bpf: Exit early if reg_bounds_sync gets invalid inputs

bpf: Exit early if reg_bounds_sync gets invalid inputs

In the subsequent commit, to prune dead branches we will rely on
detecting ill-formed ranges using range_bounds_violations()
(e.g., umin > umax) after refining register bounds using
regs_refine_cond_op().

However, reg_bounds_sync() can sometimes "repair" ill-formed bounds,
potentially masking a violation that was produced by
regs_refine_cond_op().

This commit modifies reg_bounds_sync() to exit early if an invariant
violation is already present in the input.

This ensures ill-formed reg_states remain ill-formed after
reg_bounds_sync(), allowing simulate_both_branches_taken() to correctly
identify dead branches with a single check to range_bounds_violation().

Suggested-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Harishankar Vishwanathan <harishankar.vishwanathan@gmail.com>
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/73127d628841c59cb7423d6bdcd204bf90bcdc80.1775142354.git.paul.chaignon@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>