Method and apparatus for speculative microinstruction pairing

摘要

An apparatus and method are provided for speculatively pairing micro instructions for parallel execution within a single pipeline of a microprocessor and subsequently splitting the paired micro instructions in the same clock cycle as the pairing if a resource conflict or operand dependency is detected. The apparatus includes multiplexing logic that feeds back a second of a pair of micro instructions stored in an instruction register back into the instruction register for sequential execution after the first micro instruction if a translator detects late in the clock cycle that a resource conflict or operand dependency exists. An instruction pair indicator is provided along with the pair of micro instructions down to the execution stages to inform the execution stages whether the second micro instruction is valid for parallel execution with the first micro instruction. The method may also be used in conjunction with a micro instruction queue. In one embodiment, an additional MMX adder is provided such that PADD instructions may be translated and paired for parallel execution within the single pipeline of the microprocessor.