https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81423
Davin McCall <davmac at davmac dot org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |davmac at davmac dot org
--- Comment #15 from Davin McCall <davmac at davmac dot org> ---
Apologies if I'm wrong and just making noise but doesn't the test case involve
a left shift of a value greater than the bit width of the left operand and
therefore invoke UB?
ll = -5597998501375493990LL;
ll = (5677365550390624949L - ll) - (ull1 > 0);
//ull3 = (unsigned int)
// (2067854353L <<
// (((ll + -2129105131L) ^ 10280750144413668236ULL) -
// 10280750143997242009ULL)) >> ((2873442921854271231ULL | ull2)
// - 12098357307243495419ULL);
// Above broken down:
unsigned long long int t1 = ll + -2129105131L;
unsigned long long int t2 = t1 ^ 10280750144413668236ULL;
unsigned long long int t3 = t2 - 10280750143997242009ULL;
// t3 = 9523455470476460042 !!!
long t4 = 2067854353L << t3; // UB!!
unsigned int t5 = (unsigned int)t4;
unsigned long long int t6 = 2873442921854271231ULL | ull2;
unsigned long long int t7 = t6 - 12098357307243495419ULL;
ull3 = t5 >> t7;
Fixed test case would be:
--- begin ---
unsigned long long int ll = 0;
unsigned long long int ull1 = 1ULL;
unsigned long long int ull2 = 12008284144813806346ULL;
unsigned long long int ull3;
void
foo ()
{
ll = -5597998501375493990LL;
ll = (5677365550390624949L - ll) - (ull1 > 0);
ull3 = (unsigned int)
(2067854353L <<
(((ll + -2129105131L) ^ 10280750144413668236ULL) +
17089282532945401191ULL)) >> ((2873442921854271231ULL | ull2)
- 12098357307243495419ULL);
}
int
main ()
{
foo ();
printf ("%llu expected 3998784)\n", ull3);
printf ("%llx expected 3d0440)\n", ull3);
return 0;
}
--- end ---
This still demonstrates the bug.
