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/o3/cpu.hh b/src/cpu/o3/cpu.hh
index 1589220a9..19b9a34e0 100644
--- a/src/cpu/o3/cpu.hh
+++ b/src/cpu/o3/cpu.hh
@@ -537,15 +537,15 @@ class FullO3CPU : public BaseO3CPU
     /** Function to add instruction onto the head of the list of the
      *  instructions.  Used when new instructions are fetched.
      */
-    ListIt addInst(DynInstPtr &inst);
+    ListIt addInst(const DynInstPtr &inst);
 
     /** Function to tell the CPU that an instruction has completed. */
-    void instDone(ThreadID tid, DynInstPtr &inst);
+    void instDone(ThreadID tid, const DynInstPtr &inst);
 
     /** Remove an instruction from the front end of the list.  There's
      *  no restriction on location of the instruction.
      */
-    void removeFrontInst(DynInstPtr &inst);
+    void removeFrontInst(const DynInstPtr &inst);
 
     /** Remove all instructions that are not currently in the ROB.
      *  There's also an option to not squash delay slot instructions.*/