Vector Data Transfer Instruction for Loop Unrolling
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Solution Overview
Problem
Existing vector data transfer instructions face challenges in supporting loop unrolling due to increased register pressure and overhead in initializing index registers, especially when dealing with variable vector sizes and long vectors, which limits the number of iterations that can be unrolled into a single iteration of an unrolled loop.
Innovation Solution
A vector data transfer instruction that specifies the start address of a contiguous block of addresses using a base register and an immediate offset value, where the immediate offset is defined as a multiple of the block size, allowing for efficient loop unrolling without the need to know the vector size in advance and reducing register pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional vector data transfer instructions are used with loop unrolling, then the number of iterations that can be unrolled is limited, but register pressure increases and initialization overhead increases
Solution Approach 1:
The patent changes the addressing mode parameter from traditional base-index-offset to a simplified base-immediate-offset mode where the immediate offset is defined as a multiple of block size. This parameter change eliminates the need for index register initialization and reduces register pressure, enabling more iterations to be unrolled into a single instruction
Solution Approach 2:
The patent extracts the index register initialization overhead from the loop unrolling process by using immediate offsets that are multiples of block size. This allows the offset to be directly encoded in the instruction without requiring separate index register setup, thereby reducing initialization overhead and register pressure
2Productivity
If traditional vector data transfer instructions are used with loop unrolling, then the number of iterations that can be unrolled is limited, but initialization overhead increases
Solution Approach 1:
The patent performs preliminary action by pre-calculating offsets as multiples of block size and encoding them directly in the instruction as immediate values. This eliminates the need for runtime index register initialization, reducing initialization overhead and enabling more iterations to be unrolled
Solution Approach 2:
By changing the offset parameter to be defined as a multiple of block size, the patent allows the offset to be directly encoded in the instruction without requiring separate index register setup, thereby eliminating initialization overhead
3Productivity
If vector size is fixed in advance, then code can be optimized for specific hardware, but adaptability to different hardware implementations is reduced
Solution Approach 1:
The patent creates a universal vector data transfer instruction that works across different hardware implementations with varying vector lengths. By using immediate offsets defined as multiples of block size, the same instruction can be executed on different hardware without modification, achieving both optimization and adaptability
Solution Approach 2:
The patent introduces dynamics by allowing the block size to vary based on hardware capabilities while maintaining the same instruction format. The immediate offset is adaptively calculated as a multiple of the hardware-specific block size, enabling the same code to execute efficiently on different hardware platforms
4Manufacturing precision
If more encoding space is allocated for vector size information, then more precise control is possible, but instruction encoding space is consumed
Solution Approach 1:
The patent changes the addressing parameter representation by defining immediate offsets as multiples of block size. This allows the offset to be encoded more compactly in the instruction, maintaining addressing precision while consuming less encoding space compared to traditional methods that require separate index register specifications
Data Source
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AI summary
A vector data transfer instruction is provided for triggering a data transfer between storage locations corresponding to a contiguous block of addresses and multiple data elements of at least one vector register. The instruction specifies a start address of the contiguous block using a base register and an immediate offset value specifies as a multiple of the size of the contiguous block of addresses. This is useful for loop unrolling which can help to improve performance of vectorised code by combining multiple iterations of a loop into a single iteration of an unrolled loop, to reduce the loop control overhead.