https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88916
--- Comment #3 from Wojciech Mula <wojciech_mula at poczta dot onet.pl> ---
A similar case:
---sign.c---
int different_sign(long a, long b) {
return (a >= 0 && b < 0) || (a < 0 && b >= 0);
}
---eof--
This is compiled into:
different_sign:
notq %rdi
movq %rdi, %rax
notq %rsi
shrq $63, %rax
shrq $63, %rsi
xorl %esi, %eax
movzbl %al, %eax
ret
When expressed as difference of the sign bits
((unsigned long)a ^ (unsigned long)b) >> 63
the code is way shorter:
different_sign:
xorq %rsi, %rdi
movq %rdi, %rax
shrq $63, %rax
BTW, I looked at ARM assembly, and GCC also emits
two shifts, so the observed behaviour is not limited
by a target.
