Speculative Stack Pointer Delta Register for Processor Latency Reduction
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Solution Overview
Problem
Existing techniques for maintaining a stack pointer are inefficient, as they often require frequent adjustments and serial access to the stack pointer register for each stack-dependent operation, leading to increased latency and power consumption.
Innovation Solution
The implementation of a sideband stack optimizer (SSO) that uses a stack pointer delta register to speculate on stack pointer adjustments, reducing the need for frequent updates by modifying the speculative SPD value based on instruction size and combining it with the stack pointer value, thereby minimizing dependencies on the stack pointer register.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequent updates of stack pointer register are performed for each stack-dependent operation, then stack pointer accuracy is maintained, but processor latency increases and power consumption rises
Solution Approach 1:
The patent pre-calculates and stores stack pointer delta values in a dedicated register before they are needed. By maintaining a speculative stack pointer delta register that is updated in advance based on instruction decoding, the system avoids the need for frequent serial updates of the stack pointer register during execution, thus reducing latency while maintaining accuracy.
Solution Approach 2:
The patent introduces a speculative stack pointer delta register as an intermediary between the instruction stream and the stack pointer register. This intermediary holds pre-computed delta values that can be quickly applied to the stack pointer when needed, eliminating the need for direct serial access to the stack pointer register for each stack operation.
2Measurement precision
If serial access to stack pointer register is performed for each stack-dependent instruction, then stack pointer value is accurately maintained, but processor throughput decreases
Solution Approach 1:
The system pre-computes and stores stack pointer adjustments in the speculative stack pointer delta register during instruction decoding, before execution occurs. This allows multiple stack-dependent instructions to be processed in parallel without requiring serial access to the stack pointer register, thereby improving throughput while maintaining value accuracy.
Solution Approach 2:
The patent separates the stack pointer management into two independent components: the stack pointer register itself and the speculative stack pointer delta register. This segmentation allows the delta register to be updated independently and in parallel, eliminating serialization bottlenecks and improving overall processor throughput.
3Speed
If dedicated stack engine hardware is implemented to manage stack pointer, then stack operations are accelerated, but device complexity increases
Solution Approach 1:
The patent extracts only the essential function of a dedicated stack engine - maintaining and updating the stack pointer delta - and implements it as a separate speculative stack pointer delta register. This minimal extraction provides stack operation acceleration without the full complexity of a complete dedicated stack engine, achieving speed improvement with reduced hardware overhead.
Data Source
AI summary
A technique for reducing stack pointer adjustment operations when stack dependent operations, which correspond to stack dependent instructions, are encountered includes setting a stack pointer to an initial value for a stack. A number of bytes associated with the stack dependent operation is determined. A stack pointer delta is then modified based upon the number of bytes associated with the stack dependent operation. A current location in the stack is determined based on the stack pointer and the stack pointer delta.