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      1 /*  This file is part of the program psim.
      2 
      3     Copyright (C) 1994,1995,1996, Andrew Cagney <cagney (at) 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