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
|
; RUN: llc -mtriple=x86_64-apple-macosx -O3 -debug-only=faultmaps -enable-implicit-null-checks < %s 2>&1 | FileCheck %s
; REQUIRES: asserts
; List cases where we should *not* be emitting implicit null checks.
; CHECK-NOT: Fault Map Output
define i32 @imp_null_check_load(i32* %x, i32* %y) {
entry:
%c = icmp eq i32* %x, null
; It isn't legal to move the load from %x from "not_null" to here --
; the store to %y could be aliasing it.
br i1 %c, label %is_null, label %not_null, !make.implicit !0
is_null:
ret i32 42
not_null:
store i32 0, i32* %y
%t = load i32, i32* %x
ret i32 %t
}
define i32 @imp_null_check_gep_load(i32* %x) {
entry:
%c = icmp eq i32* %x, null
br i1 %c, label %is_null, label %not_null, !make.implicit !0
is_null:
ret i32 42
not_null:
; null + 5000 * sizeof(i32) lies outside the null page and hence the
; load to %t cannot be assumed to be reliably faulting.
%x.gep = getelementptr i32, i32* %x, i32 5000
%t = load i32, i32* %x.gep
ret i32 %t
}
define i32 @imp_null_check_neg_gep_load(i32* %x) {
entry:
%c = icmp eq i32* %x, null
br i1 %c, label %is_null, label %not_null, !make.implicit !0
is_null:
ret i32 42
not_null:
; null - 5000 * sizeof(i32) lies outside the null page and hence the
; load to %t cannot be assumed to be reliably faulting.
%x.gep = getelementptr i32, i32* %x, i32 -5000
%t = load i32, i32* %x.gep
ret i32 %t
}
define i32 @imp_null_check_load_no_md(i32* %x) {
; This is fine, except it is missing the !make.implicit metadata.
entry:
%c = icmp eq i32* %x, null
br i1 %c, label %is_null, label %not_null
is_null:
ret i32 42
not_null:
%t = load i32, i32* %x
ret i32 %t
}
define i32 @imp_null_check_no_hoist_over_acquire_load(i32* %x, i32* %y) {
; We cannot hoist %t1 over %t0 since %t0 is an acquire load
entry:
%c = icmp eq i32* %x, null
br i1 %c, label %is_null, label %not_null, !make.implicit !0
is_null:
ret i32 42
not_null:
%t0 = load atomic i32, i32* %y acquire, align 4
%t1 = load i32, i32* %x
%p = add i32 %t0, %t1
ret i32 %p
}
define i32 @imp_null_check_add_result(i32* %x, i32* %y) {
; This will codegen to:
;
; movl (%rsi), %eax
; addl (%rdi), %eax
;
; The load instruction we wish to hoist is the addl, but there is a
; write-after-write hazard preventing that from happening. We could
; get fancy here and exploit the commutativity of addition, but right
; now -implicit-null-checks isn't that smart.
;
entry:
%c = icmp eq i32* %x, null
br i1 %c, label %is_null, label %not_null, !make.implicit !0
is_null:
ret i32 42
not_null:
%t0 = load i32, i32* %y
%t1 = load i32, i32* %x
%p = add i32 %t0, %t1
ret i32 %p
}
; This redefines the null check reg by doing a zero-extend, a shift on
; itself and then an add.
; Cannot be converted to implicit check since the zero reg is no longer zero.
define i64 @imp_null_check_load_shift_add_addr(i64* %x, i64 %r) {
entry:
%c = icmp eq i64* %x, null
br i1 %c, label %is_null, label %not_null, !make.implicit !0
is_null:
ret i64 42
not_null:
%y = ptrtoint i64* %x to i64
%shry = shl i64 %y, 6
%shry.add = add i64 %shry, %r
%y.ptr = inttoptr i64 %shry.add to i64*
%x.loc = getelementptr i64, i64* %y.ptr, i64 1
%t = load i64, i64* %x.loc
ret i64 %t
}
; the memory op is not within faulting page.
define i64 @imp_null_check_load_addr_outside_faulting_page(i64* %x) {
entry:
%c = icmp eq i64* %x, null
br i1 %c, label %is_null, label %not_null, !make.implicit !0
is_null:
ret i64 42
not_null:
%y = ptrtoint i64* %x to i64
%shry = shl i64 %y, 3
%shry.add = add i64 %shry, 68719472640
%y.ptr = inttoptr i64 %shry.add to i64*
%x.loc = getelementptr i64, i64* %y.ptr, i64 1
%t = load i64, i64* %x.loc
ret i64 %t
}
!0 = !{}
|
