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  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@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, $src2}";
 130   <b>list</b>&lt;dag&gt; Pattern = [(set GR32:$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> 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>&lt;8&gt; Opcode = { 0, 0, 0, 0, 0, 0, 0, 1 };
 160   Format Form = MRMDestReg;
 161   <b>bits</b>&lt;6&gt; FormBits = { 0, 0, 0, 0, 1, 1 };
 162   ImmType ImmT = NoImm;
 163   <b>bits</b>&lt;3&gt; ImmTypeBits = { 0, 0, 0 };
 164   <b>bit</b> hasOpSizePrefix = 0;
 165   <b>bit</b> hasAdSizePrefix = 0;
 166   <b>bits</b>&lt;4&gt; Prefix = { 0, 0, 0, 0 };
 167   <b>bit</b> hasREX_WPrefix = 0;
 168   FPFormat FPForm = ?;
 169   <b>bits</b>&lt;3&gt; 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&mdash;"<tt>ADD32rr</tt>" in this case&mdash;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 --&gt; X = ADD Z,Y</i>
 196     isConvertibleToThreeAddress = 1 <b>in</b> <i>// Can transform into LEA.</i>
 197 def ADD32rr  : I&lt;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))]&gt;;
 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>&lt;n&gt;</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>&lt;ty&gt;</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>&lt;Register&gt;</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 ]&lt;type&gt;</tt></dt>
 373   <dd>list value.  &lt;type&gt; 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&lt;3&gt;" 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&lt;val list&gt;</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&lt;type&gt;(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&lt;string&gt; 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&lt;string&gt; 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&lt;4&gt;</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&lt;<b>bits</b>&lt;3&gt; val&gt; {
 535   <b>bits</b>&lt;3&gt; Value = val;
 536 }
 537 <b>def</b> NotFP      : FPFormat&lt;0&gt;;
 538 <b>def</b> ZeroArgFP  : FPFormat&lt;1&gt;;
 539 <b>def</b> OneArgFP   : FPFormat&lt;2&gt;;
 540 <b>def</b> OneArgFPRW : FPFormat&lt;3&gt;;
 541 <b>def</b> TwoArgFP   : FPFormat&lt;4&gt;;
 542 <b>def</b> CompareFP  : FPFormat&lt;5&gt;;
 543 <b>def</b> CondMovFP  : FPFormat&lt;6&gt;;
 544 <b>def</b> SpecialFP  : FPFormat&lt;7&gt;;
 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&lt;<b>bits</b>&lt;2&gt; val&gt; {
 558   <b>bits</b>&lt;2&gt; Value = val;
 559 }
 560
 561 <b>def</b> None   : ModRefVal&lt;0&gt;;
 562 <b>def</b> Mod    : ModRefVal&lt;1&gt;;
 563 <b>def</b> Ref    : ModRefVal&lt;2&gt;;
 564 <b>def</b> ModRef : ModRefVal&lt;3&gt;;
 565
 566 <b>class</b> Value&lt;ModRefVal MR&gt; {
 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&lt;Mod&gt;;
 577 <b>def</b> zork : Value&lt;Ref&gt;;
 578 <b>def</b> hork : Value&lt;ModRef&gt;;
 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&lt;<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist&gt;;
 638
 639 <b>multiclass</b> ri_inst&lt;<b>int</b> opc, <b>string</b> asmstr&gt; {
 640   def _rr : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
 641                  (ops GPR:$dst, GPR:$src1, GPR:$src2)&gt;;
 642   def _ri : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
 643                  (ops GPR:$dst, GPR:$src1, Imm:$src2)&gt;;
 644 }
 645
 646 <i>// Instantiations of the ri_inst multiclass.</i>
 647 <b>defm</b> ADD : ri_inst&lt;0b111, "add"&gt;;
 648 <b>defm</b> SUB : ri_inst&lt;0b101, "sub"&gt;;
 649 <b>defm</b> MUL : ri_inst&lt;0b100, "mul"&gt;;
 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&lt;<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist&gt;;
 667
 668 <b>class</b> rrinst&lt;<b>int</b> opc, <b>string</b> asmstr&gt;
 669   : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
 670          (ops GPR:$dst, GPR:$src1, GPR:$src2)&gt;;
 671
 672 <b>class</b> riinst&lt;<b>int</b> opc, <b>string</b> asmstr&gt;
 673   : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
 674          (ops GPR:$dst, GPR:$src1, Imm:$src2)&gt;;
 675
 676 <i>// Instantiations of the ri_inst multiclass.</i>
 677 <b>def</b> ADD_rr : rrinst&lt;0b111, "add"&gt;;
 678 <b>def</b> ADD_ri : riinst&lt;0b111, "add"&gt;;
 679 <b>def</b> SUB_rr : rrinst&lt;0b101, "sub"&gt;;
 680 <b>def</b> SUB_ri : riinst&lt;0b101, "sub"&gt;;
 681 <b>def</b> MUL_rr : rrinst&lt;0b100, "mul"&gt;;
 682 <b>def</b> MUL_ri : riinst&lt;0b100, "mul"&gt;;
 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&lt;bits&lt;4&gt; opc, string Name&gt; {
 695   bits&lt;4&gt; opcode = opc;
 696   string name = Name;
 697 }
 698
 699 <b>multiclass</b> basic_r&lt;bits&lt;4&gt; opc&gt; {
 700   <b>def</b> rr : Instruction&lt;opc, "rr"&gt;;
 701   <b>def</b> rm : Instruction&lt;opc, "rm"&gt;;
 702 }
 703
 704 <b>multiclass</b> basic_s&lt;bits&lt;4&gt; opc&gt; {
 705   <b>defm</b> SS : basic_r&lt;opc&gt;;
 706   <b>defm</b> SD : basic_r&lt;opc&gt;;
 707   <b>def</b> X : Instruction&lt;opc, "x"&gt;;
 708 }
 709
 710 <b>multiclass</b> basic_p&lt;bits&lt;4&gt; opc&gt; {
 711   <b>defm</b> PS : basic_r&lt;opc&gt;;
 712   <b>defm</b> PD : basic_r&lt;opc&gt;;
 713   <b>def</b> Y : Instruction&lt;opc, "y"&gt;;
 714 }
 715
 716 <b>defm</b> ADD : basic_s&lt;0xf&gt;, basic_p&lt;0xf&gt;;
 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&lt;4&gt; Prefix = 11; }
 741 <b>class</b> XS { bits&lt;4&gt; Prefix = 12; }
 742
 743 <b>class</b> I&lt;bits<4&gt; op> {
 744   bits&lt;4&gt; opcode = op;
 745 }
 746
 747 <b>multiclass</b> R {
 748   <b>def</b> rr : I&lt;4&gt;;
 749   <b>def</b> rm : I&lt;2&gt;;
 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&lt;4&gt; opcode = { 0, 0, 1, 0 };
 762   bits&lt;4&gt; Prefix = { 1, 1, 0, 0 };
 763 }
 764 ...
 765 <b>def</b> InstrSSrr {
 766   bits&lt;4&gt; opcode = { 0, 1, 0, 0 };
 767   bits&lt;4&gt; 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&lt;0xC3, RawFrm, (outs), (ins), "ret", [(X86retflag 0)]&gt;;
 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&lt;0xE8, RawFrm, (outs), (ins i32imm:$dst,variable_ops),
 830                            "call\t${dst:call}", []&gt;;
 831     <b>def</b> CALL32r     : I&lt;0xFF, MRM2r, (outs), (ins GR32:$dst, variable_ops),
 832                         "call\t{*}$dst", [(X86call GR32:$dst)]&gt;;
 833     <b>def</b> CALL32m     : I&lt;0xFF, MRM2m, (outs), (ins i32mem:$dst, variable_ops),
 834                         "call\t{*}$dst", []&gt;;
 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&lt;bits&lt;4&gt; opc&gt; {
 850   <b>let </b>Predicates = [HasSSE2] in {
 851     <b>def </b>rr : Instruction&lt;opc, "rr"&gt;;
 852     <b>def </b>rm : Instruction&lt;opc, "rm"&gt;;
 853   }
 854   <b>let </b>Predicates = [HasSSE3] in
 855     <b>def </b>rx : Instruction&lt;opc, "rx"&gt;;
 856 }
 857
 858 <b>multiclass </b>basic_ss&lt;bits&lt;4&gt; opc&gt; {
 859   <b>let </b>IsDouble = 0 in
 860     <b>defm </b>SS : basic_r&lt;opc&gt;;
 861
 862   <b>let </b>IsDouble = 1 in
 863     <b>defm </b>SD : basic_r&lt;opc&gt;;
 864 }
 865
 866 <b>defm </b>ADD : basic_ss&lt;0xf&gt;;
 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>
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 911
 912   <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
 913   <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
 914   Last modified: $Date$
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