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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext">Thanks for the pointers. Looks like LazyValueInfo has the sort of infrastructure I had in mind. LVILatticeVal could be extended to floating point. (The
comment “this can be made a lot more rich in the future” is an invitation :-). I’m thinking a simple lattice would address most cases of interest for floating-point checks. The lattice points for floating-point could be all subsets of the eight-element
set:<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:.5in"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext">{-inf,<0,-0,+0,>0,+inf,-nan,+nan},
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext">where <0 and >0 denote finite negative/positive numbers respectively.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext">- Arch<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext"> Philip Reames [mailto:listmail@philipreames.com]
<br>
<b>Sent:</b> Wednesday, January 7, 2015 6:03 PM<br>
<b>To:</b> Robison, Arch; llvmdev@cs.uiuc.edu<br>
<b>Subject:</b> Re: [LLVMdev] Floating-point range checks<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:12.0pt">I don't believe we have much in this area currently.
<br>
<br>
Generally, something like this would existing in InstCombine and ValueTracking.<br>
<br>
Take a look at ComputeSignBit in ValueTracking.cpp. This doesn't apply (?) to floating point numbers, but we'd need something equivalent for them. It looks like there may already be a start in the form of:<br>
CannotBeNegativeZero<br>
<br>
Other places to look would be SimplifyFAdd and InstCombine::visitFAdd.<br>
<br>
For this particular example, you're probably going to want a pattern in SimplifyFCmp of the form:<br>
matcher: sqrt_call( fadd(Value(X), SpecificValue(X)), fadd(Value(Y), SpecificValue(Y)))
<br>
&& CannotBeNegativeZero(X) && CannotBeNegativeZero(Y)<br>
<br>
You might also look at LazyValueInfo, but that's probably of secondary interest. It's purely in terms of constant integer ranges currently.
<br>
<br>
Philip<br>
<br>
<br>
<o:p></o:p></p>
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<p class="MsoNormal">On 01/07/2015 02:13 PM, Robison, Arch wrote:<o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">The Julia language implements sqrt(x) with conditional branch taken if x<0. Alas this prevents vectorization of loops with sqrt. Often the argument can be proven to be non-negative.
E.g., sqrt(x*x+y*y). Is there an existing LLVM pass or analysis that does floating-point range propagation to eliminate such unnecessary checks?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Arch D. Robison<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Intel Corporation<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal"><br>
<br>
<br>
<o:p></o:p></p>
<pre>_______________________________________________<o:p></o:p></pre>
<pre>LLVM Developers mailing list<o:p></o:p></pre>
<pre><a href="mailto:LLVMdev@cs.uiuc.edu">LLVMdev@cs.uiuc.edu</a> <a href="http://llvm.cs.uiuc.edu">http://llvm.cs.uiuc.edu</a><o:p></o:p></pre>
<pre><a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev</a><o:p></o:p></pre>
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