MIR Analysis & Static Analysis

Mid-Level IR (MIR) Analysis is the primary stage for dataflow reasoning and validation in the RunMat compilation pipeline. This layer bridges the gap between the structural representation of the High-Level IR (HIR) and the execution-ready bytecode. It performs type/shape inference, definite assignment checking, and spawn-safety validation to ensure program correctness before runtime.

These facts approximate runtime values; they are not the runtime value representation itself. For the concrete Value type passed through the VM, builtins, session, GC, GPU, and host adapters, see Runtime Values & Type Model.

MIR Analysis Architecture

The analysis system operates on the MirAssembly structure, iterating through MirBody objects. The core of the analysis is a fixed-point dataflow engine that propagates "facts" across the Control Flow Graph (CFG).

Analysis Data Structures

The results of these analyses are aggregated into an AnalysisStore, which serves as a central repository for metadata about MIR locals and global function properties.

Dataflow Engine Implementation

The dataflow engine uses a worklist algorithm to compute facts for each BasicBlock.

1. Initialization: compute_simple_local_facts initializes in_states and out_states for all blocks in a MirBody
2. Transfer: The transfer_fact_block function updates facts based on MirStmtKind::Assign and MirStmtKind::MultiAssign within a block
3. Join: When multiple CFG edges meet, join_fact_state merges facts using lattice-based logic (e.g., merging specific types into TypeFact::Unknown if they conflict)

Key Analysis Domains

1. Definite Assignment (InitFact)

The InitFact analysis determines if a MirLocal is assigned before use. It tracks three states: Unassigned, MaybeAssigned, and DefinitelyAssigned This is critical for MATLAB semantics where accessing an uninitialized variable triggers a runtime error.

2. Type & Shape Inference

The SimpleValueFact tracks the evolution of array shapes and types.

• Rvalue Inference: simple_rvalue_fact determines facts from constants, aggregates (tensors/cells), and calls
• Shape Propagation: For operations like MirRvalue::Binary, the system attempts to resolve resulting shapes (e.g., matrix multiplication dimensions)

3. Spawn-Safety Checking

RunMat performs static validation on spawn expressions to ensure that closures captured for parallel execution do not violate memory safety or MATLAB's execution model.

• Capture Scanning: analyze_capture_facts walks the MIR to find all reads_captures and writes_captures
• Safety Fact: It produces a SpawnSafetyFact, identifying if a task is RequiresIsolation or is safe for shared execution

Static Analysis & Linting (runmat-static-analysis)

The runmat-static-analysis crate provides a linting layer on top of the MIR analysis. It consumes the AnalysisStore to produce user-facing diagnostics.

Shape Linting Workflow

The lint_shapes function serves as the entry point for dimension-related validation.

Logic to Code Mapping: Shape Inference

Loading diagram...

Implementation Details:

• Seeding: seed_from_analysis populates the linting environment with facts already discovered by the core MIR dataflow
• Refinement: walk_mir_assembly performs a second pass to specifically track numeric constants and integer vectors (like [1 2 3]) that are often used as shape arguments in functions like reshape or zeros
• Diagnostic Generation: If a binary operation (e.g., +) is performed on incompatible shapes, a HirDiagnostic is generated with HirDiagnosticSeverity::Error

Control Flow Lowering to MIR

The analysis relies on a well-formed CFG generated by the ControlFlowBuilder. This builder transforms nested HIR structures into BasicBlock sequences.

Logic to Code Mapping: CFG Construction

Loading diagram...

Key Builder Functions:

• lower_function_body: Entry point that initializes the BlockLoweringEnv and creates the first BasicBlock
• lower_block_from: Recursive function that handles statement-by-statement lowering. When it encounters control-flow (like If or Await), it splits the current block and creates continuations
• lower_continuation_target: Manages the "continuation-passing" style of the builder, ensuring that the code following a block (like the code after an if/end) is correctly linked via a Goto terminator