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11 <h1>TableGen Fundamentals</h1>
15 <li><a href="#introduction">Introduction</a>
17 <li><a href="#concepts">Basic concepts</a></li>
18 <li><a href="#example">An example record</a></li>
19 <li><a href="#running">Running TableGen</a></li>
21 <li><a href="#syntax">TableGen syntax</a>
23 <li><a href="#primitives">TableGen primitives</a>
25 <li><a href="#comments">TableGen comments</a></li>
26 <li><a href="#types">The TableGen type system</a></li>
27 <li><a href="#values">TableGen values and expressions</a></li>
29 <li><a href="#classesdefs">Classes and definitions</a>
31 <li><a href="#valuedef">Value definitions</a></li>
32 <li><a href="#recordlet">'let' expressions</a></li>
33 <li><a href="#templateargs">Class template arguments</a></li>
34 <li><a href="#multiclass">Multiclass definitions and instances</a></li>
36 <li><a href="#filescope">File scope entities</a>
38 <li><a href="#include">File inclusion</a></li>
39 <li><a href="#globallet">'let' expressions</a></li>
40 <li><a href="#foreach">'foreach' blocks</a></li>
43 <li><a href="#backends">TableGen backends</a>
45 <li><a href="#">todo</a></li>
50 <div class="doc_author">
51 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
54 <!-- *********************************************************************** -->
55 <h2><a name="introduction">Introduction</a></h2>
56 <!-- *********************************************************************** -->
60 <p>TableGen's purpose is to help a human develop and maintain records of
61 domain-specific information. Because there may be a large number of these
62 records, it is specifically designed to allow writing flexible descriptions and
63 for common features of these records to be factored out. This reduces the
64 amount of duplication in the description, reduces the chance of error, and
65 makes it easier to structure domain specific information.</p>
67 <p>The core part of TableGen <a href="#syntax">parses a file</a>, instantiates
68 the declarations, and hands the result off to a domain-specific "<a
69 href="#backends">TableGen backend</a>" for processing. The current major user
70 of TableGen is the <a href="CodeGenerator.html">LLVM code generator</a>.</p>
72 <p>Note that if you work on TableGen much, and use emacs or vim, that you can
73 find an emacs "TableGen mode" and a vim language file in the
74 <tt>llvm/utils/emacs</tt> and <tt>llvm/utils/vim</tt> directories of your LLVM
75 distribution, respectively.</p>
77 <!-- ======================================================================= -->
78 <h3><a name="concepts">Basic concepts</a></h3>
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 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>
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 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>
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>
114 <!-- ======================================================================= -->
115 <h3><a name="example">An example record</a></h3>
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>
124 <div class="doc_code">
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, $src2}";
132 <b>list</b><dag> Pattern = [(set GR32:$dst, (add GR32:$src1, GR32:$src2))];
133 <b>list</b><Register> Uses = [];
134 <b>list</b><Register> Defs = [EFLAGS];
135 <b>list</b><Predicate> 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><8> Opcode = { 0, 0, 0, 0, 0, 0, 0, 1 };
162 Format Form = MRMDestReg;
163 <b>bits</b><6> FormBits = { 0, 0, 0, 0, 1, 1 };
164 ImmType ImmT = NoImm;
165 <b>bits</b><3> ImmTypeBits = { 0, 0, 0 };
166 <b>bit</b> hasOpSizePrefix = 0;
167 <b>bit</b> hasAdSizePrefix = 0;
168 <b>bits</b><4> Prefix = { 0, 0, 0, 0 };
169 <b>bit</b> hasREX_WPrefix = 0;
171 <b>bits</b><3> FPFormBits = { 0, 0, 0 };
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—"<tt>ADD32rr</tt>" in this case—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>
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
194 <div class="doc_code">
197 isCommutable = 1, <i>// X = ADD Y,Z --> X = ADD Z,Y</i>
198 isConvertibleToThreeAddress = 1 <b>in</b> <i>// Can transform into LEA.</i>
199 def ADD32rr : I<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))]>;
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>
212 <p>Each def record has a special entry called "NAME." This is the
213 name of the def ("ADD32rr" above). In the general case def names can
214 be formed from various kinds of string processing expressions and NAME
215 resolves to the final value obtained after resolving all of those
216 expressions. The user may refer to NAME anywhere she desires to use
217 the ultimate name of the def. NAME should not be defined anywhere
218 else in user code to avoid conflict problems.</p>
222 <!-- ======================================================================= -->
223 <h3><a name="running">Running TableGen</a></h3>
227 <p>TableGen runs just like any other LLVM tool. The first (optional) argument
228 specifies the file to read. If a filename is not specified,
229 <tt>llvm-tblgen</tt> reads from standard input.</p>
231 <p>To be useful, one of the <a href="#backends">TableGen backends</a> must be
232 used. These backends are selectable on the command line (type '<tt>llvm-tblgen
233 -help</tt>' for a list). For example, to get a list of all of the definitions
234 that subclass a particular type (which can be useful for building up an enum
235 list of these records), use the <tt>-print-enums</tt> option:</p>
237 <div class="doc_code">
239 $ llvm-tblgen X86.td -print-enums -class=Register
240 AH, AL, AX, BH, BL, BP, BPL, BX, CH, CL, CX, DH, DI, DIL, DL, DX, EAX, EBP, EBX,
241 ECX, EDI, EDX, EFLAGS, EIP, ESI, ESP, FP0, FP1, FP2, FP3, FP4, FP5, FP6, IP,
242 MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7, R10, R10B, R10D, R10W, R11, R11B, R11D,
243 R11W, R12, R12B, R12D, R12W, R13, R13B, R13D, R13W, R14, R14B, R14D, R14W, R15,
244 R15B, R15D, R15W, R8, R8B, R8D, R8W, R9, R9B, R9D, R9W, RAX, RBP, RBX, RCX, RDI,
245 RDX, RIP, RSI, RSP, SI, SIL, SP, SPL, ST0, ST1, ST2, ST3, ST4, ST5, ST6, ST7,
246 XMM0, XMM1, XMM10, XMM11, XMM12, XMM13, XMM14, XMM15, XMM2, XMM3, XMM4, XMM5,
247 XMM6, XMM7, XMM8, XMM9,
249 $ llvm-tblgen X86.td -print-enums -class=Instruction
250 ABS_F, ABS_Fp32, ABS_Fp64, ABS_Fp80, ADC32mi, ADC32mi8, ADC32mr, ADC32ri,
251 ADC32ri8, ADC32rm, ADC32rr, ADC64mi32, ADC64mi8, ADC64mr, ADC64ri32, ADC64ri8,
252 ADC64rm, ADC64rr, ADD16mi, ADD16mi8, ADD16mr, ADD16ri, ADD16ri8, ADD16rm,
253 ADD16rr, ADD32mi, ADD32mi8, ADD32mr, ADD32ri, ADD32ri8, ADD32rm, ADD32rr,
254 ADD64mi32, ADD64mi8, ADD64mr, ADD64ri32, ...
258 <p>The default backend prints out all of the records, as described <a
259 href="#example">above</a>.</p>
261 <p>If you plan to use TableGen, you will most likely have to <a
262 href="#backends">write a backend</a> that extracts the information specific to
263 what you need and formats it in the appropriate way.</p>
269 <!-- *********************************************************************** -->
270 <h2><a name="syntax">TableGen syntax</a></h2>
271 <!-- *********************************************************************** -->
275 <p>TableGen doesn't care about the meaning of data (that is up to the backend to
276 define), but it does care about syntax, and it enforces a simple type system.
277 This section describes the syntax and the constructs allowed in a TableGen file.
280 <!-- ======================================================================= -->
281 <h3><a name="primitives">TableGen primitives</a></h3>
285 <!-- -------------------------------------------------------------------------->
286 <h4><a name="comments">TableGen comments</a></h4>
290 <p>TableGen supports BCPL style "<tt>//</tt>" comments, which run to the end of
291 the line, and it also supports <b>nestable</b> "<tt>/* */</tt>" comments.</p>
295 <!-- -------------------------------------------------------------------------->
297 <a name="types">The TableGen type system</a>
302 <p>TableGen files are strongly typed, in a simple (but complete) type-system.
303 These types are used to perform automatic conversions, check for errors, and to
304 help interface designers constrain the input that they allow. Every <a
305 href="#valuedef">value definition</a> is required to have an associated type.
308 <p>TableGen supports a mixture of very low-level types (such as <tt>bit</tt>)
309 and very high-level types (such as <tt>dag</tt>). This flexibility is what
310 allows it to describe a wide range of information conveniently and compactly.
311 The TableGen types are:</p>
314 <dt><tt><b>bit</b></tt></dt>
315 <dd>A 'bit' is a boolean value that can hold either 0 or 1.</dd>
317 <dt><tt><b>int</b></tt></dt>
318 <dd>The 'int' type represents a simple 32-bit integer value, such as 5.</dd>
320 <dt><tt><b>string</b></tt></dt>
321 <dd>The 'string' type represents an ordered sequence of characters of
322 arbitrary length.</dd>
324 <dt><tt><b>bits</b><n></tt></dt>
325 <dd>A 'bits' type is an arbitrary, but fixed, size integer that is broken up
326 into individual bits. This type is useful because it can handle some bits
327 being defined while others are undefined.</dd>
329 <dt><tt><b>list</b><ty></tt></dt>
330 <dd>This type represents a list whose elements are some other type. The
331 contained type is arbitrary: it can even be another list type.</dd>
334 <dd>Specifying a class name in a type context means that the defined value
335 must be a subclass of the specified class. This is useful in conjunction with
336 the <b><tt>list</tt></b> type, for example, to constrain the elements of the
337 list to a common base class (e.g., a <tt><b>list</b><Register></tt> can
338 only contain definitions derived from the "<tt>Register</tt>" class).</dd>
340 <dt><tt><b>dag</b></tt></dt>
341 <dd>This type represents a nestable directed graph of elements.</dd>
343 <dt><tt><b>code</b></tt></dt>
344 <dd>This represents a big hunk of text. This is lexically distinct from
345 string values because it doesn't require escapeing double quotes and other
346 common characters that occur in code.</dd>
349 <p>To date, these types have been sufficient for describing things that
350 TableGen has been used for, but it is straight-forward to extend this list if
355 <!-- -------------------------------------------------------------------------->
357 <a name="values">TableGen values and expressions</a>
362 <p>TableGen allows for a pretty reasonable number of different expression forms
363 when building up values. These forms allow the TableGen file to be written in a
364 natural syntax and flavor for the application. The current expression forms
365 supported include:</p>
369 <dd>uninitialized field</dd>
370 <dt><tt>0b1001011</tt></dt>
371 <dd>binary integer value</dd>
372 <dt><tt>07654321</tt></dt>
373 <dd>octal integer value (indicated by a leading 0)</dd>
375 <dd>decimal integer value</dd>
376 <dt><tt>0x7F</tt></dt>
377 <dd>hexadecimal integer value</dd>
378 <dt><tt>"foo"</tt></dt>
379 <dd>string value</dd>
380 <dt><tt>[{ ... }]</tt></dt>
381 <dd>code fragment</dd>
382 <dt><tt>[ X, Y, Z ]<type></tt></dt>
383 <dd>list value. <type> is the type of the list
384 element and is usually optional. In rare cases,
385 TableGen is unable to deduce the element type in
386 which case the user must specify it explicitly.</dd>
387 <dt><tt>{ a, b, c }</tt></dt>
388 <dd>initializer for a "bits<3>" value</dd>
389 <dt><tt>value</tt></dt>
390 <dd>value reference</dd>
391 <dt><tt>value{17}</tt></dt>
392 <dd>access to one bit of a value</dd>
393 <dt><tt>value{15-17}</tt></dt>
394 <dd>access to multiple bits of a value</dd>
395 <dt><tt>DEF</tt></dt>
396 <dd>reference to a record definition</dd>
397 <dt><tt>CLASS<val list></tt></dt>
398 <dd>reference to a new anonymous definition of CLASS with the specified
399 template arguments.</dd>
400 <dt><tt>X.Y</tt></dt>
401 <dd>reference to the subfield of a value</dd>
402 <dt><tt>list[4-7,17,2-3]</tt></dt>
403 <dd>A slice of the 'list' list, including elements 4,5,6,7,17,2, and 3 from
404 it. Elements may be included multiple times.</dd>
405 <dt><tt>foreach <var> = [ <list> ] in { <body> }</tt></dt>
406 <dt><tt>foreach <var> = [ <list> ] in <def></tt></dt>
407 <dd> Replicate <body> or <def>, replacing instances of
408 <var> with each value in <list>. <var> is scoped at the
409 level of the <tt>foreach</tt> loop and must not conflict with any other object
410 introduced in <body> or <def>. Currently only <tt>def</tt>s are
411 expanded within <body>.
413 <dt><tt>foreach <var> = 0-15 in ...</tt></dt>
414 <dt><tt>foreach <var> = {0-15,32-47} in ...</tt></dt>
415 <dd>Loop over ranges of integers. The braces are required for multiple
417 <dt><tt>(DEF a, b)</tt></dt>
418 <dd>a dag value. The first element is required to be a record definition, the
419 remaining elements in the list may be arbitrary other values, including nested
420 `<tt>dag</tt>' values.</dd>
421 <dt><tt>!strconcat(a, b)</tt></dt>
422 <dd>A string value that is the result of concatenating the 'a' and 'b'
424 <dt><tt>str1#str2</tt></dt>
425 <dd>"#" (paste) is a shorthand for !strconcat. It may concatenate
426 things that are not quoted strings, in which case an implicit
427 !cast<string> is done on the operand of the paste.</dd>
428 <dt><tt>!cast<type>(a)</tt></dt>
429 <dd>A symbol of type <em>type</em> obtained by looking up the string 'a' in
430 the symbol table. If the type of 'a' does not match <em>type</em>, TableGen
431 aborts with an error. !cast<string> is a special case in that the argument must
432 be an object defined by a 'def' construct.</dd>
433 <dt><tt>!subst(a, b, c)</tt></dt>
434 <dd>If 'a' and 'b' are of string type or are symbol references, substitute
435 'b' for 'a' in 'c.' This operation is analogous to $(subst) in GNU make.</dd>
436 <dt><tt>!foreach(a, b, c)</tt></dt>
437 <dd>For each member 'b' of dag or list 'a' apply operator 'c.' 'b' is a
438 dummy variable that should be declared as a member variable of an instantiated
439 class. This operation is analogous to $(foreach) in GNU make.</dd>
440 <dt><tt>!head(a)</tt></dt>
441 <dd>The first element of list 'a.'</dd>
442 <dt><tt>!tail(a)</tt></dt>
443 <dd>The 2nd-N elements of list 'a.'</dd>
444 <dt><tt>!empty(a)</tt></dt>
445 <dd>An integer {0,1} indicating whether list 'a' is empty.</dd>
446 <dt><tt>!if(a,b,c)</tt></dt>
447 <dd>'b' if the result of 'int' or 'bit' operator 'a' is nonzero,
449 <dt><tt>!eq(a,b)</tt></dt>
450 <dd>'bit 1' if string a is equal to string b, 0 otherwise. This
451 only operates on string, int and bit objects. Use !cast<string> to
452 compare other types of objects.</dd>
455 <p>Note that all of the values have rules specifying how they convert to values
456 for different types. These rules allow you to assign a value like "<tt>7</tt>"
457 to a "<tt>bits<4></tt>" value, for example.</p>
463 <!-- ======================================================================= -->
465 <a name="classesdefs">Classes and definitions</a>
470 <p>As mentioned in the <a href="#concepts">intro</a>, classes and definitions
471 (collectively known as 'records') in TableGen are the main high-level unit of
472 information that TableGen collects. Records are defined with a <tt>def</tt> or
473 <tt>class</tt> keyword, the record name, and an optional list of "<a
474 href="#templateargs">template arguments</a>". If the record has superclasses,
475 they are specified as a comma separated list that starts with a colon character
476 ("<tt>:</tt>"). If <a href="#valuedef">value definitions</a> or <a
477 href="#recordlet">let expressions</a> are needed for the class, they are
478 enclosed in curly braces ("<tt>{}</tt>"); otherwise, the record ends with a
481 <p>Here is a simple TableGen file:</p>
483 <div class="doc_code">
485 <b>class</b> C { <b>bit</b> V = 1; }
488 <b>string</b> Greeting = "hello";
493 <p>This example defines two definitions, <tt>X</tt> and <tt>Y</tt>, both of
494 which derive from the <tt>C</tt> class. Because of this, they both get the
495 <tt>V</tt> bit value. The <tt>Y</tt> definition also gets the Greeting member
498 <p>In general, classes are useful for collecting together the commonality
499 between a group of records and isolating it in a single place. Also, classes
500 permit the specification of default values for their subclasses, allowing the
501 subclasses to override them as they wish.</p>
503 <!---------------------------------------------------------------------------->
505 <a name="valuedef">Value definitions</a>
510 <p>Value definitions define named entries in records. A value must be defined
511 before it can be referred to as the operand for another value definition or
512 before the value is reset with a <a href="#recordlet">let expression</a>. A
513 value is defined by specifying a <a href="#types">TableGen type</a> and a name.
514 If an initial value is available, it may be specified after the type with an
515 equal sign. Value definitions require terminating semicolons.</p>
519 <!-- -------------------------------------------------------------------------->
521 <a name="recordlet">'let' expressions</a>
526 <p>A record-level let expression is used to change the value of a value
527 definition in a record. This is primarily useful when a superclass defines a
528 value that a derived class or definition wants to override. Let expressions
529 consist of the '<tt>let</tt>' keyword followed by a value name, an equal sign
530 ("<tt>=</tt>"), and a new value. For example, a new class could be added to the
531 example above, redefining the <tt>V</tt> field for all of its subclasses:</p>
533 <div class="doc_code">
535 <b>class</b> D : C { let V = 0; }
540 <p>In this case, the <tt>Z</tt> definition will have a zero value for its "V"
541 value, despite the fact that it derives (indirectly) from the <tt>C</tt> class,
542 because the <tt>D</tt> class overrode its value.</p>
546 <!-- -------------------------------------------------------------------------->
548 <a name="templateargs">Class template arguments</a>
553 <p>TableGen permits the definition of parameterized classes as well as normal
554 concrete classes. Parameterized TableGen classes specify a list of variable
555 bindings (which may optionally have defaults) that are bound when used. Here is
556 a simple example:</p>
558 <div class="doc_code">
560 <b>class</b> FPFormat<<b>bits</b><3> val> {
561 <b>bits</b><3> Value = val;
563 <b>def</b> NotFP : FPFormat<0>;
564 <b>def</b> ZeroArgFP : FPFormat<1>;
565 <b>def</b> OneArgFP : FPFormat<2>;
566 <b>def</b> OneArgFPRW : FPFormat<3>;
567 <b>def</b> TwoArgFP : FPFormat<4>;
568 <b>def</b> CompareFP : FPFormat<5>;
569 <b>def</b> CondMovFP : FPFormat<6>;
570 <b>def</b> SpecialFP : FPFormat<7>;
574 <p>In this case, template arguments are used as a space efficient way to specify
575 a list of "enumeration values", each with a "<tt>Value</tt>" field set to the
576 specified integer.</p>
578 <p>The more esoteric forms of <a href="#values">TableGen expressions</a> are
579 useful in conjunction with template arguments. As an example:</p>
581 <div class="doc_code">
583 <b>class</b> ModRefVal<<b>bits</b><2> val> {
584 <b>bits</b><2> Value = val;
587 <b>def</b> None : ModRefVal<0>;
588 <b>def</b> Mod : ModRefVal<1>;
589 <b>def</b> Ref : ModRefVal<2>;
590 <b>def</b> ModRef : ModRefVal<3>;
592 <b>class</b> Value<ModRefVal MR> {
593 <i>// Decode some information into a more convenient format, while providing
594 // a nice interface to the user of the "Value" class.</i>
595 <b>bit</b> isMod = MR.Value{0};
596 <b>bit</b> isRef = MR.Value{1};
598 <i>// other stuff...</i>
601 <i>// Example uses</i>
602 <b>def</b> bork : Value<Mod>;
603 <b>def</b> zork : Value<Ref>;
604 <b>def</b> hork : Value<ModRef>;
608 <p>This is obviously a contrived example, but it shows how template arguments
609 can be used to decouple the interface provided to the user of the class from the
610 actual internal data representation expected by the class. In this case,
611 running <tt>llvm-tblgen</tt> on the example prints the following
614 <div class="doc_code">
616 <b>def</b> bork { <i>// Value</i>
617 <b>bit</b> isMod = 1;
618 <b>bit</b> isRef = 0;
620 <b>def</b> hork { <i>// Value</i>
621 <b>bit</b> isMod = 1;
622 <b>bit</b> isRef = 1;
624 <b>def</b> zork { <i>// Value</i>
625 <b>bit</b> isMod = 0;
626 <b>bit</b> isRef = 1;
631 <p> This shows that TableGen was able to dig into the argument and extract a
632 piece of information that was requested by the designer of the "Value" class.
633 For more realistic examples, please see existing users of TableGen, such as the
638 <!-- -------------------------------------------------------------------------->
640 <a name="multiclass">Multiclass definitions and instances</a>
646 While classes with template arguments are a good way to factor commonality
647 between two instances of a definition, multiclasses allow a convenient notation
648 for defining multiple definitions at once (instances of implicitly constructed
649 classes). For example, consider an 3-address instruction set whose instructions
650 come in two forms: "<tt>reg = reg op reg</tt>" and "<tt>reg = reg op imm</tt>"
651 (e.g. SPARC). In this case, you'd like to specify in one place that this
652 commonality exists, then in a separate place indicate what all the ops are.
656 Here is an example TableGen fragment that shows this idea:
659 <div class="doc_code">
664 <b>class</b> inst<<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist>;
666 <b>multiclass</b> ri_inst<<b>int</b> opc, <b>string</b> asmstr> {
667 def _rr : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
668 (ops GPR:$dst, GPR:$src1, GPR:$src2)>;
669 def _ri : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
670 (ops GPR:$dst, GPR:$src1, Imm:$src2)>;
673 <i>// Instantiations of the ri_inst multiclass.</i>
674 <b>defm</b> ADD : ri_inst<0b111, "add">;
675 <b>defm</b> SUB : ri_inst<0b101, "sub">;
676 <b>defm</b> MUL : ri_inst<0b100, "mul">;
681 <p>The name of the resultant definitions has the multidef fragment names
682 appended to them, so this defines <tt>ADD_rr</tt>, <tt>ADD_ri</tt>,
683 <tt>SUB_rr</tt>, etc. A defm may inherit from multiple multiclasses,
684 instantiating definitions from each multiclass. Using a multiclass
685 this way is exactly equivalent to instantiating the classes multiple
686 times yourself, e.g. by writing:</p>
688 <div class="doc_code">
693 <b>class</b> inst<<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist>;
695 <b>class</b> rrinst<<b>int</b> opc, <b>string</b> asmstr>
696 : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
697 (ops GPR:$dst, GPR:$src1, GPR:$src2)>;
699 <b>class</b> riinst<<b>int</b> opc, <b>string</b> asmstr>
700 : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
701 (ops GPR:$dst, GPR:$src1, Imm:$src2)>;
703 <i>// Instantiations of the ri_inst multiclass.</i>
704 <b>def</b> ADD_rr : rrinst<0b111, "add">;
705 <b>def</b> ADD_ri : riinst<0b111, "add">;
706 <b>def</b> SUB_rr : rrinst<0b101, "sub">;
707 <b>def</b> SUB_ri : riinst<0b101, "sub">;
708 <b>def</b> MUL_rr : rrinst<0b100, "mul">;
709 <b>def</b> MUL_ri : riinst<0b100, "mul">;
715 A defm can also be used inside a multiclass providing several levels of
716 multiclass instanciations.
719 <div class="doc_code">
721 <b>class</b> Instruction<bits<4> opc, string Name> {
722 bits<4> opcode = opc;
726 <b>multiclass</b> basic_r<bits<4> opc> {
727 <b>def</b> rr : Instruction<opc, "rr">;
728 <b>def</b> rm : Instruction<opc, "rm">;
731 <b>multiclass</b> basic_s<bits<4> opc> {
732 <b>defm</b> SS : basic_r<opc>;
733 <b>defm</b> SD : basic_r<opc>;
734 <b>def</b> X : Instruction<opc, "x">;
737 <b>multiclass</b> basic_p<bits<4> opc> {
738 <b>defm</b> PS : basic_r<opc>;
739 <b>defm</b> PD : basic_r<opc>;
740 <b>def</b> Y : Instruction<opc, "y">;
743 <b>defm</b> ADD : basic_s<0xf>, basic_p<0xf>;
747 <b>def</b> ADDPDrm { ...
748 <b>def</b> ADDPDrr { ...
749 <b>def</b> ADDPSrm { ...
750 <b>def</b> ADDPSrr { ...
751 <b>def</b> ADDSDrm { ...
752 <b>def</b> ADDSDrr { ...
753 <b>def</b> ADDY { ...
754 <b>def</b> ADDX { ...
759 defm declarations can inherit from classes too, the
760 rule to follow is that the class list must start after the
761 last multiclass, and there must be at least one multiclass
765 <div class="doc_code">
767 <b>class</b> XD { bits<4> Prefix = 11; }
768 <b>class</b> XS { bits<4> Prefix = 12; }
770 <b>class</b> I<bits<4> op> {
771 bits<4> opcode = op;
774 <b>multiclass</b> R {
775 <b>def</b> rr : I<4>;
776 <b>def</b> rm : I<2>;
779 <b>multiclass</b> Y {
780 <b>defm</b> SS : R, XD;
781 <b>defm</b> SD : R, XS;
784 <b>defm</b> Instr : Y;
787 <b>def</b> InstrSDrm {
788 bits<4> opcode = { 0, 0, 1, 0 };
789 bits<4> Prefix = { 1, 1, 0, 0 };
792 <b>def</b> InstrSSrr {
793 bits<4> opcode = { 0, 1, 0, 0 };
794 bits<4> Prefix = { 1, 0, 1, 1 };
803 <!-- ======================================================================= -->
805 <a name="filescope">File scope entities</a>
810 <!-- -------------------------------------------------------------------------->
812 <a name="include">File inclusion</a>
816 <p>TableGen supports the '<tt>include</tt>' token, which textually substitutes
817 the specified file in place of the include directive. The filename should be
818 specified as a double quoted string immediately after the '<tt>include</tt>'
819 keyword. Example:</p>
821 <div class="doc_code">
823 <b>include</b> "foo.td"
829 <!-- -------------------------------------------------------------------------->
831 <a name="globallet">'let' expressions</a>
836 <p>"Let" expressions at file scope are similar to <a href="#recordlet">"let"
837 expressions within a record</a>, except they can specify a value binding for
838 multiple records at a time, and may be useful in certain other cases.
839 File-scope let expressions are really just another way that TableGen allows the
840 end-user to factor out commonality from the records.</p>
842 <p>File-scope "let" expressions take a comma-separated list of bindings to
843 apply, and one or more records to bind the values in. Here are some
846 <div class="doc_code">
848 <b>let</b> isTerminator = 1, isReturn = 1, isBarrier = 1, hasCtrlDep = 1 <b>in</b>
849 <b>def</b> RET : I<0xC3, RawFrm, (outs), (ins), "ret", [(X86retflag 0)]>;
851 <b>let</b> isCall = 1 <b>in</b>
852 <i>// All calls clobber the non-callee saved registers...</i>
853 <b>let</b> Defs = [EAX, ECX, EDX, FP0, FP1, FP2, FP3, FP4, FP5, FP6, ST0,
854 MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7,
855 XMM0, XMM1, XMM2, XMM3, XMM4, XMM5, XMM6, XMM7, EFLAGS] <b>in</b> {
856 <b>def</b> CALLpcrel32 : Ii32<0xE8, RawFrm, (outs), (ins i32imm:$dst,variable_ops),
857 "call\t${dst:call}", []>;
858 <b>def</b> CALL32r : I<0xFF, MRM2r, (outs), (ins GR32:$dst, variable_ops),
859 "call\t{*}$dst", [(X86call GR32:$dst)]>;
860 <b>def</b> CALL32m : I<0xFF, MRM2m, (outs), (ins i32mem:$dst, variable_ops),
861 "call\t{*}$dst", []>;
866 <p>File-scope "let" expressions are often useful when a couple of definitions
867 need to be added to several records, and the records do not otherwise need to be
868 opened, as in the case with the <tt>CALL*</tt> instructions above.</p>
870 <p>It's also possible to use "let" expressions inside multiclasses, providing
871 more ways to factor out commonality from the records, specially if using
872 several levels of multiclass instanciations. This also avoids the need of using
873 "let" expressions within subsequent records inside a multiclass.</p>
875 <pre class="doc_code">
876 <b>multiclass </b>basic_r<bits<4> opc> {
877 <b>let </b>Predicates = [HasSSE2] in {
878 <b>def </b>rr : Instruction<opc, "rr">;
879 <b>def </b>rm : Instruction<opc, "rm">;
881 <b>let </b>Predicates = [HasSSE3] in
882 <b>def </b>rx : Instruction<opc, "rx">;
885 <b>multiclass </b>basic_ss<bits<4> opc> {
886 <b>let </b>IsDouble = 0 in
887 <b>defm </b>SS : basic_r<opc>;
889 <b>let </b>IsDouble = 1 in
890 <b>defm </b>SD : basic_r<opc>;
893 <b>defm </b>ADD : basic_ss<0xf>;
897 <!-- -------------------------------------------------------------------------->
899 <a name="foreach">Looping</a>
903 <p>TableGen supports the '<tt>foreach</tt>' block, which textually replicates
904 the loop body, substituting iterator values for iterator references in the
907 <div class="doc_code">
909 <b>foreach</b> i = [0, 1, 2, 3] in {
910 <b>def</b> R#i : Register<...>;
911 <b>def</b> F#i : Register<...>;
916 <p>This will create objects <tt>R0</tt>, <tt>R1</tt>, <tt>R2</tt> and
917 <tt>R3</tt>. <tt>foreach</tt> blocks may be nested. If there is only
918 one item in the body the braces may be elided:</p>
920 <div class="doc_code">
922 <b>foreach</b> i = [0, 1, 2, 3] in
923 <b>def</b> R#i : Register<...>;
934 <!-- *********************************************************************** -->
935 <h2><a name="codegen">Code Generator backend info</a></h2>
936 <!-- *********************************************************************** -->
940 <p>Expressions used by code generator to describe instructions and isel
944 <dt><tt>(implicit a)</tt></dt>
945 <dd>an implicitly defined physical register. This tells the dag instruction
946 selection emitter the input pattern's extra definitions matches implicit
947 physical register definitions.</dd>
951 <!-- *********************************************************************** -->
952 <h2><a name="backends">TableGen backends</a></h2>
953 <!-- *********************************************************************** -->
957 <p>TODO: How they work, how to write one. This section should not contain
958 details about any particular backend, except maybe -print-enums as an example.
959 This should highlight the APIs in <tt>TableGen/Record.h</tt>.</p>
963 <!-- *********************************************************************** -->
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972 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
973 <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
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