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, 4 insertions, 4 deletions

diff --git a/src/cpu/o3/lsq_impl.hh b/src/cpu/o3/lsq_impl.hh
index 56b95a5b6..967a496f6 100644
--- a/src/cpu/o3/lsq_impl.hh
+++ b/src/cpu/o3/lsq_impl.hh
@@ -257,7 +257,7 @@ LSQ<Impl>::tick()
 
 template<class Impl>
 void
-LSQ<Impl>::insertLoad(DynInstPtr &load_inst)
+LSQ<Impl>::insertLoad(const DynInstPtr &load_inst)
 {
     ThreadID tid = load_inst->threadNumber;
 
@@ -266,7 +266,7 @@ LSQ<Impl>::insertLoad(DynInstPtr &load_inst)
 
 template<class Impl>
 void
-LSQ<Impl>::insertStore(DynInstPtr &store_inst)
+LSQ<Impl>::insertStore(const DynInstPtr &store_inst)
 {
     ThreadID tid = store_inst->threadNumber;
 
@@ -275,7 +275,7 @@ LSQ<Impl>::insertStore(DynInstPtr &store_inst)
 
 template<class Impl>
 Fault
-LSQ<Impl>::executeLoad(DynInstPtr &inst)
+LSQ<Impl>::executeLoad(const DynInstPtr &inst)
 {
     ThreadID tid = inst->threadNumber;
 
@@ -284,7 +284,7 @@ LSQ<Impl>::executeLoad(DynInstPtr &inst)
 
 template<class Impl>
 Fault
-LSQ<Impl>::executeStore(DynInstPtr &inst)
+LSQ<Impl>::executeStore(const DynInstPtr &inst)
 {
     ThreadID tid = inst->threadNumber;