llvm dev - Mar 2010 - [LLVMdev] Pass and return of large objects

Suppose you have something like 'struct foo { char data[10000000]; }',
and you want to pass such objects as function parameters, and return
them as function results, by value, does this currently work correctly
on all supported target platforms?

Hi Russell,
> Suppose you have something like 'struct foo { char data[10000000];
}',
> and you want to pass such objects as function parameters, and return
> them as function results, by value, does this currently work correctly
> on all supported target platforms?
as far as I know this only works on x86, and only with LLVM from svn.

Ciao,

Duncan.

Oh... :(

Are there any plans to change this? It's needed for a correct
implementation of C, after all.

On Mon, Mar 1, 2010 at 3:14 PM, Duncan Sands <baldrick at free.fr>
wrote:
> Hi Russell,
>
>> Suppose you have something like 'struct foo { char data[10000000];
}',
>> and you want to pass such objects as function parameters, and return
>> them as function results, by value, does this currently work correctly
>> on all supported target platforms?
>
> as far as I know this only works on x86, and only with LLVM from svn.
>
> Ciao,
>
> Duncan.
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> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
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>

> Suppose you have something like 'struct foo { char data[10000000];
}',
> and you want to pass such objects as function parameters, and return
> them as function results, by value, does this currently work correctly
> on all supported target platforms?
Yes, it should. But on many (almost all platforms) this will surely
overflow the stack.
Also, these objects are not supported on 16-bit targets :)

-- 
With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University

On Mon, Mar 1, 2010 at 3:20 PM, Anton Korobeynikov
<anton at korobeynikov.info> wrote:
> Yes, it should.
Hmm, Duncan Sands says otherwise?
> But on many (almost all platforms) this will surely
> overflow the stack.
Well, the stack size can usually be tweaked at runtime. But suppose we
have the default stack size, and replace the 10 MB object with 100 kB,
the question stands.
> Also, these objects are not supported on 16-bit targets :)
True :-) well, on a 16-bit system, can you pass and return a 1 kB object?