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, 3 insertions, 3 deletions

diff --git a/src/cpu/base_dyn_inst.hh b/src/cpu/base_dyn_inst.hh
index 93cafd694..b4431da1f 100644
--- a/src/cpu/base_dyn_inst.hh
+++ b/src/cpu/base_dyn_inst.hh
@@ -827,7 +827,7 @@ class BaseDynInst : public ExecContext, public RefCounted
     /**Read the micro PC of this instruction. */
     Addr microPC() const { return pc.microPC(); }
 
-    bool readPredicate()
+    bool readPredicate() const
     {
         return instFlags[Predicate];
     }
@@ -855,13 +855,13 @@ class BaseDynInst : public ExecContext, public RefCounted
 
   public:
     /** Returns whether or not the eff. addr. source registers are ready. */
-    bool eaSrcsReady();
+    bool eaSrcsReady() const;
 
     /** Is this instruction's memory access strictly ordered? */
     bool strictlyOrdered() const { return instFlags[IsStrictlyOrdered]; }
 
     /** Has this instruction generated a memory request. */
-    bool hasRequest() { return instFlags[ReqMade]; }
+    bool hasRequest() const { return instFlags[ReqMade]; }
 
     /** Returns iterator to this instruction in the list of all insts. */
     ListIt &getInstListIt() { return instListIt; }