"SACHA BARON COHEN’S singing has been slashed from new movie Sweeney Todd — because it is so terrible. Sound rehearsals and recordings are under way but Sacha struggled to pull off a convincing operatic performance for the many songs his character has. So Burton decided [to] chop them — and to allow Sacha to “rap” his tunes. A source on the production revealed: "Pirelli is a notoriously demanding role with some difficult songs."
Let's take a look at who sings what in the stage musical, and count the "many songs" Adolfo Pirelli has, shall we? One...t...no, wait. Stop there.
Such a demanding role with only one solo which lasts approximately 2 minutes, and (apologies in advance for the spoiler) a relatively fleeting character who dies before the story is even halfway through. In fact Cohen will only be required on set for 3 weeks. The song, "The Contest", does have the odd operatic moment, but is more 'rapped' (i.e. spoken-singing style) than anything anyway.
Take a look for yourself.