Scalars have a reg_size of 4 on sm1. In the case of a deref of a vector or
matrix resulting in a scalar, however, this yields a required_bind_count that is
one higher than it should be. reg_size is the wrong thing to be using here,
since it describes the size of a type in isolation, but this is conceptually an
embedded type that doesn't include any padding. Since we're only dealing with
scalars and vectors here, just use their width.
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