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Dear all,</div>
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Thanks a lot for your analysis and suggestion.</div>
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Currently, I walk around in a way similar to what Hongbin said, by treating SCEV of URem specially to get the range.</div>
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I guess maybe the rule of inference can be updated haha ^_^</div>
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Thanks again for your time and answer!<br>
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<div><font size="2" face="Calibri,sans-serif"><span style="font-size:12pt">Best regards,</span></font><span style="font-size:12pt">
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<div style="margin:0"><font size="2" face="Calibri,sans-serif"><span style="font-size:12pt">Tingyuan LIANG</span></font></div>
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<div style="margin:0"><font size="2" face="Calibri,sans-serif"><span style="font-size:12pt">MPhil Student</span></font></div>
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<div style="margin:0"><font size="2" face="Calibri,sans-serif"><span style="font-size:12pt">Department of Electronic and Computer Engineering</span></font></div>
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<div style="margin:0"><font size="2" face="Calibri,sans-serif"><span style="font-size:12pt">The Hong Kong University of Science and Technology</span></font></div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Hongbin Zheng <etherzhhb@gmail.com><br>
<b>Sent:</b> Wednesday, June 26, 2019 1:57 PM<br>
<b>To:</b> Sanjoy Das<br>
<b>Cc:</b> Tingyuan LIANG; llvm-dev@lists.llvm.org<br>
<b>Subject:</b> Re: [llvm-dev] Wrong Range of SCEV for URem</font>
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<div class="PlainText">I feel that we maybe able to pattern match "%x -<nuw> ((%x udiv %y)<br>
*<nuw> %y)" to infer that the results should be smaller than %y. But<br>
not sure if this approach could scale well<br>
<br>
On Tue, Jun 25, 2019 at 8:50 PM Sanjoy Das via llvm-dev<br>
<llvm-dev@lists.llvm.org> wrote:<br>
><br>
> 1. There is nothing wrong about getUnsignedRange returning a range<br>
> with a negative value. "Signed" and "Unsigned" are merely hints, the<br>
> underlying ConstantRange representation does not have a concept of<br>
> sign. [A, B) represents all the values enumerated by "for (I = A; I<br>
> != B; I++ /*wrapping addition*/) { yield(I); }"<br>
><br>
> 2. I would guess this is because SCEV does not directly represent urem<br>
> but instead represents it as "%x urem %y == %x -<nuw> ((%x udiv %y)<br>
> *<nuw> %y)". This makes it difficult for SCEV to infer that the X<br>
> urem 3 is u< 3.<br>
><br>
> On Wed, Jun 12, 2019 at 9:45 AM Tingyuan LIANG via llvm-dev<br>
> <llvm-dev@lists.llvm.org> wrote:<br>
> ><br>
> > Dear all,<br>
> ><br>
> > Hi! I noticed an interesting situation when using getUnsignedRange and getSignedRange of SCEV for URem instruction.<br>
> > Here is an example with 2 IR instructions:<br>
> ><br>
> > %rem.lhs.trunc = trunc i32 %i15.082 to i8 --> getUnsignedRange --> [1,50)<br>
> > %rem81 = urem i8 %rem.lhs.trunc, 3 --> getUnsignedRange --> [-47,50)<br>
> ><br>
> > The problems are:<br>
> > 1) From my perspective, the getUnsignedRange() function should return non-negative range but it seems not so in the example. Is there anything wrong?<br>
> > 2) The range of the IR %rem81 should be [0,3), considering the equation: X%3 < 3?<br>
> ><br>
> > Thanks in advance for your time and suggestions!<br>
> ><br>
> ><br>
> > Best regards,<br>
> > ------------------------------------------<br>
> > Tingyuan LIANG<br>
> > MPhil Student<br>
> > Department of Electronic and Computer Engineering<br>
> > The Hong Kong University of Science and Technology<br>
> > _______________________________________________<br>
> > LLVM Developers mailing list<br>
> > llvm-dev@lists.llvm.org<br>
> > <a href="https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev">https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a><br>
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