https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78317
--- Comment #5 from dhowells at redhat dot com <dhowells at redhat dot com> ---
Note that the issue doesn't require the value to be returned directly to
trigger it:
struct A { unsigned a; };
struct B { unsigned b; };
unsigned test5(struct A *x, struct B *y)
{
unsigned z = 0;
if (x->a & 0x10)
z |= 0x10;
if (x->a & 0x40)
z |= 0x40;
y->b = z;
}
is rendered as:
52: 8b 17 mov (%rdi),%edx
54: b9 10 00 00 00 mov $0x10,%ecx
59: 89 d0 mov %edx,%eax
5b: 83 e0 10 and $0x10,%eax
5e: 0f 45 c1 cmovne %ecx,%eax
61: 89 c1 mov %eax,%ecx
63: 83 c9 40 or $0x40,%ecx
66: 80 e2 40 and $0x40,%dl
69: 0f 45 c1 cmovne %ecx,%eax
6c: 89 06 mov %eax,(%rsi)
6e: c3 retq
by gcc -Os, but:
23: 8b 07 mov (%rdi),%eax
25: 83 e0 50 and $0x50,%eax
28: 89 06 mov %eax,(%rsi)
2a: c3 retq
by clang -Os.
