Plan LLVM Lowering

Guide for planning MIR -> LLVM IR lowering for a specific construct.

Prerequisites

Read before starting:

• docs/llvm-backend.md - lowering principles and decision framework
• docs/mir-design.md - MIR semantics (what you're translating)
• docs/pipeline-contract.md - layer boundaries

Mental Model

MIR is the semantic endpoint. LLVM is only an execution substrate. Lowering is not interpretation--it is faithful translation.

Key distinction: semantics are already fixed in MIR. This skill is about mechanical translation, not semantic design. If lowering needs to "decide" behavior, the MIR is underspecified--fix MIR first.