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, 9 insertions, 9 deletions

diff --git a/src/cpu/o3/lsq_unit_impl.hh b/src/cpu/o3/lsq_unit_impl.hh
index c2750be7d..d8f1c39c6 100644
--- a/src/cpu/o3/lsq_unit_impl.hh
+++ b/src/cpu/o3/lsq_unit_impl.hh
@@ -61,8 +61,8 @@
 #include "mem/request.hh"
 
 template<class Impl>
-LSQUnit<Impl>::WritebackEvent::WritebackEvent(DynInstPtr &_inst, PacketPtr _pkt,
-                                              LSQUnit *lsq_ptr)
+LSQUnit<Impl>::WritebackEvent::WritebackEvent(const DynInstPtr &_inst,
+        PacketPtr _pkt, LSQUnit *lsq_ptr)
     : Event(Default_Pri, AutoDelete),
       inst(_inst), pkt(_pkt), lsqPtr(lsq_ptr)
 {
@@ -339,7 +339,7 @@ LSQUnit<Impl>::resizeSQ(unsigned size)
 
 template <class Impl>
 void
-LSQUnit<Impl>::insert(DynInstPtr &inst)
+LSQUnit<Impl>::insert(const DynInstPtr &inst)
 {
     assert(inst->isMemRef());
 
@@ -356,7 +356,7 @@ LSQUnit<Impl>::insert(DynInstPtr &inst)
 
 template <class Impl>
 void
-LSQUnit<Impl>::insertLoad(DynInstPtr &load_inst)
+LSQUnit<Impl>::insertLoad(const DynInstPtr &load_inst)
 {
     assert((loadTail + 1) % LQEntries != loadHead);
     assert(loads < LQEntries);
@@ -381,7 +381,7 @@ LSQUnit<Impl>::insertLoad(DynInstPtr &load_inst)
 
 template <class Impl>
 void
-LSQUnit<Impl>::insertStore(DynInstPtr &store_inst)
+LSQUnit<Impl>::insertStore(const DynInstPtr &store_inst)
 {
     // Make sure it is not full before inserting an instruction.
     assert((storeTail + 1) % SQEntries != storeHead);
@@ -525,7 +525,7 @@ LSQUnit<Impl>::checkSnoop(PacketPtr pkt)
 
 template <class Impl>
 Fault
-LSQUnit<Impl>::checkViolations(int load_idx, DynInstPtr &inst)
+LSQUnit<Impl>::checkViolations(int load_idx, const DynInstPtr &inst)
 {
     Addr inst_eff_addr1 = inst->effAddr >> depCheckShift;
     Addr inst_eff_addr2 = (inst->effAddr + inst->effSize - 1) >> depCheckShift;
@@ -605,7 +605,7 @@ LSQUnit<Impl>::checkViolations(int load_idx, DynInstPtr &inst)
 
 template <class Impl>
 Fault
-LSQUnit<Impl>::executeLoad(DynInstPtr &inst)
+LSQUnit<Impl>::executeLoad(const DynInstPtr &inst)
 {
     using namespace TheISA;
     // Execute a specific load.
@@ -654,7 +654,7 @@ LSQUnit<Impl>::executeLoad(DynInstPtr &inst)
 
 template <class Impl>
 Fault
-LSQUnit<Impl>::executeStore(DynInstPtr &store_inst)
+LSQUnit<Impl>::executeStore(const DynInstPtr &store_inst)
 {
     using namespace TheISA;
     // Make sure that a store exists.
@@ -1105,7 +1105,7 @@ LSQUnit<Impl>::storePostSend(PacketPtr pkt)
 
 template <class Impl>
 void
-LSQUnit<Impl>::writeback(DynInstPtr &inst, PacketPtr pkt)
+LSQUnit<Impl>::writeback(const DynInstPtr &inst, PacketPtr pkt)
 {
     iewStage->wakeCPU();