Load-Tagged Pointer Speculative Execution Microarchitecture
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Solution Overview
Problem
Conventional microprocessors face inefficiencies in processing tagged pointer instructions due to high latency and inaccuracies in branch prediction, leading to reduced overall system performance, especially when dealing with conditional branches and load instructions in tagged architectures.
Innovation Solution
Implementing a load-tagged pointer (LTPTR) instruction that decomposes into three internal operations, allowing for speculative execution with a two-cycle or five-cycle load-use latency, depending on the embodiment, to reduce latency and ensure accurate handling of tagged pointers, thereby improving processing throughput by predicting and confirming the validity of memory addresses before execution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional microprocessors execute tagged pointer instructions with full validation, then accuracy is improved, but latency increases
Solution Approach 1:
The patent performs preliminary validation of tagged pointers by checking the validity bit in the tag field before executing the full load instruction. This preliminary action identifies invalid pointers early, allowing the system to skip expensive validation and execution steps, thereby reducing overall latency while maintaining accuracy through selective validation.
Solution Approach 2:
The patent segments the tagged pointer validation process into distinct stages: extracting the tag field and validity bit, validating the pointer format and accessibility, and then executing the load operation only if validation succeeds. This segmentation allows the system to perform quick format checks separately from the full validation process, reducing latency for valid pointers while maintaining accuracy through complete validation when needed.
2Productivity
If speculative execution is implemented to reduce latency, then processing throughput is improved, but prediction accuracy decreases
Solution Approach 1:
The patent implements feedback mechanisms where the results of speculative executions are validated against actual tagged pointer validity. When speculation is correct, the system continues at high speed; when incorrect, the system detects the error through the validity bit check and corrects by executing the non-speculative path. This feedback loop maintains prediction accuracy while enabling speculative execution to improve overall throughput.
Solution Approach 2:
The patent dynamically adjusts the execution path based on runtime conditions by combining speculative execution with runtime validation. The system transitions between speculative and non-speculative modes depending on whether the validity bit indicates a valid pointer, allowing flexible adaptation that maintains both throughput and accuracy.
3Reliability
If pipeline flushing is performed to handle branches, then correctness is improved, but productivity deteriorates
Solution Approach 1:
The patent performs preliminary validation of tagged pointers before they are needed by subsequent instructions. By checking the validity bit and pointer format in advance, the system ensures correctness is established early, allowing the pipeline to continue executing subsequent instructions without flushing, thereby maintaining both correctness and productivity.
Data Source
AI summary
A methodology and implementation of a load-tagged pointer instruction for RISC based microarchitecture is presented. A first lower latency, speculative implementation reduces overall throughput latency for a microprocessor system by estimating the results of a particular instruction and confirming the integrity of the estimate a little slower than the normal instruction execution latency. A second higher latency, non-speculative implementation that always produces correct results is invoked by the first when the first guesses incorrectly. The methodologies and structures disclosed herein are intended to be combined with predictive techniques for instruction processing to ultimately improve processing throughput.