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Re: unnecessary {de,}alloc wrappers?

From: Eric Blake
Subject: Re: unnecessary {de,}alloc wrappers?
Date: Tue, 01 Apr 2014 12:21:28 -0600
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On 04/01/2014 11:36 AM, Ondrej Oprala wrote:

>> Bruno Haible argued that the cost of a redundant if conditional is
>> cheaper than the cost of a function call in profiling runs, at least in
>> the portions of gnulib where he used that idiom.  Personally, I like
>> getting rid of the redundant if (I think the extra CPU cycles spent are
>> in the noise, until given a profile dump that proves otherwise).
> Hmm, is that still up-to-date information?
> Doing
> $ git grep -B2 '\bfree\(.*;'
> on glibc's and gnulib's upstream repo shows no occurences of code such
> as "if (foobar) free(foobar);".

Gnulib comes with a script, build-aux/useless-if-before-free, for
identifying such instances.  Despite your claim of not finding any
instances in gnulib, this script found several, such as:

./lib/glob.c: if (pglob->gl_pathv[pglob->gl_offs + i] != NULL)
          free (pglob->gl_pathv[pglob->gl_offs + i]);
./lib/csharpcomp.c: if (line[0] != NULL)
        free (line[0]);
./lib/csharpcomp.c: if (line[1] != NULL)
        free (line[1]);
./lib/fstrcmp.c: if (buffer != NULL)
        free (buffer);
./lib/vasnprintf.c: if (tmp_roomptr != NULL)
    free (tmp_roomptr);

> Either way, I find both of these code snippets very redundant.

As do I, but I'm not the one in charge of deciding whether to clean the
code base up to satisfy the useless-if-before-free script.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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