https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105011
Bug ID: 105011
Summary: [nvptx] FAIL: gcc.dg/atomic/stdatomic-flag-2.c -O1
execution test
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: vries at gcc dot gnu.org
Target Milestone: ---
On a quadro k2000 with driver 470.103.01 I'm running into this cluster of
FAILs:
...
FAIL: gcc.dg/atomic/stdatomic-flag-2.c -O1 execution test
FAIL: gcc.dg/atomic/stdatomic-flag-2.c -O3 -g execution test
FAIL: gcc.dg/atomic/stdatomic-flag.c -O3 -g execution test
...
Minimizing the first FAIL, I end up with:
...
#include <stdatomic.h>
extern void abort (void);
atomic_flag a = ATOMIC_FLAG_INIT;
int
main ()
{
int b;
if ((atomic_flag_test_and_set) (&a))
abort ();
return 0;
}
...
The atomic access is done by libatomic, using a 64-bit cas loop.
If we print the address of a, we have:
...
&a: 0000000700700200
...
so the pointer is already 64-bit aligned.
If we print the 64-bit value of *(unsigned long long *)&a before and after the
test-and-set, we have:
...
a: 0000000000024f00
a: 0000000000024f01
...
so that looks all-right as well.
At first glance, the problem is in libatomic, tas_n.c:
...
wval = (UWORD)__GCC_ATOMIC_TEST_AND_SET_TRUEVAL << shift;
woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED);
do
{
t = woldval | wval;
}
while (!atomic_compare_exchange_w (wptr, &woldval, t, true,
__ATOMIC_RELAXED, __ATOMIC_RELAXED));
post_barrier (smodel);
return woldval != 0;
...
What is returned is woldval != 0, but that tests the entire word, not just the
byte we're interested in.
It should probably do something like:
...
return (woldval & wval) != 0;
...
