lib/Target/SystemZ/SystemZFrameLowering.cpp

   1 //===-- SystemZFrameLowering.cpp - Frame lowering for SystemZ -------------===//
   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 "SystemZFrameLowering.h"
  10 #include "SystemZCallingConv.h"
  11 #include "SystemZInstrBuilder.h"
  12 #include "SystemZInstrInfo.h"
  13 #include "SystemZMachineFunctionInfo.h"
  14 #include "SystemZRegisterInfo.h"
  15 #include "SystemZSubtarget.h"
  16 #include "llvm/CodeGen/MachineModuleInfo.h"
  17 #include "llvm/CodeGen/MachineRegisterInfo.h"
  18 #include "llvm/CodeGen/RegisterScavenging.h"
  19 #include "llvm/IR/Function.h"
  20
  21 using namespace llvm;
  22
  23 namespace {
  24 // The ABI-defined register save slots, relative to the incoming stack
  25 // pointer.
  26 static const TargetFrameLowering::SpillSlot SpillOffsetTable[] = {
  27   { SystemZ::R2D,  0x10 },
  28   { SystemZ::R3D,  0x18 },
  29   { SystemZ::R4D,  0x20 },
  30   { SystemZ::R5D,  0x28 },
  31   { SystemZ::R6D,  0x30 },
  32   { SystemZ::R7D,  0x38 },
  33   { SystemZ::R8D,  0x40 },
  34   { SystemZ::R9D,  0x48 },
  35   { SystemZ::R10D, 0x50 },
  36   { SystemZ::R11D, 0x58 },
  37   { SystemZ::R12D, 0x60 },
  38   { SystemZ::R13D, 0x68 },
  39   { SystemZ::R14D, 0x70 },
  40   { SystemZ::R15D, 0x78 },
  41   { SystemZ::F0D,  0x80 },
  42   { SystemZ::F2D,  0x88 },
  43   { SystemZ::F4D,  0x90 },
  44   { SystemZ::F6D,  0x98 }
  45 };
  46 } // end anonymous namespace
  47
  48 SystemZFrameLowering::SystemZFrameLowering()
  49     : TargetFrameLowering(TargetFrameLowering::StackGrowsDown, 8,
  50                           -SystemZMC::CallFrameSize, 8,
  51                           false /* StackRealignable */) {
  52   // Create a mapping from register number to save slot offset.
  53   RegSpillOffsets.grow(SystemZ::NUM_TARGET_REGS);
  54   for (unsigned I = 0, E = array_lengthof(SpillOffsetTable); I != E; ++I)
  55     RegSpillOffsets[SpillOffsetTable[I].Reg] = SpillOffsetTable[I].Offset;
  56 }
  57
  58 const TargetFrameLowering::SpillSlot *
  59 SystemZFrameLowering::getCalleeSavedSpillSlots(unsigned &NumEntries) const {
  60   NumEntries = array_lengthof(SpillOffsetTable);
  61   return SpillOffsetTable;
  62 }
  63
  64 void SystemZFrameLowering::determineCalleeSaves(MachineFunction &MF,
  65                                                 BitVector &SavedRegs,
  66                                                 RegScavenger *RS) const {
  67   TargetFrameLowering::determineCalleeSaves(MF, SavedRegs, RS);
  68
  69   MachineFrameInfo &MFFrame = MF.getFrameInfo();
  70   const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
  71   bool HasFP = hasFP(MF);
  72   SystemZMachineFunctionInfo *MFI = MF.getInfo<SystemZMachineFunctionInfo>();
  73   bool IsVarArg = MF.getFunction().isVarArg();
  74
  75   // va_start stores incoming FPR varargs in the normal way, but delegates
  76   // the saving of incoming GPR varargs to spillCalleeSavedRegisters().
  77   // Record these pending uses, which typically include the call-saved
  78   // argument register R6D.
  79   if (IsVarArg)
  80     for (unsigned I = MFI->getVarArgsFirstGPR(); I < SystemZ::NumArgGPRs; ++I)
  81       SavedRegs.set(SystemZ::ArgGPRs[I]);
  82
  83   // If there are any landing pads, entering them will modify r6/r7.
  84   if (!MF.getLandingPads().empty()) {
  85     SavedRegs.set(SystemZ::R6D);
  86     SavedRegs.set(SystemZ::R7D);
  87   }
  88
  89   // If the function requires a frame pointer, record that the hard
  90   // frame pointer will be clobbered.
  91   if (HasFP)
  92     SavedRegs.set(SystemZ::R11D);
  93
  94   // If the function calls other functions, record that the return
  95   // address register will be clobbered.
  96   if (MFFrame.hasCalls())
  97     SavedRegs.set(SystemZ::R14D);
  98
  99   // If we are saving GPRs other than the stack pointer, we might as well
 100   // save and restore the stack pointer at the same time, via STMG and LMG.
 101   // This allows the deallocation to be done by the LMG, rather than needing
 102   // a separate %r15 addition.
 103   const MCPhysReg *CSRegs = TRI->getCalleeSavedRegs(&MF);
 104   for (unsigned I = 0; CSRegs[I]; ++I) {
 105     unsigned Reg = CSRegs[I];
 106     if (SystemZ::GR64BitRegClass.contains(Reg) && SavedRegs.test(Reg)) {
 107       SavedRegs.set(SystemZ::R15D);
 108       break;
 109     }
 110   }
 111 }
 112
 113 // Add GPR64 to the save instruction being built by MIB, which is in basic
 114 // block MBB.  IsImplicit says whether this is an explicit operand to the
 115 // instruction, or an implicit one that comes between the explicit start
 116 // and end registers.
 117 static void addSavedGPR(MachineBasicBlock &MBB, MachineInstrBuilder &MIB,
 118                         unsigned GPR64, bool IsImplicit) {
 119   const TargetRegisterInfo *RI =
 120       MBB.getParent()->getSubtarget().getRegisterInfo();
 121   unsigned GPR32 = RI->getSubReg(GPR64, SystemZ::subreg_l32);
 122   bool IsLive = MBB.isLiveIn(GPR64) || MBB.isLiveIn(GPR32);
 123   if (!IsLive || !IsImplicit) {
 124     MIB.addReg(GPR64, getImplRegState(IsImplicit) | getKillRegState(!IsLive));
 125     if (!IsLive)
 126       MBB.addLiveIn(GPR64);
 127   }
 128 }
 129
 130 bool SystemZFrameLowering::
 131 spillCalleeSavedRegisters(MachineBasicBlock &MBB,
 132                           MachineBasicBlock::iterator MBBI,
 133                           const std::vector<CalleeSavedInfo> &CSI,
 134                           const TargetRegisterInfo *TRI) const {
 135   if (CSI.empty())
 136     return false;
 137
 138   MachineFunction &MF = *MBB.getParent();
 139   const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
 140   SystemZMachineFunctionInfo *ZFI = MF.getInfo<SystemZMachineFunctionInfo>();
 141   bool IsVarArg = MF.getFunction().isVarArg();
 142   DebugLoc DL;
 143
 144   // Scan the call-saved GPRs and find the bounds of the register spill area.
 145   unsigned LowGPR = 0;
 146   unsigned HighGPR = SystemZ::R15D;
 147   unsigned StartOffset = -1U;
 148   for (unsigned I = 0, E = CSI.size(); I != E; ++I) {
 149     unsigned Reg = CSI[I].getReg();
 150     if (SystemZ::GR64BitRegClass.contains(Reg)) {
 151       unsigned Offset = RegSpillOffsets[Reg];
 152       assert(Offset && "Unexpected GPR save");
 153       if (StartOffset > Offset) {
 154         LowGPR = Reg;
 155         StartOffset = Offset;
 156       }
 157     }
 158   }
 159
 160   // Save the range of call-saved registers, for use by the epilogue inserter.
 161   ZFI->setLowSavedGPR(LowGPR);
 162   ZFI->setHighSavedGPR(HighGPR);
 163
 164   // Include the GPR varargs, if any.  R6D is call-saved, so would
 165   // be included by the loop above, but we also need to handle the
 166   // call-clobbered argument registers.
 167   if (IsVarArg) {
 168     unsigned FirstGPR = ZFI->getVarArgsFirstGPR();
 169     if (FirstGPR < SystemZ::NumArgGPRs) {
 170       unsigned Reg = SystemZ::ArgGPRs[FirstGPR];
 171       unsigned Offset = RegSpillOffsets[Reg];
 172       if (StartOffset > Offset) {
 173         LowGPR = Reg; StartOffset = Offset;
 174       }
 175     }
 176   }
 177
 178   // Save GPRs
 179   if (LowGPR) {
 180     assert(LowGPR != HighGPR && "Should be saving %r15 and something else");
 181
 182     // Build an STMG instruction.
 183     MachineInstrBuilder MIB = BuildMI(MBB, MBBI, DL, TII->get(SystemZ::STMG));
 184
 185     // Add the explicit register operands.
 186     addSavedGPR(MBB, MIB, LowGPR, false);
 187     addSavedGPR(MBB, MIB, HighGPR, false);
 188
 189     // Add the address.
 190     MIB.addReg(SystemZ::R15D).addImm(StartOffset);
 191
 192     // Make sure all call-saved GPRs are included as operands and are
 193     // marked as live on entry.
 194     for (unsigned I = 0, E = CSI.size(); I != E; ++I) {
 195       unsigned Reg = CSI[I].getReg();
 196       if (SystemZ::GR64BitRegClass.contains(Reg))
 197         addSavedGPR(MBB, MIB, Reg, true);
 198     }
 199
 200     // ...likewise GPR varargs.
 201     if (IsVarArg)
 202       for (unsigned I = ZFI->getVarArgsFirstGPR(); I < SystemZ::NumArgGPRs; ++I)
 203         addSavedGPR(MBB, MIB, SystemZ::ArgGPRs[I], true);
 204   }
 205
 206   // Save FPRs/VRs in the normal TargetInstrInfo way.
 207   for (unsigned I = 0, E = CSI.size(); I != E; ++I) {
 208     unsigned Reg = CSI[I].getReg();
 209     if (SystemZ::FP64BitRegClass.contains(Reg)) {
 210       MBB.addLiveIn(Reg);
 211       TII->storeRegToStackSlot(MBB, MBBI, Reg, true, CSI[I].getFrameIdx(),
 212                                &SystemZ::FP64BitRegClass, TRI);
 213     }
 214     if (SystemZ::VR128BitRegClass.contains(Reg)) {
 215       MBB.addLiveIn(Reg);
 216       TII->storeRegToStackSlot(MBB, MBBI, Reg, true, CSI[I].getFrameIdx(),
 217                                &SystemZ::VR128BitRegClass, TRI);
 218     }
 219   }
 220
 221   return true;
 222 }
 223
 224 bool SystemZFrameLowering::
 225 restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
 226                             MachineBasicBlock::iterator MBBI,
 227                             std::vector<CalleeSavedInfo> &CSI,
 228                             const TargetRegisterInfo *TRI) const {
 229   if (CSI.empty())
 230     return false;
 231
 232   MachineFunction &MF = *MBB.getParent();
 233   const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
 234   SystemZMachineFunctionInfo *ZFI = MF.getInfo<SystemZMachineFunctionInfo>();
 235   bool HasFP = hasFP(MF);
 236   DebugLoc DL = MBBI != MBB.end() ? MBBI->getDebugLoc() : DebugLoc();
 237
 238   // Restore FPRs/VRs in the normal TargetInstrInfo way.
 239   for (unsigned I = 0, E = CSI.size(); I != E; ++I) {
 240     unsigned Reg = CSI[I].getReg();
 241     if (SystemZ::FP64BitRegClass.contains(Reg))
 242       TII->loadRegFromStackSlot(MBB, MBBI, Reg, CSI[I].getFrameIdx(),
 243                                 &SystemZ::FP64BitRegClass, TRI);
 244     if (SystemZ::VR128BitRegClass.contains(Reg))
 245       TII->loadRegFromStackSlot(MBB, MBBI, Reg, CSI[I].getFrameIdx(),
 246                                 &SystemZ::VR128BitRegClass, TRI);
 247   }
 248
 249   // Restore call-saved GPRs (but not call-clobbered varargs, which at
 250   // this point might hold return values).
 251   unsigned LowGPR = ZFI->getLowSavedGPR();
 252   unsigned HighGPR = ZFI->getHighSavedGPR();
 253   unsigned StartOffset = RegSpillOffsets[LowGPR];
 254   if (LowGPR) {
 255     // If we saved any of %r2-%r5 as varargs, we should also be saving
 256     // and restoring %r6.  If we're saving %r6 or above, we should be
 257     // restoring it too.
 258     assert(LowGPR != HighGPR && "Should be loading %r15 and something else");
 259
 260     // Build an LMG instruction.
 261     MachineInstrBuilder MIB = BuildMI(MBB, MBBI, DL, TII->get(SystemZ::LMG));
 262
 263     // Add the explicit register operands.
 264     MIB.addReg(LowGPR, RegState::Define);
 265     MIB.addReg(HighGPR, RegState::Define);
 266
 267     // Add the address.
 268     MIB.addReg(HasFP ? SystemZ::R11D : SystemZ::R15D);
 269     MIB.addImm(StartOffset);
 270
 271     // Do a second scan adding regs as being defined by instruction
 272     for (unsigned I = 0, E = CSI.size(); I != E; ++I) {
 273       unsigned Reg = CSI[I].getReg();
 274       if (Reg != LowGPR && Reg != HighGPR &&
 275           SystemZ::GR64BitRegClass.contains(Reg))
 276         MIB.addReg(Reg, RegState::ImplicitDefine);
 277     }
 278   }
 279
 280   return true;
 281 }
 282
 283 void SystemZFrameLowering::
 284 processFunctionBeforeFrameFinalized(MachineFunction &MF,
 285                                     RegScavenger *RS) const {
 286   MachineFrameInfo &MFFrame = MF.getFrameInfo();
 287   // Get the size of our stack frame to be allocated ...
 288   uint64_t StackSize = (MFFrame.estimateStackSize(MF) +
 289                         SystemZMC::CallFrameSize);
 290   // ... and the maximum offset we may need to reach into the
 291   // caller's frame to access the save area or stack arguments.
 292   int64_t MaxArgOffset = SystemZMC::CallFrameSize;
 293   for (int I = MFFrame.getObjectIndexBegin(); I != 0; ++I)
 294     if (MFFrame.getObjectOffset(I) >= 0) {
 295       int64_t ArgOffset = SystemZMC::CallFrameSize +
 296                           MFFrame.getObjectOffset(I) +
 297                           MFFrame.getObjectSize(I);
 298       MaxArgOffset = std::max(MaxArgOffset, ArgOffset);
 299     }
 300
 301   uint64_t MaxReach = StackSize + MaxArgOffset;
 302   if (!isUInt<12>(MaxReach)) {
 303     // We may need register scavenging slots if some parts of the frame
 304     // are outside the reach of an unsigned 12-bit displacement.
 305     // Create 2 for the case where both addresses in an MVC are
 306     // out of range.
 307     RS->addScavengingFrameIndex(MFFrame.CreateStackObject(8, 8, false));
 308     RS->addScavengingFrameIndex(MFFrame.CreateStackObject(8, 8, false));
 309   }
 310 }
 311
 312 // Emit instructions before MBBI (in MBB) to add NumBytes to Reg.
 313 static void emitIncrement(MachineBasicBlock &MBB,
 314                           MachineBasicBlock::iterator &MBBI,
 315                           const DebugLoc &DL,
 316                           unsigned Reg, int64_t NumBytes,
 317                           const TargetInstrInfo *TII) {
 318   while (NumBytes) {
 319     unsigned Opcode;
 320     int64_t ThisVal = NumBytes;
 321     if (isInt<16>(NumBytes))
 322       Opcode = SystemZ::AGHI;
 323     else {
 324       Opcode = SystemZ::AGFI;
 325       // Make sure we maintain 8-byte stack alignment.
 326       int64_t MinVal = -uint64_t(1) << 31;
 327       int64_t MaxVal = (int64_t(1) << 31) - 8;
 328       if (ThisVal < MinVal)
 329         ThisVal = MinVal;
 330       else if (ThisVal > MaxVal)
 331         ThisVal = MaxVal;
 332     }
 333     MachineInstr *MI = BuildMI(MBB, MBBI, DL, TII->get(Opcode), Reg)
 334       .addReg(Reg).addImm(ThisVal);
 335     // The CC implicit def is dead.
 336     MI->getOperand(3).setIsDead();
 337     NumBytes -= ThisVal;
 338   }
 339 }
 340
 341 void SystemZFrameLowering::emitPrologue(MachineFunction &MF,
 342                                         MachineBasicBlock &MBB) const {
 343   assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
 344   MachineFrameInfo &MFFrame = MF.getFrameInfo();
 345   auto *ZII =
 346       static_cast<const SystemZInstrInfo *>(MF.getSubtarget().getInstrInfo());
 347   SystemZMachineFunctionInfo *ZFI = MF.getInfo<SystemZMachineFunctionInfo>();
 348   MachineBasicBlock::iterator MBBI = MBB.begin();
 349   MachineModuleInfo &MMI = MF.getMMI();
 350   const MCRegisterInfo *MRI = MMI.getContext().getRegisterInfo();
 351   const std::vector<CalleeSavedInfo> &CSI = MFFrame.getCalleeSavedInfo();
 352   bool HasFP = hasFP(MF);
 353
 354   // Debug location must be unknown since the first debug location is used
 355   // to determine the end of the prologue.
 356   DebugLoc DL;
 357
 358   // The current offset of the stack pointer from the CFA.
 359   int64_t SPOffsetFromCFA = -SystemZMC::CFAOffsetFromInitialSP;
 360
 361   if (ZFI->getLowSavedGPR()) {
 362     // Skip over the GPR saves.
 363     if (MBBI != MBB.end() && MBBI->getOpcode() == SystemZ::STMG)
 364       ++MBBI;
 365     else
 366       llvm_unreachable("Couldn't skip over GPR saves");
 367
 368     // Add CFI for the GPR saves.
 369     for (auto &Save : CSI) {
 370       unsigned Reg = Save.getReg();
 371       if (SystemZ::GR64BitRegClass.contains(Reg)) {
 372         int64_t Offset = SPOffsetFromCFA + RegSpillOffsets[Reg];
 373         unsigned CFIIndex = MF.addFrameInst(MCCFIInstruction::createOffset(
 374             nullptr, MRI->getDwarfRegNum(Reg, true), Offset));
 375         BuildMI(MBB, MBBI, DL, ZII->get(TargetOpcode::CFI_INSTRUCTION))
 376             .addCFIIndex(CFIIndex);
 377       }
 378     }
 379   }
 380
 381   uint64_t StackSize = MFFrame.getStackSize();
 382   // We need to allocate the ABI-defined 160-byte base area whenever
 383   // we allocate stack space for our own use and whenever we call another
 384   // function.
 385   if (StackSize || MFFrame.hasVarSizedObjects() || MFFrame.hasCalls()) {
 386     StackSize += SystemZMC::CallFrameSize;
 387     MFFrame.setStackSize(StackSize);
 388   }
 389
 390   if (StackSize) {
 391     // Determine if we want to store a backchain.
 392     bool StoreBackchain = MF.getFunction().hasFnAttribute("backchain");
 393
 394     // If we need backchain, save current stack pointer.  R1 is free at this
 395     // point.
 396     if (StoreBackchain)
 397       BuildMI(MBB, MBBI, DL, ZII->get(SystemZ::LGR))
 398         .addReg(SystemZ::R1D, RegState::Define).addReg(SystemZ::R15D);
 399
 400     // Allocate StackSize bytes.
 401     int64_t Delta = -int64_t(StackSize);
 402     emitIncrement(MBB, MBBI, DL, SystemZ::R15D, Delta, ZII);
 403
 404     // Add CFI for the allocation.
 405     unsigned CFIIndex = MF.addFrameInst(
 406         MCCFIInstruction::createDefCfaOffset(nullptr, SPOffsetFromCFA + Delta));
 407     BuildMI(MBB, MBBI, DL, ZII->get(TargetOpcode::CFI_INSTRUCTION))
 408         .addCFIIndex(CFIIndex);
 409     SPOffsetFromCFA += Delta;
 410
 411     if (StoreBackchain)
 412       BuildMI(MBB, MBBI, DL, ZII->get(SystemZ::STG))
 413         .addReg(SystemZ::R1D, RegState::Kill).addReg(SystemZ::R15D).addImm(0).addReg(0);
 414   }
 415
 416   if (HasFP) {
 417     // Copy the base of the frame to R11.
 418     BuildMI(MBB, MBBI, DL, ZII->get(SystemZ::LGR), SystemZ::R11D)
 419       .addReg(SystemZ::R15D);
 420
 421     // Add CFI for the new frame location.
 422     unsigned HardFP = MRI->getDwarfRegNum(SystemZ::R11D, true);
 423     unsigned CFIIndex = MF.addFrameInst(
 424         MCCFIInstruction::createDefCfaRegister(nullptr, HardFP));
 425     BuildMI(MBB, MBBI, DL, ZII->get(TargetOpcode::CFI_INSTRUCTION))
 426         .addCFIIndex(CFIIndex);
 427
 428     // Mark the FramePtr as live at the beginning of every block except
 429     // the entry block.  (We'll have marked R11 as live on entry when
 430     // saving the GPRs.)
 431     for (auto I = std::next(MF.begin()), E = MF.end(); I != E; ++I)
 432       I->addLiveIn(SystemZ::R11D);
 433   }
 434
 435   // Skip over the FPR/VR saves.
 436   SmallVector<unsigned, 8> CFIIndexes;
 437   for (auto &Save : CSI) {
 438     unsigned Reg = Save.getReg();
 439     if (SystemZ::FP64BitRegClass.contains(Reg)) {
 440       if (MBBI != MBB.end() &&
 441           (MBBI->getOpcode() == SystemZ::STD ||
 442            MBBI->getOpcode() == SystemZ::STDY))
 443         ++MBBI;
 444       else
 445         llvm_unreachable("Couldn't skip over FPR save");
 446     } else if (SystemZ::VR128BitRegClass.contains(Reg)) {
 447       if (MBBI != MBB.end() &&
 448           MBBI->getOpcode() == SystemZ::VST)
 449         ++MBBI;
 450       else
 451         llvm_unreachable("Couldn't skip over VR save");
 452     } else
 453       continue;
 454
 455     // Add CFI for the this save.
 456     unsigned DwarfReg = MRI->getDwarfRegNum(Reg, true);
 457     unsigned IgnoredFrameReg;
 458     int64_t Offset =
 459         getFrameIndexReference(MF, Save.getFrameIdx(), IgnoredFrameReg);
 460
 461     unsigned CFIIndex = MF.addFrameInst(MCCFIInstruction::createOffset(
 462           nullptr, DwarfReg, SPOffsetFromCFA + Offset));
 463     CFIIndexes.push_back(CFIIndex);
 464   }
 465   // Complete the CFI for the FPR/VR saves, modelling them as taking effect
 466   // after the last save.
 467   for (auto CFIIndex : CFIIndexes) {
 468     BuildMI(MBB, MBBI, DL, ZII->get(TargetOpcode::CFI_INSTRUCTION))
 469         .addCFIIndex(CFIIndex);
 470   }
 471 }
 472
 473 void SystemZFrameLowering::emitEpilogue(MachineFunction &MF,
 474                                         MachineBasicBlock &MBB) const {
 475   MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
 476   auto *ZII =
 477       static_cast<const SystemZInstrInfo *>(MF.getSubtarget().getInstrInfo());
 478   SystemZMachineFunctionInfo *ZFI = MF.getInfo<SystemZMachineFunctionInfo>();
 479   MachineFrameInfo &MFFrame = MF.getFrameInfo();
 480
 481   // Skip the return instruction.
 482   assert(MBBI->isReturn() && "Can only insert epilogue into returning blocks");
 483
 484   uint64_t StackSize = MFFrame.getStackSize();
 485   if (ZFI->getLowSavedGPR()) {
 486     --MBBI;
 487     unsigned Opcode = MBBI->getOpcode();
 488     if (Opcode != SystemZ::LMG)
 489       llvm_unreachable("Expected to see callee-save register restore code");
 490
 491     unsigned AddrOpNo = 2;
 492     DebugLoc DL = MBBI->getDebugLoc();
 493     uint64_t Offset = StackSize + MBBI->getOperand(AddrOpNo + 1).getImm();
 494     unsigned NewOpcode = ZII->getOpcodeForOffset(Opcode, Offset);
 495
 496     // If the offset is too large, use the largest stack-aligned offset
 497     // and add the rest to the base register (the stack or frame pointer).
 498     if (!NewOpcode) {
 499       uint64_t NumBytes = Offset - 0x7fff8;
 500       emitIncrement(MBB, MBBI, DL, MBBI->getOperand(AddrOpNo).getReg(),
 501                     NumBytes, ZII);
 502       Offset -= NumBytes;
 503       NewOpcode = ZII->getOpcodeForOffset(Opcode, Offset);
 504       assert(NewOpcode && "No restore instruction available");
 505     }
 506
 507     MBBI->setDesc(ZII->get(NewOpcode));
 508     MBBI->getOperand(AddrOpNo + 1).ChangeToImmediate(Offset);
 509   } else if (StackSize) {
 510     DebugLoc DL = MBBI->getDebugLoc();
 511     emitIncrement(MBB, MBBI, DL, SystemZ::R15D, StackSize, ZII);
 512   }
 513 }
 514
 515 bool SystemZFrameLowering::hasFP(const MachineFunction &MF) const {
 516   return (MF.getTarget().Options.DisableFramePointerElim(MF) ||
 517           MF.getFrameInfo().hasVarSizedObjects() ||
 518           MF.getInfo<SystemZMachineFunctionInfo>()->getManipulatesSP());
 519 }
 520
 521 bool
 522 SystemZFrameLowering::hasReservedCallFrame(const MachineFunction &MF) const {
 523   // The ABI requires us to allocate 160 bytes of stack space for the callee,
 524   // with any outgoing stack arguments being placed above that.  It seems
 525   // better to make that area a permanent feature of the frame even if
 526   // we're using a frame pointer.
 527   return true;
 528 }
 529
 530 MachineBasicBlock::iterator SystemZFrameLowering::
 531 eliminateCallFramePseudoInstr(MachineFunction &MF,
 532                               MachineBasicBlock &MBB,
 533                               MachineBasicBlock::iterator MI) const {
 534   switch (MI->getOpcode()) {
 535   case SystemZ::ADJCALLSTACKDOWN:
 536   case SystemZ::ADJCALLSTACKUP:
 537     assert(hasReservedCallFrame(MF) &&
 538            "ADJSTACKDOWN and ADJSTACKUP should be no-ops");
 539     return MBB.erase(MI);
 540     break;
 541
 542   default:
 543     llvm_unreachable("Unexpected call frame instruction");
 544   }
 545 }