<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv=Content-Type content="text/html; charset=us-ascii">
<meta name=Generator content="Microsoft Word 12 (filtered medium)">
<style>
<!--
/* Font Definitions */
@font-face
{font-family:Helvetica;
panose-1:2 11 6 4 2 2 2 2 2 4;}
@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;}
@font-face
{font-family:Tahoma;
panose-1:2 11 6 4 3 5 4 4 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
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;}
span.apple-style-span
{mso-style-name:apple-style-span;}
span.EmailStyle18
{mso-style-type:personal-reply;
font-family:"Calibri","sans-serif";
color:#1F497D;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;}
@page Section1
{size:612.0pt 792.0pt;
margin:72.0pt 72.0pt 72.0pt 72.0pt;}
div.Section1
{page:Section1;}
-->
</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]-->
</head>
<body lang=EN-US link=blue vlink=purple style='word-wrap: break-word;
-webkit-nbsp-mode: space;-webkit-line-break: after-white-space'>
<div class=Section1>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Hi Evan,<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'>Could you maybe point me to the source files where this issue
might originate? I’d like to learn more about LLVM’s innards but so
far I’ve just scraped the surface and I don’t know where what phase
of instruction selection / register allocation / stack layout / etc. happens.<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'>If I understand correctly this issue might be fixed by moving
stack pointer alignment before register allocation? Is this something that
might be reasonably straightforward or are there complicated dependencies
involved?<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'>Thanks again,<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'>Nicolas<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>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'>
<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"'>
llvmdev-bounces@cs.uiuc.edu [mailto:llvmdev-bounces@cs.uiuc.edu] <b>On Behalf
Of </b>Evan Cheng<br>
<b>Sent:</b> Monday, 14 July, 2008 20:35<br>
<b>To:</b> LLVM Developers Mailing List<br>
<b>Cc:</b> anton@korobeynikov.info<br>
<b>Subject:</b> Re: [LLVMdev] Spilled variables using unaligned moves<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>This is on Windows / Cygwin? I think the dynamic stack
pointer re-alignment doesn't happen until post- register allocation.<o:p></o:p></p>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>Assuming there aren't other instructions between the
prologue and the first movups that mess up esp (there shouldn't), this is
indeed a bug. Please file a bug and attach a bc file. Thanks.<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>Evan<o:p></o:p></p>
<div>
<p class=MsoNormal><o:p> </o:p></p>
<div>
<div>
<p class=MsoNormal>On Jul 14, 2008, at 7:43 AM, Nicolas Capens wrote:<o:p></o:p></p>
</div>
<p class=MsoNormal><br>
<br>
<o:p></o:p></p>
<div>
<div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'>Hi all,<o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'> <o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'>It looks like vector spills don’t use aligned moves even
though the stack is aligned. This seems like an optimization opportunity.<o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'> <o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'>The attached replacement of fibonacci.cpp generates x86 code like
this:<o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'> <o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:8.0pt;font-family:"Courier New";
color:gray'>03A70010 push ebp </span><span
style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:black'><o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:8.0pt;font-family:"Courier New";
color:gray'>03A70011 mov
ebp,esp</span><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'><o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:8.0pt;font-family:"Courier New";
color:gray'>03A70013 and
esp,0FFFFFFF0h</span><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'><o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:8.0pt;font-family:"Courier New";
color:gray'>03A70019 sub
esp,1A0h</span><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'><o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:8.0pt;font-family:"Courier New";
color:gray'>...</span><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'><o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:8.0pt;font-family:"Courier New";
color:gray'>03A7006C movups xmmword ptr
[esp+180h],xmm7</span><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'><o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:8.0pt;font-family:"Courier New";
color:gray'>...</span><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'><o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:8.0pt;font-family:"Courier New";
color:gray'>03A70229 mulps
xmm1,xmmword ptr [esp+180h]</span><span style='font-size:11.0pt;
font-family:"Calibri","sans-serif";color:black'><o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:8.0pt;font-family:"Courier New";
color:gray'>...</span><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'><o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:8.0pt;font-family:"Courier New";
color:gray'>03A70682 movups xmm0,xmmword
ptr [esp+180h]</span><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'><o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'> <o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'>Note how stores and loads use unaligned moves while it could use
aligned moves. It’s also interesting that the multiply does correctly
assume the stack to be 16-byte aligned.<o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'> <o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'>Is there something I’m doing wrong (again), or is this
already known?<o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'> <o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'>Thanks a lot,<o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'> <o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'>Nicolas Capens<o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:black'> <o:p></o:p></span></p>
</div>
<p class=MsoNormal><span style='font-size:9.0pt;font-family:"Helvetica","sans-serif";
color:black'><fibonacci.cpp><o:p></o:p></span></p>
</div>
<p class=MsoNormal><span style='font-size:9.0pt;font-family:"Helvetica","sans-serif";
color:black'>_______________________________________________<br>
LLVM Developers mailing list<br>
<a href="mailto:LLVMdev@cs.uiuc.edu">LLVMdev@cs.uiuc.edu</a>
<a
href="http://llvm.cs.uiuc.edu">http://llvm.cs.uiuc.edu</a><br>
<a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev</a><o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
</div>
</div>
</body>
</html>