[patch] Enable lightweight checks with _GLIBCXX_ASSERTIONS.

[Florian Weimer]

On 09/08/2015 05:45 PM, Jonathan Wakely wrote:

>> I doubt we can achieve the complexity goals in all cases.  I expect that
>>
>>  for (int i = 0; i < 10000; ++i) {
>>    vector[i];
>>  }
>>
>> is optimized away in default mode, but with _GLIBCXX_ASSERTIONS, it is
>> not.
>>
>> The last time I looked at this, GCC was unable to move bounds checks out
>> of loops.
> 
> Maybe we don't want to make _FORTIFY_SOURCE imply _GLIBCXX_ASSERTIONS
> then, so they can be enabled independently. We don't have to make that
> decision right away.

I think we should try with _FORTIFY_SOURCE first.  The above case looks
rather artificial.  If there is a visible performance impact, maybe we
can get the compiler to eliminate the vector bounds checks in many cases.

-- 
Florian Weimer / Red Hat Product Security