[Bug c/28001] New: incrementing a variable produces smaller code than an explicit assignment

[aldot at gcc dot gnu dot org]

I'd expect that at least the same code is generated for both cases as opposed
to creating worse code for the case where an explicit assignment is done.

I had hoped that the explicit assignment actually creates smaller code.

$ gcc -DDOINC -Os -march=i386 -c -o scan.o.orig scan.c
$ gcc -UDOINC -Os -march=i386 -c -o scan.o scan.c
$ size scan.o*
   text    data     bss     dec     hex filename
    127       0       0     127      7f scan.o
    123       0       0     123      7b scan.o.orig
$ cat scan.c
#include <stdio.h>
#include <dirent.h>
static void check(int pid) { fprintf(stderr,"found %i\n", pid); }
int main (void)
{
  DIR *procdir;
  struct dirent *entry;
  int foundany, pid;

  procdir = opendir ("/proc");
  foundany = 0;
  while ((entry = readdir (procdir)) != NULL)
    {
      if (sscanf (entry->d_name, "%d", &pid) != 1)
        continue;
#ifdef DOINC
      foundany++;
#else
      foundany = 1;
#endif
      check (pid);
    }
  closedir (procdir);
  if (!foundany)
    return 1; /* bb_perror_msg_and_die("nothing in /proc - not mounted?");*/
  return 0;
}


-- 
           Summary: incrementing a variable produces smaller code than an
                    explicit assignment
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: aldot at gcc dot gnu dot org
 GCC build triplet: i386-linux-gnu
  GCC host triplet: i386-linux-gnu
GCC target triplet: i386-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28001