[Bug middle-end/20968] spurious "may be used uninitialized" warning (conditional PHIs)

["davidxl at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #8 from davidxl at gcc dot gnu dot org  2010-04-21 00:27 -------
(In reply to comment #2)
> Note this is not fully a regression but really a progression.
> What is happening now is only partial optimizations is happen before the warning to happen.
> 
> >I was unable to reduce the test case further without making the warning
> >disappear.  In particular, removing the increment of v1->count makes the warning
> >disappear.
> This is because we would then jump thread he jump.
> 
> Again this is because we are emitting the warning too soon, I might be able to come up with a testcase 
> which shows that this is not really a regression but a progression in that we have warned in 3.4 and 
> 4.0:
> struct {int count;} *v1;
> int c;
> int k;
> 
> extern void baz(int);
> void foo(void)
> {
>     int i;
>     int r;
>     if (k == 4)
>     {
>         i = 1;
>         r = 1;
>     }
>     else
>         r = 0;
> 
>     if (!r)
>     {
>         if (!c)
>             return;
>         v1->count++;
>     }
>     if (!c)
>     {
>         baz(i);
>     }
> }
> 
> There is no different from the case above and the functions you gave below.
> 
> There has been some talking about moving where we warn about uninitialized variables but I feel that 
> you can get around this in your code.

To reproduce the problem -- -fno-tree-vrp  -fno-tree-dominator-opts
-fno-tree-ccp are needed. This 


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20968