[Bug c/18411] Warning not legitimate

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

------- Additional Comments From joseph at codesourcery dot com  2004-11-10 01:15 -------
Subject: Re:  Warning not legitimate

On Wed, 10 Nov 2004, manus at eiffel dot com wrote:

> Ok, so why don't you generate the warning only when it makes sense. In my 
> original case, I was passing a char and tell the C compiler it was a function 
> pointer expecting a char. In this scenario it should not produce any warning.

There is a limit to how much we care about code with undefined behavior on 
execution.  What type you pass in the source code is a red herring; if you 
cast to a prototype type then the arguments will be getting converted to 
that type, including if you'd passed a float argument.  We aim for the 
front end to pass down type-consistent code to the rest of the compiler 
(which ideally would never need to call back into the earlier parts of the 
compiler); where the standard requires type-inconsistent code to be 
compiled but gives it execution-time undefined behavior, the only sensible 
consistent structure for the rest of the compiler involves an abort in 
place of the nonsensical code.

> If you have incompatible types (such as int where you expect a float/double) 
> then I'm ok that you generate a warning (although I would prefer an error since 
> the generated code is incorrect).

Remember DR#109:

   A conforming implementation must not fail to translate a strictly
   conforming program simply because *some* possible execution of that
   program would result in undefined behavior.

The undefined behavior is only on execution, so the program must be 
accepted.  Because its execution is nonsensical - has no meaning whatever 
- an abort is generated.



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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18411