Add instructions to enable ccache

Author: mergennachin

CMakeLists.txt

@@ -48,6 +48,16 @@
 cmake_minimum_required(VERSION 3.24)
 project(executorch)
 
+# Enable ccache if available
+find_program(CCACHE_PROGRAM ccache)
+if(CCACHE_PROGRAM)
+  set(CMAKE_CXX_COMPILER_LAUNCHER "${CCACHE_PROGRAM}")
+  set(CMAKE_C_COMPILER_LAUNCHER "${CCACHE_PROGRAM}")
+  message(STATUS "ccache found and enabled for faster builds")
+else()
+  message(STATUS "ccache not found, builds will not be cached")
+endif()
+
 # MARK: - Start EXECUTORCH_H12025_BUILD_MIGRATION
 
 include(${PROJECT_SOURCE_DIR}/tools/cmake/common/preset.cmake)

docs/source/using-executorch-building-from-source.md

@@ -30,6 +30,7 @@ Windows (x86_64)
 * `g++` version 7 or higher, `clang++` version 5 or higher, or another
   C++17-compatible toolchain.
 * `python` version 3.10-3.12
+* `ccache` (optional) - A compiler cache that speeds up recompilation
 
 Note that the cross-compilable core runtime code supports a wider range of
 toolchains, down to C++17. See the [Runtime Overview](runtime-overview.md) for
@@ -64,8 +65,8 @@ Or alternatively, [install conda on your machine](https://conda.io/projects/cond
    # Intel-based macOS systems require building PyTorch from source (see below)
    ./install_executorch.sh
    ```
-  
-   See the [PyTorch instructions](https://github.com/pytorch/pytorch#installation) on how to build PyTorch from source.  
+
+   See the [PyTorch instructions](https://github.com/pytorch/pytorch#installation) on how to build PyTorch from source.
 
    Use the [`--use-pt-pinned-commit` flag](../../install_executorch.py) to install ExecuTorch with an existing PyTorch build:
 
@@ -119,6 +120,8 @@ Or alternatively, [install conda on your machine](https://conda.io/projects/cond
 > git submodule sync
 > git submodule update --init --recursive
 > ```
+>
+> The `--clean` command removes build artifacts, pip outputs, and also clears the ccache if it's installed, ensuring a completely fresh build environment.
 
 ## Build ExecuTorch C++ runtime from source
 
@@ -171,6 +174,29 @@ To further optimize the release build for size, use both:
 -DEXECUTORCH_OPTIMIZE_SIZE=ON
 ```
 
+#### Compiler Cache (ccache)
+
+ExecuTorch automatically detects and enables [ccache](https://ccache.dev/) if it's installed on your system. This significantly speeds up recompilation by caching previously compiled objects:
+
+- If ccache is detected, you'll see: `ccache found and enabled for faster builds`
+- If ccache is not installed, you'll see: `ccache not found, builds will not be cached`
+
+To install ccache:
+```bash
+# Ubuntu/Debian
+sudo apt install ccache
+
+# macOS
+brew install ccache
+
+# CentOS/RHEL
+sudo yum install ccache
+# or
+sudo dnf install ccache
+```
+
+No additional configuration is needed - the build system will automatically use ccache when available.
+
 See [CMakeLists.txt](https://github.com/pytorch/executorch/blob/main/CMakeLists.txt)
 
 ### Build the runtime components
@@ -190,6 +216,8 @@ cd executorch
 cmake --build cmake-out -j9
 ```
 
+> **_TIP:_** For faster rebuilds, consider installing ccache (see [Compiler Cache section](#compiler-cache-ccache) above). On first builds, ccache populates its cache. Subsequent builds with the same compiler flags can be significantly faster.
+
 ## Use an example binary `executor_runner` to execute a .pte file
 
 First, generate a .pte file, either by exporting an example model or following
@@ -243,7 +271,7 @@ Install ClangCL for Windows from the [official website](https://learn.microsoft.
 To check if conda is detected by the powershell prompt, try `conda list` or `conda --version`
 
 If conda is not detected, you could run the powershell script for conda named `conda-hook.ps1`.
-To verify that Conda is available in the in the powershell environment, run try `conda list` or `conda --version`. 
+To verify that Conda is available in the in the powershell environment, run try `conda list` or `conda --version`.
 If Conda is not available, run conda-hook.ps1 as follows:
 ```bash
 $miniconda_dir\\shell\\condabin\\conda-hook.ps1

install_executorch.py

@@ -50,6 +50,19 @@ def clean():
         shutil.rmtree(d, ignore_errors=True)
     print("Cleaning buck-out/...")
     shutil.rmtree("buck-out/", ignore_errors=True)
+
+    # Clean ccache if available
+    try:
+        result = subprocess.run(["ccache", "--version"], capture_output=True, text=True)
+        if result.returncode == 0:
+            print("Cleaning ccache...")
+            subprocess.run(["ccache", "--clear"], check=True)
+            print("ccache cleared successfully.")
+        else:
+            print("ccache not found, skipping ccache cleanup.")
+    except (subprocess.CalledProcessError, FileNotFoundError):
+        print("ccache not found, skipping ccache cleanup.")
+
     print("Done cleaning build artifacts.")