如何理解和解决PLY中的冲突

state 24 (134) attribute_instance_optional_list -> attribute_instance_list . (136) attribute_instance_list -> attribute_instance_list . attribute_instance (138) attribute_instance -> . LPAREN ASTERISK attr_spec_list ASTERISK RPAREN ! shift/reduce conflict for LPAREN resolved as shift PLUS reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) MINUS reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) EXCLAMATION reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) NEG reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) AMPERSAND reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) NEGAMPERSAND reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) PIPE reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) NEGPIPE reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) CARET reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) NEGCARET reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) UNBASED_UNSIZED_LITERAL reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) STRING_LITERAL reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) REAL_FLOATINGP_NUMBER reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) REAL_FIXEDP_NUMBER reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) INT_HEX_NUMBER reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) INT_BINARY_NUMBER reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) INT_OCTAL_NUMBER reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) INT_DECIMAL_NUMBER reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) UNSIGNED_NUMBER reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) DOUBLEPLUS reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) DOUBLEMINUS reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) AT reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) TAGGED reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) INOUT reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) INPUT reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) OUTPUT reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) REF reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) ID reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) ESCAPED_ID reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) MODULE reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) MACROMODULE reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) LPAREN shift and go to state 21 ! LPAREN [ reduce using rule 134 (attribute_instance_optional_list -> attribute_instance_list .) ] attribute_instance shift and go to state 49

Grammar Rule 0 S' -> source_text Rule 1 source_text -> timeunits_declaration description_list Rule 2 timeunits_declaration -> timeunit_and_precision Rule 3 timeunits_declaration -> timeunit Rule 4 timeunits_declaration -> timeprecision Rule 5 timeunits_declaration -> timeunit timeprecision Rule 6 timeunits_declaration -> timeprecision timeunit Rule 7 timeunits_declaration -> empty Rule 8 timeunit_and_precision -> TIMEUNIT time_literal SLASH time_literal SEMICOLON Rule 9 timeunit -> TIMEUNIT time_literal SEMICOLON Rule 10 timeprecision -> TIMEPRECISION time_literal SEMICOLON Rule 11 time_literal -> UNSIGNED_NUMBER time_unit Rule 12 time_literal -> REAL_FIXEDP_NUMBER time_unit Rule 13 time_unit -> S Rule 14 time_unit -> MS Rule 15 time_unit -> US Rule 16 time_unit -> NS Rule 17 time_unit -> PS Rule 18 time_unit -> FS Rule 19 description_list -> description_list description Rule 20 description_list -> description Rule 21 description -> module_declaration Rule 22 module_declaration -> module_nonansi_header timeunits_declaration module_item_list module_footer Rule 23 module_declaration -> module_ansi_header timeunits_declaration non_port_module_item_list module_footer Rule 24 module_declaration -> module_implicit_header timeunits_declaration module_item module_footer Rule 25 module_declaration -> EXTERN module_nonansi_header Rule 26 module_declaration -> EXTERN module_ansi_header Rule 27 module_nonansi_header -> attribute_instance_optional_list module_keyword lifetime module_identifier package_import_declaration_list parameter_port_list list_of_ports SEMICOLON Rule 28 module_ansi_header -> attribute_instance_optional_list module_keyword lifetime module_identifier package_import_declaration_list parameter_port_list list_of_port_declarations_list SEMICOLON Rule 29 module_implicit_header -> attribute_instance_optional_list module_keyword lifetime module_identifier LPAREN DOT ASTERISK RPAREN SEMICOLON Rule 30 module_keyword -> MODULE Rule 31 module_keyword -> MACROMODULE Rule 32 module_footer -> ENDMODULE COLON module_identifier Rule 33 module_footer -> ENDMODULE Rule 34 module_item -> port_declaration SEMICOLON Rule 35 module_item -> non_port_module_item Rule 36 port_declaration -> attribute_instance_optional_list inout_declaration Rule 37 port_declaration -> attribute_instance_optional_list input_declaration Rule 38 port_declaration -> attribute_instance_optional_list output_declaration Rule 39 port_declaration -> attribute_instance_optional_list ref_declaration Rule 40 port_declaration -> attribute_instance_optional_list interface_port_declaration Rule 41 inout_declaration -> INOUT net_port_type list_of_port_identifiers Rule 42 input_declaration -> INPUT net_port_type list_of_port_identifiers Rule 43 input_declaration -> INPUT variable_port_type list_of_variable_identifiers Rule 44 output_declaration -> OUTPUT net_port_type list_of_port_identifiers Rule 45 interface_port_declaration -> interface_identifier list_of_interface_identifiers Rule 46 interface_port_declaration -> interface_identifier DOT modport_identifier list_of_interface_identifiers Rule 47 ref_declaration -> REF variable_port_type list_of_variable_identifiers Rule 48 casting_type -> simple_type Rule 49 casting_type -> constant_primary Rule 50 casting_type -> signing Rule 51 casting_type -> STRING Rule 52 casting_type -> CONST Rule 53 data_type -> integer_vector_type optional_signing optional_packed_dimension Rule 54 data_type -> integer_atom_type optional_signing Rule 55 data_type -> non_integer_type Rule 56 data_type -> struct_union LBRACE struct_union_member_list RBRACE optional_packed_dimension_list Rule 57 data_type -> ENUM LBRACE optional_enum_name_declaration_list RBRACE optional_packed_dimension_list Rule 58 data_type -> ENUM enum_base_type LBRACE optional_enum_name_declaration_list RBRACE optional_packed_dimension_list Rule 59 data_type -> STRING Rule 60 data_type -> CHANDLE Rule 61 data_type -> VIRTUAL interface_identifier optional_parameter_value_assignment optional_modport_identifier Rule 62 data_type -> VIRTUAL INTERFACE interface_identifier optional_parameter_value_assignment optional_modport_identifier Rule 63 data_type -> type_identifier optional_packed_dimension_list Rule 64 data_type -> class_scope type_identifier optional_packed_dimension_list Rule 65 data_type -> package_scope type_identifier optional_packed_dimension_list Rule 66 data_type -> class_type Rule 67 data_type -> EVENT Rule 68 data_type -> ps_covergroup_identifier Rule 69 data_type -> type_reference Rule 70 data_type_or_implicit -> data_type Rule 71 data_type_or_implicit -> implicit_data_type Rule 72 implicit_data_type -> optional_signing optional_packed_dimension_list Rule 73 enum_base_type -> integer_atom_type optional_signing Rule 74 enum_base_type -> integer_vector_type optional_signing optional_packed_dimension Rule 75 enum_base_type -> type_identifier optional_packed_dimension Rule 76 enum_name_declaration -> enum_identifier optional_enum_identifier_pointer Rule 77 enum_name_declaration -> enum_identifier optional_enum_identifier_pointer EQUALS constant_expression Rule 78 optional_enum_identifier_pointer -> LBRACKET integral_number RBRACKET Rule 79 optional_enum_identifier_pointer -> LBRACKET integral_number COLON integral_number RBRACKET Rule 80 optional_enum_identifier_pointer -> empty Rule 81 class_scope -> class_type DOUBLECOLON Rule 82 class_type -> ps_class_identifier optional_parameter_value_assignment Rule 83 class_type -> ps_class_identifier optional_parameter_value_assignment parametrized_class_list Rule 84 parametrized_class_list -> parametrized_class_list DOUBLECOLON class_identifier optional_parameter_value_assignment Rule 85 parametrized_class_list -> DOUBLECOLON class_identifier optional_parameter_value_assignment Rule 86 integer_type -> integer_vector_type Rule 87 integer_type -> integer_atom_type Rule 88 integer_atom_type -> BYTE Rule 89 integer_atom_type -> SHORTINT Rule 90 integer_atom_type -> INT Rule 91 integer_atom_type -> LONGINT Rule 92 integer_atom_type -> INTEGER Rule 93 integer_atom_type -> TIME Rule 94 integer_vector_type -> BIT Rule 95 integer_vector_type -> LOGIC Rule 96 integer_vector_type -> REG Rule 97 non_integer_type -> SHORTREAL Rule 98 non_integer_type -> REAL Rule 99 non_integer_type -> REALTIME Rule 100 net_type -> SUPPLY0 Rule 101 net_type -> SUPPLY1 Rule 102 net_type -> TRI Rule 103 net_type -> TRIAND Rule 104 net_type -> TRIOR Rule 105 net_type -> TRIREG Rule 106 net_type -> TRI0 Rule 107 net_type -> TRI1 Rule 108 net_type -> UWIRE Rule 109 net_type -> WIRE Rule 110 net_type -> WAND Rule 111 net_type -> WOR Rule 112 net_port_type -> data_type_or_implicit Rule 113 net_port_type -> net_type data_type_or_implicit Rule 114 net_port_type -> net_type_identifier Rule 115 net_port_type -> INTERCONNECT implicit_data_type Rule 116 variable_port_type -> var_data_type Rule 117 var_data_type -> data_type Rule 118 var_data_type -> VAR data_type_or_implicit Rule 119 signing -> SIGNED Rule 120 signing -> UNSIGNED Rule 121 simple_type -> integer_type Rule 122 simple_type -> non_integer_type Rule 123 simple_type -> ps_type_identifier Rule 124 simple_type -> ps_parameter_identifier Rule 125 struct_union_member -> attribute_instance_optional_list data_type_or_void list_of_variable_decl_assignments Rule 126 struct_union_member -> attribute_instance_optional_list random_qualifier data_type_or_void list_of_variable_decl_assignments Rule 127 data_type_or_void -> data_type Rule 128 data_type_or_void -> VOID Rule 129 struct_union -> STRUCT Rule 130 struct_union -> UNION Rule 131 struct_union -> UNION TAGGED Rule 132 type_reference -> TYPE LPAREN expression RPAREN Rule 133 type_reference -> TYPE LPAREN data_type RPAREN Rule 134 attribute_instance_optional_list -> attribute_instance_list Rule 135 attribute_instance_optional_list -> empty Rule 136 attribute_instance_list -> attribute_instance_list attribute_instance Rule 137 attribute_instance_list -> attribute_instance Rule 138 attribute_instance -> LPAREN ASTERISK attr_spec_list ASTERISK RPAREN Rule 139 attr_spec_list -> attr_spec_list COMMA attr_spec Rule 140 attr_spec_list -> attr_spec Rule 141 attr_spec -> attr_name Rule 142 attr_spec -> attr_name EQUALS constant_expression Rule 143 attr_name -> identifier Rule 144 inc_or_dec_expression -> inc_or_dec_operator attribute_instance_optional_list variable_lvalue Rule 145 inc_or_dec_expression -> variable_lvalue attribute_instance_optional_list inc_or_dec_operator Rule 146 conditional_expression -> cond_predicate INTERROGATION attribute_instance_optional_list expression COLON expression Rule 147 constant_expression -> constant_primary Rule 148 constant_expression -> unary_operator attribute_instance_optional_list constant_primary Rule 149 constant_expression -> constant_expression binary_operator attribute_instance_optional_list constant_expression Rule 150 constant_expression -> constant_expression INTERROGATION attribute_instance_optional_list constant_expression COLON constant_expression Rule 151 constant_mintypmax_expression -> constant_expression Rule 152 constant_mintypmax_expression -> constant_expression COLON constant_expression COLON constant_expression Rule 153 constant_param_expression -> constant_mintypmax_expression Rule 154 constant_param_expression -> data_type Rule 155 constant_param_expression -> DOLLAR Rule 156 param_expression -> mintypmax_expression Rule 157 param_expression -> data_type Rule 158 param_expression -> DOLLAR Rule 159 constant_range_expression -> constant_expression Rule 160 constant_range_expression -> constant_part_select_range Rule 161 constant_part_select_range -> constant_range Rule 162 constant_part_select_range -> constant_indexed_range Rule 163 constant_range -> constant_expression COLON constant_expression Rule 164 constant_indexed_range -> constant_expression PLUSCOLON constant_expression Rule 165 constant_indexed_range -> constant_expression MINUSCOLON constant_expression Rule 166 expression -> primary Rule 167 expression -> unary_operator attribute_instance_optional_list primary Rule 168 expression -> inc_or_dec_expression Rule 169 expression -> LPAREN operator_assignment RPAREN Rule 170 expression -> expression binary_operator attribute_instance_optional_list expression Rule 171 expression -> conditional_expression Rule 172 expression -> inside_expression Rule 173 expression -> tagged_union_expression Rule 174 tagged_union_expression -> TAGGED member_identifier Rule 175 tagged_union_expression -> TAGGED member_identifier expression Rule 176 inside_expression -> expression INSIDE LBRACE open_range_list RBRACE Rule 177 value_range -> expression Rule 178 value_range -> LBRACKET expression COLON expression RBRACKET Rule 179 mintypmax_expression -> expression Rule 180 mintypmax_expression -> expression COLON expression COLON expression Rule 181 module_path_conditional_expression -> module_path_expression INTERROGATION attribute_instance_optional_list module_path_expression COLON module_path_expression Rule 182 module_path_expression -> module_path_primary Rule 183 module_path_expression -> unary_module_path_operator attribute_instance_optional_list module_path_primary Rule 184 module_path_expression -> module_path_expression binary_module_path_operator attribute_instance_optional_list module_path_expression Rule 185 module_path_expression -> module_path_conditional_expression Rule 186 module_path_mintypmax_expression -> module_path_expression Rule 187 module_path_mintypmax_expression -> module_path_expression COLON module_path_expression COLON module_path_expression Rule 188 part_select_range -> constant_range Rule 189 part_select_range -> indexed_range Rule 190 indexed_range -> expression PLUSCOLON constant_expression Rule 191 indexed_range -> expression MINUSCOLON constant_expression Rule 192 genvar_expression -> constant_expression Rule 193 constant_primary -> primary_literal Rule 194 primary_literal -> number Rule 195 primary_literal -> time_literal Rule 196 primary_literal -> UNBASED_UNSIZED_LITERAL Rule 197 primary_literal -> STRING_LITERAL Rule 198 number -> REAL_FLOATINGP_NUMBER Rule 199 number -> REAL_FIXEDP_NUMBER Rule 200 number -> INT_HEX_NUMBER Rule 201 number -> INT_BINARY_NUMBER Rule 202 number -> INT_OCTAL_NUMBER Rule 203 number -> INT_DECIMAL_NUMBER Rule 204 number -> UNSIGNED_NUMBER Rule 205 unary_operator -> PLUS Rule 206 unary_operator -> MINUS Rule 207 unary_operator -> EXCLAMATION Rule 208 unary_operator -> NEG Rule 209 unary_operator -> AMPERSAND Rule 210 unary_operator -> NEGAMPERSAND Rule 211 unary_operator -> PIPE Rule 212 unary_operator -> NEGPIPE Rule 213 unary_operator -> CARET Rule 214 unary_operator -> NEGCARET Rule 215 binary_operator -> PLUS Rule 216 binary_operator -> MINUS Rule 217 binary_operator -> ASTERISK Rule 218 binary_operator -> SLASH Rule 219 binary_operator -> PERCENT Rule 220 binary_operator -> ISEQUAL Rule 221 binary_operator -> NISEQUAL Rule 222 binary_operator -> CISEQUAL Rule 223 binary_operator -> NCISEQUAL Rule 224 binary_operator -> WISEQUAL Rule 225 binary_operator -> NWISEQUAL Rule 226 binary_operator -> DOUBLEAMPERSAND Rule 227 binary_operator -> DOUBLEPIPE Rule 228 binary_operator -> DOUBLEASTERISK Rule 229 binary_operator -> LT Rule 230 binary_operator -> LE Rule 231 binary_operator -> GT Rule 232 binary_operator -> GE Rule 233 binary_operator -> AMPERSAND Rule 234 binary_operator -> PIPE Rule 235 binary_operator -> CARET Rule 236 binary_operator -> NEGCARET Rule 237 binary_operator -> RSHIFT Rule 238 binary_operator -> LSHIFT Rule 239 binary_operator -> ARSHIFT Rule 240 binary_operator -> ALSHIFT Rule 241 binary_operator -> IMPLICATION Rule 242 binary_operator -> EQUIVALENCE Rule 243 inc_or_dec_operator -> DOUBLEPLUS Rule 244 inc_or_dec_operator -> DOUBLEMINUS Rule 245 unary_module_path_operator -> EXCLAMATION Rule 246 unary_module_path_operator -> NEG Rule 247 unary_module_path_operator -> AMPERSAND Rule 248 unary_module_path_operator -> NEGAMPERSAND Rule 249 unary_module_path_operator -> PIPE Rule 250 unary_module_path_operator -> NEGPIPE Rule 251 unary_module_path_operator -> CARET Rule 252 unary_module_path_operator -> NEGCARET Rule 253 binary_module_path_operator -> ISEQUAL Rule 254 binary_module_path_operator -> NISEQUAL Rule 255 binary_module_path_operator -> DOUBLEAMPERSAND Rule 256 binary_module_path_operator -> DOUBLEPIPE Rule 257 binary_module_path_operator -> AMPERSAND Rule 258 binary_module_path_operator -> PIPE Rule 259 binary_module_path_operator -> CARET Rule 260 binary_module_path_operator -> NEGCARET Rule 261 array_identifier -> identifier Rule 262 block_identifier -> identifier Rule 263 bin_identifier -> identifier Rule 264 c_identifier -> C_ID Rule 265 cell_identifier -> identifier Rule 266 checker_identifier -> identifier Rule 267 class_identifier -> identifier Rule 268 class_variable_identifier -> variable_identifier Rule 269 clocking_identifier -> identifier Rule 270 config_identifier -> identifier Rule 271 const_identifier -> identifier Rule 272 constraint_identifier -> identifier Rule 273 covergroup_identifier -> identifier Rule 274 covergroup_variable_identifier -> variable_identifier Rule 275 cover_point_identifier -> identifier Rule 276 cross_identifier -> identifier Rule 277 dynamic_array_variable_identifier -> variable_identifier Rule 278 enum_identifier -> identifier Rule 279 escaped_identifier -> ESCAPED_ID Rule 280 formal_identifier -> identifier Rule 281 formal_port_identifier -> identifier Rule 282 function_identifier -> identifier Rule 283 generate_block_identifier -> identifier Rule 284 genvar_identifier -> identifier Rule 285 hierarchical_array_identifier -> hierarchical_identifier Rule 286 hierarchical_block_identifier -> hierarchical_identifier Rule 287 hierarchical_event_identifier -> hierarchical_identifier Rule 288 hierarchical_identifier -> optional_identifier_constant_bit_select_list identifier Rule 289 hierarchical_identifier -> DOLLAR ROOT DOT optional_identifier_constant_bit_select_list identifier Rule 290 hierarchical_net_identifier -> hierarchical_identifier Rule 291 hierarchical_parameter_identifier -> hierarchical_identifier Rule 292 hierarchical_property_identifier -> hierarchical_identifier Rule 293 hierarchical_sequence_identifier -> hierarchical_identifier Rule 294 hierarchical_task_identifier -> hierarchical_identifier Rule 295 hierarchical_tf_identifier -> hierarchical_identifier Rule 296 hierarchical_variable_identifier -> hierarchical_identifier Rule 297 identifier -> simple_identifier Rule 298 identifier -> escaped_identifier Rule 299 index_variable_identifier -> identifier Rule 300 interface_identifier -> identifier Rule 301 interface_instance_identifier -> identifier Rule 302 inout_port_identifier -> identifier Rule 303 input_port_identifier -> identifier Rule 304 instance_identifier -> identifier Rule 305 library_identifier -> identifier Rule 306 member_identifier -> identifier Rule 307 method_identifier -> identifier Rule 308 modport_identifier -> identifier Rule 309 module_identifier -> identifier Rule 310 net_identifier -> identifier Rule 311 net_type_identifier -> identifier Rule 312 output_port_identifier -> identifier Rule 313 package_identifier -> identifier Rule 314 package_scope -> package_identifier DOUBLECOLON Rule 315 package_scope -> DOLLAR UNIT DOUBLECOLON Rule 316 optional_package_scope -> package_scope Rule 317 optional_package_scope -> empty Rule 318 parameter_identifier -> identifier Rule 319 port_identifier -> identifier Rule 320 production_identifier -> identifier Rule 321 program_identifier -> identifier Rule 322 property_identifier -> identifier Rule 323 ps_class_identifier -> optional_package_scope class_identifier Rule 324 ps_covergroup_identifier -> optional_package_scope covergroup_identifier Rule 325 ps_checker_identifier -> optional_package_scope checker_identifier Rule 326 ps_identifier -> optional_package_scope identifier Rule 327 ps_or_hierarchical_array_identifier -> optional_package_scope hierarchical_array_identifier Rule 328 ps_or_hierarchical_array_identifier -> implicit_class_handle DOT hierarchical_array_identifier Rule 329 ps_or_hierarchical_array_identifier -> class_scope hierarchical_array_identifier Rule 330 ps_or_hierarchical_net_identifier -> optional_package_scope net_identifier Rule 331 ps_or_hierarchical_net_identifier -> hierarchical_net_identifier Rule 332 ps_or_hierarchical_property_identifier -> optionnal_package_scope property_identifier Rule 333 ps_or_hierarchical_property_identifier -> hierarchical_property_identifier Rule 334 ps_or_hierarchical_sequence_identifier -> optional_package_scope sequence_identifier Rule 335 ps_or_hierarchical_sequence_identifier -> hierarchical_sequence_identifier Rule 336 ps_or_hierarchical_tf_identifier -> optional_package_scope tf_identifier Rule 337 ps_or_hierarchical_tf_identifier -> hierarchical_tf_identifier Rule 338 ps_parameter_identifier -> optional_package_scope parameter_identifier Rule 339 ps_parameter_identifier -> class_scope parameter_identifier Rule 340 ps_parameter_identifier -> ps_parameter_identifier_generate_list parameter_identifier Rule 341 ps_parameter_identifier_generate_list -> ps_parameter_identifier_generate_list DOT ps_parameter_identifier_generate Rule 342 ps_parameter_identifier_generate_list -> ps_parameter_identifier_generate Rule 343 ps_parameter_identifier_generate -> generate_block_identifier LBRACKET constant_expression RBRACKET Rule 344 ps_parameter_identifier_generate -> generate_block_identifier Rule 345 ps_type_identifier -> type_identifier Rule 346 ps_type_identifier -> LOCAL DOUBLECOLON type_identifier Rule 347 ps_type_identifier -> package_scope type_identifier Rule 348 sequence_identifier -> identifier Rule 349 signal_identifier -> identifier Rule 350 simple_identifier -> ID Rule 351 specparam_identifier -> identifier Rule 352 system_tf_identifier -> DOLLAR ID Rule 353 task_identifier -> identifier Rule 354 tf_identifier -> identifier Rule 355 terminal_identifier -> identifier Rule 356 topmodule_identifier -> identifier Rule 357 type_identifier -> identifier Rule 358 udp_identifier -> identifier Rule 359 variable_identifier -> identifier Rule 360 cond_predicate -> AT Rule 361 implicit_class_handle -> AT Rule 362 integral_number -> AT Rule 363 lifetime -> AT Rule 364 list_of_interface_identifiers -> AT Rule 365 list_of_port_declarations_list -> AT Rule 366 list_of_port_identifiers -> AT Rule 367 list_of_ports -> AT Rule 368 list_of_variable_decl_assignments -> AT Rule 369 list_of_variable_identifiers -> AT Rule 370 module_item_list -> AT Rule 371 module_path_primary -> AT Rule 372 non_port_module_item -> AT Rule 373 non_port_module_item_list -> AT Rule 374 open_range_list -> AT Rule 375 operator_assignment -> AT Rule 376 optional_enum_name_declaration_list -> AT Rule 377 optional_identifier_constant_bit_select_list -> AT Rule 378 optional_modport_identifier -> AT Rule 379 optional_packed_dimension -> AT Rule 380 optional_packed_dimension_list -> AT Rule 381 optional_parameter_value_assignment -> AT Rule 382 optional_signing -> AT Rule 383 optionnal_package_scope -> AT Rule 384 package_import_declaration_list -> AT Rule 385 parameter_port_list -> AT Rule 386 primary -> AT Rule 387 random_qualifier -> AT Rule 388 struct_union_member_list -> AT Rule 389 variable_lvalue -> AT Rule 390 empty -> <empty>

1条回答

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1楼 · 发布于 2024-09-21 03:28:49

在LR解析中，我们经常谈论“items”：item是一个带有进度标记的产物，通常用一个•来编写，但有时用一个简单的.。状态只是项的集合；实际上，状态告诉您解析可能在其中的一组结果。在

有一种特别特别的物品：末尾有一个圆点的物品：

(134) attribute_instance_optional_list -> attribute_instance_list .

这表示一个可以完成的生产，因为进度标记在最后。如果这是正确的结果，那么解析器必须用右手边代替左手边：这是被称为“reduction”的操作（因为它与“production”相反，而“production”就是这样做的）。在

然而，仅仅是你处于一种可能减少的状态并不意味着减少是可能的。下一个代币必须与减少的结果一致。如果下一个标记不能跟在reduced non-terminal后面（在解析器的状态上下文中），那么就不能执行缩减，所以解析器将尝试一个移位（如果可能的话）。在

换班真的很简单。如果状态中的一个或多个项在当前先行符号之前有一个点，则可能发生移位。这里，关于额外的lookahead是没有问题的，因为Ply（像许多LALR解析器生成器一样）只创建在任何状态下只有一个lookahead的LALR（1）解析器，所以我们唯一要做的就是我们当前正在查看的符号，很明显，只有当某些可用的项目在下一个位置有这个符号时，我们才能处理它。在

如果一个给定的状态和一个给定的lookahead符号可以同时执行shift和reduce操作，那么就出现了shift-reduce冲突；解析器不知道该怎么做。（如果既没有shift也没有reduce，则表示输入有语法错误。这就是LR解析器识别语法错误的方法。）

LR解析的一个重要方面是，如果要执行缩减，则必须立即执行。也就是说，如果我们处于一个具有可能的缩减的状态，并且项目的前瞻集表明前瞻性是可行的，那么我们必须执行缩减。我们不能等着看以后是否有可能，因为没有时间再降价了。换言之，项目中•左侧的任何内容都已尽可能减少。（这是LR解析中的R，它表示每个缩减都是“最右边的”。如果使用“最右边”这个词没有意义，不用担心；我只是在你想知道的情况下才提到这个事实。）

另一件事我不妨提一下，在LALR解析（“Lookahead-LR解析”）中，状态是由一组项精确定义的。每个项都有一个适用的前瞻集，但前瞻集不构成状态标识的一部分。如果解析器生成器最终生成两个具有相同项但不同的前瞻集的状态，它必须将它们合并到一个状态中，形成每个前瞻集的并集。对于完整的LR解析，这个限制并不存在；对于一组给定的项，您可以（并且确实）拥有多个状态，结果是解析表的大小要大得多，功能也稍微强一些。在

现在，如果可以进行换档操作，则可以机械地确定换档后处于激活状态。例如，从

^{pr2}$

在移动LPAREN之后，下一个状态将只有一个项：

^{3}$

（注意点是如何移动的。）

这是一个简单的例子，因为下一个符号是一个终端，ASTERISK。大多数情况下，移位后的下一个符号将是一个非终结符，在这种情况下，我们需要为该非终结符添加所有的乘积，并在开始处加上点。（这就是状态如何以一个以上的项结束）因此，例如，给定一个新状态中有一个项和一个n输入ASTERISK（任何其他操作都是错误的，因为此状态没有还原的可能性），然后我们将转换到具有移位项的状态：

(138) attribute_instance -> LPAREN ASTERISK . attr_spec_list ASTERISK RPAREN

加上attr_spec_list的所有产品：

(139)   attr_spec_list -> . attr_spec_list COMMA attr_spec
(140)   attr_spec_list -> . attr_spec

{{8{we}前面加上了cdan}项：

(141)   attr_spec -> . attr_name
(142)   attr_spec -> . attr_name EQUALS constant_expression

加上attr_name的产量：

(143)   attr_name -> . identifier

以此类推，直到我们不再看到新的非终端：

^{8}$

好的，现在下一个标记必须是ID或{}。假设它是ID。现在呢？好吧，我们将进入一个状态

(350)   simple_identifier -> ID .

有一个可能的缩减；假设lookahead符号与lookahead集匹配（我没有也不打算解释如何为每个状态计算lookahead集；这里有一个算法，但它的细节与此无关），那么ID将被缩减为simple_identifier。那么解析器去哪里呢？逻辑上，它返回到生成simple_identifier的状态，并移动simple_identifier。碰巧，这个国家就是我们刚刚创造的

(138)   attribute_instance -> LPAREN ASTERISK . attr_spec_list ASTERISK RPAREN
(139)   attr_spec_list -> . attr_spec_list COMMA attr_spec
(140)   attr_spec_list -> . attr_spec
(141)   attr_spec -> . attr_name
(142)   attr_spec -> . attr_name EQUALS constant_expression
(143)   attr_name -> . identifier
(297)   identifier -> . simple_identifier
(298)   identifier -> . escaped_identifier
(350)   simple_identifier -> . ID
(279)   escaped_identifier -> . ESCAPED_ID

在我们移动simple_identifier之后，我们得到

(297)   identifier -> simple_identifier .

这是一种需要还原为identifier的状态，因此再次回到我们发现自己处于的相同状态

(143)   attr_name -> identifier .

然后呢

(141)   attr_spec -> attr_name .
(142)   attr_spec -> attr_name . EQUALS constant_expression

但是解析器是如何知道每一个缩减都返回到哪个状态的呢？答案是解析器使用每个符号将当前状态推送到解析堆栈。当它进行缩减时，它从右侧弹出符号，丢弃每个关联的状态号，直到到达右侧的开始处，此时堆栈指示右手边来自哪个状态。然后，它查看该状态，移动经过缩减的非终结符，并将新的移位状态推送到解析堆栈中。在

所以我认为这回答了“状态描述开头的行是什么意思？”“语法分析器执行什么操作？”另外两个问题很容易回答：“不，它不会计算所有可能的前置状态”和“是的，它可以（虽然它可能会最终添加那些实际上不可能使用任何输入的前置任务），但它对解析没有用。”但由于它们与解决shift-reduce冲突没有太大关系，所以我就不解释了答案更进一步。在

回到减少冲突的实际转变，情况是我们处于这种状态

^{pr2}$
它有一个可能的减少，我们正在考虑这样一个情况，即我们看到一个LPAREN，它有一个可能的移位，结果第一个项目的前瞻集也包括LPAREN。虽然lookahead集没有显示在PLY输出中，但是我们可以在语法中查找它的来源。直接来源当然是attribute_instance_optional_list，我们可以在语法中找到，尽管有很多可能性：
(27) module_nonansi_header -> attribute_instance_optional_list module_keyword lifetime module_identifier package_import_declaration_list parameter_port_list list_of_ports SEMICOLON (28) module_ansi_header -> attribute_instance_optional_list module_keyword lifetime module_identifier package_import_declaration_list parameter_port_list list_of_port_declarations_list SEMICOLON (29) module_implicit_header -> attribute_instance_optional_list module_keyword lifetime module_identifier LPAREN DOT ASTERISK RPAREN SEMICOLON (36) port_declaration -> attribute_instance_optional_list inout_declaration (37) port_declaration -> attribute_instance_optional_list input_declaration (38) port_declaration -> attribute_instance_optional_list output_declaration (39) port_declaration -> attribute_instance_optional_list ref_declaration (40) port_declaration -> attribute_instance_optional_list interface_port_declaration (125) struct_union_member -> attribute_instance_optional_list data_type_or_void list_of_variable_decl_assignments (126) struct_union_member -> attribute_instance_optional_list random_qualifier data_type_or_void list_of_variable_decl_assignments (144) inc_or_dec_expression -> inc_or_dec_operator attribute_instance_optional_list variable_lvalue (145) inc_or_dec_expression -> variable_lvalue attribute_instance_optional_list inc_or_dec_operator (146) conditional_expression -> cond_predicate INTERROGATION attribute_instance_optional_list expression COLON expression (148) constant_expression -> unary_operator attribute_instance_optional_list constant_primary (149) constant_expression -> constant_expression binary_operator attribute_instance_optional_list constant_expression (150) constant_expression -> constant_expression INTERROGATION attribute_instance_optional_list constant_expression COLON constant_expression (167) expression -> unary_operator attribute_instance_optional_list primary (170) expression -> expression binary_operator attribute_instance_optional_list expression (181) module_path_conditional_expression -> module_path_expression INTERROGATION attribute_instance_optional_list module_path_expression COLON module_path_expression (183) module_path_expression -> unary_module_path_operator attribute_instance_optional_list module_path_primary (184) module_path_expression -> module_path_expression binary_module_path_operator attribute_instance_optional_list module_path_expression
据我所知，attribute_instance_optional_list并没有出现在这些产品的末尾，这简化了LPAREN冲突的来源。在所有这些情况下，后面是一个非终点站，可能是：
module_keyword inout_declaration input_declaration output_declaration ref_declaration interface_port_declaration data_type_or_void random_qualifier variable_lvalue inc_or_dec_operator constant_primary constant_expression primary expression module_path_primary module_path_expression
现在，如果这些非终端中的任何一个可以以LPAREN开头，我们就有可能发生移位-减少冲突。其中有两个罪魁祸首：expression和类似的。在
所以，总而言之，有一个问题：一个attribute_instance可以以括号开头，但是attribute_instance_list也可以跟在括号后面。因此，当你在一个属性实例列表中看到一个（），你就不知道该移动还是减少。在

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