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<p class="MsoNormal">OpenVMS has something called a “varstring” (IIRC) which is a 16-bit length followed by the string data. I don’t know if John Reagan has support for any VMS languages with that construct yet, but I’d expect it to be effectively a struct
with the length as the first member and a VLA-like thing holding the array. Your container might want to look something like that.<o:p></o:p></p>
<p class="MsoNormal">--paulr<o:p></o:p></p>
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<p class="MsoNormal"><b>From:</b> llvm-dev <llvm-dev-bounces@lists.llvm.org> <b>On Behalf Of
</b>David Blaikie via llvm-dev<br>
<b>Sent:</b> Tuesday, November 12, 2019 2:35 PM<br>
<b>To:</b> Christoffer Lernö <christoffer@aegik.com><br>
<b>Cc:</b> via llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Subject:</b> Re: [llvm-dev] The best way of generating a good representation for an array with header?<o:p></o:p></p>
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<p class="MsoNormal">the pointer points to the first element, and you walk backwards from there to find the header details about the bounds/etc?<br>
<br>
In any case - I'd look at something like C++'s std::vector, which is a variable length array, and model your situation similarly. I doubt there's anything in particular you'll want to/be able to teach the optimizations about your situation (nothing especially
special that they know about std::vector-like things either, that I know of - they maybe can deduce certain things about how the bounds relate, and they certainly can optimize a lot of std::vector usage) & debug info would probably look like std::vector, in
that it'd be a custom type, etc. Though if my guess above was right about using prefix data to describe the bounds - that might be hard to model in DWARF & you might be better off not being "tricky" like that & modelling this closer to something that you could
have written in C or C++ more naturally.<o:p></o:p></p>
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<p class="MsoNormal">On Tue, Nov 12, 2019 at 4:14 AM Christoffer Lernö via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">I’m considering building in variable arrays by implementing them as a stretchy buffer, that is a single allocation with header + elements with the pointer passed around pointing to the first element. (Example:
<a href="https://www.gamasutra.com/blogs/NiklasGray/20180109/312683/Minimalist_container_library_in_C_part_1.php" target="_blank">
https://www.gamasutra.com/blogs/NiklasGray/20180109/312683/Minimalist_container_library_in_C_part_1.php</a>)<br>
<br>
Is there a good way to represent this in LLVM? I mean both in terms of helping the optimizer passes understand how the layout works and to make sure the debug info looks ok.<br>
<br>
<br>
Best regards,<br>
Christoffer<o:p></o:p></p>
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