* fold-const.c (tree_nonzero_bits): New function.
        * fold-const.h (tree_nonzero_bits): Likewise.
        * match.pd (POPCOUNT): New patterns to fold BUILTIN_POPCOUNT and
        friends.  POPCOUNT(x&1) => x&1, POPCOUNT(x)==0 => x==0, etc.

        * gcc.dg/fold-popcount-1.c: New testcase.
        * gcc.dg/fold-popcount-2.c: New testcase.
        * gcc.dg/fold-popcount-3.c: New testcase.
        * gcc.dg/fold-popcount-4.c: New testcase.

From-SVN: r260689