Refactor frontend exception passing

Bundle them, and leverage regularity, so that if we have to add more
exceptions in the future, we don't need to change so much code.

src/main/scala/rocket/Frontend.scala

@@ -18,13 +18,21 @@ class FrontendReq(implicit p: Parameters) extends CoreBundle()(p) {
   val speculative = Bool()
 }
 
+class FrontendExceptions extends Bundle {
+  val pf = new Bundle {
+    val inst = Bool()
+  }
+  val ae = new Bundle {
+    val inst = Bool()
+  }
+}
+
 class FrontendResp(implicit p: Parameters) extends CoreBundle()(p) {
   val btb = Valid(new BTBResp)
   val pc = UInt(width = vaddrBitsExtended)  // ID stage PC
   val data = UInt(width = fetchWidth * coreInstBits)
   val mask = Bits(width = fetchWidth)
-  val pf = Bool()
+  val xcpt = new FrontendExceptions
-  val ae = Bool()
   val replay = Bool()
 }
 
@@ -83,9 +91,7 @@ class FrontendModule(outer: Frontend) extends LazyModuleImp(outer)
   val s2_btb_resp_valid = Reg(init=Bool(false))
   val s2_btb_resp_bits = Reg(new BTBResp)
   val s2_tlb_resp = Reg(tlb.io.resp)
-  val s2_pf = s2_tlb_resp.pf.inst && !s2_tlb_resp.miss
+  val s2_xcpt = !s2_tlb_resp.miss && fq.io.enq.bits.xcpt.asUInt.orR
-  val s2_ae = s2_tlb_resp.ae.inst && !s2_tlb_resp.miss
-  val s2_xcpt = s2_pf || s2_ae
   val s2_speculative = Reg(init=Bool(false))
 
   val fetchBytes = coreInstBytes * fetchWidth
@@ -163,8 +169,7 @@ class FrontendModule(outer: Frontend) extends LazyModuleImp(outer)
 
   fq.io.enq.bits.data := icache.io.resp.bits
   fq.io.enq.bits.mask := UInt((1 << fetchWidth)-1) << s2_pc.extract(log2Ceil(fetchWidth)+log2Ceil(coreInstBytes)-1, log2Ceil(coreInstBytes))
-  fq.io.enq.bits.pf := s2_pf
+  fq.io.enq.bits.xcpt := s2_tlb_resp
-  fq.io.enq.bits.ae := s2_ae
   fq.io.enq.bits.replay := icache.io.s2_kill && !icache.io.resp.valid && !s2_xcpt
   fq.io.enq.bits.btb.valid := s2_btb_resp_valid
   fq.io.enq.bits.btb.bits := s2_btb_resp_bits

src/main/scala/rocket/IBuf.scala

@@ -9,10 +9,8 @@ import tile._
 import util._
 
 class Instruction(implicit val p: Parameters) extends ParameterizedBundle with HasCoreParameters {
-  val pf0 = Bool() // page fault on first half of instruction
+  val xcpt0 = new FrontendExceptions // exceptions on first half of instruction
-  val pf1 = Bool() // page fault on second half of instruction
+  val xcpt1 = new FrontendExceptions // exceptions on second half of instruction
-  val ae0 = Bool() // access exception on first half of instruction
-  val ae1 = Bool() // access exception on second half of instruction
   val replay = Bool()
   val btb_hit = Bool()
   val rvc = Bool()
@@ -80,8 +78,7 @@ class IBuf(implicit p: Parameters) extends CoreModule {
 
   val valid = (UIntToOH(nValid) - 1)(fetchWidth-1, 0)
   val bufMask = UIntToOH(nBufValid) - 1
-  val pf = valid & (Mux(buf.pf, bufMask, UInt(0)) | Mux(io.imem.bits.pf, ~bufMask, UInt(0)))
+  val xcpt = (0 until bufMask.getWidth).map(i => Mux(bufMask(i), buf.xcpt, io.imem.bits.xcpt))
-  val ae = valid & (Mux(buf.ae, bufMask, UInt(0)) | Mux(io.imem.bits.ae, ~bufMask, UInt(0)))
   val ic_replay = valid & (Mux(buf.replay, bufMask, UInt(0)) | Mux(io.imem.bits.replay, ~bufMask, UInt(0)))
   val ibufBTBHitMask = Mux(ibufBTBHit, UIntToOH(ibufBTBResp.bridx), UInt(0))
   assert(!io.imem.valid || !io.imem.bits.btb.valid || io.imem.bits.btb.bits.bridx >= pcWordBits)
@@ -100,11 +97,9 @@ class IBuf(implicit p: Parameters) extends CoreModule {
 
     if (usingCompressed) {
       val replay = ic_replay(j) || (!exp.io.rvc && (btbHitMask(j) || ic_replay(j+1)))
-      io.inst(i).valid := valid(j) && (exp.io.rvc || valid(j+1) || pf(j+1) || ae(j+1) || replay)
+      io.inst(i).valid := valid(j) && (exp.io.rvc || valid(j+1) || xcpt(j+1).asUInt.orR || replay)
-      io.inst(i).bits.pf0 := pf(j)
+      io.inst(i).bits.xcpt0 := xcpt(j)
-      io.inst(i).bits.pf1 := !exp.io.rvc && pf(j+1)
+      io.inst(i).bits.xcpt1 := Mux(exp.io.rvc, 0.U, xcpt(j+1).asUInt).asTypeOf(new FrontendExceptions)
-      io.inst(i).bits.ae0 := ae(j)
-      io.inst(i).bits.ae1 := !exp.io.rvc && ae(j+1)
       io.inst(i).bits.replay := replay
       io.inst(i).bits.btb_hit := btbHitMask(j) || (!exp.io.rvc && btbHitMask(j+1))
       io.inst(i).bits.rvc := exp.io.rvc
@@ -115,10 +110,8 @@ class IBuf(implicit p: Parameters) extends CoreModule {
     } else {
       when (io.inst(i).ready) { nReady := i+1 }
       io.inst(i).valid := valid(i)
-      io.inst(i).bits.pf0 := pf(i)
+      io.inst(i).bits.xcpt0 := xcpt(i)
-      io.inst(i).bits.pf1 := false
+      io.inst(i).bits.xcpt1 := 0.U.asTypeOf(new FrontendExceptions)
-      io.inst(i).bits.ae0 := ae(i)
-      io.inst(i).bits.ae1 := false
       io.inst(i).bits.replay := ic_replay(i)
       io.inst(i).bits.rvc := false
       io.inst(i).bits.btb_hit := btbHitMask(i)

src/main/scala/rocket/Rocket.scala

@@ -231,14 +231,16 @@ class Rocket(implicit p: Parameters) extends CoreModule()(p)
   bpu.io.pc := ibuf.io.pc
   bpu.io.ea := mem_reg_wdata
 
-  val id_xcpt_pf = ibuf.io.inst(0).bits.pf0 || ibuf.io.inst(0).bits.pf1
+  val id_xcpt0 = ibuf.io.inst(0).bits.xcpt0
-  val id_xcpt_ae = ibuf.io.inst(0).bits.ae0 || ibuf.io.inst(0).bits.ae1
+  val id_xcpt1 = ibuf.io.inst(0).bits.xcpt1
   val (id_xcpt, id_cause) = checkExceptions(List(
     (csr.io.interrupt, csr.io.interrupt_cause),
     (bpu.io.debug_if,  UInt(CSR.debugTriggerCause)),
     (bpu.io.xcpt_if,   UInt(Causes.breakpoint)),
-    (id_xcpt_pf,       UInt(Causes.fetch_page_fault)),
+    (id_xcpt0.pf.inst, UInt(Causes.fetch_page_fault)),
-    (id_xcpt_ae,       UInt(Causes.fetch_access)),
+    (id_xcpt0.ae.inst, UInt(Causes.fetch_access)),
+    (id_xcpt1.pf.inst, UInt(Causes.fetch_page_fault)),
+    (id_xcpt1.ae.inst, UInt(Causes.fetch_access)),
     (id_illegal_insn,  UInt(Causes.illegal_instruction))))
 
   val dcache_bypass_data =
@@ -305,15 +307,15 @@ class Rocket(implicit p: Parameters) extends CoreModule()(p)
       ex_ctrl.alu_dw := DW_XPR
       ex_ctrl.sel_alu1 := A1_RS1 // badaddr := instruction
       ex_ctrl.sel_alu2 := A2_ZERO
-      when (bpu.io.xcpt_if || id_xcpt_pf || id_xcpt_ae) { // badaddr := PC
+      when (id_xcpt1.asUInt.orR) { // badaddr := PC+2
         ex_ctrl.sel_alu1 := A1_PC
-      }
-      val pf_second = !ibuf.io.inst(0).bits.pf0 && ibuf.io.inst(0).bits.pf1
-      val ae_second = !ibuf.io.inst(0).bits.ae0 && ibuf.io.inst(0).bits.ae1
-      when (!bpu.io.xcpt_if && (pf_second || (!id_xcpt_pf && ae_second))) { // badaddr := PC+2
         ex_ctrl.sel_alu2 := A2_SIZE
         ex_reg_rvc := true
       }
+      when (bpu.io.xcpt_if || id_xcpt0.asUInt.orR) { // badaddr := PC
+        ex_ctrl.sel_alu1 := A1_PC
+        ex_ctrl.sel_alu2 := A2_ZERO
+      }
     }
     ex_reg_flush_pipe := id_ctrl.fence_i || id_csr_flush
     ex_reg_load_use := id_load_use