Conditional Branching for Single-Cycle Loop Remainder Handling
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Solution Overview
Problem
Existing software pipelining techniques face inefficiencies due to the need for additional processing cycles and overhead from using conditional branching to handle leftover loop iterations, which diminishes the benefits of parallel execution.
Innovation Solution
A conditional branch instruction that specifies multiple branch destinations based on an iteration count, allowing the processing system to determine and execute remainder operations in a single cycle, reducing the number of processing cycles and overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If existing conditional branching techniques are used to handle leftover loop iterations, then the loop can be completed, but the number of processing cycles increases and overhead is added
Solution Approach 1:
The patent segments the loop iteration handling into multiple destination blocks (first destination block for iterations remaining, second destination block for no iterations remaining, third destination block for specific iterations remaining). This segmentation allows the processor to directly jump to the appropriate handling code based on the iteration count, avoiding sequential conditional checks and reducing processing cycles.
Solution Approach 2:
The patent performs preliminary determination of the destination block based on the iteration count before executing the conditional branch instruction. The iteration count is compared against thresholds in advance, and the appropriate destination block is selected beforehand, enabling direct branching without sequential evaluation of multiple conditions during execution.
2Productivity
If existing conditional branching techniques are used to handle leftover loop iterations, then the loop can be completed, but the complexity of the application code increases
Solution Approach 1:
The patent segments the handling logic into distinct destination blocks, each responsible for a specific range of iteration counts. This segmentation simplifies the code structure by separating concerns into modular blocks that can be independently managed, reducing the overall complexity compared to a single complex conditional branching structure.
Solution Approach 2:
The patent creates a universal conditional branch instruction that can handle multiple iteration scenarios (different ranges of remaining iterations) through a single instruction type. This multi-functional approach reduces code complexity by providing a unified mechanism for handling various loop completion scenarios rather than requiring separate instructions for each case.
3Power
If software pipelining is used to execute loop bodies in parallel, then processing efficiency is improved, but additional processing cycles are required to handle remainder operations
Solution Approach 1:
The patent extracts the remainder operation handling from the main parallel execution flow by using conditional branch instructions to jump to specific destination blocks. This extraction allows the parallel processing of loop bodies to proceed independently while the remainder operations are handled separately in dedicated blocks, minimizing interference and overhead cycles.
Solution Approach 2:
The patent performs preliminary determination of whether remainder operations are needed and directs execution to the appropriate handling block before the parallel processing completes. This preliminary action allows the system to prepare for remainder handling in advance, reducing the overhead cycles required after parallel execution by avoiding unnecessary sequential checks.
Data Source
AI summary
Various embodiments of the present disclosure relate to conditional branch instructions to support software pipelining techniques. In an example embodiment, a system including instruction fetch circuitry, decoder circuitry, and conditional branch circuitry is provided. The instruction fetch circuitry is configured to fetch a conditional branch instruction from memory and provide the instruction to the decoder circuitry. The instruction includes an iteration count and multiple branch destinations. The branch destinations include two or more branch destinations corresponding to conditions against which the conditional branch circuitry evaluates the iteration count. The decoder circuitry is configured to cause the conditional branch circuitry to select a branch destination, of the two or more branch destinations, based on a comparison of the iteration count to each of the conditions and cause the instruction fetch circuitry to fetch an indication of an instruction from a memory location stored at the selected branch destination.