[Bug tree-optimization/65178] incorrect -Wmaybe-uninitialized when using nested loops

[winter-gcc@bfw-online.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65178

--- Comment #11 from Leon Winter <winter-gcc@bfw-online.de> ---
Created attachment 37855
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=37855&action=edit
Current test case

gcc version 4.9.3

$ gcc -std=gnu99 -O1 -Wall -Wextra -o foo main.c 
$ gcc -std=gnu99 -O2 -Wall -Wextra -o foo main.c 
main.c: In function 'foo':
main.c:19:3: warning: 'buf' may be used uninitialized in this function
[-Wmaybe-uninitialized]
   return buf;
   ^
$ gcc -std=gnu99 -O3 -Wall -Wextra -o foo main.c

gcc version 5.3.1 20160205 (Debian 5.3.1-8bfw1)

$ gcc-5 -O1 -Wall -Wextra -o foo main.c -std=gnu99
main.c: In function 'foo':
main.c:19:10: warning: 'buf' may be used uninitialized in this function
[-Wmaybe-uninitialized]
   return buf;
          ^
$ gcc-5 -O2 -Wall -Wextra -o foo main.c -std=gnu99
main.c: In function 'foo':
main.c:19:10: warning: 'buf' may be used uninitialized in this function
[-Wmaybe-uninitialized]
   return buf;
          ^
$ gcc-5 -O3 -Wall -Wextra -o foo main.c -std=gnu99
main.c: In function 'foo':
main.c:19:10: warning: 'buf' may be used uninitialized in this function
[-Wmaybe-uninitialized]
   return buf;
          ^