AMDGPU: Remove m0 spilling code

[arsenm]

Summary

Since m0 isn't allocatable it should never be spilled anymore.

[nhaehnle]

LGTM

[arsenm]

r287842

lib/Target/AMDGPU/SIRegisterInfo.cpp

void SIRegisterInfo::spillSGPR(MachineBasicBlock::iterator MI,
   bool IsKill = MI->getOperand(0).isKill();
   const DebugLoc &DL = MI->getDebugLoc();
 
   SIMachineFunctionInfo *MFI = MF->getInfo<SIMachineFunctionInfo>();
   MachineFrameInfo &FrameInfo = MF->getFrameInfo();
 
   bool SpillToSMEM = ST.hasScalarStores() && EnableSpillSGPRToSMEM;
 
+  assert(SuperReg != AMDGPU::M0 && "m0 should never spill");
+
   // SubReg carries the "Kill" flag when SubReg == SuperReg.
   unsigned SubKillState = getKillRegState((NumSubRegs == 1) && IsKill);
   for (unsigned i = 0, e = NumSubRegs; i < e; ++i) {
     unsigned SubReg = NumSubRegs == 1 ?
       SuperReg : getSubReg(SuperReg, getSubRegFromChannel(i));
 
     if (SpillToSMEM) {
-      if (SuperReg == AMDGPU::M0) {
-        assert(NumSubRegs == 1);
-        unsigned CopyM0
-          = MRI.createVirtualRegister(&AMDGPU::SReg_32_XM0RegClass);
-
-        BuildMI(*MBB, MI, DL, TII->get(AMDGPU::COPY), CopyM0)
-          .addReg(AMDGPU::M0, getKillRegState(IsKill));
-
-        // The real spill now kills the temp copy.
-        SubReg = SuperReg = CopyM0;
-        IsKill = true;
-      }
-
       int64_t FrOffset = FrameInfo.getObjectOffset(Index);
       unsigned Size = FrameInfo.getObjectSize(Index);
       unsigned Align = FrameInfo.getObjectAlignment(Index);
       MachinePointerInfo PtrInfo
         = MachinePointerInfo::getFixedStack(*MF, Index);
       MachineMemOperand *MMO
         = MF->getMachineMemOperand(PtrInfo, MachineMemOperand::MOStore,
                                    Size, Align);
if (SpillToSMEM) {
         .addMemOperand(MMO);
 
       continue;
     }
 
     struct SIMachineFunctionInfo::SpilledReg Spill =
       MFI->getSpilledReg(MF, Index, i);
     if (Spill.hasReg()) {
-      if (SuperReg == AMDGPU::M0) {
-        assert(NumSubRegs == 1);
-        unsigned CopyM0
-          = MRI.createVirtualRegister(&AMDGPU::SReg_32_XM0RegClass);
-        BuildMI(*MBB, MI, DL, TII->get(AMDGPU::S_MOV_B32), CopyM0)
-          .addReg(SuperReg, getKillRegState(IsKill));
-
-        // The real spill now kills the temp copy.
-        SubReg = SuperReg = CopyM0;
-        IsKill = true;
-      }
-
       BuildMI(*MBB, MI, DL,
               TII->getMCOpcodeFromPseudo(AMDGPU::V_WRITELANE_B32),
               Spill.VGPR)
         .addReg(SubReg, getKillRegState(IsKill))
         .addImm(Spill.Lane);
 
       // FIXME: Since this spills to another register instead of an actual
       // frame index, we should delete the frame index when all references to
void SIRegisterInfo::restoreSGPR(MachineBasicBlock::iterator MI,
   const SISubtarget &ST =  MF->getSubtarget<SISubtarget>();
   const SIInstrInfo *TII = ST.getInstrInfo();
   const DebugLoc &DL = MI->getDebugLoc();
 
   unsigned NumSubRegs = getNumSubRegsForSpillOp(MI->getOpcode());
   unsigned SuperReg = MI->getOperand(0).getReg();
   bool SpillToSMEM = ST.hasScalarStores() && EnableSpillSGPRToSMEM;
 
-  // m0 is not allowed as with readlane/writelane, so a temporary SGPR and
-  // extra copy is needed.
-  bool IsM0 = (SuperReg == AMDGPU::M0);
-  if (IsM0) {
-    assert(NumSubRegs == 1);
-    SuperReg = MRI.createVirtualRegister(&AMDGPU::SReg_32_XM0RegClass);
-  }
+  assert(SuperReg != AMDGPU::M0 && "m0 should never spill");
 
   int64_t FrOffset = FrameInfo.getObjectOffset(Index);
 
   for (unsigned i = 0, e = NumSubRegs; i < e; ++i) {
     unsigned SubReg = NumSubRegs == 1 ?
       SuperReg : getSubReg(SuperReg, getSubRegFromChannel(i));
 
     if (SpillToSMEM) {
if (Spill.hasReg()) {
         .addMemOperand(MMO);
       BuildMI(*MBB, MI, DL,
               TII->get(AMDGPU::V_READFIRSTLANE_B32), SubReg)
         .addReg(TmpReg, RegState::Kill)
         .addReg(MI->getOperand(0).getReg(), RegState::ImplicitDefine);
     }
   }
 
-  if (IsM0 && SuperReg != AMDGPU::M0) {
-    BuildMI(*MBB, MI, DL, TII->get(AMDGPU::S_MOV_B32), AMDGPU::M0)
-      .addReg(SuperReg);
-  }
-
   MI->eraseFromParent();
 }
 
 void SIRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator MI,
                                         int SPAdj, unsigned FIOperandNum,
                                         RegScavenger *RS) const {
   MachineFunction *MF = MI->getParent()->getParent();
   MachineRegisterInfo &MRI = MF->getRegInfo();