> > - /* If access is not executed on every iteration, we must ensure that
> > overlow may
> > - not make the access valid later. */
> > + /* If access is not executed on every iteration, we must ensure that
> > overlow
> > + may not make the access valid later. */
> > if (!dominated_by_p (CDI_DOMINATORS, loop->latch, gimple_bb (data->stmt))
> > && scev_probably_wraps_p (initial_condition_in_loop_num (ev,
> > loop->num),
> > step, data->stmt, loop, true))
> > - reliable = false;
> > + upper = false;
> >
> > - record_nonwrapping_iv (loop, init, step, data->stmt, low, high,
> > reliable, upper);
> > + record_nonwrapping_iv (loop, init, step, data->stmt, low, high, false,
> > upper);
> > return true;
> > }
> Hi,
> I have a concern that GCC records bound information from basic blocks
> even that don't dominate loop latch. Given below example:
>
> extern int b[];
> void bar (int *);
> int foo (int x, int n)
> {
> int i;
> int arr[128] = {0};
>
> for (i = 0; i < n; i++)
> {
> if (x > i)
> {
> a[i] = i;
> b[i] = i;
> }
> }
> bar (arr);
> return 0;
> }
This testcase is not affected, becase scev_probably_wraps_p returns false in
this case.
In the wrapping case, we can't derive upper bound - this is indeed a
correctness issue.
I am experiemtning with enabling loop peeling by default. For that I extended
the code
to record likely upper bounds, which can be used to test if the loop most
probably has
low trip count. This is also useful to trottle other transformations.
In this case we can probably assume that no sane person would count
on wrapping and record this as likely bound.
Honza
