backend/issue/IssueQueue.scala

package xiangshan.backend.issue

import chisel3._
import chisel3.util._
import xiangshan._

trait IQConst{
  val iqSize = 8
  val iqIdxWidth = log2Up(iqSize)
  val layer1Size = iqSize
  val layer2Size = iqSize/2
}

sealed abstract class IQBundle extends XSBundle with IQConst
sealed abstract class IQModule extends XSModule with IQConst with NeedImpl

sealed class CmpInputBundle extends IQBundle{
  val instRdy = Input(Bool())
  val roqIdx  = Input(UInt(RoqIdxWidth.W))
  val iqIdx   = Input(UInt(iqIdxWidth.W))
}


sealed class CompareCircuitUnit(layer: Int = 0, id: Int = 0) extends IQModule {
  val io = IO(new Bundle(){
    val in1 = new CmpInputBundle
    val in2 = new CmpInputBundle
    val out = Flipped(new CmpInputBundle)
  })

  val roqIdx1 = io.in1.roqIdx
  val roqIdx2 = io.in2.roqIdx
  val iqIdx1  = io.in1.iqIdx
  val iqIdx2  = io.in2.iqIdx

  val inst1Rdy = io.in1.instRdy
  val inst2Rdy = io.in2.instRdy

  io.out.instRdy := inst1Rdy | inst2Rdy
  io.out.roqIdx := roqIdx2
  io.out.iqIdx := iqIdx2

  when((inst1Rdy && !inst2Rdy) || (inst1Rdy && inst2Rdy && (roqIdx1 < roqIdx2))){
    io.out.roqIdx := roqIdx1
    io.out.iqIdx := iqIdx1
  }

}

class IssueQueue(val fuTypeInt: BigInt, val wakeupCnt: Int, val bypassCnt: Int) extends IQModule {

  val useBypass = bypassCnt > 0

  val io = IO(new Bundle() {
    // flush Issue Queue
    val redirect = Flipped(ValidIO(new Redirect))

    // enq Ctrl sigs at dispatch-2
    val enqCtrl = Flipped(DecoupledIO(new MicroOp))
    // enq Data at next cycle (regfile has 1 cycle latency)
    val enqData = Flipped(ValidIO(new ExuInput))

    //  broadcast selected uop to other issue queues which has bypasses
    val selectedUop = if(useBypass) DecoupledIO(new MicroOp) else null

    // send to exu
    val deq = DecoupledIO(new ExuInput)

    // listen to write back bus
    val wakeUpPorts = Vec(wakeupCnt, Flipped(DecoupledIO(new ExuOutput)))

    // use bypass uops to speculative wake-up
    val bypassUops = if(useBypass) Vec(bypassCnt, Flipped(DecoupledIO(new MicroOp))) else null
  })
  //---------------------------------------------------------
  // Issue Queue
  //---------------------------------------------------------

  //Tag Queue
  val ctrlFlow = Mem(iqSize,new CtrlFlow)
  val ctrlSig = Mem(iqSize,new CtrlSignals)
  val brMask  = RegInit(VecInit(Seq.fill(iqSize)(0.U(BrqSize.W))))
  val valid   = RegInit(VecInit(Seq.fill(iqSize)(false.B)))
  val src1Rdy = RegInit(VecInit(Seq.fill(iqSize)(false.B)))
  val src2Rdy = RegInit(VecInit(Seq.fill(iqSize)(false.B)))
  val src3Rdy = RegInit(VecInit(Seq.fill(iqSize)(false.B)))
  val prfSrc1 = Reg(Vec(iqSize, UInt(PhyRegIdxWidth.W)))
  val prfSrc2 = Reg(Vec(iqSize, UInt(PhyRegIdxWidth.W)))
  val prfSrc3 = Reg(Vec(iqSize, UInt(PhyRegIdxWidth.W)))
  val prfDest = Reg(Vec(iqSize, UInt(PhyRegIdxWidth.W)))
  val oldPDest = Reg(Vec(iqSize, UInt(PhyRegIdxWidth.W)))
  val freelistAllocPtr = Reg(Vec(iqSize, UInt(PhyRegIdxWidth.W)))
  val roqIdx  = Reg(Vec(iqSize, UInt(RoqIdxWidth.W)))

  val instRdy = WireInit(VecInit(List.tabulate(iqSize)(i => src1Rdy(i) && src2Rdy(i) && valid(i))))


  //tag enqueue
  val iqEmty = !valid.asUInt.orR
  val iqFull =  valid.asUInt.andR
  val iqAllowIn = !iqFull
  io.enqCtrl.ready := iqAllowIn

  //enqueue pointer
  val emptySlot = ~valid.asUInt
  val enqueueSelect = PriorityEncoder(emptySlot)
  assert(io.enqCtrl.valid && io.redirect.valid,"enqueue valid should be false when redirect valid")

  when(io.enqCtrl.fire()){
    ctrlFlow(enqueueSelect) := io.enqCtrl.bits.cf
    ctrlSig(enqueueSelect) := io.enqCtrl.bits.ctrl
    brMask(enqueueSelect) := io.enqCtrl.bits.brMask
    valid(enqueueSelect) := true.B
    src1Rdy(enqueueSelect) := io.enqCtrl.bits.src1State === SrcState.rdy
    src2Rdy(enqueueSelect) := io.enqCtrl.bits.src2State === SrcState.rdy
    src3Rdy(enqueueSelect) := io.enqCtrl.bits.src3State === SrcState.rdy
    prfSrc1(enqueueSelect) := io.enqCtrl.bits.psrc1
    prfSrc2(enqueueSelect) := io.enqCtrl.bits.psrc2
    prfSrc3(enqueueSelect) := io.enqCtrl.bits.psrc3
    prfDest(enqueueSelect) := io.enqCtrl.bits.pdest
    oldPDest(enqueueSelect) := io.enqCtrl.bits.old_pdest
    freelistAllocPtr(enqueueSelect) := io.enqCtrl.bits.freelistAllocPtr
    roqIdx(enqueueSelect) := io.enqCtrl.bits.roqIdx

  }

  //Data Queue
  val src1Data = Reg(Vec(iqSize, UInt(XLEN.W)))
  val src2Data = Reg(Vec(iqSize, UInt(XLEN.W)))
  val src3Data = Reg(Vec(iqSize, UInt(XLEN.W)))

  val enqSelNext = RegNext(enqueueSelect)
  val enqFireNext = RegNext(io.enqCtrl.fire())

  // Read RegFile
  when (enqFireNext) {
    src1Data(enqSelNext) := io.enqData.bits.src1
    src2Data(enqSelNext) := io.enqData.bits.src2
    src3Data(enqSelNext) := io.enqData.bits.src3
  }

  // From Common Data Bus(wakeUpPort)
  // TODO: the when-style may causes long-long-long Mux(which means long latency)
  // TODO: ignore ALU'cdb srcRdy, for byPass has done it
  val cdbValid = List.tabulate(wakeupCnt)(i => io.wakeUpPorts(i).valid)
  val cdbData = List.tabulate(wakeupCnt)(i => io.wakeUpPorts(i).bits.data)
  val cdbPdest = List.tabulate(wakeupCnt)(i => io.wakeUpPorts(i).bits.uop.pdest)
  List.tabulate(iqSize)(i =>
    when (valid(i)) {
      List.tabulate(wakeupCnt)(j => {
        when(!src1Rdy(i) && prfSrc1(i) === cdbPdest(j) && cdbValid(j)) {
          src1Rdy(i) := true.B
          src1Data(i) := cdbData(j)
        }
        when(!src2Rdy(i) && prfSrc2(i) === cdbPdest(j) && cdbValid(j)) {
          src2Rdy(i) := true.B
          src2Data(i) := cdbData(j)
        }
        when(!src3Rdy(i) && prfSrc3(i) === cdbPdest(j) && cdbValid(j)) {
          src3Rdy(i) := true.B
          src3Data(i) := cdbData(j)
        }
      })
    }
  )

  // From byPass [speculative] (just for ALU to listen to other ALU's res, include itself)
  // just need Tag(Ctrl). send out Tag when Tag is decided. other ALUIQ listen to them and decide Tag
  // byPassUops is one cycle before byPassDatas
  // TODO: the when-style may causes long-long-long Mux(which means long latency)
  val selUopPdest = List.tabulate(bypassCnt)(i => io.bypassUops(i).bits.pdest)
  val selUopValid = List.tabulate(bypassCnt)(i => io.bypassUops(i).valid) // may only need valid not fire()
  List.tabulate(iqSize)(i  =>
    when (valid(i)) {
      List.tabulate(bypassCnt)(j => {
        when(!src1Rdy(i) && prfSrc1(i) === selUopPdest(j) && selUopValid(j)) {
          src1Rdy(i) := true.B
        }
        when(!src2Rdy(i) && prfSrc2(i) === selUopPdest(j) && selUopValid(j)) {
          src2Rdy(i) := true.B
        }
        when(!src3Rdy(i) && prfSrc3(i) === selUopPdest(j) && selUopValid(j)) {
          src3Rdy(i) := true.B
        }
      })
    }
  )

  //---------------------------------------------------------
  // Select Circuit
  //---------------------------------------------------------
  //layer 1
  val layer1CCUs = (0 until layer1Size by 2) map { i =>
    val CCU_1 = Module(new CompareCircuitUnit(layer = 1, id = i/2))
    CCU_1.io.in1.instRdy := instRdy(i)
    CCU_1.io.in1.roqIdx  := roqIdx(i)
    CCU_1.io.in1.iqIdx   := i.U

    CCU_1.io.in2.instRdy := instRdy(i+1)
    CCU_1.io.in2.roqIdx  := roqIdx(i+1)
    CCU_1.io.in2.iqIdx   := (i+1).U

    CCU_1
  }

  //layer 2
  val layer2CCUs = (0 until layer2Size by 2) map { i =>
    val CCU_2 = Module(new CompareCircuitUnit(layer = 2, id = i/2))
    CCU_2.io.in1.instRdy := layer1CCUs(i).io.out.instRdy
    CCU_2.io.in1.roqIdx  := layer1CCUs(i).io.out.roqIdx
    CCU_2.io.in1.iqIdx   := layer1CCUs(i).io.out.iqIdx

    CCU_2.io.in2.instRdy := layer1CCUs(i+1).io.out.instRdy
    CCU_2.io.in2.roqIdx  := layer1CCUs(i+1).io.out.roqIdx
    CCU_2.io.in2.iqIdx   := layer1CCUs(i+1).io.out.iqIdx

    CCU_2
  }

  //layer 3
  val CCU_3 = Module(new CompareCircuitUnit(layer = 3, id = 0))
  CCU_3.io.in1.instRdy := layer2CCUs(0).io.out.instRdy
  CCU_3.io.in1.roqIdx  := layer2CCUs(0).io.out.roqIdx
  CCU_3.io.in1.iqIdx   := layer2CCUs(0).io.out.iqIdx

  CCU_3.io.in2.instRdy := layer2CCUs(1).io.out.instRdy
  CCU_3.io.in2.roqIdx  := layer2CCUs(1).io.out.roqIdx
  CCU_3.io.in2.iqIdx   := layer2CCUs(1).io.out.iqIdx


  //Dequeue Logic
  //hold the sel-index to wait for data
  val selInstIdx = RegNext(CCU_3.io.out.iqIdx)
  val selInstRdy = RegNext(CCU_3.io.out.instRdy)

  //issue the select instruction
  val dequeueSelect = Wire(UInt(iqIdxWidth.W))
  dequeueSelect := selInstIdx

  val IQreadyGo = selInstRdy

  io.deq.valid := IQreadyGo

  io.deq.bits.uop.psrc1 := prfSrc1(dequeueSelect)
  io.deq.bits.uop.psrc2 := prfSrc2(dequeueSelect)
  io.deq.bits.uop.psrc3 := prfSrc3(dequeueSelect)
  io.deq.bits.uop.pdest := prfDest(dequeueSelect)
  io.deq.bits.uop.old_pdest := oldPDest(dequeueSelect)
  io.deq.bits.uop.src1State := SrcState.rdy
  io.deq.bits.uop.src2State := SrcState.rdy
  io.deq.bits.uop.src3State := SrcState.rdy
  io.deq.bits.uop.freelistAllocPtr := freelistAllocPtr(dequeueSelect)
  io.deq.bits.uop.roqIdx := roqIdx(dequeueSelect)

  //TODO
  io.deq.bits.redirect := DontCare

  io.deq.bits.src1 := src1Data(dequeueSelect)
  io.deq.bits.src2 := src2Data(dequeueSelect)
  io.deq.bits.src3 := src3Data(dequeueSelect)

  //clear the validBit of dequeued instruction in issuequeue
  when(io.deq.fire()){
    valid(dequeueSelect) := false.B
  }

  //---------------------------------------------------------
  // Redirect Logic
  //---------------------------------------------------------
  val expRedirect = io.redirect.valid && io.redirect.bits.isException
  val brRedirect = io.redirect.valid && !io.redirect.bits.isException

  UIntToOH(io.redirect.bits.brTag)
  List.tabulate(iqSize)(
    when(brRedirect && (UIntToOH(io.redirect.bits.brTag) & brMask(i)).orR && valid(i) ){
        valid(i) := false.B
    } .elsewhen(expRedirect) {
        valid(i) := false.B
    }
  )


}