Masked Packed Data Instruction Execution in SIMD Processors
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Solution Overview
Problem
Current processors with SIMD architectures face challenges in efficiently processing packed data operations, particularly in managing and executing masked packed data instructions due to limited opcode space and instruction length constraints, which restricts the ability to perform conditional operations on multiple data elements concurrently.
Innovation Solution
The implementation of masked packed data instructions and operation masks within the processor allows for conditional execution of packed data operations, enabling per-result data element granularity masking, where mask bits specify whether operations are performed and results are stored, thereby optimizing the use of opcode space and enhancing concurrent processing capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If masked packed data instructions are implemented with per-result data element granularity masking, then conditional execution capability and processing efficiency are improved, but opcode space consumption increases
Solution Approach 1:
The mask register is segmented into multiple fields, where each field corresponds to a specific packed data element and contains mask bits that control execution for that element. This segmentation allows fine-grained control without requiring a completely new instruction format, as the mask register can be reused for different instruction types.
Solution Approach 2:
The mask register serves multiple functions: it provides masking for packed data instructions, controls conditional execution at per-element granularity, and can be used with different instruction types (add, subtract, multiply, etc.). This multi-functionality reduces the need for separate opcode variants for each masked operation.
2Measurement precision
If per-result data element granularity masking is implemented, then conditional operation precision is improved, but instruction encoding complexity increases
Solution Approach 1:
The mask register is divided into multiple fields, with each field containing mask bits corresponding to specific packed data elements. This segmentation enables precise control at the element level while using a standardized register structure that doesn't significantly increase encoding complexity.
Solution Approach 2:
The mask register acts as an intermediary between the instruction opcode and the actual data elements. Instead of encoding masks directly in the instruction, the mask register serves as a mediator that can be referenced by the instruction, simplifying the encoding while enabling fine-grained control.
3Adaptability or versatility
If multiple mask bits are used for packed data elements, then conditional execution capability is improved, but register usage complexity increases
Solution Approach 1:
The mask register is designed to serve multiple purposes beyond just masking packed data operations. It can control conditional execution for various instruction types, work with different packed data formats, and provide both element-level and operation-level control, reducing the need for separate control mechanisms.
Solution Approach 2:
The mask register is segmented into multiple fields that can be independently controlled. Each field corresponds to a packed data element and can be enabled or disabled independently, providing versatile conditional execution capability while using a single register structure rather than multiple separate registers.
Data Source
AI summary
A processor includes a first mode where the processor is not to use packed data operation masking, and a second mode where the processor is to use packed data operation masking. A decode unit to decode an unmasked packed data instruction for a given packed data operation in the first mode, and to decode a masked packed data instruction for a masked version of the given packed data operation in the second mode. The instructions have a same instruction length. The masked instruction has bit(s) to specify a mask. Execution unit(s) are coupled with the decode unit. The execution unit(s), in response to the decode unit decoding the unmasked instruction in the first mode, to perform the given packed data operation. The execution unit(s), in response to the decode unit decoding the masked instruction in the second mode, to perform the masked version of the given packed data operation.