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Re: avoiding recursive calls of calloc due to optimization
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Marc Glisse <marc dot glisse at inria dot fr>
- Cc: Daniel Gutson <daniel dot gutson at tallertechnologies dot com>, gcc Mailing List <gcc at gcc dot gnu dot org>, glisse at gcc dot gnu dot org, Sebastian Huber <sebastian dot huber at embedded-brains dot de>, Jan Hubicka <hubicka at ucw dot cz>
- Date: Tue, 22 Sep 2015 10:16:46 +0200
- Subject: Re: avoiding recursive calls of calloc due to optimization
- Authentication-results: sourceware.org; auth=none
- References: <CAF5HaEWYyPpxQe_iJqF8LXn_Yp-8aJ6uzMP-nzK9Y5UhRX_JwQ at mail dot gmail dot com> <alpine dot DEB dot 2 dot 20 dot 1509212016220 dot 1947 at laptop-mg dot saclay dot inria dot fr>
On Mon, Sep 21, 2015 at 8:17 PM, Marc Glisse <marc.glisse@inria.fr> wrote:
> On Mon, 21 Sep 2015, Daniel Gutson wrote:
>
>> This is derived from https://gcc.gnu.org/ml/gcc-help/2015-03/msg00091.html
>>
>> Currently, gcc provides an optimization that transforms a call to
>> malloc and a call to memset into a call to calloc.
>> This is fine except when it takes place within the calloc() function
>> implementation itself, causing a recursive call.
>> Two alternatives have been proposed: -fno-malloc-builtin and disable
>> optimizations in calloc().
>> I think the former is suboptimal since it affects all the code just
>> because of the implementation of one function (calloc()),
>> whereas the latter is suboptimal too since it disables the
>> optimizations in the whole function (calloc too).
>> I think of two alternatives: either make -fno-calloc-builtin to
>> disable the optimization, or make the optimization aware of the
>> function context where it is operating and prevent it to do the
>> transformation if the function is calloc().
>>
>> Please help me to find the best alternative so we can implent it.
>
>
> You may want to read this PR for more context
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56888#c27
Yeah, I think the proper way is to add a helper to symtab to
query whether the current function is BUILT_IN_XXX and use that
to fend of most of the "obvious" cases.
Richard.
> --
> Marc Glisse