38 lines
2.0 KiB
Markdown
38 lines
2.0 KiB
Markdown
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# LLVM Layer Overview (Phase 15)
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Scope
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- Practical guide to LLVM lowering architecture and invariants used in Phase 15.
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- Complements LOWERING_LLVM.md (rules), RESOLVER_API.md (value resolution), and LLVM_HARNESS.md (harness).
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Module Layout
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- `src/backend/llvm/compiler/codegen/`
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- `instructions/` split by concern: `flow.rs`, `blocks.rs`, `arith.rs`, `arith_ops.rs`, `mem.rs`,
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`strings.rs`, `arrays.rs`, `maps.rs`, `boxcall/`, `externcall/`, `call.rs`, `loopform.rs`, `resolver.rs`.
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- `builder_cursor.rs`: central insertion/terminator guard.
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Core Invariants
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- Resolver-only reads: lowerers fetch MIR values through `Resolver` (no direct `vmap` access for cross-BB values).
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- Localize at block start: PHIs created at the beginning of the current BB (before non-PHI) to guarantee dominance.
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- Cast placement: perform ptr↔int and width casts outside PHIs, at BB start or just-before-pred-terminator via `with_block`.
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- Sealed SSA: successor PHIs wired by predecessor snapshots and `seal_block`; branch/jump do not push incoming directly.
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- Cursor discipline: only insert via `BuilderCursor`; post-terminator insertions are forbidden.
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LoopForm (gated)
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- Shape: `preheader → header → body → dispatch(phi) → {latch|exit} → header` with PHIs centralized in `dispatch`.
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- State: model loop-carried values via a `LoopState` aggregate (tag + payloads).
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- Goals: move all PHIs to dispatch, ensure header uses are dominated by preheader/dispatch values.
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Types and Bridges
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- Box handle is `i64` across NyRT boundary; strings prefer `i8*` fast paths.
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- Convert rules: `ensure_i64/ensure_i1/ensure_ptr` style helpers (planned extraction) to centralize casting.
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Harness (optional)
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- llvmlite harness exists for fast prototyping and structural checks.
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- Gate: `NYASH_LLVM_USE_HARNESS=1` (planned wiring); target parity tested by Acceptance A5.
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References
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- LOWERING_LLVM.md — lowering rules and runtime calls
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- RESOLVER_API.md — Resolver design and usage
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- LLVM_HARNESS.md — llvmlite harness interface and usage
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