[Bug tree-optimization/58039] -ftree-vectorizer makes a loop crash on a non-aligned memory

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58039

--- Comment #3 from Mikael Pettersson <mikpe at it dot uu.se> ---
Your code performs mis-aligned uint16_t stores, which x86 allows.  The
vectorizer turns those into larger and still mis-aligned `movdqa' stores, which
x86 does not allow, hence the SEGV.

Replace the non-portable mis-aligned stores with portable code like

#define int2store_little_endian(s,A) memcpy((s), &(A), 2)

or gcc-specific code like

struct __attribute__((__packed__)) packed_uint16 {
    uint16_t u16;
};
#define int2store_little_endian(s,A) ((struct packed_uint16*)(s))->u16 = (A)

and then the vectorizer generates large `movdqu' stores, which is pretty much
the best you can hope for unless you rewrite the code to avoid mis-aligned
stores.