nudt-compiler-cpp/SESSION_HANDOFF.md

# Session Handoff

Date: 2026-05-28

## Repo State

- Current branch: `Shrink`
- Worktree is dirty; do not reset blindly.
- Modified tracked files:
  - `include/ir/IR.h`
  - `scripts/run_all_tests.sh`
  - `scripts/verify_asm.sh`
  - `scripts/verify_ir.sh`
  - `src/ir/analysis/DominatorTree.cpp`
  - `src/ir/analysis/LoopInfo.cpp`
  - `src/ir/passes/CMakeLists.txt`
  - `src/ir/passes/PassManager.cpp`
  - `src/main.cpp`
  - `src/mir/AsmPrinter.cpp`
  - `src/mir/Lowering.cpp`
  - `src/mir/MIRFunction.cpp`
  - `src/mir/passes/Peephole.cpp`
  - `sylib/sylib.c`
- New untracked files:
  - `src/ir/passes/LICM.cpp`
  - `src/ir/passes/LoopFission.cpp`
  - `src/ir/passes/LoopIdiom.cpp`
  - `src/ir/passes/LoopParallelize.cpp`
  - `src/ir/passes/LoopPassUtils.h`
  - `src/ir/passes/LoopUnroll.cpp`
  - `src/ir/passes/StrengthReduction.cpp`

## Toolchain On Current Machine

- `cmake 3.22.1`
- `g++ 11.4.0`
- `clang 14.0.0`
- `llc 14.0.0`
- `aarch64-linux-gnu-gcc 11.4.0`
- `qemu-aarch64 6.2.0`

Required packages on a fresh Ubuntu:

```bash
sudo apt update
sudo apt install -y \
  build-essential \
  cmake \
  clang \
  llvm \
  gcc-aarch64-linux-gnu \
  qemu-user \
  libc6-arm64-cross
```

## Important Build Detail

- The repo vendors `antlr4-runtime-4.13.2` in `third_party`, so no system ANTLR runtime install is needed.
- Current frontend build consumes generated parser sources from `build/generated/antlr4` if present.
- There is also parser source in `src/antlr4/`, but current CMake does not wire that directory directly into the build.
- Safest migration path: copy the repo together with the current `build/generated/antlr4` directory, or later patch CMake to use `src/antlr4/*.cpp`.

## Implemented IR / Loop Optimizations

Stable implemented items:

- `LICM`
- `StrengthReduction`
- `LoopFission`
- `LoopUnroll`
- conservative `LoopParallelization`
- `LoopIdiom` for constant-fill loops

Analysis infra already added:

- `DominatorTree`
- `LoopInfo`

Runtime support added:

- pthread worker-pool based `__par_runN` in `sylib/sylib.c`
- `__fill_i32` helper in `sylib/sylib.c`

User constraints already decided:

- Do not optimize the real-dependence matrix multiply in `2025-MYO-20` where `A[i][j]` is written and `A[k][j]` is read.
- Reduction parallelization is still disabled.

## Timing Scripts

Timing output was added to:

- `scripts/verify_ir.sh`
- `scripts/verify_asm.sh`
- `scripts/run_all_tests.sh`

User requirement:

- Every test round should always report:
  - `test/test_case/performance/2025-MYO-20.sy`
  - `./scripts/run_all_tests.sh --both`

## Recent ASM Correctness Fixes

Fixed issues:

- AArch64 call lowering bug that could corrupt ABI argument registers due to `W/X` aliasing.
- Duplicate local labels like `.par.exit` across worker functions by prefixing block labels with the function name.
- Duplicate callee-saved save/restore of alias registers like `w8/x8`.

Relevant files:

- `src/mir/Lowering.cpp`
- `src/mir/AsmPrinter.cpp`
- `src/mir/MIRFunction.cpp`

## Recent ASM Optimization Work

Implemented recently:

- post-regalloc second peephole pass in `src/main.cpp`
- selective safe load forwarding guard for ABI argument registers
- `cbz/cbnz` lowering for integer compare-against-zero in `Cmp + CondBr` fusion
- dead overwrite elimination in peephole for adjacent load/compute that gets overwritten before use

Relevant files:

- `src/main.cpp`
- `src/mir/Lowering.cpp`
- `src/mir/passes/Peephole.cpp`

## Most Recent Measured Performance

These are the latest measured numbers observed during this session.

IR:

- `2025-MYO-20` stable reference before latest ASM-only work:
  - around `31.109s`
  - earlier stable reference before that: around `30.926s`

ASM:

- `02_mv3`
  - earlier problematic run after correctness-only fix: about `31.662s`
  - after later backend cleanup, best observed run in this session: about `31.505s`
  - another later run: about `31.529s`
- `01_mm2`
  - earlier reference in this session: about `38.010s`
  - later improved run: about `37.346s`

Interpretation:

- ASM backend improvements are real but modest so far.
- Main remaining bottleneck is still heavy stack traffic in hot loops.

## Current Long-Running Item

- A standalone `2025-MYO-20` ASM run was launched and had not finished at the time this handoff file was written.
- A full `./scripts/run_all_tests.sh --both` run had progressed to the final `2025-MYO-20` ASM item instead of failing early, but final completion time was still pending.

## Good Commands To Resume Work

Build:

```bash
cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j"$(nproc)" --target compiler
```

Quick correctness:

```bash
./scripts/verify_ir.sh test/test_case/functional/simple_add.sy /tmp/ir_check --run
./scripts/verify_asm.sh test/test_case/functional/simple_add.sy /tmp/asm_check --run
```

User-required fixed benchmarks:

```bash
./scripts/verify_ir.sh test/test_case/performance/2025-MYO-20.sy /tmp/timed_2025 --run
./scripts/run_all_tests.sh --both
```

Useful ASM profiling targets:

```bash
./scripts/verify_asm.sh test/test_case/performance/01_mm2.sy /tmp/asm_mm2 --run
./scripts/verify_asm.sh test/test_case/performance/02_mv3.sy /tmp/asm_mv3 --run
./scripts/verify_asm.sh test/test_case/performance/2025-MYO-20.sy /tmp/asm_2025 --run
```

Inspect generated assembly:

```bash
./build/bin/compiler --emit-asm test/test_case/performance/02_mv3.sy > /tmp/02_mv3.s
./build/bin/compiler --emit-asm test/test_case/performance/01_mm2.sy > /tmp/01_mm2.s
./build/bin/compiler --emit-asm test/test_case/performance/2025-MYO-20.sy > /tmp/2025.s
```

## Suggested Next Steps

Priority order:

1. Finish measuring `2025-MYO-20` ASM and a complete `--both` run on the faster Ubuntu machine.
2. Keep working on MIR/ASM backend, not IR parallelization.
3. Target hot-loop stack traffic:
   - reduce phi-related spill/reload churn
   - widen zero-compare branch simplification beyond the current fused path
   - add more dead store / dead load cleanup after frame lowering
4. Only claim speedups when confirmed with the fixed benchmark pair above.