https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91882
Bug ID: 91882
Summary: boolean XOR tautology missed optimisation
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: SztfG at yandex dot ru
Target Milestone: ---
This functions is always return true regardless of the value of the arguments:
bool bool_xor_test(bool a, bool b)
{
return (a != b) == ((a || b) && !(a && b));
}
bool bool_xor_test2(bool a, bool b)
{
return (a ^ b) == ((a || b) && !(a && b));
}
but compiler does not simplify to "return true;". Expression ((a || b) && !(a
&& b)) poorly optimized
BUT! In this case:
bool xor_test_unsigned_int(unsigned int a, unsigned int b)
{
return (a ^ b) == ((a | b) & ~(a & b));
}
It actually simlified to "return true;" :
movl $1, %eax
ret
