<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 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:SimSun;
panose-1:2 1 6 0 3 1 1 1 1 1;}
@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:"Segoe UI";
panose-1:2 11 5 2 4 2 4 2 2 3;}
@font-face
{font-family:"\@SimSun";
panose-1:2 1 6 0 3 1 1 1 1 1;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
font-size:11.0pt;
font-family:"Calibri",sans-serif;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:#0563C1;
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;
font-size:11.0pt;
font-family:"Calibri",sans-serif;}
span.EmailStyle22
{mso-style-type:personal-compose;
font-family:"Calibri",sans-serif;
color:windowtext;
font-weight:normal;
font-style:normal;
text-decoration:none none;}
.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;}
/* List Definitions */
@list l0
{mso-list-id:449978623;
mso-list-type:hybrid;
mso-list-template-ids:1801745634 1288630336 67698691 67698693 67698689 67698691 67698693 67698689 67698691 67698693;}
@list l0:level1
{mso-level-start-at:0;
mso-level-number-format:bullet;
mso-level-text:\F0D8;
mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;
font-family:Wingdings;
mso-fareast-font-family:SimSun;
mso-bidi-font-family:Calibri;}
@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:\F0A7;
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:\F0B7;
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:\F0A7;
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:\F0B7;
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:\F0A7;
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]-->
</head>
<body lang="EN-US" link="#0563C1" vlink="#954F72" style="word-wrap:break-word">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size:12.0pt;color:#1F497D">Hi Jason,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;color:#1F497D">__fp16 is a pure storage format. You cannot pass it by value, because only
<a href="https://gitlab.com/x86-psABIs/x86-64-ABI">ABI</a> permissive types can be passed by value while __fp16 is not one of them.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="color:#1F497D;margin-left:0in;mso-list:l0 level1 lfo1">
<span style="font-size:12.0pt;color:black">if "<span style="background:white">define void @foo(i8, i8, i8, i8, half) " is even legal to use</span></span><span style="font-size:12.0pt"><o:p></o:p></span></li></ul>
<p class="MsoNormal"><span style="font-size:12.0pt;color:#1F497D">half as a target independent type is legal for LLVM. It’s not legal for unsupported target like X86. The behavior depends on how we lowering it. But I don’t know why there’s differences between
Linux and Windows. Maybe because “__gnu_f2h_ieee” is a Linux only function?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
<div>
<p class="MsoNormal"><span style="color:#1F497D">Thanks<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Pengfei<o:p></o:p></span></p>
</div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:#1F497D"><o:p> </o:p></span></p>
<div>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b>From:</b> llvm-dev <llvm-dev-bounces@lists.llvm.org> <b>On Behalf Of
</b>Jason Hafer via llvm-dev<br>
<b>Sent:</b> Friday, March 5, 2021 10:46 AM<br>
<b>To:</b> llvm-dev@lists.llvm.org<br>
<b>Cc:</b> Jason Hafer <jhafer@mathworks.com><br>
<b>Subject:</b> [llvm-dev] Is it legal to pass a half by value on x86_64?<o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">Hello,<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">I am attempting to understand an anomaly I am seeing when dealing with half on Windows and could use some help.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">Using LLVM 8 or 10, if I have IR of the flavor below:<br>
define void @foo(i8, i8, i8, i8, half) { <o:p></o:p></span></p>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black"> %6 = alloca half<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black"> store half %4, half* %6, align 1<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black"> ...<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black"> ret void<o:p></o:p></span></p>
</div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">}<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">Using x86_64-pc-linux, we convert the float passed in with __gnu_f2h_ieee.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">Using x86_64-pc-windows I do not get the conversion, so we end up with incorrect math operations.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">While investigating I noticed clang gave me the error below:<o:p></o:p></span></p>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:10.5pt;font-family:"Segoe UI",sans-serif;color:black">error: parameters cannot have __fp16 type; did you forget * ?<br>
void foo(int dc1, int dc2,int dc3,int dc4, __fp16 in)<o:p></o:p></span></p>
</div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">So, this got me wondering if "<span style="background:white">define void @foo(i8, i8, i8, i8, half) " is even legal to use or if I should rather pass by ref? I have yet
to find documentation to convince me one way or the other. Thus, I was hoping someone here might be able to shed some light on the issue.</span><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">Thank you in advance!<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">Cheers,<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">JP<o:p></o:p></span></p>
</div>
</div>
</body>
</html>