Re: [PATCH] Remove useless if-before-free tests.

From: Junio C Hamano <gitster@pobox.com>
Date: Feb 22, 2008, 23:05 UTC
Message-ID: <7vd4qo7fsc.fsf@gitster.siamese.dyndns.org>
In-Reply-To: <87tzk0tzjz.fsf@rho.meyering.net>

Jim Meyering <jim@meyering.net> writes:

Show 16 quoted lines

> This change removes all obvious useless if-before-free tests.
> E.g., it replaces code like this:
>
>         if (some_expression)
>                 free (some_expression);
>
> with the now-equivalent:
>
>         free (some_expression);
>
> ...
>
> If you're interested in automating detection of the useless
> tests, you might like the useless-if-before-free script in gnulib:
> [it *does* detect brace-enclosed free statements, and has a --name=S
>  option to make it detect free-like functions with different names]

While I have your attention ;-)

I am not interested in automating useless "if (x) free(x)" tests, but one thing I recently wanted but did not know a handy tool for was to find all the calls to free() that free a pointer to an object of a particular type. More specifically, we seem to allocate and free many "struct commit_list", and I wanted to introduce a custom bulk allocator. Allocate many of them in a block, hand out one by one, and tell callers to hand them back not to free() but to the allocator so that it can keep the returned ones on a linked list and hand them back again when the next call wanted to allocate one without actually calling xmalloc()). But in order to do so, missed conversion from malloc() to the custom allocator is not fatal (just wasteful), but forgetting to convert free() really is.

I guess sparse could be hacked to do that, but do GNU folks have some checker like that?