128-bit Values - From XMM Registers To General Purpose
Answer : You cannot move the upper bits of an XMM register into a general purpose register directly. You'll have to follow a two-step process, which may or may not involve a roundtrip to memory or the destruction of a register. in registers (SSE2) movq rax,xmm0 ;lower 64 bits movhlps xmm0,xmm0 ;move high 64 bits to low 64 bits. movq rbx,xmm0 ;high 64 bits. punpckhqdq xmm0,xmm0 is the SSE2 integer equivalent of movhlps xmm0,xmm0 . Some CPUs may avoid a cycle or two of bypass latency if xmm0 was last written by an integer instruction, not FP. via memory (SSE2) movdqu [mem],xmm0 mov rax,[mem] mov rbx,[mem+8] slow, but does not destroy xmm register (SSE4.1) mov rax,xmm0 pextrq rbx,xmm0,1 ;3 cycle latency on Ryzen! (and 2 uops) A hybrid strategy is possible, e.g. store to memory, movd/q e/rax,xmm0 so it's ready quickly, then reload the higher elements. (Store-forwarding latency is not much worse than ALU, though.) That gives you a bal...