That's clearly not right - I'm not sure quite what undefined behaviour
assumption convinces GCC to optimise the whole thing away>
While the pointer casting is a bit ghastly, I don't actually think that
GCC is taking advantage of undefined behaviour here, rather it looks
like
you have a simple typo on line 3:
const __uint128_t *ul1 = (const __uint128_t *)a1;
const __uint128_t *ulm = (const __uint128_t *)m;
const __uint128_t *ul2 = (const __uint128_t *)a1;
ul2 = a2, surely?
As it is (stripping casts) you have a1 ^ a1, which will get you to 0
pretty quickly. Fixing that up for you;
bool
ipv6_masked_addr_cmp_new(const struct in6_addr *a1, const struct
in6_addr *m,
const struct in6_addr *a2)
{
const __uint128_t *ul1 = (const __uint128_t *)a1;
const __uint128_t *ulm = (const __uint128_t *)m;
const __uint128_t *ul2 = (const __uint128_t *)a2;
return !!((*ul1 ^ *ul2) & *ulm);
}
$ gcc -O2
ipv6_masked_addr_cmp_new:
ldp x4, x3, [x0]
ldp x5, x2, [x2]
ldp x0, x1, [x1]
eor x4, x4, x5
eor x2, x3, x2
and x0, x0, x4
and x1, x1, x2
orr x0, x0, x1
cmp x0, 0
cset w0, ne
ret
Which at least looks like it might calculate something useful :-)
Hi Robin / James
Thanks for checking and sorry for the confusion. I'll retest this.
--
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
Linux Foundation Collaborative Project
