Revert "[LoongArch] Eliminate the redundant sign extension of division (llvm#107971)"

This reverts commit d752f29.

Author: tru

llvm/lib/Target/LoongArch/LoongArchOptWInstrs.cpp

@@ -637,19 +637,6 @@ static bool isSignExtendedW(Register SrcReg, const LoongArchSubtarget &ST,
         break;
       }
       return false;
-    // If all incoming values are sign-extended and all users only use
-    // the lower 32 bits, then convert them to W versions.
-    case LoongArch::DIV_D: {
-      if (!AddRegToWorkList(MI->getOperand(1).getReg()))
-        return false;
-      if (!AddRegToWorkList(MI->getOperand(2).getReg()))
-        return false;
-      if (hasAllWUsers(*MI, ST, MRI)) {
-        FixableDef.insert(MI);
-        break;
-      }
-      return false;
-    }
     }
   }
 
@@ -664,8 +651,6 @@ static unsigned getWOp(unsigned Opcode) {
     return LoongArch::ADDI_W;
   case LoongArch::ADD_D:
     return LoongArch::ADD_W;
-  case LoongArch::DIV_D:
-    return LoongArch::DIV_W;
   case LoongArch::LD_D:
   case LoongArch::LD_WU:
     return LoongArch::LD_W;