143 lines
4.1 KiB
C
143 lines
4.1 KiB
C
/* This file is part of the program psim.
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Copyright (C) 1994,1995,1996, Andrew Cagney <cagney@highland.com.au>
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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/* Instruction decode table:
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<options>:<first>:<last>:<force-first>:<force-last>:<force-expand>:<special>...
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Ignore the below:
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The instruction decode table contains rules that dictate how igen
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is going to firstly break down the opcode table and secondly
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The table that follows is used by gen to construct a decision tree
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that can identify each possible instruction. Gen then outputs this
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decision tree as (according to config) a table or switch statement
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as the function idecode.
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In parallel to this, as mentioned above, WITH_EXPANDED_SEMANTICS
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determines of the semantic functions themselves should be expanded
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in a similar way.
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<first>
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<last>
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Range of bits (within the instruction) that should be searched for
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an instruction field. Within such ranges, gen looks for opcodes
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(constants), registers (strings) and reserved bits (slash) and
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according to the rules that follows includes or excludes them from
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a possible instruction field.
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<force_first>
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<force_last>
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If an instruction field was found, enlarge the field size so that
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it is forced to at least include bits starting from <force_first>
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(<force_last>). To stop this occuring, use <force_first> = <last>
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+ 1 and <force_last> = <first> - 1.
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<force_slash>
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Treat `/' fields as a constant instead of variable when looking for
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an instruction field.
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<force_expansion>
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Treat any contained register (string) fields as constant when
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determining the instruction field. For the instruction decode (and
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controled by IDECODE_EXPAND_SEMANTICS) this forces the expansion of
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what would otherwize be non constant bits of an instruction.
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<use_switch>
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Should this table be expanded using a switch statement (val 1) and
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if so, should it be padded with entries so as to force the compiler
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to generate a jump table (val 2). Or a branch table (val 3).
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<special_mask>
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<special_value>
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<special_rule>
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<special_constant>
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Special rule to fine tune how specific (or groups) of instructions
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are expanded. The applicability of the rule is determined by
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<special_mask> != 0 && (instruction> & <special_mask>) == <special_value>
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Where <instruction> is obtained by looking only at constant fields
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with in an instructions spec. When determining an expansion, the
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rule is only considered when a node contains a single instruction.
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<special_rule> can be any of:
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0: for this instruction, expand by earlier rules
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1: expand bits <force_low> .. <force_hi> only
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2: boolean expansion of only zero/non-zero cases
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3: boolean expansion of equality of special constant
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*/
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typedef enum {
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normal_decode_rule,
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expand_forced_rule,
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boolean_rule,
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nr_decode_rules
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} decode_special_type;
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typedef enum {
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invalid_gen,
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array_gen,
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switch_gen,
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padded_switch_gen,
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goto_switch_gen,
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nr_decode_gen_types,
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} decode_gen_type;
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typedef struct _decode_table decode_table;
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struct _decode_table {
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decode_special_type type;
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decode_gen_type gen;
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int first;
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int last;
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int force_first;
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int force_last;
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int force_slash;
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char *force_expansion;
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unsigned special_mask;
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unsigned special_value;
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unsigned special_constant;
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decode_table *next;
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};
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extern void force_decode_gen_type
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(const char *type);
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extern decode_table *load_decode_table
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(char *file_name,
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int hi_bit_nr);
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extern void dump_decode_rule
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(decode_table *rule,
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int indent);
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