arch: Mark FailUnimplemented instructions as Invalid instructions (#1247)

This is a follow-up on the discussion here [1].

The IsInvalid flag was previously defined as an instruction that does
not appear in the ISA. However, a micro-architecture can choose to not
recognize an instruction in and raise illegal instruction fault even if
the instruction is in the ISA.

This change modifies the definition of a Invalid instruction such that,
if a StaticInst instruction is marked as IsInvalid, it means the
instruction is not recognized by the decoder. This means that any
instruction recognized by the decoder are not invalid, even if the
instruction is not in the official ISA spec; e.g., m5
pseudo-instructions.

Note that instructions that are recognized by the decoder but are chosen
to act as a nop are not invalid. This applies to WarnUnimplemented
instructions, e.g. hint instructions.

[1] https://github.com/gem5/gem5/pull/1071

Change-Id: I1371b222d8b06793d47f434d0f148c5571672068

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

src/arch/arm/insts/pseudo.cc

@@ -116,6 +116,7 @@ FailUnimplemented::FailUnimplemented(const char *_mnemonic,
     // don't call execute() (which panics) if we're on a
     // speculative path
     flags[IsNonSpeculative] = true;
+    flags[IsInvalid] = true;
 }
 
 FailUnimplemented::FailUnimplemented(const char *_mnemonic,
@@ -127,6 +128,7 @@ FailUnimplemented::FailUnimplemented(const char *_mnemonic,
     // don't call execute() (which panics) if we're on a
     // speculative path
     flags[IsNonSpeculative] = true;
+    flags[IsInvalid] = true;
 }
 
 Fault

src/arch/mips/isa/formats/unimp.isa

@@ -49,6 +49,7 @@ output header {{
             // don't call execute() (which panics) if we're on a
             // speculative path
             flags[IsNonSpeculative] = true;
+            flags[IsInvalid] = true;
         }
 
         Fault execute(ExecContext *, trace::InstRecord *) const override;

src/arch/power/isa/formats/unimp.isa

@@ -51,6 +51,7 @@ output header {{
             // don't call execute() (which panics) if we're on a
             // speculative path
             flags[IsNonSpeculative] = true;
+            flags[IsInvalid] = true;
         }
 
         Fault execute(ExecContext *, trace::InstRecord *) const override;

src/arch/sparc/insts/unimp.hh

@@ -59,7 +59,9 @@ class FailUnimplemented : public SparcStaticInst
     /// Constructor
     FailUnimplemented(const char *_mnemonic, ExtMachInst _machInst) :
             SparcStaticInst(_mnemonic, _machInst, No_OpClass)
-    {}
+    {
+        flags[IsInvalid] = true;
+    }
 
     Fault
     execute(ExecContext *xc, trace::InstRecord *traceData) const override

src/arch/x86/isa/formats/unimp.isa

@@ -58,6 +58,7 @@ output header {{
             // don't call execute() (which panics) if we're on a
             // speculative path
             flags[IsNonSpeculative] = true;
+            flags[IsInvalid] = true;
         }
 
         Fault execute(ExecContext *, trace::InstRecord *) const override;