On Jun 7, 2008, at 7:11 PM, Chris Hanson wrote:
On Jun 6, 2008, at 5:36 PM, Quincey Morris wrote:
A little inner voice insists on asking, though, how we know some
future version of the compiler might not optimize '[data self]'
upwards before the loop, if it decides that nothing inside the loop
references anything non-local:
This won't happen because each message expression -- just as with
function-call expressions -- is a sequence point. The compiler
can't know what side-effects [data self] might have, so it can't re-
order the invocation to elsewhere.
-- Chris
This is not necessarily true. If the const and pure GCC
__attribute(())s were extended to objc methods then the compiler would
be free to perform common subexpression and loop invariant code
movement optimizations. The 'self' message would definitely fall
under the domain of these attributes, thus the original argument is
apropos. Considering the relative ease of extending this to objc
methods and the possible performance gains, it's probably a given that
this will happen eventually. Obvious candidates are immutable objects
'length', 'count', etc, which would result in a pretty big win if
these attributes were available.
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