1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" 2 "http://www.w3.org/TR/html4/strict.dtd"> 3 <html> 4 <head> 5 <title>TableGen Fundamentals</title> 6 <link rel="stylesheet" href="llvm.css" type="text/css"> 7 </head> 8 <body> 9 10 <h1>TableGen Fundamentals</h1> 11 12 <div> 13 <ul> 14 <li><a href="#introduction">Introduction</a> 15 <ol> 16 <li><a href="#concepts">Basic concepts</a></li> 17 <li><a href="#example">An example record</a></li> 18 <li><a href="#running">Running TableGen</a></li> 19 </ol></li> 20 <li><a href="#syntax">TableGen syntax</a> 21 <ol> 22 <li><a href="#primitives">TableGen primitives</a> 23 <ol> 24 <li><a href="#comments">TableGen comments</a></li> 25 <li><a href="#types">The TableGen type system</a></li> 26 <li><a href="#values">TableGen values and expressions</a></li> 27 </ol></li> 28 <li><a href="#classesdefs">Classes and definitions</a> 29 <ol> 30 <li><a href="#valuedef">Value definitions</a></li> 31 <li><a href="#recordlet">'let' expressions</a></li> 32 <li><a href="#templateargs">Class template arguments</a></li> 33 <li><a href="#multiclass">Multiclass definitions and instances</a></li> 34 </ol></li> 35 <li><a href="#filescope">File scope entities</a> 36 <ol> 37 <li><a href="#include">File inclusion</a></li> 38 <li><a href="#globallet">'let' expressions</a></li> 39 </ol></li> 40 </ol></li> 41 <li><a href="#backends">TableGen backends</a> 42 <ol> 43 <li><a href="#">todo</a></li> 44 </ol></li> 45 </ul> 46 </div> 47 48 <div class="doc_author"> 49 <p>Written by <a href="mailto:sabre (a] nondot.org">Chris Lattner</a></p> 50 </div> 51 52 <!-- *********************************************************************** --> 53 <h2><a name="introduction">Introduction</a></h2> 54 <!-- *********************************************************************** --> 55 56 <div> 57 58 <p>TableGen's purpose is to help a human develop and maintain records of 59 domain-specific information. Because there may be a large number of these 60 records, it is specifically designed to allow writing flexible descriptions and 61 for common features of these records to be factored out. This reduces the 62 amount of duplication in the description, reduces the chance of error, and 63 makes it easier to structure domain specific information.</p> 64 65 <p>The core part of TableGen <a href="#syntax">parses a file</a>, instantiates 66 the declarations, and hands the result off to a domain-specific "<a 67 href="#backends">TableGen backend</a>" for processing. The current major user 68 of TableGen is the <a href="CodeGenerator.html">LLVM code generator</a>.</p> 69 70 <p>Note that if you work on TableGen much, and use emacs or vim, that you can 71 find an emacs "TableGen mode" and a vim language file in the 72 <tt>llvm/utils/emacs</tt> and <tt>llvm/utils/vim</tt> directories of your LLVM 73 distribution, respectively.</p> 74 75 <!-- ======================================================================= --> 76 <h3><a name="concepts">Basic concepts</a></h3> 77 78 <div> 79 80 <p>TableGen files consist of two key parts: 'classes' and 'definitions', both 81 of which are considered 'records'.</p> 82 83 <p><b>TableGen records</b> have a unique name, a list of values, and a list of 84 superclasses. The list of values is the main data that TableGen builds for each 85 record; it is this that holds the domain specific information for the 86 application. The interpretation of this data is left to a specific <a 87 href="#backends">TableGen backend</a>, but the structure and format rules are 88 taken care of and are fixed by TableGen.</p> 89 90 <p><b>TableGen definitions</b> are the concrete form of 'records'. These 91 generally do not have any undefined values, and are marked with the 92 '<tt>def</tt>' keyword.</p> 93 94 <p><b>TableGen classes</b> are abstract records that are used to build and 95 describe other records. These 'classes' allow the end-user to build 96 abstractions for either the domain they are targeting (such as "Register", 97 "RegisterClass", and "Instruction" in the LLVM code generator) or for the 98 implementor to help factor out common properties of records (such as "FPInst", 99 which is used to represent floating point instructions in the X86 backend). 100 TableGen keeps track of all of the classes that are used to build up a 101 definition, so the backend can find all definitions of a particular class, such 102 as "Instruction".</p> 103 104 <p><b>TableGen multiclasses</b> are groups of abstract records that are 105 instantiated all at once. Each instantiation can result in multiple 106 TableGen definitions. If a multiclass inherits from another multiclass, 107 the definitions in the sub-multiclass become part of the current 108 multiclass, as if they were declared in the current multiclass.</p> 109 110 </div> 111 112 <!-- ======================================================================= --> 113 <h3><a name="example">An example record</a></h3> 114 115 <div> 116 117 <p>With no other arguments, TableGen parses the specified file and prints out 118 all of the classes, then all of the definitions. This is a good way to see what 119 the various definitions expand to fully. Running this on the <tt>X86.td</tt> 120 file prints this (at the time of this writing):</p> 121 122 <div class="doc_code"> 123 <pre> 124 ... 125 <b>def</b> ADD32rr { <i>// Instruction X86Inst I</i> 126 <b>string</b> Namespace = "X86"; 127 <b>dag</b> OutOperandList = (outs GR32:$dst); 128 <b>dag</b> InOperandList = (ins GR32:$src1, GR32:$src2); 129 <b>string</b> AsmString = "add{l}\t{$src2, $dst|$dst, $src2}"; 130 <b>list</b><dag> Pattern = [(set GR32:$dst, (add GR32:$src1, GR32:$src2))]; 131 <b>list</b><Register> Uses = []; 132 <b>list</b><Register> Defs = [EFLAGS]; 133 <b>list</b><Predicate> Predicates = []; 134 <b>int</b> CodeSize = 3; 135 <b>int</b> AddedComplexity = 0; 136 <b>bit</b> isReturn = 0; 137 <b>bit</b> isBranch = 0; 138 <b>bit</b> isIndirectBranch = 0; 139 <b>bit</b> isBarrier = 0; 140 <b>bit</b> isCall = 0; 141 <b>bit</b> canFoldAsLoad = 0; 142 <b>bit</b> mayLoad = 0; 143 <b>bit</b> mayStore = 0; 144 <b>bit</b> isImplicitDef = 0; 145 <b>bit</b> isConvertibleToThreeAddress = 1; 146 <b>bit</b> isCommutable = 1; 147 <b>bit</b> isTerminator = 0; 148 <b>bit</b> isReMaterializable = 0; 149 <b>bit</b> isPredicable = 0; 150 <b>bit</b> hasDelaySlot = 0; 151 <b>bit</b> usesCustomInserter = 0; 152 <b>bit</b> hasCtrlDep = 0; 153 <b>bit</b> isNotDuplicable = 0; 154 <b>bit</b> hasSideEffects = 0; 155 <b>bit</b> neverHasSideEffects = 0; 156 InstrItinClass Itinerary = NoItinerary; 157 <b>string</b> Constraints = ""; 158 <b>string</b> DisableEncoding = ""; 159 <b>bits</b><8> Opcode = { 0, 0, 0, 0, 0, 0, 0, 1 }; 160 Format Form = MRMDestReg; 161 <b>bits</b><6> FormBits = { 0, 0, 0, 0, 1, 1 }; 162 ImmType ImmT = NoImm; 163 <b>bits</b><3> ImmTypeBits = { 0, 0, 0 }; 164 <b>bit</b> hasOpSizePrefix = 0; 165 <b>bit</b> hasAdSizePrefix = 0; 166 <b>bits</b><4> Prefix = { 0, 0, 0, 0 }; 167 <b>bit</b> hasREX_WPrefix = 0; 168 FPFormat FPForm = ?; 169 <b>bits</b><3> FPFormBits = { 0, 0, 0 }; 170 } 171 ... 172 </pre> 173 </div> 174 175 <p>This definition corresponds to a 32-bit register-register add instruction in 176 the X86. The string after the '<tt>def</tt>' string indicates the name of the 177 record—"<tt>ADD32rr</tt>" in this case—and the comment at the end of 178 the line indicates the superclasses of the definition. The body of the record 179 contains all of the data that TableGen assembled for the record, indicating that 180 the instruction is part of the "X86" namespace, the pattern indicating how the 181 the instruction should be emitted into the assembly file, that it is a 182 two-address instruction, has a particular encoding, etc. The contents and 183 semantics of the information in the record is specific to the needs of the X86 184 backend, and is only shown as an example.</p> 185 186 <p>As you can see, a lot of information is needed for every instruction 187 supported by the code generator, and specifying it all manually would be 188 unmaintainable, prone to bugs, and tiring to do in the first place. Because we 189 are using TableGen, all of the information was derived from the following 190 definition:</p> 191 192 <div class="doc_code"> 193 <pre> 194 let Defs = [EFLAGS], 195 isCommutable = 1, <i>// X = ADD Y,Z --> X = ADD Z,Y</i> 196 isConvertibleToThreeAddress = 1 <b>in</b> <i>// Can transform into LEA.</i> 197 def ADD32rr : I<0x01, MRMDestReg, (outs GR32:$dst), 198 (ins GR32:$src1, GR32:$src2), 199 "add{l}\t{$src2, $dst|$dst, $src2}", 200 [(set GR32:$dst, (add GR32:$src1, GR32:$src2))]>; 201 </pre> 202 </div> 203 204 <p>This definition makes use of the custom class <tt>I</tt> (extended from the 205 custom class <tt>X86Inst</tt>), which is defined in the X86-specific TableGen 206 file, to factor out the common features that instructions of its class share. A 207 key feature of TableGen is that it allows the end-user to define the 208 abstractions they prefer to use when describing their information.</p> 209 210 </div> 211 212 <!-- ======================================================================= --> 213 <h3><a name="running">Running TableGen</a></h3> 214 215 <div> 216 217 <p>TableGen runs just like any other LLVM tool. The first (optional) argument 218 specifies the file to read. If a filename is not specified, <tt>tblgen</tt> 219 reads from standard input.</p> 220 221 <p>To be useful, one of the <a href="#backends">TableGen backends</a> must be 222 used. These backends are selectable on the command line (type '<tt>tblgen 223 -help</tt>' for a list). For example, to get a list of all of the definitions 224 that subclass a particular type (which can be useful for building up an enum 225 list of these records), use the <tt>-print-enums</tt> option:</p> 226 227 <div class="doc_code"> 228 <pre> 229 $ tblgen X86.td -print-enums -class=Register 230 AH, AL, AX, BH, BL, BP, BPL, BX, CH, CL, CX, DH, DI, DIL, DL, DX, EAX, EBP, EBX, 231 ECX, EDI, EDX, EFLAGS, EIP, ESI, ESP, FP0, FP1, FP2, FP3, FP4, FP5, FP6, IP, 232 MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7, R10, R10B, R10D, R10W, R11, R11B, R11D, 233 R11W, R12, R12B, R12D, R12W, R13, R13B, R13D, R13W, R14, R14B, R14D, R14W, R15, 234 R15B, R15D, R15W, R8, R8B, R8D, R8W, R9, R9B, R9D, R9W, RAX, RBP, RBX, RCX, RDI, 235 RDX, RIP, RSI, RSP, SI, SIL, SP, SPL, ST0, ST1, ST2, ST3, ST4, ST5, ST6, ST7, 236 XMM0, XMM1, XMM10, XMM11, XMM12, XMM13, XMM14, XMM15, XMM2, XMM3, XMM4, XMM5, 237 XMM6, XMM7, XMM8, XMM9, 238 239 $ tblgen X86.td -print-enums -class=Instruction 240 ABS_F, ABS_Fp32, ABS_Fp64, ABS_Fp80, ADC32mi, ADC32mi8, ADC32mr, ADC32ri, 241 ADC32ri8, ADC32rm, ADC32rr, ADC64mi32, ADC64mi8, ADC64mr, ADC64ri32, ADC64ri8, 242 ADC64rm, ADC64rr, ADD16mi, ADD16mi8, ADD16mr, ADD16ri, ADD16ri8, ADD16rm, 243 ADD16rr, ADD32mi, ADD32mi8, ADD32mr, ADD32ri, ADD32ri8, ADD32rm, ADD32rr, 244 ADD64mi32, ADD64mi8, ADD64mr, ADD64ri32, ... 245 </pre> 246 </div> 247 248 <p>The default backend prints out all of the records, as described <a 249 href="#example">above</a>.</p> 250 251 <p>If you plan to use TableGen, you will most likely have to <a 252 href="#backends">write a backend</a> that extracts the information specific to 253 what you need and formats it in the appropriate way.</p> 254 255 </div> 256 257 </div> 258 259 <!-- *********************************************************************** --> 260 <h2><a name="syntax">TableGen syntax</a></h2> 261 <!-- *********************************************************************** --> 262 263 <div> 264 265 <p>TableGen doesn't care about the meaning of data (that is up to the backend to 266 define), but it does care about syntax, and it enforces a simple type system. 267 This section describes the syntax and the constructs allowed in a TableGen file. 268 </p> 269 270 <!-- ======================================================================= --> 271 <h3><a name="primitives">TableGen primitives</a></h3> 272 273 <div> 274 275 <!-- --------------------------------------------------------------------------> 276 <h4><a name="comments">TableGen comments</a></h4> 277 278 <div> 279 280 <p>TableGen supports BCPL style "<tt>//</tt>" comments, which run to the end of 281 the line, and it also supports <b>nestable</b> "<tt>/* */</tt>" comments.</p> 282 283 </div> 284 285 <!-- --------------------------------------------------------------------------> 286 <h4> 287 <a name="types">The TableGen type system</a> 288 </h4> 289 290 <div> 291 292 <p>TableGen files are strongly typed, in a simple (but complete) type-system. 293 These types are used to perform automatic conversions, check for errors, and to 294 help interface designers constrain the input that they allow. Every <a 295 href="#valuedef">value definition</a> is required to have an associated type. 296 </p> 297 298 <p>TableGen supports a mixture of very low-level types (such as <tt>bit</tt>) 299 and very high-level types (such as <tt>dag</tt>). This flexibility is what 300 allows it to describe a wide range of information conveniently and compactly. 301 The TableGen types are:</p> 302 303 <dl> 304 <dt><tt><b>bit</b></tt></dt> 305 <dd>A 'bit' is a boolean value that can hold either 0 or 1.</dd> 306 307 <dt><tt><b>int</b></tt></dt> 308 <dd>The 'int' type represents a simple 32-bit integer value, such as 5.</dd> 309 310 <dt><tt><b>string</b></tt></dt> 311 <dd>The 'string' type represents an ordered sequence of characters of 312 arbitrary length.</dd> 313 314 <dt><tt><b>bits</b><n></tt></dt> 315 <dd>A 'bits' type is an arbitrary, but fixed, size integer that is broken up 316 into individual bits. This type is useful because it can handle some bits 317 being defined while others are undefined.</dd> 318 319 <dt><tt><b>list</b><ty></tt></dt> 320 <dd>This type represents a list whose elements are some other type. The 321 contained type is arbitrary: it can even be another list type.</dd> 322 323 <dt>Class type</dt> 324 <dd>Specifying a class name in a type context means that the defined value 325 must be a subclass of the specified class. This is useful in conjunction with 326 the <b><tt>list</tt></b> type, for example, to constrain the elements of the 327 list to a common base class (e.g., a <tt><b>list</b><Register></tt> can 328 only contain definitions derived from the "<tt>Register</tt>" class).</dd> 329 330 <dt><tt><b>dag</b></tt></dt> 331 <dd>This type represents a nestable directed graph of elements.</dd> 332 333 <dt><tt><b>code</b></tt></dt> 334 <dd>This represents a big hunk of text. This is lexically distinct from 335 string values because it doesn't require escapeing double quotes and other 336 common characters that occur in code.</dd> 337 </dl> 338 339 <p>To date, these types have been sufficient for describing things that 340 TableGen has been used for, but it is straight-forward to extend this list if 341 needed.</p> 342 343 </div> 344 345 <!-- --------------------------------------------------------------------------> 346 <h4> 347 <a name="values">TableGen values and expressions</a> 348 </h4> 349 350 <div> 351 352 <p>TableGen allows for a pretty reasonable number of different expression forms 353 when building up values. These forms allow the TableGen file to be written in a 354 natural syntax and flavor for the application. The current expression forms 355 supported include:</p> 356 357 <dl> 358 <dt><tt>?</tt></dt> 359 <dd>uninitialized field</dd> 360 <dt><tt>0b1001011</tt></dt> 361 <dd>binary integer value</dd> 362 <dt><tt>07654321</tt></dt> 363 <dd>octal integer value (indicated by a leading 0)</dd> 364 <dt><tt>7</tt></dt> 365 <dd>decimal integer value</dd> 366 <dt><tt>0x7F</tt></dt> 367 <dd>hexadecimal integer value</dd> 368 <dt><tt>"foo"</tt></dt> 369 <dd>string value</dd> 370 <dt><tt>[{ ... }]</tt></dt> 371 <dd>code fragment</dd> 372 <dt><tt>[ X, Y, Z ]<type></tt></dt> 373 <dd>list value. <type> is the type of the list 374 element and is usually optional. In rare cases, 375 TableGen is unable to deduce the element type in 376 which case the user must specify it explicitly.</dd> 377 <dt><tt>{ a, b, c }</tt></dt> 378 <dd>initializer for a "bits<3>" value</dd> 379 <dt><tt>value</tt></dt> 380 <dd>value reference</dd> 381 <dt><tt>value{17}</tt></dt> 382 <dd>access to one bit of a value</dd> 383 <dt><tt>value{15-17}</tt></dt> 384 <dd>access to multiple bits of a value</dd> 385 <dt><tt>DEF</tt></dt> 386 <dd>reference to a record definition</dd> 387 <dt><tt>CLASS<val list></tt></dt> 388 <dd>reference to a new anonymous definition of CLASS with the specified 389 template arguments.</dd> 390 <dt><tt>X.Y</tt></dt> 391 <dd>reference to the subfield of a value</dd> 392 <dt><tt>list[4-7,17,2-3]</tt></dt> 393 <dd>A slice of the 'list' list, including elements 4,5,6,7,17,2, and 3 from 394 it. Elements may be included multiple times.</dd> 395 <dt><tt>(DEF a, b)</tt></dt> 396 <dd>a dag value. The first element is required to be a record definition, the 397 remaining elements in the list may be arbitrary other values, including nested 398 `<tt>dag</tt>' values.</dd> 399 <dt><tt>!strconcat(a, b)</tt></dt> 400 <dd>A string value that is the result of concatenating the 'a' and 'b' 401 strings.</dd> 402 <dt><tt>!cast<type>(a)</tt></dt> 403 <dd>A symbol of type <em>type</em> obtained by looking up the string 'a' in 404 the symbol table. If the type of 'a' does not match <em>type</em>, TableGen 405 aborts with an error. !cast<string> is a special case in that the argument must 406 be an object defined by a 'def' construct.</dd> 407 <dt><tt>!subst(a, b, c)</tt></dt> 408 <dd>If 'a' and 'b' are of string type or are symbol references, substitute 409 'b' for 'a' in 'c.' This operation is analogous to $(subst) in GNU make.</dd> 410 <dt><tt>!foreach(a, b, c)</tt></dt> 411 <dd>For each member 'b' of dag or list 'a' apply operator 'c.' 'b' is a 412 dummy variable that should be declared as a member variable of an instantiated 413 class. This operation is analogous to $(foreach) in GNU make.</dd> 414 <dt><tt>!head(a)</tt></dt> 415 <dd>The first element of list 'a.'</dd> 416 <dt><tt>!tail(a)</tt></dt> 417 <dd>The 2nd-N elements of list 'a.'</dd> 418 <dt><tt>!empty(a)</tt></dt> 419 <dd>An integer {0,1} indicating whether list 'a' is empty.</dd> 420 <dt><tt>!if(a,b,c)</tt></dt> 421 <dd>'b' if the result of 'int' or 'bit' operator 'a' is nonzero, 422 'c' otherwise.</dd> 423 <dt><tt>!eq(a,b)</tt></dt> 424 <dd>'bit 1' if string a is equal to string b, 0 otherwise. This 425 only operates on string, int and bit objects. Use !cast<string> to 426 compare other types of objects.</dd> 427 </dl> 428 429 <p>Note that all of the values have rules specifying how they convert to values 430 for different types. These rules allow you to assign a value like "<tt>7</tt>" 431 to a "<tt>bits<4></tt>" value, for example.</p> 432 433 </div> 434 435 </div> 436 437 <!-- ======================================================================= --> 438 <h3> 439 <a name="classesdefs">Classes and definitions</a> 440 </h3> 441 442 <div> 443 444 <p>As mentioned in the <a href="#concepts">intro</a>, classes and definitions 445 (collectively known as 'records') in TableGen are the main high-level unit of 446 information that TableGen collects. Records are defined with a <tt>def</tt> or 447 <tt>class</tt> keyword, the record name, and an optional list of "<a 448 href="#templateargs">template arguments</a>". If the record has superclasses, 449 they are specified as a comma separated list that starts with a colon character 450 ("<tt>:</tt>"). If <a href="#valuedef">value definitions</a> or <a 451 href="#recordlet">let expressions</a> are needed for the class, they are 452 enclosed in curly braces ("<tt>{}</tt>"); otherwise, the record ends with a 453 semicolon.</p> 454 455 <p>Here is a simple TableGen file:</p> 456 457 <div class="doc_code"> 458 <pre> 459 <b>class</b> C { <b>bit</b> V = 1; } 460 <b>def</b> X : C; 461 <b>def</b> Y : C { 462 <b>string</b> Greeting = "hello"; 463 } 464 </pre> 465 </div> 466 467 <p>This example defines two definitions, <tt>X</tt> and <tt>Y</tt>, both of 468 which derive from the <tt>C</tt> class. Because of this, they both get the 469 <tt>V</tt> bit value. The <tt>Y</tt> definition also gets the Greeting member 470 as well.</p> 471 472 <p>In general, classes are useful for collecting together the commonality 473 between a group of records and isolating it in a single place. Also, classes 474 permit the specification of default values for their subclasses, allowing the 475 subclasses to override them as they wish.</p> 476 477 <!----------------------------------------------------------------------------> 478 <h4> 479 <a name="valuedef">Value definitions</a> 480 </h4> 481 482 <div> 483 484 <p>Value definitions define named entries in records. A value must be defined 485 before it can be referred to as the operand for another value definition or 486 before the value is reset with a <a href="#recordlet">let expression</a>. A 487 value is defined by specifying a <a href="#types">TableGen type</a> and a name. 488 If an initial value is available, it may be specified after the type with an 489 equal sign. Value definitions require terminating semicolons.</p> 490 491 </div> 492 493 <!-- --------------------------------------------------------------------------> 494 <h4> 495 <a name="recordlet">'let' expressions</a> 496 </h4> 497 498 <div> 499 500 <p>A record-level let expression is used to change the value of a value 501 definition in a record. This is primarily useful when a superclass defines a 502 value that a derived class or definition wants to override. Let expressions 503 consist of the '<tt>let</tt>' keyword followed by a value name, an equal sign 504 ("<tt>=</tt>"), and a new value. For example, a new class could be added to the 505 example above, redefining the <tt>V</tt> field for all of its subclasses:</p> 506 507 <div class="doc_code"> 508 <pre> 509 <b>class</b> D : C { let V = 0; } 510 <b>def</b> Z : D; 511 </pre> 512 </div> 513 514 <p>In this case, the <tt>Z</tt> definition will have a zero value for its "V" 515 value, despite the fact that it derives (indirectly) from the <tt>C</tt> class, 516 because the <tt>D</tt> class overrode its value.</p> 517 518 </div> 519 520 <!-- --------------------------------------------------------------------------> 521 <h4> 522 <a name="templateargs">Class template arguments</a> 523 </h4> 524 525 <div> 526 527 <p>TableGen permits the definition of parameterized classes as well as normal 528 concrete classes. Parameterized TableGen classes specify a list of variable 529 bindings (which may optionally have defaults) that are bound when used. Here is 530 a simple example:</p> 531 532 <div class="doc_code"> 533 <pre> 534 <b>class</b> FPFormat<<b>bits</b><3> val> { 535 <b>bits</b><3> Value = val; 536 } 537 <b>def</b> NotFP : FPFormat<0>; 538 <b>def</b> ZeroArgFP : FPFormat<1>; 539 <b>def</b> OneArgFP : FPFormat<2>; 540 <b>def</b> OneArgFPRW : FPFormat<3>; 541 <b>def</b> TwoArgFP : FPFormat<4>; 542 <b>def</b> CompareFP : FPFormat<5>; 543 <b>def</b> CondMovFP : FPFormat<6>; 544 <b>def</b> SpecialFP : FPFormat<7>; 545 </pre> 546 </div> 547 548 <p>In this case, template arguments are used as a space efficient way to specify 549 a list of "enumeration values", each with a "<tt>Value</tt>" field set to the 550 specified integer.</p> 551 552 <p>The more esoteric forms of <a href="#values">TableGen expressions</a> are 553 useful in conjunction with template arguments. As an example:</p> 554 555 <div class="doc_code"> 556 <pre> 557 <b>class</b> ModRefVal<<b>bits</b><2> val> { 558 <b>bits</b><2> Value = val; 559 } 560 561 <b>def</b> None : ModRefVal<0>; 562 <b>def</b> Mod : ModRefVal<1>; 563 <b>def</b> Ref : ModRefVal<2>; 564 <b>def</b> ModRef : ModRefVal<3>; 565 566 <b>class</b> Value<ModRefVal MR> { 567 <i>// Decode some information into a more convenient format, while providing 568 // a nice interface to the user of the "Value" class.</i> 569 <b>bit</b> isMod = MR.Value{0}; 570 <b>bit</b> isRef = MR.Value{1}; 571 572 <i>// other stuff...</i> 573 } 574 575 <i>// Example uses</i> 576 <b>def</b> bork : Value<Mod>; 577 <b>def</b> zork : Value<Ref>; 578 <b>def</b> hork : Value<ModRef>; 579 </pre> 580 </div> 581 582 <p>This is obviously a contrived example, but it shows how template arguments 583 can be used to decouple the interface provided to the user of the class from the 584 actual internal data representation expected by the class. In this case, 585 running <tt>tblgen</tt> on the example prints the following definitions:</p> 586 587 <div class="doc_code"> 588 <pre> 589 <b>def</b> bork { <i>// Value</i> 590 <b>bit</b> isMod = 1; 591 <b>bit</b> isRef = 0; 592 } 593 <b>def</b> hork { <i>// Value</i> 594 <b>bit</b> isMod = 1; 595 <b>bit</b> isRef = 1; 596 } 597 <b>def</b> zork { <i>// Value</i> 598 <b>bit</b> isMod = 0; 599 <b>bit</b> isRef = 1; 600 } 601 </pre> 602 </div> 603 604 <p> This shows that TableGen was able to dig into the argument and extract a 605 piece of information that was requested by the designer of the "Value" class. 606 For more realistic examples, please see existing users of TableGen, such as the 607 X86 backend.</p> 608 609 </div> 610 611 <!-- --------------------------------------------------------------------------> 612 <h4> 613 <a name="multiclass">Multiclass definitions and instances</a> 614 </h4> 615 616 <div> 617 618 <p> 619 While classes with template arguments are a good way to factor commonality 620 between two instances of a definition, multiclasses allow a convenient notation 621 for defining multiple definitions at once (instances of implicitly constructed 622 classes). For example, consider an 3-address instruction set whose instructions 623 come in two forms: "<tt>reg = reg op reg</tt>" and "<tt>reg = reg op imm</tt>" 624 (e.g. SPARC). In this case, you'd like to specify in one place that this 625 commonality exists, then in a separate place indicate what all the ops are. 626 </p> 627 628 <p> 629 Here is an example TableGen fragment that shows this idea: 630 </p> 631 632 <div class="doc_code"> 633 <pre> 634 <b>def</b> ops; 635 <b>def</b> GPR; 636 <b>def</b> Imm; 637 <b>class</b> inst<<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist>; 638 639 <b>multiclass</b> ri_inst<<b>int</b> opc, <b>string</b> asmstr> { 640 def _rr : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"), 641 (ops GPR:$dst, GPR:$src1, GPR:$src2)>; 642 def _ri : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"), 643 (ops GPR:$dst, GPR:$src1, Imm:$src2)>; 644 } 645 646 <i>// Instantiations of the ri_inst multiclass.</i> 647 <b>defm</b> ADD : ri_inst<0b111, "add">; 648 <b>defm</b> SUB : ri_inst<0b101, "sub">; 649 <b>defm</b> MUL : ri_inst<0b100, "mul">; 650 ... 651 </pre> 652 </div> 653 654 <p>The name of the resultant definitions has the multidef fragment names 655 appended to them, so this defines <tt>ADD_rr</tt>, <tt>ADD_ri</tt>, 656 <tt>SUB_rr</tt>, etc. A defm may inherit from multiple multiclasses, 657 instantiating definitions from each multiclass. Using a multiclass 658 this way is exactly equivalent to instantiating the classes multiple 659 times yourself, e.g. by writing:</p> 660 661 <div class="doc_code"> 662 <pre> 663 <b>def</b> ops; 664 <b>def</b> GPR; 665 <b>def</b> Imm; 666 <b>class</b> inst<<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist>; 667 668 <b>class</b> rrinst<<b>int</b> opc, <b>string</b> asmstr> 669 : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"), 670 (ops GPR:$dst, GPR:$src1, GPR:$src2)>; 671 672 <b>class</b> riinst<<b>int</b> opc, <b>string</b> asmstr> 673 : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"), 674 (ops GPR:$dst, GPR:$src1, Imm:$src2)>; 675 676 <i>// Instantiations of the ri_inst multiclass.</i> 677 <b>def</b> ADD_rr : rrinst<0b111, "add">; 678 <b>def</b> ADD_ri : riinst<0b111, "add">; 679 <b>def</b> SUB_rr : rrinst<0b101, "sub">; 680 <b>def</b> SUB_ri : riinst<0b101, "sub">; 681 <b>def</b> MUL_rr : rrinst<0b100, "mul">; 682 <b>def</b> MUL_ri : riinst<0b100, "mul">; 683 ... 684 </pre> 685 </div> 686 687 <p> 688 A defm can also be used inside a multiclass providing several levels of 689 multiclass instanciations. 690 </p> 691 692 <div class="doc_code"> 693 <pre> 694 <b>class</b> Instruction<bits<4> opc, string Name> { 695 bits<4> opcode = opc; 696 string name = Name; 697 } 698 699 <b>multiclass</b> basic_r<bits<4> opc> { 700 <b>def</b> rr : Instruction<opc, "rr">; 701 <b>def</b> rm : Instruction<opc, "rm">; 702 } 703 704 <b>multiclass</b> basic_s<bits<4> opc> { 705 <b>defm</b> SS : basic_r<opc>; 706 <b>defm</b> SD : basic_r<opc>; 707 <b>def</b> X : Instruction<opc, "x">; 708 } 709 710 <b>multiclass</b> basic_p<bits<4> opc> { 711 <b>defm</b> PS : basic_r<opc>; 712 <b>defm</b> PD : basic_r<opc>; 713 <b>def</b> Y : Instruction<opc, "y">; 714 } 715 716 <b>defm</b> ADD : basic_s<0xf>, basic_p<0xf>; 717 ... 718 719 <i>// Results</i> 720 <b>def</b> ADDPDrm { ... 721 <b>def</b> ADDPDrr { ... 722 <b>def</b> ADDPSrm { ... 723 <b>def</b> ADDPSrr { ... 724 <b>def</b> ADDSDrm { ... 725 <b>def</b> ADDSDrr { ... 726 <b>def</b> ADDY { ... 727 <b>def</b> ADDX { ... 728 </pre> 729 </div> 730 731 <p> 732 defm declarations can inherit from classes too, the 733 rule to follow is that the class list must start after the 734 last multiclass, and there must be at least one multiclass 735 before them. 736 </p> 737 738 <div class="doc_code"> 739 <pre> 740 <b>class</b> XD { bits<4> Prefix = 11; } 741 <b>class</b> XS { bits<4> Prefix = 12; } 742 743 <b>class</b> I<bits<4> op> { 744 bits<4> opcode = op; 745 } 746 747 <b>multiclass</b> R { 748 <b>def</b> rr : I<4>; 749 <b>def</b> rm : I<2>; 750 } 751 752 <b>multiclass</b> Y { 753 <b>defm</b> SS : R, XD; 754 <b>defm</b> SD : R, XS; 755 } 756 757 <b>defm</b> Instr : Y; 758 759 <i>// Results</i> 760 <b>def</b> InstrSDrm { 761 bits<4> opcode = { 0, 0, 1, 0 }; 762 bits<4> Prefix = { 1, 1, 0, 0 }; 763 } 764 ... 765 <b>def</b> InstrSSrr { 766 bits<4> opcode = { 0, 1, 0, 0 }; 767 bits<4> Prefix = { 1, 0, 1, 1 }; 768 } 769 </pre> 770 </div> 771 772 </div> 773 774 </div> 775 776 <!-- ======================================================================= --> 777 <h3> 778 <a name="filescope">File scope entities</a> 779 </h3> 780 781 <div> 782 783 <!-- --------------------------------------------------------------------------> 784 <h4> 785 <a name="include">File inclusion</a> 786 </h4> 787 788 <div> 789 <p>TableGen supports the '<tt>include</tt>' token, which textually substitutes 790 the specified file in place of the include directive. The filename should be 791 specified as a double quoted string immediately after the '<tt>include</tt>' 792 keyword. Example:</p> 793 794 <div class="doc_code"> 795 <pre> 796 <b>include</b> "foo.td" 797 </pre> 798 </div> 799 800 </div> 801 802 <!-- --------------------------------------------------------------------------> 803 <h4> 804 <a name="globallet">'let' expressions</a> 805 </h4> 806 807 <div> 808 809 <p>"Let" expressions at file scope are similar to <a href="#recordlet">"let" 810 expressions within a record</a>, except they can specify a value binding for 811 multiple records at a time, and may be useful in certain other cases. 812 File-scope let expressions are really just another way that TableGen allows the 813 end-user to factor out commonality from the records.</p> 814 815 <p>File-scope "let" expressions take a comma-separated list of bindings to 816 apply, and one or more records to bind the values in. Here are some 817 examples:</p> 818 819 <div class="doc_code"> 820 <pre> 821 <b>let</b> isTerminator = 1, isReturn = 1, isBarrier = 1, hasCtrlDep = 1 <b>in</b> 822 <b>def</b> RET : I<0xC3, RawFrm, (outs), (ins), "ret", [(X86retflag 0)]>; 823 824 <b>let</b> isCall = 1 <b>in</b> 825 <i>// All calls clobber the non-callee saved registers...</i> 826 <b>let</b> Defs = [EAX, ECX, EDX, FP0, FP1, FP2, FP3, FP4, FP5, FP6, ST0, 827 MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7, 828 XMM0, XMM1, XMM2, XMM3, XMM4, XMM5, XMM6, XMM7, EFLAGS] <b>in</b> { 829 <b>def</b> CALLpcrel32 : Ii32<0xE8, RawFrm, (outs), (ins i32imm:$dst,variable_ops), 830 "call\t${dst:call}", []>; 831 <b>def</b> CALL32r : I<0xFF, MRM2r, (outs), (ins GR32:$dst, variable_ops), 832 "call\t{*}$dst", [(X86call GR32:$dst)]>; 833 <b>def</b> CALL32m : I<0xFF, MRM2m, (outs), (ins i32mem:$dst, variable_ops), 834 "call\t{*}$dst", []>; 835 } 836 </pre> 837 </div> 838 839 <p>File-scope "let" expressions are often useful when a couple of definitions 840 need to be added to several records, and the records do not otherwise need to be 841 opened, as in the case with the <tt>CALL*</tt> instructions above.</p> 842 843 <p>It's also possible to use "let" expressions inside multiclasses, providing 844 more ways to factor out commonality from the records, specially if using 845 several levels of multiclass instanciations. This also avoids the need of using 846 "let" expressions within subsequent records inside a multiclass.</p> 847 848 <pre class="doc_code"> 849 <b>multiclass </b>basic_r<bits<4> opc> { 850 <b>let </b>Predicates = [HasSSE2] in { 851 <b>def </b>rr : Instruction<opc, "rr">; 852 <b>def </b>rm : Instruction<opc, "rm">; 853 } 854 <b>let </b>Predicates = [HasSSE3] in 855 <b>def </b>rx : Instruction<opc, "rx">; 856 } 857 858 <b>multiclass </b>basic_ss<bits<4> opc> { 859 <b>let </b>IsDouble = 0 in 860 <b>defm </b>SS : basic_r<opc>; 861 862 <b>let </b>IsDouble = 1 in 863 <b>defm </b>SD : basic_r<opc>; 864 } 865 866 <b>defm </b>ADD : basic_ss<0xf>; 867 </pre> 868 </div> 869 870 </div> 871 872 </div> 873 874 <!-- *********************************************************************** --> 875 <h2><a name="codegen">Code Generator backend info</a></h2> 876 <!-- *********************************************************************** --> 877 878 <div> 879 880 <p>Expressions used by code generator to describe instructions and isel 881 patterns:</p> 882 883 <dl> 884 <dt><tt>(implicit a)</tt></dt> 885 <dd>an implicitly defined physical register. This tells the dag instruction 886 selection emitter the input pattern's extra definitions matches implicit 887 physical register definitions.</dd> 888 </dl> 889 </div> 890 891 <!-- *********************************************************************** --> 892 <h2><a name="backends">TableGen backends</a></h2> 893 <!-- *********************************************************************** --> 894 895 <div> 896 897 <p>TODO: How they work, how to write one. This section should not contain 898 details about any particular backend, except maybe -print-enums as an example. 899 This should highlight the APIs in <tt>TableGen/Record.h</tt>.</p> 900 901 </div> 902 903 <!-- *********************************************************************** --> 904 905 <hr> 906 <address> 907 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img 908 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a> 909 <a href="http://validator.w3.org/check/referer"><img 910 src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a> 911 912 <a href="mailto:sabre (a] nondot.org">Chris Lattner</a><br> 913 <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br> 914 Last modified: $Date$ 915 </address> 916 917 </body> 918 </html> 919
