[GlobalISel] Disable vector types in narrowScalarAddSub

[porglezomp]

Summary

The implementation for vectors is broken and doesn't seem to be used by
anything. Explicitly remove support for them, they can be added again
later when they're properly implemented.

[arsenm]

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

4451–4454

Use a temporary variable for the register/type to avoid repeating this

[porglezomp]

Use a temporary variable for the destination register/type

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

 }
 
 LegalizerHelper::LegalizeResult
 LegalizerHelper::narrowScalarAddSub(MachineInstr &MI, unsigned TypeIdx,
                                     LLT NarrowTy) {
   if (TypeIdx != 0)
     return UnableToLegalize;
 
+  // FIXME: add support for vector types
+  if (MRI.getType(MI.getOperand(0).getReg()).isVector())
+    return UnableToLegalize;
+
   uint64_t SizeOp0 = MRI.getType(MI.getOperand(0).getReg()).getSizeInBits();
   uint64_t NarrowSize = NarrowTy.getSizeInBits();
 
   // FIXME: add support for when SizeOp0 isn't an exact multiple of
   // NarrowSize.
   if (SizeOp0 % NarrowSize != 0)
     return UnableToLegalize;
 
   // Expand in terms of carry-setting/consuming G_<Op>E instructions.
else {
       MIRBuilder.buildInstr(OpE, {DstReg, CarryOut},
                             {Src1Regs[i], Src2Regs[i], CarryIn});
     }
 
     DstRegs.push_back(DstReg);
     CarryIn = CarryOut;
   }
   Register DstReg = MI.getOperand(0).getReg();
-  if (MRI.getType(DstReg).isVector())
-    MIRBuilder.buildBuildVector(DstReg, DstRegs);
-  else
-    MIRBuilder.buildMerge(DstReg, DstRegs);
   MI.eraseFromParent();
   return Legalized;
 }
 
 LegalizerHelper::LegalizeResult
 LegalizerHelper::narrowScalarMul(MachineInstr &MI, LLT NarrowTy) {
   Register DstReg = MI.getOperand(0).getReg();
   Register Src1 = MI.getOperand(1).getReg();