On 2024-09-20 21:42, Siddhesh Poyarekar wrote:
On 2024-09-20 20:20, Sam James wrote:
Siddhesh Poyarekar <siddh...@gotplt.org> writes:
This series makes a few improvements to get static object size
estimates in
more cases, thus improving the success rate of the static
__builtin_object_size. This should fully fix PR116556 and also
covers a bulk
of use cases for PR77608. I started to try and fix PR77608 fully,
but in the
end it looks like too much work in the pass for what seems like a
very small
set of uses, i.e. handling volatile offsets. If that is a desirable
end goal
then it could be done in a separate patchset since it will need
tree-object-size to handle trees with side-effects.
I could try play with https://github.com/siddhesh/fortify-metrics to see
how much it happens in the wild if you can help me figure out a
condition for when it punts (not tried). But I'm sceptical it's
worth the time.
That's an interesting idea, but unfortunately the very first attempt at
folding such a __builtin_object_size () call eliminates it, which AFAICT
happens right in the frontend. Maybe if the compiler is hacked up to
move the TREE_SIDE_EFFECTS (ptr) into compute_builtin_object_size like
the attached lightly tested patch, you could look for TREE_SIDE_EFFECTS
(ptr) in fortify-metrics to identify such lost opportunities.
I forgot to add that I share your scepticism, which is why I stopped
exploring too.
Thanks,
Sid
