# # This file is part of the program psim. # # Copyright (C) 1994-1995, Andrew Cagney <cagney@highland.com.au> # # This program is free software; you can redistribute it and/or modify # it under the terms of the GNU General Public License as published by # the Free Software Foundation; either version 2 of the License, or # (at your option) any later version. # # This program is distributed in the hope that it will be useful, # but WITHOUT ANY WARRANTY; without even the implied warranty of # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the # GNU General Public License for more details. # # You should have received a copy of the GNU General Public License # along with this program; if not, write to the Free Software # Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. # # Instruction decode: # # The table that follows is used by gen to construct a decision tree # that can identify each possible instruction. Gen then outputs this # decision tree as (according to config) a table or switch statement # as the function idecode. # # In parallel to this, as mentioned above, WITH_EXPANDED_SEMANTICS # determines of the semantic functions themselves should be expanded # in a similar way. # # The table contains the following entries: # # <valid> # # Must be 1 for the entry to be considered. The last entry must be # zero. # # <first> # <last> # # Range of bits (within the instruction) that should be searched for # an instruction field. Within such ranges, gen looks for opcodes # (constants), registers (strings) and reserved bits (slash) and # according to the rules that follows includes or excludes them from # a possible instruction field. # # <force_first> # <force_last> # # If an instructioin field was found, enlarge the field size so that # it is forced to at least include bits starting from <force_first> # (<force_last>). To stop this occuring, use <force_first> = <last> # + 1 and <force_last> = <first> - 1. # # <force_slash> # # Treat `/' fields as a constant instead of variable when looking for # an instruction field. # # <force_expansion> # # Treat any contained register (string) fields as constant when # determining the instruction field. For the instruction decode (and # controled by IDECODE_EXPAND_SEMANTICS) this forces the expansion of # what would otherwize be non constant bits of an instruction. # # <use_switch> # # Should this table be expanded using a switch statement (val 1) and # if so, should it be padded with entries so as to force the compiler # to generate a jump table (val 2). # # <special_mask> # <special_value> # <special_rule> # # Special rule to fine tune how specific (or groups) of instructions # are expanded. The applicability of the rule is determined by # # <special_mask> != 0 && (instruction> & <special_mask>) == <special_value> # # Where <instruction> is obtained by looking only at constant fields # with in an instructions spec. When determining an expansion, the # rule is only considered when a node contains a single instruction. # <special_rule> can be any of: # # 0: for this instruction, expand by earlier rules # 1: expand bits <force_low> .. <force_hi> only # 2: boolean expansion of only zero/non-zero cases # 0: 5: 0: 5:0:: 2:0x00000000:0x00000000:0 21:31:32:-1:0:OE,LR,AA,Rc,LK:1:0x00000000:0x00000000:0 6: 9: 6: 9:0:BO: 1:0xfc000000:0x40000000:1 11:15:11:15:0:RA: 1:0xfc000000:0x38000000:2 11:15:11:15:0:RA: 1:0xfc000000:0x3c000000:2