mem-cache: Forward snoops when the cache is not responding

When the MSHR is handling a request that will make the block dirty the
current cache commits respond. When that's not the case the cache
should forward any snoops. This CL fixes MSHR::handleSnoop() to
implement this behavior.

Change-Id: I207e3ca4968fd9528fd4cdbfb3eb95f470b4744d
Signed-off-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23668
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>

src/mem/cache/mshr.cc

@@ -465,6 +465,10 @@ MSHR::handleSnoop(PacketPtr pkt, Counter _order)
         return true;
     }
 
+    // Start by determining if we will eventually respond or not,
+    // matching the conditions checked in Cache::handleSnoop
+    const bool will_respond = isPendingModified() && pkt->needsResponse() &&
+        !pkt->isClean();
     if (isPendingModified() || pkt->isInvalidate()) {
         // We need to save and replay the packet in two cases:
         // 1. We're awaiting a writable copy (Modified or Exclusive),
@@ -474,11 +478,6 @@ MSHR::handleSnoop(PacketPtr pkt, Counter _order)
         //    to forward the snoop up the hierarchy after the current
         //    transaction completes.
 
-        // Start by determining if we will eventually respond or not,
-        // matching the conditions checked in Cache::handleSnoop
-        bool will_respond = isPendingModified() && pkt->needsResponse() &&
-                      !pkt->isClean();
-
         // The packet we are snooping may be deleted by the time we
         // actually process the target, and we consequently need to
         // save a copy here. Clear flags and also allocate new data as
@@ -535,7 +534,7 @@ MSHR::handleSnoop(PacketPtr pkt, Counter _order)
         pkt->setHasSharers();
     }
 
-    return true;
+    return will_respond;
 }
 
 MSHR::TargetList