[PATCH] D41376: [libcxx] Implement <simd> ABI for Clang/GCC vector extension, constructors, copy_from and copy_to.

[Tim Shen via Phabricator via cfe-commits]

timshen added inline comments.


================
Comment at: libcxx/include/experimental/simd:703
+public:
+  _Tp __get(size_t __index) const { return (&__storage_)[__index]; };
+  void __set(size_t __index, _Tp __val) { (&__storage_)[__index] = __val; }
----------------
mclow.lists wrote:
> Can these (`__get` and `__set`) be noexcept? Obviously, it depends on `_Tp`.
Currently _Tp is always a subset of arithmetic type, so it's safe to say noexcept. Added them, as they may help with -O0 performance.


================
Comment at: libcxx/include/experimental/simd:811
+class __simd_reference {
+  static_assert(std::is_same<_Vp, _Tp>::value, "");
+
----------------
mclow.lists wrote:
> If `_Vp` and `_Tp` have to name the same type, why have two of them?
> What is the difference, and when would you use each one internally?
> 
>     __simd_reference(__simd_storage<_Tp, _Abi>* __ptr, size_t __index);
> vs.
>     __simd_reference operator=(_Vp __value) &&;
> 
> If _Vp and _Tp have to name the same type, why have two of them?

Currently there is no difference. It's going to be different when simd_mask is implemented (_Vp can be bool, but _Tp may not be).

> What is the difference, and when would you use each one internally?

This is not an internal class. This is part of the interface. IIRC since P0214R9 opreator=() is changed to something. In a later patch operator=() should be implemented as R9 specified.


https://reviews.llvm.org/D41376