Logical Map Table Detecting Evil Twin Dependency Conditions
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Solution Overview
Problem
Computer processors face increased execution time due to dependency conditions, particularly 'evil twin' conditions, which arise when instructions depend on partial register updates, leading to undesirable delays, especially in code with many floating-point operations.
Innovation Solution
The implementation of a logical map table (LMT) with content-addressable memory (CAM) to detect and manage dependencies, including evil twin conditions, by mapping instruction destinations to physical registers and using bits to indicate validity and recent updates, allowing for efficient detection and mitigation of such dependencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If register renaming with logical map table is used to manage instruction dependencies, then instruction execution flexibility is improved, but detection of evil twin dependencies becomes more complex
Solution Approach 1:
The patent segments the dependency detection process into distinct components: the logical map table stores mapping information between logical and physical registers, while separate dependency detection logic identifies evil twin conditions. This segmentation allows the system to maintain execution flexibility through register renaming while independently handling the complexity of dependency detection through dedicated detection mechanisms that examine the stored mapping information.
Solution Approach 2:
The logical map table acts as an intermediary structure that mediates between the register renaming mechanism and the dependency detection logic. It stores the mapping information that both the renaming process needs and the dependency detection needs, allowing these two functions to interact without direct complexity interference. The detection logic queries this intermediary structure to identify evil twin conditions without being coupled to the renaming implementation details.
2Measurement precision
If dependency detection mechanisms are added to identify evil twin conditions, then execution accuracy is improved, but processor complexity increases
Solution Approach 1:
The logical map table serves multiple functions: it maintains the logical-to-physical register mappings needed for register renaming, and it provides the data structure for dependency detection. By making this structure multi-functional, the patent avoids adding separate dedicated structures for dependency detection, thereby improving detection accuracy without proportionally increasing processor complexity. The same stored mapping information serves both renaming and detection purposes.
3Productivity
If evil twin dependencies are not detected, then processor simplicity is maintained, but execution time increases due to unwanted delays
Solution Approach 1:
The patent performs preliminary action by maintaining the logical map table during register renaming, which stores all necessary information about logical-to-physical register mappings before dependency detection occurs. This preliminary establishment of the mapping structure enables subsequent dependency detection to proceed efficiently without requiring additional complex structures, as the detection logic simply queries the pre-existing mapping information to identify evil twin conditions and prevent execution delays.
Data Source
AI summary
Techniques and structures are described which allow the detection of certain dependency conditions, including evil twin conditions, during the execution of computer instructions. Information used to detect dependencies may be stored in a logical map table, which may include a content-addressable memory. The logical map table may maintain a logical register to physical register mapping, including entries dedicated to physical registers available as rename registers. In one embodiment, each entry in the logical map table includes a first value usable to indicate whether only a portion of the physical register is valid and whether the physical register includes the most recent update to the logical register being renamed. Use of this first value may allow precise detection of dependency conditions, including evil twin conditions, upon an instruction reading from at least two portions of a logical register having an entry in the logical map table whose first value is set.