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[Bug c/67618] malloc+memset optimization breaks code
- From: "daniel.gutson at tallertechnologies dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Thu, 17 Sep 2015 19:57:32 +0000
- Subject: [Bug c/67618] malloc+memset optimization breaks code
- Auto-submitted: auto-generated
- References: <bug-67618-4 at http dot gcc dot gnu dot org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67618
--- Comment #4 from Daniel Gutson <daniel.gutson at tallertechnologies dot com> ---
(In reply to Andreas Schwab from comment #3)
> Trying to read the (uninitialized) contents of the allocated memory for x <=
> 12 would be undefined behaviour, so calling calloc instead does not change
> the defined behaviour.
Why do you assert that the program will read the memory?
The optimization ignores the 'if' statement (just comment that line and see),
so if malloc() returns NULL, memset is called unconditionally and will try to
write to address NULL. The "x > 12" was just an example that this is arbitrary.
Replace it with something else. The 'if' shall not be ignored.