vtype: fix walk vtype value after using snapshot and the redirect sig…

…anl for vtype

src/main/scala/xiangshan/backend/CtrlBlock.scala

@@ -297,6 +297,7 @@ class CtrlBlockImp(
   rob.io.fromDecode.specVtype := decode.io.specVtype
 
   decode.io.redirect := s1_s3_redirect.valid || s2_s4_pendingRedirectValid
+  decode.io.vtypeRedirect := s1_s3_redirect.valid
 
   decode.io.in.zip(io.frontend.cfVec).foreach { case (decodeIn, frontendCf) =>
     decodeIn.valid := frontendCf.valid

src/main/scala/xiangshan/backend/decode/DecodeStage.scala

@@ -41,6 +41,7 @@ class DecodeStage(implicit p: Parameters) extends XSModule
   val io = IO(new Bundle() {
     val redirect = Input(Bool())
     val canAccept = Output(Bool())
+    val vtypeRedirect = Input(Bool())
     // from Ibuffer
     val in = Vec(DecodeWidth, Flipped(DecoupledIO(new StaticInst)))
     // to Rename
@@ -106,7 +107,7 @@ class DecodeStage(implicit p: Parameters) extends XSModule
     inst.bits := io.in(i).bits.instr
   }
   vtypeGen.io.canUpdateVType := decoderComp.io.in.fire && decoderComp.io.in.bits.simpleDecodedInst.isVset
-  vtypeGen.io.redirect := io.redirect
+  vtypeGen.io.redirect := io.vtypeRedirect
   vtypeGen.io.commitVType := io.commitVType
   vtypeGen.io.walkVType := io.walkVType
   vtypeGen.io.vsetvlVType := io.vsetvlVType

src/main/scala/xiangshan/backend/decode/VTypeGen.scala

@@ -59,7 +59,9 @@ class VTypeGen(implicit p: Parameters) extends XSModule{
 
   private val vtypeNew = vsetModule.io.out.vconfig.vtype
 
-  when(io.commitVType.vtype.valid) {
+  when(io.commitVType.hasVsetvl) {
+    vtypeArchNext := io.vsetvlVType
+  }.elsewhen(io.commitVType.vtype.valid) {
     vtypeArchNext := io.commitVType.vtype.bits
   }
 
@@ -71,12 +73,10 @@ class VTypeGen(implicit p: Parameters) extends XSModule{
     lastSpecVTypeNext.bits := vtypeSpec
     vtypeSpecNext := io.vsetvlVType
   }.elsewhen(io.walkVType.valid) {
-    lastSpecVTypeNext.valid := true.B
-    lastSpecVTypeNext.bits := vtypeSpec
+    lastSpecVTypeNext.valid := false.B
     vtypeSpecNext := io.walkVType.bits
   }.elsewhen(io.redirect) {
-    lastSpecVTypeNext.valid := true.B
-    lastSpecVTypeNext.bits := vtypeSpec
+    lastSpecVTypeNext.valid := false.B
     vtypeSpecNext := vtypeArch
   }.elsewhen(inHasVset && io.canUpdateVType) {
     lastSpecVTypeNext.valid := true.B

src/main/scala/xiangshan/backend/rob/VTypeBuffer.scala

@@ -165,6 +165,8 @@ class VTypeBuffer(size: Int)(implicit p: Parameters) extends XSModule with HasCi
 
   walkPtr := walkPtrNext
 
+  private val useSnapshot = (state === s_idle && stateNext === s_walk) || (state === s_walk && io.snpt.useSnpt && io.redirect.valid)
+
   // update enq ptr
   private val enqPtrNext = Mux(
     state === s_walk && stateNext === s_idle,
@@ -217,9 +219,6 @@ class VTypeBuffer(size: Int)(implicit p: Parameters) extends XSModule with HasCi
   private val infoVec = Wire(Vec(CommitWidth, VType()))
   private val hasVsetvlVec = Wire(Vec(CommitWidth, Bool()))
 
-  private val isCommit = state === s_idle || state === s_spcl_walk
-  private val isWalk = state === s_walk || state === s_spcl_walk
-
   for (i <- 0 until CommitWidth) {
     commitValidVec(i) := state === s_idle && i.U < commitSize || state === s_spcl_walk && i.U < spclWalkSize
     walkValidVec(i) := state === s_walk && i.U < walkSize || state === s_spcl_walk && i.U < spclWalkSize
@@ -278,7 +277,7 @@ class VTypeBuffer(size: Int)(implicit p: Parameters) extends XSModule with HasCi
     // special walk use commit vtype
     decodeResumeVType.valid := commitVTypeValid
     decodeResumeVType.bits := newestArchVType
-  }.elsewhen (state === s_walk && stateLast === s_idle) {
+  }.elsewhen (useSnapshot) {
     // use snapshot vtype
     decodeResumeVType.valid := true.B
     decodeResumeVType.bits := walkVtypeSnapshots(snptSelect)
@@ -294,10 +293,10 @@ class VTypeBuffer(size: Int)(implicit p: Parameters) extends XSModule with HasCi
   // update vtype in decode when VTypeBuffer resumes from walk state
   // note that VTypeBuffer can still send resuming request in the first cycle of s_idle
   io.toDecode.isResumeVType := state =/= s_idle || decodeResumeVType.valid
-  io.toDecode.walkVType.valid := isWalk && decodeResumeVType.valid
+  io.toDecode.walkVType.valid := decodeResumeVType.valid
   io.toDecode.walkVType.bits := Mux(io.toDecode.walkVType.valid, decodeResumeVType.bits, 0.U.asTypeOf(VType()))
 
-  io.toDecode.commitVType.vtype.valid := isCommit && commitVTypeValid
+  io.toDecode.commitVType.vtype.valid := commitVTypeValid
   io.toDecode.commitVType.vtype.bits := newestArchVType
 
   // because vsetvl flush pipe, there is only one vset instruction when vsetvl is committed