[Bug c/35973] New: Incorrect warning: will never be executed

[Bug c/35973] New: Incorrect warning: will never be executed

[dot at dotat dot at]

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This bug exists in various forms in multiple versions of gcc:

$ cat gccbug.c

struct sel {
        const char  *name;
        unsigned int enabled;
};

int selog_on(struct sel *);

#define selog_on(sel) \
        (sel.enabled == 0 \
                ? selog_on(&sel) \
                : sel.enabled != 42)

void dostuff(int *);

void gccbug1(void) {
        struct sel sel = { "test", 0 };
        if(selog_on(sel)) {
                dostuff(0);
        }
}

void gccbug2(void) {
        struct sel sel = { "test", 0 };
        if(selog_on(sel)) {
                int i;
                dostuff(&i);
        }
}


$ gcc -O -Wunreachable-code -c gccbug.c
gccbug.c: In function `gccbug2':
gccbug.c:25: warning: will never be executed
$ gcc --version
gcc --version
gcc (GCC) 3.4.4 [FreeBSD] 20050518

$ gcc -O -Wunreachable-code -c gccbug.c
gccbug.c: In function ‘gccbug2’:
gccbug.c:24: warning: will never be executed
gccbug.c: In function ‘gccbug1’:
gccbug.c:17: warning: will never be executed
$ gcc -O -Werror -Wunreachable-code -c gccbug.c
cc1: warnings being treated as errors
gccbug.c: In function ‘gccbug2’:
gccbug.c:24: warning: will never be executed
$ gcc --version
gcc (GCC) 4.1.2 20070115 (prerelease) (SUSE Linux)

$ gcc -O -Wunreachable-code -c gccbug.c
gccbug.c: In function 'gccbug2':
gccbug.c:24: warning: will never be executed
gccbug.c: In function 'gccbug1':
gccbug.c:17: warning: will never be executed
$ gcc -O -Werror -Wunreachable-code -c gccbug.c
cc1: warnings being treated as errors
gccbug.c: In function 'gccbug2':
gccbug.c:24: warning: will never be executed
$ gcc --version
gcc (GCC) 4.2.1 20070719  [FreeBSD]


-- 
           Summary: Incorrect warning: will never be executed
           Product: gcc
           Version: 4.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dot at dotat dot at
  GCC host triplet: i386-undermydesk-freebsd
GCC target triplet: i386-undermydesk-freebsd


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35973

[Bug middle-end/35973] Incorrect warning: will never be executed

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2008-05-05 05:38 -------
The warning looks fine for me, it is saying selog_on(&sel) will never be
executed.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35973

[Bug middle-end/35973] Incorrect warning: will never be executed

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2008-05-05 05:40 -------
Sorry I mean:
  [t.c : 24] D.1191_5 = sel.enabled;
  [t.c : 24] iftmp.1_6 = D.1191_5 != 42;

As far as I can tell this warning is correct.


-- 

pinskia at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35973

[Bug middle-end/35973] Incorrect warning: will never be executed

[dot at dotat dot at]

------- Comment #3 from dot at dotat dot at  2008-05-05 14:52 -------
The code is executed when the function selog_on() returns true. The warning is
also inconsistent, which also points to an analysis bug.


-- 

dot at dotat dot at changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dot at dotat dot at
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35973

[Bug middle-end/35973] Incorrect warning: will never be executed

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2008-12-28 06:13 -------
This warning depends on optimizations so what you do expect with the
inconsistency.  So in one case, we decide that i can alias sel which is
obviously not true but what do you expect from aliasing.


-- 

pinskia at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35973