[Bug target/123097] [16 Regression] [RISCV] [Miscompile] GCC - riscv64 target, miscompiles at -O3 since r16-5979

[rdapp at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123097

--- Comment #4 from Robin Dapp <rdapp at gcc dot gnu.org> ---
This is very suspicious:
  _119 = BIT_FIELD_REF <{ -1, -1, -1, -1 }, 1, 4>;
  _120 = BIT_FIELD_REF <{ -1, -1, -1, -1 }, 1, 5>;
  _121 = BIT_FIELD_REF <{ -1, -1, -1, -1 }, 1, 6>;
  _122 = BIT_FIELD_REF <{ -1, -1, -1, -1 }, 1, 7>;

We're extracting elements 4-7 from a 4-element vector.  Likely an issue with
riscv's small bool vectors (small = smaller than a byte).