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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Thanks for your comments. I tried using the promotion to deal with operations on v32i8. It seems work well. As you mentioned “canonicalization”, I am wondering
where I can find the document on canonicalized form of IR. When I saw truncate to minimal bitwidth in innerloop vectorization, I thought it was kind of optimization rather than canonicalization.
<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">Shixiong<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"">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> Hal Finkel [mailto:hfinkel@anl.gov]
<br>
<b>Sent:</b> Thursday, August 18, 2016 5:10 PM<br>
<b>To:</b> Mehdi Amini<br>
<b>Cc:</b> llvm-dev@lists.llvm.org; Shixiong Xu<br>
<b>Subject:</b> Re: [llvm-dev] Cost model is missing in InstCombiner<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="font-family:"Helvetica","sans-serif";color:black">From:
</span></b><span style="font-family:"Helvetica","sans-serif";color:black">"Mehdi Amini via llvm-dev" <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>><br>
<b>To: </b>"Shixiong Xu" <<a href="mailto:shixiong@cadence.com">shixiong@cadence.com</a>><br>
<b>Cc: </b><a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a><br>
<b>Sent: </b>Thursday, August 18, 2016 11:05:35 AM<br>
<b>Subject: </b>Re: [llvm-dev] Cost model is missing in InstCombiner<br>
<br>
+David M.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica","sans-serif";color:black">On Aug 17, 2016, at 3:48 AM, Shixiong Xu via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>> wrote:<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">Hi,<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">I think canEvaluateTruncated() in InstCombiner needs use cost model to decide whether perform optimization or not.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica","sans-serif";color:black">I’ve always seen InstCombine as doing “canonicalization” of the IR and not “optimization”. So the output of InstCombine should be in a form that is the most suitable for further
analyses and transformations.<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black">This is exactly our traditional view. Why can the backend not be fixed to generate better code for mul <32 x i8>? It looks like the
widening in the IR is something natural to get from legalization (if you set up the correct promotion preferences in *ISelLowering).<br>
<br>
-Hal<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica","sans-serif";color:black">I’m not sure how this view fits with TTI, I may not be incompatible if used within some limits I guess?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica","sans-serif";color:black">— <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica","sans-serif";color:black">Mehdi<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica","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"> Without cost model from TargetTransformInfo, aggressively optimizing IR in vector types according to the number of bits demanded may lead to scalarization of
vector operations. For example, if the input IR is:<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"> %wide.load25 = load <32 x i8>, <32 x i8>* %231, align 1<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"> %232 = zext <32 x i8> %wide.load25 to <32 x i16><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"> %233 = mul nuw nsw <32 x i16> %232, %164<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"> %237 = trunc <32 x i16> %233 to <32 x i8><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"> store <32 x i8> %237, <32 x i8>* %236, align 1<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">ICE: EvaluateInDifferentType converting expression type to avoid cast: %9 = trunc <32 x i16> %6 to <32 x i8><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">IC: ADD: %6 = mul <32 x i8> %wide.load25, %wide.load<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">IC: Replacing %10 = trunc <32 x i16> %7 to <32 x i8><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"> with %6 = mul <32 x i8> %wide.load25, %wide.load<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">If the target doesn’t have support for mul <32 x i8>, the inst combiner will yield less profitable code.<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 lang="EN-IE" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">Cheers,</span><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 lang="EN-IE" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black"> </span><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 lang="EN-IE" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">Shixiong (Jason) Xu</span><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"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif";color:black">_______________________________________________<br>
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<p class="MsoNormal"><span style="font-family:"Helvetica","sans-serif";color:black"><o:p> </o:p></span></p>
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_______________________________________________<br>
LLVM Developers mailing list<br>
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<a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a><o:p></o:p></span></p>
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<br>
<br>
-- <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black">Hal Finkel<br>
Assistant Computational Scientist<br>
Leadership Computing Facility<br>
Argonne National Laboratory<o:p></o:p></span></p>
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