[llvm-dev] The best way of generating a good representation for an array with header?

David Blaikie via llvm-dev llvm-dev at lists.llvm.org
Tue Nov 12 11:34:42 PST 2019

the pointer points to the first element, and you walk backwards from there
to find the header details about the bounds/etc?

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.

On Tue, Nov 12, 2019 at 4:14 AM Christoffer Lernö via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> 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:
> https://www.gamasutra.com/blogs/NiklasGray/20180109/312683/Minimalist_container_library_in_C_part_1.php
> )
> 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.
> Best regards,
> Christoffer
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
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