1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>TableGen Fundamentals</title>
<link rel="stylesheet" href="llvm.css" type="text/css">
</head>
<body>
<div class="doc_title">TableGen Fundamentals</div>
<div class="doc_text">
<ul>
<li><a href="#introduction">Introduction</a>
<ol>
<li><a href="#concepts">Basic concepts</a></li>
<li><a href="#example">An example record</a></li>
<li><a href="#running">Running TableGen</a></li>
</ol></li>
<li><a href="#syntax">TableGen syntax</a>
<ol>
<li><a href="#primitives">TableGen primitives</a>
<ol>
<li><a href="#comments">TableGen comments</a></li>
<li><a href="#types">The TableGen type system</a></li>
<li><a href="#values">TableGen values and expressions</a></li>
</ol></li>
<li><a href="#classesdefs">Classes and definitions</a>
<ol>
<li><a href="#valuedef">Value definitions</a></li>
<li><a href="#recordlet">'let' expressions</a></li>
<li><a href="#templateargs">Class template arguments</a></li>
<li><a href="#multiclass">Multiclass definitions and instances</a></li>
</ol></li>
<li><a href="#filescope">File scope entities</a>
<ol>
<li><a href="#include">File inclusion</a></li>
<li><a href="#globallet">'let' expressions</a></li>
</ol></li>
</ol></li>
<li><a href="#backends">TableGen backends</a>
<ol>
<li><a href="#">todo</a></li>
</ol></li>
</ul>
</div>
<div class="doc_author">
<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section"><a name="introduction">Introduction</a></div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>TableGen's purpose is to help a human develop and maintain records of
domain-specific information. Because there may be a large number of these
records, it is specifically designed to allow writing flexible descriptions and
for common features of these records to be factored out. This reduces the
amount of duplication in the description, reduces the chance of error, and
makes it easier to structure domain specific information.</p>
<p>The core part of TableGen <a href="#syntax">parses a file</a>, instantiates
the declarations, and hands the result off to a domain-specific "<a
href="#backends">TableGen backend</a>" for processing. The current major user
of TableGen is the <a href="CodeGenerator.html">LLVM code generator</a>.</p>
<p>Note that if you work on TableGen much, and use emacs or vim, that you can
find an emacs "TableGen mode" and a vim language file in the
<tt>llvm/utils/emacs</tt> and <tt>llvm/utils/vim</tt> directories of your LLVM
distribution, respectively.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="concepts">Basic concepts</a></div>
<div class="doc_text">
<p>TableGen files consist of two key parts: 'classes' and 'definitions', both
of which are considered 'records'.</p>
<p><b>TableGen records</b> have a unique name, a list of values, and a list of
superclasses. The list of values is the main data that TableGen builds for each
record; it is this that holds the domain specific information for the
application. The interpretation of this data is left to a specific <a
href="#backends">TableGen backend</a>, but the structure and format rules are
taken care of and are fixed by TableGen.</p>
<p><b>TableGen definitions</b> are the concrete form of 'records'. These
generally do not have any undefined values, and are marked with the
'<tt>def</tt>' keyword.</p>
<p><b>TableGen classes</b> are abstract records that are used to build and
describe other records. These 'classes' allow the end-user to build
abstractions for either the domain they are targeting (such as "Register",
"RegisterClass", and "Instruction" in the LLVM code generator) or for the
implementor to help factor out common properties of records (such as "FPInst",
which is used to represent floating point instructions in the X86 backend).
TableGen keeps track of all of the classes that are used to build up a
definition, so the backend can find all definitions of a particular class, such
as "Instruction".</p>
<p><b>TableGen multiclasses</b> are groups of abstract records that are
instantiated all at once. Each instantiation can result in multiple
TableGen definitions. If a multiclass inherits from another multiclass,
the definitions in the sub-multiclass become part of the current
multiclass, as if they were declared in the current multiclass.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="example">An example record</a></div>
<div class="doc_text">
<p>With no other arguments, TableGen parses the specified file and prints out
all of the classes, then all of the definitions. This is a good way to see what
the various definitions expand to fully. Running this on the <tt>X86.td</tt>
file prints this (at the time of this writing):</p>
<div class="doc_code">
<pre>
...
<b>def</b> ADD32rr { <i>// Instruction X86Inst I</i>
<b>string</b> Namespace = "X86";
<b>dag</b> OutOperandList = (outs GR32:$dst);
<b>dag</b> InOperandList = (ins GR32:$src1, GR32:$src2);
<b>string</b> AsmString = "add{l}\t{$src2, $dst|$dst, $src2}";
<b>list</b><dag> Pattern = [(set GR32:$dst, (add GR32:$src1, GR32:$src2))];
<b>list</b><Register> Uses = [];
<b>list</b><Register> Defs = [EFLAGS];
<b>list</b><Predicate> Predicates = [];
<b>int</b> CodeSize = 3;
<b>int</b> AddedComplexity = 0;
<b>bit</b> isReturn = 0;
<b>bit</b> isBranch = 0;
<b>bit</b> isIndirectBranch = 0;
<b>bit</b> isBarrier = 0;
<b>bit</b> isCall = 0;
<b>bit</b> canFoldAsLoad = 0;
<b>bit</b> mayLoad = 0;
<b>bit</b> mayStore = 0;
<b>bit</b> isImplicitDef = 0;
<b>bit</b> isConvertibleToThreeAddress = 1;
<b>bit</b> isCommutable = 1;
<b>bit</b> isTerminator = 0;
<b>bit</b> isReMaterializable = 0;
<b>bit</b> isPredicable = 0;
<b>bit</b> hasDelaySlot = 0;
<b>bit</b> usesCustomInserter = 0;
<b>bit</b> hasCtrlDep = 0;
<b>bit</b> isNotDuplicable = 0;
<b>bit</b> hasSideEffects = 0;
<b>bit</b> neverHasSideEffects = 0;
InstrItinClass Itinerary = NoItinerary;
<b>string</b> Constraints = "";
<b>string</b> DisableEncoding = "";
<b>bits</b><8> Opcode = { 0, 0, 0, 0, 0, 0, 0, 1 };
Format Form = MRMDestReg;
<b>bits</b><6> FormBits = { 0, 0, 0, 0, 1, 1 };
ImmType ImmT = NoImm;
<b>bits</b><3> ImmTypeBits = { 0, 0, 0 };
<b>bit</b> hasOpSizePrefix = 0;
<b>bit</b> hasAdSizePrefix = 0;
<b>bits</b><4> Prefix = { 0, 0, 0, 0 };
<b>bit</b> hasREX_WPrefix = 0;
FPFormat FPForm = ?;
<b>bits</b><3> FPFormBits = { 0, 0, 0 };
}
...
</pre>
</div>
<p>This definition corresponds to a 32-bit register-register add instruction in
the X86. The string after the '<tt>def</tt>' string indicates the name of the
record—"<tt>ADD32rr</tt>" in this case—and the comment at the end of
the line indicates the superclasses of the definition. The body of the record
contains all of the data that TableGen assembled for the record, indicating that
the instruction is part of the "X86" namespace, the pattern indicating how the
the instruction should be emitted into the assembly file, that it is a
two-address instruction, has a particular encoding, etc. The contents and
semantics of the information in the record is specific to the needs of the X86
backend, and is only shown as an example.</p>
<p>As you can see, a lot of information is needed for every instruction
supported by the code generator, and specifying it all manually would be
unmaintainable, prone to bugs, and tiring to do in the first place. Because we
are using TableGen, all of the information was derived from the following
definition:</p>
<div class="doc_code">
<pre>
let Defs = [EFLAGS],
isCommutable = 1, <i>// X = ADD Y,Z --> X = ADD Z,Y</i>
isConvertibleToThreeAddress = 1 <b>in</b> <i>// Can transform into LEA.</i>
def ADD32rr : I<0x01, MRMDestReg, (outs GR32:$dst),
(ins GR32:$src1, GR32:$src2),
"add{l}\t{$src2, $dst|$dst, $src2}",
[(set GR32:$dst, (add GR32:$src1, GR32:$src2))]>;
</pre>
</div>
<p>This definition makes use of the custom class <tt>I</tt> (extended from the
custom class <tt>X86Inst</tt>), which is defined in the X86-specific TableGen
file, to factor out the common features that instructions of its class share. A
key feature of TableGen is that it allows the end-user to define the
abstractions they prefer to use when describing their information.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="running">Running TableGen</a></div>
<div class="doc_text">
<p>TableGen runs just like any other LLVM tool. The first (optional) argument
specifies the file to read. If a filename is not specified, <tt>tblgen</tt>
reads from standard input.</p>
<p>To be useful, one of the <a href="#backends">TableGen backends</a> must be
used. These backends are selectable on the command line (type '<tt>tblgen
-help</tt>' for a list). For example, to get a list of all of the definitions
that subclass a particular type (which can be useful for building up an enum
list of these records), use the <tt>-print-enums</tt> option:</p>
<div class="doc_code">
<pre>
$ tblgen X86.td -print-enums -class=Register
AH, AL, AX, BH, BL, BP, BPL, BX, CH, CL, CX, DH, DI, DIL, DL, DX, EAX, EBP, EBX,
ECX, EDI, EDX, EFLAGS, EIP, ESI, ESP, FP0, FP1, FP2, FP3, FP4, FP5, FP6, IP,
MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7, R10, R10B, R10D, R10W, R11, R11B, R11D,
R11W, R12, R12B, R12D, R12W, R13, R13B, R13D, R13W, R14, R14B, R14D, R14W, R15,
R15B, R15D, R15W, R8, R8B, R8D, R8W, R9, R9B, R9D, R9W, RAX, RBP, RBX, RCX, RDI,
RDX, RIP, RSI, RSP, SI, SIL, SP, SPL, ST0, ST1, ST2, ST3, ST4, ST5, ST6, ST7,
XMM0, XMM1, XMM10, XMM11, XMM12, XMM13, XMM14, XMM15, XMM2, XMM3, XMM4, XMM5,
XMM6, XMM7, XMM8, XMM9,
$ tblgen X86.td -print-enums -class=Instruction
ABS_F, ABS_Fp32, ABS_Fp64, ABS_Fp80, ADC32mi, ADC32mi8, ADC32mr, ADC32ri,
ADC32ri8, ADC32rm, ADC32rr, ADC64mi32, ADC64mi8, ADC64mr, ADC64ri32, ADC64ri8,
ADC64rm, ADC64rr, ADD16mi, ADD16mi8, ADD16mr, ADD16ri, ADD16ri8, ADD16rm,
ADD16rr, ADD32mi, ADD32mi8, ADD32mr, ADD32ri, ADD32ri8, ADD32rm, ADD32rr,
ADD64mi32, ADD64mi8, ADD64mr, ADD64ri32, ...
</pre>
</div>
<p>The default backend prints out all of the records, as described <a
href="#example">above</a>.</p>
<p>If you plan to use TableGen, you will most likely have to <a
href="#backends">write a backend</a> that extracts the information specific to
what you need and formats it in the appropriate way.</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section"><a name="syntax">TableGen syntax</a></div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>TableGen doesn't care about the meaning of data (that is up to the backend to
define), but it does care about syntax, and it enforces a simple type system.
This section describes the syntax and the constructs allowed in a TableGen file.
</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="primitives">TableGen primitives</a></div>
<!-- -------------------------------------------------------------------------->
<div class="doc_subsubsection"><a name="comments">TableGen comments</a></div>
<div class="doc_text">
<p>TableGen supports BCPL style "<tt>//</tt>" comments, which run to the end of
the line, and it also supports <b>nestable</b> "<tt>/* */</tt>" comments.</p>
</div>
<!-- -------------------------------------------------------------------------->
<div class="doc_subsubsection">
<a name="types">The TableGen type system</a>
</div>
<div class="doc_text">
<p>TableGen files are strongly typed, in a simple (but complete) type-system.
These types are used to perform automatic conversions, check for errors, and to
help interface designers constrain the input that they allow. Every <a
href="#valuedef">value definition</a> is required to have an associated type.
</p>
<p>TableGen supports a mixture of very low-level types (such as <tt>bit</tt>)
and very high-level types (such as <tt>dag</tt>). This flexibility is what
allows it to describe a wide range of information conveniently and compactly.
The TableGen types are:</p>
<dl>
<dt><tt><b>bit</b></tt></dt>
<dd>A 'bit' is a boolean value that can hold either 0 or 1.</dd>
<dt><tt><b>int</b></tt></dt>
<dd>The 'int' type represents a simple 32-bit integer value, such as 5.</dd>
<dt><tt><b>string</b></tt></dt>
<dd>The 'string' type represents an ordered sequence of characters of
arbitrary length.</dd>
<dt><tt><b>bits</b><n></tt></dt>
<dd>A 'bits' type is an arbitrary, but fixed, size integer that is broken up
into individual bits. This type is useful because it can handle some bits
being defined while others are undefined.</dd>
<dt><tt><b>list</b><ty></tt></dt>
<dd>This type represents a list whose elements are some other type. The
contained type is arbitrary: it can even be another list type.</dd>
<dt>Class type</dt>
<dd>Specifying a class name in a type context means that the defined value
must be a subclass of the specified class. This is useful in conjunction with
the <b><tt>list</tt></b> type, for example, to constrain the elements of the
list to a common base class (e.g., a <tt><b>list</b><Register></tt> can
only contain definitions derived from the "<tt>Register</tt>" class).</dd>
<dt><tt><b>dag</b></tt></dt>
<dd>This type represents a nestable directed graph of elements.</dd>
<dt><tt><b>code</b></tt></dt>
<dd>This represents a big hunk of text. This is lexically distinct from
string values because it doesn't require escapeing double quotes and other
common characters that occur in code.</dd>
</dl>
<p>To date, these types have been sufficient for describing things that
TableGen has been used for, but it is straight-forward to extend this list if
needed.</p>
</div>
<!-- -------------------------------------------------------------------------->
<div class="doc_subsubsection">
<a name="values">TableGen values and expressions</a>
</div>
<div class="doc_text">
<p>TableGen allows for a pretty reasonable number of different expression forms
when building up values. These forms allow the TableGen file to be written in a
natural syntax and flavor for the application. The current expression forms
supported include:</p>
<dl>
<dt><tt>?</tt></dt>
<dd>uninitialized field</dd>
<dt><tt>0b1001011</tt></dt>
<dd>binary integer value</dd>
<dt><tt>07654321</tt></dt>
<dd>octal integer value (indicated by a leading 0)</dd>
<dt><tt>7</tt></dt>
<dd>decimal integer value</dd>
<dt><tt>0x7F</tt></dt>
<dd>hexadecimal integer value</dd>
<dt><tt>"foo"</tt></dt>
<dd>string value</dd>
<dt><tt>[{ ... }]</tt></dt>
<dd>code fragment</dd>
<dt><tt>[ X, Y, Z ]<type></tt></dt>
<dd>list value. <type> is the type of the list
element and is usually optional. In rare cases,
TableGen is unable to deduce the element type in
which case the user must specify it explicitly.</dd>
<dt><tt>{ a, b, c }</tt></dt>
<dd>initializer for a "bits<3>" value</dd>
<dt><tt>value</tt></dt>
<dd>value reference</dd>
<dt><tt>value{17}</tt></dt>
<dd>access to one bit of a value</dd>
<dt><tt>value{15-17}</tt></dt>
<dd>access to multiple bits of a value</dd>
<dt><tt>DEF</tt></dt>
<dd>reference to a record definition</dd>
<dt><tt>CLASS<val list></tt></dt>
<dd>reference to a new anonymous definition of CLASS with the specified
template arguments.</dd>
<dt><tt>X.Y</tt></dt>
<dd>reference to the subfield of a value</dd>
<dt><tt>list[4-7,17,2-3]</tt></dt>
<dd>A slice of the 'list' list, including elements 4,5,6,7,17,2, and 3 from
it. Elements may be included multiple times.</dd>
<dt><tt>(DEF a, b)</tt></dt>
<dd>a dag value. The first element is required to be a record definition, the
remaining elements in the list may be arbitrary other values, including nested
`<tt>dag</tt>' values.</dd>
<dt><tt>!strconcat(a, b)</tt></dt>
<dd>A string value that is the result of concatenating the 'a' and 'b'
strings.</dd>
<dt><tt>!cast<type>(a)</tt></dt>
<dd>A symbol of type <em>type</em> obtained by looking up the string 'a' in
the symbol table. If the type of 'a' does not match <em>type</em>, TableGen
aborts with an error. !cast<string> is a special case in that the argument must
be an object defined by a 'def' construct.</dd>
<dt><tt>!subst(a, b, c)</tt></dt>
<dd>If 'a' and 'b' are of string type or are symbol references, substitute
'b' for 'a' in 'c.' This operation is analogous to $(subst) in GNU make.</dd>
<dt><tt>!foreach(a, b, c)</tt></dt>
<dd>For each member 'b' of dag or list 'a' apply operator 'c.' 'b' is a
dummy variable that should be declared as a member variable of an instantiated
class. This operation is analogous to $(foreach) in GNU make.</dd>
<dt><tt>!car(a)</tt></dt>
<dd>The first element of list 'a.'</dd>
<dt><tt>!cdr(a)</tt></dt>
<dd>The 2nd-N elements of list 'a.'</dd>
<dt><tt>!null(a)</tt></dt>
<dd>An integer {0,1} indicating whether list 'a' is empty.</dd>
<dt><tt>!if(a,b,c)</tt></dt>
<dd>'b' if the result of 'int' or 'bit' operator 'a' is nonzero,
'c' otherwise.</dd>
<dt><tt>!eq(a,b)</tt></dt>
<dd>Integer one if string a is equal to string b, zero otherwise. This
only operates on string, int and bit objects. Use !cast<string> to
compare other types of objects.</dd>
</dl>
<p>Note that all of the values have rules specifying how they convert to values
for different types. These rules allow you to assign a value like "<tt>7</tt>"
to a "<tt>bits<4></tt>" value, for example.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="classesdefs">Classes and definitions</a>
</div>
<div class="doc_text">
<p>As mentioned in the <a href="#concepts">intro</a>, classes and definitions
(collectively known as 'records') in TableGen are the main high-level unit of
information that TableGen collects. Records are defined with a <tt>def</tt> or
<tt>class</tt> keyword, the record name, and an optional list of "<a
href="#templateargs">template arguments</a>". If the record has superclasses,
they are specified as a comma separated list that starts with a colon character
("<tt>:</tt>"). If <a href="#valuedef">value definitions</a> or <a
href="#recordlet">let expressions</a> are needed for the class, they are
enclosed in curly braces ("<tt>{}</tt>"); otherwise, the record ends with a
semicolon.</p>
<p>Here is a simple TableGen file:</p>
<div class="doc_code">
<pre>
<b>class</b> C { <b>bit</b> V = 1; }
<b>def</b> X : C;
<b>def</b> Y : C {
<b>string</b> Greeting = "hello";
}
</pre>
</div>
<p>This example defines two definitions, <tt>X</tt> and <tt>Y</tt>, both of
which derive from the <tt>C</tt> class. Because of this, they both get the
<tt>V</tt> bit value. The <tt>Y</tt> definition also gets the Greeting member
as well.</p>
<p>In general, classes are useful for collecting together the commonality
between a group of records and isolating it in a single place. Also, classes
permit the specification of default values for their subclasses, allowing the
subclasses to override them as they wish.</p>
</div>
<!---------------------------------------------------------------------------->
<div class="doc_subsubsection">
<a name="valuedef">Value definitions</a>
</div>
<div class="doc_text">
<p>Value definitions define named entries in records. A value must be defined
before it can be referred to as the operand for another value definition or
before the value is reset with a <a href="#recordlet">let expression</a>. A
value is defined by specifying a <a href="#types">TableGen type</a> and a name.
If an initial value is available, it may be specified after the type with an
equal sign. Value definitions require terminating semicolons.</p>
</div>
<!-- -------------------------------------------------------------------------->
<div class="doc_subsubsection">
<a name="recordlet">'let' expressions</a>
</div>
<div class="doc_text">
<p>A record-level let expression is used to change the value of a value
definition in a record. This is primarily useful when a superclass defines a
value that a derived class or definition wants to override. Let expressions
consist of the '<tt>let</tt>' keyword followed by a value name, an equal sign
("<tt>=</tt>"), and a new value. For example, a new class could be added to the
example above, redefining the <tt>V</tt> field for all of its subclasses:</p>
<div class="doc_code">
<pre>
<b>class</b> D : C { let V = 0; }
<b>def</b> Z : D;
</pre>
</div>
<p>In this case, the <tt>Z</tt> definition will have a zero value for its "V"
value, despite the fact that it derives (indirectly) from the <tt>C</tt> class,
because the <tt>D</tt> class overrode its value.</p>
</div>
<!-- -------------------------------------------------------------------------->
<div class="doc_subsubsection">
<a name="templateargs">Class template arguments</a>
</div>
<div class="doc_text">
<p>TableGen permits the definition of parameterized classes as well as normal
concrete classes. Parameterized TableGen classes specify a list of variable
bindings (which may optionally have defaults) that are bound when used. Here is
a simple example:</p>
<div class="doc_code">
<pre>
<b>class</b> FPFormat<<b>bits</b><3> val> {
<b>bits</b><3> Value = val;
}
<b>def</b> NotFP : FPFormat<0>;
<b>def</b> ZeroArgFP : FPFormat<1>;
<b>def</b> OneArgFP : FPFormat<2>;
<b>def</b> OneArgFPRW : FPFormat<3>;
<b>def</b> TwoArgFP : FPFormat<4>;
<b>def</b> CompareFP : FPFormat<5>;
<b>def</b> CondMovFP : FPFormat<6>;
<b>def</b> SpecialFP : FPFormat<7>;
</pre>
</div>
<p>In this case, template arguments are used as a space efficient way to specify
a list of "enumeration values", each with a "<tt>Value</tt>" field set to the
specified integer.</p>
<p>The more esoteric forms of <a href="#values">TableGen expressions</a> are
useful in conjunction with template arguments. As an example:</p>
<div class="doc_code">
<pre>
<b>class</b> ModRefVal<<b>bits</b><2> val> {
<b>bits</b><2> Value = val;
}
<b>def</b> None : ModRefVal<0>;
<b>def</b> Mod : ModRefVal<1>;
<b>def</b> Ref : ModRefVal<2>;
<b>def</b> ModRef : ModRefVal<3>;
<b>class</b> Value<ModRefVal MR> {
<i>// Decode some information into a more convenient format, while providing
// a nice interface to the user of the "Value" class.</i>
<b>bit</b> isMod = MR.Value{0};
<b>bit</b> isRef = MR.Value{1};
<i>// other stuff...</i>
}
<i>// Example uses</i>
<b>def</b> bork : Value<Mod>;
<b>def</b> zork : Value<Ref>;
<b>def</b> hork : Value<ModRef>;
</pre>
</div>
<p>This is obviously a contrived example, but it shows how template arguments
can be used to decouple the interface provided to the user of the class from the
actual internal data representation expected by the class. In this case,
running <tt>tblgen</tt> on the example prints the following definitions:</p>
<div class="doc_code">
<pre>
<b>def</b> bork { <i>// Value</i>
<b>bit</b> isMod = 1;
<b>bit</b> isRef = 0;
}
<b>def</b> hork { <i>// Value</i>
<b>bit</b> isMod = 1;
<b>bit</b> isRef = 1;
}
<b>def</b> zork { <i>// Value</i>
<b>bit</b> isMod = 0;
<b>bit</b> isRef = 1;
}
</pre>
</div>
<p> This shows that TableGen was able to dig into the argument and extract a
piece of information that was requested by the designer of the "Value" class.
For more realistic examples, please see existing users of TableGen, such as the
X86 backend.</p>
</div>
<!-- -------------------------------------------------------------------------->
<div class="doc_subsubsection">
<a name="multiclass">Multiclass definitions and instances</a>
</div>
<div class="doc_text">
<p>
While classes with template arguments are a good way to factor commonality
between two instances of a definition, multiclasses allow a convenient notation
for defining multiple definitions at once (instances of implicitly constructed
classes). For example, consider an 3-address instruction set whose instructions
come in two forms: "<tt>reg = reg op reg</tt>" and "<tt>reg = reg op imm</tt>"
(e.g. SPARC). In this case, you'd like to specify in one place that this
commonality exists, then in a separate place indicate what all the ops are.
</p>
<p>
Here is an example TableGen fragment that shows this idea:
</p>
<div class="doc_code">
<pre>
<b>def</b> ops;
<b>def</b> GPR;
<b>def</b> Imm;
<b>class</b> inst<<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist>;
<b>multiclass</b> ri_inst<<b>int</b> opc, <b>string</b> asmstr> {
def _rr : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
(ops GPR:$dst, GPR:$src1, GPR:$src2)>;
def _ri : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
(ops GPR:$dst, GPR:$src1, Imm:$src2)>;
}
<i>// Instantiations of the ri_inst multiclass.</i>
<b>defm</b> ADD : ri_inst<0b111, "add">;
<b>defm</b> SUB : ri_inst<0b101, "sub">;
<b>defm</b> MUL : ri_inst<0b100, "mul">;
...
</pre>
</div>
<p>The name of the resultant definitions has the multidef fragment names
appended to them, so this defines <tt>ADD_rr</tt>, <tt>ADD_ri</tt>,
<tt>SUB_rr</tt>, etc. A defm may inherit from multiple multiclasses,
instantiating definitions from each multiclass. Using a multiclass
this way is exactly equivalent to instantiating the classes multiple
times yourself, e.g. by writing:</p>
<div class="doc_code">
<pre>
<b>def</b> ops;
<b>def</b> GPR;
<b>def</b> Imm;
<b>class</b> inst<<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist>;
<b>class</b> rrinst<<b>int</b> opc, <b>string</b> asmstr>
: inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
(ops GPR:$dst, GPR:$src1, GPR:$src2)>;
<b>class</b> riinst<<b>int</b> opc, <b>string</b> asmstr>
: inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
(ops GPR:$dst, GPR:$src1, Imm:$src2)>;
<i>// Instantiations of the ri_inst multiclass.</i>
<b>def</b> ADD_rr : rrinst<0b111, "add">;
<b>def</b> ADD_ri : riinst<0b111, "add">;
<b>def</b> SUB_rr : rrinst<0b101, "sub">;
<b>def</b> SUB_ri : riinst<0b101, "sub">;
<b>def</b> MUL_rr : rrinst<0b100, "mul">;
<b>def</b> MUL_ri : riinst<0b100, "mul">;
...
</pre>
</div>
<p>
A defm can also be used inside a multiclass providing several levels of
multiclass instanciations.
</p>
<div class="doc_code">
<pre>
<b>class</b> Instruction<bits<4> opc, string Name> {
bits<4> opcode = opc;
string name = Name;
}
<b>multiclass</b> basic_r<bits<4> opc> {
<b>def</b> rr : Instruction<opc, "rr">;
<b>def</b> rm : Instruction<opc, "rm">;
}
<b>multiclass</b> basic_s<bits<4> opc> {
<b>defm</b> SS : basic_r<opc>;
<b>defm</b> SD : basic_r<opc>;
<b>def</b> X : Instruction<opc, "x">;
}
<b>multiclass</b> basic_p<bits<4> opc> {
<b>defm</b> PS : basic_r<opc>;
<b>defm</b> PD : basic_r<opc>;
<b>def</b> Y : Instruction<opc, "y">;
}
<b>defm</b> ADD : basic_s<0xf>, basic_p<0xf>;
...
<i>// Results</i>
<b>def</b> ADDPDrm { ...
<b>def</b> ADDPDrr { ...
<b>def</b> ADDPSrm { ...
<b>def</b> ADDPSrr { ...
<b>def</b> ADDSDrm { ...
<b>def</b> ADDSDrr { ...
<b>def</b> ADDY { ...
<b>def</b> ADDX { ...
</pre>
</div>
<p>
defm declarations can inherit from classes too, the
rule to follow is that the class list must start after the
last multiclass, and there must be at least one multiclass
before them.
</p>
<div class="doc_code">
<pre>
<b>class</b> XD { bits<4> Prefix = 11; }
<b>class</b> XS { bits<4> Prefix = 12; }
<b>class</b> I<bits<4> op> {
bits<4> opcode = op;
}
<b>multiclass</b> R {
<b>def</b> rr : I<4>;
<b>def</b> rm : I<2>;
}
<b>multiclass</b> Y {
<b>defm</b> SS : R, XD;
<b>defm</b> SD : R, XS;
}
<b>defm</b> Instr : Y;
<i>// Results</i>
<b>def</b> InstrSDrm {
bits<4> opcode = { 0, 0, 1, 0 };
bits<4> Prefix = { 1, 1, 0, 0 };
}
...
<b>def</b> InstrSSrr {
bits<4> opcode = { 0, 1, 0, 0 };
bits<4> Prefix = { 1, 0, 1, 1 };
}
</pre>
</div>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="filescope">File scope entities</a>
</div>
<!-- -------------------------------------------------------------------------->
<div class="doc_subsubsection">
<a name="include">File inclusion</a>
</div>
<div class="doc_text">
<p>TableGen supports the '<tt>include</tt>' token, which textually substitutes
the specified file in place of the include directive. The filename should be
specified as a double quoted string immediately after the '<tt>include</tt>'
keyword. Example:</p>
<div class="doc_code">
<pre>
<b>include</b> "foo.td"
</pre>
</div>
</div>
<!-- -------------------------------------------------------------------------->
<div class="doc_subsubsection">
<a name="globallet">'let' expressions</a>
</div>
<div class="doc_text">
<p>"Let" expressions at file scope are similar to <a href="#recordlet">"let"
expressions within a record</a>, except they can specify a value binding for
multiple records at a time, and may be useful in certain other cases.
File-scope let expressions are really just another way that TableGen allows the
end-user to factor out commonality from the records.</p>
<p>File-scope "let" expressions take a comma-separated list of bindings to
apply, and one or more records to bind the values in. Here are some
examples:</p>
<pre class="doc_code">
<b>let</b> isTerminator = 1, isReturn = 1, isBarrier = 1, hasCtrlDep = 1 <b>in</b>
<b>def</b> RET : I<0xC3, RawFrm, (outs), (ins), "ret", [(X86retflag 0)]>;
<b>let</b> isCall = 1 <b>in</b>
<i>// All calls clobber the non-callee saved registers...</i>
<b>let</b> Defs = [EAX, ECX, EDX, FP0, FP1, FP2, FP3, FP4, FP5, FP6, ST0,
MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7,
XMM0, XMM1, XMM2, XMM3, XMM4, XMM5, XMM6, XMM7, EFLAGS] <b>in</b> {
<b>def</b> CALLpcrel32 : Ii32<0xE8, RawFrm, (outs), (ins i32imm:$dst,variable_ops),
"call\t${dst:call}", []>;
<b>def</b> CALL32r : I<0xFF, MRM2r, (outs), (ins GR32:$dst, variable_ops),
"call\t{*}$dst", [(X86call GR32:$dst)]>;
<b>def</b> CALL32m : I<0xFF, MRM2m, (outs), (ins i32mem:$dst, variable_ops),
"call\t{*}$dst", []>;
}
</pre>
<p>File-scope "let" expressions are often useful when a couple of definitions
need to be added to several records, and the records do not otherwise need to be
opened, as in the case with the <tt>CALL*</tt> instructions above.</p>
<p>It's also possible to use "let" expressions inside multiclasses, providing
more ways to factor out commonality from the records, specially if using
several levels of multiclass instanciations. This also avoids the need of using
"let" expressions within subsequent records inside a multiclass.</p>
<pre class="doc_code">
<b>multiclass </b>basic_r<bits<4> opc> {
<b>let </b>Predicates = [HasSSE2] in {
<b>def </b>rr : Instruction<opc, "rr">;
<b>def </b>rm : Instruction<opc, "rm">;
}
<b>let </b>Predicates = [HasSSE3] in
<b>def </b>rx : Instruction<opc, "rx">;
}
<b>multiclass </b>basic_ss<bits<4> opc> {
<b>let </b>IsDouble = 0 in
<b>defm </b>SS : basic_r<opc>;
<b>let </b>IsDouble = 1 in
<b>defm </b>SD : basic_r<opc>;
}
<b>defm </b>ADD : basic_ss<0xf>;
</pre>
</div>
<!-- *********************************************************************** -->
<div class="doc_section"><a name="codegen">Code Generator backend info</a></div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>Expressions used by code generator to describe instructions and isel
patterns:</p>
<dl>
<dt><tt>(implicit a)</tt></dt>
<dd>an implicitly defined physical register. This tells the dag instruction
selection emitter the input pattern's extra definitions matches implicit
physical register definitions.</dd>
</dl>
</div>
<!-- *********************************************************************** -->
<div class="doc_section"><a name="backends">TableGen backends</a></div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>TODO: How they work, how to write one. This section should not contain
details about any particular backend, except maybe -print-enums as an example.
This should highlight the APIs in <tt>TableGen/Record.h</tt>.</p>
</div>
<!-- *********************************************************************** -->
<hr>
<address>
<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
<a href="http://validator.w3.org/check/referer"><img
src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
<a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
Last modified: $Date$
</address>
</body>
</html>
|
