Instruction decode generator taken from the PowerPC simulator

and being made more generic.

1 files changed, 143 insertions, 0 deletions

diff --git a/sim/igen/ld-decode.h b/sim/igen/ld-decode.h
new file mode 100644
index 0000000..de23181
--- /dev/null
+++ b/sim/igen/ld-decode.h
@@ -0,0 +1,143 @@
+/*  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 2 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, write to the Free Software
+    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ 
+    */
+
+/* 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
+(char *file_name,
+ int hi_bit_nr);
+
+extern void dump_decode_rule
+(decode_table *rule,
+ int indent);