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Re: [PATCH 5/5] Make ipa-sra observe the used parameter.
On Thu, 6 Aug 2009, Martin Jambor wrote:
> I wrote this patch after I read the following message in the thread
> about debug unwinder hooks approximately two months ago:
>
> http://gcc.gnu.org/ml/gcc-patches/2009-06/msg01048.html
>
> I am no expert in this area but as far as I understand it, there is
> now a hook for the debugger in libgcc which is static and its address
> does not escape and which has a parameter which is not used because
> the function doesn't do much on its own. However (some version of)
> gdb expects it to be called and passed information by the means of the
> otherwise unused parameters at some point when handling exceptions so
> that it can intercept each run and learn whatever it needs to from the
> arguments. Thus, IPA-SRA should not prevent passing the values to an
> otherwise perfectly local function. Jakub suggested the used
> parameter and I think it is sensible.
>
> I do not think that ordinary users will find this attribute usage very
> useful and I do expect all uses to be hacks like this.
>
> I am not sure whether the above explanation is something for the
> documentation, though. I will be glad for any suggestions in this
> regard.
>
> Does it make sense now?
The above suggests to me that what you actually want is an attribute on
the function, not a parameter, to keep the function and preserve its ABI.
Why not make "used", on the function, mean that? It's defined to mean the
function is used in some way behind the compiler's back, so making it
preserve the ABI seems reasonable.
--
Joseph S. Myers
joseph@codesourcery.com