Extended Description

This:

#include <xmmintrin.h>

void foo(__m128i *A, __m128i *B) {
*A = _mm_sll_epi16 (*A, *B);
}

generates this code:

_foo:
movl 8(%esp), %eax
movdqa (%eax), %xmm0
#IMPLICIT_DEF %eax
pinsrw $2, %eax, %xmm0
xorl %ecx, %ecx
pinsrw $3, %ecx, %xmm0
pinsrw $4, %eax, %xmm0
pinsrw $5, %ecx, %xmm0
pinsrw $6, %eax, %xmm0
pinsrw $7, %ecx, %xmm0
movl 4(%esp), %eax
movdqa (%eax), %xmm1
psllw %xmm0, %xmm1
movdqa %xmm1, (%eax)
ret

This is obviously bad! We should be as good GCC at least.