<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body bgcolor="#FFFFFF" text="#000000">
<p>Hi, Kiwan,</p>
<p>What sizes are you passing to AA when you make the query (i.e., how are you constructing the MemoryLocation)? I would expect an access to the eighth element and the first element to be NoAlias, although maybe MayAlias if something is confusing the analysis.</p>
<p> -Hal<br>
</p>
<div class="moz-cite-prefix">On 11/5/19 6:05 PM, 맹기완 via llvm-dev wrote:<br>
</div>
<blockquote type="cite" cite="mid:CANHRZoh_FpiQMmwgEeu4wmZ7VYHHAOAk70PQ85=6SE9u4fmTmg@mail.gmail.com">
<div dir="ltr">
<div>I have a global 2-D array ARRAY[N][M] and I am accessing it inside the for loop like this:</div>
<div><br>
</div>
<div>for (i...)</div>
<div> for (j ...)</div>
<div> ARRAY[i][j] ...</div>
<div><br>
</div>
<div>So nothing really weird is happening. If I look at the generated IR, it is also fairly straight forward.</div>
<div><br>
</div>
<div>@ARRAY0 = dso_local global [32 x [32 x i32]] zeroinitializer, section ".slow_mem", align 32, !dbg !84<br>
...<br>
%45 = getelementptr inbounds [32 x [32 x i32]], [32 x [32 x i32]]* @ARRAY0, i32 0, i32 %22, i32 7, !dbg !180<br>
store volatile i32 %43, i32* %45, align 4, !dbg !181, !tbaa !148</div>
<div><br>
</div>
<div>As you can see, the GEPInst exactly knows it is the ARRAY0, and it knows statically that it is accessing the 7th element.</div>
<div>However, when I try to call alias analysis in the LLVM pass, as in</div>
<div><br>
</div>
<div>AliasAnalysis *AA = ...<br>
</div>
<div>AA->alias(a, b)<br>
</div>
<div><br>
</div>
<div>where a is the ARRAY0 global variable and b is the GEPInst (%45), I only get mayAlias.</div>
<div>When reading the basicaa description, it seems like it should know that the two is must alias. What am I missing?</div>
<div><br>
</div>
<div>I did not know how I should post code in the thread, so I apologize for the messy format.<br>
</div>
<div>Thank you,</div>
<div>Best Regards,</div>
<div>Kiwan<br>
</div>
</div>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<pre class="moz-quote-pre" wrap="">_______________________________________________
LLVM Developers mailing list
<a class="moz-txt-link-abbreviated" href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>
<a class="moz-txt-link-freetext" href="https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev">https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a>
</pre>
</blockquote>
<pre class="moz-signature" cols="72">--
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory</pre>
</body>
</html>