Re: [PATCH, libgomp] Fix chunk_size<1 for dynamic schedule

[Jakub Jelinek <jakub@redhat.com>]

On Thu, Jun 23, 2022 at 11:47:59PM +0800, Chung-Lin Tang wrote:
> with the way that chunk_size < 1 is handled for gomp_iter_dynamic_next:
> 
> (1) chunk_size <= -1: wraps into large unsigned value, seems to work though.
> (2) chunk_size == 0:  infinite loop
> 
> The (2) behavior is obviously not desired. This patch fixes this by changing

Why?  It is a user error, undefined behavior, we shouldn't slow down valid
code for users who don't bother reading the standard.

E.g. OpenMP 5.1 [132:14] says clearly:
"chunk_size must be a loop invariant integer expression with a positive
value."
and omp_set_schedule for chunk_size < 1 should use a default value (which it
does).

For OMP_SCHEDULE the standard says it is implementation-defined what happens
if the format isn't the specified one, so I guess the env.c change
could be acceptable (though without it it is fine too), but the
loop.c change is wrong.  Note, if the loop.c change would be ok, you'd
need to also change loop_ull.c too.

	Jakub