[X86] Merge adjacent stack adjustments in eliminateCallFramePseudoInstr (PR27140)

[hans]

Summary

For code such as:

void f(int, int);
void g() {
  f(1, 2);
}

compiled for 32-bit X86 Linux at -Os, Clang would previously generate:

subl    $12, %esp
subl    $8, %esp
pushl   $2
pushl   $1
calll   f
addl    $16, %esp
addl    $12, %esp
retl

This patch fixes that by merging adjacent stack adjustments in eliminateCallFramePseudoInstr().

Unfortunately, this means that eliminateCallFramePseudoInstr() doesn't just replace a single machine instruction, but potentially erases the previous and/or next instruction as well. To allow the caller of eliminateCallFramePseudoInstr() to continue iterating, this patch makes the function return an iterator to the next instruction. This makes the code in PEI::replaceFrameIndices() much simpler.

Note that previously, replaceFrameIndices() would try to re-visit the instruction created by eliminateCallFramePseudoInstr(). That code was added in r36625, but I can't see any reason for it: the new instructions will obviously not be pseudo instructions, they will not have FrameIndex operands, and we have already accounted for the stack adjustment.

I would probably commit the change to replaceFrameIndices() and return type of eliminateCallFramePseudoInstr() separately.

[rnk]

lib/Target/X86/X86FrameLowering.cpp

2561 ↗

(On Diff #52127)

How did mergeSPUpdates change the sign here?

test/CodeGen/X86/force-align-stack-alloca.ll

36 ↗

(On Diff #52127)

can you check for 3x pushl here to make it clear that we're allocating 32 bytes of stack?

39 ↗

(On Diff #52127)

Add a comment about why 4? (deallocate 32 bytes of outgoing callframe for memset, allocate 28 for f)

[hans]

lib/Target/X86/X86FrameLowering.cpp

2561 ↗

(On Diff #52127)

It doesn't. What's changed is that now the Amount can change above, due to the merging, and that also needs to feed into the CFAOffset.

I figured it was simpler to just spell out that CFAOffset is the opposite of the stack adjustment.

Actually, let me see if I can make this a bit more clear in a new patch..

[hans]

Addressing comments.

[rnk]

lgtm

[jpienaar]

lib/Target/Lanai/LanaiFrameLowering.cpp

142 ↗

(On Diff #52162)

Thanks for updating this too. 'void' here should probably be 'MachineBasicBlock::iterator'.

[hans]

Rebasing on top of r264966 (a few more tests needed updates), and addressing Jacques's comment.

[hans]

The actual merging was committed in r265039.

lib/Target/Lanai/LanaiFrameLowering.cpp

142 ↗

(On Diff #52162)

Oops! Thanks for spotting this!

llvm/trunk/docs/ReleaseNotes.rst

 
 * The C API function LLVMLinkModules has been removed.
 
 * The C API function LLVMAddTargetData has been removed.
 
 * The C API function LLVMGetDataLayout is deprecated
   in favor of LLVMGetDataLayoutStr.
 
+* ``TargetFrameLowering::eliminateCallFramePseudoInstr`` now returns an
+  iterator to the next instruction instead of ``void``. Targets that previously
+  did ``MBB.erase(I); return;`` now probably want ``return MBB.erase(I);``.
+
 .. NOTE
    For small 1-3 sentence descriptions, just add an entry at the end of
    this list. If your description won't fit comfortably in one bullet
    point (e.g. maybe you would like to give an example of the
    functionality, or simply have a lot to talk about), see the `NOTE` below
    for adding a new subsection.
 
 * ... next change ...

llvm/trunk/include/llvm/Target/TargetFrameLowering.h

public:
   virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF,
                                              RegScavenger *RS = nullptr) const {
   }
 
   virtual unsigned getWinEHParentFrameOffset(const MachineFunction &MF) const {
     report_fatal_error("WinEH not implemented for this target");
   }
 
-  /// eliminateCallFramePseudoInstr - This method is called during prolog/epilog
-  /// code insertion to eliminate call frame setup and destroy pseudo
-  /// instructions (but only if the Target is using them).  It is responsible
-  /// for eliminating these instructions, replacing them with concrete
-  /// instructions.  This method need only be implemented if using call frame
-  /// setup/destroy pseudo instructions.
-  ///
-  virtual void
+  /// This method is called during prolog/epilog code insertion to eliminate
+  /// call frame setup and destroy pseudo instructions (but only if the Target
+  /// is using them).  It is responsible for eliminating these instructions,
+  /// replacing them with concrete instructions.  This method need only be
+  /// implemented if using call frame setup/destroy pseudo instructions.
+  /// Returns an iterator pointing to the instruction after the replaced one.
+  virtual MachineBasicBlock::iterator
   eliminateCallFramePseudoInstr(MachineFunction &MF,
                                 MachineBasicBlock &MBB,
                                 MachineBasicBlock::iterator MI) const {
     llvm_unreachable("Call Frame Pseudo Instructions do not exist on this "
                      "target!");
   }
 
 

llvm/trunk/lib/CodeGen/PrologEpilogInserter.cpp

void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &Fn,
 
   for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
 
     if (I->getOpcode() == FrameSetupOpcode ||
         I->getOpcode() == FrameDestroyOpcode) {
       InsideCallSequence = (I->getOpcode() == FrameSetupOpcode);
       SPAdj += TII.getSPAdjust(I);
 
-      MachineBasicBlock::iterator PrevI = BB->end();
-      if (I != BB->begin()) PrevI = std::prev(I);
-      TFI->eliminateCallFramePseudoInstr(Fn, *BB, I);
-
-      // Visit the instructions created by eliminateCallFramePseudoInstr().
-      if (PrevI == BB->end())
-        I = BB->begin();     // The replaced instr was the first in the block.
-      else
-        I = std::next(PrevI);
+      I = TFI->eliminateCallFramePseudoInstr(Fn, *BB, I);
       continue;
     }
 
     MachineInstr *MI = I;
     bool DoIncr = true;
     for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
       if (!MI->getOperand(i).isFI())
         continue;

llvm/trunk/lib/Target/AArch64/AArch64FrameLowering.h

 public:
   explicit AArch64FrameLowering()
       : TargetFrameLowering(StackGrowsDown, 16, 0, 16,
                             true /*StackRealignable*/) {}
 
   void emitCalleeSavedFrameMoves(MachineBasicBlock &MBB,
                                  MachineBasicBlock::iterator MBBI) const;
 
-  void eliminateCallFramePseudoInstr(MachineFunction &MF,
-                                  MachineBasicBlock &MBB,
-                                  MachineBasicBlock::iterator I) const override;
+  MachineBasicBlock::iterator
+  eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
 
   /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
   /// the function.
   void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
   bool canUseAsPrologue(const MachineBasicBlock &MBB) const override;
 

llvm/trunk/lib/Target/AArch64/AArch64FrameLowering.cpp

 /// immediately on entry to the current function.  This eliminates the need for
 /// add/sub sp brackets around call sites.  Returns true if the call frame is
 /// included as part of the stack frame.
 bool
 AArch64FrameLowering::hasReservedCallFrame(const MachineFunction &MF) const {
   return !MF.getFrameInfo()->hasVarSizedObjects();
 }
 
-void AArch64FrameLowering::eliminateCallFramePseudoInstr(
+MachineBasicBlock::iterator AArch64FrameLowering::eliminateCallFramePseudoInstr(
     MachineFunction &MF, MachineBasicBlock &MBB,
     MachineBasicBlock::iterator I) const {
   const AArch64InstrInfo *TII =
       static_cast<const AArch64InstrInfo *>(MF.getSubtarget().getInstrInfo());
   DebugLoc DL = I->getDebugLoc();
   unsigned Opc = I->getOpcode();
   bool IsDestroy = Opc == TII->getCallFrameDestroyOpcode();
   uint64_t CalleePopAmount = IsDestroy ? I->getOperand(1).getImm() : 0;
if (!TFI->hasReservedCallFrame(MF)) {
     }
   } else if (CalleePopAmount != 0) {
     // If the calling convention demands that the callee pops arguments from the
     // stack, we want to add it back if we have a reserved call frame.
     assert(CalleePopAmount < 0xffffff && "call frame too large");
     emitFrameOffset(MBB, I, DL, AArch64::SP, AArch64::SP, -CalleePopAmount,
                     TII);
   }
-  MBB.erase(I);
+  return MBB.erase(I);
 }
 
 void AArch64FrameLowering::emitCalleeSavedFrameMoves(
     MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI) const {
   MachineFunction &MF = *MBB.getParent();
   MachineFrameInfo *MFI = MF.getFrameInfo();
   MachineModuleInfo &MMI = MF.getMMI();
   const MCRegisterInfo *MRI = MMI.getContext().getRegisterInfo();

llvm/trunk/lib/Target/ARM/ARMFrameLowering.h

void emitPushInst(MachineBasicBlock &MBB, MachineBasicBlock::iterator MI,
                     bool(*Func)(unsigned, bool), unsigned NumAlignedDPRCS2Regs,
                     unsigned MIFlags = 0) const;
   void emitPopInst(MachineBasicBlock &MBB, MachineBasicBlock::iterator MI,
                    const std::vector<CalleeSavedInfo> &CSI, unsigned LdmOpc,
                    unsigned LdrOpc, bool isVarArg, bool NoGap,
                    bool(*Func)(unsigned, bool),
                    unsigned NumAlignedDPRCS2Regs) const;
 
-  void
+  MachineBasicBlock::iterator
   eliminateCallFramePseudoInstr(MachineFunction &MF,
                                 MachineBasicBlock &MBB,
                                 MachineBasicBlock::iterator MI) const override;
 };
 
 } // End llvm namespace
 
 #endif

llvm/trunk/lib/Target/ARM/ARMFrameLowering.cpp

void ARMFrameLowering::determineCalleeSaves(MachineFunction &MF,
   }
 
   if (ForceLRSpill) {
     SavedRegs.set(ARM::LR);
     AFI->setLRIsSpilledForFarJump(true);
   }
 }
 
-
-void ARMFrameLowering::
-eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
-                              MachineBasicBlock::iterator I) const {
+MachineBasicBlock::iterator ARMFrameLowering::eliminateCallFramePseudoInstr(
+    MachineFunction &MF, MachineBasicBlock &MBB,
   const ARMBaseInstrInfo &TII =
       *static_cast<const ARMBaseInstrInfo *>(MF.getSubtarget().getInstrInfo());
   if (!hasReservedCallFrame(MF)) {
     // If we have alloca, convert as follows:
     // ADJCALLSTACKDOWN -> sub, sp, sp, amount
     // ADJCALLSTACKUP   -> add, sp, sp, amount
     MachineInstr *Old = I;
     DebugLoc dl = Old->getDebugLoc();
if (Amount != 0) {
         // Note: PredReg is operand 3 for ADJCALLSTACKUP.
         unsigned PredReg = Old->getOperand(3).getReg();
         assert(Opc == ARM::ADJCALLSTACKUP || Opc == ARM::tADJCALLSTACKUP);
         emitSPUpdate(isARM, MBB, I, dl, TII, Amount, MachineInstr::NoFlags,
                      Pred, PredReg);
       }
     }
   }
-  MBB.erase(I);
+  return 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;

llvm/trunk/lib/Target/ARM/Thumb1FrameLowering.h

bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
                                  const TargetRegisterInfo *TRI) const override;
   bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                   MachineBasicBlock::iterator MI,
                                   const std::vector<CalleeSavedInfo> &CSI,
                                   const TargetRegisterInfo *TRI) const override;
 
   bool hasReservedCallFrame(const MachineFunction &MF) const override;
 
-  void
+  MachineBasicBlock::iterator
   eliminateCallFramePseudoInstr(MachineFunction &MF,
                                 MachineBasicBlock &MBB,
                                 MachineBasicBlock::iterator MI) const override;
 
   /// Check whether or not the given \p MBB can be used as a epilogue
   /// for the target.
   /// The epilogue will be inserted before the first terminator of that block.
   /// This method is used by the shrink-wrapping pass to decide if

llvm/trunk/lib/Target/ARM/Thumb1FrameLowering.cpp

emitSPUpdate(MachineBasicBlock &MBB,
              const TargetInstrInfo &TII, DebugLoc dl,
              const ThumbRegisterInfo &MRI,
              int NumBytes, unsigned MIFlags = MachineInstr::NoFlags)  {
   emitThumbRegPlusImmediate(MBB, MBBI, dl, ARM::SP, ARM::SP, NumBytes, TII,
                             MRI, MIFlags);
 }
 
 
-void Thumb1FrameLowering::
+MachineBasicBlock::iterator Thumb1FrameLowering::
 eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
                               MachineBasicBlock::iterator I) const {
   const Thumb1InstrInfo &TII =
       *static_cast<const Thumb1InstrInfo *>(STI.getInstrInfo());
   const ThumbRegisterInfo *RegInfo =
       static_cast<const ThumbRegisterInfo *>(STI.getRegisterInfo());
   if (!hasReservedCallFrame(MF)) {
     // If we have alloca, convert as follows:
if (Amount != 0) {
       if (Opc == ARM::ADJCALLSTACKDOWN || Opc == ARM::tADJCALLSTACKDOWN) {
         emitSPUpdate(MBB, I, TII, dl, *RegInfo, -Amount);
       } else {
         assert(Opc == ARM::ADJCALLSTACKUP || Opc == ARM::tADJCALLSTACKUP);
         emitSPUpdate(MBB, I, TII, dl, *RegInfo, Amount);
       }
     }
   }
-  MBB.erase(I);
+  return MBB.erase(I);
 }
 
 void Thumb1FrameLowering::emitPrologue(MachineFunction &MF,
                                        MachineBasicBlock &MBB) const {
   MachineBasicBlock::iterator MBBI = MBB.begin();
   MachineFrameInfo  *MFI = MF.getFrameInfo();
   ARMFunctionInfo *AFI = MF.getInfo<ARMFunctionInfo>();
   MachineModuleInfo &MMI = MF.getMMI();

llvm/trunk/lib/Target/BPF/BPFFrameLowering.h

public:
 
   void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
   bool hasFP(const MachineFunction &MF) const override;
   void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs,
                             RegScavenger *RS) const override;
 
-  void
+  MachineBasicBlock::iterator
   eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
                                 MachineBasicBlock::iterator MI) const override {
-    MBB.erase(MI);
+    return MBB.erase(MI);
   }
 };
 }
 #endif

llvm/trunk/lib/Target/Hexagon/HexagonFrameLowering.h

bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
     return true;
   }
   bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
       MachineBasicBlock::iterator MI, const std::vector<CalleeSavedInfo> &CSI,
       const TargetRegisterInfo *TRI) const override {
     return true;
   }
 
-  void eliminateCallFramePseudoInstr(MachineFunction &MF,
-      MachineBasicBlock &MBB, MachineBasicBlock::iterator I) const override;
+  MachineBasicBlock::iterator
+  eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
+                                MachineBasicBlock::iterator I) const override;
   void processFunctionBeforeFrameFinalized(MachineFunction &MF,
       RegScavenger *RS = nullptr) const override;
   void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs,
       RegScavenger *RS) const override;
 
   bool targetHandlesStackFrameRounding() const override {
     return true;
   }

llvm/trunk/lib/Target/Hexagon/HexagonFrameLowering.cpp

for (unsigned i = 0; i < CSI.size(); ++i) {
     const TargetRegisterClass *RC = HRI.getMinimalPhysRegClass(Reg);
     int FI = CSI[i].getFrameIdx();
     HII.loadRegFromStackSlot(MBB, MI, Reg, FI, RC, &HRI);
   }
 
   return true;
 }
 
-
-void HexagonFrameLowering::eliminateCallFramePseudoInstr(MachineFunction &MF,
-      MachineBasicBlock &MBB, MachineBasicBlock::iterator I) const {
+MachineBasicBlock::iterator HexagonFrameLowering::eliminateCallFramePseudoInstr(
+    MachineFunction &MF, MachineBasicBlock &MBB,
+    MachineBasicBlock::iterator I) const {
   MachineInstr &MI = *I;
   unsigned Opc = MI.getOpcode();
   (void)Opc; // Silence compiler warning.
   assert((Opc == Hexagon::ADJCALLSTACKDOWN || Opc == Hexagon::ADJCALLSTACKUP) &&
          "Cannot handle this call frame pseudo instruction");
-  MBB.erase(I);
+  return MBB.erase(I);
 }
 
 
 void HexagonFrameLowering::processFunctionBeforeFrameFinalized(
     MachineFunction &MF, RegScavenger *RS) const {
   // If this function has uses aligned stack and also has variable sized stack
   // objects, then we need to map all spill slots to fixed positions, so that
   // they can be accessed through FP. Otherwise they would have to be accessed

llvm/trunk/lib/Target/Lanai/LanaiFrameLowering.h

explicit LanaiFrameLowering(const LanaiSubtarget &Subtarget)
                             /*LocalAreaOffset=*/0),
         STI(Subtarget) {}
 
   // emitProlog/emitEpilog - These methods insert prolog and epilog code into
   // the function.
   void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
-  void
+  MachineBasicBlock::iterator
   eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
                                 MachineBasicBlock::iterator I) const override;
 
   bool hasFP(const MachineFunction &MF) const override { return true; }
 
   void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs,
                             RegScavenger *RS = nullptr) const override;
 };
 
 } // namespace llvm
 
 #endif // LLVM_LIB_TARGET_LANAI_LANAIFRAMELOWERING_H

llvm/trunk/lib/Target/Lanai/LanaiFrameLowering.cpp

BuildMI(MBB, MBBI, DL, LII.get(Lanai::SUB_I_LO), Lanai::SP)
         .setMIFlag(MachineInstr::FrameSetup);
   }
 
   // Replace ADJDYNANALLOC
   if (MFI->hasVarSizedObjects())
     replaceAdjDynAllocPseudo(MF);
 }
 
-void LanaiFrameLowering::eliminateCallFramePseudoInstr(
+MachineBasicBlock::iterator LanaiFrameLowering::eliminateCallFramePseudoInstr(
     MachineFunction &MF, MachineBasicBlock &MBB,
     MachineBasicBlock::iterator I) const {
   // Discard ADJCALLSTACKDOWN, ADJCALLSTACKUP instructions.
-  MBB.erase(I);
+  return MBB.erase(I);
 }
 
 // The function epilogue should not depend on the current stack pointer!
 // It should use the frame pointer only.  This is mandatory because
 // of alloca; we also take advantage of it to omit stack adjustments
 // before returning.
 //
 // Note that when we go to restore the preserved register values we must

llvm/trunk/lib/Target/MSP430/MSP430FrameLowering.h

public:
   explicit MSP430FrameLowering()
       : TargetFrameLowering(TargetFrameLowering::StackGrowsDown, 2, -2, 2) {}
 
   /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
   /// the function.
   void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
-  void eliminateCallFramePseudoInstr(MachineFunction &MF,
-                                  MachineBasicBlock &MBB,
-                                  MachineBasicBlock::iterator I) const override;
+  MachineBasicBlock::iterator
+  eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
 
   bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
                                  MachineBasicBlock::iterator MI,
                                  const std::vector<CalleeSavedInfo> &CSI,
                                  const TargetRegisterInfo *TRI) const override;
   bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                   MachineBasicBlock::iterator MI,
                                   const std::vector<CalleeSavedInfo> &CSI,

llvm/trunk/lib/Target/MSP430/MSP430FrameLowering.cpp

MSP430FrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
   const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
 
   for (unsigned i = 0, e = CSI.size(); i != e; ++i)
     BuildMI(MBB, MI, DL, TII.get(MSP430::POP16r), CSI[i].getReg());
 
   return true;
 }
 
-void MSP430FrameLowering::
-eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
-                              MachineBasicBlock::iterator I) const {
+MachineBasicBlock::iterator MSP430FrameLowering::eliminateCallFramePseudoInstr(
+    MachineFunction &MF, MachineBasicBlock &MBB,
   const MSP430InstrInfo &TII =
       *static_cast<const MSP430InstrInfo *>(MF.getSubtarget().getInstrInfo());
   unsigned StackAlign = getStackAlignment();
 
   if (!hasReservedCallFrame(MF)) {
     // If the stack pointer can be changed after prologue, turn the
     // adjcallstackup instruction into a 'sub SP, <amt>' and the
     // adjcallstackdown instruction into 'add SP, <amt>'
if (uint64_t CalleeAmt = I->getOperand(1).getImm()) {
                 MSP430::SP).addReg(MSP430::SP).addImm(CalleeAmt);
       // The SRW implicit def is dead.
       New->getOperand(3).setIsDead();
 
       MBB.insert(I, New);
     }
   }
 
-  MBB.erase(I);
+  return MBB.erase(I);
 }
 
 void
 MSP430FrameLowering::processFunctionBeforeFrameFinalized(MachineFunction &MF,
                                                          RegScavenger *) const {
   // Create a frame entry for the FP register that must be saved.
   if (hasFP(MF)) {
     int FrameIdx = MF.getFrameInfo()->CreateFixedObject(2, -4, true);
     (void)FrameIdx;
     assert(FrameIdx == MF.getFrameInfo()->getObjectIndexBegin() &&
            "Slot for FP register must be last in order to be found!");
   }
 }

llvm/trunk/lib/Target/Mips/MipsFrameLowering.h

public:
   static const MipsFrameLowering *create(const MipsSubtarget &ST);
 
   bool hasFP(const MachineFunction &MF) const override;
 
   bool hasBP(const MachineFunction &MF) const;
 
   bool isFPCloseToIncomingSP() const override { return false; }
 
-  void
+  MachineBasicBlock::iterator
   eliminateCallFramePseudoInstr(MachineFunction &MF,
                                 MachineBasicBlock &MBB,
                                 MachineBasicBlock::iterator I) const override;
 
 protected:
   uint64_t estimateStackSize(const MachineFunction &MF) const;
 };
 
 /// Create MipsFrameLowering objects.
 const MipsFrameLowering *createMips16FrameLowering(const MipsSubtarget &ST);
 const MipsFrameLowering *createMipsSEFrameLowering(const MipsSubtarget &ST);
 
 } // End llvm namespace
 
 #endif

llvm/trunk/lib/Target/Mips/MipsFrameLowering.cpp

uint64_t MipsFrameLowering::estimateStackSize(const MachineFunction &MF) const {
   if (MFI->adjustsStack() && hasReservedCallFrame(MF))
     Offset = alignTo(Offset + MFI->getMaxCallFrameSize(),
                      std::max(MaxAlign, getStackAlignment()));
 
   return alignTo(Offset, getStackAlignment());
 }
 
 // Eliminate ADJCALLSTACKDOWN, ADJCALLSTACKUP pseudo instructions
-void MipsFrameLowering::
+MachineBasicBlock::iterator MipsFrameLowering::
 eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
                               MachineBasicBlock::iterator I) const {
   unsigned SP = STI.getABI().IsN64() ? Mips::SP_64 : Mips::SP;
 
   if (!hasReservedCallFrame(MF)) {
     int64_t Amount = I->getOperand(0).getImm();
     if (I->getOpcode() == Mips::ADJCALLSTACKDOWN)
       Amount = -Amount;
 
     STI.getInstrInfo()->adjustStackPtr(SP, Amount, MBB, I);
   }
 
-  MBB.erase(I);
+  return MBB.erase(I);
 }

llvm/trunk/lib/Target/NVPTX/NVPTXFrameLowering.h

 class NVPTXFrameLowering : public TargetFrameLowering {
 public:
   explicit NVPTXFrameLowering();
 
   bool hasFP(const MachineFunction &MF) const override;
   void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
-  void
+  MachineBasicBlock::iterator
   eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
                                 MachineBasicBlock::iterator I) const override;
 };
 
 } // End llvm namespace
 
 #endif

llvm/trunk/lib/Target/NVPTX/NVPTXFrameLowering.cpp

void NVPTXFrameLowering::emitPrologue(MachineFunction &MF,
   }
 }
 
 void NVPTXFrameLowering::emitEpilogue(MachineFunction &MF,
                                       MachineBasicBlock &MBB) const {}
 
 // This function eliminates ADJCALLSTACKDOWN,
 // ADJCALLSTACKUP pseudo instructions
-void NVPTXFrameLowering::eliminateCallFramePseudoInstr(
+MachineBasicBlock::iterator NVPTXFrameLowering::eliminateCallFramePseudoInstr(
     MachineFunction &MF, MachineBasicBlock &MBB,
     MachineBasicBlock::iterator I) const {
   // Simply discard ADJCALLSTACKDOWN,
   // ADJCALLSTACKUP instructions.
-  MBB.erase(I);
+  return MBB.erase(I);
 }

llvm/trunk/lib/Target/PowerPC/PPCFrameLowering.h

void processFunctionBeforeFrameFinalized(MachineFunction &MF,
                                      RegScavenger *RS = nullptr) const override;
   void addScavengingSpillSlot(MachineFunction &MF, RegScavenger *RS) const;
 
   bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
                                  MachineBasicBlock::iterator MI,
                                  const std::vector<CalleeSavedInfo> &CSI,
                                  const TargetRegisterInfo *TRI) const override;
 
-  void eliminateCallFramePseudoInstr(MachineFunction &MF,
-                                  MachineBasicBlock &MBB,
-                                  MachineBasicBlock::iterator I) const override;
+  MachineBasicBlock::iterator
+  eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
 
   bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                   MachineBasicBlock::iterator MI,
                                   const std::vector<CalleeSavedInfo> &CSI,
                                   const TargetRegisterInfo *TRI) const override;
 
   /// targetHandlesStackFrameRounding - Returns true if the target is
   /// responsible for rounding up the stack frame (probably at emitPrologue

llvm/trunk/lib/Target/PowerPC/PPCFrameLowering.cpp

if (CR3Spilled)
     MBB.insert(MI, BuildMI(*MF, DL, TII.get(RestoreOp), PPC::CR3)
                .addReg(MoveReg, getKillRegState(!CR4Spilled)));
 
   if (CR4Spilled)
     MBB.insert(MI, BuildMI(*MF, DL, TII.get(RestoreOp), PPC::CR4)
                .addReg(MoveReg, getKillRegState(true)));
 }
 
-void PPCFrameLowering::
+MachineBasicBlock::iterator PPCFrameLowering::
 eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
                               MachineBasicBlock::iterator I) const {
   const TargetInstrInfo &TII = *Subtarget.getInstrInfo();
   if (MF.getTarget().Options.GuaranteedTailCallOpt &&
       I->getOpcode() == PPC::ADJCALLSTACKUP) {
     // Add (actually subtract) back the amount the callee popped on return.
     if (int CalleeAmt =  I->getOperand(1).getImm()) {
       bool is64Bit = Subtarget.isPPC64();
if (int CalleeAmt =  I->getOperand(1).getImm()) {
           .addImm(CalleeAmt & 0xFFFF);
         BuildMI(MBB, MBBI, dl, TII.get(ADDInstr), StackReg)
           .addReg(StackReg, RegState::Kill)
           .addReg(TmpReg);
       }
     }
   }
   // Simply discard ADJCALLSTACKDOWN, ADJCALLSTACKUP instructions.
-  MBB.erase(I);
+  return MBB.erase(I);
 }
 
 bool
 PPCFrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                         MachineBasicBlock::iterator MI,
                                         const std::vector<CalleeSavedInfo> &CSI,
                                         const TargetRegisterInfo *TRI) const {
 

llvm/trunk/lib/Target/Sparc/SparcFrameLowering.h

 public:
   explicit SparcFrameLowering(const SparcSubtarget &ST);
 
   /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
   /// the function.
   void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
-  void
+  MachineBasicBlock::iterator
   eliminateCallFramePseudoInstr(MachineFunction &MF,
                                 MachineBasicBlock &MBB,
                                 MachineBasicBlock::iterator I) const override;
 
   bool hasReservedCallFrame(const MachineFunction &MF) const override;
   bool hasFP(const MachineFunction &MF) const override;
   void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs,
                             RegScavenger *RS = nullptr) const override;

llvm/trunk/lib/Target/Sparc/SparcFrameLowering.cpp

void SparcFrameLowering::emitPrologue(MachineFunction &MF,
 
   if (NeedsStackRealignment) {
     // andn %o6, MaxAlign-1, %o6
     int MaxAlign = MFI->getMaxAlignment();
     BuildMI(MBB, MBBI, dl, TII.get(SP::ANDNri), SP::O6).addReg(SP::O6).addImm(MaxAlign - 1);
   }
 }
 
-void SparcFrameLowering::
+MachineBasicBlock::iterator SparcFrameLowering::
 eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
                               MachineBasicBlock::iterator I) const {
   if (!hasReservedCallFrame(MF)) {
     MachineInstr &MI = *I;
     int Size = MI.getOperand(0).getImm();
     if (MI.getOpcode() == SP::ADJCALLSTACKDOWN)
       Size = -Size;
 
     if (Size)
       emitSPAdjustment(MF, MBB, I, Size, SP::ADDrr, SP::ADDri);
   }
-  MBB.erase(I);
+  return MBB.erase(I);
 }
 
 
 void SparcFrameLowering::emitEpilogue(MachineFunction &MF,
                                   MachineBasicBlock &MBB) const {
   SparcMachineFunctionInfo *FuncInfo = MF.getInfo<SparcMachineFunctionInfo>();
   MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
   const SparcInstrInfo &TII =

llvm/trunk/lib/Target/SystemZ/SystemZFrameLowering.h

public:
   void processFunctionBeforeFrameFinalized(MachineFunction &MF,
                                            RegScavenger *RS) const override;
   void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   bool hasFP(const MachineFunction &MF) const override;
   int getFrameIndexReference(const MachineFunction &MF, int FI,
                              unsigned &FrameReg) const override;
   bool hasReservedCallFrame(const MachineFunction &MF) const override;
-  void eliminateCallFramePseudoInstr(MachineFunction &MF,
-                                     MachineBasicBlock &MBB,
-                                     MachineBasicBlock::iterator MI) const
-    override;
+  MachineBasicBlock::iterator
+  eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
+                                MachineBasicBlock::iterator MI) const override;
 
   // Return the number of bytes in the callee-allocated part of the frame.
   uint64_t getAllocatedStackSize(const MachineFunction &MF) const;
 
   // Return the byte offset from the incoming stack pointer of Reg's
   // ABI-defined save slot.  Return 0 if no slot is defined for Reg.
   unsigned getRegSpillOffset(unsigned Reg) const {
     return RegSpillOffsets[Reg];
   }
 };
 } // end namespace llvm
 
 #endif

llvm/trunk/lib/Target/SystemZ/SystemZFrameLowering.cpp

 SystemZFrameLowering::hasReservedCallFrame(const MachineFunction &MF) const {
   // The ABI requires us to allocate 160 bytes of stack space for the callee,
   // with any outgoing stack arguments being placed above that.  It seems
   // better to make that area a permanent feature of the frame even if
   // we're using a frame pointer.
   return true;
 }
 
-void SystemZFrameLowering::
+MachineBasicBlock::iterator SystemZFrameLowering::
 eliminateCallFramePseudoInstr(MachineFunction &MF,
                               MachineBasicBlock &MBB,
                               MachineBasicBlock::iterator MI) const {
   switch (MI->getOpcode()) {
   case SystemZ::ADJCALLSTACKDOWN:
   case SystemZ::ADJCALLSTACKUP:
     assert(hasReservedCallFrame(MF) &&
            "ADJSTACKDOWN and ADJSTACKUP should be no-ops");
-    MBB.erase(MI);
+    return MBB.erase(MI);
     break;
 
   default:
     llvm_unreachable("Unexpected call frame instruction");
   }
 }

llvm/trunk/lib/Target/WebAssembly/WebAssemblyFrameLowering.h

public:
   static const size_t RedZoneSize = 128;
 
   WebAssemblyFrameLowering()
       : TargetFrameLowering(StackGrowsDown, /*StackAlignment=*/16,
                             /*LocalAreaOffset=*/0,
                             /*TransientStackAlignment=*/16,
                             /*StackRealignable=*/true) {}
 
-  void eliminateCallFramePseudoInstr(
+  MachineBasicBlock::iterator eliminateCallFramePseudoInstr(
       MachineFunction &MF, MachineBasicBlock &MBB,
       MachineBasicBlock::iterator I) const override;
 
   /// These methods insert prolog and epilog code into the function.
   void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
   bool hasFP(const MachineFunction &MF) const override;

llvm/trunk/lib/Target/WebAssembly/WebAssemblyFrameLowering.cpp

BuildMI(MBB, InsertStore, DL, TII->get(WebAssembly::STORE_I32),
       .addImm(0)
       .addReg(SPAddr)
       .addImm(2)  // p2align
       .addReg(SrcReg)
       .addMemOperand(MMO);
   MF.getInfo<WebAssemblyFunctionInfo>()->stackifyVReg(SPAddr);
 }
 
-void WebAssemblyFrameLowering::eliminateCallFramePseudoInstr(
+MachineBasicBlock::iterator
+WebAssemblyFrameLowering::eliminateCallFramePseudoInstr(
     MachineFunction &MF, MachineBasicBlock &MBB,
     MachineBasicBlock::iterator I) const {
   assert(!I->getOperand(0).getImm() && hasFP(MF) &&
          "Call frame pseudos should only be used for dynamic stack adjustment");
   const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
   if (I->getOpcode() == TII->getCallFrameDestroyOpcode() &&
       needsSPWriteback(MF, *MF.getFrameInfo())) {
     DebugLoc DL = I->getDebugLoc();
     writeSPToMemory(WebAssembly::SP32, MF, MBB, I, I, DL);
   }
-  MBB.erase(I);
+  return MBB.erase(I);
 }
 
 void WebAssemblyFrameLowering::emitPrologue(MachineFunction &MF,
                                             MachineBasicBlock &MBB) const {
   // TODO: Do ".setMIFlag(MachineInstr::FrameSetup)" on emitted instructions
   auto *MFI = MF.getFrameInfo();
   assert(MFI->getCalleeSavedInfo().empty() &&
          "WebAssembly should not have callee-saved registers");

llvm/trunk/lib/Target/WebAssembly/WebAssemblyPEI.cpp

void WasmPEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &Fn,
   bool InsideCallSequence = false;
 
   for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
 
     if (I->getOpcode() == FrameSetupOpcode ||
         I->getOpcode() == FrameDestroyOpcode) {
       InsideCallSequence = (I->getOpcode() == FrameSetupOpcode);
       SPAdj += TII.getSPAdjust(I);
-
-      MachineBasicBlock::iterator PrevI = BB->end();
-      if (I != BB->begin()) PrevI = std::prev(I);
-      TFI->eliminateCallFramePseudoInstr(Fn, *BB, I);
-
-      // Visit the instructions created by eliminateCallFramePseudoInstr().
-      if (PrevI == BB->end())
-        I = BB->begin();     // The replaced instr was the first in the block.
-      else
-        I = std::next(PrevI);
+      I = TFI->eliminateCallFramePseudoInstr(Fn, *BB, I);
       continue;
     }
 
     MachineInstr *MI = I;
     bool DoIncr = true;
     for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
       if (!MI->getOperand(i).isFI())
         continue;

llvm/trunk/lib/Target/X86/X86FrameLowering.h

public:
   bool needsFrameIndexResolution(const MachineFunction &MF) const override;
 
   int getFrameIndexReference(const MachineFunction &MF, int FI,
                              unsigned &FrameReg) const override;
 
   int getFrameIndexReferenceFromSP(const MachineFunction &MF, int FI,
                                    unsigned &FrameReg) const override;
 
-  void eliminateCallFramePseudoInstr(MachineFunction &MF,
-                                 MachineBasicBlock &MBB,
-                                 MachineBasicBlock::iterator MI) const override;
+  MachineBasicBlock::iterator
+  eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
 
   unsigned getWinEHParentFrameOffset(const MachineFunction &MF) const override;
 
   void processFunctionBeforeFrameFinalized(MachineFunction &MF,
                                            RegScavenger *RS) const override;
 
   /// Check the instruction before/after the passed instruction. If
   /// it is an ADD/SUB/LEA instruction it is deleted argument and the

llvm/trunk/lib/Target/X86/X86FrameLowering.cpp

bool X86FrameLowering::adjustStackWithPops(MachineBasicBlock &MBB,
 
   for (int i = 0; i < NumPops; ++i)
     BuildMI(MBB, MBBI, DL, 
             TII.get(STI.is64Bit() ? X86::POP64r : X86::POP32r), Regs[i]);
 
   return true;
 }
 
-void X86FrameLowering::
+MachineBasicBlock::iterator X86FrameLowering::
 eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
                               MachineBasicBlock::iterator I) const {
   bool reserveCallFrame = hasReservedCallFrame(MF);
   unsigned Opcode = I->getOpcode();
   bool isDestroy = Opcode == TII.getCallFrameDestroyOpcode();
   DebugLoc DL = I->getDebugLoc();
   uint64_t Amount = !reserveCallFrame ? I->getOperand(0).getImm() : 0;
   uint64_t InternalAmt = (isDestroy || Amount) ? I->getOperand(1).getImm() : 0;
bool HasDwarfEHHandlers = !WindowsCFI &&
                               !MF.getMMI().getLandingPads().empty();
 
     if (HasDwarfEHHandlers && !isDestroy &&
         MF.getInfo<X86MachineFunctionInfo>()->getHasPushSequences())
       BuildCFI(MBB, I, DL,
                MCCFIInstruction::createGnuArgsSize(nullptr, Amount));
 
     if (Amount == 0)
-      return;
+      return I;
 
     // Factor out the amount that gets handled inside the sequence
     // (Pushes of argument for frame setup, callee pops for frame destroy)
     Amount -= InternalAmt;
 
     // TODO: This is needed only if we require precise CFA.
     // If this is a callee-pop calling convention, emit a CFA adjust for
     // the amount the callee popped.
if (DwarfCFI && !hasFP(MF)) {
 
       if (CFAOffset) {
         CFAOffset = isDestroy ? -CFAOffset : CFAOffset;
         BuildCFI(MBB, I, DL, 
                  MCCFIInstruction::createAdjustCfaOffset(nullptr, CFAOffset));
       }
     }
 
-    return;
+    return I;
   }
 
   if (isDestroy && InternalAmt) {
     // If we are performing frame pointer elimination and if the callee pops
     // something off the stack pointer, add it back.  We do this until we have
     // more advanced stack pointer tracking ability.
     // We are not tracking the stack pointer adjustment by the callee, so make
     // sure we restore the stack pointer immediately after the call, there may
     // be spill code inserted between the CALL and ADJCALLSTACKUP instructions.
+    MachineBasicBlock::iterator CI = I;
     MachineBasicBlock::iterator B = MBB.begin();
-    while (I != B && !std::prev(I)->isCall())
+    while (CI != B && !std::prev(I)->isCall())
       --I;
-    BuildStackAdjustment(MBB, I, DL, -InternalAmt, /*InEpilogue=*/false);
+    BuildStackAdjustment(MBB, CI, DL, -InternalAmt, /*InEpilogue=*/false);
   }
+
+  return I;
 }
 
 bool X86FrameLowering::canUseAsEpilogue(const MachineBasicBlock &MBB) const {
   assert(MBB.getParent() && "Block is not attached to a function!");
 
   // Win64 has strict requirements in terms of epilogue and we are
   // not taking a chance at messing with them.
   // I.e., unless this block is already an exit block, we can't use

llvm/trunk/lib/Target/XCore/XCoreFrameLowering.h

bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
                                   MachineBasicBlock::iterator MI,
                                   const std::vector<CalleeSavedInfo> &CSI,
                                   const TargetRegisterInfo *TRI) const override;
     bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                   MachineBasicBlock::iterator MI,
                                   const std::vector<CalleeSavedInfo> &CSI,
                                   const TargetRegisterInfo *TRI) const override;
 
-    void eliminateCallFramePseudoInstr(MachineFunction &MF,
-                                  MachineBasicBlock &MBB,
+    MachineBasicBlock::iterator
+    eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
                                   MachineBasicBlock::iterator I) const override;
 
     bool hasFP(const MachineFunction &MF) const override;
 
     void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs,
                               RegScavenger *RS = nullptr) const override;
 
     void processFunctionBeforeFrameFinalized(MachineFunction &MF,

llvm/trunk/lib/Target/XCore/XCoreFrameLowering.cpp

else {
       ++MI;
     }
   }
   return true;
 }
 
 // This function eliminates ADJCALLSTACKDOWN,
 // ADJCALLSTACKUP pseudo instructions
-void XCoreFrameLowering::
-eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
-                              MachineBasicBlock::iterator I) const {
+MachineBasicBlock::iterator XCoreFrameLowering::eliminateCallFramePseudoInstr(
+    MachineFunction &MF, MachineBasicBlock &MBB,
   const XCoreInstrInfo &TII = *MF.getSubtarget<XCoreSubtarget>().getInstrInfo();
   if (!hasReservedCallFrame(MF)) {
     // Turn the adjcallstackdown instruction into 'extsp <amt>' and the
     // adjcallstackup instruction into 'ldaw sp, sp[<amt>]'
     MachineInstr *Old = I;
     uint64_t Amount = Old->getOperand(0).getImm();
     if (Amount != 0) {
       // We need to keep the stack aligned properly.  To do this, we round the
#endif
           .addImm(Amount);
       }
 
       // Replace the pseudo instruction with a new instruction...
       MBB.insert(I, New);
     }
   }
 
-  MBB.erase(I);
+  return MBB.erase(I);
 }
 
 void XCoreFrameLowering::determineCalleeSaves(MachineFunction &MF,
                                               BitVector &SavedRegs,
                                               RegScavenger *RS) const {
   TargetFrameLowering::determineCalleeSaves(MF, SavedRegs, RS);
 
   XCoreFunctionInfo *XFI = MF.getInfo<XCoreFunctionInfo>();