1. A processor comprising: a hardware decoder to decode instructions; a register file comprising a plurality of registers to store a plurality of blocks of data; and a hardware execution unit to execute decoded instructions decoded by the hardware decoder, the hardware execution unit including a crypto circuit to execute an Advanced Encryption Standard (AES) instruction that has at least two operands including a first operand and a second operand, the crypto circuit to encrypt the plurality of blocks of data according to a particular AES encryption mode, determine, during execution of the AES instruction, the particular AES encryption mode based at least in part on a value of the first operand, including to encrypt the second operand with a key stored in at least a first register of the register file prior to the AES instruction decoded by the hardware decoder and subsequently executed by the hardware execution unit, the at least first register an implicit register not specified by the AES instruction and included in the register file, wherein the crypto circuit is to execute the AES instruction according to the particular AES mode of Electronic Codebook (ECB) when the first operand value is zero for a plurality of iterations of a loop of hardware execution unit execution of the AES instruction as decoded by the hardware decoder for an AES instruction operation, and to execute the AES instruction according to the particular AES mode of Cipher Block Chaining (CBC) when the first operand value is an encrypted block of a prior iteration of the plurality of iterations of the loop of decoded AES instruction execution, wherein a number of the plurality of iterations of the loop of decoded AES instruction execution corresponds to a number of the plurality of blocks of data according to the particular AES encryption mode.