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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Hi Stefanus,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Thanks for verifying this. Could you patch this or should I open
a new bug report and find a generic solution first?<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Cheers,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Nicolas<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
llvmdev-bounces@cs.uiuc.edu [mailto:llvmdev-bounces@cs.uiuc.edu] <b>On Behalf
Of </b>Stefanus Du Toit<br>
<b>Sent:</b> woensdag 1 april 2009 18:59<br>
<b>To:</b> LLVM Developers Mailing List<br>
<b>Subject:</b> Re: [LLVMdev] Shuffle combine<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
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<div>
<div>
<p class=MsoNormal>On 1-Apr-09, at 12:42 PM, Nicolas Capens wrote:<o:p></o:p></p>
</div>
<blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'>
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<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Hi Stefanus,</span><span style='color:black'><o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'> </span><span style='color:black'><o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Thanks for the info. I still think it’s a bug though. Take for
example a case where the vectors each have four elements. The values in Mask[]
can range from 0 to 7, while HLSMask only has 4 elements. So LHSMask[Mask[i]]
can go out of bounds, no?</span><span style='color:black'><o:p></o:p></span></p>
</div>
</div>
</div>
</blockquote>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<p class=MsoNormal>Good point! One easy way to fix this would be to use: <o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>if (Mask[i] >= e) {<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>instead. The code could also be improved to consider the new
mask equal to lhsmask/mask in places where they both refer to undefined
elements.<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>Stefanus<o:p></o:p></p>
</div>
<div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'>
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<div>
<div>
<p class=MsoNormal><span class=apple-style-span><span style='font-size:11.5pt;
font-family:"Calibri","sans-serif";color:#1F497D'>Cheers,</span></span><span
style='color:black'><o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'> </span><span style='color:black'><o:p></o:p></span></p>
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<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Nicolas</span><span style='color:black'><o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'> </span><span style='color:black'><o:p></o:p></span></p>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";
color:black'>From:</span></b><span class=apple-converted-space><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:black'> </span></span><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:black'><a
href="mailto:llvmdev-bounces@cs.uiuc.edu">llvmdev-bounces@cs.uiuc.edu</a> [<a
href="mailto:llvmdev-bounces@cs.uiuc.edu">mailto:llvmdev-bounces@cs.uiuc.edu</a>]<span
class=apple-converted-space> </span><b>On Behalf Of<span
class=apple-converted-space> </span></b>Stefanus Du Toit<br>
<b>Sent:</b><span class=apple-converted-space> </span>woensdag 1 april
2009 16:31<br>
<b>To:</b><span class=apple-converted-space> </span>LLVM Developers
Mailing List<br>
<b>Subject:</b><span class=apple-converted-space> </span>Re: [LLVMdev]
Shuffle combine</span><span style='color:black'><o:p></o:p></span></p>
</div>
</div>
</div>
<div>
<p class=MsoNormal><span style='color:black'> <o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='color:black'>Hi Nicolas,<o:p></o:p></span></p>
</div>
<div>
<div>
<p class=MsoNormal><span style='color:black'> <o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<div>
<div>
<div>
<p class=MsoNormal><span style='color:black'>On 1-Apr-09, at 7:34 AM, Nicolas
Capens wrote:<o:p></o:p></span></p>
</div>
</div>
<blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'>
<div>
<div>
<div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'>I’m having some trouble understanding the following lines in
InstructionCombining.cpp, which possibly contain a bug:</span><span
style='color:black'><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'> </span><span style='color:black'><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:blue'>if</span><span class=apple-converted-space><span style='font-size:
10.0pt;font-family:"Courier New";color:black'> </span></span><span
style='font-size:10.0pt;font-family:"Courier New";color:black'>(Mask[i] >=
2*e)</span><span style='color:black'><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:black'> NewMask.push_back(2*e);</span><span
style='color:black'><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:blue'>else</span><span style='color:black'><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:black'> NewMask.push_back(LHSMask[Mask[i]]);</span><span
style='color:black'><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'> </span><span style='color:black'><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'>When Mask[i] is bigger than the size of LHSMask it reads out of
bounds on that last line. I believe the first line is there to try to prevent
that but then it should be comparing to LHSMask.size() not 2*e (e being
Mask.size()). </span><span style='color:black'><o:p></o:p></span></p>
</div>
</div>
</div>
</div>
</blockquote>
<div>
<div>
<p class=MsoNormal><span style='color:black'> <o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='color:black'>Upon quick inspection of the code,
I don't think this is necessarily a bug right now, but the function could be
improved.<o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='color:black'> <o:p></o:p></span></p>
</div>
</div>
<div>
<p class=MsoNormal><span style='color:black'>I believe this stems (in part at
least) from the fact that shufflevector used to require that the sources and
the mask have the same size, which was changed a few months ago to allow an
arbitrarily-sized mask.<o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='color:black'> <o:p></o:p></span></p>
</div>
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<div>
<div>
<p class=MsoNormal><span style='color:black'>This would be a bug all throughout
this function (which generally assumes this is still the case), if the function
didn't do the following check early:<o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='color:black'> <o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<div>
<p class=MsoNormal><span style='color:black'> unsigned VWidth =
cast<VectorType>(SVI.getType())->getNumElements();<o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='color:black'> <o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='color:black'> if (VWidth !=
cast<VectorType>(LHS->getType())->getNumElements())<o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='color:black'> return 0;<o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='color:black'> <o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='color:black'>In other words, if the mask size
is not equal to the number of elements in the vectors, it skips this
transformation.<o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='color:black'> <o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='color:black'>Because the LHS is a shufflevector
in the part of the code you are mentioning, and the result of a shufflevector
has the same number of elements as its mask, you are actually guaranteed that
LHSMask.size() == Mask.size(), because LHSMask.size() ==
LHS->getNumElements() == Mask.size().<o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='color:black'> <o:p></o:p></span></p>
</div>
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<div>
<div>
<p class=MsoNormal><span style='color:black'>It shouldn't be too hard to relax
the constraint that this optimization requires the number of elements being
shuffle to be equal to the mask size, but it'll probably take some careful
testing!<o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='color:black'> <o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='color:black'>Stefanus<o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='color:black'> <o:p></o:p></span></p>
</div>
</div>
</div>
<div>
<div>
<div>
<div>
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<div>
<p class=MsoNormal><span style='font-size:9.0pt;font-family:"Helvetica","sans-serif";
color:black'>--</span><span style='color:black'><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='font-size:9.0pt;font-family:"Helvetica","sans-serif";
color:black'>Stefanus Du Toit <<a href="mailto:stefanus.dutoit@rapidmind.com">stefanus.dutoit@rapidmind.com</a>></span><span
style='color:black'><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='font-size:9.0pt;font-family:"Helvetica","sans-serif";
color:black'> RapidMind Inc.</span><span style='color:black'><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='font-size:9.0pt;font-family:"Helvetica","sans-serif";
color:black'> phone: +1 519 885 5455 x116 -- fax: +1 519 885 1463</span><span
style='color:black'><o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class=MsoNormal><span style='font-size:9.0pt;font-family:"Helvetica","sans-serif";
color:black'> </span><span style='color:black'><o:p></o:p></span></p>
</div>
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</div>
</div>
</div>
</div>
<div>
<p class=MsoNormal><span style='color:black'> <o:p></o:p></span></p>
</div>
</div>
<div>
<p class=MsoNormal><span style='color:black'> <o:p></o:p></span></p>
</div>
</div>
</div>
<p class=MsoNormal><span style='font-size:9.0pt;font-family:"Helvetica","sans-serif";
color:black'><ATT00001.txt><o:p></o:p></span></p>
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</blockquote>
</div>
<p class=MsoNormal><o:p> </o:p></p>
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<div>
<p class=MsoNormal><span style='font-size:9.0pt;font-family:"Helvetica","sans-serif";
color:black'>--<o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:9.0pt;font-family:"Helvetica","sans-serif";
color:black'>Stefanus Du Toit <<a href="mailto:stefanus.dutoit@rapidmind.com">stefanus.dutoit@rapidmind.com</a>><o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:9.0pt;font-family:"Helvetica","sans-serif";
color:black'> RapidMind Inc.<o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:9.0pt;font-family:"Helvetica","sans-serif";
color:black'> phone: +1 519 885 5455 x116 -- fax: +1 519 885 1463<o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:9.0pt;font-family:"Helvetica","sans-serif";
color:black'><o:p> </o:p></span></p>
</div>
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<p class=MsoNormal><o:p> </o:p></p>
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<p class=MsoNormal><o:p> </o:p></p>
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