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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Hi Chris,<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'>I’ve attached a replacement of fibonacci.cpp that
reproduces the issue on x86/SSE systems.<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'>Regarding the definition of the VFCmp instruction, I think it
would really be a lot more valuable to define it as returning all 1’s or
all 0’s per element. Just setting the most significant bit is pretty much
worthless (someone correct me if I’m wrong). I checked and I couldn’t
actually find any instruction set that only sets the MSB when comparing
vectors, except by actually doing just a subtract. Since people need full masks
before they can do anything useful with it (requiring a shift or conditional
replace) I was thinking why not make that part of VFCmp? Note that this change
in VFCmp’s definition won’t break compatibility.<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'>Kind regards,<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>
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<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>Chris Lattner<br>
<b>Sent:</b> Saturday, 14 June, 2008 02:40<br>
<b>To:</b> LLVM Developers Mailing List<br>
<b>Subject:</b> Re: [LLVMdev] VFCmp failing when unordered or UnsafeFPMath on
x86<o:p></o:p></span></p>
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<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
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<p class=MsoNormal>On Jun 13, 2008, at 12:27 AM, Nicolas Capens wrote:<o:p></o:p></p>
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<br>
<o:p></o:p></p>
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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'>Hi all,<o:p></o:p></span></p>
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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'> <o:p></o:p></span></p>
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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'>When trying to generate a VFCmp instruction when UnsafeFPMath is
set to true I get an assert “</span><span style='font-size:10.0pt;
font-family:"Courier New";color:black'>Unexpected CondCode</span><span
style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:black'>”
on my x86 system. This also happens with UnsafeFPMath set to false and using an
unordered compare. Could someone look into this?<o:p></o:p></span></p>
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<p class=MsoNormal><o:p> </o:p></p>
</div>
<p class=MsoNormal>Please provide a testcase.<o:p></o:p></p>
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<p class=MsoNormal><br>
<br>
<o:p></o:p></p>
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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'><o:p> </o:p></span></p>
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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'>While I’m at it, is there any reason why only the most
significant bit of the return value of VFCmp is defined (according to the
documentation)? Both AltiVec and SSE set the components of the result to either
all 1’s or all 0’s. Having only the most significant bit
doesn’t seem useful to me at all, and (arithmetic) shifting vectors to
replicate the bit isn’t supported.<o:p></o:p></span></p>
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<p class=MsoNormal><o:p> </o:p></p>
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<p class=MsoNormal>LLVM is intended to support other vector instruction sets,
including SPU, Alpha, etc. The commonality was that the MSB is set, and
we would like to add support for vector shifting at some point.<o:p></o:p></p>
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<p class=MsoNormal><o:p> </o:p></p>
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<p class=MsoNormal>-Chris<o:p></o:p></p>
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