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<p><span style="font-size:12.0pt;line-height:105%"><o:p> </o:p></span></p>
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<p class="MsoNormal">On 04/26/2018 07:03 PM, Narayanaswamy, Ravi wrote:<o:p></o:p></p>
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<p class="MsoNormal"><span style="color:#1F497D">Hi Hal,</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> We are not trying to address issues where the object mapped are of different sizes between host and target with different ABI.
</span><o:p></o:p></p>
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<span style="font-size:12.0pt;font-family:"Times New Roman",serif"><br>
Why are you not trying to address that issue?</span><span style="font-size:12.0pt;font-family:"Times New Roman",serif;color:#1F497D"><o:p></o:p></span></p>
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<span style="color:#1F497D"><o:p> </o:p></span></p>
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<span style="color:#1F497D">Good question. It is a harder problem and no vendor except Intel (offloading from windows to Linux) required this and so were not pushing for this.<o:p></o:p></span></p>
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<span style="color:#1F497D"><o:p> </o:p></span></p>
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<span style="color:#1F497D">Also bring up a whole lot of problems with shared memory, how do use shared memory if the objects are different, are copies made, when is the original item synced up.<o:p></o:p></span></p>
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<span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt;line-height:normal">
<span style="color:#1F497D">Ravi<o:p></o:p></span></p>
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<span style="font-size:12.0pt;font-family:"Times New Roman",serif"><br>
<br>
<br>
<o:p></o:p></span></p>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<p class="MsoNormal"><span style="color:#1F497D">The issue is when the objects are of same size like double which is 8bytes on both 32bit and 64bit platform. If a double is used in a first_private on a target clause, the 64 bit side will pass it as value
whereas on the 32bit side since the value does not fit in the argument it will be passed as pointer to a double. There will be a mis-match at the call site and entry site on this value.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> The main reason for this change is that when we do backend outlining for target pragmas the targets information needs to be communicated to the backend to generate the tables with the right names. Generate
LLVM IR for passing this information is one mechanism and other is passing the command option to the backend. For the later each pass which needs this info will have to change.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Thanks</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Ravi</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
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<a name="_____replyseparator"></a><b><span style="color:windowtext">From:</span></b><span style="color:windowtext"> Hal Finkel [<a href="mailto:hfinkel@anl.gov">mailto:hfinkel@anl.gov</a>]
<br>
<b>Sent:</b> Wednesday, April 25, 2018 5:50 PM<br>
<b>To:</b> Lin, Jin <<a href="mailto:jin.lin@intel.com">jin.lin@intel.com</a>>; Friedman, Eli <<a href="mailto:efriedma@codeaurora.org">efriedma@codeaurora.org</a>>; '<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>' <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>><br>
<b>Subject:</b> Re: [llvm-dev] [LLVM][RFC] Representing the target device information in the LLVM IR</span><o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
<p>Hi, Jin,<o:p></o:p></p>
<p>Can you please back up a bit and talk about the programming environment in which this problem manifests?<o:p></o:p></p>
<p>If I have a host and a target with different ABIs, then it seems we have lots of problems. For one thing, the layouts of structures are different, the sizes of some integer types are different, the sizes of pointers are different, and so on. It seems like
a solution in this space should address, somehow, this general translation problem. Fixing this particular problem with the dispatch function's parameters feels like only the tip of the iceberg. What if I'm passing a pointer to some structure, or a pointer
to other pointers, etc.?<o:p></o:p></p>
<p>I understand that OpenMP v5 is expected to have some custom "mappers" to handle deep copying and translation. Is this related to the design space here?<o:p></o:p></p>
<p>Thanks again,<o:p></o:p></p>
<p>Hal<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal">On 04/25/2018 07:22 PM, Lin, Jin via llvm-dev wrote:<o:p></o:p></p>
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<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<p class="MsoNormal"><span style="color:#1F497D">For the firstprivate clause, the compiler generates code to pass it by value or by reference to the outlined function. The reason the first private scalars is generally passed by value is for the performance
reason.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">For this particular case, the compiler cannot generate code to pass the double @gg by value under i386-pc-linux-gnu since the value is 64 bit while the architecture is 32bit.
</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">For the host compilation, the compiler generates the code to pass the data as well as the outlined function name to the OMP runtime.
</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">For the target compilation, the compiler generates the outlined function so that it can be called by the OMP runtime.
</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">So, the compiler is required to generate a single call on the host to support all the targets. All the target versions must have the same interface. So the common interface of the outline function should be used.
For this particular example, the variable @gcc should be passed by reference under x86_64-mic.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Please let me know if you have more questions.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Jin</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
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<b><span style="color:windowtext">From:</span></b><span style="color:windowtext"> Friedman, Eli [<a href="mailto:efriedma@codeaurora.org">mailto:efriedma@codeaurora.org</a>]
<br>
<b>Sent:</b> Wednesday, April 25, 2018 4:14 PM<br>
<b>To:</b> Lin, Jin <a href="mailto:jin.lin@intel.com"><jin.lin@intel.com></a>; '<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>'
<a href="mailto:llvm-dev@lists.llvm.org"><llvm-dev@lists.llvm.org></a><br>
<b>Subject:</b> Re: [llvm-dev] [LLVM][RFC] Representing the target device information in the LLVM IR</span><o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal">On 4/25/2018 3:48 PM, Lin, Jin wrote:<o:p></o:p></p>
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<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<p class="MsoNormal"><span style="color:#0070C0">Given a global variable @gg, the compiler has to generate code on the host to specify whether it is passed by value or passed by reference. In the following example, if the compiler generates the code for passing
by value, the outlined function on the target </span><span style="font-family:"color:#0070C0;border:none windowtext 1.0pt;padding:0in">i386-pc-linux-gnu</span><span style="color:#0070C0"> cannot get the correct value since it assumes the variable @gg
is passed by reference. </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#0070C0"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#0070C0">Here is the corresponding IR on the host side.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:red"> %0 = load double, double* @gg, align 8, !tbaa !3</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:red"> %1 = bitcast double %0 to i64</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> …</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#0070C0"> %12 = getelementptr inbounds [4 x i8*], [4 x i8*]* %.offload_baseptrs, i32 0, i32 2</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#0070C0"> %13 = bitcast i8** %12 to i64*</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:red"> store i64 %1, i64* %13, align 8</span><o:p></o:p></p>
</blockquote>
<p class="MsoNormal" style="margin-bottom:12.0pt;line-height:normal"><span style="font-size:12.0pt;font-family:"Times New Roman",serif"><br>
Could you describe the overall process of calling an offloaded function in a bit more detail? How do you describe the ABI of the called function to the OpenMP runtime?<br>
<br>
I suspect you shouldn't be trying to store things which aren't pointers into offload_baseptrs.<br>
<br>
-Eli<br>
<br>
<br>
<br>
</span><o:p></o:p></p>
<pre>-- <o:p></o:p></pre>
<pre>Employee of Qualcomm Innovation Center, Inc.<o:p></o:p></pre>
<pre>Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project<o:p></o:p></pre>
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<br>
<br>
</span><o:p></o:p></p>
<pre>_______________________________________________<o:p></o:p></pre>
<pre>LLVM Developers mailing list<o:p></o:p></pre>
<pre><a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a><o:p></o:p></pre>
<pre><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></pre>
</blockquote>
<p class="MsoNormal" style="margin-bottom:12.0pt;line-height:normal"><span style="font-size:12.0pt;font-family:"Times New Roman ,serif",serif"> </span><o:p></o:p></p>
<pre>-- <o:p></o:p></pre>
<pre>Hal Finkel<o:p></o:p></pre>
<pre>Lead, Compiler Technology and Programming Languages<o:p></o:p></pre>
<pre>Leadership Computing Facility<o:p></o:p></pre>
<pre>Argonne National Laboratory<o:p></o:p></pre>
</blockquote>
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<span style="font-size:12.0pt;font-family:"Times New Roman",serif"><br>
<br>
<o:p></o:p></span></p>
<pre>-- <o:p></o:p></pre>
<pre>Hal Finkel<o:p></o:p></pre>
<pre>Lead, Compiler Technology and Programming Languages<o:p></o:p></pre>
<pre>Leadership Computing Facility<o:p></o:p></pre>
<pre>Argonne National Laboratory<o:p></o:p></pre>
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