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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 the
72<tt>llvm/utils/emacs</tt> and <tt>llvm/utils/vim</tt> directories 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 the 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 are 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 targeting (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
108TableGen definitions. If a multiclass inherits from another multiclass,
109the definitions in the sub-multiclass become part of the current
110multiclass, 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
120all of the classes, then all of the definitions. This is a good way to see what
121the various definitions expand to fully. Running this on the <tt>X86.td</tt>
122file prints this (at the time of this writing):</p>
123
124<div class="doc_code">
125<pre>
126...
127<b>def</b> ADD32rr { <i>// Instruction X86Inst I</i>
128 <b>string</b> Namespace = "X86";
129 <b>dag</b> OutOperandList = (outs GR32:$dst);
130 <b>dag</b> InOperandList = (ins GR32:$src1, GR32:$src2);
131 <b>string</b> AsmString = "add{l}\t{$src2, $dst|$dst, $src2}";
132 <b>list</b>&lt;dag&gt; Pattern = [(set GR32:$dst, (add GR32:$src1, GR32:$src2))];
133 <b>list</b>&lt;Register&gt; Uses = [];
134 <b>list</b>&lt;Register&gt; Defs = [EFLAGS];
135 <b>list</b>&lt;Predicate&gt; Predicates = [];
136 <b>int</b> CodeSize = 3;
137 <b>int</b> AddedComplexity = 0;
138 <b>bit</b> isReturn = 0;
139 <b>bit</b> isBranch = 0;
140 <b>bit</b> isIndirectBranch = 0;
141 <b>bit</b> isBarrier = 0;
142 <b>bit</b> isCall = 0;
143 <b>bit</b> canFoldAsLoad = 0;
144 <b>bit</b> mayLoad = 0;
145 <b>bit</b> mayStore = 0;
146 <b>bit</b> isImplicitDef = 0;
147 <b>bit</b> isTwoAddress = 1;
148 <b>bit</b> isConvertibleToThreeAddress = 1;
149 <b>bit</b> isCommutable = 1;
150 <b>bit</b> isTerminator = 0;
151 <b>bit</b> isReMaterializable = 0;
152 <b>bit</b> isPredicable = 0;
153 <b>bit</b> hasDelaySlot = 0;
154 <b>bit</b> usesCustomInserter = 0;
155 <b>bit</b> hasCtrlDep = 0;
156 <b>bit</b> isNotDuplicable = 0;
157 <b>bit</b> hasSideEffects = 0;
158 <b>bit</b> mayHaveSideEffects = 0;
159 <b>bit</b> neverHasSideEffects = 0;
160 InstrItinClass Itinerary = NoItinerary;
161 <b>string</b> Constraints = "";
162 <b>string</b> DisableEncoding = "";
163 <b>bits</b>&lt;8&gt; Opcode = { 0, 0, 0, 0, 0, 0, 0, 1 };
164 Format Form = MRMDestReg;
165 <b>bits</b>&lt;6&gt; FormBits = { 0, 0, 0, 0, 1, 1 };
166 ImmType ImmT = NoImm;
167 <b>bits</b>&lt;3&gt; ImmTypeBits = { 0, 0, 0 };
168 <b>bit</b> hasOpSizePrefix = 0;
169 <b>bit</b> hasAdSizePrefix = 0;
170 <b>bits</b>&lt;4&gt; Prefix = { 0, 0, 0, 0 };
171 <b>bit</b> hasREX_WPrefix = 0;
172 FPFormat FPForm = ?;
173 <b>bits</b>&lt;3&gt; FPFormBits = { 0, 0, 0 };
174}
175...
176</pre>
177</div>
178
179<p>This definition corresponds to a 32-bit register-register add instruction in
180the X86. The string after the '<tt>def</tt>' string indicates the name of the
181record&mdash;"<tt>ADD32rr</tt>" in this case&mdash;and the comment at the end of
182the line indicates the superclasses of the definition. The body of the record
183contains all of the data that TableGen assembled for the record, indicating that
184the instruction is part of the "X86" namespace, the pattern indicating how the
185the instruction should be emitted into the assembly file, that it is a
186two-address instruction, has a particular encoding, etc. The contents and
187semantics of the information in the record is specific to the needs of the X86
188backend, and is only shown as an example.</p>
189
190<p>As you can see, a lot of information is needed for every instruction
191supported by the code generator, and specifying it all manually would be
192unmaintainble, prone to bugs, and tiring to do in the first place. Because we
193are using TableGen, all of the information was derived from the following
194definition:</p>
195
196<div class="doc_code">
197<pre>
198let Defs = [EFLAGS],
199 isCommutable = 1, <i>// X = ADD Y,Z --&gt; X = ADD Z,Y</i>
200 isConvertibleToThreeAddress = 1 <b>in</b> <i>// Can transform into LEA.</i>
201def ADD32rr : I&lt;0x01, MRMDestReg, (outs GR32:$dst),
202 (ins GR32:$src1, GR32:$src2),
203 "add{l}\t{$src2, $dst|$dst, $src2}",
204 [(set GR32:$dst, (add GR32:$src1, GR32:$src2))]&gt;;
205</pre>
206</div>
207
208<p>This definition makes use of the custom class <tt>I</tt> (extended from the
209custom class <tt>X86Inst</tt>), which is defined in the X86-specific TableGen
210file, to factor out the common features that instructions of its class share. A
211key feature of TableGen is that it allows the end-user to define the
212abstractions they prefer to use when describing their information.</p>
213
214</div>
215
216<!-- ======================================================================= -->
217<div class="doc_subsection"><a name="running">Running TableGen</a></div>
218
219<div class="doc_text">
220
221<p>TableGen runs just like any other LLVM tool. The first (optional) argument
222specifies the file to read. If a filename is not specified, <tt>tblgen</tt>
223reads from standard input.</p>
224
225<p>To be useful, one of the <a href="#backends">TableGen backends</a> must be
226used. These backends are selectable on the command line (type '<tt>tblgen
227-help</tt>' for a list). For example, to get a list of all of the definitions
228that subclass a particular type (which can be useful for building up an enum
229list of these records), use the <tt>-print-enums</tt> option:</p>
230
231<div class="doc_code">
232<pre>
233$ tblgen X86.td -print-enums -class=Register
234AH, AL, AX, BH, BL, BP, BPL, BX, CH, CL, CX, DH, DI, DIL, DL, DX, EAX, EBP, EBX,
235ECX, EDI, EDX, EFLAGS, EIP, ESI, ESP, FP0, FP1, FP2, FP3, FP4, FP5, FP6, IP,
236MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7, R10, R10B, R10D, R10W, R11, R11B, R11D,
237R11W, R12, R12B, R12D, R12W, R13, R13B, R13D, R13W, R14, R14B, R14D, R14W, R15,
238R15B, R15D, R15W, R8, R8B, R8D, R8W, R9, R9B, R9D, R9W, RAX, RBP, RBX, RCX, RDI,
239RDX, RIP, RSI, RSP, SI, SIL, SP, SPL, ST0, ST1, ST2, ST3, ST4, ST5, ST6, ST7,
240XMM0, XMM1, XMM10, XMM11, XMM12, XMM13, XMM14, XMM15, XMM2, XMM3, XMM4, XMM5,
241XMM6, XMM7, XMM8, XMM9,
242
243$ tblgen X86.td -print-enums -class=Instruction
244ABS_F, ABS_Fp32, ABS_Fp64, ABS_Fp80, ADC32mi, ADC32mi8, ADC32mr, ADC32ri,
245ADC32ri8, ADC32rm, ADC32rr, ADC64mi32, ADC64mi8, ADC64mr, ADC64ri32, ADC64ri8,
246ADC64rm, ADC64rr, ADD16mi, ADD16mi8, ADD16mr, ADD16ri, ADD16ri8, ADD16rm,
247ADD16rr, ADD32mi, ADD32mi8, ADD32mr, ADD32ri, ADD32ri8, ADD32rm, ADD32rr,
248ADD64mi32, ADD64mi8, ADD64mr, ADD64ri32, ...
249</pre>
250</div>
251
252<p>The default backend prints out all of the records, as described <a
253href="#example">above</a>.</p>
254
255<p>If you plan to use TableGen, you will most likely have to <a
256href="#backends">write a backend</a> that extracts the information specific to
257what you need and formats it in the appropriate way.</p>
258
259</div>
260
261
262<!-- *********************************************************************** -->
263<div class="doc_section"><a name="syntax">TableGen syntax</a></div>
264<!-- *********************************************************************** -->
265
266<div class="doc_text">
267
268<p>TableGen doesn't care about the meaning of data (that is up to the backend to
269define), but it does care about syntax, and it enforces a simple type system.
270This section describes the syntax and the constructs allowed in a TableGen file.
271</p>
272
273</div>
274
275<!-- ======================================================================= -->
276<div class="doc_subsection"><a name="primitives">TableGen primitives</a></div>
277
278<!-- -------------------------------------------------------------------------->
279<div class="doc_subsubsection"><a name="comments">TableGen comments</a></div>
280
281<div class="doc_text">
282
283<p>TableGen supports BCPL style "<tt>//</tt>" comments, which run to the end of
284the line, and it also supports <b>nestable</b> "<tt>/* */</tt>" comments.</p>
285
286</div>
287
288<!-- -------------------------------------------------------------------------->
289<div class="doc_subsubsection">
290 <a name="types">The TableGen type system</a>
291</div>
292
293<div class="doc_text">
294
295<p>TableGen files are strongly typed, in a simple (but complete) type-system.
296These types are used to perform automatic conversions, check for errors, and to
297help interface designers constrain the input that they allow. Every <a
298href="#valuedef">value definition</a> is required to have an associated type.
299</p>
300
301<p>TableGen supports a mixture of very low-level types (such as <tt>bit</tt>)
302and very high-level types (such as <tt>dag</tt>). This flexibility is what
303allows it to describe a wide range of information conveniently and compactly.
304The TableGen types are:</p>
305
306<dl>
307<dt><tt><b>bit</b></tt></dt>
308 <dd>A 'bit' is a boolean value that can hold either 0 or 1.</dd>
309
310<dt><tt><b>int</b></tt></dt>
311 <dd>The 'int' type represents a simple 32-bit integer value, such as 5.</dd>
312
313<dt><tt><b>string</b></tt></dt>
314 <dd>The 'string' type represents an ordered sequence of characters of
315 arbitrary length.</dd>
316
317<dt><tt><b>bits</b>&lt;n&gt;</tt></dt>
318 <dd>A 'bits' type is an arbitrary, but fixed, size integer that is broken up
319 into individual bits. This type is useful because it can handle some bits
320 being defined while others are undefined.</dd>
321
322<dt><tt><b>list</b>&lt;ty&gt;</tt></dt>
323 <dd>This type represents a list whose elements are some other type. The
324 contained type is arbitrary: it can even be another list type.</dd>
325
326<dt>Class type</dt>
327 <dd>Specifying a class name in a type context means that the defined value
328 must be a subclass of the specified class. This is useful in conjunction with
329 the <b><tt>list</tt></b> type, for example, to constrain the elements of the
330 list to a common base class (e.g., a <tt><b>list</b>&lt;Register&gt;</tt> can
331 only contain definitions derived from the "<tt>Register</tt>" class).</dd>
332
333<dt><tt><b>dag</b></tt></dt>
334 <dd>This type represents a nestable directed graph of elements.</dd>
335
336<dt><tt><b>code</b></tt></dt>
337 <dd>This represents a big hunk of text. NOTE: I don't remember why this is
338 distinct from string!</dd>
339</dl>
340
341<p>To date, these types have been sufficient for describing things that
342TableGen has been used for, but it is straight-forward to extend this list if
343needed.</p>
344
345</div>
346
347<!-- -------------------------------------------------------------------------->
348<div class="doc_subsubsection">
349 <a name="values">TableGen values and expressions</a>
350</div>
351
352<div class="doc_text">
353
354<p>TableGen allows for a pretty reasonable number of different expression forms
355when building up values. These forms allow the TableGen file to be written in a
356natural syntax and flavor for the application. The current expression forms
357supported include:</p>
358
359<dl>
360<dt><tt>?</tt></dt>
361 <dd>uninitialized field</dd>
362<dt><tt>0b1001011</tt></dt>
363 <dd>binary integer value</dd>
364<dt><tt>07654321</tt></dt>
365 <dd>octal integer value (indicated by a leading 0)</dd>
366<dt><tt>7</tt></dt>
367 <dd>decimal integer value</dd>
368<dt><tt>0x7F</tt></dt>
369 <dd>hexadecimal integer value</dd>
370<dt><tt>"foo"</tt></dt>
371 <dd>string value</dd>
372<dt><tt>[{ ... }]</tt></dt>
373 <dd>code fragment</dd>
374<dt><tt>[ X, Y, Z ]&lt;type&gt;</tt></dt>
375 <dd>list value. &lt;type&gt; is the type of the list
376element and is usually optional. In rare cases,
377TableGen is unable to deduce the element type in
378which case the user must specify it explicitly.</dd>
379<dt><tt>{ a, b, c }</tt></dt>
380 <dd>initializer for a "bits&lt;3&gt;" value</dd>
381<dt><tt>value</tt></dt>
382 <dd>value reference</dd>
383<dt><tt>value{17}</tt></dt>
384 <dd>access to one bit of a value</dd>
385<dt><tt>value{15-17}</tt></dt>
386 <dd>access to multiple bits of a value</dd>
387<dt><tt>DEF</tt></dt>
388 <dd>reference to a record definition</dd>
389<dt><tt>CLASS&lt;val list&gt;</tt></dt>
390 <dd>reference to a new anonymous definition of CLASS with the specified
391 template arguments.</dd>
392<dt><tt>X.Y</tt></dt>
393 <dd>reference to the subfield of a value</dd>
394<dt><tt>list[4-7,17,2-3]</tt></dt>
395 <dd>A slice of the 'list' list, including elements 4,5,6,7,17,2, and 3 from
396 it. Elements may be included multiple times.</dd>
397<dt><tt>(DEF a, b)</tt></dt>
398 <dd>a dag value. The first element is required to be a record definition, the
399 remaining elements in the list may be arbitrary other values, including nested
400 `<tt>dag</tt>' values.</dd>
401<dt><tt>!strconcat(a, b)</tt></dt>
402 <dd>A string value that is the result of concatenating the 'a' and 'b'
403 strings.</dd>
404<dt><tt>!cast&lt;type&gt;(a)</tt></dt>
405 <dd>A symbol of type <em>type</em> obtained by looking up the string 'a' in
406the symbol table. If the type of 'a' does not match <em>type</em>, TableGen
407aborts with an error. !cast&lt;string&gt; is a special case in that the argument must
408be an object defined by a 'def' construct.</dd>
409<dt><tt>!nameconcat&lt;type&gt;(a, b)</tt></dt>
410 <dd>Shorthand for !cast&lt;type&gt;(!strconcat(a, b))</dd>
411<dt><tt>!subst(a, b, c)</tt></dt>
412 <dd>If 'a' and 'b' are of string type or are symbol references, substitute
413'b' for 'a' in 'c.' This operation is analogous to $(subst) in GNU make.</dd>
414<dt><tt>!foreach(a, b, c)</tt></dt>
415 <dd>For each member 'b' of dag or list 'a' apply operator 'c.' 'b' is a
416dummy variable that should be declared as a member variable of an instantiated
417class. This operation is analogous to $(foreach) in GNU make.</dd>
418<dt><tt>!car(a)</tt></dt>
419 <dd>The first element of list 'a.'</dd>
420<dt><tt>!cdr(a)</tt></dt>
421 <dd>The 2nd-N elements of list 'a.'</dd>
422<dt><tt>!null(a)</tt></dt>
423 <dd>An integer {0,1} indicating whether list 'a' is empty.</dd>
424<dt><tt>!if(a,b,c)</tt></dt>
425 <dd>'b' if the result of integer operator 'a' is nonzero, 'c' otherwise.</dd>
426<dt><tt>!eq(a,b)</tt></dt>
427 <dd>Integer one if string a is equal to string b, zero otherwise. This
428 only operates on string objects. Use !cast<string> to compare other
429 types of objects.</dd>
430</dl>
431
432<p>Note that all of the values have rules specifying how they convert to values
433for different types. These rules allow you to assign a value like "<tt>7</tt>"
434to a "<tt>bits&lt;4&gt;</tt>" value, for example.</p>
435
436</div>
437
438<!-- ======================================================================= -->
439<div class="doc_subsection">
440 <a name="classesdefs">Classes and definitions</a>
441</div>
442
443<div class="doc_text">
444
445<p>As mentioned in the <a href="#concepts">intro</a>, classes and definitions
446(collectively known as 'records') in TableGen are the main high-level unit of
447information that TableGen collects. Records are defined with a <tt>def</tt> or
448<tt>class</tt> keyword, the record name, and an optional list of "<a
449href="#templateargs">template arguments</a>". If the record has superclasses,
450they are specified as a comma separated list that starts with a colon character
451("<tt>:</tt>"). If <a href="#valuedef">value definitions</a> or <a
452href="#recordlet">let expressions</a> are needed for the class, they are
453enclosed in curly braces ("<tt>{}</tt>"); otherwise, the record ends with a
454semicolon.</p>
455
456<p>Here is a simple TableGen file:</p>
457
458<div class="doc_code">
459<pre>
460<b>class</b> C { <b>bit</b> V = 1; }
461<b>def</b> X : C;
462<b>def</b> Y : C {
463 <b>string</b> Greeting = "hello";
464}
465</pre>
466</div>
467
468<p>This example defines two definitions, <tt>X</tt> and <tt>Y</tt>, both of
469which derive from the <tt>C</tt> class. Because of this, they both get the
470<tt>V</tt> bit value. The <tt>Y</tt> definition also gets the Greeting member
471as well.</p>
472
473<p>In general, classes are useful for collecting together the commonality
474between a group of records and isolating it in a single place. Also, classes
475permit the specification of default values for their subclasses, allowing the
476subclasses to override them as they wish.</p>
477
478</div>
479
480<!---------------------------------------------------------------------------->
481<div class="doc_subsubsection">
482 <a name="valuedef">Value definitions</a>
483</div>
484
485<div class="doc_text">
486
487<p>Value definitions define named entries in records. A value must be defined
488before it can be referred to as the operand for another value definition or
489before the value is reset with a <a href="#recordlet">let expression</a>. A
490value is defined by specifying a <a href="#types">TableGen type</a> and a name.
491If an initial value is available, it may be specified after the type with an
492equal sign. Value definitions require terminating semicolons.</p>
493
494</div>
495
496<!-- -------------------------------------------------------------------------->
497<div class="doc_subsubsection">
498 <a name="recordlet">'let' expressions</a>
499</div>
500
501<div class="doc_text">
502
503<p>A record-level let expression is used to change the value of a value
504definition in a record. This is primarily useful when a superclass defines a
505value that a derived class or definition wants to override. Let expressions
506consist of the '<tt>let</tt>' keyword followed by a value name, an equal sign
507("<tt>=</tt>"), and a new value. For example, a new class could be added to the
508example above, redefining the <tt>V</tt> field for all of its subclasses:</p>
509
510<div class="doc_code">
511<pre>
512<b>class</b> D : C { let V = 0; }
513<b>def</b> Z : D;
514</pre>
515</div>
516
517<p>In this case, the <tt>Z</tt> definition will have a zero value for its "V"
518value, despite the fact that it derives (indirectly) from the <tt>C</tt> class,
519because the <tt>D</tt> class overrode its value.</p>
520
521</div>
522
523<!-- -------------------------------------------------------------------------->
524<div class="doc_subsubsection">
525 <a name="templateargs">Class template arguments</a>
526</div>
527
528<div class="doc_text">
529
530<p>TableGen permits the definition of parameterized classes as well as normal
531concrete classes. Parameterized TableGen classes specify a list of variable
532bindings (which may optionally have defaults) that are bound when used. Here is
533a simple example:</p>
534
535<div class="doc_code">
536<pre>
537<b>class</b> FPFormat&lt;<b>bits</b>&lt;3&gt; val&gt; {
538 <b>bits</b>&lt;3&gt; Value = val;
539}
540<b>def</b> NotFP : FPFormat&lt;0&gt;;
541<b>def</b> ZeroArgFP : FPFormat&lt;1&gt;;
542<b>def</b> OneArgFP : FPFormat&lt;2&gt;;
543<b>def</b> OneArgFPRW : FPFormat&lt;3&gt;;
544<b>def</b> TwoArgFP : FPFormat&lt;4&gt;;
545<b>def</b> CompareFP : FPFormat&lt;5&gt;;
546<b>def</b> CondMovFP : FPFormat&lt;6&gt;;
547<b>def</b> SpecialFP : FPFormat&lt;7&gt;;
548</pre>
549</div>
550
551<p>In this case, template arguments are used as a space efficient way to specify
552a list of "enumeration values", each with a "<tt>Value</tt>" field set to the
553specified integer.</p>
554
555<p>The more esoteric forms of <a href="#values">TableGen expressions</a> are
556useful in conjunction with template arguments. As an example:</p>
557
558<div class="doc_code">
559<pre>
560<b>class</b> ModRefVal&lt;<b>bits</b>&lt;2&gt; val&gt; {
561 <b>bits</b>&lt;2&gt; Value = val;
562}
563
564<b>def</b> None : ModRefVal&lt;0&gt;;
565<b>def</b> Mod : ModRefVal&lt;1&gt;;
566<b>def</b> Ref : ModRefVal&lt;2&gt;;
567<b>def</b> ModRef : ModRefVal&lt;3&gt;;
568
569<b>class</b> Value&lt;ModRefVal MR&gt; {
570 <i>// Decode some information into a more convenient format, while providing
571 // a nice interface to the user of the "Value" class.</i>
572 <b>bit</b> isMod = MR.Value{0};
573 <b>bit</b> isRef = MR.Value{1};
574
575 <i>// other stuff...</i>
576}
577
578<i>// Example uses</i>
579<b>def</b> bork : Value&lt;Mod&gt;;
580<b>def</b> zork : Value&lt;Ref&gt;;
581<b>def</b> hork : Value&lt;ModRef&gt;;
582</pre>
583</div>
584
585<p>This is obviously a contrived example, but it shows how template arguments
586can be used to decouple the interface provided to the user of the class from the
587actual internal data representation expected by the class. In this case,
588running <tt>tblgen</tt> on the example prints the following definitions:</p>
589
590<div class="doc_code">
591<pre>
592<b>def</b> bork { <i>// Value</i>
593 <b>bit</b> isMod = 1;
594 <b>bit</b> isRef = 0;
595}
596<b>def</b> hork { <i>// Value</i>
597 <b>bit</b> isMod = 1;
598 <b>bit</b> isRef = 1;
599}
600<b>def</b> zork { <i>// Value</i>
601 <b>bit</b> isMod = 0;
602 <b>bit</b> isRef = 1;
603}
604</pre>
605</div>
606
607<p> This shows that TableGen was able to dig into the argument and extract a
608piece of information that was requested by the designer of the "Value" class.
609For more realistic examples, please see existing users of TableGen, such as the
610X86 backend.</p>
611
612</div>
613
614<!-- -------------------------------------------------------------------------->
615<div class="doc_subsubsection">
616 <a name="multiclass">Multiclass definitions and instances</a>
617</div>
618
619<div class="doc_text">
620
621<p>
622While classes with template arguments are a good way to factor commonality
623between two instances of a definition, multiclasses allow a convenient notation
624for defining multiple definitions at once (instances of implicitly constructed
625classes). For example, consider an 3-address instruction set whose instructions
626come in two forms: "<tt>reg = reg op reg</tt>" and "<tt>reg = reg op imm</tt>"
627(e.g. SPARC). In this case, you'd like to specify in one place that this
628commonality exists, then in a separate place indicate what all the ops are.
629</p>
630
631<p>
632Here is an example TableGen fragment that shows this idea:
633</p>
634
635<div class="doc_code">
636<pre>
637<b>def</b> ops;
638<b>def</b> GPR;
639<b>def</b> Imm;
640<b>class</b> inst&lt;<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist&gt;;
641
642<b>multiclass</b> ri_inst&lt;<b>int</b> opc, <b>string</b> asmstr&gt; {
643 def _rr : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
644 (ops GPR:$dst, GPR:$src1, GPR:$src2)&gt;;
645 def _ri : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
646 (ops GPR:$dst, GPR:$src1, Imm:$src2)&gt;;
647}
648
649<i>// Instantiations of the ri_inst multiclass.</i>
650<b>defm</b> ADD : ri_inst&lt;0b111, "add"&gt;;
651<b>defm</b> SUB : ri_inst&lt;0b101, "sub"&gt;;
652<b>defm</b> MUL : ri_inst&lt;0b100, "mul"&gt;;
653...
654</pre>
655</div>
656
657<p>The name of the resultant definitions has the multidef fragment names
658 appended to them, so this defines <tt>ADD_rr</tt>, <tt>ADD_ri</tt>,
659 <tt>SUB_rr</tt>, etc. A defm may inherit from multiple multiclasses,
660 instantiating definitions from each multiclass. Using a multiclass
661 this way is exactly equivalent to instantiating the classes multiple
662 times yourself, e.g. by writing:</p>
663
664<div class="doc_code">
665<pre>
666<b>def</b> ops;
667<b>def</b> GPR;
668<b>def</b> Imm;
669<b>class</b> inst&lt;<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist&gt;;
670
671<b>class</b> rrinst&lt;<b>int</b> opc, <b>string</b> asmstr&gt;
672 : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
673 (ops GPR:$dst, GPR:$src1, GPR:$src2)&gt;;
674
675<b>class</b> riinst&lt;<b>int</b> opc, <b>string</b> asmstr&gt;
676 : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
677 (ops GPR:$dst, GPR:$src1, Imm:$src2)&gt;;
678
679<i>// Instantiations of the ri_inst multiclass.</i>
680<b>def</b> ADD_rr : rrinst&lt;0b111, "add"&gt;;
681<b>def</b> ADD_ri : riinst&lt;0b111, "add"&gt;;
682<b>def</b> SUB_rr : rrinst&lt;0b101, "sub"&gt;;
683<b>def</b> SUB_ri : riinst&lt;0b101, "sub"&gt;;
684<b>def</b> MUL_rr : rrinst&lt;0b100, "mul"&gt;;
685<b>def</b> MUL_ri : riinst&lt;0b100, "mul"&gt;;
686...
687</pre>
688</div>
689
690</div>
691
692<!-- ======================================================================= -->
693<div class="doc_subsection">
694 <a name="filescope">File scope entities</a>
695</div>
696
697<!-- -------------------------------------------------------------------------->
698<div class="doc_subsubsection">
699 <a name="include">File inclusion</a>
700</div>
701
702<div class="doc_text">
703<p>TableGen supports the '<tt>include</tt>' token, which textually substitutes
704the specified file in place of the include directive. The filename should be
705specified as a double quoted string immediately after the '<tt>include</tt>'
706keyword. Example:</p>
707
708<div class="doc_code">
709<pre>
710<b>include</b> "foo.td"
711</pre>
712</div>
713
714</div>
715
716<!-- -------------------------------------------------------------------------->
717<div class="doc_subsubsection">
718 <a name="globallet">'let' expressions</a>
719</div>
720
721<div class="doc_text">
722
723<p>"Let" expressions at file scope are similar to <a href="#recordlet">"let"
724expressions within a record</a>, except they can specify a value binding for
725multiple records at a time, and may be useful in certain other cases.
726File-scope let expressions are really just another way that TableGen allows the
727end-user to factor out commonality from the records.</p>
728
729<p>File-scope "let" expressions take a comma-separated list of bindings to
730apply, and one or more records to bind the values in. Here are some
731examples:</p>
732
733<div class="doc_code">
734<pre>
735<b>let</b> isTerminator = 1, isReturn = 1, isBarrier = 1, hasCtrlDep = 1 <b>in</b>
736 <b>def</b> RET : I&lt;0xC3, RawFrm, (outs), (ins), "ret", [(X86retflag 0)]&gt;;
737
738<b>let</b> isCall = 1 <b>in</b>
739 <i>// All calls clobber the non-callee saved registers...</i>
740 <b>let</b> Defs = [EAX, ECX, EDX, FP0, FP1, FP2, FP3, FP4, FP5, FP6, ST0,
741 MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7,
742 XMM0, XMM1, XMM2, XMM3, XMM4, XMM5, XMM6, XMM7, EFLAGS] <b>in</b> {
743 <b>def</b> CALLpcrel32 : Ii32&lt;0xE8, RawFrm, (outs), (ins i32imm:$dst,variable_ops),
744 "call\t${dst:call}", []&gt;;
745 <b>def</b> CALL32r : I&lt;0xFF, MRM2r, (outs), (ins GR32:$dst, variable_ops),
746 "call\t{*}$dst", [(X86call GR32:$dst)]&gt;;
747 <b>def</b> CALL32m : I&lt;0xFF, MRM2m, (outs), (ins i32mem:$dst, variable_ops),
748 "call\t{*}$dst", []&gt;;
749 }
750</pre>
751</div>
752
753<p>File-scope "let" expressions are often useful when a couple of definitions
754need to be added to several records, and the records do not otherwise need to be
755opened, as in the case with the <tt>CALL*</tt> instructions above.</p>
756
757</div>
758
759<!-- *********************************************************************** -->
760<div class="doc_section"><a name="codegen">Code Generator backend info</a></div>
761<!-- *********************************************************************** -->
762
763<p>Expressions used by code generator to describe instructions and isel
764patterns:</p>
765
766<div class="doc_text">
767
768<dt><tt>(implicit a)</tt></dt>
769 <dd>an implicitly defined physical register. This tells the dag instruction
770 selection emitter the input pattern's extra definitions matches implicit
771 physical register definitions.</dd>
772<dt><tt>(parallel (a), (b))</tt></dt>
773 <dd>a list of dags specifying parallel operations which map to the same
774 instruction.</dd>
775
776</div>
777
778<!-- *********************************************************************** -->
779<div class="doc_section"><a name="backends">TableGen backends</a></div>
780<!-- *********************************************************************** -->
781
782<div class="doc_text">
783
784<p>TODO: How they work, how to write one. This section should not contain
785details about any particular backend, except maybe -print-enums as an example.
786This should highlight the APIs in <tt>TableGen/Record.h</tt>.</p>
787
788</div>
789
790<!-- *********************************************************************** -->
791
792<hr>
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798
799 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
800 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
801 Last modified: $Date: 2010-01-05 11:11:42 -0800 (Tue, 05 Jan 2010) $
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