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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
 108 TableGen definitions.  If a multiclass inherits from another multiclass,
 109 the definitions in the sub-multiclass become part of the current
 110 multiclass, as if they were declared in the current multiclass.</p>
 111
 112 </div>
 113
 114 <!-- ======================================================================= -->
 115 <div class="doc_subsection"><a name="example">An example record</a></div>
 116
 117 <div class="doc_text">
 118
 119 <p>With no other arguments, TableGen parses the specified file and prints out
 120 all of the classes, then all of the definitions.  This is a good way to see what
 121 the various definitions expand to fully.  Running this on the <tt>X86.td</tt>
 122 file prints this (at the time of this writing):</p>
 123
 124 <div class="doc_code">
 125 <pre>
 126 ...
 127 <b>def</b> ADD32rr {   <i>// Instruction X86Inst I</i>
 128   <b>string</b> Namespace = "X86";
 129   <b>dag</b> OutOperandList = (outs GR32:$dst);
 130   <b>dag</b> InOperandList = (ins GR32:$src1, GR32:$src2);
 131   <b>string</b> AsmString = "add{l}\t{$src2, $dst|$dst, $src2}";
 132   <b>list</b>&lt;dag&gt; Pattern = [(set GR32:$dst, (add GR32:$src1, GR32:$src2))];
 133   <b>list</b>&lt;Register&gt; Uses = [];
 134   <b>list</b>&lt;Register&gt; Defs = [EFLAGS];
 135   <b>list</b>&lt;Predicate&gt; Predicates = [];
 136   <b>int</b> CodeSize = 3;
 137   <b>int</b> AddedComplexity = 0;
 138   <b>bit</b> isReturn = 0;
 139   <b>bit</b> isBranch = 0;
 140   <b>bit</b> isIndirectBranch = 0;
 141   <b>bit</b> isBarrier = 0;
 142   <b>bit</b> isCall = 0;
 143   <b>bit</b> canFoldAsLoad = 0;
 144   <b>bit</b> mayLoad = 0;
 145   <b>bit</b> mayStore = 0;
 146   <b>bit</b> isImplicitDef = 0;
 147   <b>bit</b> isTwoAddress = 1;
 148   <b>bit</b> isConvertibleToThreeAddress = 1;
 149   <b>bit</b> isCommutable = 1;
 150   <b>bit</b> isTerminator = 0;
 151   <b>bit</b> isReMaterializable = 0;
 152   <b>bit</b> isPredicable = 0;
 153   <b>bit</b> hasDelaySlot = 0;
 154   <b>bit</b> usesCustomDAGSchedInserter = 0;
 155   <b>bit</b> hasCtrlDep = 0;
 156   <b>bit</b> isNotDuplicable = 0;
 157   <b>bit</b> hasSideEffects = 0;
 158   <b>bit</b> mayHaveSideEffects = 0;
 159   <b>bit</b> neverHasSideEffects = 0;
 160   InstrItinClass Itinerary = NoItinerary;
 161   <b>string</b> Constraints = "";
 162   <b>string</b> DisableEncoding = "";
 163   <b>bits</b>&lt;8&gt; Opcode = { 0, 0, 0, 0, 0, 0, 0, 1 };
 164   Format Form = MRMDestReg;
 165   <b>bits</b>&lt;6&gt; FormBits = { 0, 0, 0, 0, 1, 1 };
 166   ImmType ImmT = NoImm;
 167   <b>bits</b>&lt;3&gt; ImmTypeBits = { 0, 0, 0 };
 168   <b>bit</b> hasOpSizePrefix = 0;
 169   <b>bit</b> hasAdSizePrefix = 0;
 170   <b>bits</b>&lt;4&gt; Prefix = { 0, 0, 0, 0 };
 171   <b>bit</b> hasREX_WPrefix = 0;
 172   FPFormat FPForm = ?;
 173   <b>bits</b>&lt;3&gt; FPFormBits = { 0, 0, 0 };
 174 }
 175 ...
 176 </pre>
 177 </div>
 178
 179 <p>This definition corresponds to a 32-bit register-register add instruction in
 180 the X86.  The string after the '<tt>def</tt>' string indicates the name of the
 181 record&mdash;"<tt>ADD32rr</tt>" in this case&mdash;and the comment at the end of
 182 the line indicates the superclasses of the definition.  The body of the record
 183 contains all of the data that TableGen assembled for the record, indicating that
 184 the instruction is part of the "X86" namespace, the pattern indicating how the
 185 the instruction should be emitted into the assembly file, that it is a
 186 two-address instruction, has a particular encoding, etc.  The contents and
 187 semantics of the information in the record is specific to the needs of the X86
 188 backend, and is only shown as an example.</p>
 189
 190 <p>As you can see, a lot of information is needed for every instruction
 191 supported by the code generator, and specifying it all manually would be
 192 unmaintainble, prone to bugs, and tiring to do in the first place.  Because we
 193 are using TableGen, all of the information was derived from the following
 194 definition:</p>
 195
 196 <div class="doc_code">
 197 <pre>
 198 let Defs = [EFLAGS],
 199     isCommutable = 1,                  <i>// X = ADD Y,Z --&gt; X = ADD Z,Y</i>
 200     isConvertibleToThreeAddress = 1 <b>in</b> <i>// Can transform into LEA.</i>
 201 def ADD32rr  : I&lt;0x01, MRMDestReg, (outs GR32:$dst),
 202                                    (ins GR32:$src1, GR32:$src2),
 203                  "add{l}\t{$src2, $dst|$dst, $src2}",
 204                  [(set GR32:$dst, (add GR32:$src1, GR32:$src2))]&gt;;
 205 </pre>
 206 </div>
 207
 208 <p>This definition makes use of the custom class <tt>I</tt> (extended from the
 209 custom class <tt>X86Inst</tt>), which is defined in the X86-specific TableGen
 210 file, to factor out the common features that instructions of its class share.  A
 211 key feature of TableGen is that it allows the end-user to define the
 212 abstractions they prefer to use when describing their information.</p>
 213
 214 </div>
 215
 216 <!-- ======================================================================= -->
 217 <div class="doc_subsection"><a name="running">Running TableGen</a></div>
 218
 219 <div class="doc_text">
 220
 221 <p>TableGen runs just like any other LLVM tool.  The first (optional) argument
 222 specifies the file to read.  If a filename is not specified, <tt>tblgen</tt>
 223 reads from standard input.</p>
 224
 225 <p>To be useful, one of the <a href="#backends">TableGen backends</a> must be
 226 used.  These backends are selectable on the command line (type '<tt>tblgen
 227 -help</tt>' for a list).  For example, to get a list of all of the definitions
 228 that subclass a particular type (which can be useful for building up an enum
 229 list of these records), use the <tt>-print-enums</tt> option:</p>
 230
 231 <div class="doc_code">
 232 <pre>
 233 $ tblgen X86.td -print-enums -class=Register
 234 AH, AL, AX, BH, BL, BP, BPL, BX, CH, CL, CX, DH, DI, DIL, DL, DX, EAX, EBP, EBX,
 235 ECX, EDI, EDX, EFLAGS, EIP, ESI, ESP, FP0, FP1, FP2, FP3, FP4, FP5, FP6, IP,
 236 MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7, R10, R10B, R10D, R10W, R11, R11B, R11D,
 237 R11W, R12, R12B, R12D, R12W, R13, R13B, R13D, R13W, R14, R14B, R14D, R14W, R15,
 238 R15B, R15D, R15W, R8, R8B, R8D, R8W, R9, R9B, R9D, R9W, RAX, RBP, RBX, RCX, RDI,
 239 RDX, RIP, RSI, RSP, SI, SIL, SP, SPL, ST0, ST1, ST2, ST3, ST4, ST5, ST6, ST7,
 240 XMM0, XMM1, XMM10, XMM11, XMM12, XMM13, XMM14, XMM15, XMM2, XMM3, XMM4, XMM5,
 241 XMM6, XMM7, XMM8, XMM9,
 242
 243 $ tblgen X86.td -print-enums -class=Instruction
 244 ABS_F, ABS_Fp32, ABS_Fp64, ABS_Fp80, ADC32mi, ADC32mi8, ADC32mr, ADC32ri,
 245 ADC32ri8, ADC32rm, ADC32rr, ADC64mi32, ADC64mi8, ADC64mr, ADC64ri32, ADC64ri8,
 246 ADC64rm, ADC64rr, ADD16mi, ADD16mi8, ADD16mr, ADD16ri, ADD16ri8, ADD16rm,
 247 ADD16rr, ADD32mi, ADD32mi8, ADD32mr, ADD32ri, ADD32ri8, ADD32rm, ADD32rr,
 248 ADD64mi32, ADD64mi8, ADD64mr, ADD64ri32, ...
 249 </pre>
 250 </div>
 251
 252 <p>The default backend prints out all of the records, as described <a
 253 href="#example">above</a>.</p>
 254
 255 <p>If you plan to use TableGen, you will most likely have to <a
 256 href="#backends">write a backend</a> that extracts the information specific to
 257 what you need and formats it in the appropriate way.</p>
 258
 259 </div>
 260
 261
 262 <!-- *********************************************************************** -->
 263 <div class="doc_section"><a name="syntax">TableGen syntax</a></div>
 264 <!-- *********************************************************************** -->
 265
 266 <div class="doc_text">
 267
 268 <p>TableGen doesn't care about the meaning of data (that is up to the backend to
 269 define), but it does care about syntax, and it enforces a simple type system.
 270 This section describes the syntax and the constructs allowed in a TableGen file.
 271 </p>
 272
 273 </div>
 274
 275 <!-- ======================================================================= -->
 276 <div class="doc_subsection"><a name="primitives">TableGen primitives</a></div>
 277
 278 <!-- -------------------------------------------------------------------------->
 279 <div class="doc_subsubsection"><a name="comments">TableGen comments</a></div>
 280
 281 <div class="doc_text">
 282
 283 <p>TableGen supports BCPL style "<tt>//</tt>" comments, which run to the end of
 284 the line, and it also supports <b>nestable</b> "<tt>/* */</tt>" comments.</p>
 285
 286 </div>
 287
 288 <!-- -------------------------------------------------------------------------->
 289 <div class="doc_subsubsection">
 290   <a name="types">The TableGen type system</a>
 291 </div>
 292
 293 <div class="doc_text">
 294
 295 <p>TableGen files are strongly typed, in a simple (but complete) type-system.
 296 These types are used to perform automatic conversions, check for errors, and to
 297 help interface designers constrain the input that they allow.  Every <a
 298 href="#valuedef">value definition</a> is required to have an associated type.
 299 </p>
 300
 301 <p>TableGen supports a mixture of very low-level types (such as <tt>bit</tt>)
 302 and very high-level types (such as <tt>dag</tt>).  This flexibility is what
 303 allows it to describe a wide range of information conveniently and compactly.
 304 The TableGen types are:</p>
 305
 306 <dl>
 307 <dt><tt><b>bit</b></tt></dt>
 308   <dd>A 'bit' is a boolean value that can hold either 0 or 1.</dd>
 309
 310 <dt><tt><b>int</b></tt></dt>
 311   <dd>The 'int' type represents a simple 32-bit integer value, such as 5.</dd>
 312
 313 <dt><tt><b>string</b></tt></dt>
 314   <dd>The 'string' type represents an ordered sequence of characters of
 315   arbitrary length.</dd>
 316
 317 <dt><tt><b>bits</b>&lt;n&gt;</tt></dt>
 318   <dd>A 'bits' type is an arbitrary, but fixed, size integer that is broken up
 319   into individual bits.  This type is useful because it can handle some bits
 320   being defined while others are undefined.</dd>
 321
 322 <dt><tt><b>list</b>&lt;ty&gt;</tt></dt>
 323   <dd>This type represents a list whose elements are some other type.  The
 324   contained type is arbitrary: it can even be another list type.</dd>
 325
 326 <dt>Class type</dt>
 327   <dd>Specifying a class name in a type context means that the defined value
 328   must be a subclass of the specified class.  This is useful in conjunction with
 329   the <b><tt>list</tt></b> type, for example, to constrain the elements of the
 330   list to a common base class (e.g., a <tt><b>list</b>&lt;Register&gt;</tt> can
 331   only contain definitions derived from the "<tt>Register</tt>" class).</dd>
 332
 333 <dt><tt><b>dag</b></tt></dt>
 334   <dd>This type represents a nestable directed graph of elements.</dd>
 335
 336 <dt><tt><b>code</b></tt></dt>
 337   <dd>This represents a big hunk of text. NOTE: I don't remember why this is
 338   distinct from string!</dd>
 339 </dl>
 340
 341 <p>To date, these types have been sufficient for describing things that
 342 TableGen has been used for, but it is straight-forward to extend this list if
 343 needed.</p>
 344
 345 </div>
 346
 347 <!-- -------------------------------------------------------------------------->
 348 <div class="doc_subsubsection">
 349   <a name="values">TableGen values and expressions</a>
 350 </div>
 351
 352 <div class="doc_text">
 353
 354 <p>TableGen allows for a pretty reasonable number of different expression forms
 355 when building up values.  These forms allow the TableGen file to be written in a
 356 natural syntax and flavor for the application.  The current expression forms
 357 supported include:</p>
 358
 359 <dl>
 360 <dt><tt>?</tt></dt>
 361   <dd>uninitialized field</dd>
 362 <dt><tt>0b1001011</tt></dt>
 363   <dd>binary integer value</dd>
 364 <dt><tt>07654321</tt></dt>
 365   <dd>octal integer value (indicated by a leading 0)</dd>
 366 <dt><tt>7</tt></dt>
 367   <dd>decimal integer value</dd>
 368 <dt><tt>0x7F</tt></dt>
 369   <dd>hexadecimal integer value</dd>
 370 <dt><tt>"foo"</tt></dt>
 371   <dd>string value</dd>
 372 <dt><tt>[{ ... }]</tt></dt>
 373   <dd>code fragment</dd>
 374 <dt><tt>[ X, Y, Z ]</tt></dt>
 375   <dd>list value.</dd>
 376 <dt><tt>{ a, b, c }</tt></dt>
 377   <dd>initializer for a "bits&lt;3&gt;" value</dd>
 378 <dt><tt>value</tt></dt>
 379   <dd>value reference</dd>
 380 <dt><tt>value{17}</tt></dt>
 381   <dd>access to one bit of a value</dd>
 382 <dt><tt>value{15-17}</tt></dt>
 383   <dd>access to multiple bits of a value</dd>
 384 <dt><tt>DEF</tt></dt>
 385   <dd>reference to a record definition</dd>
 386 <dt><tt>CLASS&lt;val list&gt;</tt></dt>
 387   <dd>reference to a new anonymous definition of CLASS with the specified
 388       template arguments.</dd>
 389 <dt><tt>X.Y</tt></dt>
 390   <dd>reference to the subfield of a value</dd>
 391 <dt><tt>list[4-7,17,2-3]</tt></dt>
 392   <dd>A slice of the 'list' list, including elements 4,5,6,7,17,2, and 3 from
 393   it.  Elements may be included multiple times.</dd>
 394 <dt><tt>(DEF a, b)</tt></dt>
 395   <dd>a dag value.  The first element is required to be a record definition, the
 396   remaining elements in the list may be arbitrary other values, including nested
 397   `<tt>dag</tt>' values.</dd>
 398 <dt><tt>!strconcat(a, b)</tt></dt>
 399   <dd>A string value that is the result of concatenating the 'a' and 'b'
 400   strings.</dd>
 401 <dt><tt>!nameconcat&lt;type&gt;(a, b)</tt></dt>
 402   <dd>A value that is the result of concatenating the 'a' and 'b'
 403   strings and looking up the resulting name in the symbol table.  The symbol type
 404   determines the type of the resulting value.  If the symbol is not found
 405   or the symbol type does not match 'type,' TableGen emits an error and aborts.</dd>
 406 </dl>
 407
 408 <p>Note that all of the values have rules specifying how they convert to values
 409 for different types.  These rules allow you to assign a value like "<tt>7</tt>"
 410 to a "<tt>bits&lt;4&gt;</tt>" value, for example.</p>
 411
 412 </div>
 413
 414 <!-- ======================================================================= -->
 415 <div class="doc_subsection">
 416   <a name="classesdefs">Classes and definitions</a>
 417 </div>
 418
 419 <div class="doc_text">
 420
 421 <p>As mentioned in the <a href="#concepts">intro</a>, classes and definitions
 422 (collectively known as 'records') in TableGen are the main high-level unit of
 423 information that TableGen collects.  Records are defined with a <tt>def</tt> or
 424 <tt>class</tt> keyword, the record name, and an optional list of "<a
 425 href="#templateargs">template arguments</a>".  If the record has superclasses,
 426 they are specified as a comma separated list that starts with a colon character
 427 ("<tt>:</tt>").  If <a href="#valuedef">value definitions</a> or <a
 428 href="#recordlet">let expressions</a> are needed for the class, they are
 429 enclosed in curly braces ("<tt>{}</tt>"); otherwise, the record ends with a
 430 semicolon.</p>
 431
 432 <p>Here is a simple TableGen file:</p>
 433
 434 <div class="doc_code">
 435 <pre>
 436 <b>class</b> C { <b>bit</b> V = 1; }
 437 <b>def</b> X : C;
 438 <b>def</b> Y : C {
 439   <b>string</b> Greeting = "hello";
 440 }
 441 </pre>
 442 </div>
 443
 444 <p>This example defines two definitions, <tt>X</tt> and <tt>Y</tt>, both of
 445 which derive from the <tt>C</tt> class.  Because of this, they both get the
 446 <tt>V</tt> bit value.  The <tt>Y</tt> definition also gets the Greeting member
 447 as well.</p>
 448
 449 <p>In general, classes are useful for collecting together the commonality
 450 between a group of records and isolating it in a single place.  Also, classes
 451 permit the specification of default values for their subclasses, allowing the
 452 subclasses to override them as they wish.</p>
 453
 454 </div>
 455
 456 <!---------------------------------------------------------------------------->
 457 <div class="doc_subsubsection">
 458   <a name="valuedef">Value definitions</a>
 459 </div>
 460
 461 <div class="doc_text">
 462
 463 <p>Value definitions define named entries in records.  A value must be defined
 464 before it can be referred to as the operand for another value definition or
 465 before the value is reset with a <a href="#recordlet">let expression</a>.  A
 466 value is defined by specifying a <a href="#types">TableGen type</a> and a name.
 467 If an initial value is available, it may be specified after the type with an
 468 equal sign.  Value definitions require terminating semicolons.</p>
 469
 470 </div>
 471
 472 <!-- -------------------------------------------------------------------------->
 473 <div class="doc_subsubsection">
 474   <a name="recordlet">'let' expressions</a>
 475 </div>
 476
 477 <div class="doc_text">
 478
 479 <p>A record-level let expression is used to change the value of a value
 480 definition in a record.  This is primarily useful when a superclass defines a
 481 value that a derived class or definition wants to override.  Let expressions
 482 consist of the '<tt>let</tt>' keyword followed by a value name, an equal sign
 483 ("<tt>=</tt>"), and a new value.  For example, a new class could be added to the
 484 example above, redefining the <tt>V</tt> field for all of its subclasses:</p>
 485
 486 <div class="doc_code">
 487 <pre>
 488 <b>class</b> D : C { let V = 0; }
 489 <b>def</b> Z : D;
 490 </pre>
 491 </div>
 492
 493 <p>In this case, the <tt>Z</tt> definition will have a zero value for its "V"
 494 value, despite the fact that it derives (indirectly) from the <tt>C</tt> class,
 495 because the <tt>D</tt> class overrode its value.</p>
 496
 497 </div>
 498
 499 <!-- -------------------------------------------------------------------------->
 500 <div class="doc_subsubsection">
 501   <a name="templateargs">Class template arguments</a>
 502 </div>
 503
 504 <div class="doc_text">
 505
 506 <p>TableGen permits the definition of parameterized classes as well as normal
 507 concrete classes.  Parameterized TableGen classes specify a list of variable
 508 bindings (which may optionally have defaults) that are bound when used.  Here is
 509 a simple example:</p>
 510
 511 <div class="doc_code">
 512 <pre>
 513 <b>class</b> FPFormat&lt;<b>bits</b>&lt;3&gt; val&gt; {
 514   <b>bits</b>&lt;3&gt; Value = val;
 515 }
 516 <b>def</b> NotFP      : FPFormat&lt;0&gt;;
 517 <b>def</b> ZeroArgFP  : FPFormat&lt;1&gt;;
 518 <b>def</b> OneArgFP   : FPFormat&lt;2&gt;;
 519 <b>def</b> OneArgFPRW : FPFormat&lt;3&gt;;
 520 <b>def</b> TwoArgFP   : FPFormat&lt;4&gt;;
 521 <b>def</b> CompareFP  : FPFormat&lt;5&gt;;
 522 <b>def</b> CondMovFP  : FPFormat&lt;6&gt;;
 523 <b>def</b> SpecialFP  : FPFormat&lt;7&gt;;
 524 </pre>
 525 </div>
 526
 527 <p>In this case, template arguments are used as a space efficient way to specify
 528 a list of "enumeration values", each with a "<tt>Value</tt>" field set to the
 529 specified integer.</p>
 530
 531 <p>The more esoteric forms of <a href="#values">TableGen expressions</a> are
 532 useful in conjunction with template arguments.  As an example:</p>
 533
 534 <div class="doc_code">
 535 <pre>
 536 <b>class</b> ModRefVal&lt;<b>bits</b>&lt;2&gt; val&gt; {
 537   <b>bits</b>&lt;2&gt; Value = val;
 538 }
 539
 540 <b>def</b> None   : ModRefVal&lt;0&gt;;
 541 <b>def</b> Mod    : ModRefVal&lt;1&gt;;
 542 <b>def</b> Ref    : ModRefVal&lt;2&gt;;
 543 <b>def</b> ModRef : ModRefVal&lt;3&gt;;
 544
 545 <b>class</b> Value&lt;ModRefVal MR&gt; {
 546   <i>// Decode some information into a more convenient format, while providing
 547   // a nice interface to the user of the "Value" class.</i>
 548   <b>bit</b> isMod = MR.Value{0};
 549   <b>bit</b> isRef = MR.Value{1};
 550
 551   <i>// other stuff...</i>
 552 }
 553
 554 <i>// Example uses</i>
 555 <b>def</b> bork : Value&lt;Mod&gt;;
 556 <b>def</b> zork : Value&lt;Ref&gt;;
 557 <b>def</b> hork : Value&lt;ModRef&gt;;
 558 </pre>
 559 </div>
 560
 561 <p>This is obviously a contrived example, but it shows how template arguments
 562 can be used to decouple the interface provided to the user of the class from the
 563 actual internal data representation expected by the class.  In this case,
 564 running <tt>tblgen</tt> on the example prints the following definitions:</p>
 565
 566 <div class="doc_code">
 567 <pre>
 568 <b>def</b> bork {      <i>// Value</i>
 569   <b>bit</b> isMod = 1;
 570   <b>bit</b> isRef = 0;
 571 }
 572 <b>def</b> hork {      <i>// Value</i>
 573   <b>bit</b> isMod = 1;
 574   <b>bit</b> isRef = 1;
 575 }
 576 <b>def</b> zork {      <i>// Value</i>
 577   <b>bit</b> isMod = 0;
 578   <b>bit</b> isRef = 1;
 579 }
 580 </pre>
 581 </div>
 582
 583 <p> This shows that TableGen was able to dig into the argument and extract a
 584 piece of information that was requested by the designer of the "Value" class.
 585 For more realistic examples, please see existing users of TableGen, such as the
 586 X86 backend.</p>
 587
 588 </div>
 589
 590 <!-- -------------------------------------------------------------------------->
 591 <div class="doc_subsubsection">
 592   <a name="multiclass">Multiclass definitions and instances</a>
 593 </div>
 594
 595 <div class="doc_text">
 596
 597 <p>
 598 While classes with template arguments are a good way to factor commonality
 599 between two instances of a definition, multiclasses allow a convenient notation
 600 for defining multiple definitions at once (instances of implicitly constructed
 601 classes).  For example, consider an 3-address instruction set whose instructions
 602 come in two forms: "<tt>reg = reg op reg</tt>" and "<tt>reg = reg op imm</tt>"
 603 (e.g. SPARC). In this case, you'd like to specify in one place that this
 604 commonality exists, then in a separate place indicate what all the ops are.
 605 </p>
 606
 607 <p>
 608 Here is an example TableGen fragment that shows this idea:
 609 </p>
 610
 611 <div class="doc_code">
 612 <pre>
 613 <b>def</b> ops;
 614 <b>def</b> GPR;
 615 <b>def</b> Imm;
 616 <b>class</b> inst&lt;<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist&gt;;
 617
 618 <b>multiclass</b> ri_inst&lt;<b>int</b> opc, <b>string</b> asmstr&gt; {
 619   def _rr : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
 620                  (ops GPR:$dst, GPR:$src1, GPR:$src2)&gt;;
 621   def _ri : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
 622                  (ops GPR:$dst, GPR:$src1, Imm:$src2)&gt;;
 623 }
 624
 625 <i>// Instantiations of the ri_inst multiclass.</i>
 626 <b>defm</b> ADD : ri_inst&lt;0b111, "add"&gt;;
 627 <b>defm</b> SUB : ri_inst&lt;0b101, "sub"&gt;;
 628 <b>defm</b> MUL : ri_inst&lt;0b100, "mul"&gt;;
 629 ...
 630 </pre>
 631 </div>
 632
 633 <p>The name of the resultant definitions has the multidef fragment names
 634    appended to them, so this defines <tt>ADD_rr</tt>, <tt>ADD_ri</tt>,
 635    <tt>SUB_rr</tt>, etc.  A defm may inherit from multiple multiclasses,
 636    instantiating definitions from each multiclass.  Using a multiclass
 637    this way is exactly equivalent to instantiating the classes multiple
 638    times yourself, e.g. by writing:</p>
 639
 640 <div class="doc_code">
 641 <pre>
 642 <b>def</b> ops;
 643 <b>def</b> GPR;
 644 <b>def</b> Imm;
 645 <b>class</b> inst&lt;<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist&gt;;
 646
 647 <b>class</b> rrinst&lt;<b>int</b> opc, <b>string</b> asmstr&gt;
 648   : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
 649          (ops GPR:$dst, GPR:$src1, GPR:$src2)&gt;;
 650
 651 <b>class</b> riinst&lt;<b>int</b> opc, <b>string</b> asmstr&gt;
 652   : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
 653          (ops GPR:$dst, GPR:$src1, Imm:$src2)&gt;;
 654
 655 <i>// Instantiations of the ri_inst multiclass.</i>
 656 <b>def</b> ADD_rr : rrinst&lt;0b111, "add"&gt;;
 657 <b>def</b> ADD_ri : riinst&lt;0b111, "add"&gt;;
 658 <b>def</b> SUB_rr : rrinst&lt;0b101, "sub"&gt;;
 659 <b>def</b> SUB_ri : riinst&lt;0b101, "sub"&gt;;
 660 <b>def</b> MUL_rr : rrinst&lt;0b100, "mul"&gt;;
 661 <b>def</b> MUL_ri : riinst&lt;0b100, "mul"&gt;;
 662 ...
 663 </pre>
 664 </div>
 665
 666 </div>
 667
 668 <!-- ======================================================================= -->
 669 <div class="doc_subsection">
 670   <a name="filescope">File scope entities</a>
 671 </div>
 672
 673 <!-- -------------------------------------------------------------------------->
 674 <div class="doc_subsubsection">
 675   <a name="include">File inclusion</a>
 676 </div>
 677
 678 <div class="doc_text">
 679 <p>TableGen supports the '<tt>include</tt>' token, which textually substitutes
 680 the specified file in place of the include directive.  The filename should be
 681 specified as a double quoted string immediately after the '<tt>include</tt>'
 682 keyword.  Example:</p>
 683
 684 <div class="doc_code">
 685 <pre>
 686 <b>include</b> "foo.td"
 687 </pre>
 688 </div>
 689
 690 </div>
 691
 692 <!-- -------------------------------------------------------------------------->
 693 <div class="doc_subsubsection">
 694   <a name="globallet">'let' expressions</a>
 695 </div>
 696
 697 <div class="doc_text">
 698
 699 <p>"Let" expressions at file scope are similar to <a href="#recordlet">"let"
 700 expressions within a record</a>, except they can specify a value binding for
 701 multiple records at a time, and may be useful in certain other cases.
 702 File-scope let expressions are really just another way that TableGen allows the
 703 end-user to factor out commonality from the records.</p>
 704
 705 <p>File-scope "let" expressions take a comma-separated list of bindings to
 706 apply, and one or more records to bind the values in.  Here are some
 707 examples:</p>
 708
 709 <div class="doc_code">
 710 <pre>
 711 <b>let</b> isTerminator = 1, isReturn = 1, isBarrier = 1, hasCtrlDep = 1 <b>in</b>
 712   <b>def</b> RET : I&lt;0xC3, RawFrm, (outs), (ins), "ret", [(X86retflag 0)]&gt;;
 713
 714 <b>let</b> isCall = 1 <b>in</b>
 715   <i>// All calls clobber the non-callee saved registers...</i>
 716   <b>let</b> Defs = [EAX, ECX, EDX, FP0, FP1, FP2, FP3, FP4, FP5, FP6, ST0,
 717               MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7,
 718               XMM0, XMM1, XMM2, XMM3, XMM4, XMM5, XMM6, XMM7, EFLAGS] <b>in</b> {
 719     <b>def</b> CALLpcrel32 : Ii32&lt;0xE8, RawFrm, (outs), (ins i32imm:$dst,variable_ops),
 720                            "call\t${dst:call}", []&gt;;
 721     <b>def</b> CALL32r     : I&lt;0xFF, MRM2r, (outs), (ins GR32:$dst, variable_ops),
 722                         "call\t{*}$dst", [(X86call GR32:$dst)]&gt;;
 723     <b>def</b> CALL32m     : I&lt;0xFF, MRM2m, (outs), (ins i32mem:$dst, variable_ops),
 724                         "call\t{*}$dst", []&gt;;
 725   }
 726 </pre>
 727 </div>
 728
 729 <p>File-scope "let" expressions are often useful when a couple of definitions
 730 need to be added to several records, and the records do not otherwise need to be
 731 opened, as in the case with the <tt>CALL*</tt> instructions above.</p>
 732
 733 </div>
 734
 735 <!-- *********************************************************************** -->
 736 <div class="doc_section"><a name="backends">TableGen backends</a></div>
 737 <!-- *********************************************************************** -->
 738
 739 <div class="doc_text">
 740
 741 <p>TODO: How they work, how to write one.  This section should not contain
 742 details about any particular backend, except maybe -print-enums as an example.
 743 This should highlight the APIs in <tt>TableGen/Record.h</tt>.</p>
 744
 745 </div>
 746
 747 <!-- *********************************************************************** -->
 748
 749 <hr>
 750 <address>
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 755
 756   <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
 757   <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
 758   Last modified: $Date$
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