xref: /XiangShan/src/main/scala/xiangshan/frontend/newRAS.scala (revision 9928cec7a67130f853d7dc18e380b564782f2954)

/***************************************************************************************
* Copyright (c) 2024 Beijing Institute of Open Source Chip (BOSC)
* Copyright (c) 2020-2024 Institute of Computing Technology, Chinese Academy of Sciences
* Copyright (c) 2020-2021 Peng Cheng Laboratory
*
* XiangShan is licensed under Mulan PSL v2.
* You can use this software according to the terms and conditions of the Mulan PSL v2.
* You may obtain a copy of Mulan PSL v2 at:
*          http://license.coscl.org.cn/MulanPSL2
*
* THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND,
* EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO NON-INFRINGEMENT,
* MERCHANTABILITY OR FIT FOR A PARTICULAR PURPOSE.
*
* See the Mulan PSL v2 for more details.
*
*
* Acknowledgement
*
* This implementation is inspired by several key papers:
* [1] Kevin Skadron, Pritpal S. Ahuja, Margaret Martonosi, and Douglas W. Clark. "[Improving prediction for procedure
* returns with return-address-stack repair mechanisms.](https://doi.org/10.1109/MICRO.1998.742787)" 31st Annual
* ACM/IEEE International Symposium on Microarchitecture (MICRO). 1998.
* [2] Tan Hongze, and Wang Jian. "[A Return Address Predictor Based on Persistent Stack.]
* (https://crad.ict.ac.cn/en/article/doi/10.7544/issn1000-1239.202111274)" Journal of Computer Research and Development
* (CRAD) 60.6: 1337-1345. 2023.
***************************************************************************************/
package xiangshan.frontend

import chisel3._
import chisel3.util._
import org.chipsalliance.cde.config.Parameters
import utility._
import utils._
import xiangshan._
import xiangshan.frontend._

class RASEntry()(implicit p: Parameters) extends XSBundle {
  val retAddr = UInt(VAddrBits.W)
  val ctr     = UInt(RasCtrSize.W) // layer of nested call functions
  def =/=(that: RASEntry) = this.retAddr =/= that.retAddr || this.ctr =/= that.ctr
}

class RASPtr(implicit p: Parameters) extends CircularQueuePtr[RASPtr](p => p(XSCoreParamsKey).RasSpecSize) {}

object RASPtr {
  def apply(f: Bool, v: UInt)(implicit p: Parameters): RASPtr = {
    val ptr = Wire(new RASPtr)
    ptr.flag  := f
    ptr.value := v
    ptr
  }
  def inverse(ptr: RASPtr)(implicit p: Parameters): RASPtr =
    apply(!ptr.flag, ptr.value)
}

class RASInternalMeta(implicit p: Parameters) extends XSBundle {
  val ssp  = UInt(log2Up(RasSize).W)
  val sctr = UInt(RasCtrSize.W)
  val TOSW = new RASPtr
  val TOSR = new RASPtr
  val NOS  = new RASPtr
}

object RASInternalMeta {
  def apply(ssp: UInt, sctr: UInt, TOSW: RASPtr, TOSR: RASPtr, NOS: RASPtr)(implicit p: Parameters): RASInternalMeta = {
    val e = Wire(new RASInternalMeta)
    e.ssp  := ssp
    e.TOSW := TOSW
    e.TOSR := TOSR
    e.NOS  := NOS
    e
  }
}

class RASMeta(implicit p: Parameters) extends XSBundle {
  val ssp  = UInt(log2Up(RasSize).W)
  val TOSW = new RASPtr
}

object RASMeta {
  def apply(ssp: UInt, sctr: UInt, TOSW: RASPtr, TOSR: RASPtr, NOS: RASPtr)(implicit p: Parameters): RASMeta = {
    val e = Wire(new RASMeta)
    e.ssp  := ssp
    e.TOSW := TOSW
    e
  }
}

class RASDebug(implicit p: Parameters) extends XSBundle {
  val spec_queue   = Output(Vec(RasSpecSize, new RASEntry))
  val spec_nos     = Output(Vec(RasSpecSize, new RASPtr))
  val commit_stack = Output(Vec(RasSize, new RASEntry))
}

class RAS(implicit p: Parameters) extends BasePredictor with HasCircularQueuePtrHelper {
  override val meta_size = WireInit(0.U.asTypeOf(new RASMeta)).getWidth

  object RASEntry {
    def apply(retAddr: UInt, ctr: UInt): RASEntry = {
      val e = Wire(new RASEntry)
      e.retAddr := retAddr
      e.ctr     := ctr
      e
    }
  }

  class RASStack(rasSize: Int, rasSpecSize: Int) extends XSModule with HasCircularQueuePtrHelper {
    val io = IO(new Bundle {
      val spec_push_valid = Input(Bool())
      val spec_pop_valid  = Input(Bool())
      val spec_push_addr  = Input(UInt(VAddrBits.W))
      // for write bypass between s2 and s3

      val s2_fire        = Input(Bool())
      val s3_fire        = Input(Bool())
      val s3_cancel      = Input(Bool())
      val s3_meta        = Input(new RASInternalMeta)
      val s3_missed_pop  = Input(Bool())
      val s3_missed_push = Input(Bool())
      val s3_pushAddr    = Input(UInt(VAddrBits.W))
      val spec_pop_addr  = Output(UInt(VAddrBits.W))

      val commit_valid      = Input(Bool())
      val commit_push_valid = Input(Bool())
      val commit_pop_valid  = Input(Bool())
      val commit_push_addr  = Input(UInt(VAddrBits.W))
      val commit_meta_TOSW  = Input(new RASPtr)
      // for debug purpose only
      val commit_meta_ssp = Input(UInt(log2Up(RasSize).W))

      val redirect_valid     = Input(Bool())
      val redirect_isCall    = Input(Bool())
      val redirect_isRet     = Input(Bool())
      val redirect_meta_ssp  = Input(UInt(log2Up(RasSize).W))
      val redirect_meta_sctr = Input(UInt(RasCtrSize.W))
      val redirect_meta_TOSW = Input(new RASPtr)
      val redirect_meta_TOSR = Input(new RASPtr)
      val redirect_meta_NOS  = Input(new RASPtr)
      val redirect_callAddr  = Input(UInt(VAddrBits.W))

      val ssp  = Output(UInt(log2Up(RasSize).W))
      val sctr = Output(UInt(RasCtrSize.W))
      val nsp  = Output(UInt(log2Up(RasSize).W))
      val TOSR = Output(new RASPtr)
      val TOSW = Output(new RASPtr)
      val NOS  = Output(new RASPtr)
      val BOS  = Output(new RASPtr)

      val spec_near_overflow = Output(Bool())

      val debug = new RASDebug
    })

    val commit_stack = RegInit(VecInit(Seq.fill(RasSize)(RASEntry(0.U, 0.U))))
    val spec_queue   = RegInit(VecInit(Seq.fill(rasSpecSize)(RASEntry(0.U, 0.U))))
    val spec_nos     = RegInit(VecInit(Seq.fill(rasSpecSize)(RASPtr(false.B, 0.U))))

    val nsp = RegInit(0.U(log2Up(rasSize).W))
    val ssp = RegInit(0.U(log2Up(rasSize).W))

    val sctr = RegInit(0.U(RasCtrSize.W))
    val TOSR = RegInit(RASPtr(true.B, (RasSpecSize - 1).U))
    val TOSW = RegInit(RASPtr(false.B, 0.U))
    val BOS  = RegInit(RASPtr(false.B, 0.U))

    val spec_near_overflowed = RegInit(false.B)

    val writeBypassEntry = Reg(new RASEntry)
    val writeBypassNos   = Reg(new RASPtr)

    val writeBypassValid     = RegInit(0.B)
    val writeBypassValidWire = Wire(Bool())

    def TOSRinRange(currentTOSR: RASPtr, currentTOSW: RASPtr) = {
      val inflightValid = WireInit(false.B)
      // if in range, TOSR should be no younger than BOS and strictly younger than TOSW
      when(!isBefore(currentTOSR, BOS) && isBefore(currentTOSR, currentTOSW)) {
        inflightValid := true.B
      }
      inflightValid
    }

    def getCommitTop(currentSsp: UInt) =
      commit_stack(currentSsp)

    def getTopNos(currentTOSR: RASPtr, allowBypass: Boolean): RASPtr = {
      val ret = Wire(new RASPtr)
      if (allowBypass) {
        when(writeBypassValid) {
          ret := writeBypassNos
        }.otherwise {
          ret := spec_nos(TOSR.value)
        }
      } else {
        ret := spec_nos(TOSR.value) // invalid when TOSR is not in range
      }
      ret
    }

    def getTop(
        currentSsp:  UInt,
        currentSctr: UInt,
        currentTOSR: RASPtr,
        currentTOSW: RASPtr,
        allowBypass: Boolean
    ): RASEntry = {
      val ret = Wire(new RASEntry)
      if (allowBypass) {
        when(writeBypassValid) {
          ret := writeBypassEntry
        }.elsewhen(TOSRinRange(currentTOSR, currentTOSW)) {
          ret := spec_queue(currentTOSR.value)
        }.otherwise {
          ret := getCommitTop(currentSsp)
        }
      } else {
        when(TOSRinRange(currentTOSR, currentTOSW)) {
          ret := spec_queue(currentTOSR.value)
        }.otherwise {
          ret := getCommitTop(currentSsp)
        }
      }

      ret
    }

    // it would be unsafe for specPtr manipulation if specSize is not power of 2
    assert(log2Up(RasSpecSize) == log2Floor(RasSpecSize))
    def ctrMax = ((1L << RasCtrSize) - 1).U
    def ptrInc(ptr: UInt) = ptr + 1.U
    def ptrDec(ptr: UInt) = ptr - 1.U

    def specPtrInc(ptr: RASPtr) = ptr + 1.U
    def specPtrDec(ptr: RASPtr) = ptr - 1.U

    when(io.redirect_valid && io.redirect_isCall) {
      writeBypassValidWire := true.B
      writeBypassValid     := true.B
    }.elsewhen(io.redirect_valid) {
      // clear current top writeBypass if doing redirect
      writeBypassValidWire := false.B
      writeBypassValid     := false.B
    }.elsewhen(io.s2_fire) {
      writeBypassValidWire := io.spec_push_valid
      writeBypassValid     := io.spec_push_valid
    }.elsewhen(io.s3_fire) {
      writeBypassValidWire := false.B
      writeBypassValid     := false.B
    }.otherwise {
      writeBypassValidWire := writeBypassValid
    }

    val topEntry = getTop(ssp, sctr, TOSR, TOSW, true)
    val topNos   = getTopNos(TOSR, true)
    val redirectTopEntry =
      getTop(io.redirect_meta_ssp, io.redirect_meta_sctr, io.redirect_meta_TOSR, io.redirect_meta_TOSW, false)
    val redirectTopNos = io.redirect_meta_NOS
    val s3TopEntry     = getTop(io.s3_meta.ssp, io.s3_meta.sctr, io.s3_meta.TOSR, io.s3_meta.TOSW, false)
    val s3TopNos       = io.s3_meta.NOS

    val writeEntry = Wire(new RASEntry)
    val writeNos   = Wire(new RASPtr)
    writeEntry.retAddr := Mux(io.redirect_valid && io.redirect_isCall, io.redirect_callAddr, io.spec_push_addr)
    writeEntry.ctr := Mux(
      io.redirect_valid && io.redirect_isCall,
      Mux(
        redirectTopEntry.retAddr === io.redirect_callAddr && redirectTopEntry.ctr < ctrMax,
        io.redirect_meta_sctr + 1.U,
        0.U
      ),
      Mux(topEntry.retAddr === io.spec_push_addr && topEntry.ctr < ctrMax, sctr + 1.U, 0.U)
    )

    writeNos := Mux(io.redirect_valid && io.redirect_isCall, io.redirect_meta_TOSR, TOSR)

    when(io.spec_push_valid || (io.redirect_valid && io.redirect_isCall)) {
      writeBypassEntry := writeEntry
      writeBypassNos   := writeNos
    }

    val realPush       = Wire(Bool())
    val realWriteEntry = Wire(new RASEntry)
    val timingTop      = RegInit(0.U.asTypeOf(new RASEntry))
    val timingNos      = RegInit(0.U.asTypeOf(new RASPtr))

    when(writeBypassValidWire) {
      when((io.redirect_valid && io.redirect_isCall) || io.spec_push_valid) {
        timingTop := writeEntry
        timingNos := writeNos
      }.otherwise {
        timingTop := writeBypassEntry
        timingNos := writeBypassNos
      }

    }.elsewhen(io.redirect_valid && io.redirect_isRet) {
      // getTop using redirect Nos as TOSR
      val popRedSsp  = Wire(UInt(log2Up(rasSize).W))
      val popRedSctr = Wire(UInt(RasCtrSize.W))
      val popRedTOSR = io.redirect_meta_NOS
      val popRedTOSW = io.redirect_meta_TOSW

      when(io.redirect_meta_sctr > 0.U) {
        popRedSctr := io.redirect_meta_sctr - 1.U
        popRedSsp  := io.redirect_meta_ssp
      }.elsewhen(TOSRinRange(popRedTOSR, TOSW)) {
        popRedSsp  := ptrDec(io.redirect_meta_ssp)
        popRedSctr := spec_queue(popRedTOSR.value).ctr
      }.otherwise {
        popRedSsp  := ptrDec(io.redirect_meta_ssp)
        popRedSctr := getCommitTop(ptrDec(io.redirect_meta_ssp)).ctr
      }
      // We are deciding top for the next cycle, no need to use bypass here
      timingTop := getTop(popRedSsp, popRedSctr, popRedTOSR, popRedTOSW, false)
    }.elsewhen(io.redirect_valid) {
      // Neither call nor ret
      val popSsp  = io.redirect_meta_ssp
      val popSctr = io.redirect_meta_sctr
      val popTOSR = io.redirect_meta_TOSR
      val popTOSW = io.redirect_meta_TOSW

      timingTop := getTop(popSsp, popSctr, popTOSR, popTOSW, false)

    }.elsewhen(io.spec_pop_valid) {
      // getTop using current Nos as TOSR
      val popSsp  = Wire(UInt(log2Up(rasSize).W))
      val popSctr = Wire(UInt(RasCtrSize.W))
      val popTOSR = topNos
      val popTOSW = TOSW

      when(sctr > 0.U) {
        popSctr := sctr - 1.U
        popSsp  := ssp
      }.elsewhen(TOSRinRange(popTOSR, TOSW)) {
        popSsp  := ptrDec(ssp)
        popSctr := spec_queue(popTOSR.value).ctr
      }.otherwise {
        popSsp  := ptrDec(ssp)
        popSctr := getCommitTop(ptrDec(ssp)).ctr
      }
      // We are deciding top for the next cycle, no need to use bypass here
      timingTop := getTop(popSsp, popSctr, popTOSR, popTOSW, false)
    }.elsewhen(realPush) {
      // just updating spec queue, cannot read from there
      timingTop := realWriteEntry
    }.elsewhen(io.s3_cancel) {
      // s3 is different with s2
      timingTop := getTop(io.s3_meta.ssp, io.s3_meta.sctr, io.s3_meta.TOSR, io.s3_meta.TOSW, false)
      when(io.s3_missed_push) {
        val writeEntry_s3 = Wire(new RASEntry)
        timingTop             := writeEntry_s3
        writeEntry_s3.retAddr := io.s3_pushAddr
        writeEntry_s3.ctr := Mux(
          timingTop.retAddr === io.s3_pushAddr && io.s3_meta.sctr < ctrMax,
          io.s3_meta.sctr + 1.U,
          0.U
        )
      }.elsewhen(io.s3_missed_pop) {
        val popRedSsp_s3  = Wire(UInt(log2Up(rasSize).W))
        val popRedSctr_s3 = Wire(UInt(RasCtrSize.W))
        val popRedTOSR_s3 = io.s3_meta.NOS
        val popRedTOSW_s3 = io.s3_meta.TOSW

        when(io.s3_meta.sctr > 0.U) {
          popRedSctr_s3 := io.s3_meta.sctr - 1.U
          popRedSsp_s3  := io.s3_meta.ssp
        }.elsewhen(TOSRinRange(popRedTOSR_s3, popRedTOSW_s3)) {
          popRedSsp_s3  := ptrDec(io.s3_meta.ssp)
          popRedSctr_s3 := spec_queue(popRedTOSR_s3.value).ctr
        }.otherwise {
          popRedSsp_s3  := ptrDec(io.s3_meta.ssp)
          popRedSctr_s3 := getCommitTop(ptrDec(io.s3_meta.ssp)).ctr
        }
        // We are deciding top for the next cycle, no need to use bypass here
        timingTop := getTop(popRedSsp_s3, popRedSctr_s3, popRedTOSR_s3, popRedTOSW_s3, false)
      }
    }.otherwise {
      // easy case
      val popSsp  = ssp
      val popSctr = sctr
      val popTOSR = TOSR
      val popTOSW = TOSW
      timingTop := getTop(popSsp, popSctr, popTOSR, popTOSW, false)
    }
    val diffTop = Mux(writeBypassValid, writeBypassEntry.retAddr, topEntry.retAddr)

    XSPerfAccumulate("ras_top_mismatch", diffTop =/= timingTop.retAddr);
    // could diff when more pop than push and a commit stack is updated with inflight info

    val realWriteEntry_next = RegEnable(writeEntry, io.s2_fire || io.redirect_isCall)
    val s3_missPushEntry    = Wire(new RASEntry)
    val s3_missPushAddr     = Wire(new RASPtr)
    val s3_missPushNos      = Wire(new RASPtr)

    s3_missPushEntry.retAddr := io.s3_pushAddr
    s3_missPushEntry.ctr := Mux(
      s3TopEntry.retAddr === io.s3_pushAddr && s3TopEntry.ctr < ctrMax,
      io.s3_meta.sctr + 1.U,
      0.U
    )
    s3_missPushAddr := io.s3_meta.TOSW
    s3_missPushNos  := io.s3_meta.TOSR

    realWriteEntry := Mux(
      io.redirect_isCall,
      realWriteEntry_next,
      Mux(io.s3_missed_push, s3_missPushEntry, realWriteEntry_next)
    )

    val realWriteAddr_next = RegEnable(
      Mux(io.redirect_valid && io.redirect_isCall, io.redirect_meta_TOSW, TOSW),
      io.s2_fire || (io.redirect_valid && io.redirect_isCall)
    )
    val realWriteAddr =
      Mux(io.redirect_isCall, realWriteAddr_next, Mux(io.s3_missed_push, s3_missPushAddr, realWriteAddr_next))
    val realNos_next = RegEnable(
      Mux(io.redirect_valid && io.redirect_isCall, io.redirect_meta_TOSR, TOSR),
      io.s2_fire || (io.redirect_valid && io.redirect_isCall)
    )
    val realNos = Mux(io.redirect_isCall, realNos_next, Mux(io.s3_missed_push, s3_missPushNos, realNos_next))

    realPush := (io.s3_fire && (!io.s3_cancel && RegEnable(
      io.spec_push_valid,
      io.s2_fire
    ) || io.s3_missed_push)) || RegNext(io.redirect_valid && io.redirect_isCall)

    when(realPush) {
      spec_queue(realWriteAddr.value) := realWriteEntry
      spec_nos(realWriteAddr.value)   := realNos
    }

    def specPush(
        retAddr:     UInt,
        currentSsp:  UInt,
        currentSctr: UInt,
        currentTOSR: RASPtr,
        currentTOSW: RASPtr,
        topEntry:    RASEntry
    ) = {
      TOSR := currentTOSW
      TOSW := specPtrInc(currentTOSW)
      // spec sp and ctr should always be maintained
      when(topEntry.retAddr === retAddr && currentSctr < ctrMax) {
        sctr := currentSctr + 1.U
      }.otherwise {
        ssp  := ptrInc(currentSsp)
        sctr := 0.U
      }
    }

    when(io.spec_push_valid) {
      specPush(io.spec_push_addr, ssp, sctr, TOSR, TOSW, topEntry)
    }
    def specPop(
        currentSsp:    UInt,
        currentSctr:   UInt,
        currentTOSR:   RASPtr,
        currentTOSW:   RASPtr,
        currentTopNos: RASPtr
    ) = {
      // TOSR is only maintained when spec queue is not empty
      when(TOSRinRange(currentTOSR, currentTOSW)) {
        TOSR := currentTopNos
      }
      // spec sp and ctr should always be maintained
      when(currentSctr > 0.U) {
        sctr := currentSctr - 1.U
      }.elsewhen(TOSRinRange(currentTopNos, currentTOSW)) {
        // in range, use inflight data
        ssp  := ptrDec(currentSsp)
        sctr := spec_queue(currentTopNos.value).ctr
      }.otherwise {
        // NOS not in range, use commit data
        ssp  := ptrDec(currentSsp)
        sctr := getCommitTop(ptrDec(currentSsp)).ctr
        // in overflow state, we cannot determine the next sctr, sctr here is not accurate
      }
    }
    when(io.spec_pop_valid) {
      specPop(ssp, sctr, TOSR, TOSW, topNos)
    }

    // io.spec_pop_addr := Mux(writeBypassValid, writeBypassEntry.retAddr, topEntry.retAddr)

    io.spec_pop_addr := timingTop.retAddr
    io.BOS           := BOS
    io.TOSW          := TOSW
    io.TOSR          := TOSR
    io.NOS           := topNos
    io.ssp           := ssp
    io.sctr          := sctr
    io.nsp           := nsp

    when(io.s3_cancel) {
      // recovery of all related pointers
      TOSR := io.s3_meta.TOSR
      TOSW := io.s3_meta.TOSW
      ssp  := io.s3_meta.ssp
      sctr := io.s3_meta.sctr

      // for missing pop, we also need to do a pop here
      when(io.s3_missed_pop) {
        specPop(io.s3_meta.ssp, io.s3_meta.sctr, io.s3_meta.TOSR, io.s3_meta.TOSW, io.s3_meta.NOS)
      }
      when(io.s3_missed_push) {
        // do not use any bypass from f2
        specPush(io.s3_pushAddr, io.s3_meta.ssp, io.s3_meta.sctr, io.s3_meta.TOSR, io.s3_meta.TOSW, s3TopEntry)
      }
    }

    val commitTop = commit_stack(nsp)

    when(io.commit_pop_valid) {

      val nsp_update = Wire(UInt(log2Up(rasSize).W))
      when(io.commit_meta_ssp =/= nsp) {
        // force set nsp to commit ssp to avoid permanent errors
        nsp_update := io.commit_meta_ssp
      }.otherwise {
        nsp_update := nsp
      }

      // if ctr > 0, --ctr in stack, otherwise --nsp
      when(commitTop.ctr > 0.U) {
        commit_stack(nsp_update).ctr := commitTop.ctr - 1.U
        nsp                          := nsp_update
      }.otherwise {
        nsp := ptrDec(nsp_update);
      }
      // XSError(io.commit_meta_ssp =/= nsp, "nsp mismatch with expected ssp")
    }

    val commit_push_addr = spec_queue(io.commit_meta_TOSW.value).retAddr

    when(io.commit_push_valid) {
      val nsp_update = Wire(UInt(log2Up(rasSize).W))
      when(io.commit_meta_ssp =/= nsp) {
        // force set nsp to commit ssp to avoid permanent errors
        nsp_update := io.commit_meta_ssp
      }.otherwise {
        nsp_update := nsp
      }
      // if ctr < max && topAddr == push addr, ++ctr, otherwise ++nsp
      when(commitTop.ctr < ctrMax && commitTop.retAddr === commit_push_addr) {
        commit_stack(nsp_update).ctr := commitTop.ctr + 1.U
        nsp                          := nsp_update
      }.otherwise {
        nsp                                      := ptrInc(nsp_update)
        commit_stack(ptrInc(nsp_update)).retAddr := commit_push_addr
        commit_stack(ptrInc(nsp_update)).ctr     := 0.U
      }

      // XSError(io.commit_meta_ssp =/= nsp, "nsp mismatch with expected ssp")
      // XSError(io.commit_push_addr =/= commit_push_addr, "addr from commit mismatch with addr from spec")
    }

    when(io.commit_push_valid) {
      BOS := io.commit_meta_TOSW
    }.elsewhen(io.commit_valid && (distanceBetween(io.commit_meta_TOSW, BOS) > 2.U)) {
      BOS := specPtrDec(io.commit_meta_TOSW)
    }
    XSError(
      io.commit_valid && (distanceBetween(io.commit_meta_TOSW, BOS) > 2.U),
      "The use of inference queue of the RAS module has unexpected situations"
    )

    when(io.redirect_valid) {
      TOSR := io.redirect_meta_TOSR
      TOSW := io.redirect_meta_TOSW
      ssp  := io.redirect_meta_ssp
      sctr := io.redirect_meta_sctr

      when(io.redirect_isCall) {
        specPush(
          io.redirect_callAddr,
          io.redirect_meta_ssp,
          io.redirect_meta_sctr,
          io.redirect_meta_TOSR,
          io.redirect_meta_TOSW,
          redirectTopEntry
        )
      }
      when(io.redirect_isRet) {
        specPop(
          io.redirect_meta_ssp,
          io.redirect_meta_sctr,
          io.redirect_meta_TOSR,
          io.redirect_meta_TOSW,
          redirectTopNos
        )
      }
    }

    when(distanceBetween(TOSW, BOS) > (rasSpecSize - 2).U) {
      spec_near_overflowed := true.B
    }.otherwise {
      spec_near_overflowed := false.B
    }

    io.spec_near_overflow := spec_near_overflowed
    XSPerfAccumulate("spec_near_overflow", spec_near_overflowed)
    io.debug.commit_stack.zipWithIndex.foreach { case (a, i) => a := commit_stack(i) }
    io.debug.spec_nos.zipWithIndex.foreach { case (a, i) => a := spec_nos(i) }
    io.debug.spec_queue.zipWithIndex.foreach { case (a, i) => a := spec_queue(i) }
  }

  val stack = Module(new RASStack(RasSize, RasSpecSize)).io

  val stack_near_overflow = stack.spec_near_overflow
  val s2_spec_push        = WireInit(false.B)
  val s2_spec_pop         = WireInit(false.B)
  val s2_full_pred        = io.in.bits.resp_in(0).s2.full_pred(2)
  // when last inst is an rvi call, fall through address would be set to the middle of it, so an addition is needed
  val s2_spec_new_addr = s2_full_pred.fallThroughAddr + Mux(s2_full_pred.last_may_be_rvi_call, 2.U, 0.U)
  stack.spec_push_valid := s2_spec_push && !stack_near_overflow
  stack.spec_pop_valid  := s2_spec_pop && !stack_near_overflow
  stack.spec_push_addr  := s2_spec_new_addr

  // confirm that the call/ret is the taken cfi
  s2_spec_push := io.s2_fire(2) && s2_full_pred.hit_taken_on_call && !io.s3_redirect(2)
  s2_spec_pop  := io.s2_fire(2) && s2_full_pred.hit_taken_on_ret && !io.s3_redirect(2)

  // val s2_jalr_target = io.out.s2.full_pred.jalr_target
  // val s2_last_target_in = s2_full_pred.targets.last
  // val s2_last_target_out = io.out.s2.full_pred(2).targets.last
  val s2_is_jalr = s2_full_pred.is_jalr
  val s2_is_ret  = s2_full_pred.is_ret
  val s2_top     = stack.spec_pop_addr
  // assert(is_jalr && is_ret || !is_ret)
  when(s2_is_ret && io.ctrl.ras_enable) {
    io.out.s2.full_pred.map(_.jalr_target).foreach(_ := s2_top)
    // FIXME: should use s1 globally
  }
  // s2_last_target_out := Mux(s2_is_jalr, s2_jalr_target, s2_last_target_in)
  io.out.s2.full_pred.zipWithIndex.foreach { case (a, i) =>
    a.targets.last := Mux(
      s2_is_jalr,
      io.out.s2.full_pred(i).jalr_target,
      io.in.bits.resp_in(0).s2.full_pred(i).targets.last
    )
  }

  val s2_meta = Wire(new RASInternalMeta)
  s2_meta.ssp  := stack.ssp
  s2_meta.sctr := stack.sctr
  s2_meta.TOSR := stack.TOSR
  s2_meta.TOSW := stack.TOSW
  s2_meta.NOS  := stack.NOS

  val s3_top           = RegEnable(stack.spec_pop_addr, io.s2_fire(2))
  val s3_spec_new_addr = RegEnable(s2_spec_new_addr, io.s2_fire(2))

  // val s3_jalr_target = io.out.s3.full_pred.jalr_target
  // val s3_last_target_in = io.in.bits.resp_in(0).s3.full_pred(2).targets.last
  // val s3_last_target_out = io.out.s3.full_pred(2).targets.last
  val s3_is_jalr =
    io.in.bits.resp_in(0).s3.full_pred(2).is_jalr && !io.in.bits.resp_in(0).s3.full_pred(2).fallThroughErr
  val s3_is_ret = io.in.bits.resp_in(0).s3.full_pred(2).is_ret && !io.in.bits.resp_in(0).s3.full_pred(2).fallThroughErr
  // assert(is_jalr && is_ret || !is_ret)
  when(s3_is_ret && io.ctrl.ras_enable) {
    io.out.s3.full_pred.map(_.jalr_target).foreach(_ := s3_top)
    // FIXME: should use s1 globally
  }
  // s3_last_target_out := Mux(s3_is_jalr, s3_jalr_target, s3_last_target_in)
  io.out.s3.full_pred.zipWithIndex.foreach { case (a, i) =>
    a.targets.last := Mux(
      s3_is_jalr,
      io.out.s3.full_pred(i).jalr_target,
      io.in.bits.resp_in(0).s3.full_pred(i).targets.last
    )
  }

  val s3_pushed_in_s2 = RegEnable(s2_spec_push, io.s2_fire(2))
  val s3_popped_in_s2 = RegEnable(s2_spec_pop, io.s2_fire(2))
  val s3_push =
    io.in.bits.resp_in(0).s3.full_pred(2).hit_taken_on_call && !io.in.bits.resp_in(0).s3.full_pred(2).fallThroughErr
  val s3_pop =
    io.in.bits.resp_in(0).s3.full_pred(2).hit_taken_on_ret && !io.in.bits.resp_in(0).s3.full_pred(2).fallThroughErr

  val s3_cancel = io.s3_fire(2) && (s3_pushed_in_s2 =/= s3_push || s3_popped_in_s2 =/= s3_pop)
  stack.s2_fire := io.s2_fire(2)
  stack.s3_fire := io.s3_fire(2)

  stack.s3_cancel := s3_cancel && !stack_near_overflow

  val s3_meta = RegEnable(s2_meta, io.s2_fire(2))

  stack.s3_meta        := s3_meta
  stack.s3_missed_pop  := s3_pop && !s3_popped_in_s2
  stack.s3_missed_push := s3_push && !s3_pushed_in_s2
  stack.s3_pushAddr    := s3_spec_new_addr

  // no longer need the top Entry, but TOSR, TOSW, ssp sctr
  // TODO: remove related signals

  val last_stage_meta = Wire(new RASMeta)
  last_stage_meta.ssp  := s3_meta.ssp
  last_stage_meta.TOSW := s3_meta.TOSW

  io.out.last_stage_spec_info.sctr    := s3_meta.sctr
  io.out.last_stage_spec_info.ssp     := s3_meta.ssp
  io.out.last_stage_spec_info.TOSW    := s3_meta.TOSW
  io.out.last_stage_spec_info.TOSR    := s3_meta.TOSR
  io.out.last_stage_spec_info.NOS     := s3_meta.NOS
  io.out.last_stage_spec_info.topAddr := s3_top
  io.out.last_stage_meta              := last_stage_meta.asUInt

  val redirect    = RegNextWithEnable(io.redirect)
  val do_recover  = redirect.valid
  val recover_cfi = redirect.bits.cfiUpdate

  val retMissPred  = do_recover && redirect.bits.level === 0.U && recover_cfi.pd.isRet && recover_cfi.pd.valid
  val callMissPred = do_recover && redirect.bits.level === 0.U && recover_cfi.pd.isCall && recover_cfi.pd.valid
  // when we mispredict a call, we must redo a push operation
  // similarly, when we mispredict a return, we should redo a pop
  val stack_TOSW    = stack.TOSW
  val redirect_TOSW = recover_cfi.TOSW
  stack.redirect_valid     := do_recover && (isBefore(redirect_TOSW, stack_TOSW) || !stack_near_overflow)
  stack.redirect_isCall    := callMissPred
  stack.redirect_isRet     := retMissPred
  stack.redirect_meta_ssp  := recover_cfi.ssp
  stack.redirect_meta_sctr := recover_cfi.sctr
  stack.redirect_meta_TOSW := recover_cfi.TOSW
  stack.redirect_meta_TOSR := recover_cfi.TOSR
  stack.redirect_meta_NOS  := recover_cfi.NOS
  stack.redirect_callAddr  := recover_cfi.pc + Mux(recover_cfi.pd.isRVC, 2.U, 4.U)

  val updateValid = RegNext(io.update.valid, init = false.B)
  val update      = Wire(new BranchPredictionUpdate)
  update := RegEnable(io.update.bits, io.update.valid)

  // The pc register has been moved outside of predictor, pc field of update bundle and other update data are not in the same stage
  // so io.update.bits.pc is used directly here
  val update_pc = io.update.bits.pc

  // full core power down sequence need 'val updateMeta = RegEnable(io.update.bits.meta.asTypeOf(new RASMeta), io.update.valid)' to be
  // 'val updateMeta = RegEnable(io.update.bits.meta.asTypeOf(new RASMeta), io.update.valid && (io.update.bits.is_call || io.update.bits.is_ret))',
  // but the fault-tolerance mechanism of the return stack needs to be updated in time. Using an unexpected old value on reset will cause errors.
  // Only 9 registers have clock gate efficiency affected, so we relaxed the control signals.
  val updateMeta = RegEnable(io.update.bits.meta.asTypeOf(new RASMeta), io.update.valid)

  stack.commit_valid      := updateValid
  stack.commit_push_valid := updateValid && update.is_call_taken
  stack.commit_pop_valid  := updateValid && update.is_ret_taken
  stack.commit_push_addr := update.ftb_entry.getFallThrough(update_pc) + Mux(
    update.ftb_entry.last_may_be_rvi_call,
    2.U,
    0.U
  )
  stack.commit_meta_TOSW := updateMeta.TOSW
  stack.commit_meta_ssp  := updateMeta.ssp

  XSPerfAccumulate("ras_s3_cancel", s3_cancel)
  XSPerfAccumulate("ras_redirect_recover", redirect.valid)
  XSPerfAccumulate("ras_s3_and_redirect_recover_at_the_same_time", s3_cancel && redirect.valid)

  val spec_debug = stack.debug
  XSDebug(io.s2_fire(2), "----------------RAS----------------\n")
  XSDebug(io.s2_fire(2), " TopRegister: 0x%x\n", stack.spec_pop_addr)
  XSDebug(io.s2_fire(2), "  index       addr           ctr           nos (spec part)\n")
  for (i <- 0 until RasSpecSize) {
    XSDebug(
      io.s2_fire(2),
      "  (%d)   0x%x      %d       %d",
      i.U,
      spec_debug.spec_queue(i).retAddr,
      spec_debug.spec_queue(i).ctr,
      spec_debug.spec_nos(i).value
    )
    XSDebug(io.s2_fire(2) && i.U === stack.TOSW.value, "   <----TOSW")
    XSDebug(io.s2_fire(2) && i.U === stack.TOSR.value, "   <----TOSR")
    XSDebug(io.s2_fire(2) && i.U === stack.BOS.value, "   <----BOS")
    XSDebug(io.s2_fire(2), "\n")
  }
  XSDebug(io.s2_fire(2), "  index       addr           ctr   (committed part)\n")
  for (i <- 0 until RasSize) {
    XSDebug(
      io.s2_fire(2),
      "  (%d)   0x%x      %d",
      i.U,
      spec_debug.commit_stack(i).retAddr,
      spec_debug.commit_stack(i).ctr
    )
    XSDebug(io.s2_fire(2) && i.U === stack.ssp, "   <----ssp")
    XSDebug(io.s2_fire(2) && i.U === stack.nsp, "   <----nsp")
    XSDebug(io.s2_fire(2), "\n")
  }
  /*
  XSDebug(s2_spec_push, "s2_spec_push  inAddr: 0x%x  inCtr: %d |  allocNewEntry:%d |   sp:%d \n",
  s2_spec_new_addr,spec_debug.spec_push_entry.ctr,spec_debug.spec_alloc_new,spec_debug.sp.asUInt)
  XSDebug(s2_spec_pop, "s2_spec_pop  outAddr: 0x%x \n",io.out.s2.getTarget)
  val s3_recover_entry = spec_debug.recover_push_entry
  XSDebug(s3_recover && s3_push, "s3_recover_push  inAddr: 0x%x  inCtr: %d |  allocNewEntry:%d |   sp:%d \n",
    s3_recover_entry.retAddr, s3_recover_entry.ctr, spec_debug.recover_alloc_new, s3_sp.asUInt)
  XSDebug(s3_recover && s3_pop, "s3_recover_pop  outAddr: 0x%x \n",io.out.s3.getTarget)
  val redirectUpdate = redirect.bits.cfiUpdate
  XSDebug(do_recover && callMissPred, "redirect_recover_push\n")
  XSDebug(do_recover && retMissPred, "redirect_recover_pop\n")
  XSDebug(do_recover, "redirect_recover(SP:%d retAddr:%x ctr:%d) \n",
      redirectUpdate.rasSp,redirectUpdate.rasEntry.retAddr,redirectUpdate.rasEntry.ctr)
   */

  generatePerfEvent()
}