[Bug c/24376] New: wrong-code unless -fno-sched-interblock

["seidl at feld dot cvut dot cz" <gcc-bugzilla at gcc dot gnu dot org>]

The cross-compiler gcc-3.4.4 (or 3.4.3) for v850 generates wrong-code for
example source bug2.c (see below).
The cmp instruction in expression (ps1 ? 1 : 2) was lost in the first
scheduling pass (see dump-file bug2.c.23.sched generated by compilation with
-da option). The return value of sh_dir() (see below) is random and depends on
state of PSW register at return from previous bprintf() call.

Shorted asm listing of wrong-code:
...
        jarl _x_bprintf,r31     #
        setf z,r10      # tmp73
        add 1,r10       #, <result>
...

The wrong-code may be work-arounded by -fno-sched-interblock option.
The good-code - shorted asm listing:
...
        jarl _x_bprintf,r31     #
        cmp r0,r28      # ps           <---(This is the lost instruction)
        setf z,r10      # tmp73
        add 1,r10       #, <result>
...


The problem was tested on several linux instalation (Redhat 7.2 on i686, RedHat
Enterprise release 4 on x86_64, ...).

The source file bug2.c follows:
/*****************************************************************/
#define NULL 0

extern const char *f_cwd(const char *s);
extern int x_strcmp(const char *s1, const char *s2);
extern int x_strncmp(const char *s1, const char *s2, unsigned n);
extern int x_bprintf(int f, const char *fmt, ...);


typedef struct
{
  char cline[202];
  unsigned char out;
  unsigned short dir;
} t_sloc;


int sh_dir(t_sloc *sl)
{
  const char *ps=NULL, *ps1;

  if (x_strcmp(sl->cline, "pwd") == 0)
    goto label01;

  if (x_strncmp(sl->cline, "cd ", 3) == 0 && sl->cline[3] > ' ') {
    ps = sl->cline + 3;
label01:
    if ((ps1 = ps = f_cwd(ps)) == NULL)
      ps = f_cwd(NULL);
    if (!ps)
      return 2;

    x_bprintf(sl->out, "wd: %s\r\n", ps);
    sl->dir = ps[1] != 'M';
    x_bprintf(1, "ps1=%p, %d\r\n", ps1, 2);

/* This occurs wrong code: The state of Z flag of PSW register (cc0)
 * at end of previous call x_bprintf()
 * is evaluated instead of ps1 in next line. */

    return ps1 ? 1 : 2;
  }

  return 0;
}
/* End of source file*/
/*****************************************************************/


The compiler command line:
/usr/local/bin/gcc.v -Wall -Os -mspace -ep -mghs -mno-app-regs -mzda=8 -c
-Wa,-a=bug2.lst -fverbose-asm -o bug2.o bug2.c

The cross-compiler configure line:
../gcc-3.4.4/configure --prefix=/usr/local/ --host=i586-pc-linux-gnu
--target=v850-linux-elf --program-suffix=.v


-- 
           Summary: wrong-code unless -fno-sched-interblock
           Product: gcc
           Version: 3.4.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: seidl at feld dot cvut dot cz
 GCC build triplet: i586-pc-linux-gnu
  GCC host triplet: i586-pc-linux-gnu
GCC target triplet: v850-linux-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24376