24 lines
1.1 KiB
Markdown
24 lines
1.1 KiB
Markdown
# PHI and SSA in Nyash
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Overview
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- Nyash lowers high-level control flow (If/Loop/Match) to MIR and backends that rely on SSA form.
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- We prioritize IR hygiene and observability while keeping runtime cost at zero.
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Design points
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- PHI hygiene: no empty PHIs; PHIs at block head only.
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- JoinResult hint: when both branches assign the same variable, we emit a MIR hint for diagnostics.
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- Loop carriers: loops may expose a carrier observation (≤ N variables, where N is unconstrained by design; smokes emphasize common cases).
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Normalization
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- If: may optionally wrap into LoopForm under a conservative gate (dev only). Semantics remain unchanged.
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- Match: scrutinee evaluated once, guard fused; normalized to nested If‑chain in macro/core pass.
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Testing
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- LLVM smokes: fixed small cases ensure no empty PHIs and head placement.
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- MIR smokes: trace `scope|join|loop` to validate shaping without peeking into IR details.
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Roadmap
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- Remove text-level sanitization once finalize‑PHI is trustworthy across Loop/If/Match.
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- Expand goldens to cover nested joins and multi‑carrier loops while keeping CI light.
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