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

[Chung-Lin Tang]

Hi Jakub,
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
the chunk_size initialization in gomp_loop_init to "max(1,chunk_size)"

The OMP_SCHEDULE parsing in libgomp/env.c has also been adjusted to reject
negative values.

Tested without regressions, and a new testcase for the infinite loop behavior 
added.
Okay for trunk?

Thanks,
Chung-Lin

libgomp/ChangeLog:
        * env.c (parse_schedule): Make negative values invalid for chunk_size.
        * loop.c (gomp_loop_init): For non-STATIC schedule and chunk_size <= 0,
        set initialized chunk_size to 1.

        * testsuite/libgomp.c/loop-28.c: New test.
diff --git a/libgomp/env.c b/libgomp/env.c
index 1c4ee894515..dff07617e15 100644
--- a/libgomp/env.c
+++ b/libgomp/env.c
@@ -182,6 +182,8 @@ parse_schedule (void)
     goto invalid;
 
   errno = 0;
+  if (*env == '-')
+    goto invalid;
   value = strtoul (env, &end, 10);
   if (errno || end == env)
     goto invalid;
diff --git a/libgomp/loop.c b/libgomp/loop.c
index be85162bb1e..018b4e9a8bd 100644
--- a/libgomp/loop.c
+++ b/libgomp/loop.c
@@ -41,7 +41,7 @@ gomp_loop_init (struct gomp_work_share *ws, long start, long 
end, long incr,
                enum gomp_schedule_type sched, long chunk_size)
 {
   ws->sched = sched;
-  ws->chunk_size = chunk_size;
+  ws->chunk_size = (sched == GFS_STATIC || chunk_size > 1) ? chunk_size : 1;
   /* Canonicalize loops that have zero iterations to ->next == ->end.  */
   ws->end = ((incr > 0 && start > end) || (incr < 0 && start < end))
            ? start : end;
diff --git a/libgomp/testsuite/libgomp.c/loop-28.c 
b/libgomp/testsuite/libgomp.c/loop-28.c
new file mode 100644
index 00000000000..e3f852046f4
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c/loop-28.c
@@ -0,0 +1,17 @@
+/* { dg-do run } */
+/* { dg-timeout 10 } */
+
+void __attribute__((noinline))
+foo (int a[], int n, int chunk_size)
+{
+  #pragma omp parallel for schedule (dynamic,chunk_size)
+  for (int i = 0; i < n; i++)
+    a[i] = i;
+}
+
+int main (void)
+{
+  int a[100];
+  foo (a, 100, 0);
+  return 0;
+}