[Bug tree-optimization/21982] GCC should combine adjacent stdio calls

["dnovillo at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From dnovillo at redhat dot com  2005-06-10 13:15 -------
Subject: Re:  GCC should combine adjacent stdio calls

On Thu, Jun 09, 2005 at 07:52:42PM -0000, joseph at codesourcery dot com wrote:

> > > extern char *s;
> > > extern int i;
> > > 
> > > printf("%d", i);
> > > printf("%.5s", s);
> > > 
> > > you can't merge the printf calls because the first one could have changed 
> > > what is pointed to by s.
> > > 
> > How can printing an integer to stdout affect 's'?  Unless 's' has
> > been somehow mapped to stdout's buffer?  Is that what you have in
> > mind?
> 
> (a) It could be stdio's buffer (via setvbuf).
> 
> (b) It could be a glibc memory stream opened with fmemopen (if the user 
> assigned to stdout - which glibc allows - or you do this optimization on 
> fprintf and not just printf).
> 
> (c) It could point to a memory mapping of the file being written.
> 
Good lord.  To me this is a pathological case.  I'd wager that
this happens approximately never.  How about a switch disabling
stdio merging?


Diego.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21982