https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53917
Eric Gallager <egallager at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |diagnostic
Status|UNCONFIRMED |NEW
Last reconfirmed| |2017-09-24
Ever confirmed|0 |1
--- Comment #3 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Paulo J. Matos from comment #0)
> Created attachment 27771 [details]
> Testcase
>
> Hi,
>
> I have noticed that when compiling the following test case (will attach to
> the bug):
>
> test1.c:
> int a, b;
> void fn1 ();
> typedef enum
> {
> READ_WRITE
> } TAG_STATE;
> TAG_STATE fn2 ();
> void
> fn3 ()
> {
> int c;
> if (a)
> c = 0;
> else
> switch (fn2 ())
> case 0:
> c = 1;
> b = c;
> if (b)
> fn1 ();
> }
>
> gcc says:
> $ gcc -Os -S -Wall test1.c
> test1.c: In function 'fn3':
> test1.c:19:8: warning: 'c' may be used uninitialized in this function
> [-Wuninitialized]
>
> However line 19 is 'if (b)'.
>
> Used gcc46 but also reproducible with gcc47.
gcc8 seems to get this one right now:
$ /usr/local/bin/gcc -c -Os -S -Wall -Wextra 53917.c
53917.c: In function ‘fn3’:
53917.c:18:7: warning: ‘c’ may be used uninitialized in this function
[-Wmaybe-uninitialized]
b = c;
~~^~~
$
(In reply to Paulo J. Matos from comment #1)
> Here's another example:
> void fn1 ();
> typedef struct
> {
> int hdr[0];
> } foo;
> typedef enum
> {
> READ_WRITE
> } bar;
> typedef struct
> {
> struct
> {
> foo t1;
> } mp;
> } foobar;
> bar fn2 ();
> typedef struct
> {
> foobar tag_mem_config;
> } tag;
> static int
> fn3 (foobar * p1)
> {
> int valid;
> if (p1->mp.t1.hdr[0])
> valid = 0;
> else
> switch (fn2 ())
> case 0:
> valid = 1;
> return valid;
> }
> void
> fn4 ()
> {
> tag p_t1_rw_fsm_data;
> if (fn3 (&p_t1_rw_fsm_data.tag_mem_config))
> fn1 ();
> }
>
> GCC says:
> test.c: In function 'fn4':
> test.c:38:8: warning: 'valid' may be used uninitialized in this function
> [-Wuninitialized]
>
>
> Again, line 38 is: if (fn3 (&p_t1_rw_fsm_data.tag_mem_config))
> In this case this looks like it's related to inlining.
gcc still gets this one wrong though:
$ /usr/local/bin/gcc -c -Os -S -Wall -Wextra 53917_a.c
53917_a.c: In function ‘fn4’:
53917_a.c:38:8: warning: ‘valid’ may be used uninitialized in this function
[-Wmaybe-uninitialized]
if (fn3 (&p_t1_rw_fsm_data.tag_mem_config))
^
$
So confirmed for the second testcase.
