arch, cpu: Factor out the ExecContext into a proper base class

We currently generate and compile one version of the ISA code per CPU
model. This is obviously wasting a lot of resources at compile
time. This changeset factors out the interface into a separate
ExecContext class, which also serves as documentation for the
interface between CPUs and the ISA code. While doing so, this
changeset also fixes up interface inconsistencies between the
different CPU models.

The main argument for using one set of ISA code per CPU model has
always been performance as this avoid indirect branches in the
generated code. However, this argument does not hold water. Booting
Linux on a simulated ARM system running in atomic mode
(opt/10.linux-boot/realview-simple-atomic) is actually 2% faster
(compiled using clang 3.4) after applying this patch. Additionally,
compilation time is decreased by 35%.

2 files changed, 12 insertions, 18 deletions

diff --git a/src/cpu/minor/SConsopts b/src/cpu/minor/SConsopts
index 68c420779..b74e15730 100644
--- a/src/cpu/minor/SConsopts
+++ b/src/cpu/minor/SConsopts
@@ -39,7 +39,4 @@
 
 Import('*')
 
-CpuModel('MinorCPU', 'minor_cpu_exec.cc',
-         '#include "cpu/minor/exec_context.hh"',
-         { 'CPU_exec_context': 'Minor::ExecContext' },
-         default=True)
+CpuModel('MinorCPU', default=True)
diff --git a/src/cpu/minor/exec_context.hh b/src/cpu/minor/exec_context.hh
index df909a95c..f1143498e 100644
--- a/src/cpu/minor/exec_context.hh
+++ b/src/cpu/minor/exec_context.hh
@@ -53,6 +53,7 @@
 #ifndef __CPU_MINOR_EXEC_CONTEXT_HH__
 #define __CPU_MINOR_EXEC_CONTEXT_HH__
 
+#include "cpu/exec_context.hh"
 #include "cpu/minor/execute.hh"
 #include "cpu/minor/pipeline.hh"
 #include "cpu/base.hh"
@@ -69,7 +70,7 @@ class Execute;
  *  separates that interface from other classes such as Pipeline, MinorCPU
  *  and DynMinorInst and makes it easier to see what state is accessed by it.
  */
-class ExecContext
+class ExecContext : public ::ExecContext
 {
   public:
     MinorCPU &cpu;
@@ -119,7 +120,7 @@ class ExecContext
         return NoFault;
     }
 
-    uint64_t
+    IntReg
     readIntRegOperand(const StaticInst *si, int idx)
     {
         return thread.readIntReg(si->srcRegIdx(idx));
@@ -140,7 +141,7 @@ class ExecContext
     }
 
     void
-    setIntRegOperand(const StaticInst *si, int idx, uint64_t val)
+    setIntRegOperand(const StaticInst *si, int idx, IntReg val)
     {
         thread.setIntReg(si->destRegIdx(idx), val);
     }
@@ -174,7 +175,7 @@ class ExecContext
     }
 
     TheISA::PCState
-    pcState()
+    pcState() const
     {
         return thread.pcState();
     }
@@ -250,12 +251,8 @@ class ExecContext
     ThreadContext *tcBase() { return thread.getTC(); }
 
     /* @todo, should make stCondFailures persistent somewhere */
-    unsigned int readStCondFailures() { return 0; }
-    unsigned int
-    setStCondFailures(unsigned int st_cond_failures)
-    {
-        return 0;
-    }
+    unsigned int readStCondFailures() const { return 0; }
+    void setStCondFailures(unsigned int st_cond_failures) {}
 
     int contextId() { return thread.contextId(); }
     /* ISA-specific (or at least currently ISA singleton) functions */
@@ -295,7 +292,7 @@ class ExecContext
     }
 
     /* ALPHA/POWER: Effective address storage */
-    void setEA(Addr &ea)
+    void setEA(Addr ea)
     {
         inst->ea = ea;
     }
@@ -303,14 +300,14 @@ class ExecContext
     BaseCPU *getCpuPtr() { return &cpu; }
 
     /* POWER: Effective address storage */
-    Addr getEA()
+    Addr getEA() const
     {
         return inst->ea;
     }
 
     /* MIPS: other thread register reading/writing */
     uint64_t
-    readRegOtherThread(unsigned idx, ThreadID tid = InvalidThreadID)
+    readRegOtherThread(int idx, ThreadID tid = InvalidThreadID)
     {
         SimpleThread *other_thread = (tid == InvalidThreadID
             ? &thread : cpu.threads[tid]);
@@ -327,7 +324,7 @@ class ExecContext
     }
 
     void
-    setRegOtherThread(unsigned idx, const TheISA::MiscReg &val,
+    setRegOtherThread(int idx, const TheISA::MiscReg &val,
         ThreadID tid = InvalidThreadID)
     {
         SimpleThread *other_thread = (tid == InvalidThreadID