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
|
; RUN: opt -S -basic-aa -dse < %s | FileCheck %s
; We conservative choose to prevent dead store elimination
; across release or stronger fences. It's not required
; (since the must still be a race on %addd.i), but
; it is conservatively correct. A legal optimization
; could hoist the second store above the fence, and then
; DSE one of them.
define void @test1(i32* %addr.i) {
; CHECK-LABEL: @test1
; CHECK: store i32 5
; CHECK: fence
; CHECK: store i32 5
; CHECK: ret
store i32 5, i32* %addr.i, align 4
fence release
store i32 5, i32* %addr.i, align 4
ret void
}
; Same as previous, but with different values. If we ever optimize
; this more aggressively, this allows us to check that the correct
; store is retained (the 'i32 1' store in this case)
define void @test1b(i32* %addr.i) {
; CHECK-LABEL: @test1b
; CHECK: store i32 42
; CHECK: fence release
; CHECK: store i32 1
; CHECK: ret
store i32 42, i32* %addr.i, align 4
fence release
store i32 1, i32* %addr.i, align 4
ret void
}
; We *could* DSE across this fence, but don't. No other thread can
; observe the order of the acquire fence and the store.
define void @test2(i32* %addr.i) {
; CHECK-LABEL: @test2
; CHECK: store
; CHECK: fence
; CHECK: store
; CHECK: ret
store i32 5, i32* %addr.i, align 4
fence acquire
store i32 5, i32* %addr.i, align 4
ret void
}
; We DSE stack alloc'ed and byval locations, in the presence of fences.
; Fence does not make an otherwise thread local store visible.
; Right now the DSE in presence of fence is only done in end blocks (with no successors),
; but the same logic applies to other basic blocks as well.
; The store to %addr.i can be removed since it is a byval attribute
define void @test3(i32* byval %addr.i) {
; CHECK-LABEL: @test3
; CHECK-NOT: store
; CHECK: fence
; CHECK: ret
store i32 5, i32* %addr.i, align 4
fence release
ret void
}
declare void @foo(i8* nocapture %p)
declare noalias i8* @malloc(i32)
; DSE of stores in locations allocated through library calls.
define void @test_nocapture() {
; CHECK-LABEL: @test_nocapture
; CHECK: malloc
; CHECK: foo
; CHECK-NOT: store
; CHECK: fence
%m = call i8* @malloc(i32 24)
call void @foo(i8* %m)
store i8 4, i8* %m
fence release
ret void
}
; This is a full fence, but it does not make a thread local store visible.
; We can DSE the store in presence of the fence.
define void @fence_seq_cst() {
; CHECK-LABEL: @fence_seq_cst
; CHECK-NEXT: fence seq_cst
; CHECK-NEXT: ret void
%P1 = alloca i32
store i32 0, i32* %P1, align 4
fence seq_cst
store i32 4, i32* %P1, align 4
ret void
}
|
