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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I think we can’t avoid deviating from C/C++ implementation completely. But we should certainly try to avoid it in unnecessary situations as much as we can.<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">In this case it seems like the spec enforces the rules for resolving the ambiguity that seems logical to me.<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">Is this possibly a better way to deviate OpenCL implementation than giving a hypothetical warning and an error in the case the ambiguity wasn’t resolved?
<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">Cheers,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Anastasia<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>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Bader, Alexey [mailto:alexey.bader@intel.com]
<br>
<b>Sent:</b> 06 December 2016 12:17<br>
<b>To:</b> Anastasia Stulova; Richard Smith; Bruno Cardoso Lopes via Phabricator; reviews+D27334+public+f2c5a66032c4c02e@reviews.llvm.org<br>
<b>Cc:</b> egor.churaev@gmail.com; yaxun.liu@amd.com; cfe-commits@lists.llvm.org; nd<br>
<b>Subject:</b> RE: [PATCH] D27334: [OpenCL] Ambiguous function call.<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US">Actually OpenCL specification has the following text in “Built-in Functions” chapter (OpenCL
C 2.0 rev. 33):</span></a><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US">“ User defined OpenCL C functions, behave per C standard rules for functions (C99, TC2, Section<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US">6.9.1). On entry to the function, the size of each variably modified parameter is evaluated and<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;background:yellow;mso-highlight:yellow;mso-fareast-language:EN-US">the value of each argument expression is converted to the type of the corresponding
parameter as<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;background:yellow;mso-highlight:yellow;mso-fareast-language:EN-US">per usual arithmetic conversion rules described in section 6.2.6.</span><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US">
Built-in functions described in<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US">this section behave similarly, except that in order to avoid ambiguity between multiple forms of<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US">the same built-in function, implicit scalar widening shall not occur. Note that some built-in<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US">functions described in this section do have forms that operate on mixed scalar and vector types,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US">however.”
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US">If I understand it correctly this text can help to resolve the overloading, since “usual arithmetic conversion rules”
from section 6.2.6 rank floating point and integer data types including vector flavors. On the other hand I don’t think it’s good idea to adopt this rule, since it doesn’t follow C++ overloading rules and definitely will deviate OpenCL behavior from C or C++.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Alexey<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><a name="_____replyseparator"></a><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif""> Anastasia Stulova [<a href="mailto:Anastasia.Stulova@arm.com">mailto:Anastasia.Stulova@arm.com</a>]
<br>
<b>Sent:</b> Monday, December 5, 2016 9:21 PM<br>
<b>To:</b> Richard Smith <<a href="mailto:richard@metafoo.co.uk">richard@metafoo.co.uk</a>>; Bruno Cardoso Lopes via Phabricator <<a href="mailto:reviews@reviews.llvm.org">reviews@reviews.llvm.org</a>>;
<a href="mailto:reviews+D27334+public+f2c5a66032c4c02e@reviews.llvm.org">reviews+D27334+public+f2c5a66032c4c02e@reviews.llvm.org</a><br>
<b>Cc:</b> Bader, Alexey <<a href="mailto:alexey.bader@intel.com">alexey.bader@intel.com</a>>;
<a href="mailto:egor.churaev@gmail.com">egor.churaev@gmail.com</a>; <a href="mailto:yaxun.liu@amd.com">
yaxun.liu@amd.com</a>; <a href="mailto:cfe-commits@lists.llvm.org">cfe-commits@lists.llvm.org</a>; nd <<a href="mailto:nd@arm.com">nd@arm.com</a>><br>
<b>Subject:</b> RE: [PATCH] D27334: [OpenCL] Ambiguous function call.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="RU"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">>
</span>Perhaps that is the problem (that there are two modes that do different things)? Could we make the double overload be present but unselectable to diagnose this problem in that mode too?<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>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">If we could resolve the overload candidate to prefer ‘int -> float’ than ‘int->double’, it would work best.<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"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">
<a href="mailto:metafoo@gmail.com">metafoo@gmail.com</a> [<a href="mailto:metafoo@gmail.com">mailto:metafoo@gmail.com</a>]
<b>On Behalf Of </b>Richard Smith<br>
<b>Sent:</b> 05 December 2016 17:53<br>
<b>To:</b> Bruno Cardoso Lopes via Phabricator; <a href="mailto:reviews+D27334+public+f2c5a66032c4c02e@reviews.llvm.org">
reviews+D27334+public+f2c5a66032c4c02e@reviews.llvm.org</a><br>
<b>Cc:</b> <a href="mailto:alexey.bader@intel.com">alexey.bader@intel.com</a>; <a href="mailto:egor.churaev@gmail.com">
egor.churaev@gmail.com</a>; <a href="mailto:yaxun.liu@amd.com">yaxun.liu@amd.com</a>; Anastasia Stulova;
<a href="mailto:cfe-commits@lists.llvm.org">cfe-commits@lists.llvm.org</a><br>
<b>Subject:</b> Re: [PATCH] D27334: [OpenCL] Ambiguous function call.<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On 5 Dec 2016 9:42 am, "Anastasia Stulova via Phabricator via cfe-commits" <<a href="mailto:cfe-commits@lists.llvm.org">cfe-commits@lists.llvm.org</a>> wrote:<o:p></o:p></p>
<p class="MsoNormal">Anastasia added a comment.<o:p></o:p></p>
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<p class="MsoNormal"><br>
In <a href="https://reviews.llvm.org/D27334#612858" target="_blank">https://reviews.llvm.org/D27334#612858</a>, @bader wrote:<br>
<br>
> In <a href="https://reviews.llvm.org/D27334#611703" target="_blank">https://reviews.llvm.org/D27334#611703</a>, @Anastasia wrote:<br>
><br>
> > This change seems to modify normal C behavior again. Is there any strong motivation for doing this and if yes could it be done generically with C?<br>
><br>
><br>
> Motivation:<br>
><br>
> // Non-portable OpenCL 1.2 code<br>
> __kernel void foo(global float* out) {<br>
> out[get_global_id(0)] = sin(get_global_id(0));<br>
> }<br>
><br>
><br>
> This program compiles fine on OpenCL platform w/o doubles support<o:p></o:p></p>
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<p class="MsoNormal">Perhaps that is the problem (that there are two modes that do different things)? Could we make the double overload be present but unselectable to diagnose this problem in that mode too?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">and fails otherwise.<br>
> If OpenCL driver supports doubles it provides at least two versions of 'sin' built-in math function and compiler will not be able to choose the right one for 'size_t' argument.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Do you have a real example? If someone passes an integer to 'sin', I think there's a better warning we can give them :)<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">> The goal of this warning is to let OpenCL developer know about potential issues with code portability.<o:p></o:p></p>
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<p class="MsoNormal">I would argue this improves the portability much as it can also be misleading in some situations (because it refers to a potentially hypothetical problem). For example there can be builtin functions that only have a float parameter (without
a double version of it). This is for example the case with read_image functions that take a float coordinate value between 0 and 1. Unfortunately this warning won't be triggered on read_image functions because there is an overload candidate with an int type
of the same parameter too. But we can't exclude this situations to appear in the future or from some vendor extensions or even custom OpenCL code.<o:p></o:p></p>
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<p class="MsoNormal"><br>
<br>
<a href="https://reviews.llvm.org/D27334" target="_blank">https://reviews.llvm.org/D27334</a><br>
<br>
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