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/* This file is part of the program psim.
Copyright (C) 1994,1995,1996, 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 3 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, see <http://www.gnu.org/licenses/>.
*/
/* Instruction decode table:
<options>:<first>:<last>:<force-first>:<force-last>:<force-expand>:<special>...
Ignore the below:
The instruction decode table contains rules that dictate how igen
is going to firstly break down the opcode table and secondly
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.
<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 instruction 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). Or a branch table (val 3).
<special_mask>
<special_value>
<special_rule>
<special_constant>
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
3: boolean expansion of equality of special constant
*/
typedef enum {
normal_decode_rule,
expand_forced_rule,
boolean_rule,
nr_decode_rules
} decode_special_type;
typedef enum {
invalid_gen,
array_gen,
switch_gen,
padded_switch_gen,
goto_switch_gen,
nr_decode_gen_types,
} decode_gen_type;
typedef struct _decode_table decode_table;
struct _decode_table {
decode_special_type type;
decode_gen_type gen;
int first;
int last;
int force_first;
int force_last;
int force_slash;
char *force_expansion;
unsigned special_mask;
unsigned special_value;
unsigned special_constant;
decode_table *next;
};
extern void force_decode_gen_type
(const char *type);
extern decode_table *load_decode_table
(const char *file_name,
int hi_bit_nr);
extern void dump_decode_rule
(decode_table *rule,
int indent);
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