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