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 (const char *file_name, 138 int hi_bit_nr); 139 140 extern void dump_decode_rule 141 (decode_table *rule, 142 int indent); 143