[AMDGPU] Remove unused variable AllSGPRSpilledToVGPRs. NFC

[bjope]

Summary

Removing the unused variable AllSGPRSpilledToVGPRs in
SIFrameLowering::processFunctionBeforeFrameFinalized
to avoid

error: variable 'AllSGPRSpilledToVGPRs' set but not used
[-Werror=unused-but-set-variable]

[nhaehnle]

LGTM

llvm/lib/Target/AMDGPU/SIFrameLowering.cpp

void SIFrameLowering::processFunctionBeforeFrameFinalized(
 
   if (!MFI.hasStackObjects())
     return;
 
   const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
   const SIInstrInfo *TII = ST.getInstrInfo();
   const SIRegisterInfo &TRI = TII->getRegisterInfo();
   SIMachineFunctionInfo *FuncInfo = MF.getInfo<SIMachineFunctionInfo>();
-  bool AllSGPRSpilledToVGPRs = false;
 
   if (TRI.spillSGPRToVGPR() && FuncInfo->hasSpilledSGPRs()) {
-    AllSGPRSpilledToVGPRs = true;
-
     // Process all SGPR spills before frame offsets are finalized. Ideally SGPRs
     // are spilled to VGPRs, in which case we can eliminate the stack usage.
     //
     // XXX - This operates under the assumption that only other SGPR spills are
     // users of the frame index. I'm not 100% sure this is correct. The
     // StackColoring pass has a comment saying a future improvement would be to
     // merging of allocas with spill slots, but for now according to
     // MachineFrameInfo isSpillSlot can't alias any other object.
     for (MachineBasicBlock &MBB : MF) {
       MachineBasicBlock::iterator Next;
       for (auto I = MBB.begin(), E = MBB.end(); I != E; I = Next) {
         MachineInstr &MI = *I;
         Next = std::next(I);
 
         if (TII->isSGPRSpill(MI)) {
           int FI = TII->getNamedOperand(MI, AMDGPU::OpName::addr)->getIndex();
           assert(MFI.getStackID(FI) == TargetStackID::SGPRSpill);
           if (FuncInfo->allocateSGPRSpillToVGPR(MF, FI)) {
             bool Spilled = TRI.eliminateSGPRToVGPRSpillFrameIndex(MI, FI, RS);
             (void)Spilled;
             assert(Spilled && "failed to spill SGPR to VGPR when allocated");
-          } else
-            AllSGPRSpilledToVGPRs = false;
+          }
         }
       }
     }
   }
 
   FuncInfo->removeSGPRToVGPRFrameIndices(MFI);
 
   if (!allStackObjectsAreDeadOrSGPR(MFI)) {