gcc vector instructions

есть код:

float v1[] = { 0.1, 0.2, 0.3, 0.4 };

typedef float v4sf __attribute__ ((vector_size (4*sizeof(float))));
v4sf a = {1.,2.,3.,4.};
v4sf b = {5.,6.,7.,8.};
v4sf c;

int main()
{
	float* f = v1;
	c = __builtin_ia32_addps( a, b );

	a = __builtin_ia32_loadaps( v );
}

gcc -msse main.c ругается на a = __builtin_ia32_loadaps( v ), дескать  error: incompatible types in assignment.

С какого боку они incompatible?