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Backends

Flow compiles to two native backends. This repo tests both.

C backend

The default path. Flow transpiles to C99, then clang -O3 -march=native compiles to a native binary.

pNNN.flow --c--> pNNN.c --clang -O3--> pNNN --> answer

Used by scripts/run.sh and scripts/verify.sh. Tested in the verify.yml GitHub Actions workflow.

All 855 solutions pass through this path.

MLIR backend

Flow generates MLIR in the LLVM dialect. The MLIR is lowered to LLVM IR by mlir-opt, translated by mlir-translate, then compiled by llc and linked by clang.

pNNN.flow --mlir--> pNNN.mlir
  --mlir-opt--> pNNN_lowered.mlir
  --mlir-translate--> pNNN.ll
  --llc -O3--> pNNN.s
  --clang--> pNNN --> answer

Used by scripts/verify-mlir.sh. Tested in the mlir.yml GitHub Actions workflow.

Prerequisites

The MLIR backend requires LLVM tools not shipped with macOS:

brew install llvm
export LLVM_BIN=/opt/homebrew/opt/llvm/bin

This provides mlir-opt, mlir-translate, and llc.

Current status

Problems without loops (closed-form solutions, recursive functions) generally pass through MLIR. Problems using i64 loop variables or stepped for ranges fail MLIR lowering due to a type mismatch in the Flow MLIR generator: arith.index_cast hardcodes i32 even when the operand is i64.

The verify-mlir.sh script reports three categories:

  • passed: MLIR compilation succeeded and the answer matches
  • mlir_fail: MLIR lowering or compilation failed (compiler limitation)
  • failed: MLIR compilation succeeded but the answer was wrong

Only failed (answer mismatch) causes a non-zero exit. mlir_fail is expected for a significant fraction of problems until the Flow compiler fixes the index_cast type bug.

Running locally

export FLOW_REPO=$HOME/flow
export LLVM_BIN=/opt/homebrew/opt/llvm/bin
./scripts/verify-mlir.sh          # all problems
./scripts/verify-mlir.sh 1 50     # problems 1-50

Manual MLIR compilation

export PATH="/opt/homebrew/opt/llvm/bin:$PATH"
export PYTHONPATH=$HOME/flow/src

# Flow -> MLIR
python3 -m flow.transpiler problems/p006.flow --mlir --lenient -o /tmp/p006.mlir

# MLIR -> LLVM IR
mlir-opt \
  --convert-arith-to-llvm \
  --convert-func-to-llvm \
  --convert-cf-to-llvm \
  --convert-index-to-llvm \
  --reconcile-unrealized-casts \
  /tmp/p006.mlir > /tmp/p006_lowered.mlir

mlir-translate --mlir-to-llvmir /tmp/p006_lowered.mlir -o /tmp/p006.ll

# LLVM IR -> binary
llc -O3 /tmp/p006.ll -o /tmp/p006.s
clang /tmp/p006.s -o /tmp/p006 -lm
/tmp/p006