Linear scan register allocation on SSA
7 days ago
- #linear-scan
- #compiler
- #register-allocation
- Register allocation transforms virtual registers in an IR to physical registers and stack space.
- Linear scan register allocation (LSRA) is a method that assigns registers in one pass over the IR, focusing on live ranges.
- SSA form simplifies register allocation by ensuring each virtual register has a single definition, making live ranges straightforward.
- Liveness analysis is crucial for determining which registers are live at each point in the program, aiding in efficient register allocation.
- The linear scan algorithm involves managing active intervals, spilling when necessary, and assigning registers based on live ranges.
- Handling calls and method parameters requires special consideration to preserve registers across calls and manage parameter passing.
- Critical edge splitting is necessary to correctly insert moves between blocks without affecting other edges.
- Parallel move algorithms are complex and prone to bugs, requiring careful implementation to handle register swaps and dependencies.
- Verification tools and fuzzing can help ensure the correctness of the register allocator by checking invariants and exploring edge cases.
- Future improvements could include lifetime holes, interval splitting, and better handling of register constraints.