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
|
; RUN: opt -basicaa -loop-accesses -analyze < %s | FileCheck %s
; RUN: opt -passes='require<scalar-evolution>,require<aa>,loop(print-access-info)' -disable-output < %s 2>&1 | FileCheck %s
; This loop:
;
; int **A;
; for (i)
; for (j) {
; A[i][j] = A[i-1][j] * B[j]
; B[j+1] = 2 // backward dep between this and the previous
; }
;
; is transformed by Load-PRE to stash away A[i] for the next iteration of the
; outer loop:
;
; Curr = A[0]; // Prev_0
; for (i: 1..N) {
; Prev = Curr; // Prev = PHI (Prev_0, Curr)
; Curr = A[i];
; for (j: 0..N) {
; Curr[j] = Prev[j] * B[j]
; B[j+1] = 2 // backward dep between this and the previous
; }
; }
;
; Since A[i] and A[i-1] are likely to be independent, getUnderlyingObjects
; should not assume that Curr and Prev share the same underlying object.
;
; If it did we would try to dependence-analyze Curr and Prev and the analysis
; would fail with non-constant distance.
;
; To illustrate one of the negative consequences of this, if the loop has a
; backward dependence we won't detect this but instead fully fall back on
; memchecks (that is what LAA does after encountering a case of non-constant
; distance).
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.10.0"
; CHECK: for_j.body:
; CHECK-NEXT: Report: unsafe dependent memory operations in loop
; CHECK-NEXT: Dependences:
; CHECK-NEXT: Backward:
; CHECK-NEXT: %loadB = load i8, i8* %gepB, align 1 ->
; CHECK-NEXT: store i8 2, i8* %gepB_plus_one, align 1
define void @f(i8** noalias %A, i8* noalias %B, i64 %N) {
for_i.preheader:
%prev_0 = load i8*, i8** %A, align 8
br label %for_i.body
for_i.body:
%i = phi i64 [1, %for_i.preheader], [%i.1, %for_j.end]
%prev = phi i8* [%prev_0, %for_i.preheader], [%curr, %for_j.end]
%gep = getelementptr inbounds i8*, i8** %A, i64 %i
%curr = load i8*, i8** %gep, align 8
br label %for_j.preheader
for_j.preheader:
br label %for_j.body
for_j.body:
%j = phi i64 [0, %for_j.preheader], [%j.1, %for_j.body]
%gepPrev = getelementptr inbounds i8, i8* %prev, i64 %j
%gepCurr = getelementptr inbounds i8, i8* %curr, i64 %j
%gepB = getelementptr inbounds i8, i8* %B, i64 %j
%loadPrev = load i8, i8* %gepPrev, align 1
%loadB = load i8, i8* %gepB, align 1
%mul = mul i8 %loadPrev, %loadB
store i8 %mul, i8* %gepCurr, align 1
%gepB_plus_one = getelementptr inbounds i8, i8* %gepB, i64 1
store i8 2, i8* %gepB_plus_one, align 1
%j.1 = add nuw i64 %j, 1
%exitcondj = icmp eq i64 %j.1, %N
br i1 %exitcondj, label %for_j.end, label %for_j.body
for_j.end:
%i.1 = add nuw i64 %i, 1
%exitcond = icmp eq i64 %i.1, %N
br i1 %exitcond, label %for_i.end, label %for_i.body
for_i.end:
ret void
}
|
