<div dir="ltr"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Perhaps BasicAA is telling that A and B don't alias during one particular iteration of the loop even though they are swapped?</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">1: ; preds = %0, %35<br> %2 = phi double* [ getelementptr inbounds ([1000 x double], [1000 x double]* @Ag, i64 0, i64 0), %0 ], [ %4, %35 ]<br> %3 = phi i32 [ 0, %0 ], [ %36, %35 ]<br> %4 = phi double* [ getelementptr inbounds ([1000 x double], [1000 x double]* @Bg, i64 0, i64 0), %0 ], [ %2, %35 ]<br> br label %5<br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><a href="https://godbolt.org/z/vHJmL5">https://godbolt.org/z/vHJmL5</a><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Mar 16, 2020 at 10:28 PM Chawla, Pankaj via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<p class="MsoNormal">Hi all,<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">I have this test case-<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">#define N 1000<u></u><u></u></p>
<p class="MsoNormal">extern double Ag[N];<u></u><u></u></p>
<p class="MsoNormal">extern double Bg[N];<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">void consume(double *A, double *B);<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">void swap_deps() {<u></u><u></u></p>
<p class="MsoNormal"> double *A = Ag;<u></u><u></u></p>
<p class="MsoNormal"> double *B = Bg;<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"> for (int i = 0; i < 97; ++i) {<u></u><u></u></p>
<p class="MsoNormal"> for (int j = 0; j < N; ++j) {<u></u><u></u></p>
<p class="MsoNormal"> B[j] = A[j] + 1;<u></u><u></u></p>
<p class="MsoNormal"> }<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"> double *tmp = A;<u></u><u></u></p>
<p class="MsoNormal"> A = B;<u></u><u></u></p>
<p class="MsoNormal"> B = tmp;<u></u><u></u></p>
<p class="MsoNormal"> }<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"> consume(A, B);<u></u><u></u></p>
<p class="MsoNormal">}<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">BasicAA is returning ‘NoAlias’ when queried for phis created in the i-loop for A and B.<u></u><u></u></p>
<p class="MsoNormal">I was expecting it to return MayAlias since A and B are being swapped in the outer loop and so they access same locations in alternate iterations of the i-loop.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Is BasicAA returning the correct result in this case?<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Thanks,<u></u><u></u></p>
<p class="MsoNormal">Pankaj<u></u><u></u></p>
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