Gitiles
Code Review Sign In
gerrit-public.fairphone.software / platform / external / llvm / f17a25c88b892d30c2b41ba7ecdfbdfb2b4be9cc / . / docs / TableGenFundamentals.html
blob: 90836e91bda8462c73e1fd213438a42e7aaabc62 [file] [log] [blame]
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame^]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
2 "http://www.w3.org/TR/html4/strict.dtd">
3<html>
4<head>
5 <title>TableGen Fundamentals</title>
6 <link rel="stylesheet" href="llvm.css" type="text/css">
7</head>
8<body>
9
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
59domain-specific information. Because there may be a large number of these
60records, it is specifically designed to allow writing flexible descriptions and
61for common features of these records to be factored out. This reduces the
62amount of duplication in the description, reduces the chance of error, and
63makes it easier to structure domain specific information.</p>
64
65<p>The core part of TableGen <a href="#syntax">parses a file</a>, instantiates
66the declarations, and hands the result off to a domain-specific "<a
67href="#backends">TableGen backend</a>" for processing. The current major user
68of 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
71find 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
73distribution, 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
83of which are considered 'records'.</p>
84
85<p><b>TableGen records</b> have a unique name, a list of values, and a list of
86superclasses. The list of values is main data that TableGen builds for each
87record, it is this that holds the domain specific information for the
88application. The interpretation of this data is left to a specific <a
89href="#backends">TableGen backend</a>, but the structure and format rules are
90taken care of and fixed by TableGen.</p>
91
92<p><b>TableGen definitions</b> are the concrete form of 'records'. These
93generally 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
97describe other records. These 'classes' allow the end-user to build
98abstractions for either the domain they are targetting (such as "Register",
99"RegisterClass", and "Instruction" in the LLVM code generator) or for the
100implementor to help factor out common properties of records (such as "FPInst",
101which is used to represent floating point instructions in the X86 backend).
102TableGen keeps track of all of the classes that are used to build up a
103definition, so the backend can find all definitions of a particular class, such
104as "Instruction".</p>
105
106<p><b>TableGen multiclasses</b> are groups of abstract records that are
107instantiated all at once. Each instantiation can result in multiple TableGen
108definitions.</p>
109
110</div>
111
112<!-- ======================================================================= -->
113<div class="doc_subsection"><a name="example">An example record</a></div>
114
115<div class="doc_text">
116
117<p>With no other arguments, TableGen parses the specified file and prints out
118all of the classes, then all of the definitions. This is a good way to see what
119the various definitions expand to fully. Running this on the <tt>X86.td</tt>
120file prints this (at the time of this writing):</p>
121
122<pre>
123...
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 };
145}
146...
147</pre>
148
149<p>This definition corresponds to an 8-bit register-register add instruction in
150the X86. The string after the '<tt>def</tt>' string indicates the name of the
151record ("<tt>ADDrr8</tt>" in this case), and the comment at the end of the line
152indicates the superclasses of the definition. The body of the record contains
153all of the data that TableGen assembled for the record, indicating that the
154instruction is part of the "X86" namespace, should be printed as "<tt>add</tt>"
155in the assembly file, it is a two-address instruction, has a particular
156encoding, etc. The contents and semantics of the information in the record is
157specific to the needs of the X86 backend, and is only shown as an example.</p>
158
159<p>As you can see, a lot of information is needed for every instruction
160supported by the code generator, and specifying it all manually would be
161unmaintainble, prone to bugs, and tiring to do in the first place. Because we
162are using TableGen, all of the information was derived from the following
163definition:</p>
164
165<pre>
166<b>def</b> ADDrr8 : I2A8&lt;"add", 0x00, MRMDestReg&gt;,
167 Pattern&lt;(set R8, (plus R8, R8))&gt;;
168</pre>
169
170<p>This definition makes use of the custom I2A8 (two address instruction with
1718-bit operand) class, which is defined in the X86-specific TableGen file to
172factor out the common features that instructions of its class share. A key
173feature of TableGen is that it allows the end-user to define the abstractions
174they prefer to use when describing their information.</p>
175
176</div>
177
178<!-- ======================================================================= -->
179<div class="doc_subsection"><a name="running">Running TableGen</a></div>
180
181<div class="doc_text">
182
183<p>TableGen runs just like any other LLVM tool. The first (optional) argument
184specifies the file to read. If a filename is not specified, <tt>tblgen</tt>
185reads from standard input.</p>
186
187<p>To be useful, one of the <a href="#backends">TableGen backends</a> must be
188used. 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
190that subclass a particular type (which can be useful for building up an enum
191list of these records), use the <tt>--print-enums</tt> option:</p>
192
193<pre>
194$ tblgen X86.td -print-enums -class=Register
195AH, AL, AX, BH, BL, BP, BX, CH, CL, CX, DH, DI, DL, DX,
196EAX, EBP, EBX, ECX, EDI, EDX, ESI, ESP, FP0, FP1, FP2, FP3, FP4, FP5, FP6,
197SI, SP, ST0, ST1, ST2, ST3, ST4, ST5, ST6, ST7,
198
199$ tblgen X86.td -print-enums -class=Instruction
200ADCrr32, ADDri16, ADDri16b, ADDri32, ADDri32b, ADDri8, ADDrr16, ADDrr32,
201ADDrr8, ADJCALLSTACKDOWN, ADJCALLSTACKUP, ANDri16, ANDri16b, ANDri32, ANDri32b,
202ANDri8, ANDrr16, ANDrr32, ANDrr8, BSWAPr32, CALLm32, CALLpcrel32, ...
203</pre>
204
205<p>The default backend prints out all of the records, as described <a
206href="#example">above</a>.</p>
207
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
210to what you need and formats it in the appropriate way.</p>
211
212</div>
213
214
215<!-- *********************************************************************** -->
216<div class="doc_section"><a name="syntax">TableGen syntax</a></div>
217<!-- *********************************************************************** -->
218
219<div class="doc_text">
220<p>TableGen doesn't care about the meaning of data (that is up to the backend
221to define), but it does care about syntax, and it enforces a simple type system.
222This section describes the syntax and the constructs allowed in a TableGen file.
223</p>
224</div>
225
226<!-- ======================================================================= -->
227<div class="doc_subsection"><a name="primitives">TableGen primitives</a></div>
228
229<!-- -------------------------------------------------------------------------->
230<div class="doc_subsubsection"><a name="comments">TableGen comments</a></div>
231
232<div class="doc_text">
233<p>TableGen supports BCPL style "<tt>//</tt>" comments, which run to the end of
234the line, and it also supports <b>nestable</b> "<tt>/* */</tt>" comments.</p>
235</div>
236
237<!-- -------------------------------------------------------------------------->
238<div class="doc_subsubsection">
239 <a name="types">The TableGen type system</a>
240</div>
241
242<div class="doc_text">
243<p>TableGen files are strongly typed, in a simple (but complete) type-system.
244These types are used to perform automatic conversions, check for errors, and to
245help interface designers constrain the input that they allow. Every <a
246href="#valuedef">value definition</a> is required to have an associated type.
247</p>
248
249<p>TableGen supports a mixture of very low-level types (such as <tt>bit</tt>)
250and very high-level types (such as <tt>dag</tt>). This flexibility is what
251allows it to describe a wide range of information conveniently and compactly.
252The TableGen types are:</p>
253
254<ul>
255<li>"<tt><b>bit</b></tt>" - A 'bit' is a boolean value that can hold either 0 or
2561.</li>
257
258<li>"<tt><b>int</b></tt>" - The 'int' type represents a simple 32-bit integer
259value, such as 5.</li>
260
261<li>"<tt><b>string</b></tt>" - The 'string' type represents an ordered sequence
262of characters of arbitrary length.</li>
263
264<li>"<tt><b>bits</b>&lt;n&gt;</tt>" - A 'bits' type is an arbitrary, but fixed,
265size integer that is broken up into individual bits. This type is useful
266because it can handle some bits being defined while others are undefined.</li>
267
268<li>"<tt><b>list</b>&lt;ty&gt;</tt>" - This type represents a list whose
269elements are some other type. The contained type is arbitrary: it can even be
270another list type.</li>
271
272<li>Class type - Specifying a class name in a type context means that the
273defined value must be a subclass of the specified class. This is useful in
274conjunction with the "list" type, for example, to constrain the elements of the
275list to a common base class (e.g., a <tt><b>list</b>&lt;Register&gt;</tt> can
276only contain definitions derived from the "<tt>Register</tt>" class).</li>
277
278<li>"<tt><b>code</b></tt>" - This represents a big hunk of text. NOTE: I don't
279remember why this is distinct from string!</li>
280
281<li>"<tt><b>dag</b></tt>" - This type represents a nestable directed graph of
282elements.</li>
283</ul>
284
285<p>To date, these types have been sufficient for describing things that
286TableGen has been used for, but it is straight-forward to extend this list if
287needed.</p>
288
289</div>
290
291<!-- -------------------------------------------------------------------------->
292<div class="doc_subsubsection">
293 <a name="values">TableGen values and expressions</a>
294</div>
295
296<div class="doc_text">
297
298<p>TableGen allows for a pretty reasonable number of different expression forms
299when building up values. These forms allow the TableGen file to be written in a
300natural syntax and flavor for the application. The current expression forms
301supported include:</p>
302
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
3214,5,6,7,17,2, 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
323record definition, the remaining elements in the list may be arbitrary other
324values, 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>
328
329<p>Note that all of the values have rules specifying how they convert to values
330for different types. These rules allow you to assign a value like "7" to a
331"bits&lt;4&gt;" value, for example.</p>
332
333</div>
334
335<!-- ======================================================================= -->
336<div class="doc_subsection">
337 <a name="classesdefs">Classes and definitions</a>
338</div>
339
340<div class="doc_text">
341
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
344information 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
346href="#templateargs">template arguments</a>". If the record has superclasses,
347they 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
349expressions</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
351file:</p>
352
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";
358}
359</pre>
360
361<p>This example defines two definitions, <tt>X</tt> and <tt>Y</tt>, both of
362which 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
364as well.</p>
365
366<p>In general, classes are useful for collecting together the commonality
367between a group of records and isolating it in a single place. Also, classes
368permit the specification of default values for their subclasses, allowing the
369subclasses to override them as they wish.</p>
370
371</div>
372
373<!---------------------------------------------------------------------------->
374<div class="doc_subsubsection">
375 <a name="valuedef">Value definitions</a>
376</div>
377
378<div class="doc_text">
379<p>Value definitions define named entries in records. A value must be defined
380before it can be referred to as the operand for another value definition or
381before the value is reset with a <a href="#recordlet">let expression</a>. A
382value is defined by specifying a <a href="#types">TableGen type</a> and a name.
383If an initial value is available, it may be specified after the type with an
384equal sign. Value definitions require terminating semicolons.</p>
385</div>
386
387<!-- -------------------------------------------------------------------------->
388<div class="doc_subsubsection">
389 <a name="recordlet">'let' expressions</a>
390</div>
391
392<div class="doc_text">
393<p>A record-level let expression is used to change the value of a value
394definition in a record. This is primarily useful when a superclass defines a
395value that a derived class or definition wants to override. Let expressions
396consist 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
398above, redefining the <tt>V</tt> field for all of its subclasses:</p>
399
400<pre>
401<b>class</b> D : C { let V = 0; }
402<b>def</b> Z : D;
403</pre>
404
405<p>In this case, the <tt>Z</tt> definition will have a zero value for its "V"
406value, despite the fact that it derives (indirectly) from the <tt>C</tt> class,
407because the <tt>D</tt> class overrode its value.</p>
408
409</div>
410
411<!-- -------------------------------------------------------------------------->
412<div class="doc_subsubsection">
413 <a name="templateargs">Class template arguments</a>
414</div>
415
416<div class="doc_text">
417<p>TableGen permits the definition of parameterized classes as well as normal
418concrete classes. Parameterized TableGen classes specify a list of variable
419bindings (which may optionally have defaults) that are bound when used. Here is
420a simple example:</p>
421
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;
425}
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>
433
434<p>In this case, template arguments are used as a space efficient way to specify
435a list of "enumeration values", each with a "Value" field set to the specified
436integer.</p>
437
438<p>The more esoteric forms of <a href="#values">TableGen expressions</a> are
439useful in conjunction with template arguments. As an example:</p>
440
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;
444}
445
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;;
450
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};
456
457 <i>// other stuff...</i>
458}
459
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>
465
466<p>This is obviously a contrived example, but it shows how template arguments
467can be used to decouple the interface provided to the user of the class from the
468actual internal data representation expected by the class. In this case,
469running <tt>tblgen</tt> on the example prints the following definitions:</p>
470
471<pre>
472<b>def</b> bork { <i>// Value</i>
473 <b>bit</b> isMod = 1;
474 <b>bit</b> isRef = 0;
475}
476<b>def</b> hork { <i>// Value</i>
477 <b>bit</b> isMod = 1;
478 <b>bit</b> isRef = 1;
479}
480<b>def</b> zork { <i>// Value</i>
481 <b>bit</b> isMod = 0;
482 <b>bit</b> isRef = 1;
483}
484</pre>
485
486<p> This shows that TableGen was able to dig into the argument and extract a
487piece of information that was requested by the designer of the "Value" class.
488For more realistic examples, please see existing users of TableGen, such as the
489X86 backend.</p>
490
491</div>
492
493<!-- -------------------------------------------------------------------------->
494<div class="doc_subsubsection">
495 <a name="multiclass">Multiclass definitions and instances</a>
496</div>
497
498<div class="doc_text">
499
500<p>
501While classes with template arguments are a good way to factor commonality
502between two instances of a definition, multiclasses allow a convenient notation
503for defining multiple definitions at once (instances of implicitly constructed
504classes). For example, consider an 3-address instruction set whose instructions
505come in two forms: "reg = reg op reg" and "reg = reg op imm" (e.g. SPARC). In
506this case, you'd like to specify in one place that this commonality exists, then
507in a separate place indicate what all the ops are.
508</p>
509
510<p>
511Here is an example TableGen fragment that shows this idea:
512</p>
513
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;;
519
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;;
525}
526
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;;
531...
532</pre>
533
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>
538
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;;
544
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;;
548
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;;
552
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;;
560...
561</pre>
562
563</div>
564
565<!-- ======================================================================= -->
566<div class="doc_subsection">
567 <a name="filescope">File scope entities</a>
568</div>
569
570<!-- -------------------------------------------------------------------------->
571<div class="doc_subsubsection">
572 <a name="include">File inclusion</a>
573</div>
574
575<div class="doc_text">
576<p>TableGen supports the '<tt>include</tt>' token, which textually substitutes
577the specified file in place of the include directive. The filename should be
578specified as a double quoted string immediately after the '<tt>include</tt>'
579keyword. Example:</p>
580
581<pre>
582<b>include</b> "foo.td"
583</pre>
584
585</div>
586
587<!-- -------------------------------------------------------------------------->
588<div class="doc_subsubsection">
589 <a name="globallet">'let' expressions</a>
590</div>
591
592<div class="doc_text">
593<p> "let" expressions at file scope are similar to <a href="#recordlet">"let"
594expressions within a record</a>, except they can specify a value binding for
595multiple records at a time, and may be useful in certain other cases.
596File-scope let expressions are really just another way that TableGen allows the
597end-user to factor out commonality from the records.</p>
598
599<p>File-scope "let" expressions take a comma-separated list of bindings to
600apply, and one of more records to bind the values in. Here are some
601examples:</p>
602
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;;
606
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;;
613 }
614</pre>
615
616<p>File-scope "let" expressions are often useful when a couple of definitions
617need to be added to several records, and the records do not otherwise need to be
618opened, as in the case with the CALL* instructions above.</p>
619</div>
620
621<!-- *********************************************************************** -->
622<div class="doc_section"><a name="backends">TableGen backends</a></div>
623<!-- *********************************************************************** -->
624
625<div class="doc_text">
626<p>How they work, how to write one. This section should not contain details
627about any particular backend, except maybe -print-enums as an example. This
628should highlight the APIs in <tt>TableGen/Record.h</tt>.</p>
629</div>
630
631<!-- *********************************************************************** -->
632
633<hr>
634<address>
635 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
636 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
637 <a href="http://validator.w3.org/check/referer"><img
638 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
639
640 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
641 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
642 Last modified: $Date$
643</address>
644
645</body>
646</html>