Re: Warnings with -Og - gcc 4.8

[Jeff Law <law at redhat dot com>]

On 03/05/2013 12:04 PM, Lars Gullik Bjønnes wrote:
> Jeffrey Walton <noloader@gmail.com> writes:
>
> | On Tue, Mar 5, 2013 at 1:41 PM, Lars Gullik Bjønnes <larsbj@gullik.org> wrote:
> > > I get a lot of warnings with -Og and gcc from trunk.
> > > I do not get these warnings with any other warning level.
> > >
> > > This is a reduced example:
> > > ----------
> > > int foo(void);
> > >
> > > int failing(void)
> > > {
> > >          int r;
> > >          unsigned int i;
> > >          struct h * p[3];
> > >
> > >          for (i = 0; i < sizeof(p) / sizeof(p[0]); ++i) {
> > >                  r = foo();
> > >                  if (r != 0)
> > >                          break;
> > >          }
> > >          return r >= 0;
> > > }
> > > -----------
> > >
> > > Compile with: gcc -Og -Wall -c fil.c
> > >
> > > gcc --version
> > > gcc (GCC) 4.8.0 20130304 (experimental)
> > >
> > > Should I create a bug on this, or will someone else handle that?
> | What warnings?
>
> $ gcc -Og -Wall -c fil.c
> fil.c: In function ‘failing’:
> fil.c:14:11: warning: ‘r’ may be used uninitialized in this function [-Wmaybe-uninitialized]
>    return r >= 0;

Without the optimizer enabled, GCC does not do the analysis to prove the 
loop always executes and thus does not know it can eliminate the edge 
from the entry block to the return block with its associated 
uninitialized use.

jeff