<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=utf-8">
<meta name="Generator" content="Microsoft Word 14 (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:Helvetica;
panose-1:2 11 6 4 2 2 2 2 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: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;}
span.gmailmsg
{mso-style-name:gmail_msg;}
span.apple-converted-space
{mso-style-name:apple-converted-space;}
span.EmailStyle19
{mso-style-type:personal-reply;
font-family:"Calibri","sans-serif";
color:#1F497D;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></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">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I made ABI_BREAKING_CHECKS be its own bullet point, and added advice for how to approach "should not change generated code." Maybe that's getting too detailed
for this document but it could prevent some false starts.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">--paulr<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></a></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:llvm-dev-bounces@lists.llvm.org]
<b>On Behalf Of </b>Matthias Braun via llvm-dev<br>
<b>Sent:</b> Thursday, February 02, 2017 10:25 AM<br>
<b>To:</b> Mehdi Amini<br>
<b>Cc:</b> llvm-dev@lists.llvm.org<br>
<b>Subject:</b> Re: [llvm-dev] Register allocator behaves differently when compiling with and without -g<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<div>
<p class="MsoNormal">On Feb 2, 2017, at 9:38 AM, Mehdi Amini via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<div>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif""><br>
On Feb 2, 2017, at 8:20 AM, David Blaikie via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></span></p>
</div>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif""><o:p> </o:p></span></p>
<div>
<div>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif"">The goal/intent is that debug info does not affect code generation. There are (many?) bugs. I think Apple folks (cc'd Adrian) may be looking at this a bit recently, not
sure.<br>
<br>
The fixes aren't usually too invasive (usually involve something counting instructions where it needs to skip counting debug intrinsics), if you're interested in having a go at fixing it yourself & sending a patch for review.<o:p></o:p></span></p>
</div>
</div>
</blockquote>
<div>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif""><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif"">I added a line there: <a href="https://docs.google.com/document/d/1YLK_xINSg1Ei0w8w39uAMR1n0dlf6wrzfypiX0YDQBc/edit">https://docs.google.com/document/d/1YLK_xINSg1Ei0w8w39uAMR1n0dlf6wrzfypiX0YDQBc/edit#</a><o:p></o:p></span></p>
</div>
</div>
</div>
</blockquote>
<div>
<p class="MsoNormal">Seeing that doc I also added a sentence that ENABLE_ABI_BREAKING_CHECKS (= different iteration order for hashsets) should not change code generation.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">- Matthias<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:9.0pt;font-family:"Helvetica","sans-serif""><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif"">— <o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif"">Mehdi<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif""><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif""><o:p> </o:p></span></p>
</div>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif""><br>
<br>
<o:p></o:p></span></p>
<div>
<div>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif""><o:p> </o:p></span></p>
<div>
<div>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif"">On Thu, Feb 2, 2017 at 8:18 AM Stephen Rogers via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></span></p>
</div>
<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>
<div>
<div>
<div>
<div>
<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif"">Hi all,<o:p></o:p></span></p>
</div>
<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif"">In several of our tests, I have noticed that the register allocator allocates to virtual registers in a different order when compiling with
the clang option -g. Before entering the register allocator, the code is identical when compiling with and without -g (with the exception of "</span><span class="gmailmsg"><span style="font-size:9.0pt;font-family:"Courier New"">DBG_VALUE</span></span><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif"">"
instructions). The only difference I can see is the value assigned to the slot index for each instruction. As an example, without -g a snippet of a basic block looks like this:<br>
</span><span style="font-size:9.0pt;font-family:"Courier New""><br>
<span class="gmailmsg">32B %vreg29<def> = LDImm 1; REG1:%vreg29</span><br>
<span class="gmailmsg">36B %vreg44<def> =</span><span class="apple-converted-space"> </span><span class="gmailmsg">LDImm</span><span class="apple-converted-space"> </span><span class="gmailmsg">1103515245; REG1:%vreg44</span><br>
<span class="gmailmsg">40B %vreg143:vsub32_1<def,read-undef> = LDImm 0; REG2:%vreg143</span><br>
<span class="gmailmsg">44B %vreg68<def> =</span><span class="apple-converted-space"> </span><span class="gmailmsg">LDImm</span><span class="apple-converted-space"> </span><span class="gmailmsg">12345; REG1:%vreg68</span><br>
<span class="gmailmsg">64B %vreg143:vsub32_0<def> = COPY %vreg143:vsub32_1; REG2:%vreg143</span><br>
<span class="gmailmsg">72B %vreg78<def> =</span><span class="apple-converted-space"> </span><span class="gmailmsg">LDImm</span><span class="apple-converted-space"> </span><span class="gmailmsg">32; REG1:%vreg78</span></span><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif""><o:p></o:p></span></p>
</div>
<p class="MsoNormal" style="margin-bottom:12.0pt"><span class="gmailmsg"><span style="font-size:9.0pt;font-family:"Arial","sans-serif"">But when I specify -g, this becomes:</span></span><span style="font-size:9.0pt;font-family:"Arial","sans-serif""><br>
<br>
</span><span class="gmailmsg"><span style="font-size:9.0pt;font-family:"Courier New"">32B %vreg29<def> =</span></span><span class="apple-converted-space"><span style="font-size:9.0pt;font-family:"Courier New""> </span></span><span class="gmailmsg"><span style="font-size:9.0pt;font-family:"Courier New"">LDImm</span></span><span class="apple-converted-space"><span style="font-size:9.0pt;font-family:"Courier New""> </span></span><span class="gmailmsg"><span style="font-size:9.0pt;font-family:"Courier New"">1;</span></span><span class="apple-converted-space"><span style="font-size:9.0pt;font-family:"Courier New""> </span></span><span class="gmailmsg"><span style="font-size:9.0pt;font-family:"Courier New"">REG1:%vreg29
dbg:path/to/source:9:34 @[</span></span><span class="apple-converted-space"><span style="font-size:9.0pt;font-family:"Courier New""> </span></span><span class="gmailmsg"><span style="font-size:9.0pt;font-family:"Courier New"">path/to/source:25:13 ]</span></span><span style="font-size:9.0pt;font-family:"Courier New""><br>
<span class="gmailmsg">36B %vreg44<def> =</span><span class="apple-converted-space"> </span><span class="gmailmsg">LDImm</span><span class="apple-converted-space"> </span><span class="gmailmsg">1103515245;</span><span class="apple-converted-space"> </span><span class="gmailmsg">REG1:%vreg44
dbg:path/to/source:9:34 @[ path/to/source:25:13 ]</span><br>
<span class="gmailmsg"><span style="color:red;background:white">44B</span> %vreg143:vsub32_1<def,read-undef> =</span><span class="apple-converted-space"> </span><span class="gmailmsg">LDImm</span><span class="apple-converted-space"> </span><span class="gmailmsg">0;</span><span class="apple-converted-space"> </span><span class="gmailmsg">REG2:%vreg143</span><br>
<span class="gmailmsg"><span style="color:red">48B</span> %vreg68<def> =</span><span class="apple-converted-space"> </span><span class="gmailmsg">LDImm</span><span class="apple-converted-space"> </span><span class="gmailmsg">12345;</span><span class="apple-converted-space"> </span><span class="gmailmsg">REG1:%vreg68
dbg:path/to/source:9:47 @[</span><span class="apple-converted-space"> </span><span class="gmailmsg">path/to/source:25:13 ]</span><br>
<span class="gmailmsg"><span style="color:red">56B</span> %vreg143:vsub32_0<def> = COPY %vreg143:vsub32_1;</span><span class="apple-converted-space"> </span><span class="gmailmsg">REG2:%vreg143</span><br>
<span class="gmailmsg"><span style="color:red">60B</span> %vreg78<def> =</span><span class="apple-converted-space"> </span><span class="gmailmsg">LDImm</span><span class="apple-converted-space"> </span><span class="gmailmsg">32;</span><span class="apple-converted-space"> </span><span class="gmailmsg">REG1:%vreg78</span></span><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif""><o:p></o:p></span></p>
</div>
<p class="MsoNormal" style="margin-bottom:12.0pt"><span class="gmailmsg"><span style="font-size:9.0pt;font-family:"Arial","sans-serif"">This change seems to affect the weight assigned to the</span></span><span class="apple-converted-space"><span style="font-size:9.0pt;font-family:"Arial","sans-serif""> </span></span><span class="gmailmsg"><span style="font-size:9.0pt;font-family:"Courier New"">LiveIntervals</span></span><span class="apple-converted-space"><span style="font-size:9.0pt;font-family:"Arial","sans-serif""> </span></span><span class="gmailmsg"><span style="font-size:9.0pt;font-family:"Arial","sans-serif"">for
each virtual register which in turn changes the allocation order.</span></span><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif""><o:p></o:p></span></p>
</div>
<p class="MsoNormal" style="margin-bottom:12.0pt"><span class="gmailmsg"><span style="font-size:9.0pt;font-family:"Arial","sans-serif"">It would be my expectation that LLVM should generate identical code for a source file with and without debug information
enabled. Is it possible we are missing some hook in our target backend that would prevent this? Or is this the expected behaviour in LLVM?</span></span><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif""><o:p></o:p></span></p>
</div>
<p class="MsoNormal"><span class="gmailmsg"><span style="font-size:9.0pt;font-family:"Arial","sans-serif"">Thanks,</span></span><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif""><o:p></o:p></span></p>
</div>
<p class="MsoNormal"><span class="gmailmsg"><span style="font-size:9.0pt;font-family:"Arial","sans-serif"">Stephen</span></span><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif""><o:p></o:p></span></p>
</div>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif"">_______________________________________________<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" target="_blank">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a><o:p></o:p></span></p>
</blockquote>
</div>
</div>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif"">_______________________________________________<br>
LLVM Developers mailing list<br>
<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a><br>
<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>
</div>
</div>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif""><br>
_______________________________________________<br>
LLVM Developers mailing list<br>
</span><a href="mailto:llvm-dev@lists.llvm.org"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif"">llvm-dev@lists.llvm.org</span></a><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif""><br>
</span><a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev"><span style="font-size:9.0pt;font-family:"Helvetica","sans-serif"">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</span></a><o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
</div>
</body>
</html>