93 lines
3.4 KiB
Plaintext
93 lines
3.4 KiB
Plaintext
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#
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# This file is part of the program psim.
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#
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# Copyright (C) 1994-1995, Andrew Cagney <cagney@highland.com.au>
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#
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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 2 of the License, or
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# (at your option) any later version.
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#
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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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#
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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, write to the Free Software
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# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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#
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# Instruction decode:
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#
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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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#
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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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#
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# The table contains the following entries:
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#
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# <valid>
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#
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# Must be 1 for the entry to be considered. The last entry must be
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# zero.
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#
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# <first>
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# <last>
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#
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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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#
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# <force_first>
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# <force_last>
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#
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# If an instructioin 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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#
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# <force_slash>
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#
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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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#
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# <force_expansion>
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#
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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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#
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# <use_switch>
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#
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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).
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#
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# <special_mask>
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# <special_value>
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# <special_rule>
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#
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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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#
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# <special_mask> != 0 && (instruction> & <special_mask>) == <special_value>
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#
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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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#
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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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#
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0: 5: 0: 5:0:: 1:0x00000000:0x00000000:0
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21:31:32:-1:0:: 1:0x00000000:0x00000000:0
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