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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Not only do FPGAs not support recursion, we don’t even support calls!
<b>All</b> user code must be inlined into one kernel/component, which is then used to create HDL for the FPGA.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Mark<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> Bruce Hoult <brucehoult@sifive.com>
<br>
<b>Sent:</b> December 17, 2018 9:28 AM<br>
<b>To:</b> Mendell, Mark P <mark.p.mendell@intel.com><br>
<b>Cc:</b> jjones@prc-hsv.com; LLVM Developers Mailing List <llvm-dev@lists.llvm.org><br>
<b>Subject:</b> Re: [llvm-dev] LLVM Backend for a platform with no (normal) stack<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Mon, Dec 17, 2018 at 6:14 AM Mendell, Mark P <<a href="mailto:mark.p.mendell@intel.com">mark.p.mendell@intel.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">For a machine like an FPGA with no stack, you have to ensure that you have an optimization that rewrites the alloca into either registers (such as PromoteMem2Reg) or that you rewrite
the alloca by declaring a static local, and rewriting the code to use that instead of the alloca result.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">You'll then have to make sure programs never have recursion.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">When it comes down to it, nothing we run programs on actually has a true unbounded stack. We just have a region of memory that we calculate or hope will be big enough. But over a million people (mostly amateurs) happily and regularly run
C++ programs (with virtual functions and all) compiled by gcc on machines with only 2 KB of RAM: the ATmega328 in most Arduinos.<o:p></o:p></p>
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