Revert "[RegisterCoalescer] Fix up subreg lanemasks after rematerializing. (#116191)" (#117367)

To pass tests with #117307 revert.

This reverts commit 3093b29.

Author: vitalybuka

llvm/lib/CodeGen/RegisterCoalescer.cpp

@@ -1374,27 +1374,6 @@ bool RegisterCoalescer::reMaterializeTrivialDef(const CoalescerPair &CP,
   MachineInstr &NewMI = *std::prev(MII);
   NewMI.setDebugLoc(DL);
 
-  // In a situation like the following:
-  //
-  //    undef %2.subreg:reg = INST %1:reg         ; DefMI (rematerializable),
-  //                                              ; DefSubIdx = subreg
-  //    %3:reg = COPY %2                          ; SrcIdx = DstIdx = 0
-  //    .... = SOMEINSTR %3:reg
-  //
-  // there are no subranges for %3 so after rematerialization we need
-  // to explicitly create them. Undefined subranges are removed later on.
-  if (DstReg.isVirtual() && DefSubIdx && !CP.getSrcIdx() && !CP.getDstIdx() &&
-      MRI->shouldTrackSubRegLiveness(DstReg)) {
-    LiveInterval &DstInt = LIS->getInterval(DstReg);
-    if (!DstInt.hasSubRanges()) {
-      LaneBitmask FullMask = MRI->getMaxLaneMaskForVReg(DstReg);
-      LaneBitmask UsedLanes = TRI->getSubRegIndexLaneMask(DefSubIdx);
-      LaneBitmask UnusedLanes = FullMask & ~UsedLanes;
-      DstInt.createSubRangeFrom(LIS->getVNInfoAllocator(), UsedLanes, DstInt);
-      DstInt.createSubRangeFrom(LIS->getVNInfoAllocator(), UnusedLanes, DstInt);
-    }
-  }
-
   // In a situation like the following:
   //     %0:subreg = instr              ; DefMI, subreg = DstIdx
   //     %1        = copy %0:subreg ; CopyMI, SrcIdx = 0
@@ -1507,7 +1486,6 @@ bool RegisterCoalescer::reMaterializeTrivialDef(const CoalescerPair &CP,
         NewRC = TRI->getCommonSubClass(NewRC, DefRC);
       assert(NewRC && "subreg chosen for remat incompatible with instruction");
     }
-
     // Remap subranges to new lanemask and change register class.
     LiveInterval &DstInt = LIS->getInterval(DstReg);
     for (LiveInterval::SubRange &SR : DstInt.subranges()) {