optimization: constraint propagation should be optional
Constraint propagation is often one of the larger timesinks in compilation. Turning it off for COMPILATION-SPEED > SPEED would be good -- and it seems that it was originally intended as an optional pass.
However, changes in the compiler since days of yore have made constraint propagation effectively non-optional, causing bogus WARNINGs or worse if it is omitted.
(declare (type (or simple-vector list) x))
(svref (coerce x 'simple-vector) 0))
(coerce x 'simple-vector)
(if (simple-vector-p x)
(replace (make-array (length x)) x))
which in turn causes compilation of SVREF to complain from a possible type-mismatch
(wanted SIMPLE-VECTOR, has (OR SIMPLE-VECTOR LIST)) for the first leg of the
IF. Adjusting the transform to plug in a TRULY-THE would take care of this,
but *any* transform like this is liable to cause such bogus warnings.