gistfile1.txt

Microsoft compiler appears to ignore prefetches inside a loop.  

Tested this on MSVC 2013 express edition. Microsoft's connect site says I am not authorized to submit feedback for who knows what reason, or else I'd send it there directly......

Code I used:

void Foo( char* p, int* q )
{
    for( size_t i=0; i<8; i++ )
        _mm_prefetch(p+q[i], _MM_HINT_T0 );
}

ASM I got:
	movsxd	rax, DWORD PTR [rdx]
	prefetcht0 BYTE PTR [rax+rcx]
	ret	0

Hmmm, not quite what I wanted.... Tweaking the loop makes it even more obvious.  

code:
int Foo( char* p, int* q )
{
    int j=0;
    for( size_t i=0; i<8; i++ )
    {
        _mm_prefetch(p+q[i], _MM_HINT_T0 );
        j += q[i];
    }
    return j;
}

asm:
	movsxd	rax, DWORD PTR [rdx]
	prefetcht0 BYTE PTR [rax+rcx]
	add	eax, DWORD PTR [rdx+4]
	add	eax, DWORD PTR [rdx+8]
	add	eax, DWORD PTR [rdx+12]
	add	eax, DWORD PTR [rdx+16]
	add	eax, DWORD PTR [rdx+20]
	add	eax, DWORD PTR [rdx+24]
	add	eax, DWORD PTR [rdx+28]
	ret	0