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
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>Kaleidoscope: Extending the Language: User-defined Operators</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="author" content="Chris Lattner">
<meta name="author" content="Erick Tryzelaar">
<link rel="stylesheet" href="../_static/llvm.css" type="text/css">
</head>
<body>
<h1>Kaleidoscope: Extending the Language: User-defined Operators</h1>
<ul>
<li><a href="index.html">Up to Tutorial Index</a></li>
<li>Chapter 6
<ol>
<li><a href="#intro">Chapter 6 Introduction</a></li>
<li><a href="#idea">User-defined Operators: the Idea</a></li>
<li><a href="#binary">User-defined Binary Operators</a></li>
<li><a href="#unary">User-defined Unary Operators</a></li>
<li><a href="#example">Kicking the Tires</a></li>
<li><a href="#code">Full Code Listing</a></li>
</ol>
</li>
<li><a href="OCamlLangImpl7.html">Chapter 7</a>: Extending the Language: Mutable
Variables / SSA Construction</li>
</ul>
<div class="doc_author">
<p>
Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
and <a href="mailto:idadesub@users.sourceforge.net">Erick Tryzelaar</a>
</p>
</div>
<!-- *********************************************************************** -->
<h2><a name="intro">Chapter 6 Introduction</a></h2>
<!-- *********************************************************************** -->
<div>
<p>Welcome to Chapter 6 of the "<a href="index.html">Implementing a language
with LLVM</a>" tutorial. At this point in our tutorial, we now have a fully
functional language that is fairly minimal, but also useful. There
is still one big problem with it, however. Our language doesn't have many
useful operators (like division, logical negation, or even any comparisons
besides less-than).</p>
<p>This chapter of the tutorial takes a wild digression into adding user-defined
operators to the simple and beautiful Kaleidoscope language. This digression now
gives us a simple and ugly language in some ways, but also a powerful one at the
same time. One of the great things about creating your own language is that you
get to decide what is good or bad. In this tutorial we'll assume that it is
okay to use this as a way to show some interesting parsing techniques.</p>
<p>At the end of this tutorial, we'll run through an example Kaleidoscope
application that <a href="#example">renders the Mandelbrot set</a>. This gives
an example of what you can build with Kaleidoscope and its feature set.</p>
</div>
<!-- *********************************************************************** -->
<h2><a name="idea">User-defined Operators: the Idea</a></h2>
<!-- *********************************************************************** -->
<div>
<p>
The "operator overloading" that we will add to Kaleidoscope is more general than
languages like C++. In C++, you are only allowed to redefine existing
operators: you can't programatically change the grammar, introduce new
operators, change precedence levels, etc. In this chapter, we will add this
capability to Kaleidoscope, which will let the user round out the set of
operators that are supported.</p>
<p>The point of going into user-defined operators in a tutorial like this is to
show the power and flexibility of using a hand-written parser. Thus far, the parser
we have been implementing uses recursive descent for most parts of the grammar and
operator precedence parsing for the expressions. See <a
href="OCamlLangImpl2.html">Chapter 2</a> for details. Without using operator
precedence parsing, it would be very difficult to allow the programmer to
introduce new operators into the grammar: the grammar is dynamically extensible
as the JIT runs.</p>
<p>The two specific features we'll add are programmable unary operators (right
now, Kaleidoscope has no unary operators at all) as well as binary operators.
An example of this is:</p>
<div class="doc_code">
<pre>
# Logical unary not.
def unary!(v)
if v then
0
else
1;
# Define > with the same precedence as <.
def binary> 10 (LHS RHS)
RHS < LHS;
# Binary "logical or", (note that it does not "short circuit")
def binary| 5 (LHS RHS)
if LHS then
1
else if RHS then
1
else
0;
# Define = with slightly lower precedence than relationals.
def binary= 9 (LHS RHS)
!(LHS < RHS | LHS > RHS);
</pre>
</div>
<p>Many languages aspire to being able to implement their standard runtime
library in the language itself. In Kaleidoscope, we can implement significant
parts of the language in the library!</p>
<p>We will break down implementation of these features into two parts:
implementing support for user-defined binary operators and adding unary
operators.</p>
</div>
<!-- *********************************************************************** -->
<h2><a name="binary">User-defined Binary Operators</a></h2>
<!-- *********************************************************************** -->
<div>
<p>Adding support for user-defined binary operators is pretty simple with our
current framework. We'll first add support for the unary/binary keywords:</p>
<div class="doc_code">
<pre>
type token =
...
<b>(* operators *)
| Binary | Unary</b>
...
and lex_ident buffer = parser
...
| "for" -> [< 'Token.For; stream >]
| "in" -> [< 'Token.In; stream >]
<b>| "binary" -> [< 'Token.Binary; stream >]
| "unary" -> [< 'Token.Unary; stream >]</b>
</pre>
</div>
<p>This just adds lexer support for the unary and binary keywords, like we
did in <a href="OCamlLangImpl5.html#iflexer">previous chapters</a>. One nice
thing about our current AST, is that we represent binary operators with full
generalisation by using their ASCII code as the opcode. For our extended
operators, we'll use this same representation, so we don't need any new AST or
parser support.</p>
<p>On the other hand, we have to be able to represent the definitions of these
new operators, in the "def binary| 5" part of the function definition. In our
grammar so far, the "name" for the function definition is parsed as the
"prototype" production and into the <tt>Ast.Prototype</tt> AST node. To
represent our new user-defined operators as prototypes, we have to extend
the <tt>Ast.Prototype</tt> AST node like this:</p>
<div class="doc_code">
<pre>
(* proto - This type represents the "prototype" for a function, which captures
* its name, and its argument names (thus implicitly the number of arguments the
* function takes). *)
type proto =
| Prototype of string * string array
<b>| BinOpPrototype of string * string array * int</b>
</pre>
</div>
<p>Basically, in addition to knowing a name for the prototype, we now keep track
of whether it was an operator, and if it was, what precedence level the operator
is at. The precedence is only used for binary operators (as you'll see below,
it just doesn't apply for unary operators). Now that we have a way to represent
the prototype for a user-defined operator, we need to parse it:</p>
<div class="doc_code">
<pre>
(* prototype
* ::= id '(' id* ')'
<b>* ::= binary LETTER number? (id, id)
* ::= unary LETTER number? (id) *)</b>
let parse_prototype =
let rec parse_args accumulator = parser
| [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
| [< >] -> accumulator
in
let parse_operator = parser
| [< 'Token.Unary >] -> "unary", 1
| [< 'Token.Binary >] -> "binary", 2
in
let parse_binary_precedence = parser
| [< 'Token.Number n >] -> int_of_float n
| [< >] -> 30
in
parser
| [< 'Token.Ident id;
'Token.Kwd '(' ?? "expected '(' in prototype";
args=parse_args [];
'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
(* success. *)
Ast.Prototype (id, Array.of_list (List.rev args))
<b>| [< (prefix, kind)=parse_operator;
'Token.Kwd op ?? "expected an operator";
(* Read the precedence if present. *)
binary_precedence=parse_binary_precedence;
'Token.Kwd '(' ?? "expected '(' in prototype";
args=parse_args [];
'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
let name = prefix ^ (String.make 1 op) in
let args = Array.of_list (List.rev args) in
(* Verify right number of arguments for operator. *)
if Array.length args != kind
then raise (Stream.Error "invalid number of operands for operator")
else
if kind == 1 then
Ast.Prototype (name, args)
else
Ast.BinOpPrototype (name, args, binary_precedence)</b>
| [< >] ->
raise (Stream.Error "expected function name in prototype")
</pre>
</div>
<p>This is all fairly straightforward parsing code, and we have already seen
a lot of similar code in the past. One interesting part about the code above is
the couple lines that set up <tt>name</tt> for binary operators. This builds
names like "binary@" for a newly defined "@" operator. This then takes
advantage of the fact that symbol names in the LLVM symbol table are allowed to
have any character in them, including embedded nul characters.</p>
<p>The next interesting thing to add, is codegen support for these binary
operators. Given our current structure, this is a simple addition of a default
case for our existing binary operator node:</p>
<div class="doc_code">
<pre>
let codegen_expr = function
...
| Ast.Binary (op, lhs, rhs) ->
let lhs_val = codegen_expr lhs in
let rhs_val = codegen_expr rhs in
begin
match op with
| '+' -> build_add lhs_val rhs_val "addtmp" builder
| '-' -> build_sub lhs_val rhs_val "subtmp" builder
| '*' -> build_mul lhs_val rhs_val "multmp" builder
| '<' ->
(* Convert bool 0/1 to double 0.0 or 1.0 *)
let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
build_uitofp i double_type "booltmp" builder
<b>| _ ->
(* If it wasn't a builtin binary operator, it must be a user defined
* one. Emit a call to it. *)
let callee = "binary" ^ (String.make 1 op) in
let callee =
match lookup_function callee the_module with
| Some callee -> callee
| None -> raise (Error "binary operator not found!")
in
build_call callee [|lhs_val; rhs_val|] "binop" builder</b>
end
</pre>
</div>
<p>As you can see above, the new code is actually really simple. It just does
a lookup for the appropriate operator in the symbol table and generates a
function call to it. Since user-defined operators are just built as normal
functions (because the "prototype" boils down to a function with the right
name) everything falls into place.</p>
<p>The final piece of code we are missing, is a bit of top level magic:</p>
<div class="doc_code">
<pre>
let codegen_func the_fpm = function
| Ast.Function (proto, body) ->
Hashtbl.clear named_values;
let the_function = codegen_proto proto in
<b>(* If this is an operator, install it. *)
begin match proto with
| Ast.BinOpPrototype (name, args, prec) ->
let op = name.[String.length name - 1] in
Hashtbl.add Parser.binop_precedence op prec;
| _ -> ()
end;</b>
(* Create a new basic block to start insertion into. *)
let bb = append_block context "entry" the_function in
position_at_end bb builder;
...
</pre>
</div>
<p>Basically, before codegening a function, if it is a user-defined operator, we
register it in the precedence table. This allows the binary operator parsing
logic we already have in place to handle it. Since we are working on a
fully-general operator precedence parser, this is all we need to do to "extend
the grammar".</p>
<p>Now we have useful user-defined binary operators. This builds a lot
on the previous framework we built for other operators. Adding unary operators
is a bit more challenging, because we don't have any framework for it yet - lets
see what it takes.</p>
</div>
<!-- *********************************************************************** -->
<h2><a name="unary">User-defined Unary Operators</a></h2>
<!-- *********************************************************************** -->
<div>
<p>Since we don't currently support unary operators in the Kaleidoscope
language, we'll need to add everything to support them. Above, we added simple
support for the 'unary' keyword to the lexer. In addition to that, we need an
AST node:</p>
<div class="doc_code">
<pre>
type expr =
...
(* variant for a unary operator. *)
| Unary of char * expr
...
</pre>
</div>
<p>This AST node is very simple and obvious by now. It directly mirrors the
binary operator AST node, except that it only has one child. With this, we
need to add the parsing logic. Parsing a unary operator is pretty simple: we'll
add a new function to do it:</p>
<div class="doc_code">
<pre>
(* unary
* ::= primary
* ::= '!' unary *)
and parse_unary = parser
(* If this is a unary operator, read it. *)
| [< 'Token.Kwd op when op != '(' && op != ')'; operand=parse_expr >] ->
Ast.Unary (op, operand)
(* If the current token is not an operator, it must be a primary expr. *)
| [< stream >] -> parse_primary stream
</pre>
</div>
<p>The grammar we add is pretty straightforward here. If we see a unary
operator when parsing a primary operator, we eat the operator as a prefix and
parse the remaining piece as another unary operator. This allows us to handle
multiple unary operators (e.g. "!!x"). Note that unary operators can't have
ambiguous parses like binary operators can, so there is no need for precedence
information.</p>
<p>The problem with this function, is that we need to call ParseUnary from
somewhere. To do this, we change previous callers of ParsePrimary to call
<tt>parse_unary</tt> instead:</p>
<div class="doc_code">
<pre>
(* binoprhs
* ::= ('+' primary)* *)
and parse_bin_rhs expr_prec lhs stream =
...
<b>(* Parse the unary expression after the binary operator. *)
let rhs = parse_unary stream in</b>
...
...
(* expression
* ::= primary binoprhs *)
and parse_expr = parser
| [< lhs=<b>parse_unary</b>; stream >] -> parse_bin_rhs 0 lhs stream
</pre>
</div>
<p>With these two simple changes, we are now able to parse unary operators and build the
AST for them. Next up, we need to add parser support for prototypes, to parse
the unary operator prototype. We extend the binary operator code above
with:</p>
<div class="doc_code">
<pre>
(* prototype
* ::= id '(' id* ')'
* ::= binary LETTER number? (id, id)
<b>* ::= unary LETTER number? (id)</b> *)
let parse_prototype =
let rec parse_args accumulator = parser
| [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
| [< >] -> accumulator
in
<b>let parse_operator = parser
| [< 'Token.Unary >] -> "unary", 1
| [< 'Token.Binary >] -> "binary", 2
in</b>
let parse_binary_precedence = parser
| [< 'Token.Number n >] -> int_of_float n
| [< >] -> 30
in
parser
| [< 'Token.Ident id;
'Token.Kwd '(' ?? "expected '(' in prototype";
args=parse_args [];
'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
(* success. *)
Ast.Prototype (id, Array.of_list (List.rev args))
<b>| [< (prefix, kind)=parse_operator;
'Token.Kwd op ?? "expected an operator";
(* Read the precedence if present. *)
binary_precedence=parse_binary_precedence;
'Token.Kwd '(' ?? "expected '(' in prototype";
args=parse_args [];
'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
let name = prefix ^ (String.make 1 op) in
let args = Array.of_list (List.rev args) in
(* Verify right number of arguments for operator. *)
if Array.length args != kind
then raise (Stream.Error "invalid number of operands for operator")
else
if kind == 1 then
Ast.Prototype (name, args)
else
Ast.BinOpPrototype (name, args, binary_precedence)</b>
| [< >] ->
raise (Stream.Error "expected function name in prototype")
</pre>
</div>
<p>As with binary operators, we name unary operators with a name that includes
the operator character. This assists us at code generation time. Speaking of,
the final piece we need to add is codegen support for unary operators. It looks
like this:</p>
<div class="doc_code">
<pre>
let rec codegen_expr = function
...
| Ast.Unary (op, operand) ->
let operand = codegen_expr operand in
let callee = "unary" ^ (String.make 1 op) in
let callee =
match lookup_function callee the_module with
| Some callee -> callee
| None -> raise (Error "unknown unary operator")
in
build_call callee [|operand|] "unop" builder
</pre>
</div>
<p>This code is similar to, but simpler than, the code for binary operators. It
is simpler primarily because it doesn't need to handle any predefined operators.
</p>
</div>
<!-- *********************************************************************** -->
<h2><a name="example">Kicking the Tires</a></h2>
<!-- *********************************************************************** -->
<div>
<p>It is somewhat hard to believe, but with a few simple extensions we've
covered in the last chapters, we have grown a real-ish language. With this, we
can do a lot of interesting things, including I/O, math, and a bunch of other
things. For example, we can now add a nice sequencing operator (printd is
defined to print out the specified value and a newline):</p>
<div class="doc_code">
<pre>
ready> <b>extern printd(x);</b>
Read extern: declare double @printd(double)
ready> <b>def binary : 1 (x y) 0; # Low-precedence operator that ignores operands.</b>
..
ready> <b>printd(123) : printd(456) : printd(789);</b>
123.000000
456.000000
789.000000
Evaluated to 0.000000
</pre>
</div>
<p>We can also define a bunch of other "primitive" operations, such as:</p>
<div class="doc_code">
<pre>
# Logical unary not.
def unary!(v)
if v then
0
else
1;
# Unary negate.
def unary-(v)
0-v;
# Define > with the same precedence as <.
def binary> 10 (LHS RHS)
RHS < LHS;
# Binary logical or, which does not short circuit.
def binary| 5 (LHS RHS)
if LHS then
1
else if RHS then
1
else
0;
# Binary logical and, which does not short circuit.
def binary& 6 (LHS RHS)
if !LHS then
0
else
!!RHS;
# Define = with slightly lower precedence than relationals.
def binary = 9 (LHS RHS)
!(LHS < RHS | LHS > RHS);
</pre>
</div>
<p>Given the previous if/then/else support, we can also define interesting
functions for I/O. For example, the following prints out a character whose
"density" reflects the value passed in: the lower the value, the denser the
character:</p>
<div class="doc_code">
<pre>
ready>
<b>
extern putchard(char)
def printdensity(d)
if d > 8 then
putchard(32) # ' '
else if d > 4 then
putchard(46) # '.'
else if d > 2 then
putchard(43) # '+'
else
putchard(42); # '*'</b>
...
ready> <b>printdensity(1): printdensity(2): printdensity(3) :
printdensity(4): printdensity(5): printdensity(9): putchard(10);</b>
*++..
Evaluated to 0.000000
</pre>
</div>
<p>Based on these simple primitive operations, we can start to define more
interesting things. For example, here's a little function that solves for the
number of iterations it takes a function in the complex plane to
converge:</p>
<div class="doc_code">
<pre>
# determine whether the specific location diverges.
# Solve for z = z^2 + c in the complex plane.
def mandleconverger(real imag iters creal cimag)
if iters > 255 | (real*real + imag*imag > 4) then
iters
else
mandleconverger(real*real - imag*imag + creal,
2*real*imag + cimag,
iters+1, creal, cimag);
# return the number of iterations required for the iteration to escape
def mandleconverge(real imag)
mandleconverger(real, imag, 0, real, imag);
</pre>
</div>
<p>This "z = z<sup>2</sup> + c" function is a beautiful little creature that is the basis
for computation of the <a
href="http://en.wikipedia.org/wiki/Mandelbrot_set">Mandelbrot Set</a>. Our
<tt>mandelconverge</tt> function returns the number of iterations that it takes
for a complex orbit to escape, saturating to 255. This is not a very useful
function by itself, but if you plot its value over a two-dimensional plane,
you can see the Mandelbrot set. Given that we are limited to using putchard
here, our amazing graphical output is limited, but we can whip together
something using the density plotter above:</p>
<div class="doc_code">
<pre>
# compute and plot the mandlebrot set with the specified 2 dimensional range
# info.
def mandelhelp(xmin xmax xstep ymin ymax ystep)
for y = ymin, y < ymax, ystep in (
(for x = xmin, x < xmax, xstep in
printdensity(mandleconverge(x,y)))
: putchard(10)
)
# mandel - This is a convenient helper function for plotting the mandelbrot set
# from the specified position with the specified Magnification.
def mandel(realstart imagstart realmag imagmag)
mandelhelp(realstart, realstart+realmag*78, realmag,
imagstart, imagstart+imagmag*40, imagmag);
</pre>
</div>
<p>Given this, we can try plotting out the mandlebrot set! Lets try it out:</p>
<div class="doc_code">
<pre>
ready> <b>mandel(-2.3, -1.3, 0.05, 0.07);</b>
*******************************+++++++++++*************************************
*************************+++++++++++++++++++++++*******************************
**********************+++++++++++++++++++++++++++++****************************
*******************+++++++++++++++++++++.. ...++++++++*************************
*****************++++++++++++++++++++++.... ...+++++++++***********************
***************+++++++++++++++++++++++..... ...+++++++++*********************
**************+++++++++++++++++++++++.... ....+++++++++********************
*************++++++++++++++++++++++...... .....++++++++*******************
************+++++++++++++++++++++....... .......+++++++******************
***********+++++++++++++++++++.... ... .+++++++*****************
**********+++++++++++++++++....... .+++++++****************
*********++++++++++++++........... ...+++++++***************
********++++++++++++............ ...++++++++**************
********++++++++++... .......... .++++++++**************
*******+++++++++..... .+++++++++*************
*******++++++++...... ..+++++++++*************
*******++++++....... ..+++++++++*************
*******+++++...... ..+++++++++*************
*******.... .... ...+++++++++*************
*******.... . ...+++++++++*************
*******+++++...... ...+++++++++*************
*******++++++....... ..+++++++++*************
*******++++++++...... .+++++++++*************
*******+++++++++..... ..+++++++++*************
********++++++++++... .......... .++++++++**************
********++++++++++++............ ...++++++++**************
*********++++++++++++++.......... ...+++++++***************
**********++++++++++++++++........ .+++++++****************
**********++++++++++++++++++++.... ... ..+++++++****************
***********++++++++++++++++++++++....... .......++++++++*****************
************+++++++++++++++++++++++...... ......++++++++******************
**************+++++++++++++++++++++++.... ....++++++++********************
***************+++++++++++++++++++++++..... ...+++++++++*********************
*****************++++++++++++++++++++++.... ...++++++++***********************
*******************+++++++++++++++++++++......++++++++*************************
*********************++++++++++++++++++++++.++++++++***************************
*************************+++++++++++++++++++++++*******************************
******************************+++++++++++++************************************
*******************************************************************************
*******************************************************************************
*******************************************************************************
Evaluated to 0.000000
ready> <b>mandel(-2, -1, 0.02, 0.04);</b>
**************************+++++++++++++++++++++++++++++++++++++++++++++++++++++
***********************++++++++++++++++++++++++++++++++++++++++++++++++++++++++
*********************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++.
*******************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++...
*****************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++.....
***************++++++++++++++++++++++++++++++++++++++++++++++++++++++++........
**************++++++++++++++++++++++++++++++++++++++++++++++++++++++...........
************+++++++++++++++++++++++++++++++++++++++++++++++++++++..............
***********++++++++++++++++++++++++++++++++++++++++++++++++++........ .
**********++++++++++++++++++++++++++++++++++++++++++++++.............
********+++++++++++++++++++++++++++++++++++++++++++..................
*******+++++++++++++++++++++++++++++++++++++++.......................
******+++++++++++++++++++++++++++++++++++...........................
*****++++++++++++++++++++++++++++++++............................
*****++++++++++++++++++++++++++++...............................
****++++++++++++++++++++++++++...... .........................
***++++++++++++++++++++++++......... ...... ...........
***++++++++++++++++++++++............
**+++++++++++++++++++++..............
**+++++++++++++++++++................
*++++++++++++++++++.................
*++++++++++++++++............ ...
*++++++++++++++..............
*+++....++++................
*.......... ...........
*
*.......... ...........
*+++....++++................
*++++++++++++++..............
*++++++++++++++++............ ...
*++++++++++++++++++.................
**+++++++++++++++++++................
**+++++++++++++++++++++..............
***++++++++++++++++++++++............
***++++++++++++++++++++++++......... ...... ...........
****++++++++++++++++++++++++++...... .........................
*****++++++++++++++++++++++++++++...............................
*****++++++++++++++++++++++++++++++++............................
******+++++++++++++++++++++++++++++++++++...........................
*******+++++++++++++++++++++++++++++++++++++++.......................
********+++++++++++++++++++++++++++++++++++++++++++..................
Evaluated to 0.000000
ready> <b>mandel(-0.9, -1.4, 0.02, 0.03);</b>
*******************************************************************************
*******************************************************************************
*******************************************************************************
**********+++++++++++++++++++++************************************************
*+++++++++++++++++++++++++++++++++++++++***************************************
+++++++++++++++++++++++++++++++++++++++++++++**********************************
++++++++++++++++++++++++++++++++++++++++++++++++++*****************************
++++++++++++++++++++++++++++++++++++++++++++++++++++++*************************
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++**********************
+++++++++++++++++++++++++++++++++.........++++++++++++++++++*******************
+++++++++++++++++++++++++++++++.... ......+++++++++++++++++++****************
+++++++++++++++++++++++++++++....... ........+++++++++++++++++++**************
++++++++++++++++++++++++++++........ ........++++++++++++++++++++************
+++++++++++++++++++++++++++......... .. ...+++++++++++++++++++++**********
++++++++++++++++++++++++++........... ....++++++++++++++++++++++********
++++++++++++++++++++++++............. .......++++++++++++++++++++++******
+++++++++++++++++++++++............. ........+++++++++++++++++++++++****
++++++++++++++++++++++........... ..........++++++++++++++++++++++***
++++++++++++++++++++........... .........++++++++++++++++++++++*
++++++++++++++++++............ ...........++++++++++++++++++++
++++++++++++++++............... .............++++++++++++++++++
++++++++++++++................. ...............++++++++++++++++
++++++++++++.................. .................++++++++++++++
+++++++++.................. .................+++++++++++++
++++++........ . ......... ..++++++++++++
++............ ...... ....++++++++++
.............. ...++++++++++
.............. ....+++++++++
.............. .....++++++++
............. ......++++++++
........... .......++++++++
......... ........+++++++
......... ........+++++++
......... ....+++++++
........ ...+++++++
....... ...+++++++
....+++++++
.....+++++++
....+++++++
....+++++++
....+++++++
Evaluated to 0.000000
ready> <b>^D</b>
</pre>
</div>
<p>At this point, you may be starting to realize that Kaleidoscope is a real
and powerful language. It may not be self-similar :), but it can be used to
plot things that are!</p>
<p>With this, we conclude the "adding user-defined operators" chapter of the
tutorial. We have successfully augmented our language, adding the ability to
extend the language in the library, and we have shown how this can be used to
build a simple but interesting end-user application in Kaleidoscope. At this
point, Kaleidoscope can build a variety of applications that are functional and
can call functions with side-effects, but it can't actually define and mutate a
variable itself.</p>
<p>Strikingly, variable mutation is an important feature of some
languages, and it is not at all obvious how to <a href="OCamlLangImpl7.html">add
support for mutable variables</a> without having to add an "SSA construction"
phase to your front-end. In the next chapter, we will describe how you can
add variable mutation without building SSA in your front-end.</p>
</div>
<!-- *********************************************************************** -->
<h2><a name="code">Full Code Listing</a></h2>
<!-- *********************************************************************** -->
<div>
<p>
Here is the complete code listing for our running example, enhanced with the
if/then/else and for expressions.. To build this example, use:
</p>
<div class="doc_code">
<pre>
# Compile
ocamlbuild toy.byte
# Run
./toy.byte
</pre>
</div>
<p>Here is the code:</p>
<dl>
<dt>_tags:</dt>
<dd class="doc_code">
<pre>
<{lexer,parser}.ml>: use_camlp4, pp(camlp4of)
<*.{byte,native}>: g++, use_llvm, use_llvm_analysis
<*.{byte,native}>: use_llvm_executionengine, use_llvm_target
<*.{byte,native}>: use_llvm_scalar_opts, use_bindings
</pre>
</dd>
<dt>myocamlbuild.ml:</dt>
<dd class="doc_code">
<pre>
open Ocamlbuild_plugin;;
ocaml_lib ~extern:true "llvm";;
ocaml_lib ~extern:true "llvm_analysis";;
ocaml_lib ~extern:true "llvm_executionengine";;
ocaml_lib ~extern:true "llvm_target";;
ocaml_lib ~extern:true "llvm_scalar_opts";;
flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"; A"-cclib"; A"-rdynamic"]);;
dep ["link"; "ocaml"; "use_bindings"] ["bindings.o"];;
</pre>
</dd>
<dt>token.ml:</dt>
<dd class="doc_code">
<pre>
(*===----------------------------------------------------------------------===
* Lexer Tokens
*===----------------------------------------------------------------------===*)
(* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
* these others for known things. *)
type token =
(* commands *)
| Def | Extern
(* primary *)
| Ident of string | Number of float
(* unknown *)
| Kwd of char
(* control *)
| If | Then | Else
| For | In
(* operators *)
| Binary | Unary
</pre>
</dd>
<dt>lexer.ml:</dt>
<dd class="doc_code">
<pre>
(*===----------------------------------------------------------------------===
* Lexer
*===----------------------------------------------------------------------===*)
let rec lex = parser
(* Skip any whitespace. *)
| [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream
(* identifier: [a-zA-Z][a-zA-Z0-9] *)
| [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] ->
let buffer = Buffer.create 1 in
Buffer.add_char buffer c;
lex_ident buffer stream
(* number: [0-9.]+ *)
| [< ' ('0' .. '9' as c); stream >] ->
let buffer = Buffer.create 1 in
Buffer.add_char buffer c;
lex_number buffer stream
(* Comment until end of line. *)
| [< ' ('#'); stream >] ->
lex_comment stream
(* Otherwise, just return the character as its ascii value. *)
| [< 'c; stream >] ->
[< 'Token.Kwd c; lex stream >]
(* end of stream. *)
| [< >] -> [< >]
and lex_number buffer = parser
| [< ' ('0' .. '9' | '.' as c); stream >] ->
Buffer.add_char buffer c;
lex_number buffer stream
| [< stream=lex >] ->
[< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
and lex_ident buffer = parser
| [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] ->
Buffer.add_char buffer c;
lex_ident buffer stream
| [< stream=lex >] ->
match Buffer.contents buffer with
| "def" -> [< 'Token.Def; stream >]
| "extern" -> [< 'Token.Extern; stream >]
| "if" -> [< 'Token.If; stream >]
| "then" -> [< 'Token.Then; stream >]
| "else" -> [< 'Token.Else; stream >]
| "for" -> [< 'Token.For; stream >]
| "in" -> [< 'Token.In; stream >]
| "binary" -> [< 'Token.Binary; stream >]
| "unary" -> [< 'Token.Unary; stream >]
| id -> [< 'Token.Ident id; stream >]
and lex_comment = parser
| [< ' ('\n'); stream=lex >] -> stream
| [< 'c; e=lex_comment >] -> e
| [< >] -> [< >]
</pre>
</dd>
<dt>ast.ml:</dt>
<dd class="doc_code">
<pre>
(*===----------------------------------------------------------------------===
* Abstract Syntax Tree (aka Parse Tree)
*===----------------------------------------------------------------------===*)
(* expr - Base type for all expression nodes. *)
type expr =
(* variant for numeric literals like "1.0". *)
| Number of float
(* variant for referencing a variable, like "a". *)
| Variable of string
(* variant for a unary operator. *)
| Unary of char * expr
(* variant for a binary operator. *)
| Binary of char * expr * expr
(* variant for function calls. *)
| Call of string * expr array
(* variant for if/then/else. *)
| If of expr * expr * expr
(* variant for for/in. *)
| For of string * expr * expr * expr option * expr
(* proto - This type represents the "prototype" for a function, which captures
* its name, and its argument names (thus implicitly the number of arguments the
* function takes). *)
type proto =
| Prototype of string * string array
| BinOpPrototype of string * string array * int
(* func - This type represents a function definition itself. *)
type func = Function of proto * expr
</pre>
</dd>
<dt>parser.ml:</dt>
<dd class="doc_code">
<pre>
(*===---------------------------------------------------------------------===
* Parser
*===---------------------------------------------------------------------===*)
(* binop_precedence - This holds the precedence for each binary operator that is
* defined *)
let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
(* precedence - Get the precedence of the pending binary operator token. *)
let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
(* primary
* ::= identifier
* ::= numberexpr
* ::= parenexpr
* ::= ifexpr
* ::= forexpr *)
let rec parse_primary = parser
(* numberexpr ::= number *)
| [< 'Token.Number n >] -> Ast.Number n
(* parenexpr ::= '(' expression ')' *)
| [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
(* identifierexpr
* ::= identifier
* ::= identifier '(' argumentexpr ')' *)
| [< 'Token.Ident id; stream >] ->
let rec parse_args accumulator = parser
| [< e=parse_expr; stream >] ->
begin parser
| [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
| [< >] -> e :: accumulator
end stream
| [< >] -> accumulator
in
let rec parse_ident id = parser
(* Call. *)
| [< 'Token.Kwd '(';
args=parse_args [];
'Token.Kwd ')' ?? "expected ')'">] ->
Ast.Call (id, Array.of_list (List.rev args))
(* Simple variable ref. *)
| [< >] -> Ast.Variable id
in
parse_ident id stream
(* ifexpr ::= 'if' expr 'then' expr 'else' expr *)
| [< 'Token.If; c=parse_expr;
'Token.Then ?? "expected 'then'"; t=parse_expr;
'Token.Else ?? "expected 'else'"; e=parse_expr >] ->
Ast.If (c, t, e)
(* forexpr
::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression *)
| [< 'Token.For;
'Token.Ident id ?? "expected identifier after for";
'Token.Kwd '=' ?? "expected '=' after for";
stream >] ->
begin parser
| [<
start=parse_expr;
'Token.Kwd ',' ?? "expected ',' after for";
end_=parse_expr;
stream >] ->
let step =
begin parser
| [< 'Token.Kwd ','; step=parse_expr >] -> Some step
| [< >] -> None
end stream
in
begin parser
| [< 'Token.In; body=parse_expr >] ->
Ast.For (id, start, end_, step, body)
| [< >] ->
raise (Stream.Error "expected 'in' after for")
end stream
| [< >] ->
raise (Stream.Error "expected '=' after for")
end stream
| [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
(* unary
* ::= primary
* ::= '!' unary *)
and parse_unary = parser
(* If this is a unary operator, read it. *)
| [< 'Token.Kwd op when op != '(' && op != ')'; operand=parse_expr >] ->
Ast.Unary (op, operand)
(* If the current token is not an operator, it must be a primary expr. *)
| [< stream >] -> parse_primary stream
(* binoprhs
* ::= ('+' primary)* *)
and parse_bin_rhs expr_prec lhs stream =
match Stream.peek stream with
(* If this is a binop, find its precedence. *)
| Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
let token_prec = precedence c in
(* If this is a binop that binds at least as tightly as the current binop,
* consume it, otherwise we are done. *)
if token_prec < expr_prec then lhs else begin
(* Eat the binop. *)
Stream.junk stream;
(* Parse the unary expression after the binary operator. *)
let rhs = parse_unary stream in
(* Okay, we know this is a binop. *)
let rhs =
match Stream.peek stream with
| Some (Token.Kwd c2) ->
(* If BinOp binds less tightly with rhs than the operator after
* rhs, let the pending operator take rhs as its lhs. *)
let next_prec = precedence c2 in
if token_prec < next_prec
then parse_bin_rhs (token_prec + 1) rhs stream
else rhs
| _ -> rhs
in
(* Merge lhs/rhs. *)
let lhs = Ast.Binary (c, lhs, rhs) in
parse_bin_rhs expr_prec lhs stream
end
| _ -> lhs
(* expression
* ::= primary binoprhs *)
and parse_expr = parser
| [< lhs=parse_unary; stream >] -> parse_bin_rhs 0 lhs stream
(* prototype
* ::= id '(' id* ')'
* ::= binary LETTER number? (id, id)
* ::= unary LETTER number? (id) *)
let parse_prototype =
let rec parse_args accumulator = parser
| [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
| [< >] -> accumulator
in
let parse_operator = parser
| [< 'Token.Unary >] -> "unary", 1
| [< 'Token.Binary >] -> "binary", 2
in
let parse_binary_precedence = parser
| [< 'Token.Number n >] -> int_of_float n
| [< >] -> 30
in
parser
| [< 'Token.Ident id;
'Token.Kwd '(' ?? "expected '(' in prototype";
args=parse_args [];
'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
(* success. *)
Ast.Prototype (id, Array.of_list (List.rev args))
| [< (prefix, kind)=parse_operator;
'Token.Kwd op ?? "expected an operator";
(* Read the precedence if present. *)
binary_precedence=parse_binary_precedence;
'Token.Kwd '(' ?? "expected '(' in prototype";
args=parse_args [];
'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
let name = prefix ^ (String.make 1 op) in
let args = Array.of_list (List.rev args) in
(* Verify right number of arguments for operator. *)
if Array.length args != kind
then raise (Stream.Error "invalid number of operands for operator")
else
if kind == 1 then
Ast.Prototype (name, args)
else
Ast.BinOpPrototype (name, args, binary_precedence)
| [< >] ->
raise (Stream.Error "expected function name in prototype")
(* definition ::= 'def' prototype expression *)
let parse_definition = parser
| [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
Ast.Function (p, e)
(* toplevelexpr ::= expression *)
let parse_toplevel = parser
| [< e=parse_expr >] ->
(* Make an anonymous proto. *)
Ast.Function (Ast.Prototype ("", [||]), e)
(* external ::= 'extern' prototype *)
let parse_extern = parser
| [< 'Token.Extern; e=parse_prototype >] -> e
</pre>
</dd>
<dt>codegen.ml:</dt>
<dd class="doc_code">
<pre>
(*===----------------------------------------------------------------------===
* Code Generation
*===----------------------------------------------------------------------===*)
open Llvm
exception Error of string
let context = global_context ()
let the_module = create_module context "my cool jit"
let builder = builder context
let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
let double_type = double_type context
let rec codegen_expr = function
| Ast.Number n -> const_float double_type n
| Ast.Variable name ->
(try Hashtbl.find named_values name with
| Not_found -> raise (Error "unknown variable name"))
| Ast.Unary (op, operand) ->
let operand = codegen_expr operand in
let callee = "unary" ^ (String.make 1 op) in
let callee =
match lookup_function callee the_module with
| Some callee -> callee
| None -> raise (Error "unknown unary operator")
in
build_call callee [|operand|] "unop" builder
| Ast.Binary (op, lhs, rhs) ->
let lhs_val = codegen_expr lhs in
let rhs_val = codegen_expr rhs in
begin
match op with
| '+' -> build_add lhs_val rhs_val "addtmp" builder
| '-' -> build_sub lhs_val rhs_val "subtmp" builder
| '*' -> build_mul lhs_val rhs_val "multmp" builder
| '<' ->
(* Convert bool 0/1 to double 0.0 or 1.0 *)
let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
build_uitofp i double_type "booltmp" builder
| _ ->
(* If it wasn't a builtin binary operator, it must be a user defined
* one. Emit a call to it. *)
let callee = "binary" ^ (String.make 1 op) in
let callee =
match lookup_function callee the_module with
| Some callee -> callee
| None -> raise (Error "binary operator not found!")
in
build_call callee [|lhs_val; rhs_val|] "binop" builder
end
| Ast.Call (callee, args) ->
(* Look up the name in the module table. *)
let callee =
match lookup_function callee the_module with
| Some callee -> callee
| None -> raise (Error "unknown function referenced")
in
let params = params callee in
(* If argument mismatch error. *)
if Array.length params == Array.length args then () else
raise (Error "incorrect # arguments passed");
let args = Array.map codegen_expr args in
build_call callee args "calltmp" builder
| Ast.If (cond, then_, else_) ->
let cond = codegen_expr cond in
(* Convert condition to a bool by comparing equal to 0.0 *)
let zero = const_float double_type 0.0 in
let cond_val = build_fcmp Fcmp.One cond zero "ifcond" builder in
(* Grab the first block so that we might later add the conditional branch
* to it at the end of the function. *)
let start_bb = insertion_block builder in
let the_function = block_parent start_bb in
let then_bb = append_block context "then" the_function in
(* Emit 'then' value. *)
position_at_end then_bb builder;
let then_val = codegen_expr then_ in
(* Codegen of 'then' can change the current block, update then_bb for the
* phi. We create a new name because one is used for the phi node, and the
* other is used for the conditional branch. *)
let new_then_bb = insertion_block builder in
(* Emit 'else' value. *)
let else_bb = append_block context "else" the_function in
position_at_end else_bb builder;
let else_val = codegen_expr else_ in
(* Codegen of 'else' can change the current block, update else_bb for the
* phi. *)
let new_else_bb = insertion_block builder in
(* Emit merge block. *)
let merge_bb = append_block context "ifcont" the_function in
position_at_end merge_bb builder;
let incoming = [(then_val, new_then_bb); (else_val, new_else_bb)] in
let phi = build_phi incoming "iftmp" builder in
(* Return to the start block to add the conditional branch. *)
position_at_end start_bb builder;
ignore (build_cond_br cond_val then_bb else_bb builder);
(* Set a unconditional branch at the end of the 'then' block and the
* 'else' block to the 'merge' block. *)
position_at_end new_then_bb builder; ignore (build_br merge_bb builder);
position_at_end new_else_bb builder; ignore (build_br merge_bb builder);
(* Finally, set the builder to the end of the merge block. *)
position_at_end merge_bb builder;
phi
| Ast.For (var_name, start, end_, step, body) ->
(* Emit the start code first, without 'variable' in scope. *)
let start_val = codegen_expr start in
(* Make the new basic block for the loop header, inserting after current
* block. *)
let preheader_bb = insertion_block builder in
let the_function = block_parent preheader_bb in
let loop_bb = append_block context "loop" the_function in
(* Insert an explicit fall through from the current block to the
* loop_bb. *)
ignore (build_br loop_bb builder);
(* Start insertion in loop_bb. *)
position_at_end loop_bb builder;
(* Start the PHI node with an entry for start. *)
let variable = build_phi [(start_val, preheader_bb)] var_name builder in
(* Within the loop, the variable is defined equal to the PHI node. If it
* shadows an existing variable, we have to restore it, so save it
* now. *)
let old_val =
try Some (Hashtbl.find named_values var_name) with Not_found -> None
in
Hashtbl.add named_values var_name variable;
(* Emit the body of the loop. This, like any other expr, can change the
* current BB. Note that we ignore the value computed by the body, but
* don't allow an error *)
ignore (codegen_expr body);
(* Emit the step value. *)
let step_val =
match step with
| Some step -> codegen_expr step
(* If not specified, use 1.0. *)
| None -> const_float double_type 1.0
in
let next_var = build_add variable step_val "nextvar" builder in
(* Compute the end condition. *)
let end_cond = codegen_expr end_ in
(* Convert condition to a bool by comparing equal to 0.0. *)
let zero = const_float double_type 0.0 in
let end_cond = build_fcmp Fcmp.One end_cond zero "loopcond" builder in
(* Create the "after loop" block and insert it. *)
let loop_end_bb = insertion_block builder in
let after_bb = append_block context "afterloop" the_function in
(* Insert the conditional branch into the end of loop_end_bb. *)
ignore (build_cond_br end_cond loop_bb after_bb builder);
(* Any new code will be inserted in after_bb. *)
position_at_end after_bb builder;
(* Add a new entry to the PHI node for the backedge. *)
add_incoming (next_var, loop_end_bb) variable;
(* Restore the unshadowed variable. *)
begin match old_val with
| Some old_val -> Hashtbl.add named_values var_name old_val
| None -> ()
end;
(* for expr always returns 0.0. *)
const_null double_type
let codegen_proto = function
| Ast.Prototype (name, args) | Ast.BinOpPrototype (name, args, _) ->
(* Make the function type: double(double,double) etc. *)
let doubles = Array.make (Array.length args) double_type in
let ft = function_type double_type doubles in
let f =
match lookup_function name the_module with
| None -> declare_function name ft the_module
(* If 'f' conflicted, there was already something named 'name'. If it
* has a body, don't allow redefinition or reextern. *)
| Some f ->
(* If 'f' already has a body, reject this. *)
if block_begin f <> At_end f then
raise (Error "redefinition of function");
(* If 'f' took a different number of arguments, reject. *)
if element_type (type_of f) <> ft then
raise (Error "redefinition of function with different # args");
f
in
(* Set names for all arguments. *)
Array.iteri (fun i a ->
let n = args.(i) in
set_value_name n a;
Hashtbl.add named_values n a;
) (params f);
f
let codegen_func the_fpm = function
| Ast.Function (proto, body) ->
Hashtbl.clear named_values;
let the_function = codegen_proto proto in
(* If this is an operator, install it. *)
begin match proto with
| Ast.BinOpPrototype (name, args, prec) ->
let op = name.[String.length name - 1] in
Hashtbl.add Parser.binop_precedence op prec;
| _ -> ()
end;
(* Create a new basic block to start insertion into. *)
let bb = append_block context "entry" the_function in
position_at_end bb builder;
try
let ret_val = codegen_expr body in
(* Finish off the function. *)
let _ = build_ret ret_val builder in
(* Validate the generated code, checking for consistency. *)
Llvm_analysis.assert_valid_function the_function;
(* Optimize the function. *)
let _ = PassManager.run_function the_function the_fpm in
the_function
with e ->
delete_function the_function;
raise e
</pre>
</dd>
<dt>toplevel.ml:</dt>
<dd class="doc_code">
<pre>
(*===----------------------------------------------------------------------===
* Top-Level parsing and JIT Driver
*===----------------------------------------------------------------------===*)
open Llvm
open Llvm_executionengine
(* top ::= definition | external | expression | ';' *)
let rec main_loop the_fpm the_execution_engine stream =
match Stream.peek stream with
| None -> ()
(* ignore top-level semicolons. *)
| Some (Token.Kwd ';') ->
Stream.junk stream;
main_loop the_fpm the_execution_engine stream
| Some token ->
begin
try match token with
| Token.Def ->
let e = Parser.parse_definition stream in
print_endline "parsed a function definition.";
dump_value (Codegen.codegen_func the_fpm e);
| Token.Extern ->
let e = Parser.parse_extern stream in
print_endline "parsed an extern.";
dump_value (Codegen.codegen_proto e);
| _ ->
(* Evaluate a top-level expression into an anonymous function. *)
let e = Parser.parse_toplevel stream in
print_endline "parsed a top-level expr";
let the_function = Codegen.codegen_func the_fpm e in
dump_value the_function;
(* JIT the function, returning a function pointer. *)
let result = ExecutionEngine.run_function the_function [||]
the_execution_engine in
print_string "Evaluated to ";
print_float (GenericValue.as_float Codegen.double_type result);
print_newline ();
with Stream.Error s | Codegen.Error s ->
(* Skip token for error recovery. *)
Stream.junk stream;
print_endline s;
end;
print_string "ready> "; flush stdout;
main_loop the_fpm the_execution_engine stream
</pre>
</dd>
<dt>toy.ml:</dt>
<dd class="doc_code">
<pre>
(*===----------------------------------------------------------------------===
* Main driver code.
*===----------------------------------------------------------------------===*)
open Llvm
open Llvm_executionengine
open Llvm_target
open Llvm_scalar_opts
let main () =
ignore (initialize_native_target ());
(* Install standard binary operators.
* 1 is the lowest precedence. *)
Hashtbl.add Parser.binop_precedence '<' 10;
Hashtbl.add Parser.binop_precedence '+' 20;
Hashtbl.add Parser.binop_precedence '-' 20;
Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *)
(* Prime the first token. *)
print_string "ready> "; flush stdout;
let stream = Lexer.lex (Stream.of_channel stdin) in
(* Create the JIT. *)
let the_execution_engine = ExecutionEngine.create Codegen.the_module in
let the_fpm = PassManager.create_function Codegen.the_module in
(* Set up the optimizer pipeline. Start with registering info about how the
* target lays out data structures. *)
DataLayout.add (ExecutionEngine.target_data the_execution_engine) the_fpm;
(* Do simple "peephole" optimizations and bit-twiddling optzn. *)
add_instruction_combination the_fpm;
(* reassociate expressions. *)
add_reassociation the_fpm;
(* Eliminate Common SubExpressions. *)
add_gvn the_fpm;
(* Simplify the control flow graph (deleting unreachable blocks, etc). *)
add_cfg_simplification the_fpm;
ignore (PassManager.initialize the_fpm);
(* Run the main "interpreter loop" now. *)
Toplevel.main_loop the_fpm the_execution_engine stream;
(* Print out all the generated code. *)
dump_module Codegen.the_module
;;
main ()
</pre>
</dd>
<dt>bindings.c</dt>
<dd class="doc_code">
<pre>
#include <stdio.h>
/* putchard - putchar that takes a double and returns 0. */
extern double putchard(double X) {
putchar((char)X);
return 0;
}
/* printd - printf that takes a double prints it as "%f\n", returning 0. */
extern double printd(double X) {
printf("%f\n", X);
return 0;
}
</pre>
</dd>
</dl>
<a href="OCamlLangImpl7.html">Next: Extending the language: mutable variables /
SSA construction</a>
</div>
<!-- *********************************************************************** -->
<hr>
<address>
<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
<a href="http://validator.w3.org/check/referer"><img
src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
<a href="mailto:idadesub@users.sourceforge.net">Erick Tryzelaar</a><br>
<a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
Last modified: $Date: 2012-10-08 18:39:34 +0200 (Mon, 08 Oct 2012) $
</address>
</body>
</html>
|
