From gb:
(declare (type (simple-array double-float) a b))
declares that A and B are SIMPLE-ARRAYs with unspecified
dimensionality. We'll generally only try to open-code the
AREF/CCL::ASET if the dimensionality of the array is specified
in the declaration.
In "reasonably safe" code, if the declared dimensionality of
the array was unpecified (or specified as *), we could treat
(aref a i)
as
(%typed-aref (type-of a) a i)
and typecheck that A is in fact a one-dimensional array of the
declared type before doing anything with it. If A was in
fact of the wrong dimensionality, we'd get a type error (A isn't a simple-one-dimensional-array of the specified type)
rather than a wrong-number-of-subscripts error, but I don't
think that AREF's error behavior is too rigidly specified.
In unsafe code, we crash and burn if the actual dimensionality
doesn't match, but win in more cases if it does.
