[Bug c++/43680] [DR 1022] G++ is too aggressive in optimizing away bounds checking with enums

["mark at codesourcery dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #15 from mark at codesourcery dot com  2010-04-20 22:18 -------
Subject: Re:  [DR 1022] G++ is too aggressive in optimizing
 away bounds checking with enums

jason at gcc dot gnu dot org wrote:

> Certainly optimizing away bounds checking is good when it is provably
> redundant, but that clearly doesn't apply to this case.

Do you think this is different from signed integer overflow in loops?
To me, it seems quite similar.  That's a situation where the compiler
will now optimize away the check in something like "for (int i = 0; i >=
0; ++i)", leaving us with an infinite loop.

And, of course, that can hit you in a security context too.

  /* Here we know that "i" is positive.  */
  ...
  if (i + 100 <= 0)
    abort();
  /* The check above will make sure this never overflows ...
     <scaryvoice>or will it?</scaryvoice> */
  i += 100;

> That said, I'll go ahead and add the option.

Thanks,


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43680