Laurent GUERBY wrote:
On Fri, 2009-07-24 at 12:03 -0400, Robert Dewar wrote:
Indeed an alternative approach to handling this problem in GCC would
be to adapt the Ada model for C and C++ which would not be too hard
to do I suspect. Then gcc could be improved to handle this model
better and more effectively with respect to optimization, and both
C/C++ and Ada would benefit.
IIRC the Ada rules allows to raise Constraint_Error earlier
rather than later which is interesting for check removal in loops for
very common patterns:
for I in T'First .. Dynamic_N loop
T (I) := 0.0; -- generate check I in T'First .. T'Last
end loop;
Yes, that's right, and it is exactly such cases that the
rule is designed to cover
=>
if Dynamic_N >= T'First and Dynamic_N > T'Last then
raise Constraint_Error;
end if;
for I in T'First .. Dynamic_N loop
T (I) := 0.0; -- no generated check
end loop;
But I might be wrong in my recollection (and I don't think GNAT
takes advantage of that), Robert?
We definitely don't take as much advantage as we could
I also don't know if there's a generic (shared by languages)
infrastructure to support this kind of optimization in GCC.
Not really, hence my thought that if we tried to copy Ada
semantics for C/C++ we might be able to make more progress
there that would be more generally useful.
Laurent
