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f1d9b77877
Summary: Often filter-like loops will do memory accesses that are separated by constant offsets. In these cases it is common that we will exceed the threshold for the allowable number of checks. However, it should be possible to merge such checks, sice a check of any interval againt two other intervals separated by a constant offset (a,b), (a+c, b+c) will be equivalent with a check againt (a, b+c), as long as (a,b) and (a+c, b+c) overlap. Assuming the loop will be executed for a sufficient number of iterations, this will be true. If not true, checking against (a, b+c) is still safe (although not equivalent). As long as there are no dependencies between two accesses, we can merge their checks into a single one. We use this technique to construct groups of accesses, and then check the intervals associated with the groups instead of checking the accesses directly. Reviewers: anemet Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D10386 llvm-svn: 241673
60 lines
1.9 KiB
LLVM
60 lines
1.9 KiB
LLVM
; RUN: opt -loop-accesses -analyze < %s | FileCheck %s
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; We give up analyzing the dependences in this loop due to non-constant
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; distance between A[i+offset] and A[i] and add memchecks to prove
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; independence. Make sure that no interesting dependences are reported in
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; this case.
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;
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; for (i = 0; i < n; i++)
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; A[i + offset] = A[i] * B[i] * C[i];
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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: Memory dependences are safe with run-time checks
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; CHECK-NEXT: Interesting Dependences:
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; CHECK-NEXT: Run-time memory checks:
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; CHECK-NEXT: 0:
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; CHECK-NEXT: Comparing group
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; CHECK-NEXT: %arrayidxA2 = getelementptr inbounds i16, i16* %a, i64 %idx
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; CHECK-NEXT: Against group
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; CHECK-NEXT: %arrayidxA = getelementptr inbounds i16, i16* %a, i64 %indvar
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@B = common global i16* null, align 8
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@A = common global i16* null, align 8
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@C = common global i16* null, align 8
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define void @f(i64 %offset) {
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entry:
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%a = load i16*, i16** @A, align 8
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%b = load i16*, i16** @B, align 8
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%c = load i16*, i16** @C, align 8
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br label %for.body
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for.body: ; preds = %for.body, %entry
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%indvar = phi i64 [ 0, %entry ], [ %add, %for.body ]
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%arrayidxA = getelementptr inbounds i16, i16* %a, i64 %indvar
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%loadA = load i16, i16* %arrayidxA, align 2
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%arrayidxB = getelementptr inbounds i16, i16* %b, i64 %indvar
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%loadB = load i16, i16* %arrayidxB, align 2
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%arrayidxC = getelementptr inbounds i16, i16* %c, i64 %indvar
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%loadC = load i16, i16* %arrayidxC, align 2
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%mul = mul i16 %loadB, %loadA
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%mul1 = mul i16 %mul, %loadC
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%idx = add i64 %indvar, %offset
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%arrayidxA2 = getelementptr inbounds i16, i16* %a, i64 %idx
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store i16 %mul1, i16* %arrayidxA2, align 2
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%add = add nuw nsw i64 %indvar, 1
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%exitcond = icmp eq i64 %add, 20
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br i1 %exitcond, label %for.end, label %for.body
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for.end: ; preds = %for.body
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ret void
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}
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