<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 14 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:"MS Mincho";
panose-1:2 2 6 9 4 2 5 8 3 4;}
@font-face
{font-family:"MS Mincho";
panose-1:2 2 6 9 4 2 5 8 3 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;}
@font-face
{font-family:"\@MS Mincho";
panose-1:2 2 6 9 4 2 5 8 3 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.MsoPlainText, li.MsoPlainText, div.MsoPlainText
{mso-style-priority:99;
mso-style-link:"Plain Text Char";
margin:0in;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri","sans-serif";
mso-fareast-language:JA;}
span.EmailStyle17
{mso-style-type:personal-reply;
font-family:"Calibri","sans-serif";
color:#1F497D;}
span.PlainTextChar
{mso-style-name:"Plain Text Char";
mso-style-priority:99;
mso-style-link:"Plain Text";
font-family:"Calibri","sans-serif";}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri","sans-serif";
mso-fareast-language:JA;}
@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="MsoPlainText">I was not thinking straight. In the beginning of StrChrOpt::callOptimizer(), there is already this check<o:p></o:p></p>
<p class="MsoPlainText">to make sure that llvm does not attempt this optimization if char type is not 8-bit long.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">FunctionType *FT = Callee->getFunctionType();<o:p></o:p></p>
<p class="MsoPlainText">if (FT->getNumParams() != 2 ||<o:p></o:p></p>
<p class="MsoPlainText"> FT->getReturnType() != B.getInt8PtrTy() || //<----- “char *” is a pointer to int8<o:p></o:p></p>
<p class="MsoPlainText"> FT->getParamType(0) != FT->getReturnType() ||<o:p></o:p></p>
<p class="MsoPlainText"> !FT->getParamType(1)->isIntegerTy(32))<o:p></o:p></p>
<p class="MsoPlainText"> return 0;<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">So I guess something like "(255 & value)" should just work.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Thanks,<o:p></o:p></p>
<p class="MsoPlainText">- Gao. <o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><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 #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""> Eli Friedman [mailto:eli.friedman@gmail.com]
<br>
<b>Sent:</b> Tuesday, August 13, 2013 2:35 PM<br>
<b>To:</b> Gao, Yunzhong<br>
<b>Cc:</b> Nick Lewycky; reviews+D1279+public+b2efa1ad64fbca2e@llvm-reviews.chandlerc.com; llvm-commits@cs.uiuc.edu<br>
<b>Subject:</b> Re: [PATCH] Fixing a corner-case bug in lib call optimization<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<p class="MsoNormal">On Tue, Aug 13, 2013 at 2:03 PM, Gao, Yunzhong <<a href="mailto:yunzhong_gao@playstation.sony.com" target="_blank">yunzhong_gao@playstation.sony.com</a>> wrote:<o:p></o:p></p>
<div>
<div>
<blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in">
<p class="MsoNormal">Hi Nick,<br>
Thanks for reviewing the patch.<br>
I will change the type conversion to "unsigned char" instead; that should make<br>
the result deterministic.<br>
I feel that this is probably still not an ideal solution because the host machine<br>
might have a different size for "char" type than the target machine, but in the<br>
llvm backend I did not find a way to extract the size of target "char" type. I<br>
would guess that machines with non-8-bit bytes are rare nowadays? Since<br>
the patch is only intended for a corner-case comparing a value with zero, it<br>
might suffice using a cast to "unsigned char" or even "(value & 255)".<br>
What do you think?<o:p></o:p></p>
</blockquote>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">Assuming char is 8 bits is probably good enough. You could also extract the relevant type out of the function signature; the first argument to strchr is a char*.<o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">-Eli<o:p></o:p></p>
</div>
</div>
</div>
</div>
</body>
</html>