On 12/19/2016 02:42 AM, Jakub Jelinek wrote:
The ubsan pass runs before IPA, so not sure how do you want to do that
(and it is needed to run it early).
One question is if we should perform path isolation in this case at all,
since the branches to __builtin___ubsan_handle_nonnull_arg are with
PROB_VERY_UNLIKELY, so the question is if we should be growing the
paths which is really cold. It has some small benefit (removing one
cheap comparison from the hot path), but the grows cold block.
Growing a cold path isn't terribly problematical, particularly if it
allows optimization on the hot path. In an ideal world these uber-cold
paths belong on their own pages and are never even paged in.
But I'd really like to see the full dump in this case. I've got a
fragment above and it looks like dumb duplication. ie, why did we
isolate the path.
BTW, in the testcase from the Linux kernel it is also path isolation
for error recovery path, something that ought to be predicted unlikely
(though, probably not very unlikely unlike this case), so the question is
if we want to isolate that or not too.
Agreed.
jeff
