[Bug libstdc++/21951] [4.0 only] std::vector.reserve() unusable with -Werror -Wall -O -fno-exceptions

["veksler at il dot ibm dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From veksler at il dot ibm dot com  2005-06-08 14:43 -------
(In reply to comment #7)
> It sure as hell is for those shops that require -Werror.
>
> But ok, I'll be happy if it's fixed for 4.0.2.

I think that your argument (as phrased) does not hold.
Maybe you meant "It sure as hell is for those shops that require -Werror, 
in this particular instance".
(Pardon my language, I just quoted the original ;-)

Consider:
1. 1: int main()
   2: {
   3:   int a;
   4:   never_return(); // the halting problem
   5:   return a;       // Uninitialized variable?
   6: }
   This is perfectly valid code and well defined, yet -Wall -Werror
   will reject it. No compiler will ever be able to determine if
   line 5 is ever reached.

2. 1: int main()
   2: {
   3:    int a;
   4:    if(foo())
   5:      a= bar();
   6:    if(foo())
   7:      return a;  // Uninitialized variable?
   8:    return 0;
   9: }

   Again, no compiler will be able to prove that a nontrivial foo() does
   not change over time (unless declared const/pure/whatever).
   And as a result, -Wall -Werror will reject valid code.

In both examples, the user has a simple work-around, initialize 'a'.
Adding initialization will make the code more stable, as foo() is
no longer constrained to be const/pure (forgive me for not remembering if
it is called pure or const).

In contrast (as mentioned in comment #4), this PR and PR 21183 do not
give the user the tools to shut this specific diagnostic instance up.

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21951