arc64: Determine a branch target of DBNZ correctly

DBNZ instruction was moved from BRANCH class to a separate one - DBNZ.
Thus, it must be processed separately in arc_insn_get_branch_target
to correctly determine an offset for a possible branch.

Signed-off-by: Yuriy Kolerov <ykolerov@synopsys.com>

Author: kolerov

gdb/arc64-tdep.c

@@ -420,6 +420,16 @@ arc_insn_get_branch_target (const struct arc_instruction &insn)
 	 instruction, hence last two bits should be truncated.  */
       return pcrel_addr + align_down (insn.address, 4);
     }
+  /* DBNZ is the only branch instruction that keeps a branch address in
+     the second operand. It must be intercepted and treated differently. */
+  else if (insn.insn_class == DBNZ)
+    {
+      CORE_ADDR pcrel_addr = arc_insn_get_operand_value_signed (insn, 1);
+
+      /* Offset is relative to the 4-byte aligned address of the current
+	 instruction, hence last two bits should be truncated. */
+      return pcrel_addr + align_down (insn.address, 4);
+    }
   /* B, Bcc, BL, BLcc, LP, LPcc: PC = currentPC + operand.  */
   else if (insn.insn_class == BRANCH || insn.insn_class == LOOP)
     {