binary-size

# Binary Size ## Start from the `main` branch of executorch Ask the user where the executorch repo is. ```bash git checkout main && git pull ``` ## Build and measure baseline ```bash conda activate executorch bash test/build_size_test.sh strip -o /tmp/size_test_stripped cmake-out/test/size_test strip -o /tmp/size_test_all_ops_stripped cmake-out/test/size_test_all_ops ls -la /tmp/size_test_stripped /tmp/size_test_all_ops_stripped ``` Produces two binaries: - `cmake-out/test/size_test` — ExecuTorch runtime without operator implementations - `cmake-out/test/size_test_all_ops` — ExecuTorch runtime with portable ops ## Analyze with bloaty ```bash bloaty cmake-out/test/size_test -d symbols -n 30 # by symbol bloaty cmake-out/test/size_test -d sections # by ELF section bloaty <after> -- <before> # diff two builds nm -S <binary> | sort -k2 -rn | head -30 # symbol sizes strings <binary> | less # string literals in .rodata ``` Note: `bloaty -d compileunits` requires debug info (`-g`). The Release build does not include it. ## Key build flags Set by `test/build_size_test.sh`: - `CMAKE_BUILD_TYPE=Release` - `EXECUTORCH_OPTIMIZE_SIZE=ON` — enables `-Os`, `-fno-exceptions`, `-fno-rtti`, unwind table suppression - `CXXFLAGS="-fno-exceptions -fno-rtti -Wall -Werror"` ## Constraints - Use **CMake** to build (not Buck) - **C++17 minimum** language standard - Must build on **GCC 9** (CI uses `executorch-ubuntu-22.04-gcc9-nopytorch`) and **Clang 12** — avoid compiler-specific flags or pragmas without version guards - Do not regress existing functionality — run tests for modified files - Do not change build flags in `build_size_test.sh` for size reductions - Do not increase latency in the core runtime ## Where to look for size reductions - `.text`: look for large functions, template bloat, duplicate instantiations - `.rodata`: verbose error messages, format strings, embedded file paths (`__FILE__`) - `.eh_frame`: should already be suppressed when `EXECUTORCH_OPTIMIZE_SIZE=ON` - Static init functions (`nm -S <binary> | grep GLOBAL__sub_I`): use `constexpr` constructors to constant-initialize static arrays - Logging strings: `ET_LOG_ENABLED=0` in Release eliminates format strings; ensure it propagates to consumers via `PUBLIC` compile definitions on cmake targets - Inline header functions: watch for compile-define mismatches between library and consumer TUs (e.g. `ET_LOG_ENABLED` set in library but not in consumer) ## For each change 1. Create a branch: `git checkout -b binary-size-<N>` 2. Implement, rebuild, measure stripped sizes 3. Create a separate PR — one logical change per PR 4. Record results in `binary-size-<N>.md`: | Binary | This change (N vs N-1) | Cumulative (N vs main) | |---|---|---| | `size_test` (stripped) | -X | -Y | | `size_test_all_ops` (stripped) | -X | -Y | 5. Update the CI size threshold in `.github/workflows/pull.yml` if sizes decrease