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
| ; RUN: opt < %s -loop-deletion -verify-dom-info -S | FileCheck %s
; Checking that we can delete loops that are never executed.
; We do not change the constant conditional branch statement (where the not-taken target
; is the loop) to an unconditional one.
; delete the infinite loop because it is never executed.
define void @test1(i64 %n, i64 %m) nounwind {
; CHECK-LABEL: test1
; CHECK-LABEL: entry:
; CHECK-NEXT: br i1 true, label %return, label %bb.preheader
; CHECK-NOT: bb:
entry:
br i1 true, label %return, label %bb
bb:
%x.0 = phi i64 [ 0, %entry ], [ %t0, %bb ]
%t0 = add i64 %x.0, 1
%t1 = icmp slt i64 %x.0, %n
%t3 = icmp sgt i64 %x.0, %m
%t4 = and i1 %t1, %t3
br i1 true, label %bb, label %return
return:
ret void
}
; FIXME: We can delete this infinite loop. Currently we do not,
; because the infinite loop has no exit block.
define void @test2(i64 %n, i64 %m) nounwind {
; CHECK-LABEL: test2
; CHECK-LABEL: entry:
; CHECK-NEXT: br i1 true, label %return, label %bb.preheader
; CHECK-LABEL: bb:
; CHECK: br label %bb
entry:
br i1 true, label %return, label %bb
bb:
%x.0 = phi i64 [ 0, %entry ], [ %t0, %bb ]
%t0 = add i64 %x.0, 1
%t1 = icmp slt i64 %x.0, %n
%t3 = icmp sgt i64 %x.0, %m
%t4 = and i1 %t1, %t3
br label %bb
return:
ret void
}
; There are multiple exiting blocks and a single exit block.
; Since it is a never executed loop, we do not care about the values
; from different exiting paths and we can
; delete the loop.
define i64 @test3(i64 %n, i64 %m, i64 %maybe_zero) nounwind {
; CHECK-NOT: bb:
; CHECK-NOT: bb2:
; CHECK-NOT: bb3:
; CHECK-LABEL: return.loopexit:
; CHECK-NEXT: %x.lcssa.ph = phi i64 [ undef, %bb.preheader ]
; CHECK-NEXT: br label %return
; CHECK-LABEL: return:
; CHECK-NEXT: %x.lcssa = phi i64 [ 20, %entry ], [ %x.lcssa.ph, %return.loopexit ]
; CHECK-NEXT: ret i64 %x.lcssa
entry:
br i1 false, label %bb, label %return
bb:
%x.0 = phi i64 [ 0, %entry ], [ %t0, %bb3 ]
%t0 = add i64 %x.0, 1
%t1 = icmp slt i64 %x.0, %n
br i1 %t1, label %bb2, label %return
bb2:
%t2 = icmp slt i64 %x.0, %m
%unused1 = udiv i64 42, %maybe_zero
br i1 %t2, label %bb3, label %return
bb3:
%t3 = icmp slt i64 %x.0, %m
%unused2 = sdiv i64 42, %maybe_zero
br i1 %t3, label %bb, label %return
return:
; the only valid value fo x.lcssa is 20.
%x.lcssa = phi i64 [ 12, %bb ], [ 14, %bb2 ], [ 16, %bb3 ], [20, %entry ]
ret i64 %x.lcssa
}
; Cannot delete the loop, since it may be executed at runtime.
define void @test4(i64 %n, i64 %m, i1 %cond) {
; CHECK-LABEL: test4
; CHECK-LABEL: bb:
entry:
br i1 %cond, label %looppred1, label %looppred2
looppred1:
br i1 true, label %return, label %bb
looppred2:
br i1 false, label %return, label %bb
bb:
%x.0 = phi i64 [ 0, %looppred1 ], [ 1, %looppred2 ], [ %t0, %bb ]
%t0 = add i64 %x.0, 1
%t1 = icmp slt i64 %x.0, %n
%t3 = icmp sgt i64 %x.0, %m
%t4 = and i1 %t1, %t3
br i1 true, label %bb, label %return
return:
ret void
}
; multiple constant conditional branches with loop not-taken in all cases.
define void @test5(i64 %n, i64 %m, i1 %cond) nounwind {
; CHECK-LABEL: test5
; CHECK-LABEL: looppred1:
; CHECK-NEXT: br i1 true, label %return, label %bb.preheader
; CHECK-LABEL: looppred2:
; CHECK-NEXT: br i1 true, label %return, label %bb.preheader
; CHECK-NOT: bb:
entry:
br i1 %cond, label %looppred1, label %looppred2
looppred1:
br i1 true, label %return, label %bb
looppred2:
br i1 true, label %return, label %bb
bb:
%x.0 = phi i64 [ 0, %looppred1 ], [ 1, %looppred2 ], [ %t0, %bb ]
%t0 = add i64 %x.0, 1
%t1 = icmp slt i64 %x.0, %n
%t3 = icmp sgt i64 %x.0, %m
%t4 = and i1 %t1, %t3
br i1 true, label %bb, label %return
return:
ret void
}
; Don't delete this infinite loop because the loop
; is executable at runtime.
define void @test6(i64 %n, i64 %m) nounwind {
; CHECK-LABEL: test6
; CHECK-LABEL: entry:
; CHECK-NEXT: br i1 true, label %bb.preheader, label %bb.preheader
; CHECK: bb:
entry:
br i1 true, label %bb, label %bb
bb:
%x.0 = phi i64 [ 0, %entry ], [ 0, %entry ], [ %t0, %bb ]
%t0 = add i64 %x.0, 1
%t1 = icmp slt i64 %x.0, %n
%t3 = icmp sgt i64 %x.0, %m
%t4 = and i1 %t1, %t3
br i1 true, label %bb, label %return
return:
ret void
}
declare i64 @foo(i64)
; The loop L2 is never executed and is a subloop, with an
; exit block that branches back to parent loop.
; Here we can delete loop L2, while L1 still exists.
define i64 @test7(i64 %n) {
; CHECK-LABEL: test7
; CHECK-LABEL: L1:
; CHECK: br i1 true, label %L1Latch, label %L2.preheader
; CHECK-LABEL: L2.preheader:
; CHECK-NEXT: br label %L1Latch.loopexit
; CHECK-LABEL: L1Latch.loopexit:
; CHECK: br label %L1Latch
; CHECK-LABEL: L1Latch:
; CHECK-NEXT: %y = phi i64 [ %y.next, %L1 ], [ %y.L2.lcssa, %L1Latch.loopexit ]
; CHECK: br i1 %cond2, label %exit, label %L1
entry:
br label %L1
L1:
%y.next = phi i64 [ 0, %entry ], [ %y.add, %L1Latch ]
br i1 true, label %L1Latch, label %L2
L2:
%x = phi i64 [ 0, %L1 ], [ %x.next, %L2 ]
%x.next = add i64 %x, 1
%y.L2 = call i64 @foo(i64 %x.next)
%cond = icmp slt i64 %x.next, %n
br i1 %cond, label %L2, label %L1Latch
L1Latch:
%y = phi i64 [ %y.next, %L1 ], [ %y.L2, %L2 ]
%y.add = add i64 %y, %n
%cond2 = icmp eq i64 %y.add, 42
br i1 %cond2, label %exit, label %L1
exit:
ret i64 %y.add
}
; Show recursive deletion of loops. Since we start with subloops and progress outward
; to parent loop, we first delete the loop L2. Now loop L1 becomes a non-loop since it's backedge
; from L2's preheader to L1's exit block is never taken. So, L1 gets deleted as well.
define void @test8(i64 %n) {
; CHECK-LABEL: test8
; CHECK-LABEL: entry:
; CHECK-NEXT: br label %exit
; CHECK-LABEL: exit:
; CHECK-NEXT: ret void
entry:
br label %L1
L1:
br i1 true, label %exit, label %L2
L2:
%x = phi i64 [ 0, %L1 ], [ %x.next, %L2 ]
%x.next = add i64 %x, 1
%y.L2 = call i64 @foo(i64 %x.next)
%cond = icmp slt i64 %x.next, %n
br i1 %cond, label %L2, label %L1
exit:
ret void
}
; Delete a loop (L2) which has subloop (L3).
; Here we delete loop L2, but leave L3 as is.
; FIXME: Can delete L3 as well, by iteratively going backward through the single
; predecessor of L3 until we reach L1's block that guarantees L3 is never
; executed.
define void @test9(i64 %n) {
; CHECK-LABEL: test9
; CHECK-LABEL: L2.preheader:
; CHECK-NEXT: br label %L3.preheader
; CHECK-NOT: L2:
; CHECK-LABEL: L3.preheader:
; CHECK-NEXT: %y.L2.lcssa = phi i64 [ undef, %L2.preheader ]
; CHECK-NEXT: br label %L3
; CHECK-LABEL: L3:
; CHECK: br i1 %cond2, label %L3, label %L1.loopexit
entry:
br label %L1
L1:
br i1 true, label %exit, label %L2
L2:
%x = phi i64 [ 0, %L1 ], [ %x.next, %L2 ]
%x.next = add i64 %x, 1
%y.L2 = call i64 @foo(i64 %x.next)
%cond = icmp slt i64 %x.next, %n
br i1 %cond, label %L2, label %L3
L3:
%cond2 = icmp slt i64 %y.L2, %n
br i1 %cond2, label %L3, label %L1
exit:
ret void
}
; We cannot delete L3 because of call within it.
; Since L3 is not deleted, and entirely contained within L2, L2 is also not
; deleted.
; FIXME: We can delete unexecutable loops having
; subloops contained entirely within them.
define void @test10(i64 %n) {
; CHECK-LABEL: test10
; CHECK: L2:
; CHECK: L3:
entry:
br label %L1
L1:
br i1 true, label %exit, label %L2
L2:
%x = phi i64 [ 0, %L1 ], [ %x.next, %L3 ]
%x.next = add i64 %x, 1
%y.L2 = call i64 @foo(i64 %x.next)
%cond = icmp slt i64 %x.next, %n
br i1 %cond, label %L1, label %L3
L3:
%y.L3 = phi i64 [ %y.L2, %L2 ], [ %y.L3.next, %L3 ]
%y.L3.next = add i64 %y.L3, 1
%dummy = call i64 @foo(i64 %y.L3.next)
%cond2 = icmp slt i64 %y.L3, %n
br i1 %cond2, label %L3, label %L2
exit:
ret void
}
; same as test10, but L3 does not contain call.
; So, in the first iteration, all statements of L3 are made invariant, and L3 is
; deleted.
; In the next iteration, since L2 is never executed and has no subloops, we delete
; L2 as well. Finally, the outermost loop L1 is deleted.
define void @test11(i64 %n) {
; CHECK-LABEL: test11
; CHECK-LABEL: entry:
; CHECK-NEXT: br label %exit
; CHECK-LABEL: exit:
; CHECK-NEXT: ret void
entry:
br label %L1
L1:
br i1 true, label %exit, label %L2
L2:
%x = phi i64 [ 0, %L1 ], [ %x.next, %L3 ]
%x.next = add i64 %x, 1
%y.L2 = call i64 @foo(i64 %x.next)
%cond = icmp slt i64 %x.next, %n
br i1 %cond, label %L1, label %L3
L3:
%y.L3 = phi i64 [ %y.L2, %L2 ], [ %y.L3.next, %L3 ]
%y.L3.next = add i64 %y.L3, 1
%cond2 = icmp slt i64 %y.L3, %n
br i1 %cond2, label %L3, label %L2
exit:
ret void
}
; 2 edges from a single exiting block to the exit block.
define i64 @test12(i64 %n){
;CHECK-LABEL: @test12
; CHECK-NOT: L1:
; CHECK-NOT: L1Latch:
; CHECK-LABEL: L1.preheader:
; CHECK-NEXT: br label %exit
; CHECK-LABEL: exit:
; CHECK-NEXT: %y.phi = phi i64 [ undef, %L1.preheader ]
; CHECK-NEXT: ret i64 %y.phi
entry:
br i1 true, label %exit1, label %L1
exit1:
ret i64 42
L1: ; preds = %L1Latch, %entry
%y.next = phi i64 [ 0, %entry ], [ %y.add, %L1Latch ]
br i1 true, label %L1Latch, label %exit
L1Latch: ; preds = %L1
%y = phi i64 [ %y.next, %L1 ]
%y.add = add i64 %y, %n
%cond2 = icmp eq i64 %y.add, 42
switch i64 %n, label %L1 [
i64 10, label %exit
i64 20, label %exit
]
exit: ; preds = %L1Latch, %L1Latch
%y.phi = phi i64 [ 10, %L1Latch ], [ 10, %L1Latch ], [ %y.next, %L1]
ret i64 %y.phi
}
; multiple edges to exit block from the same exiting blocks
define i64 @test13(i64 %n) {
; CHECK-LABEL: @test13
; CHECK-NOT: L1:
; CHECK-NOT: L1Latch:
; CHECK-LABEL: L1.preheader:
; CHECK-NEXT: br label %exit
; CHECK-LABEL: exit:
; CHECK-NEXT: %y.phi = phi i64 [ undef, %L1.preheader ]
; CHECK-NEXT: ret i64 %y.phi
entry:
br i1 true, label %exit1, label %L1
exit1:
ret i64 42
L1: ; preds = %L1Latch, %entry
%y.next = phi i64 [ 0, %entry ], [ %y.add, %L1Latch ]
br i1 true, label %L1Block, label %exit
L1Block: ; preds = %L1
%y = phi i64 [ %y.next, %L1 ]
%y.add = add i64 %y, %n
%cond2 = icmp eq i64 %y.add, 42
switch i64 %n, label %L1Latch [
i64 10, label %exit
i64 20, label %exit
]
L1Latch:
switch i64 %n, label %L1 [
i64 30, label %exit
i64 40, label %exit
]
exit: ; preds = %L1Block, %L1, %L1Latch
%y.phi = phi i64 [ 10, %L1Block ], [ 10, %L1Block ], [ %y.next, %L1 ], [ 30, %L1Latch ], [ 30, %L1Latch ]
ret i64 %y.phi
}
|