[Bug tree-optimization/103218] (a < 0) << signbit is not always optimized to a & signbitmask at the gimple level

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103218

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
There is code in fold_ternary_loc which does:
      /* A < 0 ? <sign bit of A> : 0 is simply (A & <sign bit of A>).  */

And this works as fold also does (a<0)<<N into (a<0) ? 1<<N : 0 which is not
done in match.pd for reasons.

We should just handle ((cast)(a < 0)) << signbit in match.pd.

Implementing that.