<div dir="ltr">I'm starting to think we should directly implement horizontal operations on vector types.<div><br></div><div><div>My suspicion is that coming up with a nice model for this would help us a lot with things like:</div><div>- Idiom recognition of reduction patterns that use horizontal arithmetic</div><div>- Ability to use horizontal operations in SLPVectorizer</div><div>- Significantly easier cost modeling of vectorizing loops with reductions in LoopVectorize</div><div>- Other things I've not thought of?</div><div><br class="inbox-inbox-Apple-interchange-newline"><span style="font-family:'helvetica neue',helvetica,arial,sans-serif"> Curious what others think?</span></div></div><div><span style="font-family:'helvetica neue',helvetica,arial,sans-serif"><br></span></div><div><span style="font-family:'helvetica neue',helvetica,arial,sans-serif">-Chandler</span></div><br><div class="gmail_quote"><div dir="ltr">On Wed, May 11, 2016 at 10:07 PM Shahid, Asghar-ahmad via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div lang="EN-US" link="blue" vlink="purple"><div>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">></span> why in order to add this particular instruction (sum elements in a vector) I need to add an insrinsic?<u></u><u></u></p>
</div></div><div lang="EN-US" link="blue" vlink="purple"><div><p class="MsoNormal">Adding intrinsic is not the only way, it is one of the way and user WILL-NOT be required to invoke<u></u><u></u></p>
<p class="MsoNormal">It specifically.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Currently LLVM does not have any instruction to directly represent “sum of elements in a vector” and<u></u><u></u></p>
<p class="MsoNormal">generate your particular instruction.However, you can do it without intrinsic by pattern matching the<u></u><u></u></p>
<p class="MsoNormal">LLVM-IRs representing “sum of elements in vector” to your particular instruction in DAGCombiner.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Regards,<u></u><u></u></p>
<p class="MsoNormal">Shahid<u></u><u></u></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<div style="border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt">
<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""> Rail Shafigulin [mailto:<a href="mailto:rail@esenciatech.com" target="_blank">rail@esenciatech.com</a>]
<br>
<b>Sent:</b> Monday, May 09, 2016 11:59 PM<br>
<b>To:</b> Shahid, Asghar-ahmad; llvm-dev<br>
<b>Cc:</b> Das, Dibyendu</span></p></div></div></div></div></div><div lang="EN-US" link="blue" vlink="purple"><div><div style="border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt"><div><div style="border:none;border-top:solid #b5c4df 1.0pt;padding:3.0pt 0in 0in 0in"><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""><br>
<b>Subject:</b> Re: [llvm-dev] sum elements in the vector<u></u><u></u></span></p></div></div></div></div></div><div lang="EN-US" link="blue" vlink="purple"><div><div style="border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt">
<p class="MsoNormal"><u></u> <u></u></p>
<div>
<p class="MsoNormal">I'm a little confused. Here is why.<u></u><u></u></p>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal">I was able to add a vector add instruction to my target without using any intrinsics and without adding any new instructions to LLVM. So here is my question: how come I managed to add a new vector instruction without adding an intrinsic
and why in order to add this particular instruction (sum elements in a vector) I need to add an insrinsic?<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal">Another question that I have is whether compiler will be able to target this new instruction (sum elements in a vector) if it is implemented as an intrinsic or the user will have to specifically invoke an instrinsic.<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal">Pardon if questions seem dumb, I'm still learning things.<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal">Any help is appreciated. <u></u><u></u></p>
</div>
</div>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
<div>
<p class="MsoNormal">On Fri, May 6, 2016 at 1:51 PM, Rail Shafigulin <<a href="mailto:rail@esenciatech.com" target="_blank">rail@esenciatech.com</a>> wrote:<u></u><u></u></p>
<div>
<p class="MsoNormal">Thanks for the reply. These steps will add an instruction as an intrinsic. Is it possible to add an actual new instruction so that a compiler could target it during an optimization? How hard is it to do it? Is that a realistic objective.<span><span style="color:#888888"><u></u><u></u></span></span></p>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<p class="MsoNormal"><span style="color:#888888">Rail<u></u><u></u></span></p>
</div>
</div>
<div>
<div>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
<div>
<p class="MsoNormal">On Mon, Apr 4, 2016 at 9:02 PM, Shahid, Asghar-ahmad <<a href="mailto:Asghar-ahmad.Shahid@amd.com" target="_blank">Asghar-ahmad.Shahid@amd.com</a>> wrote:<u></u><u></u></p>
<div>
<div>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Hi Rail,</span><u></u><u></u></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span><u></u><u></u></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">We had done this for generation of X86 PSAD (sum of absolute difference) instruction through</span><u></u><u></u></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Llvm intrinsic. Doing this requires following</span><u></u><u></u></p>
<p><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">1.</span><span style="font-size:7.0pt;color:#1f497d">
</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Define an intrinsic, xyz(), for the required instruction and corresponding SDNode</span><u></u><u></u></p>
<p><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">2.</span><span style="font-size:7.0pt;color:#1f497d">
</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Generate the “call xyz() “ IR based the matched pattern</span><u></u><u></u></p>
<p><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">3.</span><span style="font-size:7.0pt;color:#1f497d">
</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Map “call xyz()” IR to corresponding SDNode in SelectionDagBuilder.cpp</span><u></u><u></u></p>
<p><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">4.</span><span style="font-size:7.0pt;color:#1f497d">
</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Provide default expansion of the xyz() intrinsic</span><u></u><u></u></p>
<p><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">5.</span><span style="font-size:7.0pt;color:#1f497d">
</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Legalize type and/or operation</span><u></u><u></u></p>
<p><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">6.</span><span style="font-size:7.0pt;color:#1f497d">
</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Provide Lowering of intrinsic/SDNode to generate your target instruction</span><u></u><u></u></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span><u></u><u></u></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">You can visit
<a href="http://llvm.org/docs/ExtendingLLVM.html" target="_blank">http://llvm.org/docs/ExtendingLLVM.html</a> for details.</span><u></u><u></u></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span><u></u><u></u></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Regards,</span><u></u><u></u></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Shahid
</span><u></u><u></u></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span><u></u><u></u></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span><u></u><u></u></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span><u></u><u></u></p>
<div style="border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt">
<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""> llvm-dev [mailto:<a href="mailto:llvm-dev-bounces@lists.llvm.org" target="_blank">llvm-dev-bounces@lists.llvm.org</a>]
<b>On Behalf Of </b>Rail Shafigulin via llvm-dev<br>
<b>Sent:</b> Monday, April 04, 2016 11:00 PM<br>
<b>To:</b> Das, Dibyendu<br>
<b>Cc:</b> <a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a><br>
<b>Subject:</b> Re: [llvm-dev] sum elements in the vector</span><u></u><u></u></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <u></u><u></u></p>
<div>
<p class="MsoNormal">Thanks for the pointers. I looked at hadd instructions. They seem to do very similar to what I need. Unfortunately as I said before my LLVM experience is limited. My understanding
is that when I create a new type of SDNode I need to specify a pattern for it, so that when LLVM is analyzing the code and is seeing a given pattern it would create this particular node. I'm really struggling to understand how it is done. So here are the problems
that I'm having.<u></u><u></u></p>
<div>
<p class="MsoNormal"> <u></u><u></u></p>
</div>
<div>
<p class="MsoNormal">1. How do I identify that pattern that should be used?<u></u><u></u></p>
</div>
<div>
<p class="MsoNormal">2. How do I specify a given pattern? <u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"> <u></u><u></u></p>
</div>
<div>
<p class="MsoNormal">Do you (or someone else) mind helping me out? <u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"> <u></u><u></u></p>
</div>
<div>
<p class="MsoNormal">Any help is appreciated.<u></u><u></u></p>
</div>
</div>
<div>
<p class="MsoNormal"> <u></u><u></u></p>
<div>
<p class="MsoNormal">On Mon, Apr 4, 2016 at 9:59 AM, Das, Dibyendu <<a href="mailto:Dibyendu.Das@amd.com" target="_blank">Dibyendu.Das@amd.com</a>> wrote:<u></u><u></u></p>
<div>
<div>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">This is roughly along the lines of x86 hadd* instructions though the semantics of hadd* may not exactly
match what you are looking for. This is probably more in line with x86/ARM SAD-like instructions but I don’t think llvm generates SAD without intrinsics.</span><u></u><u></u></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span><u></u><u></u></p>
<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""> llvm-dev [mailto:<a href="mailto:llvm-dev-bounces@lists.llvm.org" target="_blank">llvm-dev-bounces@lists.llvm.org</a>]
<b>On Behalf Of </b>Rail Shafigulin via llvm-dev<br>
<b>Sent:</b> Monday, April 04, 2016 9:34 AM<br>
<b>To:</b> llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>><br>
<b>Subject:</b> [llvm-dev] sum elements in the vector</span><u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<div>
<p class="MsoNormal">My target has an instruction that adds up all elements in the vector and stores the result in a register. I'm trying to implement it in my compiler but I'm not sure even where to
start.<u></u><u></u></p>
<div>
<div>
<div>
<p class="MsoNormal"> <u></u><u></u></p>
</div>
<div>
<p class="MsoNormal">I did look at other targets, but they don't seem to have anything like it ( I could be wrong. My experience with LLVM is limited, so if I missed it, I'd appreciate if someone could
point it out ). <u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"> <u></u><u></u></p>
</div>
<div>
<p class="MsoNormal">My understanding is that if SDNode for such an instruction doesn't exist I have to define one. Unfortunately, I don't know how to do it. I don't even know where to start looking.
Would someone care to point me in the right direction? <u></u><u></u></p>
</div>
<div>
<p class="MsoNormal"> <u></u><u></u></p>
</div>
<div>
<p class="MsoNormal">Any help is appreciated.<br clear="all">
<u></u><u></u></p>
<div>
<p class="MsoNormal"> <u></u><u></u></p>
</div>
<p class="MsoNormal">--
<u></u><u></u></p>
<div>
<div>
<div>
<div>
<div>
<p class="MsoNormal">Rail Shafigulin<u></u><u></u></p>
</div>
<p class="MsoNormal">Software Engineer
<br>
Esencia Technologies<u></u><u></u></p>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
<p class="MsoNormal"><br>
<br clear="all">
<u></u><u></u></p>
<div>
<p class="MsoNormal"> <u></u><u></u></p>
</div>
<p class="MsoNormal">--
<u></u><u></u></p>
<div>
<div>
<div>
<div>
<div>
<p class="MsoNormal">Rail Shafigulin<u></u><u></u></p>
</div>
<p class="MsoNormal">Software Engineer
<br>
Esencia Technologies<u></u><u></u></p>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
<p class="MsoNormal"><br>
<br clear="all">
<u></u><u></u></p>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<p class="MsoNormal">-- <u></u><u></u></p>
<div>
<div>
<div>
<div>
<div>
<p class="MsoNormal">Rail Shafigulin<u></u><u></u></p>
</div>
<p class="MsoNormal">Software Engineer <br>
Esencia Technologies<u></u><u></u></p>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
<p class="MsoNormal"><br>
<br clear="all">
<u></u><u></u></p>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<p class="MsoNormal">-- <u></u><u></u></p>
<div>
<div>
<div>
<div>
<div>
<p class="MsoNormal">Rail Shafigulin<u></u><u></u></p>
</div>
<p class="MsoNormal">Software Engineer <br>
Esencia Technologies<u></u><u></u></p>
</div>
</div>
</div>
</div>
</div>
</div></div></div>
_______________________________________________<br>
LLVM Developers mailing list<br>
<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a><br>
<a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev" rel="noreferrer" target="_blank">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a><br>
</blockquote></div></div>