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<body><span class="vcard"><a class="email" href="mailto:george.burgess.iv@gmail.com" title="George Burgess <george.burgess.iv@gmail.com>"> <span class="fn">George Burgess</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - CFL-AA falsely reports NoAlias on Arguments"
href="https://llvm.org/bugs/show_bug.cgi?id=27213">bug 27213</a>
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<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>What</th>
<th>Removed</th>
<th>Added</th>
</tr>
<tr>
<td style="text-align:right;">Status</td>
<td>ASSIGNED
</td>
<td>RESOLVED
</td>
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<td style="text-align:right;">Resolution</td>
<td>---
</td>
<td>FIXED
</td>
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<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - CFL-AA falsely reports NoAlias on Arguments"
href="https://llvm.org/bugs/show_bug.cgi?id=27213#c2">Comment # 2</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - CFL-AA falsely reports NoAlias on Arguments"
href="https://llvm.org/bugs/show_bug.cgi?id=27213">bug 27213</a>
from <span class="vcard"><a class="email" href="mailto:george.burgess.iv@gmail.com" title="George Burgess <george.burgess.iv@gmail.com>"> <span class="fn">George Burgess</span></a>
</span></b>
<pre>Fix committed as r265474.
The tl;dr of the problem was a collision of a few things:
- We mark a Node as a global or arg when visiting its edges
- We don't visit edges to "boring" nodes (e.g. constants)
- Stores themselves just create a link from value-being-stored to
pointer-being-stored-to.
So, from the example:
define void @foo(i32* %A, i32* %B) #0 {
entry:
store i32 0, i32* %A, align 4
%arrayidx = getelementptr inbounds i32, i32* %B, i64 1
store i32 0, i32* %arrayidx, align 4
ret void
}
...%A only had an edge to 'i32 0', which we didn't find interesting, so we
never visited it. Because we never visited it, we never reached the code that
notes that %A is an argument. Because we never noted %A was an argument, we
were more aggressive with marking it as NoAlias %B than we should have been.
The fix makes us mark things as args/globals before we start running through
their edges. (FWIW, I think there's a slightly faster way to do this if we
change the edge-visiting loop a bit, but I wanted to keep the fix as targeted
as possible)</pre>
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