Rotate Instructions Without Carry Flag Dependency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing rotate instructions, such as the ROR instruction, require reading the carry flag, which increases execution time and serialization, limiting parallel processing and speculative execution, and also overwrite the source operand, necessitating additional data movement instructions to preserve it.
Innovation Solution
An instruction processing apparatus with an execution unit that executes rotate instructions without reading or writing the carry flag, allowing for faster execution and reduced serialization by completing the operation without relying on arithmetic flags, and explicitly specifying source and destination operands to prevent overwriting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the ROR instruction reads the carry flag, then the rotation operation can be completed with proper flag handling, but the execution time increases and serialization is increased
Solution Approach 1:
The patent extracts the carry flag reading operation from the rotate instruction execution path. The rotate instruction is modified to perform rotation without reading or writing the carry flag, separating the rotation function from flag dependency. This allows the rotation to complete faster while maintaining reliability through explicit source and destination operand specification.
Solution Approach 2:
The patent segments the rotate instruction into distinct source and destination operands, allowing the instruction to specify different registers for input and output data. This segmentation prevents overwriting issues and allows parallel processing by eliminating implicit dependencies on flag registers.
2Reliability
If the ROR instruction reads the carry flag, then arithmetic flag dependencies are maintained, but parallel processing and speculative execution are limited
Solution Approach 1:
The patent removes the carry flag reading dependency from the rotate instruction, extracting this arithmetic flag interaction from the critical execution path. This enables multiple rotate instructions to execute in parallel without serializing on flag reads, while still maintaining correct rotation functionality through explicit operand specification.
3Productivity
If the ROR instruction overwrites the source operand, then the destination operand is updated, but additional data movement instructions are needed to preserve the source
Solution Approach 1:
The patent segments the rotate instruction into explicit source and destination operands that can be different registers. This allows the source operand to be preserved in its original location while the destination receives the rotated value, eliminating the need for additional data movement instructions to preserve intermediate values.
Data Source
AI summary
A method of one aspect may include receiving a rotate instruction. The rotate instruction may indicate a source operand and a rotate amount. A result may be stored in a destination operand indicated by the rotate instruction. The result may have the source operand rotated by the rotate amount. Execution of the rotate instruction may complete without reading a carry flag.