Can't turn off overflow_warning?

Can't turn off overflow_warning?

[Bradley Lucier]

After examining the source and documentation, it appears to me that in 
4.0.* and on mainline one cannot turn off the warning generated by 
overflow_warning, in, for example,

[descartes:~] lucier% cat test.c
#include <stdio.h>

int main() {
   if (1048256 * 1048256 < 0)
     printf("1");
   else
     printf("2");

return 0;
}
[descartes:~] lucier% /pkgs/gcc-4.0.0/bin/gcc -v
Using built-in specs.
Target: powerpc-apple-darwin8.1.0
Configured with: ../configure --prefix=/pkgs/gcc-4.0.0 
--with-gmp=/pkgs/gmp-4.1.3 --with-mpfr=/pkgs/gmp-4.1.3
Thread model: posix
gcc version 4.0.0
[descartes:~] lucier% /pkgs/gcc-4.0.0/bin/gcc -O1 -Wall -W -Wextra 
-fwrapv test.c
test.c: In function 'main':
test.c:4: warning: integer overflow in expression
[descartes:~] lucier% ./a.out
1[descartes:~] lucier%

I'd like to be able to do this, since I'm auto-generating code that 
explicitly uses overflow tests that assume that signed ints overflow 
using twos-complement arithmetic and I don't want to be distracted by 
extraneous warnings when constant propagation in the Scheme system puts 
constants into this C code.

Personally, I'd like overflow_warning to be turned off for signed ints 
if -fwrapv is passed as a flag.  I suppose an explicit 
-Wno-overflow-warning would be OK, too.

If I were to propose a patch, which way should I go?

Brad

Re: Can't turn off overflow_warning?

[Andrew Pinski]

On Jul 15, 2005, at 10:27 PM, Bradley Lucier wrote:

> After examining the source and documentation, it appears to me that in 
> 4.0.* and on mainline one cannot turn off the warning generated by 
> overflow_warning, in, for example,

IIRC the C standard requires that a warning here but I could be wrong.

-- Pinski

Re: Can't turn off overflow_warning?

[Gabriel Dos Reis]

Andrew Pinski <pinskia@physics.uc.edu> writes:

| On Jul 15, 2005, at 10:27 PM, Bradley Lucier wrote:
| 
| > After examining the source and documentation, it appears to me that
| > in 4.0.* and on mainline one cannot turn off the warning generated
| > by overflow_warning, in, for example,
| 
| IIRC the C standard requires that a warning here but I could be wrong.

Please not again.  
The C standard knows nothing about warning.  There is a notion of
diagnostic but I don't think it makes any sense in the particular case
Brad describes.  

| 
| -- Pinski

-- 
                                                       Gabriel Dos Reis 
                                           gdr@integrable-solutions.net

Re: Can't turn off overflow_warning?

[DJ Delorie]

> If I were to propose a patch, which way should I go?

Why not check out my recently posted -Wpragmas patch on gcc-patches?
It takes a set of existing non-optional warnings, and gives them an
option that can be used to disable them, which defaults to on
(i.e. -Wno-pragmas is the useful option).

That way, you get control but the default action stays the same.