Where the fact that -msse2 has to be used with -O documented?

[Peng Yu]

> _mm_load_ps requires a 16-byte alignment.

How to force 16-byte alignment in GCC? The intel manual mentions
__declspec, but g++ prints the errors like the following.

main.cpp: In function ‘int main()’:
main.cpp:7: error: ‘align’ was not declared in this scope
main.cpp:7: error: ‘__declspec’ was not declared in this scope
main.cpp:7: error: expected `;' before ‘float’
main.cpp:8: error: ‘p1’ was not declared in this scope


-- 
Regards,
Peng