another question:
--------code begin----------------
vector<int> a;
...
for(int i = 0; i < a.size(); i++)
{
/*do something*/
}
-------code end---------------------
i asked that if this can be optimized to this:
----------code begin--------------
vector<int> a;
...
int size = a.size();
for(int i = 0; i < size; i++)
{
/*do something*/
}
----------code end-----------------
last time we discussed one situation may influence the optimization:
a) in function size() we may change some global variables.
there is another situation:
b) in the /*do something*/ block, we may use a.push_back(...) or some
other functions
that can change the size of a. if this happen, of course we can not do
the optimization.
so can gcc know what functions may change the size of a?
is gcc smart enough to optimize the code if those functions are not used?
well, i think the possible implementations are:
a) we tell the gcc what function may change the size of a vector
b) in the internal of gcc, gcc can find them out
which one is more reasonble? or none of them?
-- Kevin Long
