[Bug tree-optimization/55177] missed optimizations with __builtin_bswap

["dwmw2 at infradead dot org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55177

--- Comment #15 from David Woodhouse <dwmw2 at infradead dot org> ---
More missed optimistions (gcc version 4.9.2 20141101 (Red Hat 4.9.2-1) (GCC))

I see it using movbe for the pointer_abuse() function, but can't see a simple
way to make it use movbe *without* killing kittens.

gcc -march=atom -O2 -x c -o - -S - -Wstrict-aliasing <<EOF

struct pkt {
    unsigned char data[10];
};

unsigned or(struct pkt *p)
{
    return (p->data[0] << 24) | (p->data[1] << 16) | (p->data[2] << 8) |
p->data[1];
}

unsigned add(struct pkt *p)
{
    return (p->data[0] << 24) + (p->data[1] << 16) + (p->data[2] << 8) +
p->data[1];
}

unsigned pointer_abuse(struct pkt *p)
{
    return __builtin_bswap32(*(unsigned *)p->data);
}
EOF