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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#44546A">Yes, I am still working on it. I believe I have it conservatively correct. I suppose I should just go ahead and submit it<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#44546A">with comments explaining why I think it is conservatively correct, and a TODO on what I think is actually required for complete<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#44546A">generality.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#44546A"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#44546A">Kevin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#44546A"><o:p> </o:p></span></p>
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<p class="MsoNormal"><a name="_____replyseparator"></a><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"> Taewook Oh [mailto:twoh@fb.com]
<br>
<b>Sent:</b> Monday, February 01, 2016 3:46 PM<br>
<b>To:</b> Smith, Kevin B <kevin.b.smith@intel.com>; 'Sanjay Patel' <spatel@rotateright.com><br>
<b>Cc:</b> llvm-dev@lists.llvm.org<br>
<b>Subject:</b> Re: [llvm-dev] Redundant promotion of integer values in x86 target<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"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">Sanjay, Kevin, Thank you for your reply.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">Kevin, I wonder if you are still working on it and have a plan to submit your changes for the review.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">Thanks,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">Taewook<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black"><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:black">From:
</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:black">"Smith, Kevin B" <<a href="mailto:kevin.b.smith@intel.com">kevin.b.smith@intel.com</a>><br>
<b>Date: </b>Monday, February 1, 2016 at 3:30 PM<br>
<b>To: </b>'Sanjay Patel' <<a href="mailto:spatel@rotateright.com">spatel@rotateright.com</a>>, Taewook Oh <<a href="mailto:twoh@fb.com">twoh@fb.com</a>><br>
<b>Cc: </b>"<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>" <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>><br>
<b>Subject: </b>RE: [llvm-dev] Redundant promotion of integer values in x86 target<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black"><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:#44546A">This is an excerpt from Chandler's comment in
</span><span style="color:black"><a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D22473&d=CwMGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=kOsLCgQzH7N8ptZ7diJD9g&m=4GlWLa5X3i08opHX4qEinKM5A85qGzRUacht2PVZxT8&s=hdE0lOvbk0jqWq2vtN1X_3HLHfpvK-z49XSU3LyY6kU&e=" target="_blank">https://llvm.org/bugs/show_bug.cgi?id=22473</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#44546A"> </span><span style="color:black"><o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="font-family:Wingdings;color:black"><span style="mso-list:Ignore">?<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="color:black">We need to add a pass that replaces movb (and movw) with movzbl (and movzwl) when the destination is a register and the high bytes aren't used.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"> <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black">I have created such a pass, and have it working in a local workspace of mine. However, I think that the way it attempts to prove that the high bytes aren't<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black">used is flawed, and so I haven't yet submitted it for community review.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"> <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black">Kevin <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#44546A"> </span><span style="color:black"><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:black">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:black"> Sanjay Patel [<a href="mailto:spatel@rotateright.com">mailto:spatel@rotateright.com</a>]
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<b>Sent:</b> Sunday, January 31, 2016 9:57 AM<br>
<b>To:</b> Taewook Oh <<a href="mailto:twoh@fb.com">twoh@fb.com</a>><br>
<b>Cc:</b> <a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>; Smith, Kevin B <<a href="mailto:kevin.b.smith@intel.com">kevin.b.smith@intel.com</a>><br>
<b>Subject:</b> Re: [llvm-dev] Redundant promotion of integer values in x86 target</span><span style="color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"> <o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="color:black">Hi Taewook -<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black">There's a discussion about the underlying x86 micro-arch details here:<br>
<a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__comments.gmane.org_gmane.comp.compilers.llvm.cvs_167221&d=CwMGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=kOsLCgQzH7N8ptZ7diJD9g&m=4GlWLa5X3i08opHX4qEinKM5A85qGzRUacht2PVZxT8&s=GXM3c7BrHLhnmiVCIrEm9Kpa9mtVMbrW9G8HTTGUc0s&e=" target="_blank">http://comments.gmane.org/gmane.comp.compilers.llvm.cvs/167221</a><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black">The conclusion was that we should change how we currently handle these, but we don't want to regress the case that was addressed by:<br>
<a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__reviews.llvm.org_rL195496&d=CwMGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=kOsLCgQzH7N8ptZ7diJD9g&m=4GlWLa5X3i08opHX4qEinKM5A85qGzRUacht2PVZxT8&s=_8T2G8KU33uBBq3_LkXZEnpzN3J8iKCF5Pg8vXHUPEw&e=">http://reviews.llvm.org/rL195496</a><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"> <o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="color:black">There are open bugs with more discussion related to this:<br>
<a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D17113&d=CwMGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=kOsLCgQzH7N8ptZ7diJD9g&m=4GlWLa5X3i08opHX4qEinKM5A85qGzRUacht2PVZxT8&s=2mYbHl1QB1OzIdlzXfVpTlMJ_oGFldBZMKJ6_gmGtCY&e=" target="_blank">https://llvm.org/bugs/show_bug.cgi?id=17113</a><br>
<a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D22473&d=CwMGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=kOsLCgQzH7N8ptZ7diJD9g&m=4GlWLa5X3i08opHX4qEinKM5A85qGzRUacht2PVZxT8&s=hdE0lOvbk0jqWq2vtN1X_3HLHfpvK-z49XSU3LyY6kU&e=" target="_blank">https://llvm.org/bugs/show_bug.cgi?id=22473</a><br>
<a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D22532&d=CwMGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=kOsLCgQzH7N8ptZ7diJD9g&m=4GlWLa5X3i08opHX4qEinKM5A85qGzRUacht2PVZxT8&s=MMoQ-XntXWrnXU4kmdhnvXVhDiinxjSXiWQH8hcLA4w&e=" target="_blank">https://llvm.org/bugs/show_bug.cgi?id=22532</a><br>
<a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D23155&d=CwMGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=kOsLCgQzH7N8ptZ7diJD9g&m=4GlWLa5X3i08opHX4qEinKM5A85qGzRUacht2PVZxT8&s=WXDoKPefpTQwCS3vsY8ki5faY2eURdKecODSZaKywlQ&e=" target="_blank">https://llvm.org/bugs/show_bug.cgi?id=23155</a>
(cc'ing Kevin in case there's any update on this one)<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black">On Fri, Jan 29, 2016 at 10:04 PM, Taewook Oh 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:10.5pt;font-family:"Calibri",sans-serif;color:black">Hello, </span><span style="color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black"> </span><span style="color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">While looking at some internal benchmarks, I found that llvm generates codes with redundant promotion, something like:</span><span style="color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black"> </span><span style="color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">xor %al, %cl</span><span style="color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">movzbl %cl, %ecx</span><span style="color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">cmp $0x20, %ecx</span><span style="color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black"> </span><span style="color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">I believe that the promotion stems from the logic in X86TargetLowering::EmitCmp. Comments in the code says, </span><span style="color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black"> </span><span style="color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">"Do the comparison at i32 if it's smaller, besides the Atom case. This avoids subregister aliasing issues. Keep the smaller reference if we're optimizing for size,
however, as that'll allow better folding of memory operations."</span><span style="color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black"> </span><span style="color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">Can anybody please explain me more in detail about the subregister aliasing issues?</span><span style="color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black"> </span><span style="color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">Thanks,</span><span style="color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">Taewook</span><span style="color:black"><o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="color:black"><br>
_______________________________________________<br>
LLVM Developers mailing list<br>
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