From 2f515b2af652f1ed8a6cc99474d1c342a6c61716 Mon Sep 17 00:00:00 2001
From: Andrew Waterman <waterman@cs.berkeley.edu>
Date: Fri, 6 Nov 2015 23:25:33 -0800
Subject: [PATCH] Reduce critical path for fdiv valid signal

---
 rocket/src/main/scala/fpu.scala | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/rocket/src/main/scala/fpu.scala b/rocket/src/main/scala/fpu.scala
index e5582ebc..721c9898 100644
--- a/rocket/src/main/scala/fpu.scala
+++ b/rocket/src/main/scala/fpu.scala
@@ -445,6 +445,7 @@ class FPU(implicit p: Parameters) extends CoreModule()(p) {
   val divSqrt_wdata = Wire(Bits())
   val divSqrt_flags = Wire(Bits())
   val divSqrt_in_flight = Reg(init=Bool(false))
+  val divSqrt_killed = Reg(Bool())
 
   // writeback arbitration
   case class Pipe(p: Module, lat: Int, cond: (FPUCtrlSigs) => Bool, res: FPResult)
@@ -527,8 +528,7 @@ class FPU(implicit p: Parameters) extends CoreModule()(p) {
     val divSqrt = Module(new hardfloat.divSqrtRecodedFloat64)
     divSqrt_inReady := Mux(divSqrt.io.sqrtOp, divSqrt.io.inReady_sqrt, divSqrt.io.inReady_div)
     val divSqrt_outValid = divSqrt.io.outValid_div || divSqrt.io.outValid_sqrt
-    val divSqrt_wb_hazard = wen.orR
-    divSqrt.io.inValid := mem_reg_valid && !divSqrt_wb_hazard && !divSqrt_in_flight && !io.killm && (mem_ctrl.div || mem_ctrl.sqrt)
+    divSqrt.io.inValid := mem_reg_valid && (mem_ctrl.div || mem_ctrl.sqrt)
     divSqrt.io.sqrtOp := mem_ctrl.sqrt
     divSqrt.io.a := fpiu.io.as_double.in1
     divSqrt.io.b := fpiu.io.as_double.in2
@@ -536,13 +536,14 @@ class FPU(implicit p: Parameters) extends CoreModule()(p) {
 
     when (divSqrt.io.inValid && divSqrt_inReady) {
       divSqrt_in_flight := true
+      divSqrt_killed := killm
       divSqrt_single := mem_ctrl.single
       divSqrt_waddr := mem_reg_inst(11,7)
       divSqrt_rm := divSqrt.io.roundingMode
     }
 
     when (divSqrt_outValid) {
-      divSqrt_wen := true
+      divSqrt_wen := !divSqrt_killed
       divSqrt_wdata_double := divSqrt.io.out
       divSqrt_in_flight := false
       divSqrt_flags_double := divSqrt.io.exceptionFlags