> ARM intrinsics, as with most constructs in programming languages are > governed by the 'as if' rule. That is, the behaviour (from the > view-point of the abstract machine defined by the programming language) > is as if the operation were performed. If the compiler can determine > that an alternative code sequence can satisfy that requirement it is at > liberty to substitute that alternative sequence. I'm not sure I would agree. GCC needs to know intent (q.v.), and I'm guessing that's probably an NP-complete problem. C++11 got constexpr to specify intent, so I know the committee is familiar with the concept. Sorry to sound argumentative. I'm frustrated when a correct program is turned into a misbehaving program :) Maybe as a stop gap GCC could warn when its completely discarding blocks of code. As far as I know, the only warning at the moment is for -Wstrict-overflow when an optimization is taken due to integer overflow. And maybe the "unreachable" because of an early return. Jeff
