RKSimon added inline comments.
================ Comment at: emmintrin.h:1607 +/// +/// This intrinsic corresponds to the <c> VMOVSD / MOVSD </c> instruction. +/// ---------------- kromanova wrote: > kromanova wrote: > > kromanova wrote: > > > probinson wrote: > > > > should this be VMOVQ/MOVQ instead? > > > Probably yes. Let me know if you have a different opinion. > > > > > > If I use this intrinsic by itself, clang generates VMOVSD instruction. > > > It happens because the default domain is chooses to generate smaller > > > instruction code. > > > I got confused because I couldn't find Intel's documentation about > > > _mm_loadu_si64, so I just wrote a test like the one below and looked what > > > instructions got generated. > > > > > > ``` > > > __m128i foo22 (void const * __a) > > > { > > > return _mm_loadu_si64 (__a); > > > } > > > ``` > > > > > > However, if I change the test and use an intrisic to add 2 64-bit > > > integers after the load intrinsics, I can see that VMOVQ instruction gets > > > generated. > > > > > > ``` > > > __m128d foo44 (double const * __a) > > > { > > > __m128i first = _mm_loadu_si64 (__a); > > > __m128i second = _mm_loadu_si64 (__a); > > > return _mm_add_epi64(first, second); > > > > > > } > > > ``` > > > > > > So, as you see clang could generate either VMOVSD/MOVSD or VMOVSQ/MOVSQ. > > > I think it makes sense to change the documentation as Paul suggested: > > > > > > /// This intrinsic corresponds to the VMOVSQ/MOVSQ. > > > > > > Or, alternatively, we could list all the instructions that correspond to > > > this intrinsics: > > > > > > /// This intrinsic corresponds to the VMOVSQ/MOVSQ/VMOVSD/MOVSD. > > > > > > > > It will be interesting to hear Asaf Badoug opinion, since he added this > > intrisic. He probably has access to Intel's documentation for this > > intrinsic too (which I wasn't able to find online). > There is a similar situation for one intrisic just a few lines above, namely > _mm_loadu_pd. It could generate either VMOVUPD / MOVUPD or VMOVUPS/MOVUPS > instructions. > I have actually asked Simon question about it offline just a couple of days > ago. > > I decided to kept referring to VMOVUPD / MOVUPD as a corresponding > instruction for _mm_loadu_pd. However, if we end up doing things differently > for _mm_loadu_si64, we need to do a similar change to _mm_loadu_pd (and > probably to some other intrinsics). It should be VMOVQ/MOVQ (note NOT VMOVSQ/MOVSQ!). Whatever the domain fixup code does to it, that was the original intent of the code and matches what other compilers says it will (probably) be. Repository: rL LLVM https://reviews.llvm.org/D28503 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits