arch: Add some helpers to make it easier to cast PCState.

These helpers will make it easier to cast a PCStatePtr into an ISA
specific class with less syntactic fluff. They are currently implemented
with a static_cast for performance reasons, but could be implemented
with a dynamic_cast and an assert for extra debugging if you were
willing to pay the performance overhead. In the future this might be
switched/enabled as an extra debugging mode, like how locking can have
extra checks enabled in the Linux kernel.

Change-Id: Ibc2443c6b991ebc2e5d0240a88436849cb6de2b9
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/52033
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>

src/arch/generic/pcstate.hh

@@ -54,6 +54,20 @@ class PCStateBase : public Serializable
 {
   public:
     virtual ~PCStateBase() = default;
+
+    template<class Target>
+    Target &
+    as()
+    {
+        return static_cast<Target &>(*this);
+    }
+
+    template<class Target>
+    const Target &
+    as() const
+    {
+        return static_cast<const Target &>(*this);
+    }
 };
 
 namespace GenericISA