Provide "--ccache" flag for build.sh

BUILD.md

@@ -37,6 +37,7 @@ As a convenience, a `build.sh` script is provided which can be used to execute t
 $ ./build.sh                           # build the cuML libraries, tests, and python package, then
                                        # install them to $INSTALL_PREFIX if set, otherwise $CONDA_PREFIX
 ```
+For workflows that involve frequent switching among branches or between debug and release builds, it is recommended that you install [ccache](https://ccache.dev/) and make use of it by passing the `--ccache` flag to `build.sh`.
 
 To build individual components, specify them as arguments to `build.sh`
 ```bash
@@ -56,6 +57,7 @@ $ PARALLEL_LEVEL=4 ./build.sh libcuml  # build and install libcuml limiting para
 $ ./build.sh libcuml -n                # build libcuml but do not install
 $ ./build.sh prims --allgpuarch        # build the ML prims tests for all supported GPU architectures
 $ ./build.sh cuml --singlegpu          # build the cuML python package without MNMG algorithms
+$ ./build.sh --ccache                  # use ccache to cache compilations, speeding up subsequent builds
 ```
 
 To run the C++ unit tests (optional), from the repo root:
@@ -135,6 +137,12 @@ Additionally, to reduce compile times, you can specify a GPU compute capability
 $ cmake .. -DCMAKE_INSTALL_PREFIX=$CONDA_PREFIX -DGPU_ARCHS="70"
 ```
 
+You may also wish to make use of `ccache` to reduce build times when switching among branches or between debug and release builds:
+
+```bash
+$ cmake .. -DUSE_CCACHE=ON
+```
+
 There are many options to configure the build process, see the [customizing build section](#libcuml-&-libcumlc++).
 
 3. Build `libcuml++` and `libcuml`:

build.sh

@@ -19,7 +19,7 @@ ARGS=$*
 REPODIR=$(cd $(dirname $0); pwd)
 
 VALIDTARGETS="clean libcuml cuml cpp-mgtests prims bench prims-bench cppdocs pydocs"
-VALIDFLAGS="-v -g -n --allgpuarch --buildfaiss --buildgtest --singlegpu --nvtx --show_depr_warn --codecov -h --help "
+VALIDFLAGS="-v -g -n --allgpuarch --buildfaiss --buildgtest --singlegpu --nvtx --show_depr_warn --codecov --ccache -h --help "
 VALIDARGS="${VALIDTARGETS} ${VALIDFLAGS}"
 HELP="$0 [<target> ...] [<flag> ...]
  where <target> is:
@@ -45,6 +45,7 @@ HELP="$0 [<target> ...] [<flag> ...]
    --show_depr_warn - show cmake deprecation warnings
    --codecov        - Enable code coverage support by compiling with Cython linetracing
                       and profiling enabled (WARNING: Impacts performance)
+   --ccache         - Use ccache to cache previous compilations
    -h               - print this text
 
  default action (no args) is to build and install 'libcuml', 'cuml', and 'prims' targets only for the detected GPU arch
@@ -69,6 +70,7 @@ BUILD_ALL_GPU_ARCH=0
 SINGLEGPU_CPP_FLAG=""
 CUML_EXTRA_PYTHON_ARGS=${CUML_EXTRA_PYTHON_ARGS:=""}
 NVTX=OFF
+CCACHE=OFF
 CLEAN=0
 BUILD_DISABLE_DEPRECATION_WARNING=ON
 BUILD_CUML_STD_COMMS=ON
@@ -151,6 +153,9 @@ fi
 if hasArg --codecov; then
     CUML_EXTRA_PYTHON_ARGS="${CUML_EXTRA_PYTHON_ARGS} --linetrace=1 --profile"
 fi
+if hasArg --ccache; then
+    CCACHE=ON
+fi
 if hasArg clean; then
     CLEAN=1
 fi
@@ -199,6 +204,7 @@ if completeBuild || hasArg libcuml || hasArg prims || hasArg bench || hasArg pri
           -DBUILD_STATIC_FAISS=${BUILD_STATIC_FAISS} \
           -DNVTX=${NVTX} \
           -DPARALLEL_LEVEL=${PARALLEL_LEVEL} \
+          -DUSE_CCACHE=${CCACHE} \
           -DNCCL_PATH=${INSTALL_PREFIX} \
           -DDISABLE_DEPRECATION_WARNING=${BUILD_DISABLE_DEPRECATION_WARNING} \
           -DCMAKE_PREFIX_PATH=${INSTALL_PREFIX} \

cpp/CMakeLists.txt

@@ -82,6 +82,8 @@ option(NVTX "Enable nvtx markers" OFF)
 
 option(SINGLEGPU "Disable all mnmg components and comms libraries" OFF)
 
+option(USE_CCACHE "Cache build artifacts with ccache" OFF)
+
 set(BUILD_RPATH_USE_ORIGIN "Whether to use relative paths for the build RPATH." TRUE)
 
 set(PARALLEL_LEVEL "" CACHE STRING
@@ -161,6 +163,12 @@ if(BUILD_CUML_MG_TESTS AND NOT SINGLEGPU)
   set(BUILD_CUML_MPI_COMMS ON)
 endif(BUILD_CUML_MG_TESTS AND NOT SINGLEGPU)
 
+if(USE_CCACHE)
+  set(CMAKE_C_COMPILER_LAUNCHER ccache)
+  set(CMAKE_CXX_COMPILER_LAUNCHER ccache)
+  set(CMAKE_CUDA_COMPILER_LAUNCHER ccache)
+endif(USE_CCACHE)
+
 ##############################################################################
 # - Requirements -------------------------------------------------------------