combine.c (do_SUBST): Sanity check substitutions of CONST_INTs...

* combine.c (do_SUBST): Sanity check substitutions of
CONST_INTs, and reject them in SUBREGs and ZERO_EXTENDs.
(subst): Simplify SUBREG or ZERO_EXTEND instead of SUBSTing a
CONST_INT into its operand.
(known_cond): Likewise, for ZERO_EXTEND.
* simplify-rtx.c (simplify_unary_operation): Fix condition to
allow for simplification of wide modes.  Reject CONST_INTs in
ZERO_EXTEND when their actual mode is not given.

From-SVN: r49920