In the x86 assembly programming language, MOVHPD is the name for a specific action performable by modern x86 processors with 2nd-generation Streaming SIMD Extensions (SSE2). This action involves either copying a number from memory to temporary space or copying a number from temporary space to memory.
Specifically, MOVHPD causes the value at an 8-byte memory region to be either copied to or assigned from the upper half of an XMM register.
The source operand can be either an XMM register (<code>xmm</code>) or a memory address (<code>m64</code>). When the source operand is an XMM register, the destination operand must be a memory address. When the source operand is a memory address, the destination operand must be an XMM register.
Note that the lower half of the XMM register is unaffected by this operation.