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:

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:

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

Quick correctness:

./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:

./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:

./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:

./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.