sim/ppc/ld-decode.h

   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 2 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, write to the Free Software
  17     Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  18
  19     */
  20
  21 /* Instruction decode table:
  22
  23    <options>:<first>:<last>:<force-first>:<force-last>:<force-expand>:<special>...
  24
  25
  26
  27    Ignore the below:
  28
  29
  30    The instruction decode table contains rules that dictate how igen
  31    is going to firstly break down the opcode table and secondly
  32
  33    The table that follows is used by gen to construct a decision tree
  34    that can identify each possible instruction.  Gen then outputs this
  35    decision tree as (according to config) a table or switch statement
  36    as the function idecode.
  37
  38    In parallel to this, as mentioned above, WITH_EXPANDED_SEMANTICS
  39    determines of the semantic functions themselves should be expanded
  40    in a similar way.
  41
  42    <first>
  43    <last>
  44
  45    Range of bits (within the instruction) that should be searched for
  46    an instruction field.  Within such ranges, gen looks for opcodes
  47    (constants), registers (strings) and reserved bits (slash) and
  48    according to the rules that follows includes or excludes them from
  49    a possible instruction field.
  50
  51    <force_first>
  52    <force_last>
  53
  54    If an instruction field was found, enlarge the field size so that
  55    it is forced to at least include bits starting from <force_first>
  56    (<force_last>).  To stop this occuring, use <force_first> = <last>
  57    + 1 and <force_last> = <first> - 1.
  58
  59    <force_slash>
  60
  61    Treat `/' fields as a constant instead of variable when looking for
  62    an instruction field.
  63
  64    <force_expansion>
  65
  66    Treat any contained register (string) fields as constant when
  67    determining the instruction field.  For the instruction decode (and
  68    controled by IDECODE_EXPAND_SEMANTICS) this forces the expansion of
  69    what would otherwize be non constant bits of an instruction.
  70
  71    <use_switch>
  72
  73    Should this table be expanded using a switch statement (val 1) and
  74    if so, should it be padded with entries so as to force the compiler
  75    to generate a jump table (val 2). Or a branch table (val 3).
  76
  77    <special_mask>
  78    <special_value>
  79    <special_rule>
  80    <special_constant>
  81
  82    Special rule to fine tune how specific (or groups) of instructions
  83    are expanded.  The applicability of the rule is determined by
  84
  85      <special_mask> != 0 && (instruction> & <special_mask>) == <special_value>
  86
  87    Where <instruction> is obtained by looking only at constant fields
  88    with in an instructions spec.  When determining an expansion, the
  89    rule is only considered when a node contains a single instruction.
  90    <special_rule> can be any of:
  91
  92         0: for this instruction, expand by earlier rules
  93         1: expand bits <force_low> .. <force_hi> only
  94         2: boolean expansion of only zero/non-zero cases
  95         3: boolean expansion of equality of special constant
  96
  97         */
  98
  99
 100 typedef enum {
 101   normal_decode_rule,
 102   expand_forced_rule,
 103   boolean_rule,
 104   nr_decode_rules
 105 } decode_special_type;
 106
 107 typedef enum {
 108   invalid_gen,
 109   array_gen,
 110   switch_gen,
 111   padded_switch_gen,
 112   goto_switch_gen,
 113   nr_decode_gen_types,
 114 } decode_gen_type;
 115
 116
 117 typedef struct _decode_table decode_table;
 118 struct _decode_table {
 119   decode_special_type type;
 120   decode_gen_type gen;
 121   int first;
 122   int last;
 123   int force_first;
 124   int force_last;
 125   int force_slash;
 126   char *force_expansion;
 127   unsigned special_mask;
 128   unsigned special_value;
 129   unsigned special_constant;
 130   decode_table *next;
 131 };
 132
 133
 134 extern void force_decode_gen_type
 135 (const char *type);
 136
 137 extern decode_table *load_decode_table
 138 (char *file_name,
 139  int hi_bit_nr);
 140
 141 extern void dump_decode_rule
 142 (decode_table *rule,
 143  int indent);