Multi-Dimensional Loop Counter Collapse for Nested Loops
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Solution Overview
Problem
Current compilers face challenges in efficiently collapsing multi-nested loops due to non-stride memory accesses, sub-dimensional array accesses, and computations over separate loop counters, which hinder performance improvement in high-performance computing.
Innovation Solution
The solution involves maintaining loop counters in a vector format, allowing for post-computational updates in hardware responsive to a single instruction, and using instructions to control multi-dimensional loop counters for collapsing nested loops, enabling their use as indexes for array accesses and computations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multi-nested loops are collapsed using conventional methods with a new loop counter, then the number of branches is reduced and performance is improved, but the information about individual loop counters must be preserved for computations and array indexing which increases complexity
Solution Approach 1:
The patent merges multiple separate loop counters into a single multi-dimensional loop counter structure. Instead of maintaining separate counters for each nested loop level, the invention combines them into one counter that encodes all individual loop counter values, thereby reducing the number of variables to manage while preserving the ability to compute individual loop indices for array access and computations.
Solution Approach 2:
The single multi-dimensional loop counter serves multiple functions simultaneously: it tracks the iteration state of all nested loops, enables computation of individual loop indices through mathematical transformations, and provides indexing for multi-dimensional arrays. This universal counter structure eliminates the need for separate counters while maintaining all necessary loop control capabilities.
2Productivity
If compilers attempt to collapse loops, then performance may be improved, but non-stride memory accesses and sub-dimensional array accesses prevent efficient collapsing
Solution Approach 1:
The invention changes the parameter representation from separate integer counters to a single counter with a composite encoding scheme. By transforming the loop counter from a simple integer to a multi-dimensional index structure, the patent enables compilers to handle complex memory access patterns including non-stride and sub-dimensional array accesses that were previously incompatible with loop collapsing.
3Loss of information
If separate loop counters are maintained for nested loops, then individual loop information is preserved for computations, but the number of instructions and memory references increases
Solution Approach 1:
The patent extracts the essential loop counter information from multiple separate counters and encodes it into a single compact multi-dimensional counter structure. This extraction process removes redundant counter variables while preserving all necessary loop index information through mathematical encoding, thereby reducing the number of instructions needed to manage loop state.
Data Source
AI summary
In an embodiment, the present invention is directed to a processor including a decode logic to receive a multi-dimensional loop counter update instruction and to decode the multi-dimensional loop counter update instruction into at least one decoded instruction, and an execution logic to execute the at least one decoded instruction to update at least one loop counter value of a first operand associated with the multi-dimensional loop counter update instruction by a first amount. Methods to collapse loops using such instructions are also disclosed. Other embodiments are described and claimed.