optimizing out string functions when the string contains a NUL

[ohav chochmah]

On 6/20/12, Ian Lance Taylor <iant@google.com> wrote:
> ohav chochmah <philomath868@gmail.com> writes:
>
>> #define HIDDEN "\0this string starts with a NUL"
>> ...
>> AFAICT, the puts and printf are both no-ops, as the C-string stops
>> before it starts.  yet when doing 'gcc -S tst.c -O2 -march=native' or
>> even 'gcc -S tst.c -O3 -march=native', GCC generates the following:
>> ...
>> in short, the printf was removed but not the puts.  which left me
>> wondering why?
>
> You are describing an optimization in which GCC looks in constant string
> literals passed to puts and truncates them at \0.  Nobody has
> implemented that optimization.  It sounds like it would affect very very
> very few programs, so I'm not sure why anybody would bother to implement

right, but then why is the printf omitted entirely?

> it.  If anything I think it would be more useful to have a warning.  But

a warning is issued for printf (tst.c:8:5: warning: embedded ‘\0’ in
format [-Wformat-contains-nul]), but not for puts.

thanks.