Exactly - C++ compilers definitely can do this, and it's one of the things ICC's noticeably better than GCC and LLVM at, especially where intrinsics are involve

Exactly - C++ compilers definitely can do this, and it's one of the things ICC's noticeably better than GCC and LLVM at, especially where intrinsics are involved. If you have a struct/class type union wrapper for SIMD instrinsics which contains something like __m128 and pass that by reference, GCC and LLVM will often implement this as an effective pointer onto the stack (or wherever the struct is). ICC can often detect this, and keep it as a by-value __m128, which is often more efficient and keeps stuff in the registers.