Compiler Register Liveness Analysis for Contention Reduction
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Solution Overview
Problem
In contemporary computing systems, registers have become a scarce resource, and there is a need to detect and release unused registers to ensure only required registers are allocated, reducing contention and overhead in data storage and recovery operations.
Innovation Solution
Generating object code that indicates the liveness status of registers, with a compiler performing liveness analysis to insert last-use indicators, and using new instructions to store and restore liveness vectors in memory during function calls, thereby marking unused registers and optimizing register allocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If register allocation is performed without liveness analysis, then register availability is high, but register contention increases and performance deteriorates
Solution Approach 1:
The compiler performs liveness analysis during the compilation phase to determine which registers will be used and when, before the program actually runs. This preliminary analysis allows the compiler to make optimal register allocation decisions, assigning registers to variables based on their liveness patterns rather than using simple allocation strategies.
Solution Approach 2:
The system uses liveness information as feedback to guide register allocation decisions. By analyzing which variables are live at each program point and feeding this information back into the allocation process, the compiler can dynamically adjust register assignments to minimize contention and maximize performance.
2Productivity
If liveness analysis is performed to optimize register allocation, then register usage efficiency improves, but compilation complexity increases
Solution Approach 1:
The liveness analysis process is divided into distinct phases: calculating liveness sets for each basic block, merging these sets at control flow join points, and using the results for register allocation. This segmentation makes the complex analysis manageable and implementable through systematic algorithms.
Solution Approach 2:
The compiler performs the liveness analysis automatically as part of the compilation process without requiring manual intervention. The analysis serves the compilation process itself by providing the necessary information for optimal register allocation, making the system self-sufficient in optimizing its own code generation.
3Loss of energy
If unused registers are not identified and released, then register availability remains high, but overhead in data storage and recovery increases
Solution Approach 1:
The compiler identifies the last use of each variable during liveness analysis and inserts appropriate instructions to release registers at those points. This preliminary identification allows the system to free registers before they are actually needed again, reducing the time registers remain occupied and minimizing management overhead.
Data Source
AI summary
Object code is generated from an internal representation that includes a plurality of source operands. The generating includes performing for each source operand in the internal representation determining whether a last use has occurred for the source operand. The determining includes accessing a data flow graph to determine whether all uses of a live range have been emitted. If it is determined that a last use has occurred for the source operand, an architected resource associated with the source operand is marked for last-use indication. A last-use indication is then generated for the architected resource. Instructions and the last-use indications are emitted into the object code.