Use ccache in CI

.circleci/config.yml

@@ -212,22 +212,42 @@ jobs:
       resource_class: gpu.nvidia.small.gen2
     steps:
       - checkout
+      - restore_cache:
+          keys:
+            - mlx-v1-cuda-{{ arch }}-
       - run:
-          name: Install Python package
+          name: Install dependencies
           command: |
             sudo apt-get update
             sudo apt-get install libcudnn9-dev-cuda-12
             sudo apt-get install libblas-dev liblapack-dev liblapacke-dev
+            curl -sL https://github.com/ccache/ccache/releases/download/v4.11.3/ccache-4.11.3-linux-x86_64.tar.xz | tar xJf -
+            sudo mv ccache-4.11.3-linux-x86_64/ccache /usr/bin/ccache
+            rm -rf ccache-4.11.3-linux-x86_64
+      - run:
+          name: Install Python package
+          command: |
             python3 -m venv env
             source env/bin/activate
             CMAKE_ARGS="-DMLX_BUILD_CUDA=ON -DCMAKE_CUDA_COMPILER=`which nvcc`" \
-              pip install -e ".[dev]"
+              pip install -e ".[dev]" -v
       - run:
           name: Run Python tests
           command: |
             source env/bin/activate
             LOW_MEMORY=1 DEVICE=cpu python -m unittest discover python/tests -v
             LOW_MEMORY=1 DEVICE=gpu python -m tests discover python/tests -v
+      - run:
+          name: CCache report
+          command: |
+            ccache --show-stats
+            ccache --zero-stats
+            ccache --max-size 400MB
+            ccache --cleanup
+      - save_cache:
+          key: mlx-v1-cuda-{{ arch }}-{{ epoch }}
+          paths:
+            - /home/circleci/.cache/ccache
 
   build_release:
     parameters:

setup.py

@@ -113,6 +113,9 @@ class CMakeBuild(build_ext):
         if "CMAKE_BUILD_PARALLEL_LEVEL" not in os.environ:
             build_args += [f"-j{os.cpu_count()}"]
 
+        # Avoid cache miss when building from temporary dirs.
+        os.environ["CCACHE_BASEDIR"] = os.path.abspath(self.build_temp)
+
         subprocess.run(
             ["cmake", ext.sourcedir, *cmake_args], cwd=build_temp, check=True
         )