[Bug middle-end/41682] New: Need for attributes to tag code blocks so optimiser can remove more code.

[Bug middle-end/41682] New: Need for attributes to tag code blocks so optimiser can remove more code.

[oiaohm at gmail dot com]

Ok this is a really poor example bare with me.
FILE * f;
char * c;
f = fopen(file,"r")
c = fgetc(f)
fclose(f);

Let say this is a block of code inside a program c and f are never used
anywhere else.  Currently optimizer has no way to know that I know of that this
code can be junked if if its not used.  Programmer need to be able to place
markers to this effect.   One place were this could see some size reductions is
in crt0.o with processing of command line.  If the output is not used why do
the processing.

I hope I have assigned this to the right part.


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           Summary: Need for attributes to tag code blocks so optimiser can
                    remove more code.
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: oiaohm at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41682

[Bug middle-end/41682] Need for attributes to tag code blocks so optimiser can remove more code.

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2009-10-12 12:48 -------
Hm?  This code has side-effects, so it cannot be safely removed by a compiler.


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rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41682

[Bug middle-end/41682] Need for attributes to tag code blocks so optimiser can remove more code.

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2009-10-12 20:04 -------
Just to expand on that, fopen might change errno and it also it might return
NULL which case fgetc might cause the program to seg fault.  etc.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41682