and uses a constant pool value if the instruction sequence would
 185 /// be too long. This is allowed to modify the condition flags.
 186 void llvm::emitThumbRegPlusImmediate(MachineBasicBlock &MBB,
 187                                      MachineBasicBlock::iterator &MBBI,
 188                                      const DebugLoc &dl, unsigned DestReg,
 189                                      unsigned BaseReg, int NumBytes,
 190                                      const TargetInstrInfo &TII,
 191                                      const ARMBaseRegisterInfo &MRI,
 192                                      unsigned MIFlags) {
 193   bool isSub = NumBytes < 0;
 194   unsigned Bytes = (unsigned)NumBytes;
 195   if (isSub) Bytes = -NumBytes;
 196
 197   int CopyOpc = 0;
 198   unsigned CopyBits = 0;
 199   unsigned CopyScale = 1;
 200   bool CopyNeedsCC = false;
 201   int ExtraOpc = 0;
 202   unsigned ExtraBits = 0;
 203   unsigned ExtraScale = 1;
 204   bool ExtraNeedsCC = false;
 205
 206   // Strategy:
 207   // We need to select two types of instruction, maximizing the available
 208   // immediate range of each. The instructions we use will depend on whether
 209   // DestReg and BaseReg are low, high or the stack pointer.
 210   // * CopyOpc  - DestReg = BaseReg + imm
 211   //              This will be emitted once if DestReg != BaseReg, and never if
 212   //              DestReg == BaseReg.
 213   // * ExtraOpc - DestReg = DestReg + imm
 214   //              This will be emitted as many times as necessary to add the
 215   //              full immediate.
 216   // If the immediate ranges of these instructions are not large enough to cover
 217   // NumBytes with a reasonable number of instructions, we fall back to using a
 218   // value loaded from a constant pool.
 219   if (DestReg == ARM::SP) {
 220     if (BaseReg == ARM::SP) {
 221       // sp -> sp
 222       // Already in right reg, no copy needed
 223     } else {
 224       // low -> sp or high -> sp
 225       CopyOpc = ARM::tMOVr;
 226       CopyBits = 0;
 227     }
 228     ExtraOpc = isSub ? ARM::tSUBspi : ARM::tADDspi;
 229     ExtraBits = 7;
 230     ExtraScale = 4;
 231   } else if (isARMLowRegister(DestReg)) {
 232     if (BaseReg == ARM::SP) {
 233       // sp -> low
 234       assert(!isSub && "Thumb1 does not have tSUBrSPi");
 235       CopyOpc = ARM::tADDrSPi;
 236       CopyBits = 8;
 237       CopyScale = 4;
 238     } else if (DestReg == BaseReg) {
 239       // low -> same low
 240       // Already in right reg, no copy needed
 241     } else if (isARMLowRegister(BaseReg)) {
 242       // low -> different low
 243       CopyOpc = isSub ? ARM::tSUBi3 : ARM::tADDi3;
 244       CopyBits = 3;
 245       CopyNeedsCC = true;
 246     } else {
 247       // high -> low
 248       CopyOpc = ARM::tMOVr;
 249       CopyBits = 0;
 250     }
 251     ExtraOpc = isSub ? ARM::tSUBi8 : ARM::tADDi8;
 252     ExtraBits = 8;
 253     ExtraNeedsCC = true;
 254   } else /* DestReg is high */ {
 255     if (DestReg == BaseReg) {
 256       // high -> same high
 257       // Already in right reg, no copy needed
 258     } else {
 259       // {low,high,sp} -> high
 260       CopyOpc = ARM::tMOVr;
 261       CopyBits = 0;
 262     }
 263     ExtraOpc = 0;
 264   }
 265
 266   // We could handle an unaligned immediate with an unaligned copy instruction
 267   // and an aligned extra instruction, but this case is not currently needed.
 268   assert(((Bytes & 3) == 0 || ExtraScale == 1) &&
 269          "Unaligned offset, but all instructions require alignment");
 270
 271   unsigned CopyRange = ((1 << CopyBits) - 1) * CopyScale;
 272   // If we would emit the copy with an immediate of 0, just use tMOVr.
 273   if (CopyOpc && Bytes < CopyScale) {
 274     CopyOpc = ARM::tMOVr;
 275     CopyScale = 1;
 276     CopyNeedsCC = false;
 277     CopyRange = 0;
 278   }
 279   unsigned ExtraRange = ((1 << ExtraBits) - 1) * ExtraScale; // per instruction
 280   unsigned RequiredCopyInstrs = CopyOpc ? 1 : 0;
 281   unsigned RangeAfterCopy = (CopyRange > Bytes) ? 0 : (Bytes - CopyRange);
 282
 283   // We could handle this case when the copy instruction does not require an
 284   // aligned immediate, but we do not currently do this.
 285   assert(RangeAfterCopy % ExtraScale == 0 &&
 286          "Extra instruction requires immediate to be aligned");
 287
 288   unsigned RequiredExtraInstrs;
 289   if (ExtraRange)
 290     RequiredExtraInstrs = alignTo(RangeAfterCopy, ExtraRange) / ExtraRange;
 291   else if (RangeAfterCopy > 0)
 292     // We need an extra instruction but none is available
 293     RequiredExtraInstrs = 1000000;
 294   else
 295     RequiredExtraInstrs = 0;
 296   unsigned RequiredInstrs = RequiredCopyInstrs + RequiredExtraInstrs;
 297   unsigned Threshold = (DestReg == ARM::SP) ? 3 : 2;
 298
 299   // Use a constant pool, if the sequence of ADDs/SUBs is too expensive.
 300   if (RequiredInstrs > Threshold) {
 301     emitThumbRegPlusImmInReg(MBB, MBBI, dl,
 302                              DestReg, BaseReg, NumBytes, true,
 303                              TII, MRI, MIFlags);
 304     return;
 305   }
 306
 307   // Emit zero or one copy instructions
 308   if (CopyOpc) {
 309     unsigned CopyImm = std::min(Bytes, CopyRange) / CopyScale;
 310     Bytes -= CopyImm * CopyScale;
 311
 312     MachineInstrBuilder MIB = BuildMI(MBB, MBBI, dl, TII.get(CopyOpc), DestReg);
 313     if (CopyNeedsCC)
 314       MIB = MIB.add(t1CondCodeOp());
 315     MIB.addReg(BaseReg, RegState::Kill);
 316     if (CopyOpc != ARM::tMOVr) {
 317       MIB.addImm(CopyImm);
 318     }
 319     MIB.setMIFlags(MIFlags).add(predOps(ARMCC::AL));
 320
 321     BaseReg = DestReg;
 322   }
 323
 324   // Emit zero or more in-place add/sub instructions
 325   while (Bytes) {
 326     unsigned ExtraImm = std::min(Bytes, ExtraRange) / ExtraScale;
 327     Bytes -= ExtraImm * ExtraScale;
 328
 329     MachineInstrBuilder MIB = BuildMI(MBB, MBBI, dl, TII.get(ExtraOpc), DestReg);
 330     if (ExtraNeedsCC)
 331       MIB = MIB.add(t1CondCodeOp());
 332     MIB.addReg(BaseReg)
 333        .addImm(ExtraImm)
 334        .add(predOps(ARMCC::AL))
 335        .setMIFlags(MIFlags);
 336   }
 337 }
 338
 339 static void removeOperands(MachineInstr &MI, unsigned i) {
 340   unsigned Op = i;
 341   for (unsigned e = MI.getNumOperands(); i != e; ++i)
 342     MI.RemoveOperand(Op);
 343 }
 344
 345 /// convertToNonSPOpcode - Change the opcode to the non-SP version, because
 346 /// we're replacing the frame index with a non-SP register.
 347 static unsigned convertToNonSPOpcode(unsigned Opcode) {
 348   switch (Opcode) {
 349   case ARM::tLDRspi:
 350     return ARM::tLDRi;
 351
 352   case ARM::tSTRspi:
 353     return ARM::tSTRi;
 354   }
 355
 356   return Opcode;
 357 }
 358
 359 bool ThumbRegisterInfo::rewriteFrameIndex(MachineBasicBlock::iterator II,
 360                                           unsigned FrameRegIdx,
 361                                           unsigned FrameReg, int &Offset,
 362                                           const ARMBaseInstrInfo &TII) const {
 363   MachineInstr &MI = *II;
 364   MachineBasicBlock &MBB = *MI.getParent();
 365   assert(MBB.getParent()->getSubtarget<ARMSubtarget>().isThumb1Only() &&
 366          "This isn't needed for thumb2!");
 367   DebugLoc dl = MI.getDebugLoc();
 368   MachineInstrBuilder MIB(*MBB.getParent(), &MI);
 369   unsigned Opcode = MI.getOpcode();
 370   const MCInstrDesc &Desc = MI.getDesc();
 371   unsigned AddrMode = (Desc.TSFlags & ARMII::AddrModeMask);
 372
 373   if (Opcode == ARM::tADDframe) {
 374     Offset += MI.getOperand(FrameRegIdx+1).getImm();
 375     Register DestReg = MI.getOperand(0).getReg();
 376
 377     emitThumbRegPlusImmediate(MBB, II, dl, DestReg, FrameReg, Offset, TII,
 378                               *this);
 379     MBB.erase(II);
 380     return true;
 381   } else {
 382     if (AddrMode != ARMII::AddrModeT1_s)
 383       llvm_unreachable("Unsupported addressing mode!");
 384
 385     unsigned ImmIdx = FrameRegIdx + 1;
 386     int InstrOffs = MI.getOperand(ImmIdx).getImm();
 387     unsigned NumBits = (FrameReg == ARM::SP) ? 8 : 5;
 388     unsigned Scale = 4;
 389
 390     Offset += InstrOffs * Scale;
 391     assert((Offset & (Scale - 1)) == 0 && "Can't encode this offset!");
 392
 393     // Common case: small offset, fits into instruction.
 394     MachineOperand &ImmOp = MI.getOperand(ImmIdx);
 395     int ImmedOffset = Offset / Scale;
 396     unsigned Mask = (1 << NumBits) - 1;
 397
 398     if ((unsigned)Offset <= Mask * Scale) {
 399       // Replace the FrameIndex with the frame register (e.g., sp).
 400       MI.getOperand(FrameRegIdx).ChangeToRegister(FrameReg, false);
 401       ImmOp.ChangeToImmediate(ImmedOffset);
 402
 403       // If we're using a register where sp was stored, convert the instruction
 404       // to the non-SP version.
 405       unsigned NewOpc = convertToNonSPOpcode(Opcode);
 406       if (NewOpc != Opcode && FrameReg != ARM::SP)
 407         MI.setDesc(TII.get(NewOpc));
 408
 409       return true;
 410     }
 411
 412     NumBits = 5;
 413     Mask = (1 << NumBits) - 1;
 414
 415     // If this is a thumb spill / restore, we will be using a constpool load to
 416     // materialize the offset.
 417     if (Opcode == ARM::tLDRspi || Opcode == ARM::tSTRspi) {
 418       ImmOp.ChangeToImmediate(0);
 419     } else {
 420       // Otherwise, it didn't fit. Pull in what we can to simplify the immed.
 421       ImmedOffset = ImmedOffset & Mask;
 422       ImmOp.ChangeToImmediate(ImmedOffset);
 423       Offset &= ~(Mask * Scale);
 424     }
 425   }
 426
 427   return Offset == 0;
 428 }
 429
 430 void ThumbRegisterInfo::resolveFrameIndex(MachineInstr &MI, unsigned BaseReg,
 431                                            int64_t Offset) const {
 432   const MachineFunction &MF = *MI.getParent()->getParent();
 433   const ARMSubtarget &STI = MF.getSubtarget<ARMSubtarget>();
 434   if (!STI.isThumb1Only())
 435     return ARMBaseRegisterInfo::resolveFrameIndex(MI, BaseReg, Offset);
 436
 437   const ARMBaseInstrInfo &TII = *STI.getInstrInfo();
 438   int Off = Offset; // ARM doesn't need the general 64-bit offsets
 439   unsigned i = 0;
 440
 441   while (!MI.getOperand(i).isFI()) {
 442     ++i;
 443     assert(i < MI.getNumOperands() && "Instr doesn't have FrameIndex operand!");
 444   }
 445   bool Done = rewriteFrameIndex(MI, i, BaseReg, Off, TII);
 446   assert (Done && "Unable to resolve frame index!");
 447   (void)Done;
 448 }
 449
 450 void ThumbRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
 451                                             int SPAdj, unsigned FIOperandNum,
 452                                             RegScavenger *RS) const {
 453   MachineInstr &MI = *II;
 454   MachineBasicBlock &MBB = *MI.getParent();
 455   MachineFunction &MF = *MBB.getParent();
 456   const ARMSubtarget &STI = MF.getSubtarget<ARMSubtarget>();
 457   if (!STI.isThumb1Only())
 458     return ARMBaseRegisterInfo::eliminateFrameIndex(II, SPAdj, FIOperandNum,
 459                                                     RS);
 460
 461   unsigned VReg = 0;
 462   const ARMBaseInstrInfo &TII = *STI.getInstrInfo();
 463   DebugLoc dl = MI.getDebugLoc();
 464   MachineInstrBuilder MIB(*MBB.getParent(), &MI);
 465
 466   unsigned FrameReg;
 467   int FrameIndex = MI.getOperand(FIOperandNum).getIndex();
 468   const ARMFrameLowering *TFI = getFrameLowering(MF);
 469   int Offset = TFI->ResolveFrameIndexReference(MF, FrameIndex, FrameReg, SPAdj);
 470
 471   // PEI::scavengeFrameVirtualRegs() cannot accurately track SPAdj because the
 472   // call frame setup/destroy instructions have already been eliminated.  That
 473   // means the stack pointer cannot be used to access the emergency spill slot
 474   // when !hasReservedCallFrame().
 475 #ifndef NDEBUG
 476   if (RS && FrameReg == ARM::SP && RS->isScavengingFrameIndex(FrameIndex)){
 477     assert(STI.getFrameLowering()->hasReservedCallFrame(MF) &&
 478            "Cannot use SP to access the emergency spill slot in "
 479            "functions without a reserved call frame");
 480     assert(!MF.getFrameInfo().hasVarSizedObjects() &&
 481            "Cannot use SP to access the emergency spill slot in "
 482            "functions with variable sized frame objects");
 483   }
 484 #endif // NDEBUG
 485
 486   // Special handling of dbg_value instructions.
 487   if (MI.isDebugValue()) {
 488     MI.getOperand(FIOperandNum).  ChangeToRegister(FrameReg, false /*isDef*/);
 489     MI.getOperand(FIOperandNum+1).ChangeToImmediate(Offset);
 490     return;
 491   }
 492
 493   // Modify MI as necessary to handle as much of 'Offset' as possible
 494   assert(MF.getInfo<ARMFunctionInfo>()->isThumbFunction() &&
 495          "This eliminateFrameIndex only supports Thumb1!");
 496   if (rewriteFrameIndex(MI, FIOperandNum, FrameReg, Offset, TII))
 497     return;
 498
 499   // If we get here, the immediate doesn't fit into the instruction.  We folded
 500   // as much as possible above, handle the rest, providing a register that is
 501   // SP+LargeImm.
 502   assert(Offset && "This code isn't needed if offset already handled!");
 503
 504   unsigned Opcode = MI.getOpcode();
 505
 506   // Remove predicate first.
 507   int PIdx = MI.findFirstPredOperandIdx();
 508   if (PIdx != -1)
 509     removeOperands(MI, PIdx);
 510
 511   if (MI.mayLoad()) {
 512     // Use the destination register to materialize sp + offset.
 513     Register TmpReg = MI.getOperand(0).getReg();
 514     bool UseRR = false;
 515     if (Opcode == ARM::tLDRspi) {
 516       if (FrameReg == ARM::SP || STI.genExecuteOnly())
 517         emitThumbRegPlusImmInReg(MBB, II, dl, TmpReg, FrameReg,
 518                                  Offset, false, TII, *this);
 519       else {
 520         emitLoadConstPool(MBB, II, dl, TmpReg, 0, Offset);
 521         UseRR = true;
 522       }
 523     } else {
 524       emitThumbRegPlusImmediate(MBB, II, dl, TmpReg, FrameReg, Offset, TII,
 525                                 *this);
 526     }
 527
 528     MI.setDesc(TII.get(UseRR ? ARM::tLDRr : ARM::tLDRi));
 529     MI.getOperand(FIOperandNum).ChangeToRegister(TmpReg, false, false, true);
 530     if (UseRR)
 531       // Use [reg, reg] addrmode. Replace the immediate operand w/ the frame
 532       // register. The offset is already handled in the vreg value.
 533       MI.getOperand(FIOperandNum+1).ChangeToRegister(FrameReg, false, false,
 534                                                      false);
 535   } else if (MI.mayStore()) {
 536       VReg = MF.getRegInfo().createVirtualRegister(&ARM::tGPRRegClass);
 537       bool UseRR = false;
 538
 539       if (Opcode == ARM::tSTRspi) {
 540         if (FrameReg == ARM::SP || STI.genExecuteOnly())
 541           emitThumbRegPlusImmInReg(MBB, II, dl, VReg, FrameReg,
 542                                    Offset, false, TII, *this);
 543         else {
 544           emitLoadConstPool(MBB, II, dl, VReg, 0, Offset);
 545           UseRR = true;
 546         }
 547       } else
 548         emitThumbRegPlusImmediate(MBB, II, dl, VReg, FrameReg, Offset, TII,
 549                                   *this);
 550       MI.setDesc(TII.get(UseRR ? ARM::tSTRr : ARM::tSTRi));
 551       MI.getOperand(FIOperandNum).ChangeToRegister(VReg, false, false, true);
 552       if (UseRR)
 553         // Use [reg, reg] addrmode. Replace the immediate operand w/ the frame
 554         // register. The offset is already handled in the vreg value.
 555         MI.getOperand(FIOperandNum+1).ChangeToRegister(FrameReg, false, false,
 556                                                        false);
 557   } else {
 558     llvm_unreachable("Unexpected opcode!");
 559   }
 560
 561   // Add predicate back if it's needed.
 562   if (MI.isPredicable())
 563     MIB.add(predOps(ARMCC::AL));
 564 }
 565
 566 bool
 567 ThumbRegisterInfo::useFPForScavengingIndex(const MachineFunction &MF) const {
 568   if (MF.getSubtarget<ARMSubtarget>().isThumb1Only()) {
 569     // For Thumb1, the emergency spill slot must be some small positive
 570     // offset from the base/stack pointer.
 571     return false;
 572   }
 573   // For Thumb2, put the emergency spill slot next to FP.
 574   return true;
 575 }