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8912979930
Summary: Scalar evolution does not propagate the non-wrapping flags to values that are derived from a non-wrapping induction variable because the non-wrapping property could be flow-sensitive. This change is a first attempt to establish the non-wrapping property in some simple cases. The main idea is to look through the operations defining the pointer. As long as we arrive to a non-wrapping AddRec via a small chain of non-wrapping instruction, the pointer should not wrap either. I believe that this essentially is what Andy described in http://article.gmane.org/gmane.comp.compilers.llvm.cvs/220731 as the way forward. Reviewers: aschwaighofer, nadav, sanjoy, atrick Reviewed By: atrick Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D10472 llvm-svn: 240798
42 lines
1.1 KiB
LLVM
42 lines
1.1 KiB
LLVM
; RUN: opt -basicaa -loop-accesses -analyze < %s | FileCheck %s
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; For this loop:
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; for (int i = 0; i < n; i++)
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; A[2 * i] = A[2 * i] + B[i];
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;
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; , SCEV is unable to prove that A[2 * i] does not overflow. However,
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; analyzing the IR helps us to conclude it and in turn allow dependence
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; analysis.
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target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
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; CHECK: Memory dependences are safe{{$}}
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define void @f(i16* noalias %a,
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i16* noalias %b, i64 %N) {
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entry:
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br label %for.body
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for.body: ; preds = %for.body, %entry
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%ind = phi i64 [ 0, %entry ], [ %inc, %for.body ]
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%mul = mul nuw nsw i64 %ind, 2
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%arrayidxA = getelementptr inbounds i16, i16* %a, i64 %mul
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%loadA = load i16, i16* %arrayidxA, align 2
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%arrayidxB = getelementptr inbounds i16, i16* %b, i64 %ind
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%loadB = load i16, i16* %arrayidxB, align 2
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%add = mul i16 %loadA, %loadB
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store i16 %add, i16* %arrayidxA, align 2
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%inc = add nuw nsw i64 %ind, 1
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%exitcond = icmp eq i64 %inc, %N
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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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