MOVSX

Moves an immediate value or register with sign extension into a register.

Instruction	Operand 1	Operand 2	Description
MOVSX	Reg	Reg/Imm	OP1 = SX(OP2)

block->mov(X86_REG_EAX, -1)
block->movsx(X86_REG_RAX, X86_REG_EAX); // rax = -1ll