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  10 <div class="doc_title">TableGen Fundamentals</div>
  11
  12 <div class="doc_text">
  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@nondot.org">Chris Lattner</a></p>
  50 </div>
  51
  52 <!-- *********************************************************************** -->
  53 <div class="doc_section"><a name="introduction">Introduction</a></div>
  54 <!-- *********************************************************************** -->
  55
  56 <div class="doc_text">
  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 </div>
  76
  77 <!-- ======================================================================= -->
  78 <div class="doc_subsection"><a name="concepts">Basic concepts</a></div>
  79
  80 <div class="doc_text">
  81
  82 <p>TableGen files consist of two key parts: 'classes' and 'definitions', both
  83 of which are considered 'records'.</p>
  84
  85 <p><b>TableGen records</b> have a unique name, a list of values, and a list of
  86 superclasses.  The list of values is the main data that TableGen builds for each
  87 record; it is this that holds the domain specific information for the
  88 application.  The interpretation of this data is left to a specific <a
  89 href="#backends">TableGen backend</a>, but the structure and format rules are
  90 taken care of and are fixed by TableGen.</p>
  91
  92 <p><b>TableGen definitions</b> are the concrete form of 'records'.  These
  93 generally do not have any undefined values, and are marked with the
  94 '<tt>def</tt>' keyword.</p>
  95
  96 <p><b>TableGen classes</b> are abstract records that are used to build and
  97 describe other records.  These 'classes' allow the end-user to build
  98 abstractions for either the domain they are targeting (such as "Register",
  99 "RegisterClass", and "Instruction" in the LLVM code generator) or for the
 100 implementor to help factor out common properties of records (such as "FPInst",
 101 which is used to represent floating point instructions in the X86 backend).
 102 TableGen keeps track of all of the classes that are used to build up a
 103 definition, so the backend can find all definitions of a particular class, such
 104 as "Instruction".</p>
 105
 106 <p><b>TableGen multiclasses</b> are groups of abstract records that are
 107 instantiated all at once.  Each instantiation can result in multiple TableGen
 108 definitions.</p>
 109
 110 </div>
 111
 112 <!-- ======================================================================= -->
 113 <div class="doc_subsection"><a name="example">An example record</a></div>
 114
 115 <div class="doc_text">
 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, $src2}";
 130   <b>list</b>&lt;dag&gt; Pattern = [(set GR32:$dst, (add GR32:$src1, GR32:$src2))];
 131   <b>list</b>&lt;Register&gt; Uses = [];
 132   <b>list</b>&lt;Register&gt; Defs = [EFLAGS];
 133   <b>list</b>&lt;Predicate&gt; 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> isTwoAddress = 1;
 146   <b>bit</b> isConvertibleToThreeAddress = 1;
 147   <b>bit</b> isCommutable = 1;
 148   <b>bit</b> isTerminator = 0;
 149   <b>bit</b> isReMaterializable = 0;
 150   <b>bit</b> isPredicable = 0;
 151   <b>bit</b> hasDelaySlot = 0;
 152   <b>bit</b> usesCustomDAGSchedInserter = 0;
 153   <b>bit</b> hasCtrlDep = 0;
 154   <b>bit</b> isNotDuplicable = 0;
 155   <b>bit</b> hasSideEffects = 0;
 156   <b>bit</b> mayHaveSideEffects = 0;
 157   <b>bit</b> neverHasSideEffects = 0;
 158   InstrItinClass Itinerary = NoItinerary;
 159   <b>string</b> Constraints = "";
 160   <b>string</b> DisableEncoding = "";
 161   <b>bits</b>&lt;8&gt; Opcode = { 0, 0, 0, 0, 0, 0, 0, 1 };
 162   Format Form = MRMDestReg;
 163   <b>bits</b>&lt;6&gt; FormBits = { 0, 0, 0, 0, 1, 1 };
 164   ImmType ImmT = NoImm;
 165   <b>bits</b>&lt;3&gt; ImmTypeBits = { 0, 0, 0 };
 166   <b>bit</b> hasOpSizePrefix = 0;
 167   <b>bit</b> hasAdSizePrefix = 0;
 168   <b>bits</b>&lt;4&gt; Prefix = { 0, 0, 0, 0 };
 169   <b>bit</b> hasREX_WPrefix = 0;
 170   FPFormat FPForm = ?;
 171   <b>bits</b>&lt;3&gt; FPFormBits = { 0, 0, 0 };
 172 }
 173 ...
 174 </pre>
 175 </div>
 176
 177 <p>This definition corresponds to a 32-bit register-register add instruction in
 178 the X86.  The string after the '<tt>def</tt>' string indicates the name of the
 179 record&mdash;"<tt>ADD32rr</tt>" in this case&mdash;and the comment at the end of
 180 the line indicates the superclasses of the definition.  The body of the record
 181 contains all of the data that TableGen assembled for the record, indicating that
 182 the instruction is part of the "X86" namespace, the pattern indicating how the
 183 the instruction should be emitted into the assembly file, that it is a
 184 two-address instruction, has a particular encoding, etc.  The contents and
 185 semantics of the information in the record is specific to the needs of the X86
 186 backend, and is only shown as an example.</p>
 187
 188 <p>As you can see, a lot of information is needed for every instruction
 189 supported by the code generator, and specifying it all manually would be
 190 unmaintainble, prone to bugs, and tiring to do in the first place.  Because we
 191 are using TableGen, all of the information was derived from the following
 192 definition:</p>
 193
 194 <div class="doc_code">
 195 <pre>
 196 let Defs = [EFLAGS],
 197     isCommutable = 1,                  <i>// X = ADD Y,Z --&gt; X = ADD Z,Y</i>
 198     isConvertibleToThreeAddress = 1 <b>in</b> <i>// Can transform into LEA.</i>
 199 def ADD32rr  : I&lt;0x01, MRMDestReg, (outs GR32:$dst),
 200                                    (ins GR32:$src1, GR32:$src2),
 201                  "add{l}\t{$src2, $dst|$dst, $src2}",
 202                  [(set GR32:$dst, (add GR32:$src1, GR32:$src2))]&gt;;
 203 </pre>
 204 </div>
 205
 206 <p>This definition makes use of the custom class <tt>I</tt> (extended from the
 207 custom class <tt>X86Inst</tt>), which is defined in the X86-specific TableGen
 208 file, to factor out the common features that instructions of its class share.  A
 209 key feature of TableGen is that it allows the end-user to define the
 210 abstractions they prefer to use when describing their information.</p>
 211
 212 </div>
 213
 214 <!-- ======================================================================= -->
 215 <div class="doc_subsection"><a name="running">Running TableGen</a></div>
 216
 217 <div class="doc_text">
 218
 219 <p>TableGen runs just like any other LLVM tool.  The first (optional) argument
 220 specifies the file to read.  If a filename is not specified, <tt>tblgen</tt>
 221 reads from standard input.</p>
 222
 223 <p>To be useful, one of the <a href="#backends">TableGen backends</a> must be
 224 used.  These backends are selectable on the command line (type '<tt>tblgen
 225 -help</tt>' for a list).  For example, to get a list of all of the definitions
 226 that subclass a particular type (which can be useful for building up an enum
 227 list of these records), use the <tt>-print-enums</tt> option:</p>
 228
 229 <div class="doc_code">
 230 <pre>
 231 $ tblgen X86.td -print-enums -class=Register
 232 AH, AL, AX, BH, BL, BP, BPL, BX, CH, CL, CX, DH, DI, DIL, DL, DX, EAX, EBP, EBX,
 233 ECX, EDI, EDX, EFLAGS, EIP, ESI, ESP, FP0, FP1, FP2, FP3, FP4, FP5, FP6, IP,
 234 MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7, R10, R10B, R10D, R10W, R11, R11B, R11D,
 235 R11W, R12, R12B, R12D, R12W, R13, R13B, R13D, R13W, R14, R14B, R14D, R14W, R15,
 236 R15B, R15D, R15W, R8, R8B, R8D, R8W, R9, R9B, R9D, R9W, RAX, RBP, RBX, RCX, RDI,
 237 RDX, RIP, RSI, RSP, SI, SIL, SP, SPL, ST0, ST1, ST2, ST3, ST4, ST5, ST6, ST7,
 238 XMM0, XMM1, XMM10, XMM11, XMM12, XMM13, XMM14, XMM15, XMM2, XMM3, XMM4, XMM5,
 239 XMM6, XMM7, XMM8, XMM9,
 240
 241 $ tblgen X86.td -print-enums -class=Instruction
 242 ABS_F, ABS_Fp32, ABS_Fp64, ABS_Fp80, ADC32mi, ADC32mi8, ADC32mr, ADC32ri,
 243 ADC32ri8, ADC32rm, ADC32rr, ADC64mi32, ADC64mi8, ADC64mr, ADC64ri32, ADC64ri8,
 244 ADC64rm, ADC64rr, ADD16mi, ADD16mi8, ADD16mr, ADD16ri, ADD16ri8, ADD16rm,
 245 ADD16rr, ADD32mi, ADD32mi8, ADD32mr, ADD32ri, ADD32ri8, ADD32rm, ADD32rr,
 246 ADD64mi32, ADD64mi8, ADD64mr, ADD64ri32, ...
 247 </pre>
 248 </div>
 249
 250 <p>The default backend prints out all of the records, as described <a
 251 href="#example">above</a>.</p>
 252
 253 <p>If you plan to use TableGen, you will most likely have to <a
 254 href="#backends">write a backend</a> that extracts the information specific to
 255 what you need and formats it in the appropriate way.</p>
 256
 257 </div>
 258
 259
 260 <!-- *********************************************************************** -->
 261 <div class="doc_section"><a name="syntax">TableGen syntax</a></div>
 262 <!-- *********************************************************************** -->
 263
 264 <div class="doc_text">
 265
 266 <p>TableGen doesn't care about the meaning of data (that is up to the backend to
 267 define), but it does care about syntax, and it enforces a simple type system.
 268 This section describes the syntax and the constructs allowed in a TableGen file.
 269 </p>
 270
 271 </div>
 272
 273 <!-- ======================================================================= -->
 274 <div class="doc_subsection"><a name="primitives">TableGen primitives</a></div>
 275
 276 <!-- -------------------------------------------------------------------------->
 277 <div class="doc_subsubsection"><a name="comments">TableGen comments</a></div>
 278
 279 <div class="doc_text">
 280
 281 <p>TableGen supports BCPL style "<tt>//</tt>" comments, which run to the end of
 282 the line, and it also supports <b>nestable</b> "<tt>/* */</tt>" comments.</p>
 283
 284 </div>
 285
 286 <!-- -------------------------------------------------------------------------->
 287 <div class="doc_subsubsection">
 288   <a name="types">The TableGen type system</a>
 289 </div>
 290
 291 <div class="doc_text">
 292
 293 <p>TableGen files are strongly typed, in a simple (but complete) type-system.
 294 These types are used to perform automatic conversions, check for errors, and to
 295 help interface designers constrain the input that they allow.  Every <a
 296 href="#valuedef">value definition</a> is required to have an associated type.
 297 </p>
 298
 299 <p>TableGen supports a mixture of very low-level types (such as <tt>bit</tt>)
 300 and very high-level types (such as <tt>dag</tt>).  This flexibility is what
 301 allows it to describe a wide range of information conveniently and compactly.
 302 The TableGen types are:</p>
 303
 304 <dl>
 305 <dt><tt><b>bit</b></tt></dt>
 306   <dd>A 'bit' is a boolean value that can hold either 0 or 1.</dd>
 307
 308 <dt><tt><b>int</b></tt></dt>
 309   <dd>The 'int' type represents a simple 32-bit integer value, such as 5.</dd>
 310
 311 <dt><tt><b>string</b></tt></dt>
 312   <dd>The 'string' type represents an ordered sequence of characters of
 313   arbitrary length.</dd>
 314
 315 <dt><tt><b>bits</b>&lt;n&gt;</tt></dt>
 316   <dd>A 'bits' type is an arbitrary, but fixed, size integer that is broken up
 317   into individual bits.  This type is useful because it can handle some bits
 318   being defined while others are undefined.</dd>
 319
 320 <dt><tt><b>list</b>&lt;ty&gt;</tt></dt>
 321   <dd>This type represents a list whose elements are some other type.  The
 322   contained type is arbitrary: it can even be another list type.</dd>
 323
 324 <dt>Class type</dt>
 325   <dd>Specifying a class name in a type context means that the defined value
 326   must be a subclass of the specified class.  This is useful in conjunction with
 327   the <b><tt>list</tt></b> type, for example, to constrain the elements of the
 328   list to a common base class (e.g., a <tt><b>list</b>&lt;Register&gt;</tt> can
 329   only contain definitions derived from the "<tt>Register</tt>" class).</dd>
 330
 331 <dt><tt><b>dag</b></tt></dt>
 332   <dd>This type represents a nestable directed graph of elements.</dd>
 333
 334 <dt><tt><b>code</b></tt></dt>
 335   <dd>This represents a big hunk of text. NOTE: I don't remember why this is
 336   distinct from string!</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 <div class="doc_subsubsection">
 347   <a name="values">TableGen values and expressions</a>
 348 </div>
 349
 350 <div class="doc_text">
 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 ]</tt></dt>
 373   <dd>list value.</dd>
 374 <dt><tt>{ a, b, c }</tt></dt>
 375   <dd>initializer for a "bits&lt;3&gt;" value</dd>
 376 <dt><tt>value</tt></dt>
 377   <dd>value reference</dd>
 378 <dt><tt>value{17}</tt></dt>
 379   <dd>access to one bit of a value</dd>
 380 <dt><tt>value{15-17}</tt></dt>
 381   <dd>access to multiple bits of a value</dd>
 382 <dt><tt>DEF</tt></dt>
 383   <dd>reference to a record definition</dd>
 384 <dt><tt>CLASS&lt;val list&gt;</tt></dt>
 385   <dd>reference to a new anonymous definition of CLASS with the specified
 386       template arguments.</dd>
 387 <dt><tt>X.Y</tt></dt>
 388   <dd>reference to the subfield of a value</dd>
 389 <dt><tt>list[4-7,17,2-3]</tt></dt>
 390   <dd>A slice of the 'list' list, including elements 4,5,6,7,17,2, and 3 from
 391   it.  Elements may be included multiple times.</dd>
 392 <dt><tt>(DEF a, b)</tt></dt>
 393   <dd>a dag value.  The first element is required to be a record definition, the
 394   remaining elements in the list may be arbitrary other values, including nested
 395   `<tt>dag</tt>' values.</dd>
 396 <dt><tt>!strconcat(a, b)</tt></dt>
 397   <dd>A string value that is the result of concatenating the 'a' and 'b'
 398   strings.</dd>
 399 </dl>
 400
 401 <p>Note that all of the values have rules specifying how they convert to values
 402 for different types.  These rules allow you to assign a value like "<tt>7</tt>"
 403 to a "<tt>bits&lt;4&gt;</tt>" value, for example.</p>
 404
 405 </div>
 406
 407 <!-- ======================================================================= -->
 408 <div class="doc_subsection">
 409   <a name="classesdefs">Classes and definitions</a>
 410 </div>
 411
 412 <div class="doc_text">
 413
 414 <p>As mentioned in the <a href="#concepts">intro</a>, classes and definitions
 415 (collectively known as 'records') in TableGen are the main high-level unit of
 416 information that TableGen collects.  Records are defined with a <tt>def</tt> or
 417 <tt>class</tt> keyword, the record name, and an optional list of "<a
 418 href="#templateargs">template arguments</a>".  If the record has superclasses,
 419 they are specified as a comma separated list that starts with a colon character
 420 ("<tt>:</tt>").  If <a href="#valuedef">value definitions</a> or <a
 421 href="#recordlet">let expressions</a> are needed for the class, they are
 422 enclosed in curly braces ("<tt>{}</tt>"); otherwise, the record ends with a
 423 semicolon.</p>
 424
 425 <p>Here is a simple TableGen file:</p>
 426
 427 <div class="doc_code">
 428 <pre>
 429 <b>class</b> C { <b>bit</b> V = 1; }
 430 <b>def</b> X : C;
 431 <b>def</b> Y : C {
 432   <b>string</b> Greeting = "hello";
 433 }
 434 </pre>
 435 </div>
 436
 437 <p>This example defines two definitions, <tt>X</tt> and <tt>Y</tt>, both of
 438 which derive from the <tt>C</tt> class.  Because of this, they both get the
 439 <tt>V</tt> bit value.  The <tt>Y</tt> definition also gets the Greeting member
 440 as well.</p>
 441
 442 <p>In general, classes are useful for collecting together the commonality
 443 between a group of records and isolating it in a single place.  Also, classes
 444 permit the specification of default values for their subclasses, allowing the
 445 subclasses to override them as they wish.</p>
 446
 447 </div>
 448
 449 <!---------------------------------------------------------------------------->
 450 <div class="doc_subsubsection">
 451   <a name="valuedef">Value definitions</a>
 452 </div>
 453
 454 <div class="doc_text">
 455
 456 <p>Value definitions define named entries in records.  A value must be defined
 457 before it can be referred to as the operand for another value definition or
 458 before the value is reset with a <a href="#recordlet">let expression</a>.  A
 459 value is defined by specifying a <a href="#types">TableGen type</a> and a name.
 460 If an initial value is available, it may be specified after the type with an
 461 equal sign.  Value definitions require terminating semicolons.</p>
 462
 463 </div>
 464
 465 <!-- -------------------------------------------------------------------------->
 466 <div class="doc_subsubsection">
 467   <a name="recordlet">'let' expressions</a>
 468 </div>
 469
 470 <div class="doc_text">
 471
 472 <p>A record-level let expression is used to change the value of a value
 473 definition in a record.  This is primarily useful when a superclass defines a
 474 value that a derived class or definition wants to override.  Let expressions
 475 consist of the '<tt>let</tt>' keyword followed by a value name, an equal sign
 476 ("<tt>=</tt>"), and a new value.  For example, a new class could be added to the
 477 example above, redefining the <tt>V</tt> field for all of its subclasses:</p>
 478
 479 <div class="doc_code">
 480 <pre>
 481 <b>class</b> D : C { let V = 0; }
 482 <b>def</b> Z : D;
 483 </pre>
 484 </div>
 485
 486 <p>In this case, the <tt>Z</tt> definition will have a zero value for its "V"
 487 value, despite the fact that it derives (indirectly) from the <tt>C</tt> class,
 488 because the <tt>D</tt> class overrode its value.</p>
 489
 490 </div>
 491
 492 <!-- -------------------------------------------------------------------------->
 493 <div class="doc_subsubsection">
 494   <a name="templateargs">Class template arguments</a>
 495 </div>
 496
 497 <div class="doc_text">
 498
 499 <p>TableGen permits the definition of parameterized classes as well as normal
 500 concrete classes.  Parameterized TableGen classes specify a list of variable
 501 bindings (which may optionally have defaults) that are bound when used.  Here is
 502 a simple example:</p>
 503
 504 <div class="doc_code">
 505 <pre>
 506 <b>class</b> FPFormat&lt;<b>bits</b>&lt;3&gt; val&gt; {
 507   <b>bits</b>&lt;3&gt; Value = val;
 508 }
 509 <b>def</b> NotFP      : FPFormat&lt;0&gt;;
 510 <b>def</b> ZeroArgFP  : FPFormat&lt;1&gt;;
 511 <b>def</b> OneArgFP   : FPFormat&lt;2&gt;;
 512 <b>def</b> OneArgFPRW : FPFormat&lt;3&gt;;
 513 <b>def</b> TwoArgFP   : FPFormat&lt;4&gt;;
 514 <b>def</b> CompareFP  : FPFormat&lt;5&gt;;
 515 <b>def</b> CondMovFP  : FPFormat&lt;6&gt;;
 516 <b>def</b> SpecialFP  : FPFormat&lt;7&gt;;
 517 </pre>
 518 </div>
 519
 520 <p>In this case, template arguments are used as a space efficient way to specify
 521 a list of "enumeration values", each with a "<tt>Value</tt>" field set to the
 522 specified integer.</p>
 523
 524 <p>The more esoteric forms of <a href="#values">TableGen expressions</a> are
 525 useful in conjunction with template arguments.  As an example:</p>
 526
 527 <div class="doc_code">
 528 <pre>
 529 <b>class</b> ModRefVal&lt;<b>bits</b>&lt;2&gt; val&gt; {
 530   <b>bits</b>&lt;2&gt; Value = val;
 531 }
 532
 533 <b>def</b> None   : ModRefVal&lt;0&gt;;
 534 <b>def</b> Mod    : ModRefVal&lt;1&gt;;
 535 <b>def</b> Ref    : ModRefVal&lt;2&gt;;
 536 <b>def</b> ModRef : ModRefVal&lt;3&gt;;
 537
 538 <b>class</b> Value&lt;ModRefVal MR&gt; {
 539   <i>// Decode some information into a more convenient format, while providing
 540   // a nice interface to the user of the "Value" class.</i>
 541   <b>bit</b> isMod = MR.Value{0};
 542   <b>bit</b> isRef = MR.Value{1};
 543
 544   <i>// other stuff...</i>
 545 }
 546
 547 <i>// Example uses</i>
 548 <b>def</b> bork : Value&lt;Mod&gt;;
 549 <b>def</b> zork : Value&lt;Ref&gt;;
 550 <b>def</b> hork : Value&lt;ModRef&gt;;
 551 </pre>
 552 </div>
 553
 554 <p>This is obviously a contrived example, but it shows how template arguments
 555 can be used to decouple the interface provided to the user of the class from the
 556 actual internal data representation expected by the class.  In this case,
 557 running <tt>tblgen</tt> on the example prints the following definitions:</p>
 558
 559 <div class="doc_code">
 560 <pre>
 561 <b>def</b> bork {      <i>// Value</i>
 562   <b>bit</b> isMod = 1;
 563   <b>bit</b> isRef = 0;
 564 }
 565 <b>def</b> hork {      <i>// Value</i>
 566   <b>bit</b> isMod = 1;
 567   <b>bit</b> isRef = 1;
 568 }
 569 <b>def</b> zork {      <i>// Value</i>
 570   <b>bit</b> isMod = 0;
 571   <b>bit</b> isRef = 1;
 572 }
 573 </pre>
 574 </div>
 575
 576 <p> This shows that TableGen was able to dig into the argument and extract a
 577 piece of information that was requested by the designer of the "Value" class.
 578 For more realistic examples, please see existing users of TableGen, such as the
 579 X86 backend.</p>
 580
 581 </div>
 582
 583 <!-- -------------------------------------------------------------------------->
 584 <div class="doc_subsubsection">
 585   <a name="multiclass">Multiclass definitions and instances</a>
 586 </div>
 587
 588 <div class="doc_text">
 589
 590 <p>
 591 While classes with template arguments are a good way to factor commonality
 592 between two instances of a definition, multiclasses allow a convenient notation
 593 for defining multiple definitions at once (instances of implicitly constructed
 594 classes).  For example, consider an 3-address instruction set whose instructions
 595 come in two forms: "<tt>reg = reg op reg</tt>" and "<tt>reg = reg op imm</tt>"
 596 (e.g. SPARC). In this case, you'd like to specify in one place that this
 597 commonality exists, then in a separate place indicate what all the ops are.
 598 </p>
 599
 600 <p>
 601 Here is an example TableGen fragment that shows this idea:
 602 </p>
 603
 604 <div class="doc_code">
 605 <pre>
 606 <b>def</b> ops;
 607 <b>def</b> GPR;
 608 <b>def</b> Imm;
 609 <b>class</b> inst&lt;<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist&gt;;
 610
 611 <b>multiclass</b> ri_inst&lt;<b>int</b> opc, <b>string</b> asmstr&gt; {
 612   def _rr : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
 613                  (ops GPR:$dst, GPR:$src1, GPR:$src2)&gt;;
 614   def _ri : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
 615                  (ops GPR:$dst, GPR:$src1, Imm:$src2)&gt;;
 616 }
 617
 618 <i>// Instantiations of the ri_inst multiclass.</i>
 619 <b>defm</b> ADD : ri_inst&lt;0b111, "add"&gt;;
 620 <b>defm</b> SUB : ri_inst&lt;0b101, "sub"&gt;;
 621 <b>defm</b> MUL : ri_inst&lt;0b100, "mul"&gt;;
 622 ...
 623 </pre>
 624 </div>
 625
 626 <p>The name of the resultant definitions has the multidef fragment names
 627    appended to them, so this defines <tt>ADD_rr</tt>, <tt>ADD_ri</tt>,
 628    <tt>SUB_rr</tt>, etc.  Using a multiclass this way is exactly equivalent to
 629    instantiating the classes multiple times yourself, e.g. by writing:</p>
 630
 631 <div class="doc_code">
 632 <pre>
 633 <b>def</b> ops;
 634 <b>def</b> GPR;
 635 <b>def</b> Imm;
 636 <b>class</b> inst&lt;<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist&gt;;
 637
 638 <b>class</b> rrinst&lt;<b>int</b> opc, <b>string</b> asmstr&gt;
 639   : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
 640          (ops GPR:$dst, GPR:$src1, GPR:$src2)&gt;;
 641
 642 <b>class</b> riinst&lt;<b>int</b> opc, <b>string</b> asmstr&gt;
 643   : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
 644          (ops GPR:$dst, GPR:$src1, Imm:$src2)&gt;;
 645
 646 <i>// Instantiations of the ri_inst multiclass.</i>
 647 <b>def</b> ADD_rr : rrinst&lt;0b111, "add"&gt;;
 648 <b>def</b> ADD_ri : riinst&lt;0b111, "add"&gt;;
 649 <b>def</b> SUB_rr : rrinst&lt;0b101, "sub"&gt;;
 650 <b>def</b> SUB_ri : riinst&lt;0b101, "sub"&gt;;
 651 <b>def</b> MUL_rr : rrinst&lt;0b100, "mul"&gt;;
 652 <b>def</b> MUL_ri : riinst&lt;0b100, "mul"&gt;;
 653 ...
 654 </pre>
 655 </div>
 656
 657 </div>
 658
 659 <!-- ======================================================================= -->
 660 <div class="doc_subsection">
 661   <a name="filescope">File scope entities</a>
 662 </div>
 663
 664 <!-- -------------------------------------------------------------------------->
 665 <div class="doc_subsubsection">
 666   <a name="include">File inclusion</a>
 667 </div>
 668
 669 <div class="doc_text">
 670 <p>TableGen supports the '<tt>include</tt>' token, which textually substitutes
 671 the specified file in place of the include directive.  The filename should be
 672 specified as a double quoted string immediately after the '<tt>include</tt>'
 673 keyword.  Example:</p>
 674
 675 <div class="doc_code">
 676 <pre>
 677 <b>include</b> "foo.td"
 678 </pre>
 679 </div>
 680
 681 </div>
 682
 683 <!-- -------------------------------------------------------------------------->
 684 <div class="doc_subsubsection">
 685   <a name="globallet">'let' expressions</a>
 686 </div>
 687
 688 <div class="doc_text">
 689
 690 <p>"Let" expressions at file scope are similar to <a href="#recordlet">"let"
 691 expressions within a record</a>, except they can specify a value binding for
 692 multiple records at a time, and may be useful in certain other cases.
 693 File-scope let expressions are really just another way that TableGen allows the
 694 end-user to factor out commonality from the records.</p>
 695
 696 <p>File-scope "let" expressions take a comma-separated list of bindings to
 697 apply, and one or more records to bind the values in.  Here are some
 698 examples:</p>
 699
 700 <div class="doc_code">
 701 <pre>
 702 <b>let</b> isTerminator = 1, isReturn = 1, isBarrier = 1, hasCtrlDep = 1 <b>in</b>
 703   <b>def</b> RET : I&lt;0xC3, RawFrm, (outs), (ins), "ret", [(X86retflag 0)]&gt;;
 704
 705 <b>let</b> isCall = 1 <b>in</b>
 706   <i>// All calls clobber the non-callee saved registers...</i>
 707   <b>let</b> Defs = [EAX, ECX, EDX, FP0, FP1, FP2, FP3, FP4, FP5, FP6, ST0,
 708               MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7,
 709               XMM0, XMM1, XMM2, XMM3, XMM4, XMM5, XMM6, XMM7, EFLAGS] <b>in</b> {
 710     <b>def</b> CALLpcrel32 : Ii32&lt;0xE8, RawFrm, (outs), (ins i32imm:$dst,variable_ops),
 711                            "call\t${dst:call}", []&gt;;
 712     <b>def</b> CALL32r     : I&lt;0xFF, MRM2r, (outs), (ins GR32:$dst, variable_ops),
 713                         "call\t{*}$dst", [(X86call GR32:$dst)]&gt;;
 714     <b>def</b> CALL32m     : I&lt;0xFF, MRM2m, (outs), (ins i32mem:$dst, variable_ops),
 715                         "call\t{*}$dst", []&gt;;
 716   }
 717 </pre>
 718 </div>
 719
 720 <p>File-scope "let" expressions are often useful when a couple of definitions
 721 need to be added to several records, and the records do not otherwise need to be
 722 opened, as in the case with the <tt>CALL*</tt> instructions above.</p>
 723
 724 </div>
 725
 726 <!-- *********************************************************************** -->
 727 <div class="doc_section"><a name="backends">TableGen backends</a></div>
 728 <!-- *********************************************************************** -->
 729
 730 <div class="doc_text">
 731
 732 <p>TODO: How they work, how to write one.  This section should not contain
 733 details about any particular backend, except maybe -print-enums as an example.
 734 This should highlight the APIs in <tt>TableGen/Record.h</tt>.</p>
 735
 736 </div>
 737
 738 <!-- *********************************************************************** -->
 739
 740 <hr>
 741 <address>
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 746
 747   <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
 748   <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
 749   Last modified: $Date$
 750 </address>
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