[PATCH] D41516: emmintrin.h documentation fixes and updates

[Katya Romanova via Phabricator via llvm-commits]

kromanova added inline comments.


================
Comment at: cfe/trunk/lib/Headers/emmintrin.h:4683
 ///
-/// This intrinsic has no corresponding instruction.
+/// This intrinsic corresponds to the <c> MOVDQ2Q </c> instruction.
 ///
----------------
efriedma wrote:
> kromanova wrote:
> > kromanova wrote:
> > > I'm not sure about this change.
> > > 
> > > Intel documentation says they generate MOVDQ2Q (don't have icc handy to try).
> > > However, I've tried on Linux/X86_64 with clang and gcc, - and we just return.
> > > 
> > Though I suspect it's possible to generate movdq2q, I couldn't come up with an test to trigger this instruction generation.
> > Should we revert this change?
> > 
> > 
> > ```
> > __m64 fooepi64_pi64 (__m128i a, __m128 c)
> > {
> >   __m64 x;
> > 
> >   x = _mm_movepi64_pi64 (a);
> >   return x;
> > }
> > 
> > ```
> > 
> > on Linux we generate return instruction. 
> > I would expect (v)movq %xmm0,%rax to be generated instead of retq. 
> > Am I missing something? Why do we return 64 bit integer in xmm register rather than in %rax?
> > 
> The x86-64 calling convention rules say that __m64 is passed/returned in SSE registers.
> 
> Try the following, which generates movdq2q:
> ```
> __m64 foo(__m128i a, __m128 c)
> {
>   return _mm_add_pi8(_mm_movepi64_pi64(a), _mm_set1_pi8(5));
> }
> ```
Thanks! That explains it :)
I can see that MOVDQ2Q gets generated. 

What about intrinsic below, _mm_movpi64_epi64? Can we ever generate MOVD+VMOVQ as stated in the review? 
Or should we write VMOVQ / MOVQ?


Repository:
  rL LLVM

https://reviews.llvm.org/D41516