Global linear-scan register allocation for ZJIT SSA values

[Copilot]

ZJIT’s register allocator was block-local, preventing SSA values from spanning dominating blocks despite a CFG. This change makes allocation global with CFG liveness/intervals and preserves existing split/out-of-SSA passes.

• Global liveness + intervals

  • Add CFG live-in/live-out dataflow and derive VReg live ranges across block boundaries.
  • Extend BitSet with union/subtract/iteration utilities to support the analysis.

• Out-of-SSA parameter handling

  • Materialize explicit VReg block parameters for non-entry blocks.
  • Use per-block parameters in branch ParallelMov expansion.

• Validation + tests

  • Drop block-local SSA validation from validate() while keeping the helper for tests.
  • Add dominance-friendly validation and a cross-block allocator smoke test.

let param_opnd = gen_param(&mut asm, idx, is_entry_block);
if !is_entry_block {
    asm.current_block().add_parameter(param_opnd);
}
jit.opnds[insn_id.0] = Some(param_opnd);

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.

[tekknolagi]

gave you more internet access. have fun