As I suggested in the BZ, this patch rejects constants with  just the
high bit set for the recently added "bfxil" pattern.  As a result we'll
return to using "bit" for the test in the BZ.

I'm not versed enough in aarch64 performance tuning to know if "bit" is
actually a better choice than "bfxil".  "bit" results in better code for
the testcase, but that seems more a function of register allocation than
"bit" being inherently better than "bfxil".   Obviously someone with
more aarch64 knowledge needs to make a decision here.

My first iteration of the patch changed "aarch64_high_bits_all_ones_p".
We could still go that way too, though the name probably needs to change.

I've bootstrapped and regression tested on aarch64-linux-gnu and it
fixes the regression.  I've also bootstrapped aarch64_be-linux-gnu, but
haven't done any kind of regression tested on that platform.


OK for the trunk?

Jeff