[Autobackout][FuncReg]Revert of change: b697995

 Fix incorrect wrregion optimization

If wrregion intrinsic is used to write to a predefined register, it must
not be optimized by genx vector removal.

Author: Anton Sidorenko

IGC/VectorCompiler/lib/GenXCodeGen/GenXDeadVectorRemoval.cpp

@@ -217,15 +217,6 @@ static bool isRootInst(Instruction *Inst) {
   if (isa<ReturnInst>(Inst) || isa<BranchInst>(Inst) ||
       Inst->isTerminator() || Inst->mayHaveSideEffects())
     return true;
-
-  // Even if the whole region is overwritten by a chain of wrregions, wrregions
-  // to predefined register must not be optimized as they are extremely
-  // specific.
-  if (GenXIntrinsic::isWrRegion(Inst) &&
-      GenXIntrinsic::isReadPredefReg(
-          Inst->getOperand(GenXIntrinsic::GenXRegion::OldValueOperandNum)))
-    return true;
-
   if (auto CI = dyn_cast<CallInst>(Inst))
     return !CI->onlyReadsMemory();
   return false;