swift234

improve SILGen of RebindSelfInConstructorExpr in several ways:
 - In the normal optional-to-optional init case, use
   "emitUncheckedGetOptionalValueFrom" instead of
   "emitCheckedGetOptionalValueFrom" since we have already
   checked to see if the optional is present.  This avoids a
   function call (that is mandatory inlined away) along with a ton
   of SIL that gets mandatory inlined in that shows an assertion 
   failure that can never fail.

 - Teach SGF::emitDoesOptionalHaveValue and
   SILGenFunction::emitUncheckedGetOptionalValueFrom to work with
   optionals in memory and optional values.

 - Based on this, stop dropping the optional self into a materialized
   temporary all the time.  Just use whatever we have (a value or the
   address of an address-only thing) and operate on it directly.

 - Use Cleanups.emitBlockForCleanups instead of emitting a block and
   using emitBranchAndCleanups.  This leads to cleaner code in SILGen
   and avoids emitting a dead block in the common case where there are
   no cleanups to perform.

Overall, these changes lead to better super.init calls in failable
inits, and more importantly enable understanding the output of -emit-sil 
on them :-)



Swift SVN r27477