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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Gopal,
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> I gave a presentation on how AMD compiles here:<o:p></o:p></span></p>
<p class="MsoNormal"><a href="http://llvm.org/devmtg/2010-11/Villmow-OpenCL.pdf">http://llvm.org/devmtg/2010-11/Villmow-OpenCL.pdf</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Micah<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"><o:p> </o:p></span></p>
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<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""> llvmdev-bounces@cs.uiuc.edu [mailto:llvmdev-bounces@cs.uiuc.edu]
<b>On Behalf Of </b>Gopal Rastogi<br>
<b>Sent:</b> Wednesday, October 09, 2013 8:13 AM<br>
<b>To:</b> llvmdev@cs.uiuc.edu<br>
<b>Subject:</b> [LLVMdev] Backend vs JIT : GPU<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Hi guys,<br>
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I am understanding OpenCL compilation flow on GPU in order to develop OpenCL runtime for a new hardware.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I understood that OpenCL compiler is part of a vendor's runtime library which is the heart of OpenCL. Since OpenCL kernel is compiled at runtime, hence at high level its compilation takes place in two steps:
<o:p></o:p></p>
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<p class="MsoNormal">i. source code is first converted to intermediate code.<o:p></o:p></p>
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<p class="MsoNormal">ii. intermediate code is then translated to targeted binary code.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">let say for example, we have a OpenCL kernel source code vectorAdd_kernel.cl :<o:p></o:p></p>
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<p class="MsoNormal">1. OpenCL compilation flow on Nvidia GPUs<o:p></o:p></p>
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<p class="MsoNormal"> a. vectorAdd_kernel.cl is first translated to LLVM IR using clang and
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<p class="MsoNormal"> b. LLVM IR is converted into optimized LLVM IR using LLVM optimizer.<o:p></o:p></p>
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<p class="MsoNormal"> b. optimized LLVM IR is then translated to vectorAdd_kernel.ptx using Back-end<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"> c. vectorAdd_kernel.ptx is then translated to vectorAdd_kernel.bin file using JIT. Nvidia uses JIT to get benefit in-case when next-generation GPUs are encounterd.<o:p></o:p></p>
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<p class="MsoNormal">2. OpenCL compilation on AMD GPUs<o:p></o:p></p>
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<p class="MsoNormal"> a. vectorAdd_kernel.cl is first translated to LLVM IR using gcc/clang<o:p></o:p></p>
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<p class="MsoNormal"> b. LLVM IR is then converted into optimzed LLVM IR using LLVM optimizer.<o:p></o:p></p>
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<p class="MsoNormal"> c. optimized LLVM IR is then converted into AMD IL.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"> d. AMD IL is then converted into AMD ISA using shader compiler (GPU JIT).
<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">I understand that AMD uses back-end compilation as part of JIT, instead Nvidia which uses back-end separate from JIT.
<o:p></o:p></p>
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<p class="MsoNormal">Is that correct? If it is so then what are the advantages of using JIT separate from back-end?<br>
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Thanks for your comments/opinions, <o:p></o:p></p>
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<p class="MsoNormal">-Gopal<o:p></o:p></p>
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