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, 5 deletions

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*