Microprocessor Instruction Fusion for Throughput
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Solution Overview
Problem
Modern microprocessors face inefficiencies in instruction throughput due to the need to translate multiple macroinstructions into micro-operations, particularly in superscalar and out-of-order execution systems, where resources are consumed by processing individual instructions sequentially rather than in parallel.
Innovation Solution
A microprocessor is configured to fuse adjacent macroinstructions, such as MOV, ALU, and JCC instructions, into a single micro-operation, allowing the instruction translator to execute these instructions simultaneously, thereby reducing resource consumption and increasing instruction per clock cycle throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple macroinstructions are translated into separate micro-operations, then each instruction can be processed individually with clear separation of operations, but the instruction throughput decreases and resource consumption increases
Solution Approach 1:
The patent merges multiple adjacent macroinstructions (MOV, ALU, and JCC) into a single fused micro-operation. The instruction translator detects specific patterns where a MOV instruction followed by an ALU instruction followed by a JCC instruction can be combined into one unified micro-op that performs all three operations atomically, thereby increasing instruction throughput without proportionally increasing the number of micro-operations processed
2Productivity
If multiple macroinstructions are processed sequentially, then resource consumption per instruction is manageable, but the overall processing efficiency and instruction per clock cycle throughput are reduced
Solution Approach 1:
The patent combines three adjacent macroinstructions into a single fused micro-operation that executes atomically. This merging reduces the total number of micro-operations that need to be dispatched, scheduled, and executed, thereby reducing resource consumption (execution unit cycles, scheduler overhead, register file accesses) while increasing the effective instruction throughput per clock cycle
3Reliability
If the instruction translator processes each macroinstruction separately, then translation accuracy and correctness are maintained, but the translator size, power consumption, and complexity increase
Solution Approach 1:
The instruction translator performs preliminary pattern recognition to identify sequences of MOV-ALU-JCC instructions that can be fused. By detecting these patterns early in the translation phase and preparing the fused micro-operation template in advance, the translator maintains correct semantic interpretation while reducing the complexity of subsequent execution phases
Solution Approach 2:
The fused micro-operation structure is designed to be universal, handling multiple operation types (register-to-register MOV, ALU operations, conditional jumps) within a single unified micro-op format. This multi-functionality allows the translator to maintain correctness across different instruction patterns while using a standardized fused micro-op structure, reducing overall translator complexity
Data Source
AI summary
A microprocessor receives first, second, and third program-adjacent macroinstructions. The first macroinstruction moves a first operand to a first register from a second register. The second macroinstruction performs an arithmetic/logic operation using the first operand in the second register and a second operand in a third register to generate a result, loads the result back into the first register, and updates condition codes based on the result. The third macroinstruction conditionally jumps to a target address. An instruction translator simultaneously translates the first, second, and third program-adjacent macroinstructions into a single micro-operation for execution by an execution unit. The micro-operation performs the arithmetic/logic operation using the first operand in the second register and the second operand in third register to generate the result, loads the result back into the first register, updates the condition codes based on the result, and conditionally jumps to the target address.