cpu: Fix the usage of const DynInstPtr

Summary: Usage of const DynInstPtr& when possible and introduction of
move operators to RefCountingPtr.

In many places, scoped references to dynamic instructions do a copy of
the DynInstPtr when a reference would do. This is detrimental to
performance. On top of that, in case there is a need for reference
tracking for debugging, the redundant copies make the process much more
painful than it already is.

Also, from the theoretical point of view, a function/method that
defines a convenience name to access an instruction should not be
considered an owner of the data, i.e., doing a copy and not a reference
is not justified.

On a related topic, C++11 introduces move semantics, and those are
useful when, for example, there is a class modelling a HW structure that
contains a list, and has a getHeadOfList function, to prevent doing a
copy to an internal variable -> update pointer, remove from the list ->
update pointer, return value making a copy to the assined variable ->
update pointer, destroy the returned value -> update pointer.

Change-Id: I3bb46c20ef23b6873b469fd22befb251ac44d2f6
Signed-off-by: Giacomo Gabrielli <giacomo.gabrielli@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/13105
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

1 files changed, 8 insertions, 7 deletions

diff --git a/src/cpu/o3/probe/elastic_trace.hh b/src/cpu/o3/probe/elastic_trace.hh
index 08e02daef..21029b94c 100644
--- a/src/cpu/o3/probe/elastic_trace.hh
+++ b/src/cpu/o3/probe/elastic_trace.hh
@@ -90,6 +90,7 @@ class ElasticTrace : public ProbeListenerObject
 
   public:
     typedef typename O3CPUImpl::DynInstPtr DynInstPtr;
+    typedef typename O3CPUImpl::DynInstConstPtr DynInstConstPtr;
     typedef typename std::pair<InstSeqNum, PhysRegIndex> SeqNumRegPair;
 
     /** Trace record types corresponding to instruction node types */
@@ -132,7 +133,7 @@ class ElasticTrace : public ProbeListenerObject
      *
      * @param dyn_inst pointer to dynamic instruction in flight
      */
-    void recordExecTick(const DynInstPtr &dyn_inst);
+    void recordExecTick(const DynInstConstPtr& dyn_inst);
 
     /**
      * Populate the timestamp field in an InstExecInfo object for an
@@ -141,7 +142,7 @@ class ElasticTrace : public ProbeListenerObject
      *
      * @param dyn_inst pointer to dynamic instruction in flight
      */
-    void recordToCommTick(const DynInstPtr &dyn_inst);
+    void recordToCommTick(const DynInstConstPtr& dyn_inst);
 
     /**
      * Record a Read After Write physical register dependency if there has
@@ -152,7 +153,7 @@ class ElasticTrace : public ProbeListenerObject
      *
      * @param dyn_inst pointer to dynamic instruction in flight
      */
-    void updateRegDep(const DynInstPtr &dyn_inst);
+    void updateRegDep(const DynInstConstPtr& dyn_inst);
 
     /**
      * When an instruction gets squashed the destination register mapped to it
@@ -169,14 +170,14 @@ class ElasticTrace : public ProbeListenerObject
      *
      * @param head_inst pointer to dynamic instruction to be squashed
      */
-    void addSquashedInst(const DynInstPtr &head_inst);
+    void addSquashedInst(const DynInstConstPtr& head_inst);
 
     /**
      * Add an instruction that is at the head of the ROB and is committed.
      *
      * @param head_inst pointer to dynamic instruction to be committed
      */
-    void addCommittedInst(const DynInstPtr &head_inst);
+    void addCommittedInst(const DynInstConstPtr& head_inst);
 
     /** Register statistics for the elastic trace. */
     void regStats();
@@ -385,7 +386,7 @@ class ElasticTrace : public ProbeListenerObject
      * @param exec_info_ptr Pointer to InstExecInfo for that instruction
      * @param commit        True if instruction is committed, false if squashed
      */
-    void addDepTraceRecord(const DynInstPtr &head_inst,
+    void addDepTraceRecord(const DynInstConstPtr& head_inst,
                            InstExecInfo* exec_info_ptr, bool commit);
 
     /**
@@ -394,7 +395,7 @@ class ElasticTrace : public ProbeListenerObject
      *
      * @param head_inst pointer to dynamic instruction
      */
-    void clearTempStoreUntil(const DynInstPtr head_inst);
+    void clearTempStoreUntil(const DynInstConstPtr& head_inst);
 
     /**
      * Calculate the computational delay between an instruction and a