xiangshan/frontend/RAS.scala

package xiangshan.frontend

import chisel3._
import chisel3.util._
import xiangshan._
import xiangshan.backend.ALUOpType
import utils._

class RAS extends BasePredictor
{
    class RASResp extends Resp
    {
        val target =UInt(VAddrBits.W)
    }

    class RASBranchInfo extends Meta
    {
        val rasSp = UInt(log2Up(RasSize).W)
        val rasTopCtr = UInt(8.W)
        val rasToqAddr = UInt(VAddrBits.W)
    }

    class RASIO extends DefaultBasePredictorIO
    {
        val is_ret = Input(Bool())
        val callIdx = Flipped(ValidIO(UInt(log2Ceil(PredictWidth).W)))
        val isRVC = Input(Bool())
        val recover =  Flipped(ValidIO(new BranchUpdateInfo))
        val out = ValidIO(new RASResp)
        val branchInfo = Output(new RASBranchInfo)
    }

    class RASEntry() extends XSBundle {
        val retAddr = UInt(VAddrBits.W)
        val ctr = UInt(8.W) // layer of nested call functions
    }

    def rasEntry() = new RASEntry

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

    override val io = IO(new RASIO)

    class RASStack(val rasSize: Int) extends XSModule {
        val io = IO(new Bundle {
            val push_valid = Input(Bool())
            val pop_valid = Input(Bool())
            val new_addr = Input(UInt(VAddrBits.W))
            val top_addr = Output(UInt(VAddrBits.W))
            val is_empty = Output(Bool())
            val is_full = Output(Bool())
            val copy_valid = Input(Bool())
            val copy_in_mem  = Input(Vec(rasSize, rasEntry()))
            val copy_in_sp   = Input(UInt(log2Up(rasSize).W))
            val copy_out_mem = Output(Vec(rasSize, rasEntry()))
            val copy_out_sp  = Output(UInt(log2Up(rasSize).W))
        })

        class Stack(val size: Int) extends XSModule {
            val io = IO(new Bundle {
                val rIdx = Input(UInt(log2Up(size).W))
                val rdata = Output(rasEntry())
                val wen = Input(Bool())
                val wIdx = Input(UInt(log2Up(size).W))
                val wdata = Input(rasEntry())
                val copyen = Input(Bool())
                val copy_in = Input(Vec(size, rasEntry()))
                val copy_out = Output(Vec(size, rasEntry()))
            })
            val mem = Reg(Vec(size, rasEntry()))
            when (io.wen)  {
                mem(io.wIdx) := io.wdata
            }
            io.rdata := mem(io.rIdx)
            (0 until size).foreach { i => io.copy_out(i) := mem(i) }
            when (io.copyen) {
                (0 until size).foreach {i => mem(i) := io.copy_in(i) }
            }
        }
        val sp = RegInit(0.U(log2Up(rasSize).W))
        val stack = Module(new Stack(rasSize)).io

        stack.rIdx := sp - 1.U
        val top_entry = stack.rdata
        val top_addr = top_entry.retAddr
        val top_ctr = top_entry.ctr
        val alloc_new = io.new_addr =/= top_addr
        stack.wen := io.push_valid || io.pop_valid && top_ctr =/= 1.U
        stack.wIdx := Mux(io.pop_valid && top_ctr =/= 1.U, sp - 1.U, Mux(alloc_new, sp, sp - 1.U))
        stack.wdata := Mux(io.pop_valid && top_ctr =/= 1.U,
                            RASEntry(top_addr, top_ctr - 1.U),
                            Mux(alloc_new, RASEntry(io.new_addr, 1.U), RASEntry(top_addr, top_ctr + 1.U)))

        when (io.push_valid && alloc_new) {
            sp := sp + 1.U
        }

        when (io.pop_valid && top_ctr === 1.U) {
            sp := Mux(sp === 0.U, 0.U, sp - 1.U)
        }

        io.copy_out_mem := stack.copy_out
        io.copy_out_sp  := sp
        stack.copyen := io.copy_valid
        stack.copy_in := io.copy_in_mem
        when (io.copy_valid) {
            sp := io.copy_in_sp
        }

        io.top_addr := top_addr
        io.is_empty := sp === 0.U
        io.is_full  := sp === (RasSize - 1).U
    }

    // val ras_0 = Reg(Vec(RasSize, rasEntry()))  //RegInit(0.U)asTypeOf(Vec(RasSize,rasEntry)) cause comb loop
    // val ras_1 = Reg(Vec(RasSize, rasEntry()))
    // val sp_0 = RegInit(0.U(log2Up(RasSize).W))
    // val sp_1 = RegInit(0.U(log2Up(RasSize).W))
    // val choose_bit = RegInit(false.B)   //start with 0
    // val spec_ras = Mux(choose_bit, ras_1, ras_0)
    // val spec_sp = Mux(choose_bit,sp_1,sp_0)
    // val commit_ras = Mux(choose_bit, ras_0, ras_1)
    // val commit_sp = Mux(choose_bit,sp_0,sp_1)

    // val spec_ras = Reg(Vec(RasSize, rasEntry()))
    // val spec_sp = RegInit(0.U(log2Up(RasSize).W))
    // val commit_ras = Reg(Vec(RasSize, rasEntry()))
    // val commit_sp = RegInit(0.U(log2Up(RasSize).W))

    val spec_ras   = Module(new RASStack(RasSize)).io

    val spec_push = WireInit(false.B)
    val spec_pop = WireInit(false.B)
    val spec_new_addr = WireInit(io.pc.bits + (io.callIdx.bits << 1.U) + Mux(io.isRVC,2.U,4.U))
    spec_ras.push_valid := spec_push
    spec_ras.pop_valid  := spec_pop
    spec_ras.new_addr   := spec_new_addr
    val spec_is_empty = spec_ras.is_empty
    val spec_is_full = spec_ras.is_full
    val spec_top_addr = spec_ras.top_addr

    spec_push := !spec_is_full && io.callIdx.valid && io.pc.valid
    spec_pop  := !spec_is_empty && io.is_ret && io.pc.valid

    val commit_ras = Module(new RASStack(RasSize)).io

    val commit_push = WireInit(false.B)
    val commit_pop = WireInit(false.B)
    val commit_new_addr = WireInit(io.recover.bits.pc + 4.U)  //TODO: consider RVC
    commit_ras.push_valid := commit_push
    commit_ras.pop_valid  := commit_pop
    commit_ras.new_addr   := commit_new_addr
    val commit_is_empty = commit_ras.is_empty
    val commit_is_full = commit_ras.is_full
    val commit_top_addr = commit_ras.top_addr

    commit_push := !commit_is_full  && io.recover.valid && io.recover.bits.pd.isCall
    commit_pop  := !commit_is_empty && io.recover.valid && io.recover.bits.pd.isRet


    io.out.valid := !spec_is_empty && io.is_ret
    io.out.bits.target := spec_top_addr
    // TODO: back-up stack for ras
    // use checkpoint to recover RAS

    val copy_valid = io.recover.valid && io.recover.bits.isMisPred
    val copy_next = RegNext(copy_valid)
    spec_ras.copy_valid := copy_next
    spec_ras.copy_in_mem := commit_ras.copy_out_mem
    spec_ras.copy_in_sp  := commit_ras.copy_out_sp
    commit_ras.copy_valid := DontCare
    commit_ras.copy_in_mem := DontCare
    commit_ras.copy_in_sp  := DontCare

    //no need to pass the ras branchInfo
    io.branchInfo.rasSp := DontCare
    io.branchInfo.rasTopCtr := DontCare
    io.branchInfo.rasToqAddr := DontCare

    if (BPUDebug && debug) {
        // XSDebug("----------------RAS(spec)----------------\n")
        // XSDebug("  index       addr           ctr \n")
        // for(i <- 0 until RasSize){
        //     XSDebug("  (%d)   0x%x      %d",i.U,spec_ras(i).retAddr,spec_ras(i).ctr)
        //     when(i.U === spec_sp){XSDebug(false,true.B,"   <----sp")}
        //     XSDebug(false,true.B,"\n")
        // }
        // XSDebug("----------------RAS(commit)----------------\n")
        // XSDebug("  index       addr           ctr \n")
        // for(i <- 0 until RasSize){
        //     XSDebug("  (%d)   0x%x      %d",i.U,commit_ras(i).retAddr,commit_ras(i).ctr)
        //     when(i.U === commit_sp){XSDebug(false,true.B,"   <----sp")}
        //     XSDebug(false,true.B,"\n")
        // }

        // XSDebug(spec_push, "(spec_ras)push  inAddr: 0x%x  inCtr: %d |  allocNewEntry:%d |   sp:%d \n",spec_ras_write.retAddr,spec_ras_write.ctr,sepc_alloc_new,spec_sp.asUInt)
        // XSDebug(spec_pop, "(spec_ras)pop outValid:%d  outAddr: 0x%x \n",io.out.valid,io.out.bits.target)
        // XSDebug(commit_push, "(commit_ras)push  inAddr: 0x%x  inCtr: %d |  allocNewEntry:%d |   sp:%d \n",commit_ras_write.retAddr,commit_ras_write.ctr,sepc_alloc_new,commit_sp.asUInt)
        // XSDebug(commit_pop, "(commit_ras)pop outValid:%d  outAddr: 0x%x \n",io.out.valid,io.out.bits.target)
        // XSDebug("copyValid:%d copyNext:%d \n",copy_valid,copy_next)
    }


    // val recoverSp = io.recover.bits.brInfo.rasSp
    // val recoverCtr = io.recover.bits.brInfo.rasTopCtr
    // val recoverAddr = io.recover.bits.brInfo.rasToqAddr
    // val recover_top = ras(recoverSp - 1.U)
    // when (recover_valid) {
    //     sp := recoverSp
    //     recover_top.ctr := recoverCtr
    //     recover_top.retAddr := recoverAddr
    //     XSDebug("RAS update: SP:%d , Ctr:%d \n",recoverSp,recoverCtr)
    // }
    // val recover_and_push = recover_valid && push
    // val recover_and_pop = recover_valid && pop
    // val recover_alloc_new = new_addr =/= recoverAddr
    // when(recover_and_push)
    // {
    //     when(recover_alloc_new){
    //         sp := recoverSp + 1.U
    //         ras(recoverSp).retAddr := new_addr
    //         ras(recoverSp).ctr := 1.U
    //         recover_top.retAddr := recoverAddr
    //         recover_top.ctr := recoverCtr
    //     } .otherwise{
    //         sp := recoverSp
    //         recover_top.ctr := recoverCtr + 1.U
    //         recover_top.retAddr := recoverAddr
    //     }
    // } .elsewhen(recover_and_pop)
    // {
    //     io.out.bits.target := recoverAddr
    //     when ( recover_top.ctr === 1.U) {
    //         sp := recoverSp - 1.U
    //     }.otherwise {
    //         sp := recoverSp
    //        recover_top.ctr := recoverCtr - 1.U
    //     }
    // }

}