43 lines
2.4 KiB
Markdown
43 lines
2.4 KiB
Markdown
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# LLVM Lowering Rules (Phase 15)
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This document describes the active LLVM lowering rules used in Phase 15. Only the LLVM path is authoritative at this time.
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## General
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- Box values are represented as i64 handles when crossing the NyRT boundary.
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- String operations prefer i8* fast paths (AOT helpers) when possible. Handle conversions are done only at explicit boundaries.
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## NewBox
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- StringBox:
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- When constructed from a constant string, lowering produces i8* via `nyash_string_new` and keeps it as i8* (no immediate handle conversion).
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- Builder skips redundant birth calls for StringBox.
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- Other boxes:
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- Minimal birth shims exist (e.g., `nyash.box.birth_h`, `nyash.box.birth_i64`) using Box type ids.
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## BoxCall: String.concat fast path
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- If the receiver is annotated as String (or StringBox), lower to AOT helpers directly:
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- `concat_ss(i8*, i8*) -> i8*`
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- `concat_si(i8*, i64) -> i8*` (right operand is a handle coerced to string by NyRT)
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- `concat_is(i64, i8*) -> i8*`
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- For non‑String receivers or plugin cases, fall back to plugin/by‑id paths as needed.
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## BinOp Add: String concatenation
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- Primary path: AOT helpers selected by operand shapes at IR time:
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- `i8* + i8* -> concat_ss`
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- `i8* + i64 -> concat_si`
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- `i64 + i8* -> concat_is`
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- Fallback policy: keep to the minimum. Do not add implicit conversions beyond the above without clear MIR type annotations. If mixed forms miscompile, fix MIR annotations first.
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## ExternCall selection (console/debug)
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- `env.console.{log,warn,error}` and `env.debug.trace` inspect the argument at lowering time:
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- If argument is `i8*`, call the C‑string variant: `nyash.console.{log,warn,error}` / `nyash.debug.trace`.
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- Otherwise convert to `i64` and call the handle variant: `nyash.console.{log,warn,error}_handle` / `nyash.debug.trace_handle`.
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- The result values are ignored or zeroed as appropriate (side‑effecting I/O).
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## Return/Result mapping
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- For plugin/by‑id calls that return an i64 handle but the destination is annotated as pointer‑like (String/Box/Array/Future/Unknown), the handle is cast to an opaque pointer for SSA flow. Integers/Bools remain integers.
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## Backend Consistency Notes
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- VM/Cranelift/JIT are not MIR14‑ready and may not follow these rules yet. LLVM behavior takes precedence; other backends will be aligned later.
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- Any new fallback must be justified and scoped; wide catch‑alls are prohibited to prevent backend divergence.
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