mem-cache: Fix FIFO replacement

Change FIFO from using curTicks() to using timeTicks counter to
avoid issues where multiple lines are considered to have entered
the cache at the same tick.

Change-Id: I5e0b894eb9bec4f0f8bc8f48ec2766a0fc5079c6
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/65952
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Daniel Carvalho <odanrc@yahoo.com.br>
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>

src/mem/cache/replacement_policies/fifo_rp.cc

@@ -36,11 +36,9 @@
 
 namespace gem5
 {
-
 GEM5_DEPRECATED_NAMESPACE(ReplacementPolicy, replacement_policy);
 namespace replacement_policy
 {
-
 FIFO::FIFO(const Params &p)
   : Base(p)
 {
@@ -51,7 +49,7 @@ FIFO::invalidate(const std::shared_ptr<ReplacementData>& replacement_data)
 {
     // Reset insertion tick
     std::static_pointer_cast<FIFOReplData>(
-        replacement_data)->tickInserted = Tick(0);
+        replacement_data)->tickInserted = ++timeTicks;
 }
 
 void
@@ -65,7 +63,7 @@ FIFO::reset(const std::shared_ptr<ReplacementData>& replacement_data) const
 {
     // Set insertion tick
     std::static_pointer_cast<FIFOReplData>(
-        replacement_data)->tickInserted = curTick();
+        replacement_data)->tickInserted = ++timeTicks;
 }
 
 ReplaceableEntry*

src/mem/cache/replacement_policies/fifo_rp.hh

@@ -56,13 +56,19 @@ class FIFO : public Base
     {
         /** Tick on which the entry was inserted. */
         Tick tickInserted;
-
         /**
          * Default constructor. Invalidate data.
          */
         FIFOReplData() : tickInserted(0) {}
     };
 
+  private:
+    /**
+     * A counter that tracks the number of
+     * ticks since being created to avoid a tie
+     */
+    mutable Tick timeTicks;
+
   public:
     typedef FIFORPParams Params;
     FIFO(const Params &p);