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>

4 files changed, 40 insertions, 31 deletions

diff --git a/src/cpu/o3/probe/elastic_trace.cc b/src/cpu/o3/probe/elastic_trace.cc
index 508140e0c..a4a201398 100644
--- a/src/cpu/o3/probe/elastic_trace.cc
+++ b/src/cpu/o3/probe/elastic_trace.cc
@@ -124,18 +124,23 @@ ElasticTrace::regEtraceListeners()
     // each probe point.
     listeners.push_back(new ProbeListenerArg<ElasticTrace, RequestPtr>(this,
                         "FetchRequest", &ElasticTrace::fetchReqTrace));
-    listeners.push_back(new ProbeListenerArg<ElasticTrace, DynInstPtr>(this,
-                        "Execute", &ElasticTrace::recordExecTick));
-    listeners.push_back(new ProbeListenerArg<ElasticTrace, DynInstPtr>(this,
-                        "ToCommit", &ElasticTrace::recordToCommTick));
-    listeners.push_back(new ProbeListenerArg<ElasticTrace, DynInstPtr>(this,
-                        "Rename", &ElasticTrace::updateRegDep));
+    listeners.push_back(new ProbeListenerArg<ElasticTrace,
+            DynInstConstPtr>(this, "Execute",
+                &ElasticTrace::recordExecTick));
+    listeners.push_back(new ProbeListenerArg<ElasticTrace,
+            DynInstConstPtr>(this, "ToCommit",
+                &ElasticTrace::recordToCommTick));
+    listeners.push_back(new ProbeListenerArg<ElasticTrace,
+            DynInstConstPtr>(this, "Rename",
+                &ElasticTrace::updateRegDep));
     listeners.push_back(new ProbeListenerArg<ElasticTrace, SeqNumRegPair>(this,
                         "SquashInRename", &ElasticTrace::removeRegDepMapEntry));
-    listeners.push_back(new ProbeListenerArg<ElasticTrace, DynInstPtr>(this,
-                        "Squash", &ElasticTrace::addSquashedInst));
-    listeners.push_back(new ProbeListenerArg<ElasticTrace, DynInstPtr>(this,
-                        "Commit", &ElasticTrace::addCommittedInst));
+    listeners.push_back(new ProbeListenerArg<ElasticTrace,
+            DynInstConstPtr>(this, "Squash",
+                &ElasticTrace::addSquashedInst));
+    listeners.push_back(new ProbeListenerArg<ElasticTrace,
+            DynInstConstPtr>(this, "Commit",
+                &ElasticTrace::addCommittedInst));
     allProbesReg = true;
 }
 
@@ -162,7 +167,7 @@ ElasticTrace::fetchReqTrace(const RequestPtr &req)
 }
 
 void
-ElasticTrace::recordExecTick(const DynInstPtr &dyn_inst)
+ElasticTrace::recordExecTick(const DynInstConstPtr& dyn_inst)
 {
 
     // In a corner case, a retired instruction is propagated backward to the
@@ -199,7 +204,7 @@ ElasticTrace::recordExecTick(const DynInstPtr &dyn_inst)
 }
 
 void
-ElasticTrace::recordToCommTick(const DynInstPtr &dyn_inst)
+ElasticTrace::recordToCommTick(const DynInstConstPtr& dyn_inst)
 {
     // If tracing has just been enabled then the instruction at this stage of
     // execution is far enough that we cannot gather info about its past like
@@ -220,7 +225,7 @@ ElasticTrace::recordToCommTick(const DynInstPtr &dyn_inst)
 }
 
 void
-ElasticTrace::updateRegDep(const DynInstPtr &dyn_inst)
+ElasticTrace::updateRegDep(const DynInstConstPtr& dyn_inst)
 {
     // Get the sequence number of the instruction
     InstSeqNum seq_num = dyn_inst->seqNum;
@@ -298,7 +303,7 @@ ElasticTrace::removeRegDepMapEntry(const SeqNumRegPair &inst_reg_pair)
 }
 
 void
-ElasticTrace::addSquashedInst(const DynInstPtr &head_inst)
+ElasticTrace::addSquashedInst(const DynInstConstPtr& head_inst)
 {
     // If the squashed instruction was squashed before being processed by
     // execute stage then it will not be in the temporary store. In this case
@@ -326,7 +331,7 @@ ElasticTrace::addSquashedInst(const DynInstPtr &head_inst)
 }
 
 void
-ElasticTrace::addCommittedInst(const DynInstPtr &head_inst)
+ElasticTrace::addCommittedInst(const DynInstConstPtr& head_inst)
 {
     DPRINTFR(ElasticTrace, "Attempt to add committed inst [sn:%lli]\n",
                 head_inst->seqNum);
@@ -385,7 +390,7 @@ ElasticTrace::addCommittedInst(const DynInstPtr &head_inst)
 }
 
 void
-ElasticTrace::addDepTraceRecord(const DynInstPtr &head_inst,
+ElasticTrace::addDepTraceRecord(const DynInstConstPtr& head_inst,
                                 InstExecInfo* exec_info_ptr, bool commit)
 {
     // Create a record to assign dynamic intruction related fields.
@@ -648,7 +653,7 @@ ElasticTrace::hasCompCompleted(TraceInfo* past_record,
 }
 
 void
-ElasticTrace::clearTempStoreUntil(const DynInstPtr head_inst)
+ElasticTrace::clearTempStoreUntil(const DynInstConstPtr& head_inst)
 {
     // Clear from temp store starting with the execution info object
     // corresponding the head_inst and continue clearing by decrementing the
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
diff --git a/src/cpu/o3/probe/simple_trace.cc b/src/cpu/o3/probe/simple_trace.cc
index 060b4df13..4c7b676b4 100644
--- a/src/cpu/o3/probe/simple_trace.cc
+++ b/src/cpu/o3/probe/simple_trace.cc
@@ -42,14 +42,14 @@
 #include "base/trace.hh"
 #include "debug/SimpleTrace.hh"
 
-void SimpleTrace::traceCommit(const O3CPUImpl::DynInstPtr &dynInst)
+void SimpleTrace::traceCommit(const O3CPUImpl::DynInstConstPtr& dynInst)
 {
     DPRINTFR(SimpleTrace, "[%s]: Commit 0x%08x %s.\n", name(),
              dynInst->instAddr(),
              dynInst->staticInst->disassemble(dynInst->instAddr()));
 }
 
-void SimpleTrace::traceFetch(const O3CPUImpl::DynInstPtr &dynInst)
+void SimpleTrace::traceFetch(const O3CPUImpl::DynInstConstPtr& dynInst)
 {
     DPRINTFR(SimpleTrace, "[%s]: Fetch 0x%08x %s.\n", name(),
              dynInst->instAddr(),
@@ -58,9 +58,12 @@ void SimpleTrace::traceFetch(const O3CPUImpl::DynInstPtr &dynInst)
 
 void SimpleTrace::regProbeListeners()
 {
-    typedef ProbeListenerArg<SimpleTrace, O3CPUImpl::DynInstPtr> DynInstListener;
-    listeners.push_back(new DynInstListener(this, "Commit", &SimpleTrace::traceCommit));
-    listeners.push_back(new DynInstListener(this, "Fetch", &SimpleTrace::traceFetch));
+    typedef ProbeListenerArg<SimpleTrace,
+            O3CPUImpl::DynInstConstPtr> DynInstListener;
+    listeners.push_back(new DynInstListener(this, "Commit",
+                &SimpleTrace::traceCommit));
+    listeners.push_back(new DynInstListener(this, "Fetch",
+                &SimpleTrace::traceFetch));
 }
 
 SimpleTrace*
diff --git a/src/cpu/o3/probe/simple_trace.hh b/src/cpu/o3/probe/simple_trace.hh
index 663128810..928062eaa 100644
--- a/src/cpu/o3/probe/simple_trace.hh
+++ b/src/cpu/o3/probe/simple_trace.hh
@@ -66,8 +66,8 @@ class SimpleTrace : public ProbeListenerObject {
     const std::string name() const { return ProbeListenerObject::name() + ".trace"; }
 
   private:
-    void traceFetch(const O3CPUImpl::DynInstPtr &dynInst);
-    void traceCommit(const O3CPUImpl::DynInstPtr &dynInst);
+    void traceFetch(const O3CPUImpl::DynInstConstPtr& dynInst);
+    void traceCommit(const O3CPUImpl::DynInstConstPtr& dynInst);
 
 };
 #endif//__CPU_O3_PROBE_SIMPLE_TRACE_HH__