------- Comment #5 from 0xe2 dot 0x9a dot 0x9b at gmail dot com 2010-02-16
17:37 -------
(In reply to comment #4)
> There is nothing to fix. Your program triggers undefined behavior. It can do
> anything, which can include something you'd expect, or something completely
> different and it can depend on compiler options, position of stars, etc.
I understand what you are saying, but I do not agree with that. I my opinion,
an *optimization* option should never result in any change of a program's
behavior for this particular kind of undefined behaviors. I mean, there are
basically two different kinds of undefined behaviors:
1. Where the compiler has to choose a *particular* implementation.
2. Where the compiler does not choose anything or cannot choose anything
particular. (For example, what happens if accessing deallocated memory.)
The conversion test-case is of the 1st kind. Not of the 2nd kind. GCC -O0
chooses to generate a particular sequence of instructions to implement the
undefined behavior. GCC -O2 does not respect the choice made at -O0 (or vice
versa).
So, my question is: If it is possible for the problematic code to be
implemented in all contexts by the same operation, and in this case it indeed
is possible, why is GCC using two different operations? How do you justify
that?
--
0xe2 dot 0x9a dot 0x9b at gmail dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|RESOLVED |UNCONFIRMED
Resolution|INVALID |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43089
