1 ; RUN: opt -basicaa -loop-accesses -analyze < %s | FileCheck %s 2 ; RUN: opt -passes='require<scalar-evolution>,require<aa>,loop(print-access-info)' -disable-output < %s 2>&1 | FileCheck %s 3 4 ; This loop: 5 ; 6 ; int **A; 7 ; for (i) 8 ; for (j) { 9 ; A[i][j] = A[i-1][j] * B[j] 10 ; B[j+1] = 2 // backward dep between this and the previous 11 ; } 12 ; 13 ; is transformed by Load-PRE to stash away A[i] for the next iteration of the 14 ; outer loop: 15 ; 16 ; Curr = A[0]; // Prev_0 17 ; for (i: 1..N) { 18 ; Prev = Curr; // Prev = PHI (Prev_0, Curr) 19 ; Curr = A[i]; 20 ; for (j: 0..N) { 21 ; Curr[j] = Prev[j] * B[j] 22 ; B[j+1] = 2 // backward dep between this and the previous 23 ; } 24 ; } 25 ; 26 ; Since A[i] and A[i-1] are likely to be independent, getUnderlyingObjects 27 ; should not assume that Curr and Prev share the same underlying object. 28 ; 29 ; If it did we would try to dependence-analyze Curr and Prev and the analysis 30 ; would fail with non-constant distance. 31 ; 32 ; To illustrate one of the negative consequences of this, if the loop has a 33 ; backward dependence we won't detect this but instead fully fall back on 34 ; memchecks (that is what LAA does after encountering a case of non-constant 35 ; distance). 36 37 target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128" 38 target triple = "x86_64-apple-macosx10.10.0" 39 40 ; CHECK: for_j.body: 41 ; CHECK-NEXT: Report: unsafe dependent memory operations in loop 42 ; CHECK-NEXT: Dependences: 43 ; CHECK-NEXT: Backward: 44 ; CHECK-NEXT: %loadB = load i8, i8* %gepB, align 1 -> 45 ; CHECK-NEXT: store i8 2, i8* %gepB_plus_one, align 1 46 47 define void @f(i8** noalias %A, i8* noalias %B, i64 %N) { 48 for_i.preheader: 49 %prev_0 = load i8*, i8** %A, align 8 50 br label %for_i.body 51 52 for_i.body: 53 %i = phi i64 [1, %for_i.preheader], [%i.1, %for_j.end] 54 %prev = phi i8* [%prev_0, %for_i.preheader], [%curr, %for_j.end] 55 %gep = getelementptr inbounds i8*, i8** %A, i64 %i 56 %curr = load i8*, i8** %gep, align 8 57 br label %for_j.preheader 58 59 for_j.preheader: 60 br label %for_j.body 61 62 for_j.body: 63 %j = phi i64 [0, %for_j.preheader], [%j.1, %for_j.body] 64 65 %gepPrev = getelementptr inbounds i8, i8* %prev, i64 %j 66 %gepCurr = getelementptr inbounds i8, i8* %curr, i64 %j 67 %gepB = getelementptr inbounds i8, i8* %B, i64 %j 68 69 %loadPrev = load i8, i8* %gepPrev, align 1 70 %loadB = load i8, i8* %gepB, align 1 71 72 %mul = mul i8 %loadPrev, %loadB 73 74 store i8 %mul, i8* %gepCurr, align 1 75 76 %gepB_plus_one = getelementptr inbounds i8, i8* %gepB, i64 1 77 store i8 2, i8* %gepB_plus_one, align 1 78 79 %j.1 = add nuw i64 %j, 1 80 %exitcondj = icmp eq i64 %j.1, %N 81 br i1 %exitcondj, label %for_j.end, label %for_j.body 82 83 for_j.end: 84 85 %i.1 = add nuw i64 %i, 1 86 %exitcond = icmp eq i64 %i.1, %N 87 br i1 %exitcond, label %for_i.end, label %for_i.body 88 89 for_i.end: 90 ret void 91 } 92
