Microprocessor REP MOVS Execution via Instruction Translator
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Solution Overview
Problem
The execution performance of REP MOVS macroinstructions in microprocessors is poor due to the inefficiency of looping microinstruction sequences, which require many clock cycles and can lead to misprediction penalties and prevent optimization opportunities.
Innovation Solution
A microprocessor design that includes an instruction translator capable of transferring control to either a sequence of microinstructions with conditional control transfers based on the ECX register or a sequence without, depending on a flag set by immediate value operations, thereby eliminating or reducing looping and improving performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a looping microinstruction sequence is used to execute REP MOVS macroinstructions, then the number of microinstructions stored is reduced, but the execution performance deteriorates due to conditional branch instructions requiring many clock cycles and potential misprediction penalties
Solution Approach 1:
The instruction translator performs preliminary actions by setting a flag and saving the immediate ECX value when it encounters a MOV ECX, immediate macroinstruction. This preliminary preparation enables the microprocessor to later select the optimized unrolled microinstruction sequence for REP MOVS operations without requiring runtime conditional branches, thus resolving the contradiction between compact storage and high execution performance
Solution Approach 2:
The system dynamically adapts its microinstruction sequence selection based on the flag state set by previous instructions. When the flag indicates an immediate ECX value was loaded, the system switches to the unrolled sequence; otherwise, it uses the looping sequence. This dynamic adaptation allows the system to optimize for performance when conditions permit while maintaining functionality in all cases
2Loss of time
If a looping microinstruction sequence with conditional branch instructions is used, then space efficiency is improved, but execution speed deteriorates due to branch misprediction penalties and prevented optimizations
Solution Approach 1:
The instruction translator performs preliminary actions by setting a flag and saving the immediate ECX value when it encounters a MOV ECX, immediate macroinstruction. This preliminary preparation enables the microprocessor to later select the optimized unrolled microinstruction sequence for REP MOVS operations without requiring runtime conditional branches, thus resolving the contradiction between compact storage and high execution performance
Solution Approach 2:
The invention extracts and eliminates the harmful conditional branch instructions from the microinstruction sequence when conditions permit. By using the unrolled sequence with immediate values and no branches, the system removes the source of misprediction penalties and branch-related delays, directly improving execution speed while maintaining space efficiency through selective sequence usage
Data Source
AI summary
A microprocessor REP MOVS macroinstruction specifies the word length of the string in the IA-32 ECX register. The microprocessor includes a memory, configured to store a first and second sequence of microinstructions. The first sequence conditionally transfers control to a microinstruction within the first sequence based on the ECX register. The second sequence does not conditionally transfer control based on the ECX register. The microprocessor includes an instruction translator, coupled to the memory. In response to a macroinstruction that moves an immediate value into the ECX register, the instruction translator sets a flag and saves the immediate value. In response to a macroinstruction that modifies the ECX register in a different manner, the translator clears the flag. In response to a REP MOVS macroinstruction, the instruction translator transfers control to the first sequence if the flag is clear; and transfers control to the second sequence if the flag is set.