On 23/05/12 11:41, bearophile wrote:
Simen Kjaeraas:
Should this be filed as a bug, or is the plan that only pure functions be
ctfe-able? (or has someone already filed it, perhaps)
It's already in Bugzilla, see issue 7994 and 6169.
It's just happening because the purity checking is currently being done
in a very unsophisticated way.
But I think there is a semantic hole in some of the discussions about
this problem. Is a future compile-time JIT allowed to perform
purity-derived optimizations in CTFE?
Some, definitely. Eg. foo(n) + foo(n)
can be changed to 2*foo(n), where n is an integer, regardless of what
foo does.
It does need to be a bit conservative, but I think the issues aren't
CTFE specific. Eg, something like this currently gives an assert at runtime:
pure nothrow void check(int n) pure nothrow
{
assert(n == 4);
}
void main()
{
check(3);
}
even though check() can do nothing other than cause an error, it still
cannot be optimized away. But you can get rid of all subsequent calls to
it, because they'll produce the same error every time.
