cpu: Add IsInvalid flag to StaticInstFlags

The IsInvalid flag indicates that the static instruction is not part
of the executing ISA and not part of m5's pseudo-instructions. This
flag provides a way to recognize an illegal instruction at the decode
stage.

Change-Id: I2779c6edcd8c5e6a77ea11cad3ff73bacb79d800
Signed-off-by: Hoa Nguyen <hn@hnpl.org>

src/cpu/StaticInstFlags.py

@@ -99,4 +99,5 @@ class StaticInstFlags(Enum):
         "IsHtmStart",  # Starts a HTM transaction
         "IsHtmStop",  # Stops (commits) a HTM transaction
         "IsHtmCancel",  # Explicitely aborts a HTM transaction
+        "IsInvalid",  # An invalid instruction
     ]

src/cpu/static_inst.hh

@@ -196,6 +196,8 @@ class StaticInst : public RefCounted, public StaticInstFlags
     bool isHtmStop() const { return flags[IsHtmStop]; }
     bool isHtmCancel() const { return flags[IsHtmCancel]; }
 
+    bool isInvalid() const { return flags[IsInvalid]; }
+
     bool
     isHtmCmd() const
     {