<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
</head>
<body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; color: rgb(0, 0, 0); font-size: 14px; font-family: Calibri, sans-serif;">
<div>Sanjay, Kevin, Thank you for your reply.</div>
<div><br>
</div>
<div>Kevin, I wonder if you are still working on it and have a plan to submit your changes for the review.</div>
<div><br>
</div>
<div>Thanks,</div>
<div>Taewook</div>
<div><br>
</div>
<span id="OLK_SRC_BODY_SECTION">
<div style="font-family:Calibri; font-size:11pt; text-align:left; color:black; BORDER-BOTTOM: medium none; BORDER-LEFT: medium none; PADDING-BOTTOM: 0in; PADDING-LEFT: 0in; PADDING-RIGHT: 0in; BORDER-TOP: #b5c4df 1pt solid; BORDER-RIGHT: medium none; PADDING-TOP: 3pt">
<span style="font-weight:bold">From: </span>"Smith, Kevin B" <<a href="mailto:kevin.b.smith@intel.com">kevin.b.smith@intel.com</a>><br>
<span style="font-weight:bold">Date: </span>Monday, February 1, 2016 at 3:30 PM<br>
<span style="font-weight:bold">To: </span>'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>
<span style="font-weight:bold">Cc: </span>"<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>
<span style="font-weight:bold">Subject: </span>RE: [llvm-dev] Redundant promotion of integer values in x86 target<br>
</div>
<div><br>
</div>
<div>
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:Wingdings;
panose-1:5 0 0 0 0 0 0 0 0 0;}
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Times New Roman",serif;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
p.MsoListParagraph, li.MsoListParagraph, div.MsoListParagraph
{mso-style-priority:34;
margin-top:0in;
margin-right:0in;
margin-bottom:0in;
margin-left:.5in;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Times New Roman",serif;}
span.EmailStyle17
{mso-style-type:personal-reply;
font-family:"Arial",sans-serif;
color:#44546A;
font-weight:normal;
font-style:normal;
text-decoration:none none;}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri",sans-serif;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
/* List Definitions */
@list l0
{mso-list-id:1783186317;
mso-list-type:hybrid;
mso-list-template-ids:-1725656410 1203688328 67698691 67698693 67698689 67698691 67698693 67698689 67698691 67698693;}
@list l0:level1
{mso-level-start-at:0;
mso-level-number-format:bullet;
mso-level-text:?;
mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;
font-family:Wingdings;
mso-fareast-font-family:Calibri;
mso-bidi-font-family:"Times New Roman";}
@list l0:level2
{mso-level-number-format:bullet;
mso-level-text:o;
mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;
font-family:"Courier New";}
@list l0:level3
{mso-level-number-format:bullet;
mso-level-text:?;
mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;
font-family:Wingdings;}
@list l0:level4
{mso-level-number-format:bullet;
mso-level-text:?;
mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;
font-family:Symbol;}
@list l0:level5
{mso-level-number-format:bullet;
mso-level-text:o;
mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;
font-family:"Courier New";}
@list l0:level6
{mso-level-number-format:bullet;
mso-level-text:?;
mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;
font-family:Wingdings;}
@list l0:level7
{mso-level-number-format:bullet;
mso-level-text:?;
mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;
font-family:Symbol;}
@list l0:level8
{mso-level-number-format:bullet;
mso-level-text:o;
mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;
font-family:"Courier New";}
@list l0:level9
{mso-level-number-format:bullet;
mso-level-text:?;
mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;
font-family:Wingdings;}
ol
{margin-bottom:0in;}
ul
{margin-bottom:0in;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
<div lang="EN-US" link="blue" vlink="purple">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size: 10pt; font-family: Arial, sans-serif; color: rgb(68, 84, 106);">This is an excerpt from Chandler's comment in
</span><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></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family: Arial, sans-serif; color: rgb(68, 84, 106);"><o:p> </o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><!--[if !supportLists]--><span style="font-family:Wingdings;color:black"><span style="mso-list:Ignore">Ø<span style="font-style: normal; font-variant: normal; font-weight: normal; font-size: 7pt; line-height: normal; font-family: '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: 10pt; font-family: Arial, sans-serif; color: rgb(68, 84, 106);"><o:p> </o:p></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 #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><a name="_____replyseparator"></a><b><span style="font-size: 11pt; font-family: Calibri, sans-serif;">From:</span></b><span style="font-size: 11pt; font-family: Calibri, sans-serif;"> Sanjay Patel [<a href="mailto:spatel@rotateright.com">mailto:spatel@rotateright.com</a>]
<br>
<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<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<div>
<p class="MsoNormal" style="margin-bottom:12.0pt">Hi Taewook -<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">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></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">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></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<p class="MsoNormal" style="margin-bottom:12.0pt">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></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<p class="MsoNormal">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></p>
<blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in">
<div>
<div>
<div>
<p class="MsoNormal"><span style="font-size: 10.5pt; font-family: Calibri, sans-serif; color: black;">Hello, <o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size: 10.5pt; font-family: Calibri, sans-serif; color: black;"><o:p> </o:p></span></p>
</div>
<div>
<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:<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size: 10.5pt; font-family: Calibri, sans-serif; color: black;"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size: 10.5pt; font-family: Calibri, sans-serif; color: black;">xor %al, %cl<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size: 10.5pt; font-family: Calibri, sans-serif; color: black;">movzbl %cl, %ecx<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size: 10.5pt; font-family: Calibri, sans-serif; color: black;">cmp $0x20, %ecx<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size: 10.5pt; font-family: Calibri, sans-serif; color: black;"><o:p> </o:p></span></p>
</div>
<div>
<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, <o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size: 10.5pt; font-family: Calibri, sans-serif; color: black;"><o:p> </o:p></span></p>
</div>
<div>
<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."<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size: 10.5pt; font-family: Calibri, sans-serif; color: black;"><o:p> </o:p></span></p>
</div>
<div>
<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?<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size: 10.5pt; font-family: Calibri, sans-serif; color: black;"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size: 10.5pt; font-family: Calibri, sans-serif; color: black;">Thanks,<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size: 10.5pt; font-family: Calibri, sans-serif; color: black;">Taewook<o:p></o:p></span></p>
</div>
</div>
</div>
<p class="MsoNormal" style="margin-bottom:12.0pt"><br>
_______________________________________________<br>
LLVM Developers mailing list<br>
<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a><br>
<a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__lists.llvm.org_cgi-2Dbin_mailman_listinfo_llvm-2Ddev&d=CwMGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=kOsLCgQzH7N8ptZ7diJD9g&m=4GlWLa5X3i08opHX4qEinKM5A85qGzRUacht2PVZxT8&s=SLs62ig3RuWWdvCIeqTpSLIkus8-NwvppqkNCTZATro&e=" target="_blank">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a><o:p></o:p></p>
</blockquote>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
</div>
</div>
</div>
</div>
</span>
</body>
</html>