Intel’s compiler generates code as the AVX’s instructions, and later (SSE 4/3/2); How does the compiler UE4 - I unfortunately do not know;
Intel® Compiler Options for Intel® SSE and Intel® AVX generation (SSE2, SSE3, SSSE3, ATOM_SSSE3, SSE4.1, SSE4.2, ATOM_SSE4.2, AVX, AVX2, AVX-512) and processor-specific optimizations
and
The significance of SIMD, SSE and AVX