SIMD Shift Instruction with Per-Element Shift Counts
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Solution Overview
Problem
Current approaches for handling packed data, such as co-processor solutions and instruction-level solutions, face limitations in flexibility, overhead, and scalability, especially when dealing with data widths larger than 64 bits, and require significant control logic and multiple hardware copies in modern CPU designs.
Innovation Solution
A SIMD shift instruction that allows each element in a vector to be associated with a different shift count, enabling flexible and efficient shifting of data elements by using a shift count register to specify unique shift operations for each output element, thereby allowing bits from anywhere in the source register to be shifted into the output register.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If co-processor solutions are used for handling packed data, then data packing and unpacking can be performed, but significant overhead is required for controlling the co-processor's actions and gathering its results
Solution Approach 1:
The patent merges the data packing/unpacking functionality directly into the main CPU instruction set rather than using a separate co-processor. The shift instruction integrates multiple data elements and shift counts into a single instruction execution, eliminating the need for separate co-processor control sequences and result gathering operations.
Solution Approach 2:
The shift instruction is designed to handle multiple data elements simultaneously with different shift counts, making it a universal instruction that can perform various packing and unpacking operations. This multi-functional instruction replaces multiple specialized co-processor operations, reducing overhead and improving efficiency.
2Productivity
If co-processor solutions are used for handling packed data, then data packing and unpacking can be performed, but multiple copies of co-processor hardware are needed in modern, highly-threaded CPU designs
Solution Approach 1:
The patent combines the data packing/unpacking functionality into the main CPU architecture rather than requiring separate co-processor hardware. The shift instruction uses existing CPU registers and execution units, eliminating the need for multiple co-processor copies in multi-threaded CPU designs.
3Device complexity
If instruction-level solutions such as parallel deposit and parallel extract are used, then less overhead and relatively less logic are required, but separate hardware structures and significant control logic are needed
Solution Approach 1:
The shift instruction uses dynamic shift counts stored in vector registers rather than fixed hardware control logic. This allows the same instruction to handle different data widths and shift amounts by loading different shift count values from the vector register, providing flexibility without requiring multiple specialized hardware structures.
Solution Approach 2:
The instruction changes parameters (shift counts) dynamically based on data width requirements. By loading different shift count values from the vector register, the same shift instruction can efficiently handle various data widths without requiring separate hardware paths for each width.
4Device complexity
If current instruction-level solutions are used, then less overhead and relatively less logic are required, but they do not extend well when dealing with data widths larger than 64 bits
Solution Approach 1:
The shift instruction is designed as a universal instruction that can handle various data widths (8-bit, 16-bit, 32-bit, 64-bit, and beyond) by using vector registers to store different shift counts. This single instruction pattern can be adapted to process different data widths without requiring width-specific hardware implementations.
Data Source
AI summary
Techniques for packing and unpacking data from a source register using a particular shift instruction are provided. The shift instructions takes, as input, a source register that contains a plurality of elements and a shift count register that contains a plurality of shift counts. Each shift count indicates how much to shift bits from the source registers. Where “source” bits are shifted (or copied) to in an output register depends on the position of the shift count in the shift count register. The shift counts may correspond to one or more bytes from the source register. The shift instruction may initiate a left shift operation or a right shift operation.