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10 <div class="doc_title">TableGen Fundamentals</div>
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>
48 <div class="doc_author">
49 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
50 </div>
52 <!-- *********************************************************************** -->
53 <div class="doc_section"><a name="introduction">Introduction</a></div>
54 <!-- *********************************************************************** -->
56 <div class="doc_text">
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>
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>
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
72 <tt>llvm/utils/emacs</tt> and <tt>llvm/utils/vim</tt> directory of your LLVM
73 distribution, respectively.</p>
75 </div>
77 <!-- ======================================================================= -->
78 <div class="doc_subsection"><a name="concepts">Basic concepts</a></div>
80 <div class="doc_text">
82 <p>TableGen files consist of two key parts: 'classes' and 'definitions', both
83 of which are considered 'records'.</p>
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 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 fixed by TableGen.</p>
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>
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 targetting (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>
106 <p><b>TableGen multiclasses</b> are groups of abstract records that are
107 instantiated all at once. Each instantiation can result in multiple TableGen
108 definitions.</p>
110 </div>
112 <!-- ======================================================================= -->
113 <div class="doc_subsection"><a name="example">An example record</a></div>
115 <div class="doc_text">
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>
122 <pre>
124 <b>def</b> ADDrr8 { <i>// Instruction X86Inst I2A8 Pattern</i>
125 <b>string</b> Name = "add";
126 <b>string</b> Namespace = "X86";
127 <b>list</b>&lt;Register&gt; Uses = [];
128 <b>list</b>&lt;Register&gt; Defs = [];
129 <b>bit</b> isReturn = 0;
130 <b>bit</b> isBranch = 0;
131 <b>bit</b> isCall = 0;
132 <b>bit</b> isTwoAddress = 1;
133 <b>bit</b> isTerminator = 0;
134 <b>dag</b> Pattern = (set R8, (plus R8, R8));
135 <b>bits</b>&lt;8&gt; Opcode = { 0, 0, 0, 0, 0, 0, 0, 0 };
136 Format Form = MRMDestReg;
137 <b>bits</b>&lt;5&gt; FormBits = { 0, 0, 0, 1, 1 };
138 ArgType Type = Arg8;
139 <b>bits</b>&lt;3&gt; TypeBits = { 0, 0, 1 };
140 <b>bit</b> hasOpSizePrefix = 0;
141 <b>bit</b> printImplicitUses = 0;
142 <b>bits</b>&lt;4&gt; Prefix = { 0, 0, 0, 0 };
143 FPFormat FPForm = ?;
144 <b>bits</b>&lt;3&gt; FPFormBits = { 0, 0, 0 };
147 </pre>
149 <p>This definition corresponds to an 8-bit register-register add instruction in
150 the X86. The string after the '<tt>def</tt>' string indicates the name of the
151 record ("<tt>ADDrr8</tt>" in this case), and the comment at the end of the line
152 indicates the superclasses of the definition. The body of the record contains
153 all of the data that TableGen assembled for the record, indicating that the
154 instruction is part of the "X86" namespace, should be printed as "<tt>add</tt>"
155 in the assembly file, it is a two-address instruction, has a particular
156 encoding, etc. The contents and semantics of the information in the record is
157 specific to the needs of the X86 backend, and is only shown as an example.</p>
159 <p>As you can see, a lot of information is needed for every instruction
160 supported by the code generator, and specifying it all manually would be
161 unmaintainble, prone to bugs, and tiring to do in the first place. Because we
162 are using TableGen, all of the information was derived from the following
163 definition:</p>
165 <pre>
166 <b>def</b> ADDrr8 : I2A8&lt;"add", 0x00, MRMDestReg&gt;,
167 Pattern&lt;(set R8, (plus R8, R8))&gt;;
168 </pre>
170 <p>This definition makes use of the custom I2A8 (two address instruction with
171 8-bit operand) class, which is defined in the X86-specific TableGen file to
172 factor out the common features that instructions of its class share. A key
173 feature of TableGen is that it allows the end-user to define the abstractions
174 they prefer to use when describing their information.</p>
176 </div>
178 <!-- ======================================================================= -->
179 <div class="doc_subsection"><a name="running">Running TableGen</a></div>
181 <div class="doc_text">
183 <p>TableGen runs just like any other LLVM tool. The first (optional) argument
184 specifies the file to read. If a filename is not specified, <tt>tblgen</tt>
185 reads from standard input.</p>
187 <p>To be useful, one of the <a href="#backends">TableGen backends</a> must be
188 used. These backends are selectable on the command line (type '<tt>tblgen
189 --help</tt>' for a list). For example, to get a list of all of the definitions
190 that subclass a particular type (which can be useful for building up an enum
191 list of these records), use the <tt>--print-enums</tt> option:</p>
193 <pre>
194 $ tblgen X86.td -print-enums -class=Register
195 AH, AL, AX, BH, BL, BP, BX, CH, CL, CX, DH, DI, DL, DX,
196 EAX, EBP, EBX, ECX, EDI, EDX, ESI, ESP, FP0, FP1, FP2, FP3, FP4, FP5, FP6,
197 SI, SP, ST0, ST1, ST2, ST3, ST4, ST5, ST6, ST7,
199 $ tblgen X86.td -print-enums -class=Instruction
200 ADCrr32, ADDri16, ADDri16b, ADDri32, ADDri32b, ADDri8, ADDrr16, ADDrr32,
201 ADDrr8, ADJCALLSTACKDOWN, ADJCALLSTACKUP, ANDri16, ANDri16b, ANDri32, ANDri32b,
202 ANDri8, ANDrr16, ANDrr32, ANDrr8, BSWAPr32, CALLm32, CALLpcrel32, ...
203 </pre>
205 <p>The default backend prints out all of the records, as described <a
206 href="#example">above</a>.</p>
208 <p>If you plan to use TableGen for some purpose, you will most likely have to
209 <a href="#backends">write a backend</a> that extracts the information specific
210 to what you need and formats it in the appropriate way.</p>
212 </div>
215 <!-- *********************************************************************** -->
216 <div class="doc_section"><a name="syntax">TableGen syntax</a></div>
217 <!-- *********************************************************************** -->
219 <div class="doc_text">
220 <p>TableGen doesn't care about the meaning of data (that is up to the backend
221 to define), but it does care about syntax, and it enforces a simple type system.
222 This section describes the syntax and the constructs allowed in a TableGen file.
223 </p>
224 </div>
226 <!-- ======================================================================= -->
227 <div class="doc_subsection"><a name="primitives">TableGen primitives</a></div>
229 <!-- -------------------------------------------------------------------------->
230 <div class="doc_subsubsection"><a name="comments">TableGen comments</a></div>
232 <div class="doc_text">
233 <p>TableGen supports BCPL style "<tt>//</tt>" comments, which run to the end of
234 the line, and it also supports <b>nestable</b> "<tt>/* */</tt>" comments.</p>
235 </div>
237 <!-- -------------------------------------------------------------------------->
238 <div class="doc_subsubsection">
239 <a name="types">The TableGen type system</a>
240 </div>
242 <div class="doc_text">
243 <p>TableGen files are strongly typed, in a simple (but complete) type-system.
244 These types are used to perform automatic conversions, check for errors, and to
245 help interface designers constrain the input that they allow. Every <a
246 href="#valuedef">value definition</a> is required to have an associated type.
247 </p>
249 <p>TableGen supports a mixture of very low-level types (such as <tt>bit</tt>)
250 and very high-level types (such as <tt>dag</tt>). This flexibility is what
251 allows it to describe a wide range of information conveniently and compactly.
252 The TableGen types are:</p>
254 <ul>
255 <li>"<tt><b>bit</b></tt>" - A 'bit' is a boolean value that can hold either 0 or
256 1.</li>
258 <li>"<tt><b>int</b></tt>" - The 'int' type represents a simple 32-bit integer
259 value, such as 5.</li>
261 <li>"<tt><b>string</b></tt>" - The 'string' type represents an ordered sequence
262 of characters of arbitrary length.</li>
264 <li>"<tt><b>bits</b>&lt;n&gt;</tt>" - A 'bits' type is an arbitrary, but fixed,
265 size integer that is broken up into individual bits. This type is useful
266 because it can handle some bits being defined while others are undefined.</li>
268 <li>"<tt><b>list</b>&lt;ty&gt;</tt>" - This type represents a list whose
269 elements are some other type. The contained type is arbitrary: it can even be
270 another list type.</li>
272 <li>Class type - Specifying a class name in a type context means that the
273 defined value must be a subclass of the specified class. This is useful in
274 conjunction with the "list" type, for example, to constrain the elements of the
275 list to a common base class (e.g., a <tt><b>list</b>&lt;Register&gt;</tt> can
276 only contain definitions derived from the "<tt>Register</tt>" class).</li>
278 <li>"<tt><b>code</b></tt>" - This represents a big hunk of text. NOTE: I don't
279 remember why this is distinct from string!</li>
281 <li>"<tt><b>dag</b></tt>" - This type represents a nestable directed graph of
282 elements.</li>
283 </ul>
285 <p>To date, these types have been sufficient for describing things that
286 TableGen has been used for, but it is straight-forward to extend this list if
287 needed.</p>
289 </div>
291 <!-- -------------------------------------------------------------------------->
292 <div class="doc_subsubsection">
293 <a name="values">TableGen values and expressions</a>
294 </div>
296 <div class="doc_text">
298 <p>TableGen allows for a pretty reasonable number of different expression forms
299 when building up values. These forms allow the TableGen file to be written in a
300 natural syntax and flavor for the application. The current expression forms
301 supported include:</p>
303 <ul>
304 <li><tt>?</tt> - uninitialized field</li>
305 <li><tt>0b1001011</tt> - binary integer value</li>
306 <li><tt>07654321</tt> - octal integer value (indicated by a leading 0)</li>
307 <li><tt>7</tt> - decimal integer value</li>
308 <li><tt>0x7F</tt> - hexadecimal integer value</li>
309 <li><tt>"foo"</tt> - string value</li>
310 <li><tt>[{ ... }]</tt> - code fragment</li>
311 <li><tt>[ X, Y, Z ]</tt> - list value.</li>
312 <li><tt>{ a, b, c }</tt> - initializer for a "bits&lt;3&gt;" value</li>
313 <li><tt>value</tt> - value reference</li>
314 <li><tt>value{17}</tt> - access to one bit of a value</li>
315 <li><tt>value{15-17}</tt> - access to multiple bits of a value</li>
316 <li><tt>DEF</tt> - reference to a record definition</li>
317 <li><tt>CLASS&lt;val list&gt;</tt> - reference to a new anonymous definition of
318 CLASS with the specified template arguments.</li>
319 <li><tt>X.Y</tt> - reference to the subfield of a value</li>
320 <li><tt>list[4-7,17,2-3]</tt> - A slice of the 'list' list, including elements
321 4,5,6,7,17,2, and 3 from it. Elements may be included multiple times.</li>
322 <li><tt>(DEF a, b)</tt> - a dag value. The first element is required to be a
323 record definition, the remaining elements in the list may be arbitrary other
324 values, including nested `<tt>dag</tt>' values.</li>
325 <li><tt>!strconcat(a, b)</tt> - A string value that is the result of
326 concatenating the 'a' and 'b' strings.</li>
327 </ul>
329 <p>Note that all of the values have rules specifying how they convert to values
330 for different types. These rules allow you to assign a value like "7" to a
331 "bits&lt;4&gt;" value, for example.</p>
333 </div>
335 <!-- ======================================================================= -->
336 <div class="doc_subsection">
337 <a name="classesdefs">Classes and definitions</a>
338 </div>
340 <div class="doc_text">
342 <p>As mentioned in the <a href="#concepts">intro</a>, classes and definitions
343 (collectively known as 'records') in TableGen are the main high-level unit of
344 information that TableGen collects. Records are defined with a <tt>def</tt> or
345 <tt>class</tt> keyword, the record name, and an optional list of "<a
346 href="#templateargs">template arguments</a>". If the record has superclasses,
347 they are specified as a comma separated list that starts with a colon character
348 (":"). If <a href="#valuedef">value definitions</a> or <a href="#recordlet">let
349 expressions</a> are needed for the class, they are enclosed in curly braces
350 ("{}"); otherwise, the record ends with a semicolon. Here is a simple TableGen
351 file:</p>
353 <pre>
354 <b>class</b> C { <b>bit</b> V = 1; }
355 <b>def</b> X : C;
356 <b>def</b> Y : C {
357 <b>string</b> Greeting = "hello";
359 </pre>
361 <p>This example defines two definitions, <tt>X</tt> and <tt>Y</tt>, both of
362 which derive from the <tt>C</tt> class. Because of this, they both get the
363 <tt>V</tt> bit value. The <tt>Y</tt> definition also gets the Greeting member
364 as well.</p>
366 <p>In general, classes are useful for collecting together the commonality
367 between a group of records and isolating it in a single place. Also, classes
368 permit the specification of default values for their subclasses, allowing the
369 subclasses to override them as they wish.</p>
371 </div>
373 <!---------------------------------------------------------------------------->
374 <div class="doc_subsubsection">
375 <a name="valuedef">Value definitions</a>
376 </div>
378 <div class="doc_text">
379 <p>Value definitions define named entries in records. A value must be defined
380 before it can be referred to as the operand for another value definition or
381 before the value is reset with a <a href="#recordlet">let expression</a>. A
382 value is defined by specifying a <a href="#types">TableGen type</a> and a name.
383 If an initial value is available, it may be specified after the type with an
384 equal sign. Value definitions require terminating semicolons.</p>
385 </div>
387 <!-- -------------------------------------------------------------------------->
388 <div class="doc_subsubsection">
389 <a name="recordlet">'let' expressions</a>
390 </div>
392 <div class="doc_text">
393 <p>A record-level let expression is used to change the value of a value
394 definition in a record. This is primarily useful when a superclass defines a
395 value that a derived class or definition wants to override. Let expressions
396 consist of the '<tt>let</tt>' keyword followed by a value name, an equal sign
397 ("="), and a new value. For example, a new class could be added to the example
398 above, redefining the <tt>V</tt> field for all of its subclasses:</p>
400 <pre>
401 <b>class</b> D : C { let V = 0; }
402 <b>def</b> Z : D;
403 </pre>
405 <p>In this case, the <tt>Z</tt> definition will have a zero value for its "V"
406 value, despite the fact that it derives (indirectly) from the <tt>C</tt> class,
407 because the <tt>D</tt> class overrode its value.</p>
409 </div>
411 <!-- -------------------------------------------------------------------------->
412 <div class="doc_subsubsection">
413 <a name="templateargs">Class template arguments</a>
414 </div>
416 <div class="doc_text">
417 <p>TableGen permits the definition of parameterized classes as well as normal
418 concrete classes. Parameterized TableGen classes specify a list of variable
419 bindings (which may optionally have defaults) that are bound when used. Here is
420 a simple example:</p>
422 <pre>
423 <b>class</b> FPFormat&lt;<b>bits</b>&lt;3&gt; val&gt; {
424 <b>bits</b>&lt;3&gt; Value = val;
426 <b>def</b> NotFP : FPFormat&lt;0&gt;;
427 <b>def</b> ZeroArgFP : FPFormat&lt;1&gt;;
428 <b>def</b> OneArgFP : FPFormat&lt;2&gt;;
429 <b>def</b> OneArgFPRW : FPFormat&lt;3&gt;;
430 <b>def</b> TwoArgFP : FPFormat&lt;4&gt;;
431 <b>def</b> SpecialFP : FPFormat&lt;5&gt;;
432 </pre>
434 <p>In this case, template arguments are used as a space efficient way to specify
435 a list of "enumeration values", each with a "Value" field set to the specified
436 integer.</p>
438 <p>The more esoteric forms of <a href="#values">TableGen expressions</a> are
439 useful in conjunction with template arguments. As an example:</p>
441 <pre>
442 <b>class</b> ModRefVal&lt;<b>bits</b>&lt;2&gt; val&gt; {
443 <b>bits</b>&lt;2&gt; Value = val;
446 <b>def</b> None : ModRefVal&lt;0&gt;;
447 <b>def</b> Mod : ModRefVal&lt;1&gt;;
448 <b>def</b> Ref : ModRefVal&lt;2&gt;;
449 <b>def</b> ModRef : ModRefVal&lt;3&gt;;
451 <b>class</b> Value&lt;ModRefVal MR&gt; {
452 <i>// decode some information into a more convenient format, while providing
453 // a nice interface to the user of the "Value" class.</i>
454 <b>bit</b> isMod = MR.Value{0};
455 <b>bit</b> isRef = MR.Value{1};
457 <i>// other stuff...</i>
460 <i>// Example uses</i>
461 <b>def</b> bork : Value&lt;Mod&gt;;
462 <b>def</b> zork : Value&lt;Ref&gt;;
463 <b>def</b> hork : Value&lt;ModRef&gt;;
464 </pre>
466 <p>This is obviously a contrived example, but it shows how template arguments
467 can be used to decouple the interface provided to the user of the class from the
468 actual internal data representation expected by the class. In this case,
469 running <tt>tblgen</tt> on the example prints the following definitions:</p>
471 <pre>
472 <b>def</b> bork { <i>// Value</i>
473 <b>bit</b> isMod = 1;
474 <b>bit</b> isRef = 0;
476 <b>def</b> hork { <i>// Value</i>
477 <b>bit</b> isMod = 1;
478 <b>bit</b> isRef = 1;
480 <b>def</b> zork { <i>// Value</i>
481 <b>bit</b> isMod = 0;
482 <b>bit</b> isRef = 1;
484 </pre>
486 <p> This shows that TableGen was able to dig into the argument and extract a
487 piece of information that was requested by the designer of the "Value" class.
488 For more realistic examples, please see existing users of TableGen, such as the
489 X86 backend.</p>
491 </div>
493 <!-- -------------------------------------------------------------------------->
494 <div class="doc_subsubsection">
495 <a name="multiclass">Multiclass definitions and instances</a>
496 </div>
498 <div class="doc_text">
501 While classes with template arguments are a good way to factor commonality
502 between two instances of a definition, multiclasses allow a convenient notation
503 for defining multiple definitions at once (instances of implicitly constructed
504 classes). For example, consider an 3-address instruction set whose instructions
505 come in two forms: "reg = reg op reg" and "reg = reg op imm" (e.g. SPARC). In
506 this case, you'd like to specify in one place that this commonality exists, then
507 in a separate place indicate what all the ops are.
508 </p>
511 Here is an example TableGen fragment that shows this idea:
512 </p>
514 <pre>
515 <b>def</b> ops;
516 <b>def</b> GPR;
517 <b>def</b> Imm;
518 <b>class</b> inst&lt;<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist&gt;;
520 <b>multiclass</b> ri_inst&lt;<b>int</b> opc, <b>string</b> asmstr&gt; {
521 def _rr : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
522 (ops GPR:$dst, GPR:$src1, GPR:$src2)&gt;;
523 def _ri : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
524 (ops GPR:$dst, GPR:$src1, Imm:$src2)&gt;;
527 // Instantiations of the ri_inst multiclass.
528 <b>defm</b> ADD : ri_inst&lt;0b111, "add"&gt;;
529 <b>defm</b> SUB : ri_inst&lt;0b101, "sub"&gt;;
530 <b>defm</b> MUL : ri_inst&lt;0b100, "mul"&gt;;
532 </pre>
534 <p>The name of the resultant definitions has the multidef fragment names
535 appended to them, so this defines ADD_rr, ADD_ri, SUB_rr, etc. Using a
536 multiclass this way is exactly equivalent to instantiating the
537 classes multiple times yourself, e.g. by writing:</p>
539 <pre>
540 <b>def</b> ops;
541 <b>def</b> GPR;
542 <b>def</b> Imm;
543 <b>class</b> inst&lt;<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist&gt;;
545 <b>class</b> rrinst&lt;<b>int</b> opc, <b>string</b> asmstr&gt;
546 : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
547 (ops GPR:$dst, GPR:$src1, GPR:$src2)&gt;;
549 <b>class</b> riinst&lt;<b>int</b> opc, <b>string</b> asmstr&gt;
550 : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
551 (ops GPR:$dst, GPR:$src1, Imm:$src2)&gt;;
553 // Instantiations of the ri_inst multiclass.
554 <b>def</b> ADD_rr : rrinst&lt;0b111, "add"&gt;;
555 <b>def</b> ADD_ri : riinst&lt;0b111, "add"&gt;;
556 <b>def</b> SUB_rr : rrinst&lt;0b101, "sub"&gt;;
557 <b>def</b> SUB_ri : riinst&lt;0b101, "sub"&gt;;
558 <b>def</b> MUL_rr : rrinst&lt;0b100, "mul"&gt;;
559 <b>def</b> MUL_ri : riinst&lt;0b100, "mul"&gt;;
561 </pre>
563 </div>
565 <!-- ======================================================================= -->
566 <div class="doc_subsection">
567 <a name="filescope">File scope entities</a>
568 </div>
570 <!-- -------------------------------------------------------------------------->
571 <div class="doc_subsubsection">
572 <a name="include">File inclusion</a>
573 </div>
575 <div class="doc_text">
576 <p>TableGen supports the '<tt>include</tt>' token, which textually substitutes
577 the specified file in place of the include directive. The filename should be
578 specified as a double quoted string immediately after the '<tt>include</tt>'
579 keyword. Example:</p>
581 <pre>
582 <b>include</b> "foo.td"
583 </pre>
585 </div>
587 <!-- -------------------------------------------------------------------------->
588 <div class="doc_subsubsection">
589 <a name="globallet">'let' expressions</a>
590 </div>
592 <div class="doc_text">
593 <p> "let" expressions at file scope are similar to <a href="#recordlet">"let"
594 expressions within a record</a>, except they can specify a value binding for
595 multiple records at a time, and may be useful in certain other cases.
596 File-scope let expressions are really just another way that TableGen allows the
597 end-user to factor out commonality from the records.</p>
599 <p>File-scope "let" expressions take a comma-separated list of bindings to
600 apply, and one of more records to bind the values in. Here are some
601 examples:</p>
603 <pre>
604 <b>let</b> isTerminator = 1, isReturn = 1 <b>in</b>
605 <b>def</b> RET : X86Inst&lt;"ret", 0xC3, RawFrm, NoArg&gt;;
607 <b>let</b> isCall = 1 <b>in</b>
608 <i>// All calls clobber the non-callee saved registers...</i>
609 <b>let</b> Defs = [EAX, ECX, EDX, FP0, FP1, FP2, FP3, FP4, FP5, FP6] in {
610 <b>def</b> CALLpcrel32 : X86Inst&lt;"call", 0xE8, RawFrm, NoArg&gt;;
611 <b>def</b> CALLr32 : X86Inst&lt;"call", 0xFF, MRMS2r, Arg32&gt;;
612 <b>def</b> CALLm32 : X86Inst&lt;"call", 0xFF, MRMS2m, Arg32&gt;;
614 </pre>
616 <p>File-scope "let" expressions are often useful when a couple of definitions
617 need to be added to several records, and the records do not otherwise need to be
618 opened, as in the case with the CALL* instructions above.</p>
619 </div>
621 <!-- *********************************************************************** -->
622 <div class="doc_section"><a name="backends">TableGen backends</a></div>
623 <!-- *********************************************************************** -->
625 <div class="doc_text">
626 <p>How they work, how to write one. This section should not contain details
627 about any particular backend, except maybe -print-enums as an example. This
628 should highlight the APIs in <tt>TableGen/Record.h</tt>.</p>
629 </div>
631 <!-- *********************************************************************** -->
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