https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98474
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|incorrect results using |[8/9/10/11 Regression]
|__uint128_t |incorrect results using
| |__uint128_t
CC| |jakub at gcc dot gnu.org
Component|c++ |tree-optimization
Target Milestone|--- |8.5
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with r5-424-g807e902eea17f3132488c256c963823976b2348c
C testcase that just needs -O2:
__attribute__ ((noipa)) void
foo (__uint128_t *x)
{
asm volatile ("" : : "r" (x) : "memory");
}
int
main ()
{
__uint128_t a = ((__uint128_t) 1) << 65;
__uint128_t b = a;
__uint128_t n;
foo (&b);
n = b;
while (n >= a)
n -= a;
if ((int) (n >> 64) != 0)
__builtin_abort ();
return 0;
}
Works fine with unsigned long long instead of __uint128_t and 33 instead of 65
and 32 instead of 64, so either a wide-int bug or number of loop iterations
bug.
On the ullong testcase, e.g. profile_estimate prints:
Analyzing # of iterations of loop 1
exit condition 8589934591 < [n_8, + , 18446744065119617024]
bounds on difference of bases: -8589934591 ... 18446744065119617024
result:
# of iterations n_8 / 8589934592, bounded by 2147483647
but on the uint128_t testcase it prints:
Analyzing # of iterations of loop 1
exit condition 0x1ffffffffffffffff < [n_8, + ,
0xfffffffffffffffe0000000000000000]
bounds on difference of bases: -36893488147419103231 ...
-18446744073709551616
result:
# of iterations n_8 / 0x20000000000000000, bounded by 0
