From 7216fc8e2910db4ad9928944989b4a5d36e0ac86 Mon Sep 17 00:00:00 2001
From: Gabe Black <gabe.black@gmail.com>
Date: Sun, 24 Oct 2021 23:50:05 -0700
Subject: [PATCH] cpu-simple: Use a local temporary for the PC in preExecute.

This avoids having to dynamically allocate and then free a temporary
when working with the pc in preExecute.

Change-Id: Ic86e23d0f0c7e786122a6024a154bb2907a6afcb
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/52071
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
---
 src/cpu/simple/base.cc | 19 ++++++++++---------
 src/cpu/simple/base.hh |  5 +++++
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/src/cpu/simple/base.cc b/src/cpu/simple/base.cc
index 0f11eb982a..48809b5a61 100644
--- a/src/cpu/simple/base.cc
+++ b/src/cpu/simple/base.cc
@@ -313,14 +313,15 @@ BaseSimpleCPU::preExecute()
     t_info.setMemAccPredicate(true);
 
     // decode the instruction
-    std::unique_ptr<PCStateBase> pc_state(thread->pcState().clone());
+    set(preExecuteTempPC, thread->pcState());
+    auto &pc_state = *preExecuteTempPC;
 
     auto &decoder = thread->decoder;
 
-    if (isRomMicroPC(pc_state->microPC())) {
+    if (isRomMicroPC(pc_state.microPC())) {
         t_info.stayAtPC = false;
         curStaticInst = decoder.fetchRomMicroop(
-                pc_state->microPC(), curMacroStaticInst);
+                pc_state.microPC(), curMacroStaticInst);
     } else if (!curMacroStaticInst) {
         //We're not in the middle of a macro instruction
         StaticInstPtr instPtr = NULL;
@@ -328,16 +329,16 @@ BaseSimpleCPU::preExecute()
         //Predecode, ie bundle up an ExtMachInst
         //If more fetch data is needed, pass it in.
         Addr fetch_pc =
-            (pc_state->instAddr() & decoder.pcMask()) + t_info.fetchOffset;
+            (pc_state.instAddr() & decoder.pcMask()) + t_info.fetchOffset;
 
-        decoder.moreBytes(*pc_state, fetch_pc);
+        decoder.moreBytes(pc_state, fetch_pc);
 
         //Decode an instruction if one is ready. Otherwise, we'll have to
         //fetch beyond the MachInst at the current pc.
-        instPtr = decoder.decode(*pc_state);
+        instPtr = decoder.decode(pc_state);
         if (instPtr) {
             t_info.stayAtPC = false;
-            thread->pcState(*pc_state);
+            thread->pcState(pc_state);
         } else {
             t_info.stayAtPC = true;
             t_info.fetchOffset += decoder.moreBytesSize();
@@ -348,13 +349,13 @@ BaseSimpleCPU::preExecute()
         if (instPtr && instPtr->isMacroop()) {
             curMacroStaticInst = instPtr;
             curStaticInst =
-                curMacroStaticInst->fetchMicroop(pc_state->microPC());
+                curMacroStaticInst->fetchMicroop(pc_state.microPC());
         } else {
             curStaticInst = instPtr;
         }
     } else {
         //Read the next micro op from the macro op
-        curStaticInst = curMacroStaticInst->fetchMicroop(pc_state->microPC());
+        curStaticInst = curMacroStaticInst->fetchMicroop(pc_state.microPC());
     }
 
     //If we decoded an instruction this "tick", record information about it.
diff --git a/src/cpu/simple/base.hh b/src/cpu/simple/base.hh
index 8c84ff9944..45fd5ea969 100644
--- a/src/cpu/simple/base.hh
+++ b/src/cpu/simple/base.hh
@@ -42,6 +42,9 @@
 #ifndef __CPU_SIMPLE_BASE_HH__
 #define __CPU_SIMPLE_BASE_HH__
 
+#include <memory>
+
+#include "arch/generic/pcstate.hh"
 #include "base/statistics.hh"
 #include "cpu/base.hh"
 #include "cpu/checker/cpu.hh"
@@ -129,6 +132,8 @@ class BaseSimpleCPU : public BaseCPU
      */
     void traceFault();
 
+    std::unique_ptr<PCStateBase> preExecuteTempPC;
+
   public:
     void checkForInterrupts();
     void setupFetchRequest(const RequestPtr &req);