Fidelity MLIR Plugins

MLIR pass plugins for the Fidelity Framework. These plugins extend the MLIR lowering pipeline with transformations required by the Fidelity compilation model.

Each plugin is a shared library loaded via mlir-opt --load-pass-plugin=<plugin>.so.

Plugins

Plugin	Pass	Purpose
flat-closure-lowering	--resolve-closure-casts	Resolve closure-related type casts during LLVM lowering
reconcile-ffi-externs	--reconcile-ffi-externs	Reconcile FFI extern declarations with MLIR infrastructure

flat-closure-lowering

Resolves closure-related type casts during LLVM lowering. The Fidelity compiler represents closures as flat structures containing captured values and a function pointer. During lowering to the LLVM dialect, type mismatches arise between the generic closure representation and the concrete function signatures. This pass resolves those casts so that --reconcile-unrealized-casts can complete cleanly.

Pass flag: --resolve-closure-casts

reconcile-ffi-externs

Reconciles FFI extern declarations with infrastructure declarations that MLIR's standard lowering passes generate internally. The Fidelity compiler emits FFI calls with a ffi. prefix (e.g., @ffi.malloc) to avoid symbol collisions with declarations that passes like finalize-memref-to-llvm create (e.g., @malloc). After standard lowering is complete, this pass strips the ffi. prefix from non-colliding declarations and rewrites call sites for colliding declarations to use the infrastructure signature with explicit ptrtoint/inttoptr casts.

Pass flag: --reconcile-ffi-externs

Building

Requires MLIR/LLVM development headers (tested with LLVM 21).

cmake -B build -G Ninja
cmake --build build

The built plugins are placed in build/<plugin-name>/.

Usage

mlir-opt input.mlir \
  --load-pass-plugin=build/reconcile-ffi-externs/reconcile-ffi-externs.so \
  --reconcile-ffi-externs \
  --load-pass-plugin=build/flat-closure-lowering/flat-closure-lowering.so \
  --resolve-closure-casts

Architecture

These plugins operate exclusively in the BackEnd of the Composer compilation pipeline. The MiddleEnd (Alex) emits target-agnostic MLIR using standard dialects. Plugins bridge the semantic gap between that representation and target-specific lowering requirements.

Plugins do not modify or depend on the MiddleEnd. They are loaded by the BackEnd's mlir-opt invocation at the appropriate pipeline position.

Known Issues

Arch Linux: MLIR cmake version mismatch

On Arch Linux, the mlir package may ship an MLIRConfig.cmake that hardcodes a stale LLVM version (e.g. 21.1.6 when LLVM 21.1.8 is installed). This causes cmake to fail with a version mismatch when MLIRConfig.cmake calls find_package(LLVM 21.1.6) against a newer LLVM.

Diagnosis: The error will mention an LLVM version that doesn't match your installed version:

Could not find a configuration file for package "LLVM" that is compatible
with requested version "21.1.6".

Fix: Correct the hardcoded version in MLIRConfig.cmake:

sudo sed -i 's/set(LLVM_VERSION 21.1.6)/set(LLVM_VERSION 21.1.8)/' /usr/lib/cmake/mlir/MLIRConfig.cmake

Adjust the version strings to match your actual installed LLVM version (llvm-config --version). This is a packaging bug — the MLIR and LLVM packages should agree on the version string.

License

Apache License 2.0