mem: Remove Packet source from ForwardResponseRecord

This patch removes the source field from the ForwardResponseRecord,
but keeps the class as it is part of how the cache identifies
responses to hardware prefetches that are snooped upwards.

src/mem/cache/cache_impl.hh

@@ -385,10 +385,7 @@ class ForwardResponseRecord : public Packet::SenderState
 {
   public:
 
-    PortID prevSrc;
-
-    ForwardResponseRecord(PortID prev_src) : prevSrc(prev_src)
-    {}
+    ForwardResponseRecord() {}
 };
 
 template<class TagStore>
@@ -407,6 +404,9 @@ Cache<TagStore>::recvTimingSnoopResp(PacketPtr pkt)
     assert(!system->bypassCaches());
 
     if (rec == NULL) {
+        // @todo What guarantee do we have that this HardPFResp is
+        // actually for this cache, and not a cache closer to the
+        // memory?
         assert(pkt->cmd == MemCmd::HardPFResp);
         // Check if it's a prefetch response and handle it. We shouldn't
         // get any other kinds of responses without FRRs.
@@ -417,7 +417,6 @@ Cache<TagStore>::recvTimingSnoopResp(PacketPtr pkt)
     }
 
     pkt->popSenderState();
-    pkt->setDest(rec->prevSrc);
     delete rec;
     // @todo someone should pay for this
     pkt->firstWordDelay = pkt->lastWordDelay = 0;
@@ -1542,7 +1541,7 @@ Cache<TagStore>::handleSnoop(PacketPtr pkt, BlkType *blk,
         if (is_timing) {
             Packet snoopPkt(pkt, true, false);  // clear flags, no allocation
             snoopPkt.setExpressSnoop();
-            snoopPkt.pushSenderState(new ForwardResponseRecord(pkt->getSrc()));
+            snoopPkt.pushSenderState(new ForwardResponseRecord());
             // the snoop packet does not need to wait any additional
             // time
             snoopPkt.firstWordDelay = snoopPkt.lastWordDelay = 0;