Marina Polyakova <m.polyak...@postgrespro.ru> writes:
> On 13-01-2018 21:10, Tom Lane wrote:
>> I'm not sure there's much we can do about this. Dropping the use
>> of the alignment spec isn't a workable option. If there were a
>> simple way for configure to detect that the compiler generates bad
>> code for that, we could have it do so and reject use of __int128,
>> but it'd be up to you to come up with a workable test.
> I'll think about it..
Attached is a possible test program. I can confirm it passes on a
machine with working __int128, but I have no idea whether it will
detect the problem on yours. If not, maybe you can tweak it?
regards, tom lane
#include <stddef.h>
#include <stdio.h>
/* GCC, Sunpro and XLC support aligned */
#if defined(__GNUC__) || defined(__SUNPRO_C) || defined(__IBMC__)
#define pg_attribute_aligned(a) __attribute__((aligned(a)))
#endif
typedef __int128 int128a
#if defined(pg_attribute_aligned)
pg_attribute_aligned(8)
#endif
;
/*
* These are globals to discourage the compiler from folding all the
* arithmetic tests down to compile-time constants. We do not have
* convenient support for 128bit literals at this point...
*/
struct glob128
{
__int128 start;
char pad;
int128a a;
int128a b;
int128a c;
int128a d;
} g = {0, 'p', 48828125, 97656255, 0, 0};
int
main()
{
if (offsetof(struct glob128, a) < 17 ||
offsetof(struct glob128, a) > 24)
{
printf("wrong alignment, %d\n", (int) offsetof(struct glob128, a));
return 1;
}
g.a = (g.a << 12) + 1; /* 200000000001 */
g.b = (g.b << 12) + 5; /* 400000000005 */
/* use the most relevant arithmetic ops */
g.c = g.a * g.b;
g.d = (g.c + g.b) / g.b;
/* return different values, to prevent optimizations */
if (g.d != g.a + 1)
{
printf("wrong arithmetic result\n");
return 1;
}
printf("A-OK!\n");
return 0;
}
