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On 10/13/11 6:05 AM, Justin Holewinski wrote:
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<div class="gmail_quote">On Thu, Oct 13, 2011 at 3:24 AM, Duncan
Sands <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:baldrick@free.fr">baldrick@free.fr</a>></span>
wrote:<br>
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Hi Justin,<br>
<div class="im"><br>
> Any opinions from the core developers? It would be
possible to add this pass to<br>
> the default alias analysis passes for some target
triples.<br>
<br>
</div>
I guess either Chris can pronounce from on high whether it is
OK to say that<br>
pointers in different address spaces cannot alias each other,
or you can contact<br>
the main developers for each LLVM target and ask them what the
situation is for<br>
their target. If pointers in different address spaces don't
alias for any of<br>
the currently supported LLVM targets then I think you can just
add the logic to<br>
basic alias analysis.<br>
</blockquote>
<div><br>
</div>
<div>Following the LLVM language reference, it is not required
that they be alias-free.</div>
<div><br>
</div>
<div>In the interests of getting this in before the branch, I
could add it to the basic alias analysis, but leave it
dependent on a command-line option that is off by default.
Does this sound reasonable?</div>
</div>
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<br>
The only problem with this approach is that it doesn't allow a tool
that links in the pass to programatically enable or disable the
feature.<br>
<br>
I would recommend:<br>
<br>
1) Enhancing TargetData to know whether the different address spaces
on a particular target are disjoint.<br>
<br>
2) Instead of using a command-line option to enable a feature, use
an AnalysisGroup that BasicAA queries to see what to do. The
default pass in the AnalysisGroup tells BasicAA to turn the feature
off. A different pass in the Analysis Group tells BasicAA to turn
the feature on. That way, a user or a tool just schedules an
additional pass to enable the feature.<br>
<br>
My two cents.<br>
<br>
-- John T.<br>
<br>
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<br>
Ciao, Duncan.<br>
<div>
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</div>
<br>
<br clear="all">
<div><br>
</div>
-- <br>
<br>
<div>Thanks,</div>
<div><br>
</div>
<div>Justin Holewinski</div>
<br>
<br>
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