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>

2 files changed, 14 insertions, 13 deletions

diff --git a/src/cpu/checker/cpu.hh b/src/cpu/checker/cpu.hh
index bee72253e..cb87f622a 100644
--- a/src/cpu/checker/cpu.hh
+++ b/src/cpu/checker/cpu.hh
@@ -397,7 +397,8 @@ class CheckerCPU : public BaseCPU, public ExecContext
         setVecElemResult(val);
     }
 
-    bool readPredicate() override { return thread->readPredicate(); }
+    bool readPredicate() const override { return thread->readPredicate(); }
+
     void setPredicate(bool val) override
     {
         thread->setPredicate(val);
@@ -572,18 +573,18 @@ class Checker : public CheckerCPU
 
     void advancePC(const Fault &fault);
 
-    void verify(DynInstPtr &inst);
+    void verify(const DynInstPtr &inst);
 
-    void validateInst(DynInstPtr &inst);
-    void validateExecution(DynInstPtr &inst);
+    void validateInst(const DynInstPtr &inst);
+    void validateExecution(const DynInstPtr &inst);
     void validateState();
 
-    void copyResult(DynInstPtr &inst, const InstResult& mismatch_val,
+    void copyResult(const DynInstPtr &inst, const InstResult& mismatch_val,
                     int start_idx);
     void handlePendingInt();
 
   private:
-    void handleError(DynInstPtr &inst)
+    void handleError(const DynInstPtr &inst)
     {
         if (exitOnError) {
             dumpAndExit(inst);
@@ -592,7 +593,7 @@ class Checker : public CheckerCPU
         }
     }
 
-    void dumpAndExit(DynInstPtr &inst);
+    void dumpAndExit(const DynInstPtr &inst);
 
     bool updateThisCycle;
 
diff --git a/src/cpu/checker/cpu_impl.hh b/src/cpu/checker/cpu_impl.hh
index 57282cd13..4fa59564a 100644
--- a/src/cpu/checker/cpu_impl.hh
+++ b/src/cpu/checker/cpu_impl.hh
@@ -124,7 +124,7 @@ Checker<Impl>::handlePendingInt()
 
 template <class Impl>
 void
-Checker<Impl>::verify(DynInstPtr &completed_inst)
+Checker<Impl>::verify(const DynInstPtr &completed_inst)
 {
     DynInstPtr inst;
 
@@ -456,7 +456,7 @@ Checker<Impl>::takeOverFrom(BaseCPU *oldCPU)
 
 template <class Impl>
 void
-Checker<Impl>::validateInst(DynInstPtr &inst)
+Checker<Impl>::validateInst(const DynInstPtr &inst)
 {
     if (inst->instAddr() != thread->instAddr()) {
         warn("%lli: PCs do not match! Inst: %s, checker: %s",
@@ -477,7 +477,7 @@ Checker<Impl>::validateInst(DynInstPtr &inst)
 
 template <class Impl>
 void
-Checker<Impl>::validateExecution(DynInstPtr &inst)
+Checker<Impl>::validateExecution(const DynInstPtr &inst)
 {
     InstResult checker_val;
     InstResult inst_val;
@@ -595,8 +595,8 @@ Checker<Impl>::validateState()
 
 template <class Impl>
 void
-Checker<Impl>::copyResult(DynInstPtr &inst, const InstResult& mismatch_val,
-                          int start_idx)
+Checker<Impl>::copyResult(const DynInstPtr &inst,
+                          const InstResult& mismatch_val, int start_idx)
 {
     // We've already popped one dest off the queue,
     // so do the fix-up then start with the next dest reg;
@@ -672,7 +672,7 @@ Checker<Impl>::copyResult(DynInstPtr &inst, const InstResult& mismatch_val,
 
 template <class Impl>
 void
-Checker<Impl>::dumpAndExit(DynInstPtr &inst)
+Checker<Impl>::dumpAndExit(const DynInstPtr &inst)
 {
     cprintf("Error detected, instruction information:\n");
     cprintf("PC:%s, nextPC:%#x\n[sn:%lli]\n[tid:%i]\n"