arch-power: Add time base instructions

This models a pseudo time base using the simulator ticks
and adds the following instructions.
  * Move From Time Base (mftb)
  * Move From Time Base Upper (mftbu)

Change-Id: Idb619ec3179b2a85925998282075bde8651c68c2
Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40937
Reviewed-by: Boris Shingarov <shingarov@labware.com>
Maintainer: Boris Shingarov <shingarov@labware.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/power/insts/integer.cc

@@ -46,13 +46,17 @@ IntOp::generateDisassembly(Addr pc, const loader::SymbolTable *symtab) const
         myMnemonic == "mtxer" ||
         myMnemonic == "mtlr"  ||
         myMnemonic == "mtctr" ||
-        myMnemonic == "mttar") {
+        myMnemonic == "mttar" ||
+        myMnemonic == "mttb"  ||
+        myMnemonic == "mttbu") {
         printDest = false;
     } else if (myMnemonic == "mfcr"  ||
                myMnemonic == "mfxer" ||
                myMnemonic == "mflr"  ||
                myMnemonic == "mfctr" ||
-               myMnemonic == "mftar") {
+               myMnemonic == "mftar" ||
+               myMnemonic == "mftb"  ||
+               myMnemonic == "mftbu") {
         printSrcs = false;
     }
 

src/arch/power/isa/decoder.isa

@@ -1023,6 +1023,8 @@ decode PO default Unknown::unknown() {
                             0x100: mflr({{ Rt = LR; }});
                             0x120: mfctr({{ Rt = CTR; }});
                             0x1f9: mftar({{ Rt = TAR; }});
+                            0x188: mftb({{ Rt = curTick(); }});
+                            0x1a8: mftbu({{ Rt_uw = curTick() >> 32; }});
                         }
 
                         467: decode SPR {