movsxr
Movsxr is not an official x86-64 instruction. In many reference materials it appears not as a distinct, hardware-supported mnemonic but rather as a nickname, alias, or macro used in some assemblers or codebases to indicate a sign-extension move to a 64-bit destination register. Because it is not standardized, its exact meaning can vary between projects.
In actual x86-64 instruction sets, sign-extension moves are performed with the MOVSX family (move with sign-extend)
When movsxr appears in source text, it should be treated as an abstraction rather than a new
Example intent (using standard instructions): sign-extend an 8-bit value to 64 bits, producing a value in RAX;
See also: MOVSX, MOVSXD, sign extension, x86-64 instruction set.