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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> isConvertibleToThreeAddress = 1;
 148   <b>bit</b> isCommutable = 1;
 149   <b>bit</b> isTerminator = 0;
 150   <b>bit</b> isReMaterializable = 0;
 151   <b>bit</b> isPredicable = 0;
 152   <b>bit</b> hasDelaySlot = 0;
 153   <b>bit</b> usesCustomInserter = 0;
 154   <b>bit</b> hasCtrlDep = 0;
 155   <b>bit</b> isNotDuplicable = 0;
 156   <b>bit</b> hasSideEffects = 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 unmaintainable, 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.  This is lexically distinct from
 336   string values because it doesn't require escapeing double quotes and other
 337   common characters that occur in code.</dd>
 338 </dl>
 339
 340 <p>To date, these types have been sufficient for describing things that
 341 TableGen has been used for, but it is straight-forward to extend this list if
 342 needed.</p>
 343
 344 </div>
 345
 346 <!-- -------------------------------------------------------------------------->
 347 <div class="doc_subsubsection">
 348   <a name="values">TableGen values and expressions</a>
 349 </div>
 350
 351 <div class="doc_text">
 352
 353 <p>TableGen allows for a pretty reasonable number of different expression forms
 354 when building up values.  These forms allow the TableGen file to be written in a
 355 natural syntax and flavor for the application.  The current expression forms
 356 supported include:</p>
 357
 358 <dl>
 359 <dt><tt>?</tt></dt>
 360   <dd>uninitialized field</dd>
 361 <dt><tt>0b1001011</tt></dt>
 362   <dd>binary integer value</dd>
 363 <dt><tt>07654321</tt></dt>
 364   <dd>octal integer value (indicated by a leading 0)</dd>
 365 <dt><tt>7</tt></dt>
 366   <dd>decimal integer value</dd>
 367 <dt><tt>0x7F</tt></dt>
 368   <dd>hexadecimal integer value</dd>
 369 <dt><tt>"foo"</tt></dt>
 370   <dd>string value</dd>
 371 <dt><tt>[{ ... }]</tt></dt>
 372   <dd>code fragment</dd>
 373 <dt><tt>[ X, Y, Z ]&lt;type&gt;</tt></dt>
 374   <dd>list value.  &lt;type&gt; is the type of the list
 375 element and is usually optional.  In rare cases,
 376 TableGen is unable to deduce the element type in
 377 which case the user must specify it explicitly.</dd>
 378 <dt><tt>{ a, b, c }</tt></dt>
 379   <dd>initializer for a "bits&lt;3&gt;" value</dd>
 380 <dt><tt>value</tt></dt>
 381   <dd>value reference</dd>
 382 <dt><tt>value{17}</tt></dt>
 383   <dd>access to one bit of a value</dd>
 384 <dt><tt>value{15-17}</tt></dt>
 385   <dd>access to multiple bits of a value</dd>
 386 <dt><tt>DEF</tt></dt>
 387   <dd>reference to a record definition</dd>
 388 <dt><tt>CLASS&lt;val list&gt;</tt></dt>
 389   <dd>reference to a new anonymous definition of CLASS with the specified
 390       template arguments.</dd>
 391 <dt><tt>X.Y</tt></dt>
 392   <dd>reference to the subfield of a value</dd>
 393 <dt><tt>list[4-7,17,2-3]</tt></dt>
 394   <dd>A slice of the 'list' list, including elements 4,5,6,7,17,2, and 3 from
 395   it.  Elements may be included multiple times.</dd>
 396 <dt><tt>(DEF a, b)</tt></dt>
 397   <dd>a dag value.  The first element is required to be a record definition, the
 398   remaining elements in the list may be arbitrary other values, including nested
 399   `<tt>dag</tt>' values.</dd>
 400 <dt><tt>!strconcat(a, b)</tt></dt>
 401   <dd>A string value that is the result of concatenating the 'a' and 'b'
 402   strings.</dd>
 403 <dt><tt>!cast&lt;type&gt;(a)</tt></dt>
 404   <dd>A symbol of type <em>type</em> obtained by looking up the string 'a' in
 405 the symbol table.  If the type of 'a' does not match <em>type</em>, TableGen
 406 aborts with an error. !cast&lt;string&gt; is a special case in that the argument must
 407 be an object defined by a 'def' construct.</dd>
 408 <dt><tt>!subst(a, b, c)</tt></dt>
 409   <dd>If 'a' and 'b' are of string type or are symbol references, substitute
 410 'b' for 'a' in 'c.'  This operation is analogous to $(subst) in GNU make.</dd>
 411 <dt><tt>!foreach(a, b, c)</tt></dt>
 412   <dd>For each member 'b' of dag or list 'a' apply operator 'c.'  'b' is a
 413 dummy variable that should be declared as a member variable of an instantiated
 414 class.  This operation is analogous to $(foreach) in GNU make.</dd>
 415 <dt><tt>!head(a)</tt></dt>
 416   <dd>The first element of list 'a.'</dd>
 417 <dt><tt>!tail(a)</tt></dt>
 418   <dd>The 2nd-N elements of list 'a.'</dd>
 419 <dt><tt>!empty(a)</tt></dt>
 420   <dd>An integer {0,1} indicating whether list 'a' is empty.</dd>
 421 <dt><tt>!if(a,b,c)</tt></dt>
 422   <dd>'b' if the result of 'int' or 'bit' operator 'a' is nonzero,
 423       'c' otherwise.</dd>
 424 <dt><tt>!eq(a,b)</tt></dt>
 425   <dd>'bit 1' if string a is equal to string b, 0 otherwise.  This
 426       only operates on string, int and bit objects.  Use !cast&lt;string&gt; to
 427       compare other types of objects.</dd>
 428 </dl>
 429
 430 <p>Note that all of the values have rules specifying how they convert to values
 431 for different types.  These rules allow you to assign a value like "<tt>7</tt>"
 432 to a "<tt>bits&lt;4&gt;</tt>" value, for example.</p>
 433
 434 </div>
 435
 436 <!-- ======================================================================= -->
 437 <div class="doc_subsection">
 438   <a name="classesdefs">Classes and definitions</a>
 439 </div>
 440
 441 <div class="doc_text">
 442
 443 <p>As mentioned in the <a href="#concepts">intro</a>, classes and definitions
 444 (collectively known as 'records') in TableGen are the main high-level unit of
 445 information that TableGen collects.  Records are defined with a <tt>def</tt> or
 446 <tt>class</tt> keyword, the record name, and an optional list of "<a
 447 href="#templateargs">template arguments</a>".  If the record has superclasses,
 448 they are specified as a comma separated list that starts with a colon character
 449 ("<tt>:</tt>").  If <a href="#valuedef">value definitions</a> or <a
 450 href="#recordlet">let expressions</a> are needed for the class, they are
 451 enclosed in curly braces ("<tt>{}</tt>"); otherwise, the record ends with a
 452 semicolon.</p>
 453
 454 <p>Here is a simple TableGen file:</p>
 455
 456 <div class="doc_code">
 457 <pre>
 458 <b>class</b> C { <b>bit</b> V = 1; }
 459 <b>def</b> X : C;
 460 <b>def</b> Y : C {
 461   <b>string</b> Greeting = "hello";
 462 }
 463 </pre>
 464 </div>
 465
 466 <p>This example defines two definitions, <tt>X</tt> and <tt>Y</tt>, both of
 467 which derive from the <tt>C</tt> class.  Because of this, they both get the
 468 <tt>V</tt> bit value.  The <tt>Y</tt> definition also gets the Greeting member
 469 as well.</p>
 470
 471 <p>In general, classes are useful for collecting together the commonality
 472 between a group of records and isolating it in a single place.  Also, classes
 473 permit the specification of default values for their subclasses, allowing the
 474 subclasses to override them as they wish.</p>
 475
 476 </div>
 477
 478 <!---------------------------------------------------------------------------->
 479 <div class="doc_subsubsection">
 480   <a name="valuedef">Value definitions</a>
 481 </div>
 482
 483 <div class="doc_text">
 484
 485 <p>Value definitions define named entries in records.  A value must be defined
 486 before it can be referred to as the operand for another value definition or
 487 before the value is reset with a <a href="#recordlet">let expression</a>.  A
 488 value is defined by specifying a <a href="#types">TableGen type</a> and a name.
 489 If an initial value is available, it may be specified after the type with an
 490 equal sign.  Value definitions require terminating semicolons.</p>
 491
 492 </div>
 493
 494 <!-- -------------------------------------------------------------------------->
 495 <div class="doc_subsubsection">
 496   <a name="recordlet">'let' expressions</a>
 497 </div>
 498
 499 <div class="doc_text">
 500
 501 <p>A record-level let expression is used to change the value of a value
 502 definition in a record.  This is primarily useful when a superclass defines a
 503 value that a derived class or definition wants to override.  Let expressions
 504 consist of the '<tt>let</tt>' keyword followed by a value name, an equal sign
 505 ("<tt>=</tt>"), and a new value.  For example, a new class could be added to the
 506 example above, redefining the <tt>V</tt> field for all of its subclasses:</p>
 507
 508 <div class="doc_code">
 509 <pre>
 510 <b>class</b> D : C { let V = 0; }
 511 <b>def</b> Z : D;
 512 </pre>
 513 </div>
 514
 515 <p>In this case, the <tt>Z</tt> definition will have a zero value for its "V"
 516 value, despite the fact that it derives (indirectly) from the <tt>C</tt> class,
 517 because the <tt>D</tt> class overrode its value.</p>
 518
 519 </div>
 520
 521 <!-- -------------------------------------------------------------------------->
 522 <div class="doc_subsubsection">
 523   <a name="templateargs">Class template arguments</a>
 524 </div>
 525
 526 <div class="doc_text">
 527
 528 <p>TableGen permits the definition of parameterized classes as well as normal
 529 concrete classes.  Parameterized TableGen classes specify a list of variable
 530 bindings (which may optionally have defaults) that are bound when used.  Here is
 531 a simple example:</p>
 532
 533 <div class="doc_code">
 534 <pre>
 535 <b>class</b> FPFormat&lt;<b>bits</b>&lt;3&gt; val&gt; {
 536   <b>bits</b>&lt;3&gt; Value = val;
 537 }
 538 <b>def</b> NotFP      : FPFormat&lt;0&gt;;
 539 <b>def</b> ZeroArgFP  : FPFormat&lt;1&gt;;
 540 <b>def</b> OneArgFP   : FPFormat&lt;2&gt;;
 541 <b>def</b> OneArgFPRW : FPFormat&lt;3&gt;;
 542 <b>def</b> TwoArgFP   : FPFormat&lt;4&gt;;
 543 <b>def</b> CompareFP  : FPFormat&lt;5&gt;;
 544 <b>def</b> CondMovFP  : FPFormat&lt;6&gt;;
 545 <b>def</b> SpecialFP  : FPFormat&lt;7&gt;;
 546 </pre>
 547 </div>
 548
 549 <p>In this case, template arguments are used as a space efficient way to specify
 550 a list of "enumeration values", each with a "<tt>Value</tt>" field set to the
 551 specified integer.</p>
 552
 553 <p>The more esoteric forms of <a href="#values">TableGen expressions</a> are
 554 useful in conjunction with template arguments.  As an example:</p>
 555
 556 <div class="doc_code">
 557 <pre>
 558 <b>class</b> ModRefVal&lt;<b>bits</b>&lt;2&gt; val&gt; {
 559   <b>bits</b>&lt;2&gt; Value = val;
 560 }
 561
 562 <b>def</b> None   : ModRefVal&lt;0&gt;;
 563 <b>def</b> Mod    : ModRefVal&lt;1&gt;;
 564 <b>def</b> Ref    : ModRefVal&lt;2&gt;;
 565 <b>def</b> ModRef : ModRefVal&lt;3&gt;;
 566
 567 <b>class</b> Value&lt;ModRefVal MR&gt; {
 568   <i>// Decode some information into a more convenient format, while providing
 569   // a nice interface to the user of the "Value" class.</i>
 570   <b>bit</b> isMod = MR.Value{0};
 571   <b>bit</b> isRef = MR.Value{1};
 572
 573   <i>// other stuff...</i>
 574 }
 575
 576 <i>// Example uses</i>
 577 <b>def</b> bork : Value&lt;Mod&gt;;
 578 <b>def</b> zork : Value&lt;Ref&gt;;
 579 <b>def</b> hork : Value&lt;ModRef&gt;;
 580 </pre>
 581 </div>
 582
 583 <p>This is obviously a contrived example, but it shows how template arguments
 584 can be used to decouple the interface provided to the user of the class from the
 585 actual internal data representation expected by the class.  In this case,
 586 running <tt>tblgen</tt> on the example prints the following definitions:</p>
 587
 588 <div class="doc_code">
 589 <pre>
 590 <b>def</b> bork {      <i>// Value</i>
 591   <b>bit</b> isMod = 1;
 592   <b>bit</b> isRef = 0;
 593 }
 594 <b>def</b> hork {      <i>// Value</i>
 595   <b>bit</b> isMod = 1;
 596   <b>bit</b> isRef = 1;
 597 }
 598 <b>def</b> zork {      <i>// Value</i>
 599   <b>bit</b> isMod = 0;
 600   <b>bit</b> isRef = 1;
 601 }
 602 </pre>
 603 </div>
 604
 605 <p> This shows that TableGen was able to dig into the argument and extract a
 606 piece of information that was requested by the designer of the "Value" class.
 607 For more realistic examples, please see existing users of TableGen, such as the
 608 X86 backend.</p>
 609
 610 </div>
 611
 612 <!-- -------------------------------------------------------------------------->
 613 <div class="doc_subsubsection">
 614   <a name="multiclass">Multiclass definitions and instances</a>
 615 </div>
 616
 617 <div class="doc_text">
 618
 619 <p>
 620 While classes with template arguments are a good way to factor commonality
 621 between two instances of a definition, multiclasses allow a convenient notation
 622 for defining multiple definitions at once (instances of implicitly constructed
 623 classes).  For example, consider an 3-address instruction set whose instructions
 624 come in two forms: "<tt>reg = reg op reg</tt>" and "<tt>reg = reg op imm</tt>"
 625 (e.g. SPARC). In this case, you'd like to specify in one place that this
 626 commonality exists, then in a separate place indicate what all the ops are.
 627 </p>
 628
 629 <p>
 630 Here is an example TableGen fragment that shows this idea:
 631 </p>
 632
 633 <div class="doc_code">
 634 <pre>
 635 <b>def</b> ops;
 636 <b>def</b> GPR;
 637 <b>def</b> Imm;
 638 <b>class</b> inst&lt;<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist&gt;;
 639
 640 <b>multiclass</b> ri_inst&lt;<b>int</b> opc, <b>string</b> asmstr&gt; {
 641   def _rr : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
 642                  (ops GPR:$dst, GPR:$src1, GPR:$src2)&gt;;
 643   def _ri : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
 644                  (ops GPR:$dst, GPR:$src1, Imm:$src2)&gt;;
 645 }
 646
 647 <i>// Instantiations of the ri_inst multiclass.</i>
 648 <b>defm</b> ADD : ri_inst&lt;0b111, "add"&gt;;
 649 <b>defm</b> SUB : ri_inst&lt;0b101, "sub"&gt;;
 650 <b>defm</b> MUL : ri_inst&lt;0b100, "mul"&gt;;
 651 ...
 652 </pre>
 653 </div>
 654
 655 <p>The name of the resultant definitions has the multidef fragment names
 656    appended to them, so this defines <tt>ADD_rr</tt>, <tt>ADD_ri</tt>,
 657    <tt>SUB_rr</tt>, etc.  A defm may inherit from multiple multiclasses,
 658    instantiating definitions from each multiclass.  Using a multiclass
 659    this way is exactly equivalent to instantiating the classes multiple
 660    times yourself, e.g. by writing:</p>
 661
 662 <div class="doc_code">
 663 <pre>
 664 <b>def</b> ops;
 665 <b>def</b> GPR;
 666 <b>def</b> Imm;
 667 <b>class</b> inst&lt;<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist&gt;;
 668
 669 <b>class</b> rrinst&lt;<b>int</b> opc, <b>string</b> asmstr&gt;
 670   : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
 671          (ops GPR:$dst, GPR:$src1, GPR:$src2)&gt;;
 672
 673 <b>class</b> riinst&lt;<b>int</b> opc, <b>string</b> asmstr&gt;
 674   : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
 675          (ops GPR:$dst, GPR:$src1, Imm:$src2)&gt;;
 676
 677 <i>// Instantiations of the ri_inst multiclass.</i>
 678 <b>def</b> ADD_rr : rrinst&lt;0b111, "add"&gt;;
 679 <b>def</b> ADD_ri : riinst&lt;0b111, "add"&gt;;
 680 <b>def</b> SUB_rr : rrinst&lt;0b101, "sub"&gt;;
 681 <b>def</b> SUB_ri : riinst&lt;0b101, "sub"&gt;;
 682 <b>def</b> MUL_rr : rrinst&lt;0b100, "mul"&gt;;
 683 <b>def</b> MUL_ri : riinst&lt;0b100, "mul"&gt;;
 684 ...
 685 </pre>
 686 </div>
 687
 688 <p>
 689 A defm can also be used inside a multiclass providing several levels of
 690 multiclass instanciations.
 691 </p>
 692
 693 <div class="doc_code">
 694 <pre>
 695 <b>class</b> Instruction&lt;bits&lt;4&gt; opc, string Name&gt; {
 696   bits&lt;4&gt; opcode = opc;
 697   string name = Name;
 698 }
 699
 700 <b>multiclass</b> basic_r&lt;bits&lt;4&gt; opc&gt; {
 701   <b>def</b> rr : Instruction&lt;opc, "rr"&gt;;
 702   <b>def</b> rm : Instruction&lt;opc, "rm"&gt;;
 703 }
 704
 705 <b>multiclass</b> basic_s&lt;bits&lt;4&gt; opc&gt; {
 706   <b>defm</b> SS : basic_r&lt;opc&gt;;
 707   <b>defm</b> SD : basic_r&lt;opc&gt;;
 708   <b>def</b> X : Instruction&lt;opc, "x"&gt;;
 709 }
 710
 711 <b>multiclass</b> basic_p&lt;bits&lt;4&gt; opc&gt; {
 712   <b>defm</b> PS : basic_r&lt;opc&gt;;
 713   <b>defm</b> PD : basic_r&lt;opc&gt;;
 714   <b>def</b> Y : Instruction&lt;opc, "y"&gt;;
 715 }
 716
 717 <b>defm</b> ADD : basic_s&lt;0xf&gt;, basic_p&lt;0xf&gt;;
 718 ...
 719
 720 <i>// Results</i>
 721 <b>def</b> ADDPDrm { ...
 722 <b>def</b> ADDPDrr { ...
 723 <b>def</b> ADDPSrm { ...
 724 <b>def</b> ADDPSrr { ...
 725 <b>def</b> ADDSDrm { ...
 726 <b>def</b> ADDSDrr { ...
 727 <b>def</b> ADDY { ...
 728 <b>def</b> ADDX { ...
 729 </pre>
 730 </div>
 731
 732 <p>
 733 defm declarations can inherit from classes too, the
 734 rule to follow is that the class list must start after the
 735 last multiclass, and there must be at least one multiclass
 736 before them.
 737 </p>
 738
 739 <div class="doc_code">
 740 <pre>
 741 <b>class</b> XD { bits&lt;4&gt; Prefix = 11; }
 742 <b>class</b> XS { bits&lt;4&gt; Prefix = 12; }
 743
 744 <b>class</b> I&lt;bits<4&gt; op> {
 745   bits&lt;4&gt; opcode = op;
 746 }
 747
 748 <b>multiclass</b> R {
 749   <b>def</b> rr : I&lt;4&gt;;
 750   <b>def</b> rm : I&lt;2&gt;;
 751 }
 752
 753 <b>multiclass</b> Y {
 754   <b>defm</b> SS : R, XD;
 755   <b>defm</b> SD : R, XS;
 756 }
 757
 758 <b>defm</b> Instr : Y;
 759
 760 <i>// Results</i>
 761 <b>def</b> InstrSDrm {
 762   bits&lt;4&gt; opcode = { 0, 0, 1, 0 };
 763   bits&lt;4&gt; Prefix = { 1, 1, 0, 0 };
 764 }
 765 ...
 766 <b>def</b> InstrSSrr {
 767   bits&lt;4&gt; opcode = { 0, 1, 0, 0 };
 768   bits&lt;4&gt; Prefix = { 1, 0, 1, 1 };
 769 }
 770 </pre>
 771 </div>
 772
 773 </div>
 774
 775 <!-- ======================================================================= -->
 776 <div class="doc_subsection">
 777   <a name="filescope">File scope entities</a>
 778 </div>
 779
 780 <!-- -------------------------------------------------------------------------->
 781 <div class="doc_subsubsection">
 782   <a name="include">File inclusion</a>
 783 </div>
 784
 785 <div class="doc_text">
 786 <p>TableGen supports the '<tt>include</tt>' token, which textually substitutes
 787 the specified file in place of the include directive.  The filename should be
 788 specified as a double quoted string immediately after the '<tt>include</tt>'
 789 keyword.  Example:</p>
 790
 791 <div class="doc_code">
 792 <pre>
 793 <b>include</b> "foo.td"
 794 </pre>
 795 </div>
 796
 797 </div>
 798
 799 <!-- -------------------------------------------------------------------------->
 800 <div class="doc_subsubsection">
 801   <a name="globallet">'let' expressions</a>
 802 </div>
 803
 804 <div class="doc_text">
 805
 806 <p>"Let" expressions at file scope are similar to <a href="#recordlet">"let"
 807 expressions within a record</a>, except they can specify a value binding for
 808 multiple records at a time, and may be useful in certain other cases.
 809 File-scope let expressions are really just another way that TableGen allows the
 810 end-user to factor out commonality from the records.</p>
 811
 812 <p>File-scope "let" expressions take a comma-separated list of bindings to
 813 apply, and one or more records to bind the values in.  Here are some
 814 examples:</p>
 815
 816 <div class="doc_code">
 817 <pre>
 818 <b>let</b> isTerminator = 1, isReturn = 1, isBarrier = 1, hasCtrlDep = 1 <b>in</b>
 819   <b>def</b> RET : I&lt;0xC3, RawFrm, (outs), (ins), "ret", [(X86retflag 0)]&gt;;
 820
 821 <b>let</b> isCall = 1 <b>in</b>
 822   <i>// All calls clobber the non-callee saved registers...</i>
 823   <b>let</b> Defs = [EAX, ECX, EDX, FP0, FP1, FP2, FP3, FP4, FP5, FP6, ST0,
 824               MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7,
 825               XMM0, XMM1, XMM2, XMM3, XMM4, XMM5, XMM6, XMM7, EFLAGS] <b>in</b> {
 826     <b>def</b> CALLpcrel32 : Ii32&lt;0xE8, RawFrm, (outs), (ins i32imm:$dst,variable_ops),
 827                            "call\t${dst:call}", []&gt;;
 828     <b>def</b> CALL32r     : I&lt;0xFF, MRM2r, (outs), (ins GR32:$dst, variable_ops),
 829                         "call\t{*}$dst", [(X86call GR32:$dst)]&gt;;
 830     <b>def</b> CALL32m     : I&lt;0xFF, MRM2m, (outs), (ins i32mem:$dst, variable_ops),
 831                         "call\t{*}$dst", []&gt;;
 832   }
 833 </pre>
 834 </div>
 835
 836 <p>File-scope "let" expressions are often useful when a couple of definitions
 837 need to be added to several records, and the records do not otherwise need to be
 838 opened, as in the case with the <tt>CALL*</tt> instructions above.</p>
 839
 840 <p>It's also possible to use "let" expressions inside multiclasses, providing
 841 more ways to factor out commonality from the records, specially if using
 842 several levels of multiclass instanciations. This also avoids the need of using
 843 "let" expressions within subsequent records inside a multiclass.</p>
 844
 845 <pre class="doc_code">
 846 <b>multiclass </b>basic_r&lt;bits&lt;4&gt; opc&gt; {
 847   <b>let </b>Predicates = [HasSSE2] in {
 848     <b>def </b>rr : Instruction&lt;opc, "rr"&gt;;
 849     <b>def </b>rm : Instruction&lt;opc, "rm"&gt;;
 850   }
 851   <b>let </b>Predicates = [HasSSE3] in
 852     <b>def </b>rx : Instruction&lt;opc, "rx"&gt;;
 853 }
 854
 855 <b>multiclass </b>basic_ss&lt;bits&lt;4&gt; opc&gt; {
 856   <b>let </b>IsDouble = 0 in
 857     <b>defm </b>SS : basic_r&lt;opc&gt;;
 858
 859   <b>let </b>IsDouble = 1 in
 860     <b>defm </b>SD : basic_r&lt;opc&gt;;
 861 }
 862
 863 <b>defm </b>ADD : basic_ss&lt;0xf&gt;;
 864 </pre>
 865 </div>
 866
 867 <!-- *********************************************************************** -->
 868 <div class="doc_section"><a name="codegen">Code Generator backend info</a></div>
 869 <!-- *********************************************************************** -->
 870
 871 <div class="doc_text">
 872
 873 <p>Expressions used by code generator to describe instructions and isel
 874 patterns:</p>
 875
 876 <dl>
 877 <dt><tt>(implicit a)</tt></dt>
 878   <dd>an implicitly defined physical register.  This tells the dag instruction
 879   selection emitter the input pattern's extra definitions matches implicit
 880   physical register definitions.</dd>
 881 </dl>
 882 </div>
 883
 884 <!-- *********************************************************************** -->
 885 <div class="doc_section"><a name="backends">TableGen backends</a></div>
 886 <!-- *********************************************************************** -->
 887
 888 <div class="doc_text">
 889
 890 <p>TODO: How they work, how to write one.  This section should not contain
 891 details about any particular backend, except maybe -print-enums as an example.
 892 This should highlight the APIs in <tt>TableGen/Record.h</tt>.</p>
 893
 894 </div>
 895
 896 <!-- *********************************************************************** -->
 897
 898 <hr>
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 905   <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
 906   <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
 907   Last modified: $Date$
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