xref: /XiangShan/src/main/scala/xiangshan/backend/fu/Alu.scala (revision e18c367f538130ef8e8c577e982d5e20161011b1)

package xiangshan.backend.fu

import chisel3._
import chisel3.util._
import utils.{LookupTree, LookupTreeDefault, SignExt, XSDebug, ZeroExt}
import xiangshan._
import xiangshan.backend.ALUOpType

class Alu extends FunctionUnit(FuConfig(
  fuType = FuType.alu,
  numIntSrc = 2,
  numFpSrc = 0,
  writeIntRf = true,
  writeFpRf = false,
  hasRedirect = true
)) with HasRedirectOut {

  val (src1, src2, offset, func, pc, uop) = (
    io.in.bits.src(0),
    io.in.bits.src(1),
    io.in.bits.uop.ctrl.imm,
    io.in.bits.uop.ctrl.fuOpType,
    SignExt(io.in.bits.uop.cf.pc, AddrBits),
    io.in.bits.uop
  )

  val redirectHit = uop.roqIdx.needFlush(io.redirectIn)
  val valid = io.in.valid && !redirectHit

  val isAdderSub = (func =/= ALUOpType.add) && (func =/= ALUOpType.addw)
  val adderRes = (src1 +& (src2 ^ Fill(XLEN, isAdderSub))) + isAdderSub
  val xorRes = src1 ^ src2
  val sltu = !adderRes(XLEN)
  val slt = xorRes(XLEN-1) ^ sltu

  val shsrc1 = LookupTreeDefault(func, src1, List(
    ALUOpType.srlw -> ZeroExt(src1(31,0), 64),
    ALUOpType.sraw -> SignExt(src1(31,0), 64)
  ))
  val shamt = Mux(ALUOpType.isWordOp(func), src2(4, 0), src2(5, 0))
  val res = LookupTreeDefault(func(3, 0), adderRes, List(
    ALUOpType.sll  -> ((shsrc1  << shamt)(XLEN-1, 0)),
    ALUOpType.slt  -> ZeroExt(slt, XLEN),
    ALUOpType.sltu -> ZeroExt(sltu, XLEN),
    ALUOpType.xor  -> xorRes,
    ALUOpType.srl  -> (shsrc1  >> shamt),
    ALUOpType.or   -> (src1  |  src2),
    ALUOpType.and  -> (src1  &  src2),
    ALUOpType.sra  -> ((shsrc1.asSInt >> shamt).asUInt)
  ))
  val aluRes = Mux(ALUOpType.isWordOp(func), SignExt(res(31,0), 64), res)

  val branchOpTable = List(
    ALUOpType.getBranchType(ALUOpType.beq)  -> !xorRes.orR,
    ALUOpType.getBranchType(ALUOpType.blt)  -> slt,
    ALUOpType.getBranchType(ALUOpType.bltu) -> sltu
  )

  val isBranch = uop.cf.brUpdate.pd.isBr// ALUOpType.isBranch(func)
  val isRVC = uop.cf.brUpdate.pd.isRVC//(io.in.bits.cf.instr(1,0) =/= "b11".U)
  val taken = LookupTree(ALUOpType.getBranchType(func), branchOpTable) ^ ALUOpType.isBranchInvert(func)
  val target = Mux(isBranch, pc + offset, adderRes)(VAddrBits-1,0)
  val snpc = Mux(isRVC, pc + 2.U, pc + 4.U)

  redirectOutValid := io.out.valid && isBranch
  redirectOut.pc := uop.cf.pc
  redirectOut.target := Mux(!taken && isBranch, snpc, target)
  redirectOut.brTag := uop.brTag
  redirectOut.isException := false.B
  redirectOut.isMisPred := DontCare // check this in brq
  redirectOut.isFlushPipe := false.B
  redirectOut.isReplay := false.B
  redirectOut.roqIdx := uop.roqIdx

  brUpdate := uop.cf.brUpdate
  // override brUpdate
  brUpdate.pc := uop.cf.pc
  brUpdate.target := Mux(!taken && isBranch, snpc, target)
  brUpdate.brTarget := target
  brUpdate.taken := isBranch && taken
  brUpdate.brTag := uop.brTag

  io.in.ready := io.out.ready
  io.out.valid := valid
  io.out.bits.uop <> io.in.bits.uop
  io.out.bits.data := aluRes

  XSDebug(io.in.valid || io.redirectIn.valid,
    "In(%d %d) Out(%d %d) Redirect:(%d %d %d %d) brTag:f:%d v:%d\n",
    io.in.valid,
    io.in.ready,
    io.out.valid,
    io.out.ready,
    io.redirectIn.valid,
    io.redirectIn.bits.isException,
    io.redirectIn.bits.isFlushPipe,
    redirectHit,
    io.redirectIn.bits.brTag.flag,
    io.redirectIn.bits.brTag.value
  )
  XSDebug(io.in.valid,
    p"src1:${Hexadecimal(src1)} src2:${Hexadecimal(src2)} " +
      p"offset:${Hexadecimal(offset)} func:${Binary(func)} " +
      p"pc:${Hexadecimal(pc)} roqIdx:${uop.roqIdx}\n"
  )
  XSDebug(io.out.valid,
    p"res:${Hexadecimal(io.out.bits.data)} aluRes:${Hexadecimal(aluRes)} " +
      p"isRVC:${isRVC} isBranch:${isBranch} " +
      p"target:${Hexadecimal(target)} taken:${taken}\n"
  )
}