Update to LLVM 3.5a.

Change-Id: Ifadecab779f128e62e430c2b4f6ddd84953ed617

1 files changed, 572 insertions, 40 deletions

diff --git a/lib/Target/ARM/ARMFrameLowering.cpp b/lib/Target/ARM/ARMFrameLowering.cpp
index d32bdbc..36ecfca 100644
--- a/lib/Target/ARM/ARMFrameLowering.cpp
+++ b/lib/Target/ARM/ARMFrameLowering.cpp
@@ -14,15 +14,18 @@
 #include "ARMFrameLowering.h"
 #include "ARMBaseInstrInfo.h"
 #include "ARMBaseRegisterInfo.h"
+#include "ARMConstantPoolValue.h"
 #include "ARMMachineFunctionInfo.h"
 #include "MCTargetDesc/ARMAddressingModes.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/RegisterScavenging.h"
 #include "llvm/IR/CallingConv.h"
 #include "llvm/IR/Function.h"
+#include "llvm/MC/MCContext.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Target/TargetOptions.h"
 
@@ -129,11 +132,24 @@ static void emitSPUpdate(bool isARM, MachineBasicBlock &MBB,
                        MIFlags, Pred, PredReg);
 }
 
+static int sizeOfSPAdjustment(const MachineInstr *MI) {
+  assert(MI->getOpcode() == ARM::VSTMDDB_UPD);
+  int count = 0;
+  // ARM and Thumb2 push/pop insts have explicit "sp, sp" operands (+
+  // pred) so the list starts at 4.
+  for (int i = MI->getNumOperands() - 1; i >= 4; --i)
+    count += 8;
+  return count;
+}
+
 void ARMFrameLowering::emitPrologue(MachineFunction &MF) const {
   MachineBasicBlock &MBB = MF.front();
   MachineBasicBlock::iterator MBBI = MBB.begin();
   MachineFrameInfo  *MFI = MF.getFrameInfo();
   ARMFunctionInfo *AFI = MF.getInfo<ARMFunctionInfo>();
+  MachineModuleInfo &MMI = MF.getMMI();
+  MCContext &Context = MMI.getContext();
+  const MCRegisterInfo *MRI = Context.getRegisterInfo();
   const ARMBaseRegisterInfo *RegInfo =
     static_cast<const ARMBaseRegisterInfo*>(MF.getTarget().getRegisterInfo());
   const ARMBaseInstrInfo &TII =
@@ -147,6 +163,7 @@ void ARMFrameLowering::emitPrologue(MachineFunction &MF) const {
   const std::vector<CalleeSavedInfo> &CSI = MFI->getCalleeSavedInfo();
   DebugLoc dl = MBBI != MBB.end() ? MBBI->getDebugLoc() : DebugLoc();
   unsigned FramePtr = RegInfo->getFrameRegister(MF);
+  int CFAOffset = 0;
 
   // Determine the sizes of each callee-save spill areas and record which frame
   // belongs to which callee-save spill areas.
@@ -159,22 +176,45 @@ void ARMFrameLowering::emitPrologue(MachineFunction &MF) const {
   if (MF.getFunction()->getCallingConv() == CallingConv::GHC)
     return;
 
-  // Allocate the vararg register save area. This is not counted in NumBytes.
-  if (ArgRegsSaveSize)
+  // Allocate the vararg register save area.
+  if (ArgRegsSaveSize) {
     emitSPUpdate(isARM, MBB, MBBI, dl, TII, -ArgRegsSaveSize,
                  MachineInstr::FrameSetup);
+    CFAOffset -= ArgRegsSaveSize;
+    unsigned CFIIndex = MMI.addFrameInst(
+        MCCFIInstruction::createDefCfaOffset(nullptr, CFAOffset));
+    BuildMI(MBB, MBBI, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
+        .addCFIIndex(CFIIndex);
+  }
 
   if (!AFI->hasStackFrame()) {
-    if (NumBytes != 0)
-      emitSPUpdate(isARM, MBB, MBBI, dl, TII, -NumBytes,
+    if (NumBytes - ArgRegsSaveSize != 0) {
+      emitSPUpdate(isARM, MBB, MBBI, dl, TII, -(NumBytes - ArgRegsSaveSize),
                    MachineInstr::FrameSetup);
+      CFAOffset -= NumBytes - ArgRegsSaveSize;
+      unsigned CFIIndex = MMI.addFrameInst(
+          MCCFIInstruction::createDefCfaOffset(nullptr, CFAOffset));
+      BuildMI(MBB, MBBI, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
+          .addCFIIndex(CFIIndex);
+    }
     return;
   }
 
+  // Determine spill area sizes.
   for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
     unsigned Reg = CSI[i].getReg();
     int FI = CSI[i].getFrameIdx();
     switch (Reg) {
+    case ARM::R8:
+    case ARM::R9:
+    case ARM::R10:
+    case ARM::R11:
+    case ARM::R12:
+      if (STI.isTargetMachO()) {
+        GPRCS2Size += 4;
+        break;
+      }
+      // fallthrough
     case ARM::R0:
     case ARM::R1:
     case ARM::R2:
@@ -188,18 +228,6 @@ void ARMFrameLowering::emitPrologue(MachineFunction &MF) const {
         FramePtrSpillFI = FI;
       GPRCS1Size += 4;
       break;
-    case ARM::R8:
-    case ARM::R9:
-    case ARM::R10:
-    case ARM::R11:
-    case ARM::R12:
-      if (Reg == FramePtr)
-        FramePtrSpillFI = FI;
-      if (STI.isTargetIOS())
-        GPRCS2Size += 4;
-      else
-        GPRCS1Size += 4;
-      break;
     default:
       // This is a DPR. Exclude the aligned DPRCS2 spills.
       if (Reg == ARM::D8)
@@ -210,18 +238,21 @@ void ARMFrameLowering::emitPrologue(MachineFunction &MF) const {
   }
 
   // Move past area 1.
-  MachineBasicBlock::iterator LastPush = MBB.end(), FramePtrPush;
+  MachineBasicBlock::iterator LastPush = MBB.end(), GPRCS1Push, GPRCS2Push,
+      DPRCSPush;
   if (GPRCS1Size > 0)
-    FramePtrPush = LastPush = MBBI++;
+    GPRCS1Push = LastPush = MBBI++;
 
   // Determine starting offsets of spill areas.
   bool HasFP = hasFP(MF);
-  unsigned DPRCSOffset  = NumBytes - (GPRCS1Size + GPRCS2Size + DPRCSSize);
+  unsigned DPRCSOffset  = NumBytes - (ArgRegsSaveSize + GPRCS1Size
+                                      + GPRCS2Size + DPRCSSize);
   unsigned GPRCS2Offset = DPRCSOffset + DPRCSSize;
   unsigned GPRCS1Offset = GPRCS2Offset + GPRCS2Size;
   int FramePtrOffsetInPush = 0;
   if (HasFP) {
-    FramePtrOffsetInPush = MFI->getObjectOffset(FramePtrSpillFI) + GPRCS1Size;
+    FramePtrOffsetInPush = MFI->getObjectOffset(FramePtrSpillFI)
+                           + GPRCS1Size + ArgRegsSaveSize;
     AFI->setFramePtrSpillOffset(MFI->getObjectOffset(FramePtrSpillFI) +
                                 NumBytes);
   }
@@ -230,13 +261,12 @@ void ARMFrameLowering::emitPrologue(MachineFunction &MF) const {
   AFI->setDPRCalleeSavedAreaOffset(DPRCSOffset);
 
   // Move past area 2.
-  if (GPRCS2Size > 0) {
-    LastPush = MBBI++;
-  }
+  if (GPRCS2Size > 0)
+    GPRCS2Push = LastPush = MBBI++;
 
   // Move past area 3.
   if (DPRCSSize > 0) {
-    LastPush = MBBI++;
+    DPRCSPush = MBBI;
     // Since vpush register list cannot have gaps, there may be multiple vpush
     // instructions in the prologue.
     while (MBBI->getOpcode() == ARM::VSTMDDB_UPD)
@@ -254,11 +284,15 @@ void ARMFrameLowering::emitPrologue(MachineFunction &MF) const {
   } else
     NumBytes = DPRCSOffset;
 
+  unsigned adjustedGPRCS1Size = GPRCS1Size;
   if (NumBytes) {
     // Adjust SP after all the callee-save spills.
-    if (tryFoldSPUpdateIntoPushPop(MF, LastPush, NumBytes)) {
-      if (LastPush == FramePtrPush)
+    if (tryFoldSPUpdateIntoPushPop(STI, MF, LastPush, NumBytes)) {
+      if (LastPush == GPRCS1Push) {
         FramePtrOffsetInPush += NumBytes;
+        adjustedGPRCS1Size += NumBytes;
+        NumBytes = 0;
+      }
     } else
       emitSPUpdate(isARM, MBB, MBBI, dl, TII, -NumBytes,
                    MachineInstr::FrameSetup);
@@ -275,17 +309,141 @@ void ARMFrameLowering::emitPrologue(MachineFunction &MF) const {
       AFI->setShouldRestoreSPFromFP(true);
   }
 
+  if (adjustedGPRCS1Size > 0) {
+    CFAOffset -= adjustedGPRCS1Size;
+    unsigned CFIIndex = MMI.addFrameInst(
+        MCCFIInstruction::createDefCfaOffset(nullptr, CFAOffset));
+    MachineBasicBlock::iterator Pos = ++GPRCS1Push;
+    BuildMI(MBB, Pos, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
+        .addCFIIndex(CFIIndex);
+    for (std::vector<CalleeSavedInfo>::const_iterator I = CSI.begin(),
+           E = CSI.end(); I != E; ++I) {
+      unsigned Reg = I->getReg();
+      int FI = I->getFrameIdx();
+      switch (Reg) {
+      case ARM::R8:
+      case ARM::R9:
+      case ARM::R10:
+      case ARM::R11:
+      case ARM::R12:
+        if (STI.isTargetMachO())
+          break;
+        // fallthrough
+      case ARM::R0:
+      case ARM::R1:
+      case ARM::R2:
+      case ARM::R3:
+      case ARM::R4:
+      case ARM::R5:
+      case ARM::R6:
+      case ARM::R7:
+      case ARM::LR:
+        CFIIndex = MMI.addFrameInst(MCCFIInstruction::createOffset(
+            nullptr, MRI->getDwarfRegNum(Reg, true), MFI->getObjectOffset(FI)));
+        BuildMI(MBB, Pos, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
+            .addCFIIndex(CFIIndex);
+        break;
+      }
+    }
+  }
+
   // Set FP to point to the stack slot that contains the previous FP.
   // For iOS, FP is R7, which has now been stored in spill area 1.
   // Otherwise, if this is not iOS, all the callee-saved registers go
   // into spill area 1, including the FP in R11.  In either case, it
   // is in area one and the adjustment needs to take place just after
   // that push.
-  if (HasFP)
-    emitRegPlusImmediate(!AFI->isThumbFunction(), MBB, ++FramePtrPush, dl, TII,
+  if (HasFP) {
+    emitRegPlusImmediate(!AFI->isThumbFunction(), MBB, GPRCS1Push, dl, TII,
                          FramePtr, ARM::SP, FramePtrOffsetInPush,
                          MachineInstr::FrameSetup);
+    if (FramePtrOffsetInPush) {
+      CFAOffset += FramePtrOffsetInPush;
+      unsigned CFIIndex = MMI.addFrameInst(MCCFIInstruction::createDefCfa(
+          nullptr, MRI->getDwarfRegNum(FramePtr, true), CFAOffset));
+      BuildMI(MBB, GPRCS1Push, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
+          .addCFIIndex(CFIIndex);
+
+    } else {
+      unsigned CFIIndex =
+          MMI.addFrameInst(MCCFIInstruction::createDefCfaRegister(
+              nullptr, MRI->getDwarfRegNum(FramePtr, true)));
+      BuildMI(MBB, GPRCS1Push, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
+          .addCFIIndex(CFIIndex);
+    }
+  }
+
+  if (GPRCS2Size > 0) {
+    MachineBasicBlock::iterator Pos = ++GPRCS2Push;
+    if (!HasFP) {
+      CFAOffset -= GPRCS2Size;
+      unsigned CFIIndex = MMI.addFrameInst(
+          MCCFIInstruction::createDefCfaOffset(nullptr, CFAOffset));
+      BuildMI(MBB, Pos, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
+          .addCFIIndex(CFIIndex);
+    }
+    for (std::vector<CalleeSavedInfo>::const_iterator I = CSI.begin(),
+           E = CSI.end(); I != E; ++I) {
+      unsigned Reg = I->getReg();
+      int FI = I->getFrameIdx();
+      switch (Reg) {
+      case ARM::R8:
+      case ARM::R9:
+      case ARM::R10:
+      case ARM::R11:
+      case ARM::R12:
+        if (STI.isTargetMachO()) {
+          unsigned DwarfReg =  MRI->getDwarfRegNum(Reg, true);
+          unsigned Offset = MFI->getObjectOffset(FI);
+          unsigned CFIIndex = MMI.addFrameInst(
+              MCCFIInstruction::createOffset(nullptr, DwarfReg, Offset));
+          BuildMI(MBB, Pos, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
+              .addCFIIndex(CFIIndex);
+        }
+        break;
+      }
+    }
+  }
 
+  if (DPRCSSize > 0) {
+    // Since vpush register list cannot have gaps, there may be multiple vpush
+    // instructions in the prologue.
+    do {
+      MachineBasicBlock::iterator Push = DPRCSPush++;
+      if (!HasFP) {
+        CFAOffset -= sizeOfSPAdjustment(Push);;
+        unsigned CFIIndex = MMI.addFrameInst(
+            MCCFIInstruction::createDefCfaOffset(nullptr, CFAOffset));
+        BuildMI(MBB, DPRCSPush, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
+            .addCFIIndex(CFIIndex);
+      }
+    } while (DPRCSPush->getOpcode() == ARM::VSTMDDB_UPD);
+
+    for (std::vector<CalleeSavedInfo>::const_iterator I = CSI.begin(),
+           E = CSI.end(); I != E; ++I) {
+      unsigned Reg = I->getReg();
+      int FI = I->getFrameIdx();
+      if ((Reg >= ARM::D0 && Reg <= ARM::D31) &&
+          (Reg < ARM::D8 || Reg >= ARM::D8 + AFI->getNumAlignedDPRCS2Regs())) {
+        unsigned DwarfReg = MRI->getDwarfRegNum(Reg, true);
+        unsigned Offset = MFI->getObjectOffset(FI);
+        unsigned CFIIndex = MMI.addFrameInst(
+            MCCFIInstruction::createOffset(nullptr, DwarfReg, Offset));
+        BuildMI(MBB, DPRCSPush, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
+            .addCFIIndex(CFIIndex);
+      }
+    }
+  }
+
+  if (NumBytes) {
+    if (!HasFP) {
+      CFAOffset -= NumBytes;
+      unsigned CFIIndex = MMI.addFrameInst(
+          MCCFIInstruction::createDefCfaOffset(nullptr, CFAOffset));
+      BuildMI(MBB, MBBI, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
+          .addCFIIndex(CFIIndex);
+    }
+  }
 
   if (STI.isTargetELF() && hasFP(MF))
     MFI->setOffsetAdjustment(MFI->getOffsetAdjustment() -
@@ -378,8 +536,8 @@ void ARMFrameLowering::emitEpilogue(MachineFunction &MF,
     return;
 
   if (!AFI->hasStackFrame()) {
-    if (NumBytes != 0)
-      emitSPUpdate(isARM, MBB, MBBI, dl, TII, NumBytes);
+    if (NumBytes - ArgRegsSaveSize != 0)
+      emitSPUpdate(isARM, MBB, MBBI, dl, TII, NumBytes - ArgRegsSaveSize);
   } else {
     // Unwind MBBI to point to first LDR / VLDRD.
     const uint16_t *CSRegs = RegInfo->getCalleeSavedRegs(&MF);
@@ -392,7 +550,8 @@ void ARMFrameLowering::emitEpilogue(MachineFunction &MF,
     }
 
     // Move SP to start of FP callee save spill area.
-    NumBytes -= (AFI->getGPRCalleeSavedArea1Size() +
+    NumBytes -= (ArgRegsSaveSize +
+                 AFI->getGPRCalleeSavedArea1Size() +
                  AFI->getGPRCalleeSavedArea2Size() +
                  AFI->getDPRCalleeSavedAreaSize());
 
@@ -430,7 +589,8 @@ void ARMFrameLowering::emitEpilogue(MachineFunction &MF,
                                  ARM::SP)
             .addReg(FramePtr));
       }
-    } else if (NumBytes && !tryFoldSPUpdateIntoPushPop(MF, MBBI, NumBytes))
+    } else if (NumBytes &&
+               !tryFoldSPUpdateIntoPushPop(STI, MF, MBBI, NumBytes))
         emitSPUpdate(isARM, MBB, MBBI, dl, TII, NumBytes);
 
     // Increment past our save areas.
@@ -453,7 +613,7 @@ void ARMFrameLowering::emitEpilogue(MachineFunction &MF,
     // Jump to label or value in register.
     if (RetOpcode == ARM::TCRETURNdi) {
       unsigned TCOpcode = STI.isThumb() ?
-               (STI.isTargetIOS() ? ARM::tTAILJMPd : ARM::tTAILJMPdND) :
+               (STI.isTargetMachO() ? ARM::tTAILJMPd : ARM::tTAILJMPdND) :
                ARM::TAILJMPd;
       MachineInstrBuilder MIB = BuildMI(MBB, MBBI, dl, TII.get(TCOpcode));
       if (JumpTarget.isGlobal())
@@ -473,7 +633,7 @@ void ARMFrameLowering::emitEpilogue(MachineFunction &MF,
         addReg(JumpTarget.getReg(), RegState::Kill);
     }
 
-    MachineInstr *NewMI = prior(MBBI);
+    MachineInstr *NewMI = std::prev(MBBI);
     for (unsigned i = 1, e = MBBI->getNumOperands(); i != e; ++i)
       NewMI->addOperand(MBBI->getOperand(i));
 
@@ -598,7 +758,7 @@ void ARMFrameLowering::emitPushInst(MachineBasicBlock &MBB,
     unsigned LastReg = 0;
     for (; i != 0; --i) {
       unsigned Reg = CSI[i-1].getReg();
-      if (!(Func)(Reg, STI.isTargetIOS())) continue;
+      if (!(Func)(Reg, STI.isTargetMachO())) continue;
 
       // D-registers in the aligned area DPRCS2 are NOT spilled here.
       if (Reg >= ARM::D8 && Reg < ARM::D8 + NumAlignedDPRCS2Regs)
@@ -644,6 +804,11 @@ void ARMFrameLowering::emitPushInst(MachineBasicBlock &MBB,
       AddDefaultPred(MIB);
     }
     Regs.clear();
+
+    // Put any subsequent vpush instructions before this one: they will refer to
+    // higher register numbers so need to be pushed first in order to preserve
+    // monotonicity.
+    --MI;
   }
 }
 
@@ -671,7 +836,7 @@ void ARMFrameLowering::emitPopInst(MachineBasicBlock &MBB,
     bool DeleteRet = false;
     for (; i != 0; --i) {
       unsigned Reg = CSI[i-1].getReg();
-      if (!(Func)(Reg, STI.isTargetIOS())) continue;
+      if (!(Func)(Reg, STI.isTargetMachO())) continue;
 
       // The aligned reloads from area DPRCS2 are not inserted here.
       if (Reg >= ARM::D8 && Reg < ARM::D8 + NumAlignedDPRCS2Regs)
@@ -727,6 +892,10 @@ void ARMFrameLowering::emitPopInst(MachineBasicBlock &MBB,
       AddDefaultPred(MIB);
     }
     Regs.clear();
+
+    // Put any subsequent vpop instructions after this one: they will refer to
+    // higher register numbers so need to be popped afterwards.
+    ++MI;
   }
 }
 
@@ -858,7 +1027,7 @@ static void emitAlignedDPRCS2Spills(MachineBasicBlock &MBB,
   }
 
   // The last spill instruction inserted should kill the scratch register r4.
-  llvm::prior(MI)->addRegisterKilled(ARM::R4, TRI);
+  std::prev(MI)->addRegisterKilled(ARM::R4, TRI);
 }
 
 /// Skip past the code inserted by emitAlignedDPRCS2Spills, and return an
@@ -968,7 +1137,7 @@ static void emitAlignedDPRCS2Restores(MachineBasicBlock &MBB,
                    .addReg(ARM::R4).addImm(2*(NextReg-R4BaseReg)));
 
   // Last store kills r4.
-  llvm::prior(MI)->addRegisterKilled(ARM::R4, TRI);
+  std::prev(MI)->addRegisterKilled(ARM::R4, TRI);
 }
 
 bool ARMFrameLowering::spillCalleeSavedRegisters(MachineBasicBlock &MBB,
@@ -1220,7 +1389,7 @@ ARMFrameLowering::processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
     if (Spilled) {
       NumGPRSpills++;
 
-      if (!STI.isTargetIOS()) {
+      if (!STI.isTargetMachO()) {
         if (Reg == ARM::LR)
           LRSpilled = true;
         CS1Spilled = true;
@@ -1242,7 +1411,7 @@ ARMFrameLowering::processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
         break;
       }
     } else {
-      if (!STI.isTargetIOS()) {
+      if (!STI.isTargetMachO()) {
         UnspilledCS1GPRs.push_back(Reg);
         continue;
       }
@@ -1444,3 +1613,366 @@ eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
   MBB.erase(I);
 }
 
+/// Get the minimum constant for ARM that is greater than or equal to the
+/// argument. In ARM, constants can have any value that can be produced by
+/// rotating an 8-bit value to the right by an even number of bits within a
+/// 32-bit word.
+static uint32_t alignToARMConstant(uint32_t Value) {
+  unsigned Shifted = 0;
+
+  if (Value == 0)
+      return 0;
+
+  while (!(Value & 0xC0000000)) {
+      Value = Value << 2;
+      Shifted += 2;
+  }
+
+  bool Carry = (Value & 0x00FFFFFF);
+  Value = ((Value & 0xFF000000) >> 24) + Carry;
+
+  if (Value & 0x0000100)
+      Value = Value & 0x000001FC;
+
+  if (Shifted > 24)
+      Value = Value >> (Shifted - 24);
+  else
+      Value = Value << (24 - Shifted);
+
+  return Value;
+}
+
+// The stack limit in the TCB is set to this many bytes above the actual
+// stack limit.
+static const uint64_t kSplitStackAvailable = 256;
+
+// Adjust the function prologue to enable split stacks. This currently only
+// supports android and linux.
+//
+// The ABI of the segmented stack prologue is a little arbitrarily chosen, but
+// must be well defined in order to allow for consistent implementations of the
+// __morestack helper function. The ABI is also not a normal ABI in that it
+// doesn't follow the normal calling conventions because this allows the
+// prologue of each function to be optimized further.
+//
+// Currently, the ABI looks like (when calling __morestack)
+//
+//  * r4 holds the minimum stack size requested for this function call
+//  * r5 holds the stack size of the arguments to the function
+//  * the beginning of the function is 3 instructions after the call to
+//    __morestack
+//
+// Implementations of __morestack should use r4 to allocate a new stack, r5 to
+// place the arguments on to the new stack, and the 3-instruction knowledge to
+// jump directly to the body of the function when working on the new stack.
+//
+// An old (and possibly no longer compatible) implementation of __morestack for
+// ARM can be found at [1].
+//
+// [1] - https://github.com/mozilla/rust/blob/86efd9/src/rt/arch/arm/morestack.S
+void ARMFrameLowering::adjustForSegmentedStacks(MachineFunction &MF) const {
+  unsigned Opcode;
+  unsigned CFIIndex;
+  const ARMSubtarget *ST = &MF.getTarget().getSubtarget<ARMSubtarget>();
+  bool Thumb = ST->isThumb();
+
+  // Sadly, this currently doesn't support varargs, platforms other than
+  // android/linux. Note that thumb1/thumb2 are support for android/linux.
+  if (MF.getFunction()->isVarArg())
+    report_fatal_error("Segmented stacks do not support vararg functions.");
+  if (!ST->isTargetAndroid() && !ST->isTargetLinux())
+    report_fatal_error("Segmented stacks not supported on this platfrom.");
+
+  MachineBasicBlock &prologueMBB = MF.front();
+  MachineFrameInfo *MFI = MF.getFrameInfo();
+  MachineModuleInfo &MMI = MF.getMMI();
+  MCContext &Context = MMI.getContext();
+  const MCRegisterInfo *MRI = Context.getRegisterInfo();
+  const ARMBaseInstrInfo &TII =
+      *static_cast<const ARMBaseInstrInfo*>(MF.getTarget().getInstrInfo());
+  ARMFunctionInfo *ARMFI = MF.getInfo<ARMFunctionInfo>();
+  DebugLoc DL;
+
+  // Use R4 and R5 as scratch registers.
+  // We save R4 and R5 before use and restore them before leaving the function.
+  unsigned ScratchReg0 = ARM::R4;
+  unsigned ScratchReg1 = ARM::R5;
+  uint64_t AlignedStackSize;
+
+  MachineBasicBlock *PrevStackMBB = MF.CreateMachineBasicBlock();
+  MachineBasicBlock *PostStackMBB = MF.CreateMachineBasicBlock();
+  MachineBasicBlock *AllocMBB = MF.CreateMachineBasicBlock();
+  MachineBasicBlock *GetMBB = MF.CreateMachineBasicBlock();
+  MachineBasicBlock *McrMBB = MF.CreateMachineBasicBlock();
+
+  for (MachineBasicBlock::livein_iterator i = prologueMBB.livein_begin(),
+                                          e = prologueMBB.livein_end();
+       i != e; ++i) {
+    AllocMBB->addLiveIn(*i);
+    GetMBB->addLiveIn(*i);
+    McrMBB->addLiveIn(*i);
+    PrevStackMBB->addLiveIn(*i);
+    PostStackMBB->addLiveIn(*i);
+  }
+
+  MF.push_front(PostStackMBB);
+  MF.push_front(AllocMBB);
+  MF.push_front(GetMBB);
+  MF.push_front(McrMBB);
+  MF.push_front(PrevStackMBB);
+
+  // The required stack size that is aligned to ARM constant criterion.
+  uint64_t StackSize = MFI->getStackSize();
+
+  AlignedStackSize = alignToARMConstant(StackSize);
+
+  // When the frame size is less than 256 we just compare the stack
+  // boundary directly to the value of the stack pointer, per gcc.
+  bool CompareStackPointer = AlignedStackSize < kSplitStackAvailable;
+
+  // We will use two of the callee save registers as scratch registers so we
+  // need to save those registers onto the stack.
+  // We will use SR0 to hold stack limit and SR1 to hold the stack size
+  // requested and arguments for __morestack().
+  // SR0: Scratch Register #0
+  // SR1: Scratch Register #1
+  // push {SR0, SR1}
+  if (Thumb) {
+    AddDefaultPred(BuildMI(PrevStackMBB, DL, TII.get(ARM::tPUSH)))
+        .addReg(ScratchReg0).addReg(ScratchReg1);
+  } else {
+    AddDefaultPred(BuildMI(PrevStackMBB, DL, TII.get(ARM::STMDB_UPD))
+                   .addReg(ARM::SP, RegState::Define).addReg(ARM::SP))
+        .addReg(ScratchReg0).addReg(ScratchReg1);
+  }
+
+  // Emit the relevant DWARF information about the change in stack pointer as
+  // well as where to find both r4 and r5 (the callee-save registers)
+  CFIIndex =
+      MMI.addFrameInst(MCCFIInstruction::createDefCfaOffset(nullptr, -8));
+  BuildMI(PrevStackMBB, DL, TII.get(TargetOpcode::CFI_INSTRUCTION))
+      .addCFIIndex(CFIIndex);
+  CFIIndex = MMI.addFrameInst(MCCFIInstruction::createOffset(
+      nullptr, MRI->getDwarfRegNum(ScratchReg1, true), -4));
+  BuildMI(PrevStackMBB, DL, TII.get(TargetOpcode::CFI_INSTRUCTION))
+      .addCFIIndex(CFIIndex);
+  CFIIndex = MMI.addFrameInst(MCCFIInstruction::createOffset(
+      nullptr, MRI->getDwarfRegNum(ScratchReg0, true), -8));
+  BuildMI(PrevStackMBB, DL, TII.get(TargetOpcode::CFI_INSTRUCTION))
+      .addCFIIndex(CFIIndex);
+
+  // mov SR1, sp
+  if (Thumb) {
+    AddDefaultPred(BuildMI(McrMBB, DL, TII.get(ARM::tMOVr), ScratchReg1)
+                      .addReg(ARM::SP));
+  } else if (CompareStackPointer) {
+    AddDefaultPred(BuildMI(McrMBB, DL, TII.get(ARM::MOVr), ScratchReg1)
+                      .addReg(ARM::SP)).addReg(0);
+  }
+
+  // sub SR1, sp, #StackSize
+  if (!CompareStackPointer && Thumb) {
+    AddDefaultPred(
+        AddDefaultCC(BuildMI(McrMBB, DL, TII.get(ARM::tSUBi8), ScratchReg1))
+            .addReg(ScratchReg1).addImm(AlignedStackSize));
+  } else if (!CompareStackPointer) {
+    AddDefaultPred(BuildMI(McrMBB, DL, TII.get(ARM::SUBri), ScratchReg1)
+                      .addReg(ARM::SP).addImm(AlignedStackSize)).addReg(0);
+  }
+
+  if (Thumb && ST->isThumb1Only()) {
+    unsigned PCLabelId = ARMFI->createPICLabelUId();
+    ARMConstantPoolValue *NewCPV = ARMConstantPoolSymbol::Create(
+        MF.getFunction()->getContext(), "__STACK_LIMIT", PCLabelId, 0);
+    MachineConstantPool *MCP = MF.getConstantPool();
+    unsigned CPI = MCP->getConstantPoolIndex(NewCPV, MF.getAlignment());
+
+    // ldr SR0, [pc, offset(STACK_LIMIT)]
+    AddDefaultPred(BuildMI(GetMBB, DL, TII.get(ARM::tLDRpci), ScratchReg0)
+                      .addConstantPoolIndex(CPI));
+
+    // ldr SR0, [SR0]
+    AddDefaultPred(BuildMI(GetMBB, DL, TII.get(ARM::tLDRi), ScratchReg0)
+                      .addReg(ScratchReg0).addImm(0));
+  } else {
+    // Get TLS base address from the coprocessor
+    // mrc p15, #0, SR0, c13, c0, #3
+    AddDefaultPred(BuildMI(McrMBB, DL, TII.get(ARM::MRC), ScratchReg0)
+                     .addImm(15)
+                     .addImm(0)
+                     .addImm(13)
+                     .addImm(0)
+                     .addImm(3));
+
+    // Use the last tls slot on android and a private field of the TCP on linux.
+    assert(ST->isTargetAndroid() || ST->isTargetLinux());
+    unsigned TlsOffset = ST->isTargetAndroid() ? 63 : 1;
+
+    // Get the stack limit from the right offset
+    // ldr SR0, [sr0, #4 * TlsOffset]
+    AddDefaultPred(BuildMI(GetMBB, DL, TII.get(ARM::LDRi12), ScratchReg0)
+                      .addReg(ScratchReg0).addImm(4 * TlsOffset));
+  }
+
+  // Compare stack limit with stack size requested.
+  // cmp SR0, SR1
+  Opcode = Thumb ? ARM::tCMPr : ARM::CMPrr;
+  AddDefaultPred(BuildMI(GetMBB, DL, TII.get(Opcode))
+                    .addReg(ScratchReg0)
+                    .addReg(ScratchReg1));
+
+  // This jump is taken if StackLimit < SP - stack required.
+  Opcode = Thumb ? ARM::tBcc : ARM::Bcc;
+  BuildMI(GetMBB, DL, TII.get(Opcode)).addMBB(PostStackMBB)
+       .addImm(ARMCC::LO)
+       .addReg(ARM::CPSR);
+
+
+  // Calling __morestack(StackSize, Size of stack arguments).
+  // __morestack knows that the stack size requested is in SR0(r4)
+  // and amount size of stack arguments is in SR1(r5).
+
+  // Pass first argument for the __morestack by Scratch Register #0.
+  //   The amount size of stack required
+  if (Thumb) {
+    AddDefaultPred(AddDefaultCC(BuildMI(AllocMBB, DL, TII.get(ARM::tMOVi8),
+                                        ScratchReg0)).addImm(AlignedStackSize));
+  } else {
+    AddDefaultPred(BuildMI(AllocMBB, DL, TII.get(ARM::MOVi), ScratchReg0)
+                      .addImm(AlignedStackSize)).addReg(0);
+  }
+  // Pass second argument for the __morestack by Scratch Register #1.
+  //   The amount size of stack consumed to save function arguments.
+  if (Thumb) {
+    AddDefaultPred(
+        AddDefaultCC(BuildMI(AllocMBB, DL, TII.get(ARM::tMOVi8), ScratchReg1))
+            .addImm(alignToARMConstant(ARMFI->getArgumentStackSize())));
+  } else {
+    AddDefaultPred(BuildMI(AllocMBB, DL, TII.get(ARM::MOVi), ScratchReg1)
+                   .addImm(alignToARMConstant(ARMFI->getArgumentStackSize())))
+                   .addReg(0);
+  }
+
+  // push {lr} - Save return address of this function.
+  if (Thumb) {
+    AddDefaultPred(BuildMI(AllocMBB, DL, TII.get(ARM::tPUSH)))
+        .addReg(ARM::LR);
+  } else {
+    AddDefaultPred(BuildMI(AllocMBB, DL, TII.get(ARM::STMDB_UPD))
+                   .addReg(ARM::SP, RegState::Define)
+                   .addReg(ARM::SP))
+        .addReg(ARM::LR);
+  }
+
+  // Emit the DWARF info about the change in stack as well as where to find the
+  // previous link register
+  CFIIndex =
+      MMI.addFrameInst(MCCFIInstruction::createDefCfaOffset(nullptr, -12));
+  BuildMI(AllocMBB, DL, TII.get(TargetOpcode::CFI_INSTRUCTION))
+      .addCFIIndex(CFIIndex);
+  CFIIndex = MMI.addFrameInst(MCCFIInstruction::createOffset(
+        nullptr, MRI->getDwarfRegNum(ARM::LR, true), -12));
+  BuildMI(AllocMBB, DL, TII.get(TargetOpcode::CFI_INSTRUCTION))
+      .addCFIIndex(CFIIndex);
+
+  // Call __morestack().
+  if (Thumb) {
+    AddDefaultPred(BuildMI(AllocMBB, DL, TII.get(ARM::tBL)))
+        .addExternalSymbol("__morestack");
+  } else {
+    BuildMI(AllocMBB, DL, TII.get(ARM::BL))
+        .addExternalSymbol("__morestack");
+  }
+
+  // pop {lr} - Restore return address of this original function.
+  if (Thumb) {
+    if (ST->isThumb1Only()) {
+      AddDefaultPred(BuildMI(AllocMBB, DL, TII.get(ARM::tPOP)))
+                     .addReg(ScratchReg0);
+      AddDefaultPred(BuildMI(AllocMBB, DL, TII.get(ARM::tMOVr), ARM::LR)
+                     .addReg(ScratchReg0));
+    } else {
+      AddDefaultPred(BuildMI(AllocMBB, DL, TII.get(ARM::t2LDR_POST))
+                     .addReg(ARM::LR, RegState::Define)
+                     .addReg(ARM::SP, RegState::Define)
+                     .addReg(ARM::SP)
+                     .addImm(4));
+    }
+  } else {
+    AddDefaultPred(BuildMI(AllocMBB, DL, TII.get(ARM::LDMIA_UPD))
+                   .addReg(ARM::SP, RegState::Define)
+                   .addReg(ARM::SP))
+      .addReg(ARM::LR);
+  }
+
+  // Restore SR0 and SR1 in case of __morestack() was called.
+  // __morestack() will skip PostStackMBB block so we need to restore
+  // scratch registers from here.
+  // pop {SR0, SR1}
+  if (Thumb) {
+    AddDefaultPred(BuildMI(AllocMBB, DL, TII.get(ARM::tPOP)))
+      .addReg(ScratchReg0)
+      .addReg(ScratchReg1);
+  } else {
+    AddDefaultPred(BuildMI(AllocMBB, DL, TII.get(ARM::LDMIA_UPD))
+                   .addReg(ARM::SP, RegState::Define)
+                   .addReg(ARM::SP))
+      .addReg(ScratchReg0)
+      .addReg(ScratchReg1);
+  }
+
+  // Update the CFA offset now that we've popped
+  CFIIndex = MMI.addFrameInst(MCCFIInstruction::createDefCfaOffset(nullptr, 0));
+  BuildMI(AllocMBB, DL, TII.get(TargetOpcode::CFI_INSTRUCTION))
+      .addCFIIndex(CFIIndex);
+
+  // bx lr - Return from this function.
+  Opcode = Thumb ? ARM::tBX_RET : ARM::BX_RET;
+  AddDefaultPred(BuildMI(AllocMBB, DL, TII.get(Opcode)));
+
+  // Restore SR0 and SR1 in case of __morestack() was not called.
+  // pop {SR0, SR1}
+  if (Thumb) {
+    AddDefaultPred(BuildMI(PostStackMBB, DL, TII.get(ARM::tPOP)))
+      .addReg(ScratchReg0)
+      .addReg(ScratchReg1);
+  } else {
+    AddDefaultPred(BuildMI(PostStackMBB, DL, TII.get(ARM::LDMIA_UPD))
+                   .addReg(ARM::SP, RegState::Define)
+                   .addReg(ARM::SP))
+      .addReg(ScratchReg0)
+      .addReg(ScratchReg1);
+  }
+
+  // Update the CFA offset now that we've popped
+  CFIIndex = MMI.addFrameInst(MCCFIInstruction::createDefCfaOffset(nullptr, 0));
+  BuildMI(PostStackMBB, DL, TII.get(TargetOpcode::CFI_INSTRUCTION))
+      .addCFIIndex(CFIIndex);
+
+  // Tell debuggers that r4 and r5 are now the same as they were in the
+  // previous function, that they're the "Same Value".
+  CFIIndex = MMI.addFrameInst(MCCFIInstruction::createSameValue(
+      nullptr, MRI->getDwarfRegNum(ScratchReg0, true)));
+  BuildMI(PostStackMBB, DL, TII.get(TargetOpcode::CFI_INSTRUCTION))
+      .addCFIIndex(CFIIndex);
+  CFIIndex = MMI.addFrameInst(MCCFIInstruction::createSameValue(
+      nullptr, MRI->getDwarfRegNum(ScratchReg1, true)));
+  BuildMI(PostStackMBB, DL, TII.get(TargetOpcode::CFI_INSTRUCTION))
+      .addCFIIndex(CFIIndex);
+
+  // Organizing MBB lists
+  PostStackMBB->addSuccessor(&prologueMBB);
+
+  AllocMBB->addSuccessor(PostStackMBB);
+
+  GetMBB->addSuccessor(PostStackMBB);
+  GetMBB->addSuccessor(AllocMBB);
+
+  McrMBB->addSuccessor(GetMBB);
+
+  PrevStackMBB->addSuccessor(McrMBB);
+
+#ifdef XDEBUG
+  MF.verify();
+#endif
+}