Patch for PR15832 and PR28071

[Vladimir Makarov]

Jan Hubicka wrote:

>
>Perhaps you was just hitting bug in reg-stack concerning partially
>initialized vars that was later fixed independently or am I missing
>something?
>
I think your are right.  That was added because of the bug in reg-stack.

If removing the code for stack regs in global.c does not work, I could 
modify algorithm to keep pavin sparse.  Just let me know.