Proof with eauto 12 using val_erasure_cmpu with regs_erasure val_erasure.
intros.
unfold compare_ints...
Qed.
Hint Extern 0 (val_erasure Vundef _) => reflexivity : val_erasure.

Lemma compare_floats_erasure:
forall v1 v2 v1' v2' rs rs'
(Hval_erasure: val_erasure v1 v1')
(Hval_erasure2: val_erasure v2 v2')
(Hrs: regs_erasure rs rs'),
regs_erasure (compare_floats v1 v2 rs)
(compare_floats v1' v2' rs').