swift234

[dead-object-elim] Add SILInstruction::mayTrap(), change SILInstruction::mayHaveSideEffects() to call it, and change dead object elimination to call mayHaveSideEffects().

Note that I did not change any actual memory behavior. That will come via a
later cleanup phase. Since this is a correctness fix I wanted to only make
things more conservative.

rdar://18568601

Swift SVN r23311