Actually I was able to solve the issue declaring the int128 integers stored in perl-malloc'ed memory as follows: 
typedef int128_t int128_t_a8 __attribute__ ((aligned(8)));
typedef uint128_t uint128_t_a8 __attribute__ ((aligned(8)));

[download]
Now gcc generates MOVDQU instructions to load them. MOVDQU is just a 40% slower than MOVDQA and so the performance degradation probably unnoticeable for a perl program.

In reply to Re^4: Debugging XS modules under Strawberry perl by salva
in thread Debugging XS modules under Strawberry perl by salva

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