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<p class="MsoNormal">Hi Alexey,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">We have semantic checks to enforce the restrictions on half type when cl_khr_fp16 is not enabled. We could keep these checks if we switch to _Float16.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Sam<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><b>From:</b> Bader, Alexey <alexey.bader@intel.com> <br>
<b>Sent:</b> Friday, October 19, 2018 9:16 AM<br>
<b>To:</b> Liu, Yaxun (Sam) <Yaxun.Liu@amd.com>; 'anastasia.stulova@arm.com' <anastasia.stulova@arm.com>; Sumner, Brian <Brian.Sumner@amd.com>; cfe-dev (cfe-dev@lists.llvm.org) <cfe-dev@lists.llvm.org><br>
<b>Subject:</b> RE: [OpenCL] Representing OpenCL half type by _Float16 type<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Hi Sam,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I assume OpenCL half type mapped to __fp16 as OpenCL specification defines it as “A 16-bit floating-point conforming to the IEEE 754-2008 half precision storage format”. This aligned with __fp16 description from
clang documentation.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">OpenCL cl_khr_fp16 extension enables arithmetic operations on ‘half’ data types and I think it’s reasonable to map ‘half’ data type to _Float16 if cl_khr_fp16 is enabled.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Is it possible to map ‘half’ data type to _Float16 and keep the restrictions of OpenCL core specification?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Alexey<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><a name="_____replyseparator"></a><b>From:</b> Liu, Yaxun (Sam) [<a href="mailto:Yaxun.Liu@amd.com">mailto:Yaxun.Liu@amd.com</a>]
<br>
<b>Sent:</b> Wednesday, October 17, 2018 7:31 PM<br>
<b>To:</b> 'anastasia.stulova@arm.com' <<a href="mailto:anastasia.stulova@arm.com">anastasia.stulova@arm.com</a>>; Bader, Alexey <<a href="mailto:alexey.bader@intel.com">alexey.bader@intel.com</a>>; Sumner, Brian <<a href="mailto:Brian.Sumner@amd.com">Brian.Sumner@amd.com</a>>;
cfe-dev (<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>) <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>><br>
<b>Subject:</b> [OpenCL] Representing OpenCL half type by _Float16 type<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hi,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Clang supports two 16 bit floating point builtin types: __fp16 and _Float16. Their differences are here<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><a href="https://clang.llvm.org/docs/LanguageExtensions.html#half-precision-floating-point">https://clang.llvm.org/docs/LanguageExtensions.html#half-precision-floating-point</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Currently clang supports OpenCL half type as __fp16, one significant disadvantage of which is that arithmetic operations are emitted as fp32 instead of fp16 instructions in LLVM IR. Another disadvantage is interoperability with C++ programs,
which uses _Float16 mostly since it is an ISO standard whereas __fp16 is not.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">OpenCL spec v 2.0 s 6.1.1.1 (<a href="https://www.khronos.org/registry/OpenCL/specs/opencl-2.0-openclc.pdf">https://www.khronos.org/registry/OpenCL/specs/opencl-2.0-openclc.pdf</a> ) defines half type. There is no requirement that it has
to be __fp16 or _Float16 type in clang. Actually, it seems both __fp16 and _Float16 can be used to represent OpenCL half type.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Considering the advantages of _Float16 type, I am wondering whether we should consider using _Float16 to represent OpenCL half type.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Any comments are welcome.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Yaxun (Sam) Liu<o:p></o:p></p>
<p class="MsoNormal">AMD<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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