| 1 | /* This file is part of the program psim. |
| 2 | |
| 3 | Copyright (C) 1994,1995,1996, Andrew Cagney <cagney@highland.com.au> |
| 4 | |
| 5 | This program is free software; you can redistribute it and/or modify |
| 6 | it under the terms of the GNU General Public License as published by |
| 7 | the Free Software Foundation; either version 3 of the License, or |
| 8 | (at your option) any later version. |
| 9 | |
| 10 | This program is distributed in the hope that it will be useful, |
| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 13 | GNU General Public License for more details. |
| 14 | |
| 15 | You should have received a copy of the GNU General Public License |
| 16 | along with this program; if not, see <http://www.gnu.org/licenses/>. |
| 17 | |
| 18 | */ |
| 19 | |
| 20 | /* Instruction decode table: |
| 21 | |
| 22 | <options>:<first>:<last>:<force-first>:<force-last>:<force-expand>:<special>... |
| 23 | |
| 24 | |
| 25 | |
| 26 | Ignore the below: |
| 27 | |
| 28 | |
| 29 | The instruction decode table contains rules that dictate how igen |
| 30 | is going to firstly break down the opcode table and secondly |
| 31 | |
| 32 | The table that follows is used by gen to construct a decision tree |
| 33 | that can identify each possible instruction. Gen then outputs this |
| 34 | decision tree as (according to config) a table or switch statement |
| 35 | as the function idecode. |
| 36 | |
| 37 | In parallel to this, as mentioned above, WITH_EXPANDED_SEMANTICS |
| 38 | determines of the semantic functions themselves should be expanded |
| 39 | in a similar way. |
| 40 | |
| 41 | <first> |
| 42 | <last> |
| 43 | |
| 44 | Range of bits (within the instruction) that should be searched for |
| 45 | an instruction field. Within such ranges, gen looks for opcodes |
| 46 | (constants), registers (strings) and reserved bits (slash) and |
| 47 | according to the rules that follows includes or excludes them from |
| 48 | a possible instruction field. |
| 49 | |
| 50 | <force_first> |
| 51 | <force_last> |
| 52 | |
| 53 | If an instruction field was found, enlarge the field size so that |
| 54 | it is forced to at least include bits starting from <force_first> |
| 55 | (<force_last>). To stop this occuring, use <force_first> = <last> |
| 56 | + 1 and <force_last> = <first> - 1. |
| 57 | |
| 58 | <force_slash> |
| 59 | |
| 60 | Treat `/' fields as a constant instead of variable when looking for |
| 61 | an instruction field. |
| 62 | |
| 63 | <force_expansion> |
| 64 | |
| 65 | Treat any contained register (string) fields as constant when |
| 66 | determining the instruction field. For the instruction decode (and |
| 67 | controled by IDECODE_EXPAND_SEMANTICS) this forces the expansion of |
| 68 | what would otherwize be non constant bits of an instruction. |
| 69 | |
| 70 | <use_switch> |
| 71 | |
| 72 | Should this table be expanded using a switch statement (val 1) and |
| 73 | if so, should it be padded with entries so as to force the compiler |
| 74 | to generate a jump table (val 2). Or a branch table (val 3). |
| 75 | |
| 76 | <special_mask> |
| 77 | <special_value> |
| 78 | <special_rule> |
| 79 | <special_constant> |
| 80 | |
| 81 | Special rule to fine tune how specific (or groups) of instructions |
| 82 | are expanded. The applicability of the rule is determined by |
| 83 | |
| 84 | <special_mask> != 0 && (instruction> & <special_mask>) == <special_value> |
| 85 | |
| 86 | Where <instruction> is obtained by looking only at constant fields |
| 87 | with in an instructions spec. When determining an expansion, the |
| 88 | rule is only considered when a node contains a single instruction. |
| 89 | <special_rule> can be any of: |
| 90 | |
| 91 | 0: for this instruction, expand by earlier rules |
| 92 | 1: expand bits <force_low> .. <force_hi> only |
| 93 | 2: boolean expansion of only zero/non-zero cases |
| 94 | 3: boolean expansion of equality of special constant |
| 95 | |
| 96 | */ |
| 97 | |
| 98 | |
| 99 | typedef enum { |
| 100 | normal_decode_rule, |
| 101 | expand_forced_rule, |
| 102 | boolean_rule, |
| 103 | nr_decode_rules |
| 104 | } decode_special_type; |
| 105 | |
| 106 | typedef enum { |
| 107 | invalid_gen, |
| 108 | array_gen, |
| 109 | switch_gen, |
| 110 | padded_switch_gen, |
| 111 | goto_switch_gen, |
| 112 | nr_decode_gen_types, |
| 113 | } decode_gen_type; |
| 114 | |
| 115 | |
| 116 | typedef struct _decode_table decode_table; |
| 117 | struct _decode_table { |
| 118 | decode_special_type type; |
| 119 | decode_gen_type gen; |
| 120 | int first; |
| 121 | int last; |
| 122 | int force_first; |
| 123 | int force_last; |
| 124 | int force_slash; |
| 125 | char *force_expansion; |
| 126 | unsigned special_mask; |
| 127 | unsigned special_value; |
| 128 | unsigned special_constant; |
| 129 | decode_table *next; |
| 130 | }; |
| 131 | |
| 132 | |
| 133 | extern void force_decode_gen_type |
| 134 | (const char *type); |
| 135 | |
| 136 | extern decode_table *load_decode_table |
| 137 | (char *file_name, |
| 138 | int hi_bit_nr); |
| 139 | |
| 140 | extern void dump_decode_rule |
| 141 | (decode_table *rule, |
| 142 | int indent); |